期刊
JOURNAL OF APPLIED PHYSIOLOGY
卷 100, 期 5, 页码 1727-1732出版社
AMER PHYSIOLOGICAL SOC
DOI: 10.1152/japplphysiol.01244.2005
关键词
fever; force-frequency relationship; beta-adrenergic stimulation; isoproterenol; thermoregulation
资金
- NHLBI NIH HHS [R01 HL-738616] Funding Source: Medline
The body is from time to time exposed to nonnormothermic conditions; both hypo- and hyperthermia can occur as a result of external ( environment) or internal ( pathogens, allergens) stressors. To preserve life under hypo- and hyperthermic conditions, adequate perfusion of vital organs is mandated. Although cardiac output regulation under hyperthermic conditions has been studied, the mechanical response of basic contractile function of the myocardium itself is incompletely understood. Accordingly, we set out to test mechanical output of isolated myocardium under hyperthermic conditions and to compare the results with the hypo- and normothermic response in the same tissue. We observed that, in absence of a frequency change, developed force decreased markedly. At a physiological normal stimulation rate of 6 Hz, developed force decreases to 67.2 +/- 2.6% at 42 degrees C compared with 37 degrees C. In addition, twitch timing characteristics also accelerate, allowing for a faster relaxation; time from peak tension to 50% relaxation is similar to 23% faster ( from 31.4 +/- 2.6 to 24.4 +/- 1.7 ms). Although this faster relaxation in turn prevents a steep increase in diastolic tension at high frequencies, the very fast calcium kinetics now prevent a more complete activation of the myofilaments, resulting in a lower twitch-force maximum at hyperthermic conditions. Even at maximal beta-adrenergic stimulation, developed force is well below levels reached at physiological temperature.
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