P. Subhasree Badrinarayan1, K.E. Bradbury1,3, J. Davis2, C.T. Minson1, N. Charkoudian3, A.T. Lovering1

1University of Oregon, Eugene, OR, USA; 2Indiana University Bloomington, Bloomington, IN, USA; 3US Army Research Institute of Environmental Medicine, Natick, MA, USA

A patent foramen ovale (PFO) is an intracardiac shunt between the right and left atria that allows blood to flow directly from the right atrium to the left atrium. Previous studies have shown that men with a PFO (PFO+) had a higher core temperature (Tc) of ~0.3-0.4 °C during passive heating (hot tub immersion), passive cooling (cold tub immersion), and active heating (exercise) than men who do not have a PFO (PFO-). PURPOSE: The purpose of this study was to analyze the relationship between metabolic heat production (Hprod) and Tc in men with and without a PFO at rest, exercise, and passive heating and cooling. METHODS: During passive heating and cooling, PFO+ (n=13) and PFO- (n=14) men were immersed in hot (40.5 ± 0.2°C) and cold (19.5 ± 0.9°C) tubs, respectively. During active heating, PFO+ (n=15) and PFO- (n=15) men completed 2 exercise trials on a cycle ergometer in a thermoneutral environment (20.6 ± 1.0°C, humidity: 13 ± 4%): 1) a VO2max test and 2) a graded exercise protocol where subjects cycled at 4 workloads (25%, 50%, 75%, 90% of VO2max) for 2.5 min each. During all 3 conditions, Tc was measured via esophageal probe and metabolic data were measured with a metabolic cart. RESULTS: During passive heating and cooling there was a curvilinear relationship between Hprod and Tc. During passive heating, the rate of change between Hprod and Tc was higher after reaching the ventilatory threshold than before for both PFO+ men and PFO- men. During passive cooling, the relationship between Hprod and Tcore was positive until subjects reached their maximum Tc, and then exhibited a negative relationship. During active heating, there was a strong positive correlation between Hprod and Tc during stages 25% Max to 90% Max, indicating that the increase in Hprod due to increased exercise intensity contributed to the increase in the Tc in both groups (PFO-: R2 = 0.98, PFO+: R2 = 0.99). There were no differences in Hprod between PFO+ and PFO- subjects at any time point and there were no differences between PFO+ and PFO- for any of the relationships measured (P>0.05). CONCLUSION: Despite having a significantly higher Tc, PFO+ men had the same Hprod as PFO- men at each time point during all 3 conditions. Our results suggest that Hprod is not a mechanism contributing to the higher Tc in PFO+ men vs PFO- men seen during short duration exercise and passive heating and cooling.

This study was funded by American Physiological Society’s Giles F. Filley Memorial Award for Excellence in Respiratory Physiology and Medicine, the Eugene and Clarissa Evonuk Memorial Graduate Fellowship, the National Institute of Health (R25HD0708), the Defense Medical Research and Development Program (W81XWH-10-2-0114), and the University of Oregon Summer Program for Undergraduate Research.

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