Pressure-Volume Changes in the Forearm Veins of Man During Hyperventilation12

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Abstract
Forearm venous pressure-volume curves were obtained plethysmographically along with measurements of peripheral venous pressure before and during voluntary hyperventilation while breathing air and while breathing 5 or 7% CO2. Forearm venous pressure decreased during hyperventilation while breathing air and averaged a slight increase during hyperventilation while breathing CO2-Active forearm venous constriction occurred regularly during hyperventilation. The response observed while overbreathing air was not significantly different from that observed while overbreathing CO2. Blood shifted out of the forearm veins in each instance during hyperventilation while breathing air. This decrease in forearm venous volume averaged 30.9%; the decrease attributable to venous constriction alone averaged 23.6%; and the decrease caused by the fall in venous pressure alone averaged 7.3% of the average resting value. Blood also shifted from the forearm veins during hyperventilation while breathing CO2. However, the volume change was significantly less than while overbreathing air because forearm venous pressure failed to fall. It is suggested that peripheral venous constriction may serve to increase the availability of blood to the heart during hyperventilation.