[Left ventricular function during hypoxia--II: Effects of intramyocardial pH]

Area of Science:

• Cardiology
• Physiology
• Biochemistry

Background:

• Hypoxia significantly impacts cardiac function.
• Intramyocardial acidosis is a critical factor during hypoxic conditions.
• Understanding the role of lactic acid in cardiac response to hypoxia is crucial.

Purpose of the Study:

• To investigate the effects of intramyocardial acidosis on cardiac function during hypoxia.
• To determine the relationship between intramyocardial pH and various physiological parameters.
• To elucidate the role of myocardial lactic acid production in maintaining cardiac function under hypoxic stress.

Main Methods:

• Continuous measurement of intramyocardial pH in mongrel dogs using pH electrodes.
• Induction of hypoxia by inhalation of low oxygen fraction.
• Measurement of arterial blood gases, lactic acid levels, and left ventricular pressure parameters.

Main Results:

• Hypoxia led to a significant decrease in intramyocardial pH.
• Intramyocardial pH correlated with arterial pH, base excess, lactic acid, and coronary sinus PCO2.
• Myocardial lactic acid production was associated with maintained left ventricular contractile function despite decreased pH.

Conclusions:

• Intramyocardial acidosis during hypoxia is multifactorial, involving arterial lactic acid, myocardial anaerobic glycolysis, and ATP breakdown.
• Increased arterial lactic acid levels contribute to intramyocardial acidosis and worsen left ventricular function.
• Myocardial lactic acid production may serve a protective role in maintaining left ventricular contractile function during hypoxia.