Ventilatory Response to Passive Head Up Tilt
Humans have several adaptive mechanisms to deal with the effect of gravity during upright postures. The effect of passive upright tilt (HUT) on respiration has been shown to reduce the end tidal partial pressure of carbon dioxide (PETCO2) and increase the end tidal partial pressure of oxygen (PETO2) (1,4,5,9,15–19). The typical 4 mmHg drop in PETCO2 has been shown to correspond with a decrease in arterial CO2 (PaCO2) of approximately 2 mmHg (1,5). McHenry et al. (17) found that PaCO2 decreased by ~1 mmHg during 30° HUT. Boutellier and coworkers (6) demonstrated that as subjects went from +1 Gz force to +2 and +3, PaCO2 continued to decrease.
KeywordsVentilatory Response Breathing Frequency Central Chemoreceptor Upright Tilt Accommodation Period
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