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

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 V̇(O2max) 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 (T(oesoph)) (P < 0.05) than PFO- subjects on Trial 1. During exercise breathing cold and dry air, PFO+ subjects achieved a higher T(oesoph) than PFO- subjects (P < 0.05). Subjects with a large PFO, but not those with a small PFO, had a higher T(oesoph) than PFO- subjects (P < 0.05) during Trial 1 and increased T(oesoph) breathing cold and dry air. These data suggest that the presence and size of a PFO are associated with T(oesoph) in healthy humans but this is explained only partially by absence of respiratory system cooling of shunted blood.