THE EFFECTS OF POSTURE ON CAPILLARY BLOOD FLOW PULSE AND GAS EXCHANGE IN THE LUNGS OF MAN

Cardiac output and pulmonary capillary blood flow were measured on 5 normal subjects by dye dilution and N2O-body plethysmograph method, respectively. To facilitate calculations and to improve signal to noise ratio, a computer of average transient was used. Cardiac output increased from 7.16 ± SEM 0.86 L/min to 8.46 ± 0.72 L/min after the subject changed his posture from upright to supine. Pulmonary capillary blood flow also increased from 5.2 ± 0.44 L/min to 6.95 ± 0.48 L/min. These changes were mostly due to changes in stroke volume. The differences between cardiac output and pulmonary capillary blood flow were 19% and 15% in upright and supine positions, respectively. Conduction time of blood flow pulse from pulmonic valve to pulmonary capillary beds prolonged signifrcantly in supine position. Flow acceleration and pulsatility index did not change by posture. Changes in flow acceleration and changes in PaO2 were significantly correlated. These results indicate: l) profiles of pulmonary capillary blood flow pulse do not alter by posture except conduction time, 2) zone I which is normally closed because of gravity in upright position seems to recruit in supine position, and 3) blood flow acceleration is responsible at least partially for postural changes in PaO2.