Influence of a Patent Foramen Ovale on Heart Rate‐Core Temperature Relationship at Rest and During Exercise in Young, Healthy Men

Abstract

During both passive and active heat stress, there is a relationship between increases in core temperature (Tcore) and the heart rate (HR) response. As Tcore rises, HR increases as a result of sympathetic nervous system stimulation and due to the direct effects of temperature on the sinoatrial node. Young, healthy men with a patent foramen ovale (PFO+) have a higher Tcore at rest and during exercise so they may have altered thermoregulatory (Tcore) and cardiovascular (HR) coupling compared to those without a PFO (PFO-). We aimed to test two hypotheses: 1) That there is a relationship between inter-individual values for HR and Tcore at rest and during exercise and 2) The presence of a PFO alters the HR-Tcore inter-individual relationship at rest and during exercise. Thirty male subjects free of cardiometabolic and respiratory diseases (ages 19-36) participated in the study (15 PFO+/15 PFO-) and performed a graded exercise protocol that included cycling at exercise intensities of 50% (154 ± 22 W) and 90% (277 ± 40 W) of VO2max. HR and Tcore (esophageal probe) were measured at rest and continuously during the exercise test. Linear regression analyses were performed to determine the relationships between Tcore and HR at rest and at 50% and 90% of VO2max as a main group and in both PFO- and PFO+ subgroups. Absolute workload was not different at 50% and 90% VO2max between PFO+ and PFO- groups (p > 0.05). A positive relationship between Tcore and HR was seen at rest (r = 0.45, p < 0.05), 50% (r = 0.50, p < 0.05), and 90% (r = 0.44, p < 0.05) VO2max for combined group data. PFO+ subjects had higher resting HR (66 ± 8 vs 58 ± 9 bpm, p < 0.05) and Tcore (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 for both intensities). A positive relationship existed between individual values for resting Tcore and HR in PFO+ (r = 0.66, p < 0.05) but not in PFO- subjects. In PFO+ subjects, there was no relationship between the two variables during exercise. In PFO- subjects, there was a positive relationship between Tcore and HR at 50% (r = 0.65, p < 0.05) and 90% (r = 0.54, p < 0.05) VO2max. 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 core temperatures at rest, thus contributing to the greater variability in the HR-Tcore responses during exercise.