심실근의 수축현상에 미치는 O₂, CO₂ 및 pH의 영향 = Effects of Oxygen, Carbon Dioxide, and pH on the Contractility in the Isolated Perfused Ventricle

다국어 초록 (Multilingual Abstract)

It has been well known that increased hydrogen ion concentration causes the negative inotropic effect on the heart. But in the status of acid base imbalance, metabolic or respiratory, the question of which status has more profound effect on the cardiac muscle contractility remains unsolved. Furthermore, whether such effect is attributable to the change of the intracellular pH or the extracellular change is a matter of controversy.
In many studies concerning to the effect of carbon dioxide tension on the cardiac contractility, the effect of excess oxygen has been ignored despite of its significant influence upon the cellular function.
The author intended to investigate the effects of the change of carbon dioxide tension, which causes the pH change simultaneously, as well as the effect of excess oxygen on the cardiac ventricular contractility. Also, to prove which change, metabolic or respiratory, has more profound effect and which change, intracellulcr or extracellular, has more crucial effect, the author examined the contractility of the ventricle under two different conditions. They were as follows:
a) PCO_2 was varying despite of same magnitude of the change in pH.
b) pH was varying despite of the same magnitude of the change in PCO_2
Turtle hearts were used and the Langendorf preparations were made. The perfusate was Tris-buffer solution for turtle, saturated with various gases, such as air, pure oxygen, nitrogen, or different concentrations of CO_2 balanced with oxygen or nitrogen. The tension and maximal dT/dt were recorded with the Physiograph and its accessories.
The results were summarized as follows.
1. The excess oxygen enhanced the ventricular contractility.
2. Increased carbon dioxide tension, which decreases the pH simultaneously, reduced the ventricular contractility and that was more pronounced when CO_2 was balanced with nitrogen gas rather than with oxygen gas.
3. The relationships among several physiological parameters were estimated as follows:
a) Y=1.01X-0.56
X: percent change of the tension
Y: percent change of maximal contration dT/dt
b) Z=1.06X-4.56
Z: percent change of maximal relation dT/dt
The corelation coefficient in a) is 0.939 and in b) is 0.926, being significant statistically (P<0.005).
4. When the change of pH were same but the changes of PCO_2 were different, the change of ventricular contractility was more profound in the respiratory decrease of pH, that was higher PCO_2, more depressing effect (P<0.005) was manifested, than in the case of metabolic origin (p<0.005).
5. When the changes of PCO_2 were same but the changes of pH were different, the influence of the latter parameter on the contractility was not significant (P<0.1).
From the above results it was suggested that the increased PCO_2, which also causes the decrease of pH, has negative inotropic effect and excess oxygen has positive inotropic effect on the ventricular muscle of the turtle.
The negative inotropic effect of the lowered pH on the ventricular muscle was revealed to be more profound when it was induced by respiratory distress rather than motabolic and may be affected by change of intracellular pH rather than extracellular pH.