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We have studied the effects of positive expiratory pressure (PEP), continuous positive airway pressure (CPAP) and hyperventilation on 9 hypoxemic and hypercapnic chronic obstructive pulmonary disease (COPD) patients. All the patients were in a stable condition and received continuous oxygen. PEP and nasal CPAP were each given for 3 days in random order once every hour during the day and 3 times overnight. The effects of treatment were compared with a 3-day period in which the patients had no treatment for CO2 elimination. The effects were based on transcutaneous measurements of PO2 (PtcO2), PCO2 (PtcCO2) and SO2 (SpO2) and arterial blood gas measurements. The transcutaneous measurements showed that the PEP treatment reduced the PtcCO2 in COPD patients by 0.5 kPa and the CPAP treatment reduced it by 0.1 kPa (p < 0.05). The hyperventilation maneuver caused a decrease in the PtcCO2 of 0.7 kPa. The nocturnal treatments and measurements were all similar to the daytime measurements; the PtcCO2 decreased by 0.6 kPa using PEP and by 0.3 kPa using CPAP (p < 0.01). This indicated that all 3 methods reduced the PtcCO2, but only in the short term as the effects lasted for less than 4 min. COPD patients had no "late response" after any form of treatment. Arterial blood gases in COPD patients showed an elevation in PaCO2 (1.2 kPa) and a decrease in PaO2 and SaO2 during the night (11 pm to 7 am) without treatment. After 3 days of treatment with PEP and CPAP, the same pattern was noticed. The PaCO2 increased with both therapies, 1.3 kPa with PEP and 0.6 kPa with CPAP. Our data indicate that the effects were not of clinical significance and there is no justification for treating stable hypercapnic COPD patients with these methods.

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