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排序方式: 共有441条查询结果,搜索用时 15 毫秒
1.
Freund B. J.; Joyner M. J.; Jilka S. M.; Kalis J.; Nittolo J. M.; Taylor J. A.; Peters H.; Feese G.; Wilmore J. H. 《Journal of applied physiology》1987,63(3):930-936
Thermoregulation and cardiovascular drift were studied under conditions of prolonged exercise in a warm environment (dry bulb temperature 31.7 +/- 0.3 degrees C, rh 44.7 +/- 4.7%) during beta-adrenergic blockade. Fourteen subjects performed 90-min rides on a cycle ergometer at a work rate equivalent to 40% of their control maximal O2 uptake under each of three treatments provided in a randomized double-blind manner: atenolol (100 mg/day), propranolol (160 mg/day), and a placebo. Exercise during the propranolol trial resulted in significantly higher forearm vascular resistance values and significantly lower forearm blood flows (FBF) compared with the placebo trial. However, the significantly lower FBF during propranolol did not significantly alter the rectal temperature (Tre) response to prolonged exercise. In addition, both beta-blockers produced lower FBF for any given Tre, suggesting that beta-adrenergic blockade affects FBF through nonthermal factors. The slight differences in Tre, despite the large differences in FBF between the various treatments, are apparently the result of an enhanced sweat loss and a lower mean skin temperature during exercise with beta-blockade. The uncoupling of FBF and sweat loss provides evidence of independent regulation. The reduction in FBF at any given Tre was concomitant to lower blood pressure values during beta-blockade and suggests that baroreflexes provide significant input to the control of skin blood flow when both pressure and temperature maintenance are simultaneously challenged. 相似文献
2.
Postexercise reductions in blood pressure at rest have been reported for hypertensive subjects. To determine whether post-exercise hypotension would occur in spontaneously hypertensive rats and to test the hypothesis that any reductions would result because of decreases in regional vascular resistances, hypertensive rats (n = 19) were instrumented with indwelling arterial catheters and Doppler probes to measure regional blood flows from the iliac, superior mesenteric, and renal arteries. Data were collected from animals who performed a 20- and a 40-min treadmill test at between 60 and 70% of their maximum O2 uptake. When the animals ran for 20 min, there was a pre- to postexercise drop in mean arterial pressure (MAP) from 158 +/- 3.6 to 150 +/- 3.6 mmHg (P less than 0.05), which was recorded 30 min after the exercise had ceased. The pre- to postexercise reduction in MAP after 40 min of treadmill running was from 154 +/- 3.1 to 138 +/- 3.0 mmHg (P less than 0.05) as recorded 30 min postexercise. Postexercise heart rate was significantly lower after the 40-min exercise bout, from a preexercise mean of 351 +/- 3 beats/min to 324 +/- 5 beats/min 30 min after the treadmill had stopped. Surprisingly, marked pre- to postexercise reductions in regional vascular resistance were not observed in either the iliac, superior mesenteric, or renal vascular beds. These data demonstrated the existence of postexercise hypotension in genetic hypertensive rats and suggested that reductions in cardiac output were the primary hemodynamic mechanism for this finding. 相似文献
3.
4.
A comparison of two laboratory strains of Eimeria tenella 总被引:2,自引:0,他引:2
5.
Differential control of forearm and calf vascular resistance during one-leg exercise 总被引:3,自引:0,他引:3
Taylor J. A.; Joyner M. J.; Chase P. B.; Seals D. R. 《Journal of applied physiology》1989,67(5):1791-1800
The purpose of this study was to determine whether blood flow (BF) and vascular resistance (VR) are controlled differently in the nonactive arm and leg during submaximal rhythmic exercise. In eight healthy men we simultaneously measured BF to the forearm and calf (venous occlusion plethysmography) and arterial blood pressure (sphygmomanometry) and calculated whole limb VR before (control) and during 3 min of cycling with the contralateral leg at 38, 56, and 75% of peak one-leg O2 uptake (VO2). During the initial phase of exercise (0-1.5 min) at all work loads, BF increased and VR decreased in the forearm (P less than 0.05), whereas calf BF and VR remained at control levels. Thereafter, BF decreased and VR increased in parallel and progressive fashion in both limbs. At end exercise, forearm BF and VR were not different from control values (P greater than 0.05); however, in the calf, BF tended to be lower (P less than 0.05 at 75% peak VO2 only) and VR was higher (23 +/- 9, 44 +/- 14, and 88 +/- 23% above control at 38, 56, and 75% of peak VO2, respectively, all P less than 0.05). In a second series of studies, forearm and calf skin blood flow (laser-Doppler velocimetry) and arterial pressure were measured during the same levels of exercise in six of the subjects. Compared with control, skin BF was unchanged and VR was increased (P less than 0.05) in the forearm by end exercise at all work loads, whereas calf skin BF increased (P less than 0.05) and VR decreased (P less than 0.05). The present findings indicate that skeletal muscle and skin VR are controlled differently in the nonactive forearm and calf during the initial phase of rhythmic exercise with the contralateral leg. Skeletal muscle vasodilation occurs in the forearm but not in the calf; forearm skin vasoconstricts, whereas calf skin vasodilates. Finally, during exercise a time-dependent vasoconstriction occurs in the skeletal muscle of both limbs. 相似文献
6.
Action potential conduction between a ventricular cell model and an isolated ventricular cell. 总被引:4,自引:1,他引:3
R Wilders R Kumar R W Joyner H J Jongsma E E Verheijck D Golod A C van Ginneken W N Goolsby 《Biophysical journal》1996,70(1):281-295
We used the Luo and Rudy (LR) mathematical model of the guinea pig ventricular cell coupled to experimentally recorded guinea pig ventricular cells to investigate the effects of geometrical asymmetry on action potential propagation. The overall correspondence of the LR cell model with the recorded real cell action potentials was quite good, and the strength-duration curves for the real cells and for the LR model cell were in general correspondence. The experimental protocol allowed us to modify the effective size of either the simulation model or the real cell. 1) When we normalized real cell size to LR model cell size, required conductance for propagation between model cell and real cell was greater than that found for conduction between two LR model cells (5.4 nS), with a greater disparity when we stimulated the LR model cell (8.3 +/- 0.6 nS) than when we stimulated the real cell (7.0 +/- 0.2 nS). 2) Electrical loading of the action potential waveform was greater for real cell than for LR model cell even when real cell size was normalized to be equal to that of LR model cell. 3) When the size of the follower cell was doubled, required conductance for propagation was dramatically increased; but this increase was greatest for conduction from real cell to LR model cell, less for conduction from LR model cell to real cell, and least for conduction from LR model cell to LR model cell. The introduction of this "model clamp" technique allows testing of proposed membrane models of cardiac cells in terms of their source-sink behavior under conditions of extreme coupling by examining the symmetry of conduction of a cell pair composed of a model cell and a real cardiac cell. We have focused our experimental work with this technique on situations of extreme uncoupling that can lead to conduction block. In addition, the analysis of the geometrical factors that determine success or failure of conduction is important in the understanding of the process of discontinuous conduction, which occurs in myocardial infarction. 相似文献
7.
Anesthesia and chest wall function in dogs 总被引:4,自引:0,他引:4
8.
A line of Eimeria maxima acquired resistance to Lerbek (a mixture of clopidol and methyl benzoquate) after serial passage against rising drug levels. Abnormal bisporocystic oocysts which appeared throughout this series were picked out individually and these produced infections in further groups of chicks. Serial passages of selected bisporocystic forms raised their proportion in oocyst yields to about 80% after 10-14 passages, but a few normal oocysts were still present. 相似文献
9.
Proctor David N.; Shen Peter H.; Dietz Niki M.; Eickhoff Tamara J.; Lawler Lori A.; Ebersold Ethan J.; Loeffler Darrell L.; Joyner Michael J. 《Journal of applied physiology》1998,85(1):68-75
It is currentlyunclear whether aging alters the perfusion of active muscles duringlarge-muscle dynamic exercise in humans. To study this issue, directmeasurements of leg blood flow (femoral vein thermodilution) andsystemic arterial pressure during submaximal cycle ergometry (70, 140, and 210 W) were compared between six younger (Y; 22-30 yr) and sixolder (O; 55-68 yr) chronically endurance-trainedmen. Whole body O2uptake, ventilation, and arterial and femoral venous samples forblood-gas, catecholamine, and lactate determinations were alsoobtained. Training duration (min/day), estimated leg muscle mass(dual-energy X-ray absorptiometry; Y, 21.5 ± 1.2 vs. O, 19.9 ± 0.9 kg), and blood hemoglobin concentration (Y, 14.9 ± 0.4 vs. O, 14.7 ± 0.2 g/dl) did not significantly differ (P > 0.05) between groups. Leg bloodflow, leg vascular conductance, and femoral venousO2 saturation were ~20-30%lower in the older men at each work rate (allP < 0.05), despite similarlevels of whole body O2 uptake. At210 W, leg norepinephrine spillover rates and femoral venous lactateconcentrations were more than twofold higher in the older men.Pulmonary ventilation was also higher in the older men at 140 (+24%)and 210 (+39%) W. These results indicate that leg blood flow andvascular conductance during cycle ergometer exercise are significantlylower in older endurance-trained men in comparison to their youngercounterparts. The mechanisms responsible for this phenomenon and theextent to which they operate in other groups of older subjects deservefurther attention. 相似文献
10.
Differential effect of three-repeat and four-repeat tau on mitochondrial axonal transport 总被引:1,自引:0,他引:1
Will Stoothoff† Phillip B. Jones Tara L. Spires-Jones Daniel Joyner Ekta Chhabra Kathryn Bercury‡ Zhanyun Fan Hong Xie Brian Bacskai Jon Edd§ Daniel Irimia§ Bradley T. Hyman 《Journal of neurochemistry》2009,111(2):417-427
Tau protein is present in six different splice forms in the human brain and interacts with microtubules via either 3 or 4 microtubule binding repeats. An increased ratio of 3 repeat to 4 repeat isoforms is associated with neurodegeneration in inherited forms of frontotemporal dementia. Tau over-expression diminishes axonal transport in several systems, but differential effects of 3 repeat and 4 repeat isoforms have not been studied. We examined the effects of tau on mitochondrial transport and found that both 3 repeat and 4 repeat tau change normal mitochondrial distribution within the cell body and reduce mitochondrial localization to axons; 4 repeat tau has a greater effect than 3 repeat tau. Further, we observed that the 3 repeat and 4 repeat tau cause different alterations in retrograde and anterograde transport dynamics with 3 repeat tau having a slightly stronger effect on axon transport dynamics. Our results indicate that tau-induced changes in axonal transport may be an underlying theme in neurodegenerative diseases associated with isoform specific changes in tau's interaction with microtubules. 相似文献