Central chemosensitivity is augmented during 2h of thermoneutral head-out water immersion in healthy men and women.

Abstract

What is the central question of the study? Is central chemosensitivity blunted during thermoneutral head-out water immersion in healthy humans? What is the main finding and its importance? Central chemosensitivity is augmented during thermoneutral head-out water immersion in healthy men and women. Thus, we suggest that the central chemoreceptors do not contribute to CO2 retention during head-out water immersion. Carbon dioxide retention occurs during water immersion. Therefore, we tested the hypothesis that central chemosensitivity to hypercapnia is blunted during 2h of thermoneutral head-out water immersion (HOWI) in healthy young adults. Twenty-six participants (age 22±2years; body mass index 24±3kgm-2 ; 14 women) participated in two experimental visits: a HOWI visit (HOWI) and a dry time-control visit (Control). Central chemosensitivity was assessed via a rebreathing test at baseline, 10, 60, 90 and 120min and after HOWI and Control. End-tidal CO2 tension (P ET ,CO2), minute ventilation, blood pressure and heart rate were recorded continuously. The P ET ,CO2 increased from baseline throughout HOWI (peak increase at 120min 2±2mmHg; P<0.001), and the change in P ET ,CO2 was greater throughout HOWI than Control (P<0.001). The change in minute and alveolar ventilation was not different throughout time (P≥0.173) or between conditions (P≥0.052). Central chemosensitivity was greater than at baseline throughout HOWI (peak increase 0.74±1.01lmin-1 mmHg-1 at 120min; P<0.001), and the change in central chemosensitivity was greater throughout HOWI than Control (P ≤ 0.006). We also divided the cohort into tertiles based on baseline central chemosensitivity (i.e. Low, Intermediate and High) and compared Low versus High during HOWI. Low demonstrated an increase in P ET ,CO2 starting at 10min (2±3mmHg; P<0.001), whereas High did not exhibit an increase in P ET ,CO2 until 60min (2±2mmHg; P=0.018). These data indicate that CO2 retention occurs throughout HOWI despite augmented central chemosensitivity and that having a high baseline central chemosensitivity might delay the onset of CO2 retention.