Positive pressure on neck reduces baroreflex response to apnoea.

This study was designed to evaluate the arterial blood pressure and heart rate responses to positive pressure applied to the neck during repetitive inspiratory apnoea. Twenty-five subjects (aged 20-40 years) were trained to exert a positive pressure on the neck by actively contracting the neck muscles and pressing the chin in the jugular notch. Blood pressure and heart rate were evaluated during 5-min long periods at rest, at the beginning and end of a 25-min period of apnoea with and without positive pressure and after a second period of rest. Positive pressure diminished the initial hypotensive and bradycardiac reactions to apnoea and augmented the heart rate and blood pressure increase towards the end of apnoea. Both systolic and diastolic pressures and heart rate were significantly elevated during both apnoeic sequences, and also remained significantly elevated after the release of pressure. Spectral analysis (FFT) and auto-regressive model showed the entrainment of the slow 0.03 Hz oscillations by repetitive apnoea and the occurrence of 0.1 Hz and respiratory 0.2 Hz components in the heart rate and blood pressure in both types of apnoea. It is suggested, since the positive pressure decreases the baroreflex and the increased sympathetic tone persists after apnoea, that such effects may contribute to the development of cardiac complications in prediposed individuals with obstructive apnoea syndrome.