Higher oesophageal temperature at rest and during exercise in humans with patent foramen ovale

Abstract

Patent foramen ovale (PFO) is present in ∼35% of the general population. The respiratory system participates in thermoregulation via evaporative and convective heat loss so blood flow that bypasses the respiratory system, e.g. through a PFO, may not participate in respiratory system cooling. We found that subjects with a PFO (PFO+) had a ∼0.4°C higher oesophageal temperature (Toesoph) than subjects without a PFO (PFO-) during pre-exercise and exercise. Toesoph in PFO+ subjects was associated with the estimated size of the PFO whereby subjects with a large PFO had a greater Toesoph than PFO- subjects and subjects with a small PFO. During high intensity exercise breathing cold and dry air, PFO+ subjects achieved a higher Toesoph than PFO- subjects. Absence of respiratory system cooling of shunted blood partially explains the differences in Toesoph between PFO+ and PFO- subjects; other differences in thermoregulatory responses that impact core temperature also likely exist. Respiratory system cooling occurs via convective and evaporative heat loss, so right-to-left shunted blood flow through a patent foramen ovale (PFO) would not be cooled. Accordingly, we hypothesized that PFO+ subjects would have a higher core temperature than PFO- subjects due, in part, to absence of respiratory system cooling of the shunted blood and that this effect would be dependent upon the estimated PFO size and inspired air temperature. Subjects were screened for the presence and size of a PFO using saline contrast echocardiography. Thirty well-matched males (15 PFO-, 8 large PFO+, 7 small PFO+) completed cycle ergometer exercise trials on three separate days. During Trial 1, subjects completed a V˙O2 max test. For Trials 2 and 3, randomized, subjects completed four 2.5 min stages at 25, 50, 75 and 90% of the maximum workload achieved during Trial 1, breathing either ambient air (20.6 ± 1.0°C) or cold air (1.9 ± 3.5°C). PFO+ subjects had a higher oesophageal temperature (Toesoph) (P < 0.05) than PFO- subjects on Trial 1. During exercise breathing cold and dry air, PFO+ subjects achieved a higher Toesoph than PFO- subjects (P < 0.05). Subjects with a large PFO, but not those with a small PFO, had a higher Toesoph than PFO- subjects (P < 0.05) during Trial 1 and increased Toesoph breathing cold and dry air. These data suggest that the presence and size of a PFO are associated with Toesoph in healthy humans but this is explained only partially by absence of respiratory system cooling of shunted blood.