Cardiovascular responses to water immersion in humans: impact on cerebral perfusion

Abstract

Episodic increases in cerebrovascular perfusion and shear stress may have beneficial impacts on endothelial function that improve brain health. We hypothesized that water immersion to the level of the right atrium in humans would increase cerebral perfusion. We continuously measured, in 9 young (means ± SD, 24.6 ± 2.0 yr) healthy men, systemic hemodynamic variables along with blood flows in the common carotid and middle and posterior cerebral arteries during controlled filling and emptying of a water tank to the level of the right atrium. Mean arterial pressure (80 ± 9 vs. 91 ± 12 mmHg, P < 0.05), cardiac output (4.8 ± 0.7 vs. 5.1 ± 0.6 l/min, P < 0.05) and end-tidal carbon dioxide (PetCO2, 39.5 ± 2.0 vs. 44.4 ± 3.5 mmHg, P < 0.05) increased with water immersion, along with middle (59 ± 6 vs. 64 ± 6 cm/s, P < 0.05) and posterior cerebral artery blood flow velocities (41 ± 9 vs. 44 ± 10 cm/s, P < 0.05). These changes were reversed when the tank was emptied. Water immersion is associated with hemodynamic and PetCO2 changes, which increase cerebral blood velocities in humans. This study provides an evidence base for future studies to examine the potential additive effect of exercise in water on improving cerebrovascular health.

Keywords: cardiovascular; cerebral blood flow; hemodynamics; water immersion.

Figures

Fig. 1.

Middle cerebral (A) and posterior cerebral artery (B) velocities, mean arterial pressure (C), and end-tidal carbon dioxide (PetCO2) (D) at rest, during, and after water immersion. Repeated-measures ANOVA revealed that immersion significantly increased middle and posterior cerebral artery velocities, mean arterial pressure and PetCO2 (all P < 0.05). *Significantly different from rest at P < 0.05. Data are means ± SE.

Fig. 2.

Pearson correlations calculated from data derived from n = 7 subjects, for changes from baseline at each data collection point. Significant relationships existed between changes in middle cerebral artery velocities (MCAV) in response to water immersion and changes in both mean arterial pressure (MAP) (A) and PetCO2 (B).