J. Gonzalezalonso et al., DEHYDRATION REDUCES CARDIAC-OUTPUT AND INCREASES SYSTEMIC AND CUTANEOUS VASCULAR-RESISTANCE DURING EXERCISE, Journal of applied physiology, 79(5), 1995, pp. 1487-1496
This investigation determined the manner in which the cardiovascualr s
ystem 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 O-2 consumption 4.70 +/- 0.4
1 l/min) cycled in the heat (35 degrees C) for 2 h, beginning at 62 +/
- 2% maximal O-2 consumption During exercise, they randomly received e
ither 0.2 liter of fluid and became dehydrated by 4.9 +/- 0.2% of thei
r body weight [i.e., dehydration trial (DE)] or 3.6 +/- 0.4 liter of f
luid 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 temper
ature 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, com
pared with EU (P < 0.05). This was associated with a significantly hig
her 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 temperture (P < 0.05). In conclusi
on, significant reductions in Q are accompanied by significant increas
es in SVR and plasma norepinephrine and a slight although significant
decline in MAP. The cutaneous circulation participates in this systemi
c vasoconstriction as indicated by increases in CVR despite significan
t hyperthermia.