Cardiovascular and pulmonary adaptations during short-term 15° and 30° head-down posture in healthy male volunteers.

Introduction: Healthy male volunteers were investigated for cardiopulmonary adaptations to a head-down posture (HDT).

Methods: Thirty-three volunteers were enrolled in this study. Their changes in cardiopulmonary parameters at 15° and 30° HDT, for 7.5 minutes in each posture, were studied using echocardiography. Spirometric measurements of pulmonary function were performed during sitting and supine positions, and 15° and 30° HDT, while measurements of blood pressure, carotid blood flow, and electrocardiographic (ECG) and echocardiographic examinations were performed in the supine position and under 15° and 30° HDT.

Results: A significant increase (p<0.05) in mean, systolic, and diastolic pressure, and a decrease in heart rate (p<0.05) were observed during the HDT postures. Right ventricular diameter increased (p<0.05) from supine to 15° and 30° HDT. Forced vital capacity, forced expiratory volume in 1 s, and peak flow rate decreased significantly from supine to 15° and 30° HDT. Maximum ventilatory volume decreased significantly only from the sitting to the supine posture and then remained steady in the HDT postures.

Conclusions: During short-term HDT, the cardiovascular system maintains a stable ejection fraction, with a significant in heart rate, and a decrease in pulmonary ventilation.