Short term effect of continuous positive airway pressure on muscle sympathetic nerve activity in patients with chronic heart failure

Objective-To test the hypothesis that the short term application of continu ous positive airways pressure (CPAP) increases muscle sympathetic nerve act ivity in patients with congestive heart failure. Setting-University hospital and tertiary referral centre. Patients-10 patients with congestive heart failure (New York Heart Associat ion 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 mi croneurography of the peroneal nerve, blood pressure, heart rate, minute ve ntilation, transcutaneous oxygen saturation, and end tidal PCO2 were measur ed during normal breathing, mask breathing, and CPAP at 5 and 10 cm H2O. Results-CPAP induced an increase in muscle sympathetic nerve activity and b lood pressure in both the patients and the control subjects. In the patient s, sympathetic nerve activity increased from 43 (14) bursts/min during mask breathing to 47 (13) bursts/min at CPAP 10 cm H2O (p = 0.03); mean blood p ressure increased from 80 (3) mm Hg to 86 (4) mm Hg (p < 0.001). Oxygen sat uration 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 effec t of CPAP on minute ventilation or heart rate. Conclusions- In patients with congestive heart failure, short term CPAP eli cits sympathetic activation, probably because of unloading of the aortic or cardiopulmonary baroreceptors.