OBJECTIVE To test the hypothesis that the short term application of continuous positive airways pressure (CPAP) increases muscle sympathetic nerve activity in patients with congestive heart failure.

SETTING University hospital and tertiary referral centre.

PATIENTS 10 patients with congestive heart failure (New York Heart Association functional class III; mean (SEM) left ventricular ejection fraction 22 (1)%) and 10 healthy subjects matched for age, sex, and weight.

MAIN OUTCOME MEASUREMENTS Muscle sympathetic nerve activity, assessed by microneurography of the peroneal nerve, blood pressure, heart rate, minute ventilation, transcutaneous oxygen saturation, and end tidal Pco ₂ were measured during normal breathing, mask breathing, and CPAP at 5 and 10 cm H₂O.

RESULTS CPAP induced an increase in muscle sympathetic nerve activity and blood pressure in both the patients and the control subjects. In the patients, sympathetic nerve activity increased from 43 (14) bursts/min during mask breathing to 47 (13) bursts/min at CPAP 10 cm H₂0 (p = 0.03); mean blood pressure increased from 80 (3) mm Hg to 86 (4) mm Hg (p < 0.001). Oxygen saturation improved during CPAP in the patients, from 95.7 (0.6)% to 96.6 (0.7)% (p = 0.004) and remained stable in the control group. There was no effect of CPAP on minute ventilation or heart rate.

CONCLUSIONS In patients with congestive heart failure, short term CPAP elicits sympathetic activation, probably because of unloading of the aortic or cardiopulmonary baroreceptors.