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

New Findings 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 CO2 retention during head out water immersion. Abstract Carbon dioxide (CO2) retention occurs during water immersion. Therefore, we tested the hypothesis that central chemosensitivity to hypercapnia is blunted during two hours of thermoneutral head out water immersion (HOWI) in healthy young adults. Twenty-six participants (age: 22 ± 2 years, BMI: 24 ± 3 kg/m2, 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 minutes, 60 minutes, 90 minutes, 120 minutes, and post HOWI and Control. End tidal CO2 tension (PETCO2), minute ventilation, blood pressure, and heart rate were recorded continuously. PETCO2 increased from baseline throughout HOWI (peak increase at 120 minutes: 2 ± 2 mmHg; p