呼吸性アルカローシスおよびアシドーシスにおけるCa2＋の左心室収縮・弛緩機能に及ぼす効果

Effects of Ca2+ on left ventricular contraction and relaxation during acute respiratory alkalosis and acidosis in dogs

　カルシウムイオンCa^2＋の投与により心臓の収縮が増強されることはよく知られている^1,2）。臨床的にはCa^2＋はアシドーシス，アルカローシスあるいは低酸素血症のような血液ガス異常の存在する状況下で投与されることが多い^3〜6）。しかし，カルシウムCaのイオン化はアシドーシスでは促進され，アルカローシスでは減弱される^7）。したがって，血液ガス異常の下で投与されるCa^2＋が心機能に対してどのような効果をもたらすかはきわめて輿味のある問題ではあるが，この点に関する検討はほとんどなされていない。近年，心臓の収縮機能ばかりではなく，弛緩機能が注目されるようになり，これが種々の要因によって影響を受けることが指摘されている^8〜10）。我我は，急性呼吸性アルカローシスおよび急性呼吸性アシドーシスのもとで，Ca^2＋が左心室の収縮および弛緩櫟能にどのような影響を及ぼすかを検討した。

The effects of ionized calcium on left ventricular contraction and relaxation during acute respiratory alkalosis and acidosis have been studied.

Methods : In pentobarbitone-pancuronium anaesthe-tized open chest dogs ventilated using pure oxygen, left ventricular pressure (LVP), first derivative of LVP (dP/dt), and left ventricular end-diastolic pre-ssure (LVEDP) were measured through a catheter tip micromanometer inserted into the cardiac apex. In addition, arterial pressure and electrocardiagram were monitored. As an index of contraction, maxi-mum positive dP/dt ( + dP/dt max), and as an index of relaxation, the time constant (T) were employed,respectively. T is the inverse negative of the slope of the line which is obtained by plotting the natural logarithm of LVP against time, beginning at the time of maximum negative dP/dt to the level of LVEDP. Respiratory alkalosis was obtained by hyper-ventilating the animals until the pH of arterial blood ranged between 7.6 and 7.7. Respiratory acidosis was produced by adding carbon dioxide to the inspi-red oxygen until the arterial blood pH ranged bet-ween 7. 2 and 7. 1. Calcium chloride in a dose of 10 mg･kg^-1 was administered intravenously and bloodionized calcium measurements were made according to the haemodynamic changes.

Results : During respiratory alkalosis, the admini-stration of CaCl₂ increased ionized calcium from 1.190± 0.050 to 1.762± 0.077 mM (p< O.01), incre-ased + dP/dt max from 2,450±250 to 5,550±740 mmHg ･ sec^-1 (p<0.01) and shortened T from 39.2 ± 2.7 to 31.6 ±2.1 msec (p< 0.01) , respectively.During respiratory acidosis, the administration of CaClz increased ionized calcium from 1.304 ± 0.053 to 1.858 ± 0.080 mM (p< 0.01), increased + dP/dt max from 2, 400±210 to 5, 930±810 mmHg ･sec^-1 (p < 0.01) and shortened T from 31.6 ±1.3 to 24.5 ± 1.4 msec (p< O.01), respectively.

It was concluded that a clinical dose of ionized calcium augmented both left ventricular contraction and relaxation even during acute respiratory alkalo-sis and acidosis.