Morikawa T, Sagawa S, Torii R, Endo Y, Yamazaki F, Shiraki K
Department of Physiology, School of Medicine, University of Occupational and Environmental Health, 1-1 Iseigaoka, Yahatanishi-ku, 807-8555 Kitakyushu, Japan.
Med Sci Sports Exerc. 2001 Dec;33(12):2058-64. doi: 10.1097/00005768-200112000-00013.
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.
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).
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.
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.
有报道称耐力训练的男性运动员存在压力反射反应减弱和体位性不耐受的情况；然而，女性是否也会出现这种情况仍不清楚。本研究的目的是检验耐力运动训练的女性是否易发生体位性失代偿，如果是，哪些致病因素可能导致体位性不耐受。
我们研究了26名中距离女跑步运动员（18.6±0.1岁）作为运动训练（ET）组受试者和23名年龄匹配的未训练（UT）对照组受试者对分级下肢负压（LBNP）（0至-60 mmHg）的心血管和激素反应。根据LBNP期间晕厥发作的情况，ET组和UT组受试者进一步分为两组；有晕厥前症状的ET组（ET+晕厥）和无晕厥前症状的ET组（ET-晕厥）以及有晕厥前症状的UT组（UT+晕厥）和无晕厥前症状的UT组（UT-晕厥）。
LBNP期间ET组晕厥前症状的发生率（65.4%，P<0.05）高于UT组（34.8%）。ET组的腿部顺应性高于UT组（P<0.05）。与其他组相比，ET+晕厥组LBNP使每搏输出量（SV）降低更多（P<0.05），心率（HR）升高更多（P<0.05），前臂血管阻力（FVR）增加更多。除去甲肾上腺素（NE）外，ET+晕厥组血管活性激素对LBNP的反应高于其他组（P<0.05）；ET+晕厥组和UT+晕厥组的NE反应均较高。LBNP期间，SV与NE（交感神经反应指标）之间的关系没有与训练相关的变化。
我们得出结论，运动训练的女性在LBNP期间体位性不耐受的发生率较高，SV的降低幅度更大，且与压力反射和神经体液功能的变化无关。UT组LBNP不耐受发生率较低可能是由于LBNP期间SV降低幅度较小。运动训练女性腿部顺应性的增加可能在导致SV显著降低从而引起LBNP不耐受方面起重要作用。
