RESPIRATORY AND CIRCULATORY ADJUSTMENTS TO THE ERECT POSTURE

Abstract

Expts. on adult [male] human subjects show that the following adjustments occur upon assuming the erect posture: a drop in the alveolar CO2; the accumulation of an O2 debt and the retention of CO2; a decrease in the CO2 content of venous blood in the arms and an increase in the feet; an increase in the vol. of the functional residual air. These changes are independent of alterations in pulmonary ventilation. The primary cause of the lowered alveolar CO2 is probably simple dilution resulting from the increased vol. of functional residual air, and this lower level is maintained by an impairment of the CO2 transport from the dependent parts of the body and an increased circulation rate in the arms and thorax. It is apparently unnecessary to postulate any proprioceptive stimuli to the respiratory center.