Conical-PEP is safe, reduces lung hyperinflation and contributes to improved exercise endurance in patients with COPD: a randomised cross-over trial.
Expiratory flow limitation, which is the primary pathophysiological hallmark of chronic obstructive pulmonary disease, is caused by reduced lung elastic recoil and increased airway resistance. Forced expiration associated with the increased ventilatory demands of exercise can induce premature airway closure (O'Donnell 1994, Rabe et al 2007) leading to air trapping and dynamic hyperinflation. Dynamic hyperinflation contributes to increased elastic and mechanical loads on the inspiratory muscles and to neuroventilatory dissociation which further exacerbate the shortness of breath, leading to exercise intolerance, limited physical activity, and thus to a poor quality of life (Christopher 2006, O'Donnell 1994, O'Donnell et al 2007).
Various strategies have been explored to manage dynamic hyperinflation. One recommendation is to increase expiratory time as a result of slowing the respiratory rate by using low-level positive expiratory pressure (O'Donnell 1994, Wouters 2006). Pursed lips breathing, essentially a low level positive expiratory pressure of 5 cm[H.sub.2]O suggested by van der Schans et al (1995), is often adopted spontaneously by patients with chronic obstructive pulmonary disease to prolong expiration and lower respiratory rate. A previous study has shown a trend for pursed lips breathing to decrease end expiratory lung capacity and consequently dyspnoea (Fregonezi et al 2004). However, the evidence that pursed lips breathing is beneficial for dyspnoea, exercise endurance, and dynamic hyperinflation remains uncertain (Fregonezi et al 2004, Spahija et al 2005). This uncertainty might be the result of variation in the severity of chronic obstructive pulmonary disease and/or the extent of positive expiratory pressure generated by pursed lips breathing.
Positive expiratory pressure devices can prolong expiratory time and decrease respiratory rate (van der Schans et al 1994), thereby reducing airway closure (Marini et al 1989) and dynamic hyperinflation, and have been used in the management of lung disease in which airway collapse is a problem. However, there has been little investigation of the effect of positive expiratory pressure in chronic obstructive pulmonary disease in terms of exercise endurance, dyspnoea, or dynamic hyperinflation. Van der Schans et al (1994) showed that patients with chronic obstructive pulmonary disease who breathed through a positive expiratory pressure device at 5 cm[H.sub.2]O decreased minute ventilation during exercise and had a tendency to decrease respiratory rate. However, dyspnoea and C[O.sub.2] retention were increased. They hypothesised that insufficient positive pressure was generated to reduce airway closure and that using higher positive expiratory pressure would be more effective during exercise. Consequently, we developed a small conical positive expiratory pressure device (conical-PEP) that can generate higher positive expiratory pressures compared to commercial cylindrical positive expiratory pressure devices. In addition, a recent controlled case report of the effects of conical-PEP on lung hyperinflation during arm exercise in a patient with moderate chronic obstructive pulmonary disease demonstrated that exhaling through the device was safe with no hypoxaemia or hypercapnia, and tended to decrease lung hyperinflation (Padkao et al 2008).
Therefore the specific research questions for this study were:
1. Does conical-PEP breathing decrease dynamic lung hyperinflation during exercise in patients with moderate to severe chronic obstructive pulmonary disease compared to normal breathing?
2. Does it increase the duration of exercise?
We hypothesised that conical-PEP would be beneficial in increasing expiratory time via a reduction in respiratory rate and, consequently, reducing dynamic hyperinflation during exercise.
A randomised cross-over trial was conducted in which participants received each intervention twice. Patients with moderate-to-severe chronic obstructive pulmonary disease were recruited from the Outpatients Department, Srinagarind Hospital, Khon Kaen, Thailand. One to two weeks before the study, participants visited the Pulmonary Research Room at Khon Kaen University to determine one repetition maximum (1 RM) of both quadriceps muscles (Armstrong et al 2006) and familiarise themselves with the procedures. Participants were randomised to receive the experimental intervention (breathing with conical-PEP during exercise) and the control intervention (normal breathing during exercise) in the following order: either conical-PEP breathing followed by normal breathing and then vice versa or normal breathing followed by conical-PEP breathing and then vice versa (Figure 1). The recruiters were blinded to order of intervention because randomisation happened at a different site from recruitment. There was a washout period of at least 30 minutes between the four interventions where participants rested so that heart rate, blood pressure, and inspiratory capacity returned to their initial pre-exercise level. Lung capacity, breathlessness and leg discomfort were measured pre and immediately post each intervention and cardiorespiratory function was measured pre and during the last 30 seconds of exercise by an assessor not blinded to the order of intervention. Statistical analysis was carried out by an investigator blinded to the order of intervention.
Patients were included in the trial if they had moderate-to-severe chronic obstructive pulmonary disease defined as forced expiratory volume in one second per forced vital capacity < 70%; forced expiratory volume in one second that was 30-79% predicted and this reduction was not fully reversible after inhalation of a bronchodilator (Rabe et al 2007); were clinically stable and free of exacerbations for more than four weeks defined by change to pharmacological therapy, admission to hospital or emergency room, or unscheduled clinic visit; were independent of long term oxygen or domiciliary non-invasive positive pressure ventilation; and could communicate well. They were excluded if they had musculoskeletal impairments that limited leg mobility, cardiovascular disease, neurological or psychiatric illness, or any other co-morbidities which would interfere with exercise. Medications were not changed and patients were administered a long lasting bronchodilator two hours prior to the start of the protocol to reduce static hyperinflation.
The experimental intervention was conical-PEP breathing during exercise. Leg extension exercise at a load 30% of 1 RM with weights firmly strapped to the ankles, was carried out with the participants in sitting. Both legs were exercised, alternately, with approximately 15 contractions per leg per minute, while breathing through the mouthpiece fitted with conical-PEP (Figure 2). The conical-PEP device has a fixed orifice resistor consisting of a small conical plastic tube 4 cm in length and 2.5 cm and 0.6 cm in internal diameter at the proximal and distal openings, respectively. The expiratory flow retardation created by the distal end produces positive back pressure on the airway. The expiratory pressure induced by resistance of the conical-PEP is flow dependent; the greater the expiratory flow the greater the back pressure (Mitchell 2007, Weng 1984). It produces a positive mouth pressure of 4.2-10.9 cm[H.SUB.2]O at expiratory flows of 0.06-0.41 L/s at rest and 4-20 cm[H.SUB.2]O at flow rates of 0.09-0.51 L/s during exercise. This pressure range has been reported to be optimal for retarding airway collapse in patients with chronic obstructive pulmonary disease (O'Donnell et al 1988, Petrof et al 1990, Plant et al 2000). Exercise was terminated when one of the following symptoms occurred: breathlessness [greater than or equal to] 5/10 on the modified Borg scale, leg discomfort, or any other unpleasant symptoms such as dizziness.
The control intervention was normal breathing during exercise.
Lung function was measured as inspiratory capacity and slow vital capacity in litres according to ATS/ERS taskforce guidelines (Miller et al 2005) with a portable automated spirometer (a). The volume sensor was calibrated before each test. The duration of exercise and the reasons for exercise termination were collected. Breathlessness was measured using the modified Borg scale (0 to 10) where 0 is no breathlessness and leg discomfort was measured using a 0-10 visual analogue scale where 0 is no discomfort.
Cardiorespiratory function was also measured. Sp[O.sub.2] was measured by finger pulse oximeter and end tidal pressure of carbon dioxide ([P.sub.ET]C[O.sub.2]) was measured in a side-stream of expired air with a capnometer (b). Electrocardiogram, expiratory mouth pressure and expiratory flow rate were continuously recorded on a PC with an A/D converter (c). The flow and pressure sensors were calibrated before each data collection. Tidal volume, respiratory rate, inspiratory time, expiratory time and ratio (I:E ratio) were determined from the flow signal. Minute ventilation was calculated for the last minute of exercise.
A pilot study of two elderly participants without lung disease showed a between-intervention difference of 150 ml (SD 130) for inspiratory capacity. Therefore, we needed 11 participants to have a 90% power to detect between intervention difference of 150 mL at p = 0.05.
[FIGURE 1 OMITTED]
[FIGURE 2 OMITTED]
Student's paired t tests showed no evidence of either period effects or intervention-period interaction of the primary outcome and, therefore, the data for the two tests in each intervention were averaged to provide a single value for each participant. Statistical significance was considered at p < 0.05, therefore mean between-intervention differences (95% CI) are presented.
Flow of participants, therapists through the trial
Forty-three patients with moderate-severe stages of chronic obstructive pulmonary disease were screened and 17 (40%) agreed to participate in the study. Of these, 4 (24%) withdrew prior to randomisation for reasons that were unrelated to the procedures of the study. Thirteen patients (1 female and 12 male) were included in the study and all completed the interventions (Figure 1). Their baseline characteristics are presented in Table 1. The thirteen participants had moderate to moderately severe airflow obstruction (Knudson et al 1983) and only two patients were slightly breathless at rest (ie, breathlessness = 1 and 0.5 out of 10).
One physiotherapist delivered the interventions at the Pulmonary Research Room of the Physical Therapy Department at Khon Kaen University in Thailand. The therapist had a degree in physiotherapy and three years experience working in the Easy Asthma and COPD Clinic of Srinakharind Hospital.
Compliance with trial method
The participants found breathing through conical-PEP during exercise to be acceptable and there were no complications or adverse events. The exercise resulted in heart rates that were approximately 70% of the age-predicted maximum. The following criteria would have been considered unsafe: Sp[O.sub.2] < 88%, [P.sub.ET]C[O.sub.2] > 50 mmHg, or changes > 20% from control values while using conical-PEP. Oxygen saturation (Sp[O.sub.2]) was > 92% during exercise, and there was no evidence of hypercapnia or abnormal electrocardiogram.
Effect of intervention
Group data for lung capacity are presented in Table 2 and for cardiorespiratory function in Table 3. Individual data is presented in Table 4 (see eAddenda for Table 4). Inspiratory capacity increased 200 ml (95% CI 0 to 400) more after the experimental intervention and slow vital capacity increased 200 ml (95% CI 0 to 400) more after the experimental intervention than the control intervention.
Participants exercised for 687 s (SD 287) during the experimental intervention compared with 580 s (SD 248) during the control intervention (mean difference 107 s, 95% CI -23 to 238). Participants stopped exercising either because of breathlessness (n = 6) or because of leg discomfort (n = 7). The median breathlessness score for all patients was 4 out of 10 (IQR 2.0-5.0) immediately after the experimental intervention, and 4 (IQR 3.0-5.0) after the control intervention. The median leg discomfort was 10 out of 10 (IQR 0-10) immediately after the experimental intervention, and 10 (IQR 0-10) after the control intervention.
Change in cardiorespiratory function (heart rate, tidal volume, minute ventilation, [P.sub.ET]C[O.sub.2] or Sp[O.sub.2]) from rest to the last 30 s of exercise was not different between the interventions. A longer inspiratory time during the experimental intervention compared with the control intervention (mean difference 0.3 s, 95% CI 0.0 to 0.7) and longer expiratory time (mean difference 0.9 s, 95% CI 0.3 to 1.5) resulted in a slower respiratory rate (mean difference -6.1 breaths/min, 95% CI -10.8 to -1.4). However, this slower respiratory rate did not have any adverse effects on CO2 retention or oxygen saturation. In addition, mouth pressure was 8.5 cm[H.sub.2]O (95% CI 5.9 to 11.2) higher and respiratory flow rate 0.21 L/s (95% CI 0.12 to 0.31) slower during the experimental intervention compared to the control intervention. The I:E ratio went from 1:1.5 to 1:1.7 during the experimental intervention and from 1:1.6 to 1: 1.4 during the control intervention.
There was no effect of order of intervention.
This is the first report of positive expiratory pressure being used successfully to prevent hyperinflation during exercise in patients with chronic obstructive pulmonary disease. The only previous, and unsuccessful, attempt to use positive expiratory pressure during exercise employed a cylindrical device to increase the expiratory pressure but this probably did not provide sufficient resistance to be effective. The data confirmed our hypothesis that PEP would prevent hyperinflation during exercise.
The device proved to be acceptable to the patients when used during exercise. Over 80% of those eligible were willing to try it and of those who were willing, all found it acceptable. Furthermore, when used with the regimen of exercise in the study, there were no adverse effects. The expiratory mouth pressure developed during exercise with the conical-PEP device averaged about 13 cm[H.sub.2]O which is the level recommended to maintain patent airways in such patients. Respiratory rate was reduced, largely as a consequence of increased expiratory time. End tidal C[O.sub.2] and oxygen saturation were not significantly altered by conical-PEP indicating that the physical dimensions of the new conical-PEP device we have used allow appropriate gas exchange in these patients.
Constant work load cycling exercise is recommended for the investigation of exercise capacity in clinical trials (Maltais et al 2005, O'Donnell et al 2001), but the upper body movement involved in cycling makes it difficult to measure some of the parameters of ventilatory pressure and air flow. Consequently we used dynamic quadriceps exercise whilst sitting which reduces these problems while still using large muscle groups and placing a significant load on the cardiovascular and respiratory systems. When using leg weights of 30% 1 RM, the patients were exercising at about 70% of their age-predicted maximum heart rate in a type of activity that is often recommended for pulmonary rehabilitation and training in patients with chronic obstructive pulmonary disease (Spruit et al 2002). Thus, the training regimen we used is probably a good training protocol for improving aerobic capacity (Spalding et al 2004).
Our results clearly indicated that conical-PEP reduced dynamic hyperinflation. Although it did not reach statistical significance, the results also suggest that patients with chronic obstructive pulmonary disease might be able to achieve a greater training load when using conical-PEP. Exercising at 30% 1 RM may involve an element of anaerobic metabolism and consequently we may have underestimated the benefit of conical-PEP during purely aerobic exercise such as walking.
Although, on average, the exercise duration was longer with conical-PEP, the wide confidence intervals reflect a lack of precision of the estimate of the mean difference between conical-PEP and normal breathing. Those patients who improved their exercise duration did not necessarily report a decrease in breathlessness as a reason, leg fatigue being an equally common reason for ceasing exercise. Although some patients reported lower ratings of perceived breathlessness and leg fatigue at the end of exercise with conical-PEP, this was not a consistent observation and, on average, there were no differences between conical-PEP and control interventions. However, it should be noted that the exercise protocol was designed to be symptom limited and so it is to be expected that the patients would naturally continue exercising until their symptoms reached similar values in the different protocols.
The finding that conical-PEP breathing significantly improved inspiratory capacity and slow vital capacity confirms that it has a real effect on exercise-induced hyperinflation. The fact that this carried over to a strong trend in exercise endurance suggests that it was probably a key element in determining volitional fatigue during the exercise test. It is reasonable that the significant improvement in hyperinflation did not carry over to a significant difference in endurance time because many factors affect the point of volitional fatigue. In addition to breathlessness, which is the main interest here, leg muscle fatigue, pains and sensations associated with joints and tendons, and an increase in body temperature, as well as boredom, may all contribute.
The finding that inspiratory capacity did not change during exercise in the control intervention was surprising but may reflect the fact that these patients had only moderate airflow obstruction. Therefore the lung hyperinflation might have been reduced by bronchodilator administration prior to the protocol and the exercise did not exacerbate the degree of hyperinflation that may have existed at rest. A useful control would have been to test the effect of conical-PEP on these patients at rest where we would anticipate that they would show a similar increase in inspiratory capacity.
Exercise training is the key component of pulmonary rehabilitation programs for chronic obstructive pulmonary disease but is often limited by early exercise-induced dyspnoea aggravated by dynamic hyperinflation (O'Donnell and Webb 2008). Pharmaceutical approaches (O'Donnell et al 2004) and non-invasive CPAP have been suggested as ways of minimising dynamic hyperinflation. Conical-PEP, a very simple and cheap device, was effective in reducing dynamic hyperinflation. It also has the potential to be used in a wide range of activities since it is not limited by a power supply. Conical-PEP may have the potential for use as an economical and non-invasive tool for increasing exercise in a pulmonary rehabilitation program in this population.
While the results are encouraging, there a number of limitations to this study. The study could have been undertaken with patients in whom there is more clearly defined hyperinflation and with exercise protocols that are closer to the activities of daily life. Also, more complex exploration of the physiological mechanisms involved in exercise limitation as a consequence of dynamic hyperinflation would have been valuable. The rather limited form of exercise used in the present study was necessary to measure pressure and airflow. However, in terms of assessing the functional benefits of conical-PEP, other forms of unrestricted exercise such as during pulmonary rehabilitation or the activities of daily living could be investigated without making the physiological measurements.
We conclude that this novel and simple conical-PEP device is safe and effective for COPD patients to use during exercise and that the reduction in hyperinflation makes a small, but potentially useful, contribution to improving exercise performance.
Footnotes: (a) KoKo spirometer, PDS Healthcare Products, Inc., USA. bBCI 9004 Capnocheck[R] Plus, SIMS BCI Inc., Nagold, Germany. cMP30, Biopac, Santa Barbara, CA., USA.
eAddenda: Table 4 available at JoP.physiotherapy.asn.au.
Ethics: The Ethical Committee for human research of Khon Kaen University approved this study. All participants gave informed consent before data collection began.
Competing interests: None declared.
Support: Graduate School and Faculty of Associated Medical Sciences, Khon Kaen University, Thailand.
Acknowledgements: The authors are grateful to the patients, nurses, and officers of the Respiratory Unit of Srinagarind Hospital for their assistance in the conduct of this study, to Assistant Prof. Dr J Khiewyoo for her helpful advice on the statistical analysis, and to Prof. DA Jones for helpful discussion and preparation of the manuscript.
Correspondence: Dr Chulee Jones, Department of Physical Therapy, Khon Kaen University, Thailand. Email: chulee@ kku.ac.th
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Tadsawiya Padkao, Watchara Boonsawat and Chulee U Jones
Khon Kaen University, Thailand
Table 1. Baseline characteristics of participants. Characteristic n = 13 Age (yr), mean (SD) 59 (9) BMI (kg/[m.sup.2]), mean (SD) 21.7 (2.7) [FEV.sub.1] (% predicted), mean (SD) GOLD stage II (n = 10) 65.3 (12.2) GOLD stage III (n = 3) 41.7 (5.7) [FEV.sub.1]/ FVC (%), mean (SD) 55.5 (9.3) Smoking history, mean (SD) Pack-yr 33 (31) Duration of smoking cessation (yr) 4.5 (5.3) Medication, n (%) Inhaled glucocorticosteriods 2 (15) Combination [[beta].sub.2]-agonists plus 8 (62) glucocorticosteroids Bronchodilators 8 (62) Combination P2-agonists plus 6 (46) anticholenergic Duration of medical intervention (yr), 3.1 (2.8) mean (SD) BMI = body mass index; GOLD = Global Initiative for Obstructive Lung Disease. Table 2. Mean (SD) of lung capacity pre and post each intervention, mean (SD) difference within interventions, and mean (95% CI) difference between interventions. Outcome Interventions Pre exercise Post exercise Exp Con Exp Con Inspiratory capacity# 2.65# 2.67# 2.85# 2.67# (L)# (0.48)# (0.46)# (0.52)# (0.58)# Slow vital capacity 3.70 3.69 3.98 3.77 (L) (0.96) (0.95) (1.01) (0.90) Difference Outcome Difference within between interventions interventions Post minus pre exercise Post minus pre exercise Exp Con Exp minus Con Inspiratory capacity# 0.20# 0.00# 0.20# (L)# (0.26)# (0.33)# (0.00 to 0.40)# Slow vital capacity 0.28 0.08 0.20 (L) (0.57) (0.50) (0.00 to 0.40) Exp = conical-PEP breathing, Con = normal breathing, shaded row = primary outcome Note: Primary outcome indicated with #. Table 3. Mean (SD) of cardiorespiratory function for both interventions, mean (SD) difference within interventions, mean (95% CI) difference between interventions at rest and during the last 30 s exercise. Outcome Interventions Rest Last 30 s exercise Exp Con Exp Con Heart rate (beats/min) 81.8 81.2 113.2 111.2 (10.1) (9.5) (15.5) (14.4) Respiratory rate 16.1 16.3 20.7 27.0 (breaths/min) (4.2) (4.1) (6.3) (5.8) Inspiratory time (s) 1.5 1.5 1.3 1.0 (0.7) (0.8) (0.6) (0.2) Expiratory time (s) 2.3 2.3 2.2 1.4 (1.3) (1.4) (0.9) (0.4) Expiratory flow rate (L/s) 0.26 0.26 0.33 0.55 (0.09) (0.09) (0.09) (0.18) Expiratory mouth pressure 2.8 2.9 12.9 4.5 (cm[H.sub.2]O) (1.9) (1.8) (3.7) (1.6) Tidal volume (L) 0.53 0.52 0.73 0.69 (0.22) (0.20) (0.33) (0.16) Minute ventilation (L/min) 8.0 8.2 13.4 18.2 (2.6) (2.7) (2.9) (5.2) [P.sub.ET]C[O.sub.2] 38.8 38.7 46.6 44.6 (mmHg) (6.21) (6.17) (6.57) (5.45) Sp[O.sub.2] (%) 96.2 96.2 95.1 94.7 (1.1) (1.1) (2.1) (1.9) Outcome Difference within Difference between interventions interventions Last 30 s exercise Last 30 s exercise minus Rest minus Rest Exp Con Exp minus Con Heart rate (beats/min) 31.4 30.0 1.4 (16.6) (17.4) (-2.2 to 5.0) Respiratory rate 4.7 10.7 -6.1 (breaths/min) (6.0) (6.3) (-10.8 to -1.4) Inspiratory time (s) -0.2 -0.5 0.3 (0.7) (0.7) (0.0 to 0.7) Expiratory time (s) -0.1 -1.0 0.9 (1.6) (1.3) (0.3 to 1.5) Expiratory flow rate (L/s) 0.07 0.28 -0.21 (0.14) (0.21) (-0.31 to -0.12) Expiratory mouth pressure 10.2 1.6 8.5 (cm[H.sub.2]O) (5.1) (1.6) (5.9 to 11.2) Tidal volume (L) 0.20 0.16 0.04 (0.24) (0.23) (-0.12 to 0.19) Minute ventilation (L/min) 5.3 10.1 -4.7 (3.8) (6.6) (-7.7 to -1.6) [P.sub.ET]C[O.sub.2] 7.8 5.9 1.8 (mmHg) (5.4) (4.6) (-1.8 to 5.7) Sp[O.sub.2] (%) -1.2 -1.5 0.4 (2.0) (2.1) (-0.6 to 1.4) Exp = conical-PEP breathing, Con = normal breathing, [P.sub.ET]C[O.sub.2] = fraction of end tidal carbon dioxide pressure, Sp[O.sub.2] = oxygen pulse saturation.
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|Author:||Padkao, Tadsawiya; Boonsawat, Watchara; Jones, Chulee U.|
|Publication:||Australian Journal of Physiotherapy|
|Article Type:||Clinical report|
|Date:||Mar 1, 2010|
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