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1.
Summary The resting membrane potential data existing in the literature for the giant axon of the squid, frog muscle and barnacle muscle have been analyzed from the standpoint of the theory of membrane potential due to Kobatake and co-workers. The average values derived for the effective charge density
(where
is a constant,
, and represents the fraction of counterions that are free, and
is the stoichiometric charge density in the membrane) present on the different biomembranes existing in their normal ionic environment are 0.3, 0.325 and 0.17 M for the squid axon, frog and barnacle muscles, respectively. On the assumption that the values of
are 0.4 and 0.2 for nerve and muscle membranes, respectively, values of 0.75, 1.62 and 0.85 M have been derived for the stoichiometric charge density
present in the respective biological membranes. These correspond to 1 negative charge per 222, 103 and 195 Å of the membrane area of the squid axon, frog and barnacle muscles, respectively. 相似文献
2.
An analytical model is developed to describe the performance of a packed-bed immobilized enzyme reactor in which parallel processes take place. In particular, two-substrate reaction, inhibition of the enzyme by one of the reaction products, and binding of one substrate and/or one product to an added ligand are taken into account. In addition, substrates and product diffusion into the porous catalyst are also considered. Using this model, numerical simulations were performed. The results point to the fact that, when all the above processes occur concomitantly, a variety of performance characteristics can be obtained, depending on the particular values of the related parameters. Moreover, under certain conditions, the reactor performance can be improved by controlled addition of ligand.List of Symbols
A
total concentration of ligand
-
C
1,i
concentration of Substrate-1 in the pores of stage i
-
C
2,i
concentration of Substrate-2 in its free form in the pores of stage i
-
2,i
concentration of the Substrate-2-Ligand Complex in the pores of stage i
-
total concentration of Substrate-2 in the pores of stage i
-
i
concentration of the Product-Ligand Complex in the pores of stage i
-
concentration of the free Product in the pores of stage i
-
total concentration of the Product in the pores of stage i
-
internal (pore) diffusion coefficient for the Substrate-Ligand Complex
-
D
1
internal (pore) diffusion coefficient of Substrate-1
-
D
2
internal (pore) diffusion coefficient of Substrate-2
-
effective (pore) diffusion coefficient for Substrate-2
-
internal (pore) diffusion coefficient for the Product
-
internal (pore) diffusion coefficient for the Product-Ligand Complex
-
effective (pore) diffusion coefficient for the Product
-
K
thermodynamic equilibrium constant for binding Substrate-2 to Ligand
-
K
m,1,K
m,2
Michaelis constants for Substrates-1 and 2, respectively
-
effective Michaelis constant for Substrate-2
-
K
p
thermodynamic equilibrium constant for binding the reaction Product to Ligand
-
effective equilibrium constant for binding Substrate-2 to Ligand
-
effective equilibrium constant for binding the reaction Product to Ligand.
-
K
b
inhibition constant
-
K
q
inhibition constant
-
effective inhibition constant
-
effective inhibition constant
-
k
a, k
d
association and dissociation rate constants for Substrate-2 — Ligand complex
-
association and dissociation constants for Product —Ligand complex
-
n
total number of elementary stages in the reactor
-
Q
volumetric flow rate throughout the reactor
-
R
j,i
reaction rate of Substrate-j in stage i, in terms of volumetric units
-
S
1,0
concentration of Substrate-1 in the reactor feed
-
total concentration of Substrate-2 in the reactor feed
-
S
1,i–1,S
1,i
concentration of Substrate-1 in the bulk phase leaving stages i–1 and i, respectively
-
S
2,i
concentration of Substrate-2 in its free form, in the bulk phase leaving stage i
-
2,i–1,
2,i
concentration of Substrate-2 in the bulk phase leaving stage i–1 and i, respectively
-
total concentration of Substrate-2 in the bulk phase leaving stages i–1 and i, respectively
-
i
concentration of the Product-Ligand Complex in the bulk phase of stage i
-
concentration of free Product in the bulk phase of stage i
-
total concentration of Product in the bulk phase of stage i
-
V
total volume of the reactor
-
V
m
maximal reaction rate in terms of volumetric units
-
y
axial coordinate of the pores
-
y
0
depth of the pores
Greek Symbols
1
dimensionless parameter
-
dimensionless parameter
-
dimensionless parameter
-
1
dimensionless parameter
-
dimensionless parameter
-
1,i
dimensionless concentration of Substrate-1 in pores of stage i
-
dimensionless total concentration of Substrate-2 (in both free and bound form) in pores of stage i
-
dimensionless total concentration of the reaction product in the pores of stage i
-
1
dimensionless parameter
-
dimensionless parameter
-
dimensionless parameter
-
dimensionless parameter
-
dimensionless parameter
-
dimensionless position along the pore
-
volumetric packing density of catalytic particles (dimensionless)
-
porosity of the catalytic particles (dimensionless)
-
1,i
dimensionless concentration of Substrate-1 in the bulk phase of stage i
-
dimensionless total concentration of Substrate-2 (in both free and bound form) in the bulk phase of stage i 相似文献
3.
D. L. Evans R. J. Rose 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1988,157(6):791-799
Summary Six Standardbred horses were used to evaluate the time course of pulmonary gas exchange, ventilation, heart rate (HR) and acid base balance during different intensities of constant-load treadmill exercise. Horses were exercised at approximately 50%, 75% and 100% maximum oxygen uptake (
max) for 5 min and measurements taken every 30 s throughout exercise. At all work rates, the minute ventilation, respiratory frequency and tidal volume reached steady state values by 60 s of exercise. At 100%
max, the oxygen consumption (
) increased to mean values of approximately 130 ml/kg·min, which represents a 40-fold increase above resting
. At the low and moderate work rates,
showed no significant change from 30 s to 300 s of exercise. At the high work rate, the mean
at 30 s was 80% of the value at 300 s. The HR showed no significant change over time at the moderate work rate but differing responses at the low and high work rates. At the low work rate, the mean HR decreased from 188 beats/min at 30 s to 172 beats/min at 300 s exercise, whereas at the high work rate the mean HR increased from 204 beats/min at 30 s to 221 beats/min at 300 s exercise. No changes in acid base status occurred during exercise at the low work rate. At the moderate work rate, a mild metabolic acidosis occurred which was nonprogressive with time, whereas the high work rate resulted in a progressive metabolic acidosis with a base deficit of 16 mmol/l by 300 s exercise. It is concluded that the kinetics of gas exchange during exercise are more rapid in the horse than in man, despite the relatively greater change in
in the horse when going from rest to high intensity exercise.Symbols and abbreviations E
minute ventilation
-
V
T
tidal volume
-
oxygen uptake
-
carbon dioxide output
-
oxygen pulse
-
ventilatory equivalent for oxygen
-
ventilatory equivalent for carbon dioxide
- R
respiratory exchange ratio
- HR
heart rate
- SBC
standard bicarbonate
- STPD
standard temperature and pressure dry
- BTPS
body temperature and pressure saturated
-
arterial oxygen content
-
arteriovenous oxygen content difference
- Rf
respiratory frequency 相似文献
4.
B. Grubb G. E. Folk Jr. 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1978,128(2):185-188
Summary The rate of oxygen consumption (
) by skeletal muscle was investigated in isolated perfused hindlimbs of laboratory rats and lemmings (Lemmus). In both species,
increased in proportion to blood flow rate, even at flow rates 4–5 times above resting level. The slope of the line relating
to skeletal muscle blood flow was significantly greater in the lemming than in the rat. This may be related to the inverse relationship between body weight and metabolic rate. These data support the hypothesis that in small animals a dependent relationship exists between blood flow and skeletal muscle
. 相似文献
5.
Veronique Billat Jean C. Renoux Jacques Pinoteau Bernard Petit Jean P. Koralsztein 《European journal of applied physiology and occupational physiology》1994,69(3):271-273
The aim of this study was to measure running times to exhaustion (Tlim) on a treadmill at 100% of the minimum velocity which elicits
max
max in 38 elite male long - distance runners
max = 71.4 ± 5.5 ml.kg–1.min–1 and
max = 21.8 ± 1.2 km.h–1). The lactate threshold (LT) was defined as a starting point of accelerated lactate accumulation around 4 mM and was expressed in
max. Tlim value was negatively correlated with
max (r = -0.362, p< 0.05) and
max (r = –0.347, p< 0.05) but positively with LT (%v
max) (r = 0.378, p < 0.05). These data demonstrate that running time to exhaustion at
max in a homogeneous group of elite male long-distance runners was inversely related to
max and experimentally illustrates the model of Monod and Scherrer regarding the time limit-velocity relationship adapted from local exercise for running by Hughson et al. (1984) . 相似文献
6.
Stephen C. Wood Kjell Johansen Mogens L. Glass G. M. O. Maloiy 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1978,127(4):331-336
Summary Oxygen consumption
was measured at rest and during spontaneous activity at body temperatures of 25 and 35°C in 14 fasting Savanna monitor lizards,Varanus exanthematicus ranging in weight from 172 to 7500 g. The allometric relationship between metabolic rate at 25°C and body weight (W) is given by:
(ml O2 STPD·g–1·hr–1)=0.88W
–0.43 (Fig. 2). Although statistical comparisons are equivocal, this intraspecific size dependence exceeds that reported for interspecific comparisons among reptiles and other vertebrate groups (Fig 3). A reproducible diurnal pattern of activity was observed in undisturbed animals with minimum values of
between 2400 and 0800 h (Fig. 1). Spontaneous activity and
generally reached peak values between 1200 and 2000 hrs. The average ratio of active aerobic metabolic rate (AMR) to minimum (standard) aerobic metabolic rate (SMR) was 8.2. This voluntary AMR/SMR inVaranus exceeds the AMR/SMR for most reptiles stimulated to exhaustion. The high aerobic capacity is consistent with other evidence for efficient exchange and transport of respiratory gases inV. exanthematicus; e.g., low or absent intracardiac shunt flow resulting in high arterial saturation and low ventilation
and perfusion
requirements. 相似文献
7.
Linkage analysis using multiple DNA polymorphic markers in normal families and in families with fragile X syndrome 总被引:4,自引:1,他引:3
S. N. Thibodeau H. R. Dorkins K. R. Faulk R. Berry A. C. M. Smith R. Hagerman A. King K. E. Davies 《Human genetics》1988,79(3):219-227
Summary Linkage data, using the polymorphic markers 52A (DXS51), F9, 4D-8(DXS98), and St14(DXS52), are presented from 14 fragile X pedigrees and from 7 normal pedigrees derived from the collection of the Centre d'Étude du Polymorphisme Humaine. A multipoint linkage analysis indicates that the most probable order of these four loci in normal families is DXS51-F9-DXS98-DXS52. Recombination frequencies (
) corresponding to maximum LOD scores (
) were obtained by two-point linkage analysis for a nuber of linkage groups, including: DXS51-F9 (
=5.94,
=0.03), F9-DXS98 (
=0.51,
=0.26), F9-DXS52 (
=0.84,
=0.27), and DXS98-DXS52 (
=0.32,
=0.20). A multipoint linkage analysis of these loci, including the fragile X locus, was also performed for the fragile X population and the data support the relative order (DSX51, F9, DXS98)-FRAXA-DXS52. Recombination frequencies and maximum LOD scores, which again were derived from two-point linkage analyses, were obtained for the linkage groups DXS51-F9 (
=9.96,
=0) and F9-DXS52 (
=0.07,
=0.45), as well as for the groups DXS51-FRAXA (
=2.42,
=0.15), F9-FRAXA (
=1.30,
=0.18), DXS98-FRAXA (
=0.05
=0.36), and DXS52-FRAXA (
=2.42
=0.15). The linkage data was further tested for the presence of genetic heterogeneity both within and between the fragile X and normal families for the intervals DXS51-F9, F9-DXS52, F9-FRAXA, and DXS52-FRAXA using a modification of the A test. Except for the interval F9-FRAXA (P<0.10) there was no evidence of genetic heterogeneity for each of the various linkage groups examined. The heterogeneity detected for the interval F9-FRAXA, however, was most likely due to one family (Fx-28) that displayed very tight linkage between these two loci. 相似文献
8.
Jacopo P. Mortola anna Noworaj 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1985,155(2):171-176
Summary The resting oxygen consumption
and breathing pattern of nine newborn and adult species (ranging in body size from mouse to human) have been compared on the basis of data collected from the literature. Minute ventilation
is similarly linked to
at both ages, the percent of
extracted as O2
about 2.2. Tidal volume/kg is an interspecies constant in newborns and adults, approximately 8 ml/kg. Breathing frequency decreases with the increase in size in a different way at the two ages: large species have newborns breathing at rates 2–3 times above the corresponding adults' values, while in the small species newborns and adults breathe at almost the same rate. Therefore the newborns of the smallest species have both
and
below the expected values, implying a greater inability to cope with the external demands than newborns of larger species. Several considerations indicate that in the smallest newborns the mechanical properties of the respiratory system could be a constraint to resting ventilations larger than observed. It is therefore possible that their low
is the cause, and not the effect, of the relatively small
. 相似文献
9.
Summary
D. melanogaster males of
bb/O genetic constitution undergoing rDNA magnification were mated singly to XXbb
+/O females, yielding
bb/O male progeny, and to XNO-w sn bb
+ fameles, yielding
bb/XNO- females. The male and female offspring were scored for the bb
+ phenotype.Results show that there is a higher percentage of bb
+ flies in the
bb/O male progeny than in
bb/XNO- females progeny, in single crosses as well as in the combined data. rRNA/DNA hybridization experiments agree with this observation, by showing that the rDNA content in the progeny of premagnified flies was higher in the sons than in the daughters.These data indicate that the increase of ribosomal RNA genes is not due to a stable event such as an unequal mitotic sister exchange, whereas they do not contrast with the extracopy model. 相似文献
10.
Summary Barley plants (Hordeum vulgare L.) grown from seed for 28 days in flowing solution culture were subjected to different root temperatures (3, 5, 7, 9, 11, 13, 17, 25°C) for 14 days with a common air temperature of 25/15°C (day/night). Uptake of NH4 and NO3 ions was monitored separately and continuously from solutions maintained at 10 M NH4NO3 and pH 6.0. Effects of root temperature on unit absorption rate
, flux
and inflow
were compared. After 5 days
,
and
increased with temperature over the range 3–11°C for NH4 ions and over the range 3–13°C for NO3 ions, with little change for either ion above these temperatures. Q10 temperature coefficients for NH4 ions (3–13°C) were 1.9, 1.7 and 1.6 for
,
and
respectively, the corresponding values for NO3 ions being 5.0, 4.5 and 4.6. For both ions,
,
and
changed with time as did their temperature dependence over the range 3–25°C, suggesting that rates of ontogenetic development and the extent of adaptation to temperature may have varied among treatments. 相似文献
11.
Jack P. Hayes 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1989,159(4):453-459
Summary I compared the maximal aerobic metabolic rates (
), field metabolic rates (FMR), aerobic reserves (
-FMR), and basal metabolic rates (BMR) of wild and recently captured deer mice from low (440 m) and high (3800 m) altitudes. To separate the effects of the thermal environment from other altitudinal effects, I examined mice from different altitudes, but similar thermal environments (i.e., summer mice from high altitude and winter mice from low altitude). When the thermal environment was similar,
, FMR, and aerobic reserve of low and high altitude mice did not differ, but BMR was significantly higher at high altitude. Thus, in the absence of thermal differences, altitude had only minor effects on the aerobic metabolism of wild or recently captured deer mice.At low altitude, there was significant seasonal variation in
, FMR, and aerobic reserve, but not BMR. BMR was correlated with
, but not with FMR. The significant positive correlation of BMR with
indicates a cost of high
, because higher BMR increases food requirements and energy use during periods of thermoneutral conditions.Abbreviations
BMR
basal metabolic rate
-
FMR
field metabolic rate
-
partial pressure of oxygen
-
T
a
ambient temperature
-
T
b
body temperature
-
T
e
operative temperature
-
maximal aerobic metabolic rate 相似文献
12.
Effects of ambient temperature and altitude on ventilation and gas exchange in deer mice (Peromyscus maniculatus) 总被引:2,自引:1,他引:1
Mark A. Chappell 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1985,155(6):751-758
Summary The effects of different ambient temperatures (T
a) on gas exchange and ventilation in deer mice (Peromyscus maniculatus) were determined after acclimation to low and high altitude (340 and 3,800 m).At both low and high altitude, oxygen consumption (
) decreased with increasingT
a atT
a from –10 to 30 °C. The
was 15–20% smaller at high altitude than at low altitude atT
a below 30 °C.Increased
atT
a below thermoneutrality was supported by increased minute volume (
) at both low and high altitude. At mostT
a, the change in
was primarily a function of changing respiration frequency (f); relatively little change occurred in tidal volume (V
T) or oxygen extraction efficiency (O2EE). AtT
a=0 °C and below at high altitude,
was constant due to decliningV
T and O2EE increased in order to maintain high
.At high altitude,
(BTP) was 30–40% higher at a givenT
a than at low altitude, except atT
a below 10 °C. The increased
at high altitude was due primarily to a proportional increase inf, which attained mean values of 450–500 breaths/min atT
a below 0 °C. The
(STP) was equivalent at high and low altitude atT
a of 10 °C and above. At lowerT
a,
(STPD) was larger at low altitude.At both altitudes, respiratory heat loss was a small fraction (<10%) of metabolic heat production, except at highT
a (20–30 °C).Abbreviations
EHL
evaporative heat loss
-
f
respiration frequency
-
HL
a
heat loss from warming tidal air
-
HL
e
evaporative heat loss in tidal air
-
HL
total respiratory heat loss
-
MHP
metabolic heat production
-
O
2
EE
oxygen extraction efficiency
-
RQ
respiratory quotient
-
T
a
ambient temperature
-
T
b
body temperatureT
lc lower critical temperature
-
carbon dioxide production
-
evaporative water loss
-
oxygen consumption
-
minute volume
-
V
T
tidal volume 相似文献
13.
V. Billat F. Dalmay M. T. Antonini A. P. Chassain 《European journal of applied physiology and occupational physiology》1994,69(3):196-202
The aim of this study was to estimate the characteristic exercise intensity
CL which produces the maximal steady state of blood lactate concentration (MLSS) from submaximal intensities of 20 min carried out on the same day and separated by 40 min. Ten fit male adults [maximal oxygen uptake
max 62 (SD 7) ml · min–1 · kg–1] exercisOed for two 30-min periods on a cycle ergometer at 67% (test 1.1) and 82% of
max (test 1.2) separated by 40 min. They exercised 4 days later for 30 min at 82% of
max without prior exercise (test 2). Blood lactate was collected for determination of lactic acid concentration every 5 min and heart rate and O2 uptake
were measured every 30 s. There were no significant differences at the 5th, 10th, 15th, 20th, 25th, or 30th min between
, lactacidaemia, and heart rate during tests 1.2 and 2. Moreover, we compared the exercise intensities
CL which produced the MLSS obtained during tests 1.1 and 1.2 or during tests 1.1 and 2 calculated from differential values of lactic acid blood concentration ([1a–]b) between the 30th and the 5th min or between the 20th and the 5th min. There was no significant difference between the different values of
CL [68 (SD 9), 71 (SD 7), 73 (SD 6),71 (SD 11) % of
max (ANOVA test,P<0.05). Four subjects ran for 60 min at their
CL determined from periods performed on the same day (test 1.1 and 1.2) and the difference between the [la–]b at 5 min and at 20 min ( ([la–]b)) was computed. The [la–]b remained constant during exercise and ranged from 2.2 to 6.7 mmol · l–1 [mean value equal to 3.9 (SD 1) mmol · l–1]. These data suggest that the
CL protocol did not overestimate the exercise intensity corresponding to the maximal fractional utilization of
max at MLSS. For half of the subjects the
CL was very close to the higher stage (82% of
max where an accumulation of lactate in the blood with time was observed. It can be hypothesized that
CL was very close to the real MLSS considering the level of accuracy of [la–]b measurement. This study showed that exercise at only two intensities, performed at 65% and 80% of
max and separated by 40 min of complete rest, can be used to determine the intensity yielding a steady state of [la–1]b near the real MLSS workload value. 相似文献
14.
Bovine adenohypophysial tissue was dissociated by sequential enzymatic incubation in a continuous flow system. Dispersed cells
separated into discrete fractions after centrifugation in isopycnic bovine serum albumin gradients. The dispersed and separated
cells were prepared for microscopic identification and differential counts by centrifugal cytology. Radioimmunoassays for
LH, FSH, TSH, and Prl were used to corroborate the differential counts and determine the homogeneity of the fractions. The
thyrotrophs banded at an average density (
) of 1.0417, the FSH-secretory cells at
, the LH-secretory cells at
, and the Prl-secretory cells at
. A 7–16 fold enrichment of different cell populations was possible. In bovine hypophyses each hormone appears to be formed
by specific cells: the average TSH concentrations of the thyrotrophs were 5.1 pg/cell and the average LH and FSH concentrations
were 4.7 and 4.9 pg/cell for LH-and FSH-secreting cells, respectively. The average Prl concentration was 4.9 pg/cell for Prl-secreting
cells. 相似文献
15.
Summary The complete sequence of the 5S rRNA from the bioluminescent bacterium,Beneckea harveyi has been determined to be p U G C U U G G C G
C C A U A G C G A
U U-G G A C C C A
C U G A (U) C U U C
A U U C C-G A A C
C A G A A G U G A
A C G A A U U A-G
G C C G A U G G U
G U G U G G G G C
U-C C C C A U G U
A G A G U A G G A
A U C G-C C A G G
U (U)OH.Two sites of sensitivity to ribonuclease T2 cleavage were identified; at A41 and either A54 or A55. Comparison with existing sequence information fromEscherichia coli andPhotobacterium phosphoreum clarifies the amount of diversity among the bioluminescent bacteria and provides further insight into their phylogenetic position. Sequence heterogeneities were encountered and the importance of these in interpreting 5S rRNA data is discussed. 相似文献
16.
Gregory K. Snyder Wesley W. Weathers 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1977,117(3):291-301
Summary Resting rates of O2 consumption
against
, exercise endurance times and
during recovery from vigorous exercise were measured inSceloporus occidentalis captured near sea level and inS. graciosus captured above 2850 m. Oxygen consumption against
was also measured inS. occidentalis captured above 2850 m. When
was recorded continuously, as ambient
was slowly reduced from 155 Torr, it became directly dependent upon ambient
between 110 and 120 Torr. The critical
for the high altitude lizards was lower than that for the lowland lizards, which enabled the former to maintain relatively higher
's when ambient
was reduced below 120 Torr. The high altitude lizards also had significantly greater endurance when stimulated to exercise at 1600 m (
130 Torr). Both the higher
under hypoxia and the greater endurance roughly parallel a significantly greater maximum
in the high altitude lizards. At a simulated altitude of 3600 m (
100 Torr), maximum
and rate of recovery of the O2 debt calculated from post active
were significantly reduced in the lowland but not the high altitude lizards. The effects of simulated altitude conditions on the lowland but not the mountaine animals indicate adaptations to altitude in these sceloporine lizards. We did not find any consistent relationship between organ/body weight ratios or hematocrit and our measures of
endurance or the altitude at which the lizards were captured. 相似文献
17.
18.
Body temperatures during rest and exercise in residents and sojourners in hot climate 总被引:1,自引:0,他引:1
J. Raynaud J. P. Martineaud O. P. Bhatnagar H. Vieillefond J. Durand 《International journal of biometeorology》1976,20(4):309-317
Rectal (Tre), mean skin temperature (
sk) and sweating rate (
) were measured in 4 residents of temperate climate under acute moderate heat exposure (designated EE in such an experimental situation), after 3 weeks in India (designated as EI) and in 8 Indian residents (designated as II) both at rest and during submaximal exercises at 2 different intensities. At rest, Tre is higher in EI (37.6°C) than in EE (36.8°C, P<0.01) and reaches 37.8°C in II. At the end of exercise, the increment in Tre seems to depend on work load only and to be independent of thermal environment; S follows a similar pattern in the 3 groups of subjects:
sk is altered neither by exercise nor acclimatization. Under chronic heat exposure compared to acute conditions: (1) identical
is achieved with higher Tre and similar
sk so that the linear relationships
vs Tre is shifted to the right. (2) the Tre —
sk difference is greater at rest and during exercise: hence, skin blood flow, calculated from heat balance equation diminishes. In hot climate, a rise in Tre seems to be an adaptive response which allows the body to reduce skin blood flow. 相似文献
19.
Lawrence A. Baker Dr. Wesley W. Weathers Fred N. White 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1972,80(3):312-323
Summary The influence of local temperature changes within the posterior portion of the body on dorsal aorta blood flow (
), femoral arterial pressure (P
a
), peripheral resistance (R), skin blood flow (
) and skeletal muscle blood flow (
) was examined in unanesthetized lizards (Iguana iguana andTubinambis nigropunctatus). In response to local heating of the hind legs and tail
and
increased,P
a
was generally unchanged,R decreased and
decreased or was unchanged (Fig. 2). It is suggested that the acquisition of heat may be favored by diverting the increase in
away from the muscle to the warmer skin. In response to cooling
and
decreased,P
a
was generally unchanged, R increased and
increased or was unchanged. Hence, during cooling the retention of heat may be favored by diverting blood away from the skin to the deeper muscle. The muscle-skin shunt is under sympathetic control since following blockade with phenoxybenzamine HCL (Dibenzyline) muscle blood flow changes in response to temperature were qualitatively similar to those of skin (Fig. 4). These changes in peripheral circulatory patterns are independent of changes in heart rate or deep body temperature.Baker and Weathers were predoctoral and postdoctoral trainees, respectively, under USPHS Grant HE-05696. This study was also supported by NSF Grant GB-8523 and Los Angeles County Heart Association Grant 437IG. 相似文献
20.
Takayoshi Yoshida Koji Yamamoto Masao Udo 《European journal of applied physiology and occupational physiology》1993,66(2):155-160
The purpose of the present study was to assess the relationship between the rapidity of increased gas exchange (i.e. oxygen uptake
) and increased cardiac output (
) during the transient phase following the onset of exercise. Five healthy male subjects performed multiple rest-exercise or light exercise (25 W)-exercise transitions on an electrically braked ergometer at exercise intensities of 50, 75, or 100 W for 6 min, respectively. Each transition was performed at least eight times for each load in random order. The
was obtained by a breath-by-breath method, and
was measured by an impedance method during normal breathing, using an ensemble average. On transitions from rest to exercise,
rapidly increased during phase I with time constants of 6.8–7.3 s. The
also showed a similar rapid increment with time constants of 6.0–6.8 s with an apparent increase in stroke volume (SV). In this phase I,
increased to about 29.7%–34.1% of the steady-state value and
increased to about 58.3%–87.0%. Thereafter, some 20 s after the onset of exercise a mono-exponential increase to steady-state occurred both in
and
with time constants of 26.7–32.3 and 23.7–34.4 s, respectively. The insignificant difference between
and
time constants in phase I and the abrupt increase in both
and SV at the onset of exercise from rest provided further evidence for a cardiodynamic contribution to
following the onset of exercise from rest. 相似文献