Simon B A, Tsuzaki K, Venegas J G
Department of Anesthesia, Massachusetts General Hospital, Harvard Medical School, Boston 02114, USA.
J Appl Physiol (1985). 1997 Mar;82(3):882-91. doi: 10.1152/jappl.1997.82.3.882.
Regional pneumoconstriction induced by alveolar hypocapnia is an important homeostatic mechanism for optimization of ventilation-perfusion matching. We used positron imaging of 13NN-equilibrated lungs to measure the distribution of regional tidal volume (VT), lung volume (VL), and lung impedance (Z) before and after left (L) pulmonary artery occlusion (PAO) in eight anesthetized, open-chest dogs. Measurements were made during eucapnic sinusoidal ventilation at 0.2 Hz with 4-cmH2O positive end expiratory pressure. Right (R) and L lung impedances (ZR and ZL) were determined from carinal pressure and positron imaging of dynamic regional VL. LPAO caused an increase in magnitude of ZL relative to magnitude of ZR, resulting in a shift in VT away from the PAO side, with a L/R magnitude of Z ratio changing from 1.20 +/- 0.07 (mean +/- SE) to 2.79 +/- 0.85 after LPAO (P < 0.05). Although mean L lung VL decreased slightly, the VL normalized parameters specific admittance and specific compliance both significantly decreased with PAO. Lung recoil pressure at 50% total lung capacity also increased after PAO. We conclude that PAO results in an increase in regional lung Z that shifts ventilation away from the affected area at normal breathing frequencies and that this effect is not due to a change in VL but reflects mechanical constriction at the tissue level.
肺泡低碳酸血症引起的局部肺血管收缩是优化通气-灌注匹配的重要稳态机制。我们利用13NN平衡肺的正电子成像技术，在8只麻醉开胸犬左肺动脉闭塞（PAO）前后，测量局部潮气量（VT）、肺容积（VL）和肺阻抗（Z）的分布。测量在呼气末正压为4 cmH2O、频率为0.2 Hz的等碳酸正弦通气过程中进行。右肺（R）和左肺阻抗（ZR和ZL）由隆突压力和动态局部VL的正电子成像确定。左肺动脉闭塞导致ZL相对于ZR的幅度增加，导致VT从肺动脉闭塞侧转移，左/右Z比值幅度从1.20±0.07（平均值±标准误）变为左肺动脉闭塞后的2.79±0.85（P<0.05）。虽然左肺平均VL略有下降，但VL归一化参数比导纳和比顺应性均随PAO显著降低。总肺容量50%时的肺回缩压在PAO后也增加。我们得出结论，肺动脉闭塞导致局部肺Z增加，在正常呼吸频率下使通气从受影响区域转移，这种效应不是由于肺容积的变化，而是反映了组织水平的机械性收缩。
