GRAVITY EFFECTS ON UPPER AIRWAY AREA AND LUNG-VOLUMES DURING PARABOLIC FLIGHT

We measured upper airway caliber and lung volumes in six normal subjec ts in the sitting and supine positions during 20-s periods in normogra vity, hypergravity [1.8 + head-to-foot acceleration (G(z))], and micro gravity (similar to 0 G(z)) induced by parabolic flights. Airway calib er and lung volumes were inferred by the acoustic reflection method an d inductance plethysmography, respectively. In subjects in the sitting position, an increase in gravity from 0 to 1.8 + G(z) was associated with increases in the calibers of the retrobasitongue and palatopharyn geal regions (+20 and +30%, respectively) and with a concomitant 0.5-l iter increase in end-expiratory lung volume (functional residual capac ity, FRC). In subjects in the supine position, no changes in the areas of these regions were observed, despite significant decreases in FRC from microgravity to normogravity (-0.6 liter) and from microgravity t o hypergravity (-0.5 liter). Laryngeal narrowing also occurred in both positions (about -15%) when gravity increased from 0 to 1.8 +G(z). We concluded that variation in lung volume is insufficient to explain al l upper airway caliber variation but that direct gravity effects on ti ssues surrounding the upper airway should be taken into account.