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1.
Carling D. Gerlinsky David A. S. Rosen Andrew W. Trites 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》2013,183(5):699-708
The diving capacity of marine mammals is typically defined by the aerobic dive limit (ADL) which, in lieu of direct measurements, can be calculated (cADL) from total body oxygen stores (TBO) and diving metabolic rate (DMR). To estimate cADL, we measured blood oxygen stores, and combined this with diving oxygen consumption rates (VO2) recorded from 4 trained Steller sea lions diving in the open ocean to depths of 10 or 40 m. We also examined the effect of diving exercise on O2 stores by comparing blood O2 stores of our diving animals to non-diving individuals at an aquarium. Mass-specific blood volume of the non-diving individuals was higher in the winter than in summer, but there was no overall difference in blood O2 stores between the diving and non-diving groups. Estimated TBO (35.9 ml O2 kg?1) was slightly lower than previously reported for Steller sea lions and other Otariids. Calculated ADL was 3.0 min (based on an average DMR of 2.24 L O2 min?1) and was significantly shorter than the average 4.4 min dives our study animals performed when making single long dives—but was similar to the times recorded during diving bouts (a series of 4 dives followed by a recovery period on the surface), as well as the dive times of wild animals. Our study is the first to estimate cADL based on direct measures of VO2 and blood oxygen stores for an Otariid and indicates they have a much shorter ADL than previously thought. 相似文献
2.
M. D. Baustian S. Q. Wang K. W. Beyenbach 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1997,167(1):61-70
Plasma and urine of toadfish (Opsanus tau) in sea water and 10% sea water were analyzed to assess responses of an aglomerular fish to hypoosmotic challenge. Following
transfer to 10% sea water, plasma osmotic pressure decreased slowly from 318 to 241 mmol · kg H2O−1, over a period of 10–15 days. Urine osmotic pressure decreased in parallel from 299 to 207 mmol · kg H2O−1, leaving urine/plasma ratios of osmotic pressure essentially unchanged. In contrast, the volume and composition of urine
changed rapidly following transfer to 10% sea water. Urine flow rate increased 110% from 3.0 to 6.3 μl · 100g−1 · h−1 and Na+ excretion increased 346%, while excretion of Mg2− and SO4
2− decreased 81% and 90%, respectively. Excretion rates for Cl− were low in seawater toadfish and decreased further in 10% sea water. An unknown sulfur-containing anion, present in the
urine of seawater toadfish, contributed significantly to the composition and ionic balance in urine of toadfish in 10% sea
water. These results suggest that the inability to produce strongly dilute urine obliges toadfish to lose salt in order to
excrete water, in hypoosmotic media. The decrease in plasma osmotic pressure may be both a strategy to reduce osmotic and
ionic gradients in dilute media and a consequence of the kidney's inability to excrete water without salt.
Accepted: 22 August 1996 相似文献
3.
C. J. Gore S. C. Little A. G. Hahn G. C. Scroop K. I. Norton P. C. Bourdon S. M. Woolford J. D. Buckley T. Stanef D. P. Campbell D. B. Watson D. L. Emonson 《European journal of applied physiology and occupational physiology》1997,75(2):136-143
This study examined the effect of mild hypobaria (MH) on the peak oxygen consumption (O2peak) and performance of ten trained male athletes [ (SEM); O2peak = 72.4 (2.2) ml · kg−1 · min−1] and ten trained female athletes [O2peak = 60.8 (2.1) ml · kg−1 · min−1]. Subjects performed 5-min maximal work tests on a cycle ergometer within a hypobaric chamber at both normobaria (N, 99.33
kPa) and at MH (92.66 kPa), using a counter-balanced design. MH was equivalent to 580 m altitude. O2peak at MH decreased significantly compared with N in both men [− 5.9 (0.9)%] and women [− 3.7 (1.0)%]. Performance (total kJ)
at MH was also reduced significantly in men [− 3.6 (0.8)%] and women [− 3.8 (1.2)%]. Arterial oxyhaemoglobin saturation (SaO2) at O2peak was significantly lower at MH compared with N in both men [90.1 (0.6)% versus 92.0 (0.6)%] and women [89.7 (3.1)% versus
92.1 (3.0)%]. While SaO2 at O2peak was not different between men and women, it was concluded that relative, rather than absolute, O2peak may be a more appropriate predictor of exercise-induced hypoxaemia. For men and women, it was calculated that 67–76% of the
decrease in O2peak could be accounted for by a decrease in O2 delivery, which indicates that reduced O2 tension at mild altitude (580 m) leads to impairment of exercise performance in a maximal work bout lasting ≈ 5 min.
Accepted: 30 July 1996 相似文献
4.
D. P. Heil T. R. Derrick S. Whittlesey 《European journal of applied physiology and occupational physiology》1997,75(2):160-165
This study was designed to determine how changes in oxygen uptake (O2) and heart rate (HR) during submaximal cycle ergometry were determined by changes in cycle geometry and/or lower-limb kinematics.
Fourteen trained cyclists [Mean (SD): age, 25.5 (6.4) years; body mass 74.4 (8.8) kg; peak O2, 4.76 (0.79) l. min−1 peak] were tested at three seat-tube angles (70°, 80°, 90°) at each of three trunk angles (10°, 20°, 30°) using a modified
Monark cycle ergometer. All conditions were tested at a power output corresponding to 95% of the O2 at each subject's ventilatory threshold while pedalling at 90 rpm and using aerodynamic handlebars. Sagittal-view kinematics
for the hip, knee, and ankle joints were also recorded for all conditions and for the subjects' preferred positioning on their
own bicycles. No combination of seat-tube and trunk angle could be considered optimal since many of the nine conditions elicited
statistically similar mean O2 and HR values. Mean hip angle (HA) was the only kinematic variable that changed consistently across conditions. A regression
relationship was not observed between mean O2 or HR and mean hip angle values (P > 0.45). Significant curvilinear relationships were observed, however, between ΔO2 (O2 − minimum O2) and ΔHA (mean HA − preferred HA) using the data from all subjects (R = 0.45, SEE = 0.13 l . min−1) and using group mean values (R = 0.93, SEE = 0.03 l . min−1). In both cases ΔO2 minimized at ΔHA = 0, which corresponded to the subjects' preferred HA from their own bicycles. Thus, subjects optimized
their O2 cost at cycle geometries that elicited similar lower-limb kinematics as the preferred geometries from their own bicycles.
Accepted: 3 July 1996 相似文献
5.
Gordon D. Hastie David A.S. Rosen 《Journal of experimental marine biology and ecology》2006,336(2):163-170
Diving animals must endeavor to increase their dive depths and prolong the time they spend exploiting resources at depth. Results from captive and wild studies suggest that many diving animals extend their foraging bouts by decreasing their metabolisms while submerged. We measured metabolic rates of Steller sea lions (Eumetopias jubatus) trained to dive to depth in the open ocean to investigate the relationships between diving behaviour and the energetic costs of diving. We also constructed a general linear model to predict the oxygen consumption of sea lions diving in the wild. The resultant model suggests that swimming distance and depth of dives significantly influence the oxygen consumption of diving Steller sea lions. The predictive power of the model was tested using a cross-validation approach, whereby models reconstructed using data from pairs of sea lions were found to accurately predict the oxygen consumption of the third diving animal. Predicted oxygen consumption during dives to depth ranged from 3.37 L min− 1 at 10 m, to 1.40 L min− 1 at 300 m over a standardized swimming distance of 600 m. This equated to an estimated metabolic rate of 97.54 and 40.52 MJ day− 1, and an estimated daily feeding requirement of 18.92 and 7.96 kg day− 1 for dives between 10 and 300 m, respectively. The model thereby provides information on the potential energetic consequences that alterations in foraging strategies due to changes in prey availability could have on wild populations of sea lions. 相似文献
6.
Carling D. Gerlinsky David A. S. Rosen Andrew W. Trites 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》2014,184(4):535-544
The diving ability of marine mammals is a function of how they use and store oxygen and the physiological control of ventilation, which is in turn dependent on the accumulation of CO2. To assess the influence of CO2 on physiological control of dive behaviour, we tested how increasing levels of inspired CO2 (hypercarbia) and decreasing inspired O2 (hypoxia) affected the diving metabolic rate, submergence times, and dive recovery times (time to replenish O2 stores and eliminate CO2) of freely diving Steller sea lions. We also measured changes in breathing frequency of diving and non-diving individuals. Our findings show that hypercarbia increased breathing frequency (as low as 2 % CO2), but did not affect metabolic rate, or the duration of dives or surface intervals (up to 3 % CO2). Changes in breathing rates indicated respiratory drive was altered by hypercarbia at rest, but blood CO2 levels remained below the threshold that would alter normal dive behaviour. It took the sea lions longer to remove accumulated CO2 than it did for them to replenish their O2 stores following dives (whether breathing ambient air, hypercarbia, or hypoxia). This difference between O2 and CO2 recovery times grew with increasing dive durations, increasing hypercarbia, and was greater for bout dives, suggesting there could be a build-up of CO2 load with repeated dives. Although we saw no evidence of CO2 limiting dive behaviour, the longer time required to remove CO2 may eventually exhibit control over the overall time they can spend in apnoea and overall foraging duration. 相似文献
7.
Daniel P. Costa Nicholas J. Gales Michael E. Goebel 《Comparative biochemistry and physiology. Part A, Molecular & integrative physiology》2001,129(4):771-783
Diving animals offer a unique opportunity to study the importance of physiological constraint in their everyday behaviors. An important component of the physiological capability of any diving animal is its aerobic dive limit (ADL). The ADL has only been measured in a few species. The goal of this study was to estimate the aerobic dive limit from measurements of body oxygen stores and at sea metabolism. This calculated ADL (cADL) was then compared to measurements of diving behavior of individual animals of three species of otariids, the Antarctic fur seal, Arctocephalus gazella, the Australian sea lion, Neophoca cinerea, and the New Zealand sea lion, Phocarctos hookeri. Antarctic fur seals dove well within the cADL. In contrast, many individuals of both sea lion species exceeded the cADL, some by significant amounts. Australian sea lions typically dove 1.4 times longer than the cADL, while New Zealand sea lions on average dove 1.5 times longer than the cADL. The tendency to exceed the cADL was correlated with the dive pattern of individual animals. In both Antarctic Fur Seals and Australian sea lions, deeper diving females made longer dives that approached or exceeded the cADL (P<0.01, r(2)=0.54). Australian and New Zealand sea lions with longer bottom times also exceeded the cADL to a greater degree. The two sea lions forage on the benthos while the fur seals feed shallow in the water column. It appears that benthic foraging requires these animals to reach or exceed their aerobic dive limit. 相似文献
8.
R. Turcotte L. Kiteala J. E. Marcotte H. Perrault 《European journal of applied physiology and occupational physiology》1997,75(5):425-430
The purpose of this investigation was to examine if exercise-induced arterial oxyhemoglobin desaturation selectively observed
in highly trained endurance athletes could be related to differences in the pulmonary diffusing capacity (D
L) measured during exercise. The D
L of 24 male endurance athletes was measured using a 3-s breath-hold carbon monoxide procedure (to give D
LCO) at rest as well as during cycling at 60% and 90% of these previously determined O2max. Oxyhemoglobin saturation (S
aO2%) was monitored throughout both exercise protocols using an Ohmeda Biox II oximeter. Exercise-induced oxyhemoglobin desaturation
(DS) (S
aO2% < 91% at O2max) was observed in 13 subjects [88.2 (0.6)%] but not in the other 11 nondesaturation subjects [NDS: 92.9 (0.4)%] (P ≤ 0.05), although O2max was not significantly different between the groups [DS: 4.34 (0.65) l / min vs NDS: 4.1 (0.49) l / min]. At rest, no differences
in either D
LCO [m1 CO · mmHg−1 · min−1: 41.7 (1.7) (DS) vs 41.1 (1.8) (NDS)], D
LCO /
A
[8.2 (0.4) (DS) vs 7.3 (0.9) (NDS)], MVV [l / min: 196.0 (10.4) (DS) vs 182.0 (9.9) (NDS)] or FEV1/FVC [86.3 (2.2) (DS) vs 82.9 (4.7) (NDS)] were found between groups (P ≥ 0.05). However,
E /O2 at O2max was lower in the DS group [33.0 (1.1)] compared to the NDS group [36.8 (1.5)] (P ≤ 0.05). Exercise D
LCO (m1 CO · mmHg−1 · min−1 ) was not different between groups at either 60% O2max [DS: 55.1 (1.4) vs NDS: 57.2 (2.1)] or at 90% O2max [DS: 61.0 (1.8) vs NDS: 61.4 (2.9)]. A significant relationship (r = 0.698) was calculated to occur between S
aO2% and
E /O2 during maximal exercise. The present findings indicate that the exercise-induced oxyhemoglobin desaturation seen during submaximal
and near-maximal exercise is not related to differences in D
L, although during maximal exercise S
aO2 may be limited by a relatively lower exercise ventilation.
Accepted: 25 September 1996 相似文献
9.
H. J. Bogaard H. H. Woltjer B. M. Dekker A. R. J. van Keimpema P. E. Postmus P. M. J. M. de Vries 《European journal of applied physiology and occupational physiology》1997,75(5):435-442
Whereas with advancing age, peak heart rate (HR) and cardiac index (CI) are clearly reduced, peak stroke index (SI) may decrease,
remain constant or even increase. The aim of this study was to describe the patterns of HR, SI, CI, arteriovenous difference
in oxygen concentration (C
a-vO2), mean arterial pressure (MAP), systemic vascular resistance index (SVRI), stroke work index (SWI) and mean systolic ejection
rate index (MSERI) in two age groups (A: 20–30 years, n = 20; B: 50–60 years n = 20. After determination of pulmonary function, an incremental bicycle exercise test was performed, with standard gas-exchange
measurements and SI assessment using electrical impedance cardiography. The following age-related changes were found: similar
submaximal HR response to exercise in both groups and a higher peak HR in A than in B[185 (SD 9) vs 167 (SD 14) beats · min−1, P < 0.0005]; increase in SI with exercise up to 60–90 W and subsequent stabilization in both groups. As SI decreased towards
the end of exercise in B, a higher peak SI was found in A [57.5 (SD 14.0) vs 43.6 (SD 7.7) ml · m−2, P < 0.0005]; similar submaximal CI response to exercise, higher peak CI in A [10.6 (SD 2.5) vs 7.2 (SD 1.3) l · min−1 · m−2, P < 0.0005]; no differences in C
a-vO2 during exercise; higher MAP at all levels of exercise in B; higher SVRI at all levels of exercise in B; lower SWI in B after
recovery; higher MSERI at all levels of exercise in A. The decrease in SI with advancing age would seem to be related to a
decrease in myocardial contractility, which can no longer be compensated for by an increase in preload (as during submaximal
exercise). Increases in systemic blood pressure may also compromise ventricular function but would seem to be of minor importance.
Accepted: 24 September 1996 相似文献
10.
Robert A. MacArthur 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1990,160(5):593-599
Summary The oxygen storage capacity and partitioning of body oxygen reserves were compared in summer-and winter-acclimatized muskrats (Ondatra zibethicus). Blood volume, blood oxygen capacity, and skeletal muscle myoglobin content were higher in December than in July (P<0.02). Total lung capacity increased only slightly in winter (P>0.05). The oxygen storage capacity of a diving muskrat was calculated at 25.2 ml O2 STPD · kg-1 in July, compared to 35.7 ml O2 STPD · kg-1 in December. Blood comprised the major storage compartment in both seasons, accounting for 57% and 65% of the total oxygen stores in summer and winter, respectively. Based on available oxygen stores and previous estimates of the cost of diving, the aerobic dive limit (ADL) increased from 40.9 s in July to 57.9 s in December. Concurrent behavioral studies suggested that most voluntary diving by muskrats is aerobic. However, the proportion of dives exceeding the calculated ADL of these animals was shown to vary with the context of the dive. Only 3.5% of all dives initiated by muskrats floating in the water exceeded their estimated ADL. Provision of a dry resting site and access to a submerged food source increased this proportion to 18–61%, depending on the underwater distance that foraging muskrats were required to swim. Serial dives exceeding the estimated ADL were not accompanied by extended postdive recovery periods.Abbreviations
ADL
acrobic dive limit
-
Hb
hemoglobin
-
Hct
hematocrit
-
Mb
myoglobin
-
PaO2
arterial O2 tension
-
STPD
standard temperature and pressure, dry 相似文献
11.
Jessica U. Meir Patrick W. Robinson L. Ignacio Vilchis Gerald L. Kooyman Daniel P. Costa Paul J. Ponganis 《PloS one》2013,8(12)
Although energetics is fundamental to animal ecology, traditional methods of determining metabolic rate are neither direct nor instantaneous. Recently, continuous blood oxygen (O2) measurements were used to assess energy expenditure in diving elephant seals (Mirounga angustirostris), demonstrating that an exceptional hypoxemic tolerance and exquisite management of blood O2 stores underlie the extraordinary diving capability of this consummate diver. As the detailed relationship of energy expenditure and dive behavior remains unknown, we integrated behavior, ecology, and physiology to characterize the costs of different types of dives of elephant seals. Elephant seal dive profiles were analyzed and O2 utilization was classified according to dive type (overall function of dive: transit, foraging, food processing/rest). This is the first account linking behavior at this level with in vivo blood O2 measurements in an animal freely diving at sea, allowing us to assess patterns of O2 utilization and energy expenditure between various behaviors and activities in an animal in the wild. In routine dives of elephant seals, the blood O2 store was significantly depleted to a similar range irrespective of dive function, suggesting that all dive types have equal costs in terms of blood O2 depletion. Here, we present the first physiological evidence that all dive types have similarly high blood O2 demands, supporting an energy balance strategy achieved by devoting one major task to a given dive, thereby separating dive functions into distinct dive types. This strategy may optimize O2 store utilization and recovery, consequently maximizing time underwater and allowing these animals to take full advantage of their underwater resources. This approach may be important to optimizing energy expenditure throughout a dive bout or at-sea foraging trip and is well suited to the lifestyle of an elephant seal, which spends > 90% of its time at sea submerged making diving its most “natural” state. 相似文献
12.
C. Schirlo A. Bub C. Reize A. Bührer J. Kohl E. A. Koller 《European journal of applied physiology and occupational physiology》1997,75(2):124-131
To investigate the role of fluid shifts during the short-term adjustment to acute hypobaric hypoxia (AHH), the changes in
lower limb (LV) and forearm volumes (FV) were measured using a strain-gauge plethysmograph technique in ten healthy volunteers
exposed to different altitudes (450 m, 2500 m, 3500 m, 4500 m) in a hypobaric chamber. Arterial blood pressure, heart rate,
arterial oxygen saturation (S
aO2), endtidal gases, minute ventilation and urine flow were also determined. A control experiment was performed with an analogous
protocol under normobaric normoxic conditions. The results showed mean decreases both in LV and FV of −0.52 (SD 0.39) ml · 100
ml−1 and −0.65 (SD 0.32) ml · 100 ml−1, respectively, in the hypoxia experiments [controls: LV −0.28 (SD 0.37), FV −0.41 (SD 0.47) ml · 100 ml−1]. Descent to normoxia resulted in further small but not significant decreases in mean LV [−0.02 (SD 0.11) ml · 100 ml−1], whereas mean FV tended to increase slightly [ + 0.02 (SD 0.14) ml · 100 ml−1]; in the control experiments mean LV and FV decreased continuously during the corresponding times [−0.19 (SD 0.31), −0.18
(SD 0.10) ml · 100 ml−1, respectively]. During the whole AHH, mean urine flow increased significantly from 0.84 (SD 0.41) ml · min−1 to 3.29 (SD 1.43) ml · min−1 in contrast to the control conditions. We concluded that peripheral fluid volume shifts form a part of the hypoxia-induced
acute cardiovascular changes at high altitude. In contrast to the often reported formation of peripheral oedema after prolonged
exposure to hypobaric hypoxia, the results provided no evidence for the development of peripheral oedema during acute induction
to high altitude. However, the marked increase in interindividual variance in S
aO2 and urine flow points to the appearance of the first differences in the short-term adjustment even after 2 h of acute hypobaric
hypoxia.
Accepted: 27 August 1996 相似文献
13.
J. M. Burns M. A. Castellini 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1996,166(8):473-483
The aerobic dive limit, as defined by an increase in plasma lactate levels following dives, has to date only been determined
in adult and juvenile Weddell seals (Leptonychotes weddellii). However, theoretical aerobic dive limits based on calculated total body oxygen stores, estimated metabolic rates, and dive
duration frequencies have been published for several species. Using data collected over the past 3 years in McMurdo Sound.
Antarctica, the aerobic dive limit of Weddell seal pups was determined by both the physiological and modeling methods. Time-depth
diving recorders deployed on 36 pups between 2 and 14 weeks of age allowed the aerobic dive limit to be predicted from duration-frequency
histograms. The aerobic dive limit was also calculated from estimates of total body oxygen stores and predicted diving metabolic
rates. Finally, these two estimates were compared with aerobic dive limits determined from post-dive lactate levels in three
pups between 5 and 7 weeks old. The aerobic dive limits of pups increased with age, but pup aerobic dive limits were still
significantly shorter than those of yearlings and adults. In addition, the aerobic dive limits determined by the three methods
were not equivalent for pups, yearlings, or adults, and indicate that care should be taken when modeling methods are used
to estimate the aerobic dive limit in other species. Changes in hematocrit, plasma glucose, and plasma lactate levels during
and between rest, diving, and recovery in pups were compared to known values for juveniles and adults. Plasma metabolite levels
were more highly regulated in older pups, and together with the increasing aerobic dive limit, suggest that Weddell seal pups
are not refined divers until after they are weaned, and that their diving ability continues to develop over several years. 相似文献
14.
Davis RW Polasek L Watson R Fuson A Williams TM Kanatous SB 《Comparative biochemistry and physiology. Part A, Molecular & integrative physiology》2004,138(3):263-268
When aquatic reptiles, birds and mammals submerge, they typically exhibit a dive response in which breathing ceases, heart rate slows, and blood flow to peripheral tissues is reduced. The profound dive response that occurs during forced submergence sequesters blood oxygen for the brain and heart while allowing peripheral tissues to become anaerobic, thus protecting the animal from immediate asphyxiation. However, the decrease in peripheral blood flow is in direct conflict with the exercise response necessary for supporting muscle metabolism during submerged swimming. In free diving animals, a dive response still occurs, but it is less intense than during forced submergence, and whole-body metabolism remains aerobic. If blood oxygen is not sequestered for brain and heart metabolism during normal diving, then what is the purpose of the dive response? Here, we show that its primary role may be to regulate the degree of hypoxia in skeletal muscle so that blood and muscle oxygen stores can be efficiently used. Paradoxically, the muscles of diving vertebrates must become hypoxic to maximize aerobic dive duration. At the same time, morphological and enzymatic adaptations enhance intracellular oxygen diffusion at low partial pressures of oxygen. Optimizing the use of blood and muscle oxygen stores allows aquatic, air-breathing vertebrates to exercise for prolonged periods while holding their breath. 相似文献
15.
Richmond JP Burns JM Rea LD 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》2006,176(6):535-545
Two key factors influence the diving and hence foraging ability of marine mammals: increased oxygen stores prolong aerobic metabolism and decreased metabolism slows rate of fuel consumption. In young animals, foraging ability may be physiologically limited due to low total body oxygen stores and high mass specific metabolic rates. To examine the development of dive physiology in Steller sea lions, total body oxygen stores were measured in animals from 1 to 29 months of age and used to estimate aerobic dive limit (ADL). Blood oxygen stores were determined by measuring hematocrit, hemoglobin, and plasma volume, while muscle oxygen stores were determined by measuring myoglobin concentration and total muscle mass. Around 2 years of age, juveniles attained mass specific total body oxygen stores that were similar to those of adult females; however, their estimated ADL remained less than that of adults, most likely due to their smaller size and higher mass specific metabolic rates. These findings indicate that juvenile Steller sea lion oxygen stores remain immature for more than a year, and therefore may constrain dive behavior during the transition to nutritional independence. 相似文献
16.
A. D. Taylor R. Bronks P. Smith B. Humphries 《European journal of applied physiology and occupational physiology》1997,75(2):151-159
Integrated electromyography (iEMG) of the m. vastus lateralis was analysed during cycle ergometry in male subjects (n = 8). Two work trials were conducted, one under normoxia (N), the other under environmental normobaric hypoxia (EH in which
the oxygen fraction in inspired gas = 0.116), each trial lasting 10 min. The absolute power output (180 W) was the same for
both trials and was equivalent to 77 (4)% of maximum heart rate in trial N. Maximal voluntary isometric contractions were
performed after each trial to assess changes in force, muscle fibre conduction velocity (MFCV), electromechanical delay (EMD),
median frequency of EMG (MF) and maximal iEMG (iEMGmax). Biopy samples of muscle were obtained from the m. vastus medialis before testing. Myosin heavy chain (MHC) differences
were determined through sodium dodecyl-polyacrylamide gel electrophoresis followed by densitometric analysis. No differences
in submaximal iEMG were observed between EH and N trials during the first minute of work. At the end of both work trials iEMG
was significantly elevated compared with starting values, however the iEMG recorded in EH exceeded N values by 15%. At the
end of the EH trials the following were observed: a decrease in isometric force, MFCV and MF with an increase in EMD and the
iEMGmax/force ratio. The iEMGmax was unchanged. No differences in any of these variables were observed after the N trial. Mean (SD) lactate concentrations
following EH and N trials were 9.2 (4.4) mmol · 1−1 and 3.5 (1.1) mmol · 1−1, respectively. Results indicate that an increased motor unit recruitment and rate coding was needed in EH to maintain the
required power output. The increased motor unit recruitment and rate coding were associated with myoelectric evidence of “peripheral”
muscle fatigue. Subjects with higher compositions of type II MHC accumulated more lactate and displayed greater reductions
in MF and MFCV during fatigue.
Accepted: 16 June 1996 相似文献
17.
T. J. Vasankari U. M. Kujala H. Rusko S. Sarna M. Ahotupa 《European journal of applied physiology and occupational physiology》1997,75(5):396-399
We investigated the effect of training and racing at moderate altitude (MA) on oxidative stress by assessment of serum diene
conjugation (DC) and serum antioxidant potential (TRAP). Nine male top level skiers were studied during a national race (20–30
km) at sea level (SL). Thereafter, the athletes trained for 2 weeks at MA, after which they participated in a 20–30 km race
at MA. Venous blood samples were taken before and after the race. The DC, indicating early events of lipid peroxi dation,
did not change during the race at SL (16 850 vs 15 900 ΔAbsorbance · l−1) or at MA (19 870 vs. 20 630 ΔAbs · l−1). At MA serum DC was higher than at SL both before (25%) and after (30%) the race, the postrace difference being statistically
significant (P < 0.05). The TRAP increased during the race at MA (from 1387 to 1943 μmol · 1−1, P = 0.016), but not at SL (1713 vs 1582 μmol · l−1). These observations would suggest that the level of oxidative stress might be greater during living, training and racing
at MA (higher DC levels). Increased TRAP during the race at MA may indicate that the physiological adaptation to extreme acute
oxidative stress was altered. The physiological significance of this observation remains to be investigated.
Accepted: 18 October 1996 相似文献
18.
Interseasonal comparison of CO2 concentrations, isotopic composition, and carbon dynamics in an Amazonian rainforest (French Guiana) 总被引:2,自引:0,他引:2
Canopy CO2 concentrations in a tropical rainforest in French Guiana were measured continuously for 5 days during the 1994 dry season
and the 1995 wet season. Carbon dioxide concentrations ([CO2]) throughout the canopy (0.02–38 m) showed a distinct daily pattern, were well-stratified and decreased with increasing height
into the canopy. During both seasons, daytime [CO2] in the upper and middle canopy decreased on average 7–10 μmol mol−1 below tropospheric baseline values measured at Barbados. Within the main part of the canopy (≥ 0.7 m), [CO2] did not differ between the wet and dry seasons. In contrast, [CO2] below 0.7 m were generally higher during the dry season, resulting in larger [CO2] gradients. Supporting this observation, soil CO2 efflux was on average higher during the dry season than during the wet season, either due to diffusive limitations and/or
to oxygen deficiency of root and microbial respiration. Soil respiration rates decreased by 40% after strong rain events,
resulting in a rapid decrease in canopy [CO2] immediately above the forest floor of about 50␣μmol mol−1. Temporal and spatial variations in [CO2]canopy were reflected in changes of δ13Ccanopy and δ18Ocanopy values. Tight relationships were observed between δ13C and δ18O of canopy CO2 during both seasons (r
2 > 0.86). The most depleted δ13Ccanopy and δ18Ocanopy values were measured immediately above the forest floor (δ13C = −16.4‰; δ18O = 39.1‰ SMOW). Gradients in the isotope ratios of CO2 between the top of the canopy and the forest floor ranged between 2.0‰ and 6.3‰ for δ13C, and between 1.0‰ and 3.5‰ for δ18O. The δ13Cleaf and calculated c
i/c
a of foliage at three different positions were similar for the dry and wet seasons indicating that the canopy maintained a
constant ratio of photosynthesis to stomatal conductance. About 20% of the differences in δ13Cleaf within the canopy was accounted for by source air effects, the remaining 80% must be due to changes in c
i/c
a. Plotting 1/[CO2] vs. the corresponding δ13C ratios resulted in very tight, linear relationships (r
2 = 0.99), with no significant differences between the two seasons, suggesting negligible seasonal variability in turbulent
mixing relative to ecosystem gas exchange. The intercepts of these relationships that should be indicative of the δ13C of respired sources were close to the measured δ13C of soil respired CO2 and to the δ13C of litter and soil organic matter. Estimates of carbon isotope discrimination of the entire ecosystem, Δe, were calculated as 20.3‰ during the dry season and as 20.5‰ during the wet season.
Received: 3 March 1996 / Accepted: 19 October 1996 相似文献
19.
Accurate estimates of diving metabolic rate are central to assessing the energy needs of marine mammals. To circumvent some of the limitations inherent with conducting energy studies in both the wild and captivity, we measured diving oxygen consumption of two trained Steller sea lions ( Eumetopias jubatus ) in the open ocean. The animals dived to predetermined depths (5–30 m) for controlled periods of time (50–200 s). Rates of oxygen consumption were measured using open-circuit respirometry before and after each dive. Mean resting rates of oxygen consumption prior to the dives were 1.34 (±0.18) and 1.95 (±0.19) liter/min for individual sea lions. Mean rates of oxygen consumption during the dives were 0.71 (±0.24) and 1.10 (±0.39) liter/min, respectively. Overall, rates of oxygen consumption during dives were significantly lower (45% and 41%) than the corresponding rates measured before dives. These results provide the first estimates of diving oxygen consumption rate for Steller sea lions and show that this species can exhibit a marked decrease in oxygen consumption relative to surface rates while submerged. This has important consequences in the evaluation of physiological limitations associated with diving such as dive duration and subsequent interpretations of diving behavior in the wild. 相似文献
20.
Theodore J. Angelopoulos Robert J. Robertson F. L. Goss Allan Utter 《European journal of applied physiology and occupational physiology》1997,75(2):132-135
Eight fit men [maximum oxygen consumption (O2max) 64.6 (1.9) ml · kg−1 · min−1, aged 28.3 (1.7) years (SE in parentheses) were studied during two treadmill exercise trials to determine the effect of endogenous
opioids on insulin and glucagon immunoreactivity during intense exercise (80% O2max). A double-blind experimental design was used with subjects undertaking the two exercise trials in counterbalanced order.
Exercise trials were 20 min in duration and were conducted 7 days apart. One exercise trial was undertaken following administration
of naloxone (N; 1.2 mg; 3 ml) and the other after receiving a placebo (P; 0.9% NaCl saline; 3 ml). Prior to each experimental
trial a flexible catheter was placed into an antecubital vein and baseline blood samples were collected. Immediately after,
each subject received either a N or P bolus injection. Blood samples were also collected after 20 min of continuous exercise
(running). Glucagon was higher (P < 0.05), while insulin was lower (P < 0.05), during exercise compared with pre-exercise values in both trials. However, glucagon was higher (P < 0.05) in the P than in the N exercise trial [141.4 (8.3) ng · l−1 vs 127.2 (7.6) ng · l−1]. There were no differences in insulin during exercise between the P and N trials [50.2 (4.3) pmol · l−1 vs 43.8 (5) pmol · l−1]. These data suggest that endogenous opioids may augment the glucagon response during intense exercise.
Accepted: 15 June 1996 相似文献