Thermoregulatory and Ventilatory Responses in Humans with a Patent Foramen Ovale During Passive Cooling While Immersed in 20 °C Water

Approximately 35% of the general healthy population has a patent foramen ovale (PFO). People without a PFO (PFO−) have a lower esophageal temperature (T esoph ) under resting conditions and during exercise. Additionally, while breathing super cooled (−2.0 °C) air at the end of a 10‐minute exercise bout (2:30 stages at 25, 50, 75 and 90% of VO 2MAX ), PFO− subjects did not increase T esoph as much as subjects with a PFO (PFO+). These data suggest blunted respiratory system cooling in PFO+ subjects. Taken together, these data suggest differences between PFO− and PFO+ subjects in thermoregulatory and ventilatory responses at rest and during exercise. However, to our knowledge it has not been prospectively determined if a PFO has any role on thermoregulatory and ventilatory responses to passive cooling. Fourteen males matched for height, weight and age participated in this study (9 PFO−; age: 26 ± 6 yrs, height: 180.1 ± 7.2 cm, weight: 83.3 ± 12.3 kg, BSA: 2.0 ± 0.2 m 2 ; 5 PFO+; age: 28 ± 6 yrs, height: 175.8 ± 7.3 cm, weight: 77.7 ± 6.0 kg, BSA: 2.0 ± 0.1 m 2 ). Subjects came to the lab at the same time each morning and laid in a reclined position, immersed to the nipple line in a water bath (19.6 ± 0.7 °C) until 1) 60 minutes elapsed, 2) T esoph decreased to 35.5 °C, 3) sustained shivering occurred (oxygen uptake [VO 2 ] > 25% of resting values for 5 consecutive minutes), or 4) subjects asked to get out of the water. We measured T esoph , VO 2 and minute ventilation (V E ) every 5 minutes. At rest before immersion PFO− subjects had a lower T esoph than PFO+ subjects (PFO−: 36.5 ± 0.2, PFO+: 36.8 ± 0.2, p = .04). At the end of immersion PFO− subjects also had a lower T esoph than PFO+ subjects (PFO− : 36.0 ± 0.4, PFO+: 36.5 ± 0.3, p = .04). There were no differences in VO 2 or V E at any time point. Furthermore, after the initial increase in T esoph upon immersion, PFO− subjects decreased T esoph throughout the remainder of the trial; while PFO+ subjects drop in T esoph plateaued after 50 minutes of immersion. These data suggest that PFO− subjects are unable to retain heat as effectively as PFO+ subjects during passive cooling. This may be due to the possibility that PFO− subjects have greater respiratory system heat loss than PFO+ subjects. Support or Funding Information 2015 Eugene and Clarissa Evonuk Memorial Graduate Fellowship