体外循環直後の肺機能の変化--動脈血-肺胞気窒素分圧較差による検討
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Pulmonary functions after cardiopulmonary bypass (CPB) were studied in dogs by measuring alveolar-arterial difference (A-aD<SUB>O2</SUB>) and arterial-alveolar nitrogen difference (a-AD<SUB>N2</SUB>), which are regarded as indicators of ventilation-perfusion ratio (V<SUB>A</SUB>/Q) uneveness, and by measuring physiological shunt (Q<SUB>S</SUB>/Q<SUB>T</SUB>) . Effects of inflating the lungs during CPB on pulmonary functions were also studied. 27 mongrel dogs were divided into 4 groups. Group 1 (7 dogs) : Open chest only, control group. Group 2 (7 dogs) : CPB for 30 min with the lungs collapsed. Group 3 (6 dogs) : CPB for 60 min with the lungs collapsed. Group 4 (7 dogs) : CPB for 60 min with static lung inflation. Arterial oxygen tension (Pa<SUB>O2</SUB>) decreased significantly by open chest in group 1 and after CPB in other 3 groups. The changes were prominent in CPB groups and proportional to the perfusion time. Pa<SUB>CO2</SUB> increased and pH decrease in groups 2 and 3. These changes were proportional to the perfusion time and appeared to result from both increased deadspace to tidal vol ratio (V<SUB>D</SUB>/V<SUB>T</SUB>) and impairment of tissue perfusion. However, the changes in Pa<SUB>CO2</SUB> and pH were not marked in group 4, where the lungs were inflated statically during PCB. As the cause of postoperative hypoxemia, V<SUB>A</SUB>/Q ratio uneveness seemed to play a major role in the open chest group, because A-aD<SUB>O2</SUB> and a-AD<SUB>N2</SUB> increase in parallel. In CPB groups, on the contrary, true shunt played a role in the postperfusion hypoxemia, because of the increase in A-aD<SUB>O2</SUB> without a parallel change in a-AD<SUB>N2</SUB> in addition to the marked increase in Q<SUB>S</SUB>/Q<SUB>T</SUB>·Q<SUB>S</SUB>/Q<SUB>T</SUB> and V<SUB>D</SUB>/V<SUB>T</SUB> increase significantly in the groups in which lungs were collapsed during CPB, while minimal changes were seen in the lungs which were statically inflated. In conclusion, the major contributing factors to postoperative hypoxemia are <SUB>A</SUB>/Q ratio uneveness due to open chest operation, and the increase in true shunt due to cardiopulmonary bypass. Static lung inflation during CPB could improve postoperative pulmonary dysfunction.
- 学校法人 昭和大学・昭和医学会の論文
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