The Effect of a Patent Forman Ovale on Thermoregulatory and Ventilatory Responses During Passive Heating and Cooling

Abstract

A patent foramen ovale (PFO) is an intracardiac shunt present in ~1/3 of the general population that allows varying degrees of blood flow to bypass pulmonary circulation and respiratory cooling. The aim of this research was to determine how the presence of a PFO affected thermoregulatory and ventilatory responses to passive heating and cooling. During passive heating, ventilation increases in order to augment heat dissipation from the respiratory system. Because individuals with a PFO (PFO+) have a higher resting core temperature (Tcore), it was hypothesized that PFO+ subjects would increase their ventilation at a higher Tcore than subjects without a PFO (PFO-) during passive heating. Additionally, shivering is implemented in order to generate heat during passive cooling. Because PFO+ individuals have a higher resting Tcore, it was hypothesized that the PFO+ group would shiver at a higher Tcore, To test these hypotheses, 22 well-matched males (11 PFO+ and 11 PFO-) completed a passive heating and a passive cooling trial. In the passive heating environment, individuals were immersed in a 40.5±0.3°C water bath until 1) 30 minutes had elapsed, 2) their esophageal temperature (Tesoph) reached 39.5°C, 3) they became lightheaded, or 4) they requested to get out. In the passive cooling environment, individuals were immersed in a 19.7±0.6°C water bath until 1) 60 minutes elapsed, 2) their Tesoph dropped to 35.5°C, 3) sustained shivering occurred, or 4) they requested to get out. In both trials, PFO+ had a higher Tesoph (p < 0.05). At the end of hot water immersion, PFO+ subjects had significantly lower minute ventilation than PFO- subjects (p < 0.05). Additionally, PFO+ subjects shivered at a significantly higher Tesoph than the PFO- subjects during the cold water immersion (p < 0.05). The results suggest that individuals with a PFO have a significantly higher Tcore, and that this greater temperature is defended in both hot and cold environments. These results may help us further understand how the presence of a PFO affects an individual’s response to environmental conditions, as well as why some people may be more prone to certain thermal illnesses.