Abstract
Carbon dioxide (CO2) retention occurs during water immersion, but it is not known if peripheral chemosensitivity is altered during water immersion, which could contribute to CO2 retention. We tested the hypothesis that peripheral chemosensitivity to hypercapnia and hypoxia is blunted during 2 h of thermoneutral head out water immersion (HOWI) in healthy young adults. Peripheral chemosensitivity was assessed by the ventilatory, heart rate, and blood pressure responses to hypercapnia and hypoxia at baseline, 10, 60, 120 min, and post HOWI and a time‐control visit (control). Subjects inhaled 1 breath of 13% CO2, 21% O2, and 66% N2 to test peripheral chemosensitivity to hypercapnia and 2–6 breaths of 100% N2 to test peripheral chemosensitivity to hypoxia. Each gas was administered four separate times at each time point. Partial pressure of end‐tidal CO2 (PETCO2), arterial oxygen saturation (SpO2), ventilation, heart rate, and blood pressure were recorded continuously. Ventilation was higher during HOWI versus control at post (P = 0.037). PETCO2 was higher during HOWI versus control at 10 min (46 ± 2 vs. 44 ± 2 mmHg), 60 min (46 ± 2 vs. 44 ± 2 mmHg), and 120 min (46 ± 3 vs. 43 ± 3 mmHg) (all P < 0.001). Ventilatory (P = 0.898), heart rate (P = 0.760), and blood pressure (P = 0.092) responses to hypercapnia were not different during HOWI versus control at any time point. Ventilatory (P = 0.714), heart rate (P = 0.258), and blood pressure (P = 0.051) responses to hypoxia were not different during HOWI versus control at any time point. These data indicate that CO2 retention occurs during thermoneutral HOWI despite no changes in peripheral chemosensitivity.
Highlights
Our study demonstrates that pressure of end-tidal CO2 (PETCO2) increases during 2 h of thermoneutral head out water immersion (HOWI) in humans without a change in ventilation or peripheral chemosensitivity (Figs 1, 4, and 5)
It has been shown that CO2 retention occurs during water immersion at depth due a reduction in alveolar ventilation that is caused by increased dead space (Salzano et al 1984; Mummery et al 2003)
2 h of thermoneutral HOWI caused an increase in PETCO2, which indicates that subjects experienced CO2 retention, without a decrease in ventilation
Summary
Carbon dioxide (CO2) retention occurs during water immersion (Lambertsen et al 1959; Jarrett 1966; Lollgen et al 1976; Kerem et al 1980, 1995; Salzano et al 1984; Warkander et al 1990; Lanphier and Bookspan 1999; Pendergast and Lundgren 2009; Pendergast et al 2015). The thoracic cavity is subjected to an elevated hydrostatic pressure from the water column that causes high external breathing resistance (i.e., static lung load), which can contribute to respiratory muscle fatigue (Pendergast and Lundgren 2009; Pendergast et al 2015).
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