Alveolar Gas Exchanges and Cardiovascular Funtions During Breath-Holding with Air

摘要

During 4 min breath-holding (BH) with TLC or 160 sec BH with FRC PAO2 decreased continuously, reaching approximately 30 mm Hg at the end, while PACO2 increased during first 30 sec after which it leveled off at approximately 50 mm Hg. During 4 min BH the lung supplied 700 ml of O2 into the blood while it gained only 160 ml of CO2 from the blood, indicating a significant retention of CO2. Both PaO2 and PaCO2 changed during BH in a manner similar to those of alveolar gas. Arterial O2 content decreased by 12.5 vols. % and CO2 content increased by 17.0 vols. % during 4 min BH. Mixed venous O2 pressure and content approached arterial blood values toward the end of BH. On the other hand, mixed venous CO2 pressure and content approached arterial values after 30 to 60 sec of BH. The systolic pressure increased only slightlyduring 1 to 2 min of BH, after which it increased rather sharply. The pulse pressure tended to increase toward the end of BH. The heart rate decreased by 15% within 20 sec and was maintained at this level until the end of BH. The right artial and intraesophageal pressures increased immediately to and were maintained at 10 to 20 mm Hg during BH. Cardiac outputs measured during 1.5 to 2 min BH by dye-dilution method were not significantly different from those measured before BH. (Author)