Chest
Volume 111, Issue 4, April 1997, Pages 948-954
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Clinical Investigations: COPD
Proportional Assist Ventilation and Exercise Tolerance in Subjects With COPD

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Study objective

This study determined whether proportional assist ventilation (PAV) applied during constant power submaximal exercise could enable individuals with severe but stable COPD to increase their exercise tolerance.

Design

Prospective controlled study having a randomized order of intervention.

Setting

Pulmonary function exercise laboratory.

Participants

Ten subjects with severe stable COPD (mean [SD]: age=59 [6] years; FEV1=29 [7]% predicted; FEV1/FVC=33 [7]%; thoracic gas volume=201 [47]% predicted; diffusion of carbon monoxide=36 [10]% predicted; PaO2= 76 [8] mm Hg; and PaCO2=41 [4] mm Hg).

Intervention

Each subject completed five sessions of cycling at 60 to 70% of their maximum power. The sessions differed only in the type of inspiratory assist: (1) baseline (airway pressure [Paw]=0 cm H2O); (2) proportional assist ventilation (PAV) (volume assist=6 [3] cm H2O/L, flow assist=3 [1] cm H2O/L/s); (3) continuous positive airway pressure (CPAP) (5 [2] cm H2O); (4) PAV+CPAP; and (5) sham (Paw=0 cm H2O).

Measurements and results

Dyspnea was measured using a modified Borg scale. Subjects reached the same level of dyspnea during all sessions but only PAV+CPAP significantly (p<0.05) increased exercise tolerance (12.88 [8.74] min) vs the sham session (6.60 [3.12] min). Exercise time during the PAV and CPAP sessions was 7.10 [2.83] and 8.26 [5.54] min, respectively. Minute ventilation increased during exercise but only during PAV+CPAP was the end exercise minute ventilation greater than the unassisted baseline end exercise minute ventilation (36.2 [6.7] vs 26.6 [6.4] L/min, respectively; p<0.05).

Conclusions

In this study, PAV+CPAP provided ventilatory assistance during cycle exercise sufficient to increase the endurance time. It is now appropriate to evaluate whether PAV+CPAP will facilitate exercise training.

Section snippets

Subjects

Subjects with a clear diagnosis of COPD (based on history, clinical, chest radiographic, and physiologic evidence), who were clinically stable nonsmokers and who had given their informed consent, were included in the study. Subjects were excluded if they showed the presence of coexisting symptomatic disease, ie, a history or findings consistent with associated medical conditions that might influence exercise tolerance, evidence (by history or ECG) of any contraindications to exercise, or

Results

Ten subjects between the ages of 47 and 67 years with moderate to severe COPD completed the five exercise sessions. Their height, weight, and body mass index were 166 [12] cm, 70 [13] kg, and 25 [4] kg/m2, respectively. A description of their anthropometric and pulmonary function data is shown in Table 1. Three subjects did not complete their last session, one subject because of an acute respiratory exacerbation, one subject for personal family reasons, and one subject missed two sessions (CPAP

Discussion

The cornerstone of respiratory rehabilitation is exercise training. Other modalities such as education and psychosocial support may be useful as adjuncts to exercise training but by themselves are unlikely to influence exercise tolerance or health-related quality of life.3, 11 The magnitude of the physiologic training effect is strongly influenced by the intensity of the exercise.4 However, many subjects with COPD are unable to tolerate high workloads because they are limited by severe dyspnea.

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Supported by the West Park Hospital Foundation and the Network of Centres of Excellence—Respiratory Health.

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