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Methodological and physiological variability within the ventilatory response to hypoxia in humans
1University Laboratory of Physiology, University of Oxford, Oxford OX1 3PT, United Kingdom.
Summary
Assessing the acute hypoxic ventilatory response (AHVR) involves choosing the right hypoxic stimulus. This study found that while AHVR measurement techniques showed little systematic variation, the response itself physiologically varies over time.
Area of Science:
- Physiology
- Respiratory Medicine
Background:
- Accurate measurement of the acute hypoxic ventilatory response (AHVR) is crucial for research and clinical applications.
- The selection of an appropriate hypoxic stimulus is critical to avoid incomplete responses or hypoxic ventilatory depression.
Purpose of the Study:
- To compare three distinct techniques for assessing AHVR using different hypoxic stimuli.
- To investigate the between-day variability of AHVR measurements.
Main Methods:
- Ten subjects underwent AHVR assessment on six separate occasions, spaced at least one week apart.
- Three protocols were employed: square waves of hypoxia (SW), incremental steps of hypoxia (IS), and simulated isocapnic rebreathing (RB).
Main Results:
- Mean hypoxic sensitivity values varied significantly across the protocols (SW: 1.02 ± 0.48, IS: 1.15 ± 0.55, RB: 0.93 ± 0.60 L·min⁻¹·%⁻¹).
- Coefficients of variation for AHVR measurement were comparable across protocols (20% for SW, 23% for IS, 36% for RB).
- A significant physiological variation in AHVR was observed over time (26% coefficient of variation).
Conclusions:
- There were minimal systematic differences in AHVR measurements between the three tested protocols.
- Physiological variability over time is a significant factor influencing AHVR measurements.