異常条件下の肺内ガス交換に関する実験的研究（2）

Alveolar Arterial Gas Tension Difference under Abnormal Conditions (2)

はじめに

　肺における血液酸素化の指標としての，肺胞気動脈血O₂分圧較差（AaDo₂）は従来いわれていた短絡，拡散障害，換気血流比不均等分布の外，O₂解離曲線にも影響され，肺胞気O₂分圧によっては低体温と平常体温とでAaDo₂がことなることがあると予想した。この予想は低体温における実験によってうらづけられたが，低体温では呼吸循環動態にいろいろな変化がおこるので，はたしてAaDo₂の異常がO₂解離曲線の左方移動のみの結果であるかどうかを断定すべきではないと考えた。低体温の他にもO₂解離曲線を左方に偏移させる異常条件がいくつか知られているので，それらを比較することによってO₂解離曲線の左方移動がAaDo₂に影響をあたえる，というわれわれの作業仮説を実証しようと考えた。これらの異常条件のひとつひとつが臨床上重要な病的状態を代表しており興味ある問題がいろいろあるが，ここではAaDo₂に焦点をしぼった。

The effect of shift of oxygen dissociation curve upon alveolar arterial oxygen tension difference was studied under 4 different ab-normal conditions.

1. Anemia; Alveolar arterial oxygen tension difference on dogs with induced anemia was measured. Alveolar arterial oxygen tension difference was 10.3±1.3 mmHg when breath-ing 21 percent oxygen while that was 19.6 ± 3.8 mmHg when breathing 39.1 percent oxy-gen. This data was considered to remain within normal range.

2. Carbon monoxide inhalation; Alveolar ar-terial oxygen and nitrogen tension differences were measured when the anesthetized dogs breathed 21 percent oxygen and gas mixture containing 0.07 percent carbon monoxide and 19.5 percent oxygen. Statistical differencewas not significant between the alveolar arte-rial nitrogen tension difference prior to and after carbon monoxide inhalation. Alveolar arterial oxygen tension difference was signi-ficantly increased after carbon monoxide inha-lation.

3. Alkaline and acid infusion; To change blood hydrogen ion concentration, 0.3N NaOH or 0.3 N HCl were injected intravenously. Statistical differences were not found on the alveolar arterial nitrogen tension difference prior to and after the maneuver. Alveolar arterial oxygen tension difference prior to and after acid infusion was also not found. Alveo-lar arterial oxygen tension difference was sig-nificantly increased after alkaline infusion.

4. Conclusion; Leftward shifting of oxygen dissociation curve caused an significant incr-ease in the alveolar arterial oxygen tension difference.