title: Cardiac output but not high pulmonary artery pressure varies with FIO2 in exercising horses.
abstract: Horses have high mean pulmonary artery pressure (Ppa) both at rest and during exercise (approximately 30 and > or = 80 mmHg, respectively). The mechanisms are unknown. To see if hypoxic pulmonary vasoconstriction (HPV) plays a role, we compared pulmonary artery pressure-flow (Ppa-Q) curves when inspired O2 fraction (FIO2) was 0.16, 0.21, and 0.30, in 5 normal Thoroughbred horses standing quietly and while galloping at 10 and 14 m/sec on a level treadmill. We calculated O2 consumption (VO2) from measurements of respired gas composition and flow, and calculated Q from VO2 and measurements of oxygen content in arterial and mixed venous blood (CaO2 and CVO2). VO2 was 3.8, 74 and 128 ml.min-1.kg-1, at rest and at 10 and 14 m/sec, and did not vary with FIO2 at any speed. At 14 m/sec only, when FIO2 was lowered to 0.16, CaO2 fell (to 14.7 from 20 ml/dl on air), Q increased (to 0.86 from 0.66 L.min-1.kg-1 on air), and stroke volume increased (to 4.1 from 3.2 ml.kg-1 on air). Slopes and intercepts of Ppa-Q curves did not vary with FIO2. We conclude that HPV does not contribute to the high Ppa of exercising horses breathing air near sea level.
authors.affiliation: Department of Clinical Sciences, College of Veterinary Medicine, Kansas State University, Manhattan 66506.
authors.forename: N
authors.initials: N
authors.lastname: Pelletier
authors.forename: D E
authors.initials: DE
authors.lastname: Leith
mesh_terms: D000818:Animals; D001794:Blood Pressure; D002245:Carbon Dioxide / Q000502:physiology; D002302:Cardiac Output; D006339:Heart Rate; D006736:Horses / Q000502:physiology*; D008297:Male; D010100:Oxygen / Q000502:physiology*; D010101:Oxygen Consumption; D010805:Physical Conditioning, Animal; D013318:Stroke Volume; D014661:Vasoconstriction
chemical_list: D002245:Carbon Dioxide; D010100:Oxygen