title: Supine exercise restores arterial blood pressure and skin blood flow despite dehydration and hyperthermia.
abstract: We determined whether the deleterious effects of dehydration and hyperthermia on cardiovascular function during upright exercise were attenuated by elevating central blood volume with supine exercise. Seven trained men [maximal oxygen consumption (VO(2 max)) 4.7 +/- 0. 4 l/min (mean +/- SE)] cycled for 30 min in the heat (35 degrees C) in the upright and in the supine positions (VO(2) 2.93 +/- 0.27 l/min) while maintaining euhydration by fluid ingestion or while being dehydrated by 5% of body weight after 2 h of upright exercise. When subjects were euhydrated, esophageal temperature (T(es)) was 37. 8-38.0 degrees C in both body postures. Dehydration caused equal hyperthermia during both upright and supine exercise (T(es) = 38. 7-38.8 degrees C). During upright exercise, dehydration lowered stroke volume (SV), cardiac output, mean arterial pressure (MAP), and cutaneous vascular conductance and increased heart rate and plasma catecholamines [30 +/- 6 ml, 3.0 +/- 0.7 l/min, 6 +/- 2 mmHg, 22 +/- 8%, 14 +/- 2 beats/min, and 50-96%, respectively; all P < 0. 05]. In contrast, during supine exercise, dehydration did not cause significant alterations in MAP, cutaneous vascular conductance, or plasma catecholamines. Furthermore, supine versus upright exercise attenuated the increases in heart rate (7 +/- 2 vs. 9 +/- 1%) and the reductions in SV (13 +/- 4 vs. 21 +/- 3%) and cardiac output (8 +/- 3 vs. 14 +/- 3%) (all P < 0.05). These results suggest that the decline in cutaneous vascular conductance and the increase in plasma norepinephrine concentration, independent of hyperthermia, are associated with a reduction in central blood volume and a lower arterial blood pressure.
authors.affiliation: Human Performance Laboratory, Department of Kinesiology and Health Education, The University of Texas at Austin, Austin, Texas 78712, USA.
authors.forename: J
authors.initials: J
authors.lastname: González-Alonso
authors.forename: R
authors.initials: R
authors.lastname: Mora-Rodríguez
authors.forename: E F
authors.initials: EF
authors.lastname: Coyle
mesh_terms: D000328:Adult; D001786:Blood Glucose / Q000032:analysis; D001794:Blood Pressure / Q000502:physiology*; D001831:Body Temperature; D001833:Body Temperature Regulation / Q000502:physiology; D001834:Body Water / Q000378:metabolism; D002395:Catecholamines / Q000097:blood; D003681:Dehydration / Q000097:blood / Q000503:physiopathology*; D015444:Exercise / Q000502:physiology*; D005334:Fever / Q000097:blood / Q000503:physiopathology*; D005542:Forearm / Q000098:blood supply; D006801:Humans; D019344:Lactic Acid / Q000097:blood; D008297:Male; D010101:Oxygen Consumption / Q000502:physiology; D012039:Regional Blood Flow / Q000502:physiology; D012867:Skin / Q000098:blood supply*; D016683:Supine Position / Q000502:physiology*; D014797:Vital Capacity
chemical_list: D001786:Blood Glucose; D002395:Catecholamines; D019344:Lactic Acid