Human circulatory system response to changes in alveolar pressure and lung volume

The response of hemodynamic parameters in healthy volunteers to changes in alveolar pressure and lung volume was studied by noninvasive methods during respiratory maneuvers similar to Valsalva and Muller maneuvers (in a sitting position and lying on the back horizontally). The following lung volumes and values of pressure (relative to atmospheric pressure) were considered in various combinations: total lung capacity, functional residual capacity, residual volume, -30, -15, 0, +15, +30 mmHg. Changes in hemodynamic parameters averaged over the duration of a maneuver were studied (the duration of a maneuver was 30 s). Changes in alveolar and, accordingly, intrathoracic pressure influenced hemodynamic more strongly than changes in lung volume or body position. Stroke volume decreased with increasing alveolar pressure and increased with decreasing pressure regardless of lung volume and body position; changes ranged from -35 to +15 ml. The effect of changes in alveolar pressure was more pronounced in a sitting position. Heart rate increased with increasing alveolar pressure (up to +20 bpm) but changed little with decrease in pressure. Mean arterial pressure decreased with decreasing alveolar pressure regardless of lung volume and body position; with increasing alveolar pressure, the result depended on lung volume. When performing maneuvers at total lung capacity, mean arterial pressure remained below baseline values, in other cases it increased. Changes in mean arterial pressure were within {+/-}20 mmHg. Regardless of lung volume and body position, total peripheral resistance decreased with decreasing alveolar pressure and increased with increasing alveolar pressure; the range of changes in total peripheral resistance was -0.3 to +0.7 mmHg{middle dot}s/ml.