Oxygen transport deficits in systemic disease and implications for physical therapy.

[Dean E. Oxygen transport deficits in systemic disease and implications for physical therapy. Phys Ther. 1997;77:187-202.]

Key Words: Cardiac, general; Oxygen transport; Pulmonary, general; Systemic conditions.

In addition to treating primary conditions of the heart and lungs, physical therapists treat patients with primary diagnoses of conditions that have secondary cardiopulmonary complications. Although these complications can be subtle, their consequences can be serious. The purposes of this article are to discuss the effects of some common systemic diseases on cardiopulmonary function and oxygen transport and to describe the implications for physical therapists with respect to assessment, treatment, and prevention. Compared with the oxygen transport deficits associated with primary cardiopulmonary pathology, the secondary cardiopulmonary manifestations of systemic diseases are less well known. Pathology of every major organ system may have a secondary effect on cardiopulmonary function and oxygen transport, such as impaired ventilation, perfusion, and ventilation-perfusion matching; reduced lung volumes, capacities, and flow rates; atelectasis; reduced surfactant production and distribution; impaired mucociliary transport; secretion accumulation; pulmonary aspiration; impaired lymphatic drainage; pulmonary edema; impaired coughing; respiratory muscle weakness or fatigue; hypoxemia; dysrhythmias; hemodynamic instability; and mechanical encroachment on the heart.

In this article, the effects on the cardiopulmonary system of common hematologic, neuromuscular, musculoskeletal, gastrointestinal, hepatic, renal, collagen vascular and connective tissue, endocrine, and immunologic conditions are considered. The cardiopulmonary manifestations of some common nutritional disorders (eg, obesity, anorexia nervosa) are also considered. For each type of condition, the physical therapist must identify all the steps in the oxygen transport pathway that are affected so that treatment can be directed to the underlying problem as much as possible (Figure).

[Figure ILLUSTRATION OMITTED]

Because impairment of oxygen transport can result from diseases other than cardiopulmonary conditions, physical therapists in all specialties need expertise in anticipating and detecting cardiopulmonary dysfunction in the absence of primary cardiopulmonary disease. Such information is essential in modifying treatment prescription, preventing complications, and establishing when a patient should be referred to another health care professional. Examples of such cases include:

* an 11-year-old boy with a primary diagnosis of Down syndrome and a secondary diagnosis of atrioventricular septal defect 

* a 37-year-old woman with a primary diagnosis of scleroderma and a secondary diagnosis of restrictive lung disease 

* a 75-year-old man with a primary diagnosis of right cerebrovascular accident and secondary alveolar hypoventilation (de, reduced ventilation of the alveolar tissue of the lungs)

* a 42-year-old woman with a primary diagnosis of the late sequelae of poliomyelitis and secondary residual scoliosis and reduced endurance

* a 16-year-old girl with an anterior cruciate ligament repair and a secondary diagnosis of type I diabetes 

* a 59-year-old woman with a primary diagnosis of rheumatoid arthritis and shortness of breath 

* a 25-year-old man with a primary diagnosis of Crohn's disease and a secondary diagnosis of anemia

Hematologic Conditions

Pathophysiology

Hematologic conditions alter the oxygen-carrying capacity of the blood and the constituents, structure, consistency, and rheology of the blood.[1,2] Anemia associated with reduced hemoglobin and reduced oxygen-carrying capacity of the blood leads to increased demand on other steps in the oxygen transport pathway (eg, increased alveolarventilation, increased cardiac output). Altered constituents, consistency, and rheology of the blood contribute to hypocoagulopathy, hypercoagulopathy, increased work of the heart and breathing, impaired tissue perfusion, and increased risk of thrombosis. Hypocoagulopathy can lead to hemorrhage and edema, whereas hypercoagulopathy predisposes the patient to thrombus formation, emboli, and increased work of the heart and breathing.[3]

Altered plasma proteins affect the oncotic pressure of the blood and interstitium, which is essential in preserving compartmentalization of intravascular and extravascular fluid volume.[4] Albumen is a primary plasma protein that maintains circulatory oncotic pressure by retaining plasma in the circulation. Normally, minimal amounts of protein leak through the capillary membrane; thus, the oncotic pressure in the interstitial tissues is low. Excesses or deficits of blood protein constituents alter this important transcapillary fluid balance in all tissues of the body, which in turn may affect circulating blood volume.

Coagulopathies interfere with the normal clotting mechanisms of the blood. Both deficits and excesses of blood clotting factors are pathologic and interfere with oxygen transport.[3] Deficits contribute to bleeding abnormalities and hemorrhage. Excesses contribute to abnormal clotting and obstruction of blood flow to vital organs, including the brain, heart, kidneys, and lungs, which in turn contributes to thromboemboli and tissue infarction.[3] Increased blood viscosity and increased biventricular stroke work can result.

Pulmonary emboli resulting from blood clots are relatively common. Although frequently silent, there are three primary symptoms, namely, shortness of breath, pleuritic chest pain, and hemoptysis. Pulmonary emboli are life-threatening and are managed medically with an aggressive course of thrombolytic and anticoagulant therapy.[5]

Implications for Physical Therapy Management

Hematologic abnormalites require that the results of the patient's blood analysis and clotting factors be monitored so that physical therapy treatments can be modified to minimize risks.

Patients with anemia fatigue easily; thus, treatments need to be modified accordingly. If exercise is indicated for a patient with anemia, pacing and training that distributes the intensity of the workload over time can be used to promote physiological recovery. Getting a patient mobile refers to exercise stimuli such as walking transferring, standing, and chair and bed exercises that can be used to optimize ventilation, perfusion, and ventilation-perfusion matching and to promote mucociliary transport. Mobilization often is prescribed in conjunction with a gravitational stimulus (de, variants of the upright position) to elicit hemodynamic responses to gravity. Training in a progressive form involves alternating bouts of high-intensity exercise with bouts of either low-intensity exercise or rest. The patient's response to treatment is used as a guide to progress and modify treatments.

Patients with clotting abnormalities are prone to emboli or bleeding.[4] The dangers of clotting include arterial occlusion and thromboemboli becoming lodged in arteries supplying vital organs (eg, brain, kidney, lungs, heart).[6] Common causes of abnormal blood clotting are restricted mobility and an increase in red blood cells, which increase blood viscosity and work of the heart.[7] Most clots originate in the deep veins of the legs.[7] Although the degree to which movement can dislodge a blood clot has not been established conclusively, the presence of clots usually rules out movement in the affected limbs.

Lower-extremity exercises, compression stockings, and intermittent pneumatic compression devices are used to prevent thrombus formation in the legs, particularly in patients following surgery and patients who have had trauma. Compression stockings prevent peripheral pooling of the blood and augment venous return. Specially designed stockings used with a pneumatic compression device are programmed to inflate to a certain pressure and then deflate several times a minute, thereby simulating the normal action of the muscle pump in the legs.[8] Stockings are applied with special attention to uniformity of pressure along the leg. They should be inspected for wrinkles, and they should be removed frequently for short periods (10 minutes) and reapplied. Bleeding secondary to hypocoagulopathy tends to occur within major organs and around areas of stress (eg, joints). Therapists need to consider the relative risk of movement and activity with respect to increasing bleeding versus the negative sequelae of restricted mobility and recumbency on oxygen transport. Gentle mobilization and modified exercise are usually resumed when the thrombi have resolved, based on ultrasound and other clinical studies.

Neuromuscular Conditions

Pathophysiology

The type and severity of oxygen transport deficits resulting from neurological lesions depend on the type and distribution of the lesions.[9-11] Neuromuscular conditions that have been associated with cardiopulmonary manifestations include cerebral lesions (eg, stroke, cerebral palsy, tumors, brain injuries), disorders of the spinal cord (eg, poliomyelitis, spinal cord injury), demyelination diseases (eg, Guillain-Barre syndrome, amyotrophic lateral sclerosis, multiple sclerosis), pathology of the neuromuscular junction (eg, myasthenia gravis), and failure of the contractile mechanism of muscle (eg, myopathies).[12] Central lesions associated with cerebral palsy and stroke tend to have peripheral effects (eg, altered tone of the muscles of the chest wall and chest wall deformity).

In patients with cerebral palsy, breathing can be episodic and dysrhythmic, and chest wall movement can be compromised by spasticity and rigidity.[13] Reduced capacity to manage airway secretions and saliva makes these patients prone to aspiration. In addition, patients with cerebral palsy may be deconditioned due to restricted movement. Spasticity and abnormal movement patterns increase the energy cost of moving and ambulating. In the acute stage of stroke, chest wall movement and activity of the inspiratory muscles on the paralyzed side are reduced.[10] The effects of restricted movement and spasticity can contribute to the same problems observed in patients with cerebral palsy and similar neuromuscular conditions.

The cardiopulmonary manifestations of spinal cord injuries depend on the level of the lesion. Although cervical lesions involving C-3 through C-5 result in diaphragmatic paresis, impaired accessory muscle function, and potential ventilator dependence, involvement of lower spinal segments also affects respiratory function.[14] The thoracic spinal nerves supply the intercostal, oblique, abdominal, and paravertebral muscles.[14] The lumbar spinal nerves supply the paravertebral muscles of that region and quadratus lumborum muscle, and the sacral nerves supply the paravertebral muscles of the lower-most portion of the back.[14] Residual volume is usually increased in patients with spinal cord lesions, and inspiratory and expiratory capacities are decreased.[14] Ventilation of the lung bases is also diminished.[15] Because of the loss of thoracic and abdominal muscle function in high lesions, normal position-induced changes in respiratory function can be accentuated with changes in body position.[16,17] In addition, patients with spinal cord injuries are hemodynamically unstable initially due to the effects of spinal shock and secondary abnormal fluid shifts and hypotension. Even though these patients tend to be younger, dysrhythmias can be precipitated by hypoxemia in the absence of primary heart disease.

Anterior horn cell diseases such as poliomyelitis may result in peripheral and central lesions, either at onset or several decades later, that negatively affect cardiopulmonary function and gas exchange.[18] Common problems include shortness of breath, reduced endurance, choking and swallowing problems, impaired mucociliary transport, ineffective coughing, risk of aspiration, and sleep apnea.[19]

Pathologies of muscle such as occur with muscular dystrophy, amyotrophic lateral sclerosis, and dystonias are progressive and can compromise ventilation due to hypotonia and consequent respiratory muscle dysfunction.[20] Hypotonia of the upper airway structures and weak abdominal muscle strength contribute to choking, impaired swallowing, and aspiration.

Depending on the level, distribution, and severity of involvement, neuromuscular disorders may reduce respiratory muscle strength and endurance, inspiratory and expiratory pressures, lung volumes, and flow rates and may contribute to hypoventilation, airway closure, hypoxemia, and hypercapnia.

Implications for Physical Therapy Management

The primary cardiopulmonary problems in patients with neuromuscular dysfunction include alveolar hypoventilation, atelectasis, impaired mucociliary transport, secretion accumulation, aspiration, impaired ventilation-perfusion matching, and impaired coughing effectiveness. Conditions associated with autonomic nervous system dysfunction contribute to abnormal fluid distribution, relative hypovolemia, and orthostatic hypotension.[21] In addition, these patients often have minimal aerobic reserve capacity because of restricted mobility.

Patients who have autonomic nervous system dysfunction warrant stringent monitoring because they are prone to hemodynamic instability. Although tilt tables may have a role in this process, they may contribute to orthostatic intolerance because the patient cannot recruit the pumping action of the muscles of the legs even if the legs are not paralyzed.

Interventions such as mobilization and body positioning (particularly in an upright position), breathing control and coughing maneuvers, and postural drainage are prescribed to enhance alveolar ventilation, resolve atelectasis, enhance ventilation-perfusion matching, optimize mucociliary transport, and maximize coughing effectiveness in the patient with neuromuscular dysfunction.[22]

Optimizing alveolar ventilation is a primary goal for patients with progressive neuromuscular dysfunction. End-tidal carbon dioxide, arterial saturation, and the sensation of dyspnea are important indicators of hypoventilation.[23] Glossopharyngeal breathing, which has been used extensively by patients with poliomyelitis to maximize vital capacity and inspiratory reserve, may have a role in the management of patients with other types of neuromuscular deficits.[24]

Airway protection is a priority to avoid aspiration. The patient should be instructed in deep breathing and supported coughing maneuvers in conjunction with mobilization and body positioning. Specific supported coughing interventions include costophrenic-assisted coughing, Heimlich-type assist, abdominal thrust, and chest wall compression maneuvers.[25,26] In addition, coughing can be self-assisted, as well as coordinated with flexion and extension movements of the trunk in different body positions. The patient inspires during extension and attempts to forcefully exhale during flexion movements. These maneuvers are coordinated with mobilization and body positions (eg, upright, hands-and-knees, and semirecumbent positions) to enhance respiratory muscle efficiency and expiratory flow rates. Patients who are at risk of aspiration and their families should be instructed in the Heimlich maneuver an emergency procedure to relieve upper airway obstruction.

Although the supine and Trendelenburg positions reduce the risk of passive regurgitation, these positions promote aspiration of pharyngeal contents. To prevent both regurgitation and aspiration, the optimal position is the lateral Trendelenburg position.[27] This position, however, may be contraindicated for patients with increased intracranial pressure or gastric dysfunction. Regardless of body position, patients are particularly prone to aspiration when on sedatives, tranquilizers, narcotics, and muscle relaxants and when they are under the influence of anesthesia.[28] These agents blunt the airway reflexes and prolong gastric emptying.

Patients should be encouraged to identify situations and foods that contribute to choking or impaired swallowing and to avoid them as much as possible. Eating during social situations, for example, when the patient may be talking and laughing, increases the risk of aspiration; thus, patients should be instructed to be particularly attentive at these times.

In cases when the patient is unable to remove airway secretions effectively with conservative measures, suctioning may be indicated. The negative effects of suctioning on oxygen transport, however, have been well documented.[29] If mechanically ventilated, the patient is hyperventilated and hyperoxygenated prior to suctioning if she or he is likely to become desaturated. The procedure is performed quickly and with adequate rest periods between passes of the suction catheter. The patient's respirations and hemodynamic responses to suctioning are monitored.[30]

Altered function of skeletal muscle, including the respiratory muscles, compromises ventilation. Excessive or reduced activity impairs breathing efficiency and increases the work of breathing. Reduced activity of the pharyngeal and laryngeal muscles that protect the upper airway predisposes the patient to obstructive sleep apnea and aspiration.[31,32]

Generalized or local muscle weakness or paresis has particular implications for physical therapy management. In patients with weakness and deformity resulting from long-term disability (eg, poliomyelitis, spinal cord injury), viable muscle compensates for nonworking motor units or entire muscles. These muscles incur abuse secondary to overuse.[33] In patients with a history of poliomyelitis, for example, reduction in the motor unit pool results in excessive demands being placed on remaining motor units.[34] The remaining motor units are chronically overworked and do not benefit from bouts of rest, in contrast to normal motor units.[35] Over time, age-related decrement in motor units contributes to a disproportionate loss of function.[36] Increasing exercise load on these muscles, therefore, can contribute to further deterioration and loss of function.[37] Thus, exercise (both general aerobic conditioning and individual muscle training) should be prescribed to achieve goals without inflicting further damage and loss of function. Weak muscles that respond to strengthening stimuli need to be distinguished from fatigued muscles that need to rest.

Muscular weakness or paresis of the diaphragm and other respiratory muscles is of considerable clinical importance. Paresis of these muscles impairs ventilation and gas exchange. The corresponding increase in the work of breathing is superimposed on an already compromised oxygen transport delivery system. Comparable to peripheral muscles, weak respiratory muscles respond to resistive muscle training[38]; however, the function of fatigued respiratory muscles will deteriorate.[39] To ensure that the appropriate treatment is prescribed, weak ventilatory muscles must be distinguished from fatigued ventilatory muscles.[38,40,41] Optimizing respiratory muscle strength and endurance with mobilization and exercise should be a priority for patients with chronic lung disease, and specific ventilatory muscle training may augment this effect in some patients.[42]

Respiratory muscle fatigue is assessed by evaluating force development in response to stimulation over time and fatigue patterns, relaxation rates, and electromyographic activity.[39] The differentiation of weakness and fatigue of ventilatory muscles is complicated when they coexist.[43] For routine clinical purposes, distinguishing weakness and fatigue is based on history, assessment, and the patient's response to a trial of inspiratory muscle training or rest. Patients who deteriorate or fail to demonstrate an improvement in ventilatory muscle strength with training most likely have fatigued respiratory muscles. These ventilatory muscles require rest rather than training. The respiratory muscles of patients who have difficulty weaning from mechanical ventilation may also require rest. Alternatively, inspiratory muscle training may augment weaning from mechanical ventilation in some patients.

Patients with spinal cord injuries often show unique breathing patterns during the first year postinjury.[44] Initially, respiratory function is impaired when a person sits compared with when the person is positioned supine. Ventilatory adaptation to the sitting position may reflect improvements in accessory muscle function, chest wall stability, thoracoabdominal coupling, or some combination of these compensations. Despite these compensations, patients with chronic cervical spinal cord injuries tend to have rapid shallow breathing.[45] Patients with high cervical lesions with partial or complete sparing of spinal nerves C3 through C5 have impaired ventilatory reserve due to partial innervation of the respiratory muscles. Training of the ventilatory muscles using inspiratory resistive loading devices has a role in improving ventilatory muscle strength and endurance, which in turn can increase exercise tolerance.[42]

Patients with progressive neuromuscular diseases (eg, muscular dystrophy, multiple sclerosis) are living longer. These patients are at risk of developing respiratory muscle weakness as the disease progresses. Nighttime ventilation (eg, continuous positive airway pressure delivered by face mask) has been one means of providing intermittent rest to the respiratory muscles. A major priority for these patients is to avoid or delay the need for intubation and mechanical ventilation, particularly invasive mechanical ventilation. Patients with progressive neuromuscular diseases have a poor prognosis for being weaned from invasive mechanical ventilation.[46,47]

The aerobic capacity of patients with neuromuscular dysfunction may be variable, as has been reported for patients with a history of poliomyelitis.[48] Physical disability reduces activity and may therefore reduce aerobic capacity due to increased exercise stress and energy demand.[46] In other cases, disability may provide an aerobic stimulus that enhances aerobic capacity. The overall aerobic capacity of patients with neuromuscular dysfunction should be assessed to determine (1) whether cardiopulmonary conditioning is indicated, (2) whether the patient's disability is contributing to overtraining and overuse, and (3) whether preventive measures (eg, flu shots, cessation of smoking, avoidance of secondhand smoke and other poor air quality environments, minimizing contact with persons with respiratory infections) are indicated. Although cardiopulmonary conditioning may also be indicated, exercises should be modified to adjust for the loss of physiologic reserve capacity and to avoid musculoskeletal strain, overuse, and excessive exertion."' Commensurate with the type and severity of the disease, cardiopulmonary conditioning is prescribed to optimize the efficiency of the oxygen transport system. These exercise-induced effects may include either central or peripheral effects, or both (eg, the heart and lungs improve their efficiency at pumping and oxygenating blood, collateral vascularization is increased to optimize blood-flow distribution through the muscles, muscle oxidative enzymes and myoglobin concentrations are increased to maximize peripheral extraction of oxygen at the tissue level).[49-50]

Another consideration in the management of the patient with neuromuscular dysfunction is movement economy. Movement economy refers to the metabolic efficiency of energy expenditure during movement. Normally, movement is performed such that the metabolic cost is minimized and energy is not wasted. Patients with abnormal asymmetric muscle function, particularly of the postural muscles, and patients with musculoskeletal deformities (structural or functional) expend more energy during activities and locomotion.[51,52] This increased metabolic demand imposes an increased load on the patient's oxygen transport system. Thus, to minimize excessive energy expenditure, treatment should be directed at minimizing these effects and optimizing the efficient use of energy using postural correction exercises; proper biomechanics and postural alignment; gait education; prescription of walking aids, devices, and lightweight footwear; and activity-pacing and energy-conservation interventions. Orthotic devices may reduce this energy cost by normalizing gait and reducing excessive movements and sway.[51,55]

The prescription of activity-pacing and energy-conservation interventions for patients with neuromuscular dysfunction has not been well studied or defined.[54] For the patient with low functional work capacity, paced training is one of the most justifiable modes of training of the aerobic system, given the enhanced recovery and greater work capacity associated with it.[55-17] Such training promotes bouts of relatively high- to low-intensity activity or of low-intensity activity to rest over a prolonged period of time. Thus, the amount of muscular work that can be achieved with paced training is greater than the amount of muscular work that can be achieved in a single bout of activity or exercise. In addition, fatigue can be minimized by promoting degradation of lactate with reduced intensities of exercise, and the rate and quality of recovery can be enhanced.[55]

The approach to the management of some patients with neuromuscular conditions is becoming increasingly aggressive. Malouin et al,[58] for example, advocate an intensive task-oriented gait training program in the early stages of recovery from stroke. Strokes primarily affect older adults, who have a high incidence of coronary artery disease, hypertension, and dysrhythmias.[59] In addition, such individuals may have been deconditioned before their strokes, or they may become deconditioned after their strokes. Given these considerations, patients being treated following strokes should be monitored with respect to their cardiopulmonary and cardiovascular status (eg, heart rate, blood pressure, rate-pressure product, electrocardiographic activity, breathing pattern, dyspnea, chest discomfort, exertion). Changes in these responses should lead therapists to make appropriate treatment modifications and to ensure that the physiologic stress imposed on patients is safe and not excessive.

Musculoskeletal Conditions

Pathophysiology

Respiratory insufficiency can result from abnormalities of the chest wall secondary to congenital deformities acquired diseases, and traumas.[12,26] Deformity of the chest wall reduces the mobility of the thorax and thereby increases the work of breathing.[12] Shallow, rapid breathing often results, which increases minute ventilation at the expense of alveolar ventilation. Examples of chronic deformities that impinge on cardiopulmonary function include kyphosis, kyphoscoliosis, tuberculous osteomyelitis, and ankylosing spondylitis.[60] Other causes of chest wall deformity include traumatic injury of the vertebral column, ribs, and sternum. Age-related changes of the lungs and chest wall also contribute to chest wall deformity, displacement of the diaphragm and abdominal muscles, and altered respiratory mechanics.[59] The effects of these changes on gas exchange are accentuated because of the age-related decrease in arterial oxygen tension and gas exchange.

Normal cardiopulmonary function and gas exchange depend on the normal configuration of the cardiopulmonary anatomy. Asymmetry of the chest wall, for example, interferes with the regional gradients of ventilation and perfusion. Physiologic dead space and shunt are exaggerated, leading to hypoxemia and hypercapnia. Severe chest wall deformity and reduced adherence and ventilatory efficiency can result in hypoxemia, hypercapnia, and respiratory acidosis.[61] Chronic hypoxemia leads to hypoxic pulmonary vasoconstriction, pulmonary hypertension, and right heart failure.

Chronic chest wall deformities often result from kyphosis, kyphoscoliosis, ankylosing spondylitis, chest wall hyperinflation, and flattening of the diaphragm secondary to chronic airflow limitation, and protrusion and retraction of the sternum (pigeon breast and funnel breast). Postthoracotomy deformity may be encountered in patients who had thoracoplasty surgery for tuberculosis several decades ago.

Chest wall trauma is a primary cause of acute chest wall deformity. This injury is often complicated by heart and lung contusions, bleeding, and internal injuries. Multiple rib fractures, specifically, two or more fractures it two or more places, can lead to a flail segment or a flail chest. This flail segment moves paradoxically on breathing.[62] Impaired chest wall stability and motion are associated with encroachment and atelectasis of the underlying airways and lung parenchyma, which contributes to alveolar hypoventilation and impaired mucociliary transport.[62] In addition, pain from fractured ribs limits deep breathing and coughing even when the chest wall is intact. If pharmacologic analgesia interferes with patient arousal and capacity to cooperate with treatment, the physician needs to be informed and alternative analgesia needs to be considered.

Implications for Physical Therapy Management

The management of chest wall deformities includes optimization of postural and biomechanical alignment; thoracic mobilization; and minimization of the neuro-muscular, musculoskeletal, and cardiopulmonary sequelae. Range-of-motion exercises, stretching, and strengthening of the chest wall muscles are often prescribed. Severe deformity can lead to respiratory insufficiency and, in extreme cases, to respiratory failure. In acute cases, musculoskeletal deformities restrict mobilization and body positioning. Restricted mobility and reduced positioning alternatives threaten oxygen transport by removing the normal physiologic "stir-up" that is associated with normal movement and changes in position. Alveolar ventilation is reduced, tidal volume and vital capacity are reduced, and the work of breathing is increased. In chronic cases, patients with deformities, particularly spinal abnormalities, may be less able to engage in physical activities; thus, they are prone to deconditioning. In addition, the energy cost of movement may be increased due to spinal malalignment, increased postural sway, and gait deviation.

Management of the cardiopulmonary complications of acute rib fractures primarily involves pain control. Without optimal pain control, the patient's ability to cooperate fully with treatment is compromised. Varied body positions and frequent changes in body position that simulate position changes that normally occur are necessary to maximize effective alveolar ventilation, ventilation-perfusion matching and gas exchange, surfactant production and distribution, and mucociliary transport.[63] Interventions to control pain include relaxation procedures, strategic pacing and selection of positions and movement, and transcutaneous electrical nerve stimulation. In addition, pharmacologic management may include a range of medications. Medications with minimal systemic effects (as opposed to medications with greater systemic effects, such as narcotic analgesics), are usually preferred, whenever possible, to ensure that the patient can cooperate fully with the therapist. Epidural analgesia is often favored to reduce many of the systemic effects of analgesic medications, particularly narcotics.[64] Physical therapy treatments should be coordinated with the patient's analgesia schedule. Mobilization and body positioning coordinated with breathing control and coughing maneuvers are the mainstays of treatment.[25,65,66]

Gastrointestinal, Hepatic, and Renal Conditions

Pathophysiology

Although the cardiopulmonary system is anatomically distinct from the gastrointestinal, hepatic, and renal systems, these organ systems are functionally integrated with the heart and lungs. Thus, primary pathology affecting the gastrointestinal tract, liver, and kidneys can lead to cardiopulmonary manifestations and pose a threat to oxygen transport.

Despite the general anatomic distinction between the gastrointestinal and cardiopulmonary systems, there are numerous lymphatic channels between the abdominal and thoracic cavities.[20] In addition, mass and volume changes in the abdominal cavity alter thoracoabdominal interaction and the relative position of the diaphragm, which separates the two cavities. These effects emanate from abnormal fluid dynamics within the gastrointestinal system. Coughing and bronchospasm can result from a vagally mediated reflex secondary to refluxed acid contents in the esophagus.[67] Reflux is potentiated in obese patients with increased intra-abdominal pressure[68] and in immature infants. Reflux is also potentiated in smokers and heavy alcohol consumers, in whom esophageal sphincter function is reduced.

Aspiration of foreign substances into the lungs is associated with numerous conditions, such as decreased levels of consciousness and reduced pharyngeal, esophageal, and gastrointestinal motility.[69,70] In addition, gastroesophageal reflux is associated with iatrogenic factors, including intubation, tracheostomy, anesthesia, and nasogastric tubes. Chronic bronchitis, asthma, hemoptysis, coughing, and pulmonary fibrosis have been associated with reflux.[73]

Cardiopulmonary dysfunction (eg, impaired coughing, increased pulmonary markings on chest roentgenograms, submucosal inflammatory changes) can be a manifestation of ulcerative colitis.[72] Asymptomatic patients with Crohn's disease and normal chest roentgenograms have been reported to have reduced forced vital capacity and diffusing capacity.[73]

Hypoxemia is common in patients with chronic liver disease.[74] Several mechanisms appear to be responsible.[75-77] Pulmonary closing volume is increased, resulting in areas of low ventilation-perfusion matching. Ascites increases intra-abdominal pressure, which contributes to increased pulmonary closing volume (de, closure of the dependent airways and alveoli).[78] A diffusion defect has also been implicated. Arterial partial pressure of oxygen is correspondingly reduced, and arterial desaturation is potentiated; these effects are accentuated with recumbency. The rich lymphatic drainage system of the gastrointestinal tract is overwhelmed, which creates back pressure for lymphatic drainage from the lungs and may contribute to pleural effusions. Diffusing capacity is reduced, and the alveolar-arterial oxygen difference is increased.

Chronic liver disease is also associated with intrapulmonary shunting; anastomoses connecting the portal, mediastinal, and pulmonary venous beds; and reduced pulmonary vascular function. Pulmonary edema occurs secondary to hepatic encephalopathy and cerebral edema.[79] Vascular changes in the lungs have been well documented in patients with chronic liver disease and reflect the importance of the liver in the control of vasoactive substances that regulate normal fluid balance, including lung fluids. The major pulmonary abnormality, however, is intrapulmonary shunting secondary to pulmonary vascular dilatation.[80] Chest roentgenography shows bibasilar interstitial infiltrates. Pulmonary vascular dilatation contributes to hypoxemia, which can be worsened when the patient assumes an upright position (ie, orthodeoxia). Dyspnea occurring in an upright position and relieved with recumbency is termed platypnea (unlike orthotnea, in which dyspnea occurs with recumbency and is relieved by assuming an upright position).

Parenchymal changes associated with chronic liver disease can be associated with infiltrates, obstructive airflow limitation, and the secondary effects of ascites and pleural effusions on lung volumes. Oliguric renal failure is also seen in severe liver disease and is known as hepatorenal syndrome. Fluid overload and increased peribronchial fluid contribute to airway closure. After dialysis, a fall in body weight correlates with reduced airway closure.[80] In addition, vital capacity increases, residual volume is reduced, and forced expiratory flow rates increase.[81] Acute fulminant liver failure is associated with multisystemic complications and high mortality. Cerebral edema is a lethal complication that leads to respiratory depression, cardiorespiratory arrest, and death. Noncardiogenic pulmonary edema is also a common complication, necessitating positive end-expiratory pressure during mechanical ventilation and pulmonary artery pressure monitoring.

Secondary cardiopulmonary complications of renal disorders are termed pulmonary-renal syndromes. Some common features of these syndromes include alveolar hemorrhage, which leads to an increased diffusing capacity, interstitial and alveolar inflammation, pulmonary vascular changes, and immunological changes.[82]

Patients with liver disease are prone to hypoxemia, airflow obstruction, and, in severe cases, cardiac arrest. These factors can indicate the need for intubation and mechanical ventilation. Because distress can be reduced with supplemental oxygen, the pathophysiologic defect has been considered a diffusion-perfusion defect rather than an anatomical shunt.[83] Oxygenation should be monitored carefully during treatment, given that hypoxemia and dyspnea can be worsened in patients when they assume an upright position from a supine position or when they change body positions.

The kidneys have an essential role in the production and regulation of certain humoral regulators of metabolism and of hemodynamic and fluid balance.[84] These organs have a major effect on oxygen transport.84 Thus, pathology of the kidneys affects these life-sustaining processes.

Implications for Physical Therapy Management

With respect to gastrointestinal conditions, reflux and aspiration are largely preventable. Although head-up positions minimize reflux, they can promote aspiration of pharyngeal contents. Side-lying positions prevent regurgitation and aspiration.[85] These positions promote oropharyngeal accumulation of secretions and ease of suctioning. Upright positions minimize the risk of aspiration in part because they reduce intra-abdominal pressure. Signs and symptoms of aspiration include acute bronchospasm, increased airway resistance, and dyspnea. Ensuing ventilation-perfusion mismatch and shunting lead to arterial hypoxemia. Positioning patients with gastrointestinal dysfunction for breathing control and coughing maneuvers requires special attention to minimize the risk of aspiration.

Patients with gastrointestinal dysfunction are at risk for impaired metabolism due to their medications being evacuated, not being absorbed properly, or both. The responses of these patients to medications will therefore be less predictable, which may also affect the response to treatment. Monitoring of gastrointestinal status and medication responses is essential in conjunction with the patient's response to physical therapy.

Because of the fundamental role of the kidneys in fluid and electrolyte balance, the fluid status of the patient and his or her ability to maintain plasma volume and regulate fluid balance at rest and during physical exertion must be monitored by clinical indices of hydration and urinary output. Associated electrolyte changes must also be observed. Electrolyte changes will affect excitable tissues (eg, cardiac muscle, smooth muscle, nervous tissue) as well as homeostasis. Renal insufficiency leads to extracellular volume excess, which ultimately affects the electrolyte concentrations in the blood. Severe hyperpotassemia, for example, occurs with anuria or oliguria.[86]

The kidneys have a primary role in the production and regulation of renin and the synthesis of angiotensin, a potent vasoactive mediator. Thus, hemodynamic lability, particularly abnormal blood pressure control, may result from kidney disease. Blood pressure and heart rate should be closely monitored at rest and during treatment to ensure that hemodynamic responses are not attenuated or inappropriate. Erythropoietin, which is responsible for stimulating red blood cell production from bone marrow, is primarily secreted by the kidneys; thus, anemia is a common complication of renal dysfunction. Patients with anemia are readily fatigued. Treatments and activity, therefore, should be paced to minimize fatigue.

Collagen Vascular and Connective Tissue Conditions

Pathophysiology

The collagen vascular and connective tissue diseases (eg, systemic lupus erythematosus, scleroderma, rheumatoid arthritis) are characterized by inflammation of the connective tissue.[87,88] Collagen and connective tissue are constituents of most organs; thus, chronic inflammation and related injury can impair organ function systemically. In many patients with systemic lupus erythematosus and scleroderma, cardiopulmonary manifestations are apparent.[89] Oxygen transport is compromised by involvement of the airways, lungs, alveolar capillary membrane, chest wall, heart, and vasculature.[90] Connective tissue changes and fibrosis of the structures of the chest wall and within the lung parenchyma result in a loss of alveolar tissue, reduced diffusing capacity, reduced lung volumes, and reduced chest wall expansion.[91] Lung compliance is reduced, and the work of breathing is increased. This "shrinking lung syndrome" associated with connective tissue conditions may predispose the patient to ventilatory insufficiency.[92] Both the electrical and mechanical behaviors of the heart can be compromised, leading to impaired electromechanical coupling and cardiac pumping insufficiency.[93] Reduced cardiac output and hypoxemia may ensue. Oxygen extraction at the tissue level may also be affected by the presence of increased connective tissue.

Patients with rheumatoid arthritis may have various types of associated cardiopulmonary pathology. Common pulmonary pathologies include diffuse interstitial pulmonary fibrosis, reduced diffusing capacity, bronchiolitis, pleuritis, pulmonary effusions, and airflow obstruction.[94] The restrictive pattern of lung disease associated with rheumatoid arthritis may reflect an increase in collagenase.[95] With respect to cardiac pathology, pericarditis and pericardial effusion with associated electrocardiographic changes are not uncommon findings.[96,97] Constrictive pericarditis may result from acute pericarditis; however, this condition may occur with no documented history of pericarditis.[98]

Implications for Physical Therapy Management

The relative involvement of the heart, lungs, kidneys, and blood vessels for a patient with collagen vascular or connective tissue disease must be established. The effectiveness of lymphatic drainage and its role in fluid balance regulation may also be affected. Treatment is directed at maximizing alveolar volume, promoting mucociliary transport, optimizing ventilation-perfusion matching, reducing undue work of the heart and of breathing, and optimizing circulatory fluid balance and distribution.[99] Body positioning is prescribed to manipulate the intrapleural pressure gradient, and thus the alveolar volume, as well as the distributions of ventilation and perfusion and gas exchange. Body positioning also promotes lymphatic drainage. Breathing control and coughing maneuvers are coupled with body positioning to augment inspiratory volumes, flow rates, and mucociliary transport and to reduce airway resistance. Body positioning, specifically the upright position, is also prescribed to optimize circulatory fluid volume and to reduce the work of the heart.

General body conditioning is a priority for patients with collagen vascular or connective tissue conditions to maximize the efficiency of the oxygen transport system by exploiting the reserve of the unaffected steps in the pathway, thereby minimizing undue increases in the work of breathing and of the heart. Optimal cardiopulmonary conditioning is a priority to reduce the effects of associated cardiopulmonary manifestations of the collagen vascular and connective tissue diseases. The exercise prescription is based on each patient's multiple problems, limitations, and goals.

Endocrine and Metabolic Conditions

Pathophysiology

Endocrine and metabolic disorders, such as disorders of the thyroid gland, pancreas (diabetes mellitus), and adrenal glands, can adversely affect cardiopulmonary function and oxygen transport.[4,100] Thyroid hormone has an important role in the drive to breathe and surfactant synthesis. Hypothyroidism contributes to obstructive sleep apnea, pleural effusions secondary to altered capillary membrane fluid balance, and pericardial effusions. Muscle weakness associated with hypothyroidism leads to reduced vital capacity and to reduced inspiratory and expiratory pressures. Hyperthyroidism increases the cellular metabolic rate, thus increasing oxygen consumption and carbon dioxide production.

Patients with diabetes are prone to cardiopulmonary complications such as aspiration, respiratory infections, reduced sensation of respiratory loading, and microangiopathy.[10,102] Late complications include autonomic neuropathy, peripheral vascular disease, cardiomyopathy, and renal insufficiency.[103] Autonomic neuropathy affects vagal activity and airway function. Ischemic heart disease, which is accelerated in patients with diabetes, and cardiomyopathies are common and may lead to congestive heart failure, cardiogenic pulmonary edema, and renal insufficiency. Peripheral vascular disease may result in tissue ischemia, necrosis, and lower-extremity amputation.

Although primary adrenal insufficiency is rare, the indirect effects of pathology, illness, medications, and arousal are clinically important.[4] The primary catecholamines, norepinephrine and epinephrine, are the two principal vasoactive humoral transmitters in the body. The inhibition and facilitation of the release of these essential transmitters affect airway smooth muscle activity and cardiac activity (at rest or during exercise) and contribute to the regulation of vascular smooth muscle activity for regulation of peripheral blood flow for blood pressure control, tissue nutrition, and thermoregulation.[4]

Implications for Physical Therapy Management

Altered metabolic and endocrine function requires medical attention, usually in the form of pharmacologic support. The effectiveness of this support and whether deficits have been remediated determine the modifications needed in physical therapy treatments.

Physical therapists may be consulted to prescribe exercise for persons with insulin-dependent diabetes to adjust insulin administration, help minimize or eliminate pharmacologic support, and maximize overall fitness and well being.[104] Exercise is known to increase cellular insulin sensitivity, which may reduce or even eliminate the need for insulin or other medications for some individuals with type II diabetes.[105] In addition, exercise increases the efficiency of the oxygen transport system and cellular respiration in patients with diabetes.[50,104] The improved aerobic capacity and health benefits of exercise, along with optimal nutrition (ie, low-fat, low-sugar, complex carbohydrate, and high-fiber diet) and medical management, may minimize the devastating long-term multisystemic effects of diabetes and thus reduce the morbidity and mortality associated with this condition.

Immunological Conditions

Pathophysiology

Both congenital immunodeficiency and acquired immunodeficiency can lead to cardiopulmonary compromise. Inflammation and infection associated with immunodeficiency are the common primary pathophysiological problems.[106,107] Acquired immunodeficiency syndrome (AIDS) is a disorder of cell-mediated immunity, which leads to lymphocyte death. Pneumocystis carinii pneumonia is the leading pulmonary infection associated with AIDS.[108]

Implications for Physical Therapy Management

A primary goal of physical therapy in the management of patients who are immunocompromised is infection control. The primary means of controlling infection is hygienic practices, including hand washing, gloving, masking, and gowning as required. Pulmonary complications can be anticipated in these patients.[109] Patients with pulmonary complications secondary to being immunocompromised have reduced alveolar ventilation, are prone to impaired mucociliary transport, have poor cough reflexes and an inability to cough effectively, and are prone to pulmonary and other opportunistic infections. In addition, these patients are often debilitated and easily fatigued. In extreme cases (eg, end-stage AIDS), the patient may have considerable pain. Frequent and judicious mobilization and body positioning enhance gas exchange[110,111] and promote patient comfort and maintenance of strength. If pneumonia develops, breathing control and coughing maneuvers may be indicated. Postural drainage may be required for some patients. If suctioning is indicated, strict procedures are used to minimize the introduction or spread of infectious microorganisms.

Physical activity is known to have beneficial effects on immunity in the healthy individual.[112] Thus, mobilization that is prescribed commensurate with the patient's overall status may augment immunologic function. Mobilization for its additional immunoprotective effects is a controversial approach, and further investigation is needed, particularly in the management of patients who are severely ill and immunocompromised.

Nutritional Disorders

Pathophysiology

Obesity contributes to deficits in oxygen transport and impaired gas exchange.[113] The degree of severity of oxygen transport deficit is commensurate with the individual's body weight and level of deconditioning. Deficits include alveolar hypoventilation due to the increased mass of the chest wall and abdomen and the increased energy required to displace that mass during respiration, systemic and pulmonary hypertension, increased intra-abdominal mass and pressure, impaired diaphragmatic excursion, cardiomegaly and displacement of the heart and lungs within the thoracic cavity, axis deviation of the heart, and dysrhythmias.[12,113] Weakness and laxity of the oropharyngeal and hypopharyngeal structures contribute to upper airway obstruction and obstructive sleep apnea.

In severe cases, morbid obesity leads to chronic alveolar hypoventilation, hypoxemia, arterial desaturation, reactive pulmonary vasoconstriction, right ventricular insufficiency and failure, peripheral swelling, and increased work of breathing and of the heart.[12] Other symptoms include daytime somnolence, sleep apnea, labored and rapid shallow breathing, and reduced exercise tolerance. Although patients who are moderately obese may be asymptomatic, they are at increased risk of cardiopulmonary complications[14] in conjunction with even minor medical problems or surgical interventions, and they are at increased risk of adverse reactions to pharmacological support. Morbid obesity can contribute directly to respiratory insufficiency (ie, alveolar hypoventilation syndrome).[68]

Reduced activity and loss of conditioning are factors contributing to the cardiopulmonary manifestations of obesity. Reduced activity contributes to increased production of fat-storing enzymes and reduced production of fat-burning enzymes.[113,115] Increased activity and exercise, therefore, result in increased production of fat-burning enzymes and reduced production of fat-storing enzymes. Although aerobic exercise generally contributes to fat breakdown and its metabolic utilization, prolonged exercise (ie, greater than 90 minutes) at a heart rate below the aerobic training zone (ie, 60%-70% of maximum heart rate) has been associated with the greatest fat-burning effects.[104] Optimal weight loss and health result from a combination of proper nutrition (ie, low-fat, low-sugar, high-complex carbohydrate, and high-fiber diet) and exercise.[116-118]

Eating disorders such as anorexia nervosa contribute to deficits in oxygen transport secondary to general debility and metabolic catabolism.[119] The strength and endurance of the respiratory muscles are correspondingly reduced. Coughing is weak and inefficient. Nutritional deficits include anemia and fluid and electrolyte imbalance, which can precipitate cardiac dysrhythmias and death in advanced cases.[4]

Implications for Physical Therapy Management

Management of the patient with obesity for any condition warrants careful attention to deficits in and threats to oxygen transport. These patients are more easily compromised during treatment compared with patients who are not obese. Recumbency may exacerbate symptoms. Patients with obesity often experience less distress with the head of the bed elevated. Patients with obesity should not slouch when they are recumbent because doing so compromises diaphragmatic descent and contributes to closure of the dependent airways. In a supine position, the weight of the abdomen encroaches on the underside of the diaphragm, limiting its excursion. Thus, patients with obesity are often less compromised in a side-lying position in which the abdomen can be displaced forward, permitting increased diaphragmatic excursion (ie, semiprone with abdomen free). The semiprone position provides many of the benefits of the prone position without increasing abdominal pressure. Patients with obesity need to be monitored for signs of cardiopulmonary distress during body positioning, particularly in recumbent positions.[119] In addition to restriction of diaphragmatic motion from the shift of the abdominal mass toward the thoracic cavity in recumbent positions, the heart is compressed and compromised by surrounding structures. Cardiac output is reduced, hypoxemia is potentiated, and cardiac dysrhythmias can ensue.

Anorexia nervosa may be viewed by physical therapists as either a primary or a secondary condition. Primary physical therapy management ranges from intensive care to a judicious modified exercise program prescribed to maintain some degree of mobility, strength, and overall conditioning. Patients with this condition are malnourished; thus, an assessment should be done to establish the impact on cardiopulmonary function. The focus of a mobilization program is to avert the negative sequelae of restricted activity rather than to maximize aerobic capacity, endurance, and strength. It is essential that the oxygen and energy demands do not exceed the patient's capacity to meet these demands physiologically.[120] Dehydration and electrolyte imbalance may accompany malnutrition in the patient with anorexia; thus, blood volume, hemodynamic, and electrocardiographic responses may be abnormal.[100](pp417-420) Due to nutritional deficits, patients with anorexia may also be anemic and have abnormal immunity. Thus, the physical therapist needs to monitor serial blood laboratory values. Patients with anorexia fatigue readily.

Some patients with anorexia nervosa are compulsive exercisers, which increases metabolic demand. In conjunction with psychological and nutritional counseling, the patient should be counseled with respect to reducing excessive physical exercise and conserving energy.

Summary and Conclusion

The example of the 75-year-old man with a primary diagnosis of right cerebrovascular accident described at the beginning of the article can be used to illustrate the cardiopulmonary manifestations of a systemic disease affecting an older person and some of the key points that must be considered in the physical therapy management. Neurological physical therapy for this older patient with a stroke includes control of muscle function, control of pain secondary to overactive muscles, increasing muscle activity in paretic muscles, balance and coordination training, range-of-motion exercises, strengthening exercises, gait reeducation (often with aids such as an ankle-foot orthosis and a quad cane), and endurance training. Many of these interventions elicit an exercise stimulus and stress the oxygen transport system; thus, the patient's cardiopulmonary status needs to be monitored. In view of this patient's age, arterial oxygen tensions can be expected to be low. If the patient smoked, arterial desaturation would likely be accentuated. Intensive aerobic training has been advocated for patients following a stroke.[58] Such intensive training, however, is risky for this patient population without appropriate monitoring and exercise prescription. Patients with stroke are usually older, are often hypertensive, have evidence of coronary artery disease, and have cardiac dyschythmias. Thus, treatments including any form of exercise stress warrant the inclusion of hemodynamic monitoring. In addition, beta-blocking agents that are commonly used for blood pressure control attenuate exercise-induced heart rate and blood pressure responses; thus, other cardiovascular and cardiopulmonary measures of exercise response must be used.

Obesity may complicate the oxygen transport status of some patients following a stroke; thus, nutritional status should be considered. In addition, many older persons tend to be dehydrated, requiring consideration of fluid balance. Sleep apnea and impaired sleep should be assessed to ensure that the patient is adequately restoring physiologically from a night's sleep. Without adequate sleep, the patient cannot perform well physically during the day.

Because dysfunction in almost every organ system of the body can have cardiopulmonary consequences, physical therapists need to be able to predict and detect such manifestations. Although the presentation of these cardiopulmonary manifestations may be subtle, the patient's prognosis is often poorer with even relatively mild cardiopulmonary involvement. The patient therefore should be appropriately monitored, and treatment for cardiopulmonary manifestations or the patient's primary diagnosis should be modified accordingly.

With an increasing trend toward direct access in the profession, physical therapists need to be vigilant about secondary underlying conditions. Known or suspected underlying conditions need to be assessed thoroughly so that the physical therapist can determine whether physical therapy is contraindicated, what therapies are indicated, and how therapy should be modified. Furthermore, physical therapists need to be able to anticipate abnormal treatment responses and to determine when a patient needs to be referred to another health care professional. Virtually all physical therapy interventions are associated with hemodynamic stress and demands on the oxygen transport system. Thus, this stress on oxygen demand must be considered with respect to the capacity of every patient to transport oxygen, which encompasses the delivery, uptake, and utilization of oxygen.

With changes in the demography of the population and in health care problems, physical therapists are seeing more patients than ever before who have complex, multisystem problems. Such problems can be seen in the medically stable individual living in the community or a nursing home, in the medically stable patient being treated in the hospital, and in the unstable patient in intensive care with multiorgan system failure. High-risk patients are not restricted to the intensive care setting. Physical therapists in all specialties need an understanding of the cardiopulmonary consequences of systemic diseases because these effects can range from being relatively minor with little effect on function to being life threatening.

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E Dean, PhD, PT, is Associate Professor, School of Rehabilitation Sciences, University of British Columbia, 2211 Wesbrook Mall, Vancouver, British Columbia, Canada V6T 1Z3 ([e-mail]), and Clinical Associate, Physiotherapy Department, Royal Columbian Hospital, New Westminster, British Columbia, Canada, and Physiotherapy Department, St Paul's Hospital, Vancouver, British Columbia, Canada. Address all correspondence to Dr Dean at the first address.