Effect of a patent foramen ovale in humans on thermal responses to passive cooling and heating.

Humans with a patent foramen ovale (PFO) have a higher esophageal temperature (T) than humans without a PFO (PFO-). Thus the presence of a PFO might also be associated with differences in thermal responsiveness to passive cooling and heating such as shivering and hyperpnea, respectively. The purpose of this study was to determine whether thermal responses to passive cooling and heating are different between PFO- subjects and subjects with a PFO (PFO+). We hypothesized that compared with PFO- subjects PFO+ subjects would cool down more rapidly and heat up slower and that PFO+ subjects who experienced thermal hyperpnea would have a blunted increase in ventilation. Twenty-seven men (13 PFO+) completed two trials separated by >48 h: ) 60 min of cold water immersion (19.5 ± 0.9°C) and ) 30 min of hot water immersion (40.5 ± 0.2°C). PFO+ subjects had a higher T before and during cold water and hot water immersion ( < 0.05). However, the rate of temperature change was similar between groups for each condition. Within a subset of 18 subjects (8 PFO+) who experienced thermal hyperpnea, PFO+ subjects experienced thermal hyperpnea at a higher absolute T but with a blunted magnitude compared with PFO- subjects. These data suggest that PFO+ subjects have a higher T at rest and have blunted thermal hyperpnea during passive heating. Patent foramen ovale (PFO) is found in ~25-40% of the population. The presence of a PFO appears to be associated with a greater core body temperature and blunted ventilatory responses during passive heating. The reason for this blunted ventilatory response to passive heating is unknown but may suggest differences in thermal sensitivity in PFO+ subjects compared with PFO- subjects.