Respiratory alkalemia during exercise reduces angina threshold

Area of Science:

• Cardiology
• Exercise Physiology
• Biochemistry

Background:

• Coronary artery disease (CAD) can lead to angina during physical exertion.
• Hyperventilation can cause respiratory alkalosis, altering blood pH.
• The impact of alkalosis on exercise-induced angina is not fully understood.

Purpose of the Study:

• To investigate the effect of hyperventilation-induced alkalemia on the angina threshold in individuals with a history of exertional chest pain.
• To determine if arterial alkalemia during hyperventilation exercise influences the cardiovascular response at the onset of angina.

Main Methods:

• Nine subjects with consistent exercise-induced angina performed graded bicycle ergometry.
• Exercise tests were conducted under two conditions: normal breathing and voluntary hyperventilation.
• Arterial blood gases and cardiovascular parameters (heart rate, blood pressure) were monitored to determine the angina threshold (defined by HR x BP product).

Main Results:

• No significant difference in maximal workload was observed between normal breathing and hyperventilation.
• In five subjects who developed arterial alkalemia (mean pH 7.52) during hyperventilation, the heart rate x blood pressure product at angina was significantly lower (224 x 10^2) compared to normal breathing (240 x 10^2; P < 0.05).
• Four subjects who hyperventilated but did not develop alkalemia (mean pH 7.40) showed no significant change in their angina threshold.

Conclusions:

• Hyperventilation-induced alkalemia significantly lowers the angina threshold during exercise.
• The findings suggest that alkalemia interferes with myocardial oxygen supply, precipitating angina at lower workloads.
• Alkalemia, rather than hyperventilation alone, appears to be the critical factor affecting angina onset in susceptible individuals.