Cardiac and ventilatory responses to apneic exercise

Area of Science:

• Physiology
• Sports Science
• Cardiovascular Research

Background:

• Breath-hold diving involves voluntary apnea (breath-holding).
• Dynamic apnea, common in diving, combines breath-holding with exercise.
• Understanding physiological responses to apnea with exercise is crucial for diver safety and performance.

Purpose of the Study:

• To investigate the cardiovascular and respiratory effects of dynamic apneas combined with exercise.
• To determine how different exercise intensities influence physiological responses during apnea.
• To assess the oxygen-conserving effects of simultaneous apnea and exercise.

Main Methods:

• Ten trained breath-hold divers performed maximal duration apneas with face immersion.
• Experiments were conducted under rest and varying exercise workloads (40 W, 80 W, 120 W) on a cycle ergometer.
• Measurements included apneic time, heart rate (HR), mean arterial pressure (MAP), arterial oxygen saturation, and O2 (.VO2) and CO2 exchange.

Main Results:

• End-apnea heart rates were lower than control values; higher workloads delayed the onset of bradycardia.
• Mean arterial pressure increased significantly towards the end of apnea, especially at higher workloads.
• Apneic oxygen consumption (.VO2) was reduced by 25% during exercise and 40% during resting apneas compared to eupneic (normal breathing) conditions.

Conclusions:

• The magnitude and timing of diving bradycardia are intensity-dependent, with higher workloads potentially increasing sympathetic activity.
• Apnea combined with exercise demonstrates an oxygen-conserving effect compared to exercise alone.
• Laboratory findings provide insights but have limitations regarding hydrostatic pressure and body cooling effects inherent in real diving.