Cardiorespiratory hysteresis during incremental high‐altitude ascent–descent quantifies the magnitude of ventilatory acclimatization

• Published in: Experimental physiology 2021-01, Vol.106 (1), p.139-150
• Main Authors: Leacy, Jack K., Linares, Andrea M., Zouboules, Shaelynn M., Rampuri, Zahrah H., Bird, Jordan D., Herrington, Brittney A., Mann, Leah M., Soriano, Jan E., Thrall, Scott F., Kalker, Anne, Brutsaert, Tom D., O'Halloran, Ken D., Sherpa, Mingma T., Day, Trevor A.
• Format: Article
• Language: English
• Subjects: Acclimatization; Acclimatization - physiology; Acetazolamide; acute mountain sickness; Adult; Altitude; Altitude Sickness - physiopathology; Carbon dioxide; Chemoreception (internal); Gases; high altitude; Humans; Hyperventilation; Hypoxia; Hypoxia - physiopathology; Hysteresis; Lung - physiopathology; Mechanical ventilation; Oxygen; Oxygen - blood; Oxygen saturation; Oxygen Saturation - physiology; respiratory chemoreflexes; Ventilation; ventilatory acclimatization
• ISSN: 0958-0670; 1469-445X
• DOI: 10.1113/EP088488

New Findings What is the central question of this study? We assessed the utility of a new metric for quantifying ventilatory acclimatization to high altitude, derived from differential ascent and descent steady‐state cardiorespiratory variables (i.e. hysteresis). Furthermore, we aimed to investigate whether the magnitude of cardiorespiratory hysteresis was associated with the development of acute mountain sickness. What is the main finding and its importance? Hysteresis in steady‐state cardiorespiratory variables quantifies ventilatory acclimatization to high altitude. The magnitude of cardiorespiratory hysteresis during ascent to and descent from high altitude was significantly related to the development of symptoms of acute mountain sickness. Hysteresis in steady‐state chemoreflex drive can provide a simple, non‐invasive method of tracking ventilatory acclimatization to high altitude. Maintenance of arterial blood gases is achieved through sophisticated regulation of ventilation, mediated by central and peripheral chemoreflexes. Respiratory chemoreflexes are important during exposure to high altitude owing to the competing influence of hypoxia and hypoxic hyperventilation‐mediated hypocapnia on steady‐state ventilatory drive. Inter‐individual variability exists in ventilatory acclimatization to high altitude, potentially affecting the development of acute mountain sickness (AMS). We aimed to quantify ventilatory acclimatization to high altitude by comparing differential ascent and descent values (i.e. hysteresis) in steady‐state cardiorespiratory variables. We hypothesized that: (i) the hysteresis area formed by cardiorespiratory variables during ascent and descent would quantify the magnitude of ventilatory acclimatization; and (ii) larger hysteresis areas would be associated with lower AMS symptom scores during ascent. In 25 healthy, acetazolamide‐free trekkers ascending to and descending from 5160 m, cardiorespiratory hysteresis was measured in the partial pressure of end‐tidal CO2, peripheral oxygen saturation, minute ventilation, chemoreceptor stimulus index (end‐tidal CO2/peripheral oxygen saturation) and the calculated steady‐state chemoreflex drive (SS‐CD; minute ventilation/chemoreceptor stimulus index) using portable devices (capnograph, peripheral pulse oximeter and respirometer, respectively). Symptoms of AMS were assessed daily using the Lake Louise questionnaire. We found that: (i) ascent–descent hysteresis was present in all cardiorespirat