Stroke volume during exercise: interaction of environment and hydration

• Published in: American journal of physiology. Heart and circulatory physiology Vol. 278; no. 2; pp. H321 - H330
• Main Authors: Gonzalez-Alonso, Jose, Mora-Rodriguez, Ricardo, Coyle, Edward F
• Format: Journal Article
• Language: English
• Published: United States 01.02.2000
• Subjects: Adult; Blood Glucose - analysis; Body Temperature - physiology; Body Water - metabolism; Catecholamines - blood; Differential Threshold; Esophagus - physiology; Exercise - physiology; Forearm - blood supply; Hemodynamics; Humans; Lactic Acid - blood; Male; Regional Blood Flow; Skin - blood supply; Skin Temperature; Space life sciences; Stroke Volume - physiology; Sweating; Temperature; Vasodilation - physiology
• ISSN: 0363-6135; 1522-1539
• DOI: 10.1152/ajpheart.2000.278.2.h321

Human Performance Laboratory, Department of Kinesiology and Health Education, The University of Texas, Austin, Texas 78712 Euhydrated and dehydrated subjects exercised in a hot and a cold environment with our aim to identify factors that relate to reductions in stroke volume (SV). We hypothesized that reductions in SV with heat stress are related to the interaction of several factors rather than the effect of elevated skin blood flow. Eight male endurance-trained cyclists [maximal O 2 consumption ( O 2 max ) 4.5 ± 0.1 l/min; means ± SE] cycled for 30 min (72% O 2 max ) in the heat (H; 35°C) or the cold (C; 8°C) when euhydrated or dehydrated by 1.5, 3.0, or 4.2% of their body weight. When euhydrated, SV and esophageal temperature (T es 38.2-38.3°C) were similar in H and C, whereas skin blood flow was much higher in H vs. C (365   ± 64% higher; P  < 0.05). With each 1% body weight loss, SV declined 6.4 ± 1.3 ml (4.8%) in H and 3.4 ± 0.4 ml (2.5%) in C, whereas T es increased 0.21 ± 0.02 and 0.10 ± 0.02°C in H and C, respectively ( P <  0.05). However, reductions in SV were not associated with increases in skin blood flow. The reduced SV was highly associated with increased heart rate and reduced blood volume in both H ( R = 0.96; P <  0.01) and C ( R = 0.85; P <  0.01). In conclusion, these results suggest that SV is maintained in trained subjects during exercise in euhydrated conditions despite large differences in skin blood flow. Furthermore, the lowering of SV with dehydration appears largely related to increases in heart rate and reductions in blood volume. heart rate; skin blood flow; hemodynamics; hyperthermia