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INFLUENCE OF A PATENT FORAMEN OVALE ON HEART RATE-CORE TEMPERATURE RELATIONSHIP AT REST AND DURING EXERCISE IN YOUNG, HEALTHY MEN

Abstract

K.E. Bradbury1, J. Davis1, N. Charkoudian2 and A.T. Lovering1

1University of Oregon, Eugene OR; 2United States Army Research Institute of Environmental Medicine, Natick MA

During both passive and active heat stress, there is a relationship between increased core temperature (Tc) and heart rate (HR). As Tc rises, HR increases due to sympathetic nervous system stimulation and the direct effect of temperature on the SA node. Men with a patent foramen ovale (PFO+) have a higher Tc at rest and during exercise so they may have altered thermoregulatory (Tc) and cardiovascular (HR) coupling compared to those without a PFO (PFO-). PURPOSE: To test whether 1) There is a relationship between inter-individual values for HR and Tc at rest and during exercise; & 2) The presence of a PFO alters the inter-individual HR-Tc relationship. METHODS: Thirty men (19-36 y/o), free of cardiometabolic and respiratory diseases participated in the study (15 PFO+/15 PFO-) and performed a graded exercise protocol that included cycling at 50% (154 ± 22 W) and 90% (277 ± 40 W) of VO2max. HR and Tc (esophageal probe) were measured at rest and during exercise. Linear regression analyses were performed to determine the relationship between Tc and HR at rest, at 50% and 90% of VO2max as a main group and in PFO- and PFO+ subgroups. RESULTS: Absolute workload was not different at 50% or 90% VO2max between subgroups (p > 0.05). A positive Tc-HR relationship was seen at rest (r = 0.45), 50% (r = 0.50), and 90% (r = 0.44, p < 0.05 for all) VO2max for combined group data. PFO+ subjects had higher resting HR (66 ± 8 vs 58 ± 9 bpm, p < 0.05) and Tc (36.67 ± 0.23 vs 36.41 ± 0.28 °C; p < 0.05) vs PFO- subjects; no group differences were seen during exercise (p > 0.05). A positive relationship existed between individual values for resting Tc and HR in PFO+ (r = 0.66, p < 0.05) but not in PFO- subjects. In PFO+ subjects, there was no relationship between the Tc and HR during exercise. In PFO- subjects, there was a positive relationship between Tc and HR at 50% (r = 0.65, p < 0.05) and 90% (r = 0.54, p < 0.05) VO2max. CONCLUSION: Our data are consistent with the idea that there are differences in thermoregulatory and/or cardiovascular coupling between PFO+ and PFO- subjects at rest and during exercise. A possible explanation is that PFO+ subjects may have higher levels of inflammatory markers (interleukins, TNFα, etc), leading to elevated Tc at rest & contributing to the greater variability in the HR-Tc responses during exercise.

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