Carbonic anhydrase 阻害剤の肺機能に及ぼす影響, 特に血中CO₂動態に及ばす影響について

抄録

Carbonic anhydrase inhibitor, especially acetazolamide, has been reported to be effective in tretment of respiratory acidosis.
The purpose of the experiment reported here is to observe CO₂ transfer in the lung, following inhibition of blood carbonic anhydrase by acetazolamide in anesthetized dogs in which one lung was rebreathed into a small rubber bag and the other lung was ventilated freely on pure oxygen.
100mg/kg of acetazolamide were given intravenously at the end of the control period.
The P_CO2 of a sample of the gas in the rebreathing bag (bag P_CO2) was compared with the P_CO2 in a sample of mixed venous blood.
The measurement fo carbonic anhydrase activity in the erythrocyte was carried as described by Roughton & Booth.
Calculation of fractional CO₂ output was as follows: The rate of CO₂ output derived from that transported in physical solution was calculated from the data of Sendroy. The estimations of carbamino CO₂ contents were based on the data of Ferguson & Roughton. The rate of output of CO₂ transported as bicarbonate was assumed to be difference between the total CO₂ content and the sum of carbamino and dissolved CO₂ contents.
The results thus obtained are summarized as follows:
(1) Inhibition of enzyme activity was about 50% throughout the experiments.
(2) The expired minute volume increased after the injection of acetazolamide. After 60min, it was 194% of the control level.
(3) 30min, after injection of acetazolamide, CO₂ output decreased to 78% of the control level and gradually returned. At 60min, it was 92% of the control.
(4) Before the injection of acetazolamide, the difference between the bag P_CO2 and the mixed venous P_CO2 was not significant. After acetazolamide, the bag P_CO2 averaged 7mmHg higher than the blood values.
Apparently, when carbonic anhydrase was inhibited, the dissolved CO₂ of mixed venous blood did not attain equilibrium with bicarbonate by the time the blood entered the lung.
(5) The partition of the total CO₂ output into the forms in which CO₂ was carried was as follows:
Before acetazolamide, 16.9% of the CO₂ output was derived from dissolved CO₂, 23.4% from carbamino CO₂, After the CO₂ output had returned to the control level following acetazolamide, 41.1% was derived from dissolved CO₂, 39.7% from carbamino CO₂, The fraction of CO₂ output derived from bicarbonate was reduced from. 59.6% to 19.2%.