Hypoxic Respiratory Chemoreflex Control in Young Trained Swimmers

Area of Science:

• Physiology
• Sports Science
• Cardiovascular Research

Background:

• Peripheral chemoreceptors regulate respiratory drive during apnea by sensing changes in partial pressure of oxygen (PaO2).
• Athletes engaging in prolonged apnea, like breath-hold divers, often display a diminished hypoxic ventilatory response (HVR).
• The HVR in swimmers, a group with significant voluntary apnea experience, has not been previously investigated.

Purpose of the Study:

• To investigate the hypothesis that trained swimmers possess a decreased HVR, potentially contributing to their extended apnea durations.
• To assess cardiovascular adjustments and autonomic responses during maximal voluntary apnea in young-trained swimmers.

Main Methods:

• Fifteen trained swimmers and twenty-seven control subjects underwent tests for acute chemoreflex activation and maximal voluntary apnea.
• Measurements included minute ventilation (V), arterial oxygen saturation (SpO2), heart rate (HR), and heart rate variability (HRV) analysis.
• The protocol involved five inhalations of pure nitrogen (N2) for chemoreflex activation.

Main Results:

• Swimmers demonstrated significantly longer maximal voluntary apnea times and higher end-apnea heart rates compared to controls.
• The low-frequency component of heart rate variability (HRV), indicative of autonomic response, was higher in swimmers.
• Crucially, swimmers exhibited a significantly lower hypoxic ventilatory response (HVR) than controls, while cardiac hypoxic response (CHR) showed no significant difference.

Conclusions:

• Trained swimmers possess a reduced hypoxic ventilatory response (HVR) compared to untrained individuals.
• This diminished HVR is likely a contributing factor to the enhanced maximal voluntary apnea duration observed in swimmers.
• Cardiovascular hypoxic response does not appear to be a differentiating factor in apnea performance between swimmers and controls.