Rea H H, Withy S J, Seelye E R, Harris E A
Am Rev Respir Dis. 1977 Apr;115(4):571-80. doi: 10.1164/arrd.1977.115.4.571.
Alveolar-arterial PO2 difference ([A-a]PO2), venous admixture, and physiologic dead space were measured in 24 healthy men and women 23 to 72 years of age in the sitting and supine positions, breathing air, breathing O2, and breathing O2 in deep breaths. In the supine (but not the sitting) position, (A-a)PO2 and venous admixture, breathing both air and O2, were more highly correlated with the difference between closing volume and expiratory reserve volume than with age. The change in (A-a)PO2 and venous admixture from sitting to lying was related to the change in closing volume minus expiratory reserve volume, during both air and O2 breathing. These results confirm previous work on the contribution of gravity-dependent airway closure to the air-breathing venous admixture. They further indicate that the same mechanism is important when O2 is breathed, and it may account for most of the alveoli that close during O2 breathing because of critically low ventilation perfusion ratios. Physiologic dead space in the supine position may be predicted by subtracting 12.5% from the normal sitting value for the same tidal volume and respiratory frequency.
对24名年龄在23至72岁之间的健康男性和女性，在坐位和仰卧位时分别进行测量，测量项目包括肺泡-动脉血氧分压差（[A-a]PO2）、静脉血掺杂和生理死腔，测量时分别进行呼吸空气、呼吸氧气以及深呼吸氧气的操作。在仰卧位（而非坐位）时，呼吸空气和氧气时的（A-a）PO2和静脉血掺杂，与闭合气量和呼气储备量之间的差值的相关性，高于与年龄的相关性。从坐位到卧位时，（A-a）PO2和静脉血掺杂的变化，与呼吸空气和氧气时闭合气量减去呼气储备量的变化相关。这些结果证实了先前关于重力依赖性气道闭合对呼吸空气时静脉血掺杂的作用的研究。它们进一步表明，呼吸氧气时同样的机制也很重要，并且它可能是氧气呼吸期间由于通气灌注比极低而闭合的大部分肺泡的原因。对于相同的潮气量和呼吸频率，仰卧位时的生理死腔可通过从正常坐位值中减去12.5%来预测。
