Pulmonary haemodynamics in obstructive sleep apnoea

The time course of right ventricular output (RVO) and transmural pulmonary artery pressure (PAP) changes, detected beat-by-beat, were analysed in a sample of obstructive sleep apnoea (OSA) episodes recorded in six patients with OSA syndrome. RVO showed a trend to a decrease during apnoeas, due to a decrease in heart rate, and decreased further in the immediate post-apnoeic period, due to a decrease in right ventricular stroke volume [post-apnoeic RVO = 82.6 +/- 9.3 (SD) % of the value in the immediate pre-apnoeic period; P < 0.01]. Both systolic and diastolic transmural PAP showed a progressive increase throughout apnoeas (from 23.7 +/- 7.3 to 29 +/- 6.9 and from 9.1 +/- 4.4 to 14.3 +/- 3.3 mmHg, respectively, from early to late apnoeic period; P < 0.01), and similarly high values in the late apnoeic and in the immediate post-apnoeic period. Therefore, cardiac output and arterial pressure in the pulmonary circulation undergo simultaneous inverse changes in OSA, similar to what was previously shown in the systemic circulation. Although these data cannot define accurately the behaviour of pulmonary vascular resistance, they suggest that pulmonary vascular resistance could also undergo continuous oscillations in OSA, with recurring peaks detectable between apnoea termination and the immediate post-apnoeic period.