Haemodynamic effects of continuous positive airway pressure in humans with normal and impaired left ventricular function

1. Continuous positive airway pressure increases intrathoracic pressure, thereby decreasing left ventricular preload and afterload. We hypothesized that there would be a dose-related alteration in cardiac and stroke volume indices in response to continuous positive airway pressure in normal subjects and patients with congestive heart failure and that the direction of response among those with heart failure would be related to left ventricular preload. 2. Cardiac and stroke volume indices were measured at baseline and after 10 min of continuous positive airway pressure at both 5 and 10 cmH₂O (0.5 and 0.99 kPa respectively) in 16 patients with heart failure and five control subjects with normal cardiac function. Among the eight patients with heart failure and elevated pulmonary capillary wedge pressure (≥12 mmHg) (≥1.6 kPa), cardiac index increased from 2.47 ± 0.34 at baseline to 2.91 ± 0.32 to 3.12 ± 0.40 l min^-1 m^-2 (P < 0.025) while on 5 and 10 cm H₂O of continuous positive airway pressure respectively. In the same patients stroke volume index increased from 27.8 ± 3.9 to 33.9 ± 4.2 to 36.8 ± 5.5 ml/m² (P < 0.05). In contrast, in both the control subjects and patients with heart failure and normal pulmonary capillary wedge pressure (<12 mmHg) there was a dose-related decrease in cardiac and stroke volume indices while on continuous positive airway pressure. 3. Continuous positive airway pressure causes dose-related increases in cardiac and stroke volume indices among patients with chronic heart failure and elevated left ventricular filling pressure. However, it induces dose-related reductions in cardiac and stroke volume indices among normal subjects as well as patients with heart failure and normal left ventricular filling pressures.