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71.
Hanns-Christof Spatz 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1991,161(3):231-236
Summary This paper attempts to explain Kleiber's rule, which relates metabolic rate of mammals to their body mass, from the structure and function of the blood circulation system.Abbreviations
a
scaling factor
-
fractal dimension
-
hydrodynamic conductivity
-
l
n
length of an arterial blood vessel at bifurcation level n
-
M
body mass
-
N
maximal number of bifurcation levels
-
p
pressure
-
Q
flow
-
r
size of Bohr effect
-
r
n
radius of an arterial blood vessel at bifurcation level n
-
V
volume
-
VO
2
rate of oxygen unloading
-
Z
n
number of arterial blood vessels at bifurcation level n 相似文献
72.
P. J. N. Bloem L. M. G. C. Goessens P. Zamparo M. Sacher R. Paviotti P. E. di Prampero 《European journal of applied physiology and occupational physiology》1991,62(3):204-210
Thirteen male subjects performed a running test on the treadmill consisting of four standard exercise intensities [65%, 75%, 85%, 95% maximal O2 uptake (VO2 max)] presented in ascending, descending or random order. At the end of each exercise intensity, O2 consumption, heart rate (fc), venous blood lactate concentration [( Ia]b) and perceived exertion were assessed. This last variable was determined according to the Borg nonlinear CR-20 scale. The same variables were also determined during exercise at a standard intensity (65% or 95% VO2 max) performed before and after a Finnish sauna bath. Ratings of perceived exertion showed a good test-retest reliability (r = 0.77); they were the same when the exercise intensity was expressed in relative (%VO2 max) or absolute (speed) terms, and were independent of the order of presentation of the exercise. The latter had no effect on fc either but it did, however, influence [Ia]b, which was significantly higher in the descending, as compared to the ascending or random modes of presentation. The sauna bath increased fc at a given exercise intensity, but left perceived exertion and [Ia]b unchanged. It was concluded that at least under the present experimental conditions, fc and venous [Ia]b do not play a major role as determinants of perceived exertion. 相似文献
73.
Effect of lowered muscle temperature on the physiological response to exercise in men 总被引:1,自引:0,他引:1
A. Beelen A. J. Sargeant 《European journal of applied physiology and occupational physiology》1991,63(5):387-392
The effect of low muscle temperature on the response to dynamic exercise was studied in six healthy men who performed 42 min of exercise on a cycle ergometer at an intensity of 70% of their maximal O2 uptake. Experiments were performed under control conditions, i.e. from rest at room temperature, and following 45 min standing with legs immersed in a water bath at 12 degrees C. The water bath reduced quadriceps muscle temperature (at 3 cm depth) from 36.4 (SD 0.5) degrees C to 30.5 (SD 1.7) degrees C. Following cooling, exercise heart rate was initially lower, the mean difference ranged from 13 (SD 4) beats.min-1 after 6 min of exercise, to 4 (SD 2) beats.min-1 after 24 min of exercise. Steady-state oxygen uptake was consistently higher (0.2 l.min-1). However, no difference could be discerned in the kinetics of oxygen uptake at the onset of exercise. During exercise after cooling a significantly higher peak value was found for the blood lactate concentration compared to that under control conditions. The peak values were both reached after approximately 9 min of exercise. After 42 min of exercise the blood lactate concentrations did not differ significantly, indicating a faster rate of removal during exercise after cooling. We interpreted these observations as reflecting a relatively higher level of muscle hypoxia at the onset of exercise as a consequence of a cold-induced vasoconstriction. The elevated steady-state oxygen uptake may in part have been accounted for by the energetic costs of removal of the extra lactate released into the blood consequent upon initial tissue hypoxia. 相似文献
74.
P. Foxdal A. Sj?din B. ?stman B. Sj?din 《European journal of applied physiology and occupational physiology》1991,63(1):52-54
The aim of the study was to examine whether the difference in lactate concentration in different blood fractions is of practical importance when using blood lactate as a test variable of aerobic endurance capacity. Ten male firefighters performed submaximally graded exercise on a cycle ergometer for 20-25 min. Venous and capillary blood samples were taken every 5 min for determination of haematocrit and lactate concentrations in plasma, venous and capillary blood. At the same time, expired air was collected in Douglas bags for determination of the oxygen consumption. A lactate concentration of 4.0 mmol.l-1 was used as the reference value to compare the oxygen consumption and exercise intensity when different types of blood specimen and sampling sites were used for lactate analysis. At this concentration the exercise intensity was 17% lower (P less than 0.01) when plasma lactate was compared to venous blood lactate, and 12% lower (P less than 0.05) when capillary blood lactate was used. Similar discrepancies were seen in oxygen consumption. The results illustrated the importance of standardizing sampling and handling of blood specimens for lactate determination to enable direct comparisons to be made among results obtained in different studies. 相似文献
75.
Reduced orthostatic tolerance following 4 h head-down tilt 总被引:2,自引:0,他引:2
Gary C. Butler Huacheng Xing David R. Northey Richard L. Hughson 《European journal of applied physiology and occupational physiology》1991,62(1):26-30
The cardiovascular responses to a 10-min 1.22 rad (70 degrees) head-up tilt orthostatic tolerance test (OST) was observed in eight healthy men following each of a 5-min supine baseline (control), 4 h of 0.1 rad (6 degrees) head-down tilt (HDT), or 4 h 0.52 rad (30 degrees) head-up tilt (HUT). An important clinical observation was presyncopal symptoms in six of eight subjects following 4 h HDT, but in no subjects following 4 h HUT. Immediately prior to the OST, there were no differences in heart rate, stroke volume, cardiac output, mean arterial pressure and total peripheral resistance for HDT and HUT. However, stroke volume and cardiac output were greater for the control group. Mean arterial pressure for the control group was less than HDT but not HUT. Over the full 10-min period of OST, the mean arterial pressure was not different between groups. Heart rate increased to the same level for all three treatments. Stroke volume decreased across the full time period for control and HDT, but only at 3 and 9 min for HUT. There was a higher total peripheral resistance in the HDT group than control or HUT. The pre-ejection period to left ventricular ejection time ratio was less in HDT than for control or HUT groups. These data indicate a rapid adaptation of the cardiovascular system to 4 h HDT that appears to be inappropriate on reapplication of a head to foot gravity vector. We speculate that the cause of the impaired orthostatic tolerance is decreased tone in venous capacitance vessels so that venous return is inadequate. 相似文献
76.
77.
Statistical methods are introduced for analysis of the migration component of genetic drift, i.e., of the stochastic changes that affect allele frequencies during migration between local groups. Attention focuses on alpha M, a parameter that measures the extent to which this component of drift departs from the ideal of independent random sampling, and which can be interpreted as a measure of the extent to which migration is kin-structured. It is shown that alpha M can be estimated from genetic data, even in the absence of information about the genealogical relationships of migrants, and Monte-Carlo simulations are used to approximate the sampling distribution of the estimator under the null hypothesis of independent random sampling. Application of these methods to data from the Aland Islands, Finland, shows that the migration pattern there is consistent with the hypothesis of independent random sampling. 相似文献
78.
Summary The gap junction morphology was quantified in freeze-fracture replicas prepared from rat auricles that had been either quickly frozen at 6 K or chemically fixed by glutaraldehyde, in a state of normal cell-to-cell conduction or in a state of electrical uncoupling. The general appearance of the gap junctions was similar after both preparative procedures. A quantitative analysis of three gap junctional dimensions provided the following measurements in the quickly frozen conducting auricles (mean±sd): (a) P-face particles' diameter 8.27±0.74 nm (n =5709), (b) P-face particles' center-to-center distance 10.78±2.12 nm (n=4800), and (c) E-face pits' distance 9.99±2.19 nm (n=1600). Corresponding values obtained from chemically fixed tissues were decreased by about 3% for the particle's diameter and about 5% for the particles' and pits' distances. Electrical uncoupling by the action of either 1 mM 2–4-dinitrophenol (DNP), or 3.5 mMn-Heptan-1-ol (heptanol), induced a decrease of the particle's diameter, which amounted to –0.69±0.01 nm (mean ±se) in the quickly frozen preparations and –0.71±0.01 nm in the chemically fixed ones. The particles' distance was decreased by –0.96±0.04 nm in the quickly frozen samples and by –0.90 ±0.03 nm in the chemically fixed ones and the E-face pits' distance was similarly reduced. All differences were statistically significant (P<0.001 for all dimensions). Electrical recoupling after the heptanol effect promoted a return of these gap junctional dimensions towards normal values, which was about 50% complete within 20 min. It is concluded that very similar morphological alterations of the gap junctional structure are induced in the mammalian heart by different treatments promoting electrical uncoupling and that these conformational changes appear independently of the preparative procedure. The suggestion that the observed decrease of the particles' diameter is genuinely related to the closing mechanism of the unit cell-to-cell channel set in thei centers is thus confirmed. 相似文献
79.
Regional Kinetic Constants for Blood–Brain Barrier Pyruvic Acid Transport in Conscious Rats by the Monocarboxylic Acid Carrier 总被引:1,自引:1,他引:0
The present investigation using labeled pyruvate describes the regional distribution and kinetics of the monocarboxylic acid carrier at the blood-brain barrier of conscious rats. The experimental procedure involved the arterial injection of a single bolus of 200 microliter containing [1-14C]pyruvate, [3H]water, and varying concentrations of unlabeled pyruvate into the common carotid via an indwelling externalized catheter. The hemisphere ipsi-lateral to the injection and rostral to the midbrain was removed and dissected into five regions. A kinetic analysis revealed no significant regional differences in Km values with an overall average of 1.37 mM. However, there was regional variation in the density of the monocarboxylic acid carrier as indicated by varied levels of the kinetic constant Vmax. The cortex showed the highest Vmax value of 0.42 +/- 0.08 mumol/min/g whereas values for the caudate/putamen, thalamus/hypothalamus, and remaining portion of hemisphere ranged significantly lower at 0.22-0.27 mumol/min/g. The Vmax for the hippocampus was intermediate at 0.37 +/- 0.12 mumol/min/g. The nonsaturable carrier described kinetically by KD had an overall average of 0.034 ml/min/g. The present study confirms quantitatively previous results suggesting a variable regional distribution of the monocarboxylic acid carrier. 相似文献
80.
利用南京地区夏季炎热的自然条件,连续两年在高温季节(7—8月)进行实验。第一年(系列Ⅰ)的实验动物为四头装置瘤胃瘘管的空怀母水牛,研究高温初期(27.5~33.4℃)和持续高温期(28.0~35℃)对水牛瘤胃消化代谢的影响。第二年实验(系列Ⅱ)利用三头装置瘤胃瘘管的海仔母水牛重复高温(26~35.3℃)实验。 夏季高温期间,实验水牛的呼吸率、瘤胃温度和直肠温度升高,采食量减少,饮水量增加,瘤胃液流速减缓。高温初期出现瘤胃代谢升高[总挥发性脂肪酸(TVFA)和氨氮(NH_3-N)浓度及乙酸/丙酸(A/P)比率升高]。但在持续高温情况下,水牛的采食和瘤胃代谢均明显抑制。采取瘤胃内降温措施(投入冰袋)或冷水淋浴,均能迅速降低呼吸率、直肠和瘤胃温度,恢复采食和反刍,并缓解瘤胃代谢的抑制。提示动物机体参与调节瘤胃代谢的变化,并为改善水牛夏季的饲养管理提供生理学依据。 相似文献