Hypovolemic intolerance to lower body negative pressure in female runners.

T Morikawa, S Sagawa, R Torii, Y Endo… - Medicine and science …, 2001 - europepmc.org
T Morikawa, S Sagawa, R Torii, Y Endo, F Yamazaki, K Shiraki
Medicine and science in sports and exercise, 2001europepmc.org
Purpose An attenuated baroreflex response and orthostatic intolerance have been reported
in endurance-trained male athletes; however, it is still unknown whether this occurs also in
females. The purpose of the present study was to examine whether endurance exercise-
trained women had a predisposition to orthostatic compromise, and if so, what causative
factor (s) may induce orthostatic intolerance. Methods We studied cardiovascular and
hormonal responses to graded lower body negative pressure (LBNP)(0 to-60 mm Hg) in 26 …
Purpose
An attenuated baroreflex response and orthostatic intolerance have been reported in endurance-trained male athletes; however, it is still unknown whether this occurs also in females. The purpose of the present study was to examine whether endurance exercise-trained women had a predisposition to orthostatic compromise, and if so, what causative factor (s) may induce orthostatic intolerance.
Methods
We studied cardiovascular and hormonal responses to graded lower body negative pressure (LBNP)(0 to-60 mm Hg) in 26 middle-distance female runners (18.6+/-0.1 yr) as the exercise-trained (ET) subjects and 23 age-matched untrained (UT) control subjects. On the basis of the occurrence of syncope episodes during LBNP, ET and UT subjects were further allocated to two groups; ET with presyncope (ET+ syncope) and without presyncope (ET-syncope) and UT with presyncope (UT+ syncope) and without presyncope (UT-syncope).
Results
Occurrence of presyncope episodes during LBNP was higher in ET (65.4%, P< 0.05) than that for UT (34.8%). Leg compliance was higher (P< 0.05) in ET than in UT. LBNP reduced stroke volume (SV) more (P< 0.05), increased heart rate (HR) higher (P< 0.05), and increased forearm vascular resistance (FVR) more in ET+ syncope as compared with the other groups. Response of vasoactive hormones to LBNP was higher in ET+ syncope (P< 0.05) than that of the other groups except for norepinephrine (NE); high in both ET+ syncope and UT+ syncope. The relationship between SV and NE, an index of sympathetic neuronal response, had no training-related changes during LBNP.
Conclusion
We conclude that exercise-trained females have a high incidence of orthostatic intolerance during LBNP, with a greater reduction of SV independent of changes in baroreflex and neurohumoral function. A lower incidence of LBNP intolerance in UT may be accounted for by a lower reduction of SV during LBNP. An increase in leg compliance in the exercise-trained females may play an important role in inducing pronounced reduction of SV and hence the intolerance to LBNP.
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