Diurnal variation in pulmonary artery pressure.

Previous observations have suggested that pulmonary artery pressure rises during sleep, whereas systemic artery pressure falls. A system has been developed for careful and accurate recording of pulmonary arterial pressure, and applied it to two groups of subjects: patients with heart failure, and patients with chronic stable angina. The results have largely confirmed the nocturnal pressure rise in pulmonary arterial pressure. Detailed analysis strongly suggests that the same physiological mechanisms producing a fall in systemic pressure are responsible for the rise in pulmonary pressure. The precise mechanism remains to be elucidated.