ALPHA-MOTONEURON EXCITABILITY AT HIGH-ALTITUDE

被引:28
作者
KAYSER, B [1 ]
BOKENKAMP, R [1 ]
BINZONI, T [1 ]
机构
[1] ITALIAN ALTITUDE RES LAB PYRAMID,KHUMBU,NEPAL
来源
EUROPEAN JOURNAL OF APPLIED PHYSIOLOGY AND OCCUPATIONAL PHYSIOLOGY | 1993年 / 66卷 / 01期
关键词
ALTITUDE; CENTRAL NERVOUS SYSTEM; H-REFLEX; MUSCLE; HYPOXIA;
D O I
10.1007/BF00863391
中图分类号
Q4 [生理学];
学科分类号
071003 ;
摘要
It has been hypothesized that chronic hypobaric hypoxia could lead to inhibition of the alpha-motoneuron pool, thus limiting the maximal activation of working skeletal muscles. To test this hypothesis six subjects [32 (SEM 2) years] were evaluated in resting conditions, at sea level and after acclimatization at 5,050 m. The recruitment curves of the Hofmann-reflex (H-) and the direct muscle-response (M-) of the right soleus muscle were obtained by stimulating the posterior tibeal nerve with different intensities while recording the electromyogram of the soleus muscle. From the recorded data the net alpha-motoneuron excitability (ratio of maximal H-reflex to M-response H(max): M(max) ratio), the threshold and gain for both responses, obtained from linear regressions through the rising phase of the recruitment curves of both responses, as well as the latency times of both responses were determined. The latency times and the H(max): M(max) ratio were unchanged at altitude. The thresholds of both responses and the gain of the M-response were unaltered. The gain of the H-response was significantly higher at altitude when compared to sea level. It is concluded that in the acclimatized subjects at rest the signal conduction velocity through the different parts of both pathways was unaltered and therefore nerve and muscle conduction velocity as well as synaptic and muscle end-plate transmission were unchanged, that the recruitment of the H-reflex was slightly facilitated after acclimatization to high altitude suggesting increased excitability of the alpha-motoneurons, through either postsynaptic facilitatory changes in the soma or a different descending drive, and that the unchanged H(max): M(max), ratio indicated no change in the net excitatory and inhibitory influences on the alpha-motoneuron pool. The above hypothesis is thus not strengthened by the results that were, however, obtained in resting conditions.
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页码:1 / 4
页数:4
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