title: Dehydration reduces cardiac output and increases systemic and cutaneous vascular resistance during exercise.
abstract: This investigation determined the manner in which the cardiovascular system copes with the dehydration-induced reductions in cardiac output (Q) during prolonged exercise in the heat. On two separate occasions, seven endurance-trained subjects (maximal O2 consumption 4.70 +/- 0.41 l/min) cycled in the heat (35 degrees C) for 2 h, beginning at 62 +/- 2% maximal O2 consumption. During exercise, they randomly received either 0.2 liter of fluid and became dehydrated by 4.9 +/- 0.2% of their body weight [i.e., dehydration trial (DE)] or 3.6 +/- 0.4 liter of fluid and replaced 95% of fluid losses [i.e., euhydration trial (EU)]. During the 10- to 120-min period of EU, Q, mean arterial pressure (MAP), systemic vascular resistance (SVR), cutaneous vascular resistance (CVR), and plasma catecholamines did not change while esophageal temperature stabilized at 38.0 +/- 0.1 degrees C. Conversely, after 120 min of DE, Q and MAP were reduced 18 +/- 3 and 5 +/- 2%, respectively, compared with EU (P < 0.05). This was associated with a significantly higher SVR (17 +/- 6%) and plasma norepinephrine concentration (50 +/- 19%, P < 0.05). In addition, CVR was also significantly higher (126 +/- 16 vs. 102 +/- 6% of 20-min value; P < 0.05) during DE despite a 1.2 +/- 0.1 degrees C greater esophageal temperature (P < 0.05). In conclusion, significant reductions in Q are accompanied by significant increases in SVR and plasma norepinephrine and a slight although significant decline in MAP. The cutaneous circulation participates in this systemic vasoconstriction as indicated by increases in CVR despite significant hyperthermia.
authors.affiliation: Department of Kinesiology and Health Education, University of Texas at Austin 78712, USA.
authors.forename: J
authors.initials: J
authors.lastname: González-Alonso
authors.forename: R
authors.initials: R
authors.lastname: Mora-Rodríguez
authors.forename: P R
authors.initials: PR
authors.lastname: Below
authors.forename: E F
authors.initials: EF
authors.lastname: Coyle
mesh_terms: D000328:Adult; D001783:Blood Flow Velocity; D001786:Blood Glucose / Q000378:metabolism; D001831:Body Temperature; D002302:Cardiac Output / Q000502:physiology*; D002395:Catecholamines / Q000097:blood; D003681:Dehydration / Q000097:blood / Q000503:physiopathology*; D015444:Exercise / Q000502:physiology*; D005334:Fever / Q000097:blood / Q000503:physiopathology; D006801:Humans; D007773:Lactates / Q000097:blood; D019344:Lactic Acid; D012867:Skin / Q000098:blood supply*; D014655:Vascular Resistance / Q000502:physiology*
chemical_list: D001786:Blood Glucose; D002395:Catecholamines; D007773:Lactates; D019344:Lactic Acid