Howell S, Maarek J M, Fournier M, Sullivan K, Zhan W Z, Sieck G C
Department of Biokinesiology and Physical Therapy, University of Southern California, Los Angeles 90033, USA.
J Appl Physiol (1985). 1995 Aug;79(2):389-97. doi: 10.1152/jappl.1995.79.2.389.
Diaphragm and latissimus dorsi muscle functions, histochemistries, and morphometries were studied in anesthetized male Yucatan minipigs with congestive heart failure (CHF) induced by supraventricular tachycardia (n = 5). Sham-operated animals served as a control group (n = 5). In CHF animals, transdiaphragmatic pressure measured during supramaximal phrenic stimulation was reduced by 40% at low frequencies (< or = 20 Hz) and by 60% at higher frequencies. Twitch amplitude and half-relaxation time were also decreased. The cross-sectional areas of type I, IIa, and IIb fibers were reduced in the diaphragm. The proportion of type I fibers increased, whereas type IIa fibers decreased. Succinate dehydrogenase activity was elevated in type IIa and IIb fibers, but diaphragmatic fatigability was not altered. CHF reduced latissimus dorsi isometric force by 40% for stimulation frequencies > or = 30 Hz. The cross-sectional area of latissimus dorsi type IIb fibers was decreased, but twitch characteristics, fiber type composition, succinate dehydrogenase activity, and fatigability were unchanged. Experimental CHF appears to cause greater intrinsic adaptive changes in the diaphragm compared with those in the latissimus dorsi in the minipig. For both muscles, reduced contractile function was associated with atrophy. Impaired performance of the diaphragm may also be attributed to an increase in the relative contribution of type I fibers to the total tension-generating capacity of the muscle and to the pathophysiological mechanisms underlying the shortened relaxation time of the twitch response.
对通过室上性心动过速诱导充血性心力衰竭（CHF）的麻醉雄性尤卡坦小型猪（n = 5）的膈肌和背阔肌功能、组织化学和形态计量学进行了研究。假手术动物作为对照组（n = 5）。在CHF动物中，在最大膈神经刺激期间测量的经膈压力在低频（≤20 Hz）时降低了40%，在高频时降低了60%。抽搐幅度和半松弛时间也降低了。膈肌中I型、IIa型和IIb型纤维的横截面积减小。I型纤维的比例增加，而IIa型纤维减少。IIa型和IIb型纤维中的琥珀酸脱氢酶活性升高，但膈肌疲劳性未改变。对于刺激频率≥30 Hz，CHF使背阔肌等长力降低了40%。背阔肌IIb型纤维的横截面积减小，但抽搐特征、纤维类型组成、琥珀酸脱氢酶活性和疲劳性未改变。实验性CHF似乎在小型猪中导致膈肌比背阔肌出现更大的内在适应性变化。对于这两块肌肉，收缩功能降低均与萎缩有关。膈肌功能受损也可能归因于I型纤维对肌肉总张力产生能力的相对贡献增加，以及抽搐反应松弛时间缩短背后的病理生理机制。
