You are here

Effects of Exercise on Hemodynamic Properties, Blood Viscosity and Nitric Oxide Production

A clinical study of 9 recreationally active adults demonstrated relationships between hemodynamic markers and key cardiovascular parameters. After exercise, systemic vascular resistance (SVR) was observed to decrease by 45% and vascular hindrance (VH) decreased by 38%.  However, cardiac output (CO), nitric oxide concentration (NOx), and blood viscosity (BV) increased by 16%, 24%, and 76%, respectively.

Classic hemodynamic theory suggests that during exercise, increased metabolic demand is typically met with an increase in CO.  Left unchanged, this would cause a subsequent increase in SVR.  However, compliant vessels dilate and SVR is reduced via shear-dependent nitric oxide release from the endothelium.   The present study suggests, paradoxically, that increased blood viscosity also contributes to decreased SVR during exercise.  In fact, it may be imperative for adequate shear-dependent NOx production and vasodilation.

The observed relationships suggest that the hemodynamic and vascular adjustments in healthy vessels require an increase, to a certain threshold, in CO and an increase in BV to facilitate greater endothelial shear stress and a subsequent release of NOx .  Exercise-induced BV increases are likely secondary to enhanced sympathetic tone in addition to hemoconcentration from fluid loss.  NOx activates guanylyl cyclase which catalyzes the production of cyclic GMP.  Cyclic GMP promotes smooth muscle relaxation and vasodilation via multiple biochemical mechanisms.   Ultimately, NOx promotes the vasodilation necessary to reduce SVR beyond the opposing effect of increased BV.  Therefore, perhaps counter-intuitively, increased BVfacilitate blood flow.  This is especially important during exercise where decreased SVR is required for adequate delivery of oxygen to tissues.  The authors speculated that diuretic-induced blood pressure reductions may be secondary to hemoconcentration and a resultant increase in BV, ultimately resulting in a similar compensatory NOx-mediated vasodilation.  Correlations between the various hemodynamic and hemorheological parameters are presented in Table 1.  The only significant correlations found were a positive correlation between BV and NOx and a negative correlation between CO and VH.  The authors stated, “while exercise-induced increases of CO and blood flow during exercise probably stimulate the endothelium by shear-dependent mechanisms, and thus increase the production of NOx, the results of the present study suggest that the rise in BV during exercise could also facilitate NOx production and thus directly contribute as well to vasodilation.”

Table 1. Correlations between hemodynamic and hemorheological parameters 

↑ BV

 ↑ NOx

Significant*

↑ NOx

↓ VH

NS

↑ BV

↓ SVR

NS

↑ CO

↓ VH

Significant

↔ NOx

↔ CO

NS

↑ = increase; ↓ = decrease; ↔ no change/no effect

* = Significance level defined as p < 0.05

NS = Not Significant


Reference:

Connes P, Pichon A, Hardy-Dessources MD, et al. Blood viscosity and hemodynamics during exercise. Clinical hemorheology and microcirculation. 2012.

 

Stay Connected