Effect of Continuous Positive Airway Pressure on Respiratory Sensation in Patients with Chronic Obstructive Pulmonary Disease during Submaximal Exercise

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Abstract
We wished to evaluate the role of dynamic hyperinflation and dynamic airway compression as potential sources of exertional dyspnea in patients with chronic obstructive pulmonary disease (COPD). The rationale was that if such factors contribute importantly, then the administration of continuous positive airway pressure (CPAP), which serves to unload the inspiratory muscles and attenuate dynamic compression on expiration, should improve respiratory sensation. Further partitioning of CPAP into its continuous positive inspiratory pressure (CPIP) and continuous positive expiratory pressure (CPEP) components permitted an assessment of the relative importance of the above factors with respect to respiratory sensation. CPAP, CPIP, and CPEP (4 to 5 cm H2O each) were administered intermittently (for intervals of 40 to 60 s on each occasion) in random order during steady-state submaximal exercise in five patients with COPD (average FEV1, 40% predicted) and in five normal healthy subjects. Changes in the sense of breathing effort during the various pressure applications were assessed by asking the subjects to point to a category scale of -5 to +5, where -5 indicated that breathing was markedly easier and +5 indicated that breathing was markedly harder, CPAP, when administered to the COPD group, resulted in a highly significant (p < 0.005) reduction in the sense of breathing effort. By contrast, CPAP significantly increased the sense of breathing effort in the normal group (p < 0.01). CPIP facilitated breathing in both the COPD group and the normal group (p < 0.05 and p < 0.01, respectively). CPEP, however, significantly increased the sense of breathing effort in the normal group (p < 0.0005), whereas CPEP responses in the COPD group were inconsistent and insignificant. We conclude that CPAP reliably improved respiratory sensation during submaximal exertion in patients with COPD, principally through its effect of unloading the inspiratory muscles.