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Hemodynamics of orthostatic intolerance: implications for gender differences
Qi Fu1, Armin Arbab-Zadeh, Merja A Perhonen
1Institute for Exercise and Environmental Medicine, 7232 Greenville Ave., Suite 435, Dallas, TX 75231, USA.
American Journal of Physiology. Heart and Circulatory Physiology
|October 7, 2003
Summary
Women experience more orthostatic intolerance due to reduced cardiac filling, not vascular resistance. This study highlights the role of cardiac mechanics in gender differences in orthostatic tolerance.
Area of Science:
- Cardiovascular Physiology
- Human Physiology
- Gender Medicine
Background:
- Women exhibit a higher incidence of orthostatic intolerance compared to men.
- Existing hypotheses suggest differences in vascular resistance responsiveness or hemodynamic regulation during orthostatic stress.
Purpose of the Study:
- To investigate the hypothesis that gender differences in orthostatic intolerance are linked to hemodynamic regulation of cardiac filling, rather than vascular resistance.
- To compare the Frank-Starling relationship and orthostatic tolerance between healthy young women and men.
Main Methods:
- Constructed Frank-Starling curves using pulmonary capillary wedge pressure (PCWP), stroke volume (SV), and stroke index (SI) during lower body negative pressure (LBNP) and saline infusion.
- Assessed orthostatic tolerance by progressive LBNP until presyncope in 10 women and 13 men.
- Measured vascular resistance and plasma norepinephrine concentrations.
Main Results:
- Women exhibited significantly lower LBNP tolerance than men.
- Women demonstrated steeper maximal slopes of the Frank-Starling curves (SV and SI) compared to men.
- At presyncope, women had lower SV and SI, but similar mean arterial pressure and vascular resistance, with higher heart rates than men.
Conclusions:
- Lower orthostatic tolerance in women is associated with decreased cardiac filling, as indicated by the Frank-Starling relationship.
- Reduced responsiveness of vascular resistance does not appear to be the primary mechanism for gender differences in orthostatic intolerance.
- Cardiac mechanics and the Frank-Starling relationship are likely key factors underlying gender disparities in orthostatic tolerance.