[Effects of -30 degrees head down tilt on lung function]

To investigate the effects of short-term simulated weightlessness on lung function in healthy males.

-30 degrees head down tilt for 45 min was used to simulate short-period weightlessness. Lung function of 12 healthy males, aged 18-21, were studied with plethysmography during seating, supine and head down tilt positions. At the same time, blood flow in pulmonary artery and function of right ventricle were measured with Doppler Echo-Cardiography. Comparative analysis was done.

As body position changed from seating or supine into head down tilt, FVC, FEV1, FEV1%, MVV, VA and IVC decreased. The change of MVV was the most prominent (P < 0.000). As the position changed, pulmonary diffusion increased dramatically (DL(CO) P<0.001, K(CO) P<0.000).

HDT may lead to a decrease of pulmonary ventilation and lung capacity. The increased pulmonary diffusion might be related to uniform distribution of pulmonary blood flow and increased effective pulmonary vascular bed.