IS VO2 SUPRESSED DURING NON-APNOEIC FACIAL SUBMERSION?

S. Anderson, M. Chamberlain, S. Musgrove, A. Partusch, K. Tice and D.B. Thorp, PhD Gonzaga University, Spokane, WA The mammalian dive response (DR) elicited by facial submersion in water is characterized by a decreased heart rate (HR) and an elevated blood pressure (BP). The DR is said to be an oxygen-conserving mechanism based primarily on the bradycardia, peripheral vasoconstriction and decreased ventilation (VE) that occurs. Immediately upon facial submersion in cold water a transient period of tachycardia and increased VE, termed the cold shock response (CSR), is observed prior to the changes characteristic of the DR. PURPOSE: The purpose of this study was to determine if the DR in humans is an oxygen-conserving mechanism by quantifying oxygen consumption (VO2) during facial submersion in different water temperatures. METHODS: Ten male and nine female participants (21 ± 0.7 yr) performed four non-apnoeic, 2 min facial submersions to the temples with 8 min of rest prior to each facial submersion. Two facial submersions were performed in 5°C water and two in 25°C water; the order of which were randomized between subjects. HR was collected throughout using chest strap HR monitors. A tube was connected to the inspired port of a watertight non-rebreathing valve and extended above the surface of the water allowing participants to breathe during facial submersion. Expired air was directed to a metabolic cart to determine VO2 and VE. Baseline (BL) values for HR, VO2 and VE were taken as the average during the two minutes prior to facial submersion, CSR values were taken as the maximum for each variable during the first 30 seconds of facial submersion, and DR values were taken as the minimum during the last 90 seconds of facial submersion. These were averaged between the 5°C and 25°C trials to obtain one BL, CSR and DR value for each water temperature. A two-way repeated measures ANOVA was used to compare BL, CSR, and DR for each variable between temperatures. RESULTS: Both HR and VE were greater during the CSR (92.5±3.6 bpm, 16.3±0.8 L/min, respectively) compared to BL (78.9±3.2 bpm, 8.7±0.4 L/min), while both were decreased from BL during the DR (60.0±4.0 bpm, and 6.0±0.4 L/min) (main effect of facial submersion, all p\u3c0.05). The combined effect of facial submersion and cold water augmented the HR response, such that HRCSR was higher and HRDR was lower in the 5°C condition (interaction effect, p\u3c0.05). There was a main effect of water temperature such that VE was greater in the 5°C condition (p\u3c0.05). Like HR and VE, the effect of facial submersion was such that VO2 exceeded BL during the CSR and decreased below BL during the DR (BL: 5.3±0.1, CSR: 9.8±0.4, DR: 3.1±0.2 mL/kg/min, p\u3c0.05). CONCLUSION: The VO2 data illustrate that the DR is an oxygen-conserving mechanism in humans, regardless of water temperature