Breathing exercises for the medical patient: the art and the science.

Breathing Exercises for the Medical Patient: The Art and the Science The use of breathing exercises to maximize gas exchange has been discussed for years, including in an article in the 1800s by Nicholson [1] regarding the art of deep breathing and in articles by Ewart [2] and MacMahon [3] in the early 1900s. since this time, adjunctive techniques and devices for increasing the strength and endurance of the respiratory muscles have been adopted.

This article will review the present state of the art of breathing exercises for the medical patient. The skills of performing these techniques are well established; the need for specific research to validate the efficacy of these techniqus is an issue critical to patient care and to our profession. Breathing exercises for the postoperative latient, including techniques for facilitating maximal inspiration, will not be covered in this article.

Ventilatory Muscles

The ventilatory muscles may be divided into three groups: 1) the diaphragm, 2) the intercostal and accessory muscles, and 3) the abdominal muscles. [4] Contrary to common perception, all three groups have an inspiratory and an expiratory function. [4]

The diaphragm provides the major inspiratory pump action, particularly at low lung volumes. [5] The diaphragm is well equipped for repetitive contractions, because it contains muscle fibers rich in mitochrandrial enzymes and as a result aerobic metabolism is favored. [6]

About 75% of the diaphragm and intercostal muscle fibers are slow-oxidative (type I) and fast-twitch, high-oxidative fibers (type IIa), which have a high endurance capability and are quite resistant to fatigue. [6] The optimal resting length at which the diaphragm can generate maximum tension is most likely to be at low lung volumes, just below functional residual capacity in healthy individuals. [7] The muscles' contractile force is greatly reduced when the diaphragm contracts from the shortened position. [4] At any given load, hyperinflation of the lung also predisposes the inspiratory muscles to fatigue. [7,8]

The variation of pressure achieved and of muscle length is particularly important when dealing with the patient with chronic obstructive pulmonary disease (COPD) who has a chronically shortened or flattened diaphragm. If the normal diaphragm in humans is shortened to one half of its resting length, the contractile tension of the muscle is zero. [6] There is evidence in the animal model that the diaphragm readjusts to a shortened range over a long period of time by losing sarcomeres and readjusting its tension-length relationship. No documentation of this occurrence in humans, however, is available. [6]

The accessory muscles primarily comprise the scalene and sternocleiodomastoid muscles. The scalene muscles, which are thought to be inactive during quiet breathing, are active ith inspiration in the upright and supine positions. [9] The sternocleidomastoid muscles, or the muscles that can produce the pumping action on the rib cage, are usually inactive during quiet breathing, but they are very active when a person is breathing at high lung volumes or during high levels of ventilation, such as during exercise. [9]

The abdominal muscles, traditionally tagged as only expiratory muscles, can be very important to the inspiratory phase of ventilation. The exact inspiratory contribution in humans is not clear. As the abdominal muscles contract during active exhalation, the diaphragm is pushed cephalad to a resting position of greater length or stretch. This more favorable length them permits a greater volume of inspiration with less activation of the muscle. [9]

Indicators of Muscle Fatigue

or Pump Failure

Fatigue generally occurs when the energy demand exceeds the supply and may be due to many factors, including high resistive breathing, hypoxia, or low cardiac output. [9] Whatever the cause, the result leads to alveolar hypoventilation and carbon dioxide retention. Clinical features and blood gas changes of inspiratory muscle fatigue in patients, including those being weaned from ventilatory support, include (in order of appearance):

1. Dyspnea (shortness of breath).

2. Increased respiratory rate, or the rate that becomes necessary to maintain minute ventilation and to optimize arterial oxygen and carbon dioxide values.

3. Asynchronous breathing pattern with abdominal or chest-wall discoordination. This thoracoabdominal discoordination is an indicator of ventilatory muscle fatigue, which has been noted both in nonintubated patients and in patients being weaned from mechanical ventilation. [10] However, one must be aware of Roussos and Macklem's [11] observation that subjects alternated breathing patterns and muscle groups during ventilation. These investigators initially labeled this asynchronous breathing pattern "discoordination," but they further observed it to be a coordinated effort that seemed to protect the muscles from exhaustion by alternating muscle activity.

4. Increase in arterial carbon dioxide pressure.

Therapy

Expiratory muscle fatigue is often not the major factor or cause of general respiratory failure, the notable exception being denervated or weakened expiratory force to cough or clear secretions. Expiratory muscle training will not be further covered in this review.

Treatment programs to improve inspiratory muscle function can be divided into three categories [12]:

1) programs designed to reduce the load on the inspiratory muscles, including reducing the mechanical disadvantage; 2) programs designed to improve the muscles' contractile characteristics, including strength and endurance; and 3) programs designed to rest the inspiratory muscles with mechanical ventilation if the muscles have an inability to maintain ventilatory function

Reducing Loan on the

Inspiratory Muscles

Two types of techniques are used to reduce load on the inspiratory muscles: 1) techniques designed to decrease airway resistance or maximize lung compliance and 2) techniques designed to decrease the work of breathing and decrease the work of position of the diaphragm and the intercostal muscles. The use of drug therapy to decrease airway resistance and increase lung compliance is an essential element of treatment. Methylxanthines, traditionally prescribed to facilitate bronchodilation, are now being recognized for their effect on the restoration or prevention of diaphragmatic fatigue. [13] Theophylline, usually in the form of aminophylline, has bene found to increase contractility in health individuals as well as in those who are paralyzed or have COPD. [13]

The techniques used since the late 1800s in Great Britain have included techniques to maximize use of the diaphragm and strengthen the abdominal muscles in relation to ventilation. Since that time, techniques such as diaphragmatic and pursed-lip breathing have been used in an attempt to control dyspnea, improve ventilation, and decrease the work of breathing. [14-20]

Diaphragmatic breathing exercises. Barach, [17] in the 1960s, discussed the value of optimizing the resting position of the diaphragm. He believed he could decrease the work of breathing and hyperinflation while maximizing the resting position of the diaphragm through the use of the Barach belt. This elasticized belt allowed patients to increase their functional activity. The belt can be thought of as an active abdominal contraction that provides the force to move the diaphragm to a more lengthened position prior to the next contraction. It also provides some resistance for the diaphragm to contract against, possibly increasing maximal inspiratory force.

Investigators have attempted to evaluate the efficacy of diaphragmatic breathing exercises, but little information is available in the literature regarding actual techniques for facilitating or maximizing the resting position of the diaphragm.

Diaphragmatic breathing is often instructed with such clues as "place your hand on the patient's abdomen and have the person make the abdomen protrude on inspiration." The therapist's hand is passive, used simply to indicate the place of expected movement. Clinicians have noted that it is sometimes difficult for the patient to make this initial inspiratory movement. This difficulty is not surprising, with a shortened diaphragm attempting to contract from an essentially dysfunctional position and unable to increase its work capacity.

The techniques we use in our clinic (Physical Therapy Services, Massachusetts General Hospital, Boston, Mass) to maximize the contraction are stretch and resistance to the diaphragm, with controlled abdominal contraction on exhalation. The patient is requested to exhale while the therapist places his or her hand below the rib cage over the diaphragm, pushing up and in during exhalation (Fig. 1). This maneuver ostensibly shifts the resting position of the diaphragm, similarly to the Barach belt. As the patient finishes exhalation, a "quick stretch" or slight increase in lressure immediately precedes the command for the patient to inhale. The therapist provides graded resistance or pressure on inhalation, increasing the recruitment of motor units with some overload or resistance. If the patient is unable to tolerate resistance, the therapist's hand follows the diaphragmatic motion without resistance. Once inhalation is complete, the patient is instructed to exhale with slow, controlled contraction of the abdominal muscles. This action is similar to the therapist's hand and is used with self-practice (Fig. 2).

The techniques have some sound physiological support for a number of reasons:

1. It is felt that the resting position of the diaphragm can be shifted through mechanical change (Barach belt) [17] or position (45[degrees] of flexion). [21]

2. The abdominal muscles are now recognized as maintaining motor unit activity even during inspiration, defending the diaphragmatic length during inspiration. [22] The graded resistance on inspiration and eventual patient awareness of abdominal tone (co-contraction) on inspiration are somewhat synonymous. [23]

3. Inspiratory resistance applied at the mouth has resulted in increased respiratory muscle strength and endurance. [24] It seems logical that resistance applied over the muscle belly could provide similar changes with graded overload or overload that the muscle can still contract against. These techniques have been used successfully in nonintubated patients with dyspnea secondary to respiratory failure as well as in patients with diaphragmatic shortening and lung hyperinflation being weaned from mechanical ventilation.

Pursed-lip breathing. Pursed-lip breathing is initiated by many patients, and taught to others, with similar relief of duspnea reported by both groups. [16,25-27] This technique has not received careful scrutiny, but researchers have felt that the use of pursed-lip breathing may delay or prevent airway collapse, allowing for better gas exchange. This may be why the use of pursed-lip breathing can decrease the respiratory rate of an individual and increase the tidal volume per breath. [27,28] However, the mechanical advantage that results from pursed-lip breathing may be equally important or advantageous. During pursed-lip breathing in patients who have self-initiated the use of this technique, the abdominal muscles are usually noted to actively contract on exhalation. This contraction, therefore, may result in a mechanical shift of the diaphragm during exhalation, putting it at amore lengthened position prior to the next contraction. [27].

Training Ventilatory Muscles for

Strength and Endurance

Definitions often used for strength, endurance, and fatigue in relationship to nonrespiratory muscles can also be applied to the ventilatory muscles. Strength is the maximal force that a muscle can develop. Endurance is measured as the length of time a muscle can contract against a given load. Fatigue is the inability to maintain a predetermined force during contraction.

Leith and Bradley [28] were the first researchers to demonstrate the respiratory muscle strength and endurance can be improved in healthy subjects. Evaluation of the results of applying weights or resistance to the ventialatory muscles, however, w{as not a new concept or goal. [29]

The concepts of ventilatory muscle training are similar to those of other skeletal muscles. These muscle training characteristics include 1) overload, 2) specificity, and 3) reversibility. [30]

Overload. A muscle must experience a load greater than the stress it normally carries for training to take effect. The overload for strength is high, with fast, short repetitions. The overload for endurance is of lower intensity, and it is sustained or repeated for long periods of time.

Specificity. The training must be similar or identical to the activity that the therapist wishes to improve (ie, directed toward the functional characteristics of the muscle) and must directly involve the muscles that are to be trained. [31]

Reversibility. Reversibility simply means that if the training or overload is stopped, the training effects will be lost and the muscles and functional characteristics will return to baseline levels.

The strength and endurance capabilities are often both decreased in the patient with chronic respiratory failure or with respiratory failure attributable to neuromuscular or musculoskeletal defects. A training program may be designed to emphasize or train for strength or endurance.

Strength may be increased by contracting the muscles against high loads, which can be achieved by inspiratory resistive training, [24h static maximal inspiratory efforts, [28] or application of weights directly on the muscles. [32] Endurance may be increased by performing numerous contractions against resistance that can be sustained without fatigue. These changes have been observed with inspiratory resistance at the mouth. [24]

Gross et al [33] have shown that patients with quadriplegia secondary to spinal cord injury experience decreased muscle strength and endurance after injury, which predisposes them to inspiratory muscle fatigue. Six nonintubated patients with chronic quadriplegia (at least 1 year postinjury) participated in a ventilatory muscle training program that consisted of breathing for 15 minutes, two times a day, 6 days a week against inspiratory resistance at the mouth. Measurements were taken at 8, 12, and 16 weeks of training. The patients showed an increase in both strength and undurance with this program.

Lane [32] trained the diiaphragm for strenth through use of weights in 16 nonintubated patients with acute spinal cord injury (Fig. 3). A program of progressive resistive exercise resulted in improvement in the treatment group's mean vital capacity of from 1,463 cc to 2,460 cc, whereas the control group's mean vital capacity increased from 1,310 cc to 1,897 cc. The average hospital stay was 17.3 and 9.9 weeks for the control group and the treatment group, respectively. The results of this study support the need for muscle strengthening exercises in this population after the patient is stabilized postinjury. No published work is currently available in which the spinal cord injured patient has begun a training program while still on mechanical ventilation or being weaned from ventilatory support.

The respiratory muscles of the patient sith COPD are in a condition of constant overload, frequently to the point of fatigue. One might surmise that this constant overload could cause these muscles to have increased strenth and endurance and perhaps to hypertrophy. Because it is well recognized that the diaphragm of patients in this population is in an inefficient position to contribute effectively to the inspiratory motion, it has been a common belief that the constant use of accessory muscles causes these muscles to hypertrophy as the diaphragm atrophies. Postautopsy evaluation of the muscle bulk of patients with COPD has revealed both the diaphragm and the sternocleidomastoid muscles to be atrophied. [10]

The majority of work in relation to inspiratory muscle training for patients with COPD has been done with the patient in the chronic or stable state. [24,34-37] Studies performed on stable patients with COPD have demonstrated the following:

1. Breathing retraining may increase ventilatory efficiency and therefore increase function. [35]

2. Inspiratory resistance and hypernea (patient breathing as deeply and as a fast as possible for a specified period of time) can produce increases in respiratory muscle strength or endurance as well as increased exercise capability. [24,35,37]

3. General body conditioning may not result in increased respiratory strength and endurance, [34] a finding in contrast to upper extremity training resulting in increased respiratory endurance in patients with cystic fibrosis. [36]

Although this previous work cannot be immediately used as an indication of how patients in respiratory failure on mechanical ventilation will necessarily respond, it has led to recent research with the use of inspiratory muscle training in patients who are unable to be weaned from mechanical support systems.

aldrich and Karpel [38] used inspiratory resistance training to treat four patients with artificial airways (two with a history of COPD) for their inability to be weaned from mechanical ventilation. The patients were trained 5 to 15 minutes in the initial session, and their inspiratory treatment time was increased to 30 minutes before increasing the resistance. Treatment sessions were conducted a minimum of 2 hours apart. Each patient had undergone repeated attempts at weaning and could tolerate 30 minutes to 24 hours off ventilation. Each patient's peak negative inspiratory pressure was measured near residual volume. The inspiratory resistance training was begun at 15% to 30% of the patient's peak negative inspiratory pressure. If the respiratory rate reached 30 breaths per minute or respiratory distress (no definition provided by authors of article) occurred, the investigators ceased treatment. Two times a week a trial wean was attempted on the T-piece (oxygen support provided to artificial airway with no additional pressure or mechanical ventilatory support). The number of treatment days ranged from 11 to 24, and the number of sessions ranged from 17 to 21. The investigators were able to successfully wean three of the four patients from mechanical ventilation. These three patients had an increase in inspiratory muscle strength and vital capacity, as well as an increased tolerance to the T-piece trials.

Belman [39] was also able to successfully wean two patients with COPD, who were in acute respiratory failure, from mechanical ventilatory support by using a program of isocapnic hypernea (patient breathing as deeply and as fast as possible for 15 minutes, with a controlled flow of oxyten to maintain end tidal volume within physiologic limits). The hypernea was continued for 15 minutes, if tolerated, three to six times a day. After extubation and discharge, muscle training was continued for 5 weeks.

The therapist need not rely solely on inspiratory resistance or hypernea for the ability to train the respiratory muscles of the weaning patient. The ability to provide graded resistance with the hand for the individual with very poor muscle contraction has been found useful in our clinic (Fig. 4).

In our clinic, we have used stretch and graded resistance to train the patient who is unable to wean from mechanical ventilation and who exhibits extremely weakened inspiratory strength or endurance. A case, shown in Figure 4, of a patient with quadriparesis following cerebral aneurysm repair who was unable to wean from mechanical ventilatory support, resulted in a dramatic change in tidal volume and vital capacity. The patient's inability to wean from mechanical ventilation was believed to be attributable to phrenic nerve paralysis, central nervous system dysfunction, or simple ventilatory muscle fatigue and failure. The program, which consisted of brief periods off mechanical support (2-3 minutes initially, with oxygen support maintained) combined with stretch and graded resistance to the diaphragm provided by a therapist, was repeated three or four times a day. The patient's tidal volume was monitored during each treatment session, which was terminated when a decrease in muscle contractile force was noted through palpation. This decreased contraction was considered the earliest clinical indicator of fatigue and preceded any decrease in tidal volume. This treatment program resulted in an increase in tidal volume from 100 cc to 500 cc, a decrease in inspiratory force from -15 cm [H.sub.2.O] to -30 cm [H.sub.2.O], and an increase in |ital capacity from 600 cc to 900 cc. These changes were slow, but steady, with the patient off mechanical ventilation for 12 hours a day at the end of 3 months of treatment.

Resting the Inspiratory Muscles

Numerous researchers [40,41] are currently evaluating intermittent inspiratory muscle rest for the patient with COPD. Negative-pressure mechanical ventilation has been used for as little as 1 hour with a resultant increase in transdiaphragmatic pressure. [41] Other investigators [42,43] have found no change in respiratory muscle strength or patient activity level after use of negative pressure for 2 months, 2 to 7 hours a day.

The issue yet to be resolved revolves around clinically recognizing respiratory muscle fatigue and adapting care to limit or decrease fatigue. The use of intermittent mechanical support may allow the fatigued muscles to rest. The appropriate level of support to the fatigued muscles, combined with the subsequent appropriate load applied to the muscles to increase strength or endurance, is essential to care and has not yet been adequately evaluated.

References

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C Kigin, MS, MPA, PT, is Director, Physical Therapy Services, Massachusetts General Hospital, Boston, MA 02114 (USA).