Human temperature regulation during narcosis induced by inhalation of 30% nitrous oxide

1992 ◽  
Vol 73 (6) ◽  
pp. 2246-2254 ◽  
Author(s):  
I. B. Mekjavic ◽  
C. J. Sundberg
Keyword(s):  
Nitrous Oxide ◽  
Temperature Regulation ◽  
Recovery Period ◽  
Cycle Ergometer ◽  
Work Rate ◽  
O2 Uptake ◽  
The Core ◽  
Maximum Work ◽  
Male Subjects ◽  
Shivering Thermogenesis

The study investigated the effect of inhalation of 30% nitrous oxide (N2O) on temperature regulation in humans. Seven male subjects were immersed to the neck in 28 degrees C water on two separate occasions. They exercised at a rate equivalent to 50% of their maximum work rate on an underwater cycle ergometer for 20 min and remained immersed for an additional 100 min after the exercise. In one trial (AIR) the subjects inspired compressed air, and in the other trial (N2O) they inspired a gas mixture containing N2O (20.93% O2–30% N2O-49.07% N2). Sweating, measured at the forehead, and shivering thermogenesis, as reflected by O2 uptake, were monitored throughout the 100-min recovery period. The threshold core temperatures at which sweating was extinguished and shivering was initiated were established relative to resting preexercise levels. Neither the magnitude of the sweating response nor the core threshold at which it was extinguished was significantly affected by the inhalation of N2O. In contrast, shivering thermogenesis was both significantly reduced during the N2O condition and initiated at significantly lower core temperatures [change in esophageal temperature (delta T(es)) = -0.98 +/- 0.33 degrees C and change in rectal temperature (delta T(re)) = -1.26 degrees C] during the N2O than during the AIR condition (delta T(es) = -0.36 +/- 0.31 degrees C and delta T(re) = -0.44 +/- 0.22 degrees C).(ABSTRACT TRUNCATED AT 250 WORDS)

Core temperature "null zone"

1991 ◽  
Vol 71 (4) ◽  
pp. 1289-1295 ◽  
Author(s):  
I. B. Mekjavic ◽  
C. J. Sundberg ◽  
D. Linnarsson
Keyword(s):  
Core Temperature ◽  
Recovery Period ◽  
Rest Period ◽  
Cycle Ergometer ◽  
Work Rate ◽  
The Core ◽  
Maximum Work ◽  
Male Subjects ◽  
Shivering Thermogenesis ◽  
Peak Value

An experimental protocol was designed to investigate whether human core temperature is regulated at a “set point” or whether there is a neutral zone between the core thresholds for shivering thermogenesis and sweating. Nine male subjects exercised on an underwater cycle ergometer at a work rate equivalent to 50% of their maximum work rate. Throughout an initial 2-min rest period, the 20-min exercise protocol, and the 100-min recovery period, subjects remained immersed to the chin in water maintained at 28 degrees C. On completion of the exercise, the rate of forehead sweating (Esw) decayed from a mean peak value of 7.7 +/- 4.2 (SD) to 0.6 +/- 0.3 g.m-2.min-1, which corresponds to the rate of passive transpiration, at core temperatures of 37.42 +/- 0.29 and 37.39 +/- 0.48 degrees C, as measured in the esophagus (Tes) and rectum (Tre), respectively. Oxygen uptake (VO2) decreased rapidly from an exercising level of 2.11 +/- 0.25 to 0.46 +/- 0.09 l/min within 4 min of the recovery period. Thereafter, VO2 remained stable for approximately 20 min, eventually increased with progressive cooling of the core region, and was elevated above the median resting values determined between 15 and 20 min at Tes = 36.84 +/- 0.38 degrees C and Tre = 36.80 +/- 0.39 degrees C. These results indicate that the core temperatures at which sweating ceases and shivering commences are significantly different (P less than 0.001) regardless of whether core temperature is measured within the esophagus or rectum.(ABSTRACT TRUNCATED AT 250 WORDS)

Lactate accumulation during incremental exercise with varied inspired oxygen fractions

1983 ◽  
Vol 55 (4) ◽  
pp. 1134-1140 ◽  
Author(s):  
M. C. Hogan ◽  
R. H. Cox ◽  
H. G. Welch
Keyword(s):  
Cycle Ergometer ◽  
Work Rate ◽  
O2 Uptake ◽  
Lactate Accumulation ◽  
Oxygen Fraction ◽  
Co2 Output ◽  
Break Points ◽  
Expired Gas ◽  
Gas Fractions ◽  
Inspired Oxygen

Six subjects pedaled a stationary cycle ergometer to exhaustion on three separate occasions while breathing gas mixtures of 17, 21, or 60% O2 in N2. Each subject rode for 3 min at work rates of 60, 90, 105 W, followed by 15-W increases every 3 min until exhaustion. Inspired and expired gas fractions, ventilation (V), heart rate, and blood lactate were measured. O2 uptake (VO2) and CO2 output (VCO2) were calculated for the last minute of each work rate; blood samples were drawn during the last 5 s. “Break points” for lactate, V, VCO2, V/VO2, and expired oxygen fraction (FEO2) were mathematically determined. VO2 was not significantly different at any work rate among the three different conditions. Nor did maximal VO2 differ significantly among the three treatments (P greater than 0.05). Lactate concentrations were significantly lower during hyperoxia and significantly higher during hypoxia compared with normoxia. Lactate values at exhaustion were not significantly different among the three treatments. Four subjects were able to work for a longer period of time during hyperoxic breathing. The variations in lactate accumulation as reported in this study cannot be explained on the basis of differences in VO2. The results of this research lend support to the hypothesis that differences in the performance of subjects breathing altered fractions of inspired oxygen may be caused by differences in lactate (or H+) accumulation.

Effect of duration of exercise on excess postexercise O2 consumption

1987 ◽  
Vol 62 (2) ◽  
pp. 485-490 ◽  
Author(s):  
R. Bahr ◽  
I. Ingnes ◽  
O. Vaage ◽  
O. M. Sejersted ◽  
E. A. Newsholme
Keyword(s):  
Rectal Temperature ◽  
Time Course ◽  
Control Experiment ◽  
Respiratory Exchange Ratio ◽  
Exercise Duration ◽  
Cycle Ergometer ◽  
O2 Consumption ◽  
Work Intensity ◽  
O2 Uptake ◽  
Male Subjects

This study was undertaken to determine the effect of exercise duration on the time course and magnitude of excess postexercise O2 consumption (EPOC). Six healthy male subjects exercised on separate days for 80, 40, and 20 min at 70% of maximal O2 consumption on a cycle ergometer. A control experiment without exercise was performed. O2 uptake, respiratory exchange ratio (R), and rectal temperature were monitored while the subjects rested in bed 24 h postexercise. An increase in O2 uptake lasting 12 h was observed for all exercise durations, but no increase was seen after 24 h. The magnitude of 12-h EPOC was proportional to exercise duration and equaled 14.4 +/- 1.2, 6.8 +/- 1.7, and 5.1 +/- 1.2% after 80, 40, and 20 min of exercise, respectively. On the average, 12-h EPOC equaled 15.2 +/- 2.0% of total exercise O2 consumption (EOC). There was no difference in EPOC:EOC for different exercise durations. A linear decrease with exercise duration was observed in R between 2 and 24 h postexercise. No change was observed in recovery rectal temperature. It is concluded that EPOC increases linearly with exercise duration at a work intensity of 70% of maximal O2 consumption.

Responses of sweating and body temperature to sinusoidal exercise

1994 ◽  
Vol 76 (6) ◽  
pp. 2541-2545 ◽  
Author(s):  
F. Yamazaki ◽  
R. Sone ◽  
H. Ikegami
Keyword(s):  
Sensory Stimulation ◽  
Constant Load ◽  
Cycle Ergometer ◽  
Healthy Male ◽  
O2 Uptake ◽  
Amplitude Response ◽  
Short Period ◽  
Sinusoidal Load ◽  
Sinusoidal Pattern ◽  
Male Subjects

This study determined the phase response and amplitude response (delta) of esophageal temperature (T(es)), mean skin temperature (Tsk), and forearm sweating rate (Msw) to sinusoidal work. Six healthy male subjects exercised on a cycle ergometer with a constant load (approximately 35% maximal O2 uptake) for a 30-min period; for the next 40 min they exercised with a sinusoidal load at 25 degrees C at 35% relative humidity. The sinusoidal load varied between approximately 10 and 60% maximal O2 uptake, and three different time periods (1.3, 4, and 8 min) were selected. Each subject performed three experiments that differed only in the timing of sinusoidal work. During the 4- and 8-min periods, T(es), Tsk, and Msw changed almost sinusoidally. The phase of Msw change significantly preceded those of T(es) and Tsk changes (P < 0.05). During the 1.3-min period, the level of T(es) and Tsk remained almost constant (delta T(es) 0.01 +/- 0.00 degrees C, delta Tsk 0.03 +/- 0.01 degrees C), whereas Msw showed a clear sinusoidal pattern. We conclude that the sweating response during sinusoidal work depends on both thermal and nonthermal factors, the latter being emotional, mental, or sensory stimulation. The contribution of the nonthermal factors to the general sweating response during exercise can be separated from that of the thermal factors by using sinusoidal work during a short period (e.g., 1.3 min).

Muscular efficiency during steady-rate exercise: effects of speed and work rate

1975 ◽  
Vol 38 (6) ◽  
pp. 1132-1139 ◽  
Author(s):  
G. A. Gaesser ◽  
G. A. Brooks
Keyword(s):  
Coupling Efficiency ◽  
Cycle Ergometer ◽  
Work Rate ◽  
Base Line ◽  
Exponential Relationship ◽  
Steady Rate ◽  
Resting Metabolism ◽  
Traditional Mode ◽  
Delta G ◽  
Male Subjects

In a comparison of traditional and theoretical exercise efficiency calculations male subjects were studied during steady-rate cycle ergometer exercises of “0,” 200, 400, 600, and 800 kgm/min while pedaling at 40, 60, 80, and 100 rpm. Gross (no base-line correction), net (resting metabolism as base-line correction), work (unloading cycling as base-line correction), and delta (measurable work rate as base-line correction) efficiencies were computed. The result that gross (range 7.5–20.4%) and net (9.8–24.1%) efficiencies increased with increments in work rate was considered to be an artifact of calculation. A LINEAR OR SLIGHTLY EXPONENTIAL RELATIONSHIP BETWEEN CALORIC OUTPUT AND WORK RATE DICTATES EITHER CONSTANT OR DECREASING EFFICIENCY WITH INCREMENTS IN WORK. The delta efficiency (24.4–34.0%) definition produced this result. Due to the difficulty in obtaining 0 work equivalents, the work efficiency definition proved difficult to apply. All definitions yielded the result of decreasing efficiency with increments in speed. Since the theoretical-thermodynamic computation (assuming mitochondrial P/O = 3.0 and delta G = -11.0 kcal/mol for ATP) holds only for CHO, the traditional mode of computation (based upon VO2 and R) was judged to be superior since R less than 1.0. Assuming a constant phosphorylative-coupling efficiency of 60%, the mechanical contraction-coupling efficiency appears to vary between 41 and 57%.

Exercise hyperpnea and hyperthermia in humans

1996 ◽  
Vol 81 (3) ◽  
pp. 1249-1254 ◽  
Author(s):  
M. D. White ◽  
M. Cabanac
Keyword(s):  
Work Capacity ◽  
Cycle Ergometer ◽  
Work Rate ◽  
Brain Cooling ◽  
Supportive Evidence ◽  
Climatic Chamber ◽  
Selective Brain Cooling ◽  
Temperature Thresholds ◽  
Exercise Hyperpnea ◽  
Male Subjects

The problem of the relative hyperpnea occurring at high levels of exercise remains unresolved. This study examined whether the hyperpnea observed in humans during exercise at approximately 70% of maximal work capacity was related to cranial (tympanic) and thoracic (esophageal) temperatures. Six trained male subjects pedaled at approximately 60 revolutions/min on an electrically braked cycle ergometer in a climatic chamber at 25 degrees C and approximately 35% relative humidity in two sessions. The subjects pedaled until exhaustion in two sessions. In one session work rate was increased by 40 W every 2 min and in the other session by 20 W every 2 min. In both exercise sessions, core temperature thresholds for ventilation were evident and subsequently tympanic and esophageal temperatures diverged. This suggested that the hyperpnea in humans observed after approximately 70% of an individual's maximal work rate was determined, in part, by core temperatures and revealed supportive evidence for selective brain cooling in humans.

Slow component of O2 uptake during heavy exercise: adaptation to endurance training

1995 ◽  
Vol 79 (3) ◽  
pp. 838-845 ◽  
Author(s):  
C. J. Womack ◽  
S. E. Davis ◽  
J. L. Blumer ◽  
E. Barrett ◽  
A. L. Weltman ◽  
...  
Keyword(s):  
Heart Rate ◽  
Power Output ◽  
Slow Component ◽  
Exercise Bout ◽  
Cycle Ergometer ◽  
O2 Uptake ◽  
Heavy Exercise ◽  
Absolute Power ◽  
Exercise Adaptation ◽  
Male Subjects

Seven untrained male subjects [age 25.6 +/- 1.5 (SE) yr, peak O2 uptake (VO2) 3.20 +/- 0.19 l/min] trained on a cycle ergometer 4 days/wk for 6 wk, with the absolute training workload held constant for the duration of training. Before and at the end of each week of training, the subjects performed 20 min of constant-power exercise at a power designed to elicit a pronounced slow component of VO2 (end-exercise VO2-VO2 at minute 3 of exercise) in the pretraining session. An additional 20-min exercise bout was performed after training at this same absolute power output during which epinephrine (Epi) was infused at a rate of 100 ng.kg-1.min-1 between minutes 10 and 20. After 2 wk of training, significant decreases in VO2 slow component, end-exercise VO2, blood lactate ([La-] and glucose concentrations, plasma Epi ([Epi]) and norepinephrine concentrations, ventilation (VE), and heart rate (HR) were observed (P < 0.05). Although the rapid attenuation of the VO2 slow component coincided temporally with reductions in plasma [Epi], blood [La-], and VE, the infusion of Epi after training significantly increased plasma [Epi] (delta 2.22 ng/ml), blood [La-] (delta 2.4 mmol/l) and VE (delta 10.0 l/min) without any change in exercise VO2. We therefore conclude that diminution of the VO2 slow component with training is attributable to factors other than the reduction in plasma [Epi], blood [La-] and VE.

Effects of glycogen depletion and pedaling speed on "anaerobic threshold"

1982 ◽  
Vol 52 (6) ◽  
pp. 1598-1607 ◽  
Author(s):  
E. F. Hughes ◽  
S. C. Turner ◽  
G. A. Brooks
Keyword(s):  
Anaerobic Threshold ◽  
Glycogen Content ◽  
Bicycle Ergometer ◽  
Minute Volume ◽  
Work Rate ◽  
Glycogen Depletion ◽  
O2 Uptake ◽  
Significant Divergence ◽  
Male Subjects ◽  
Pedaling Frequency

Nine male subjects performed continuous incremental exercise on a bicycle ergometer pedaling at 50 and 90 rpm in a normal glycogen state (NG) and at 50 rpm in a glycogen-depleted state (GD) to determine if alterations in pedaling frequency and muscle glycogen content would affect their “anaerobic thresholds.” Ventilatory [T(vent)] and lactate [T(lac)] thresholds were identified as the points after which expired minute volume and blood lactate began to increase nonlinearly as a function of work rate. The GD protocol elicited a significant divergence between the two thresholds shifting the T(vent) to a lesser and the T(lac) to a greater work rate relative to the NG state. When the pedaling frequency was increased to 90 rpm in the NG condition, the T(lac) was shifted to a lesser work rate relative to the 50-rpm NG condition. A correlation of only 0.71 was obtained between subjects' T(vent) and T(lac). In subjects of less than 70 kg body wt, the T(lac) came at a work rate 400 kg.m.min-1 less than in subjects of greater than 80 kg body wt despite equivalent O2 uptake. The observation that the T(vent) and T(lac) could be manipulated independently of each other reveals limitations in using the T(vent) to estimate the so-called anaerobic threshold.

Lactate, pyruvate, and lactate-to-pyruvate ratio during exercise and recovery

1985 ◽  
Vol 59 (3) ◽  
pp. 935-940 ◽  
Author(s):  
K. Wasserman ◽  
W. L. Beaver ◽  
J. A. Davis ◽  
J. Z. Pu ◽  
D. Heber ◽  
...  
Keyword(s):  
Normal Subjects ◽  
Cycle Ergometer ◽  
Work Rate ◽  
O2 Uptake ◽  
Abrupt Increase ◽  
Early Recovery ◽  
Rate Of Increase ◽  
Lactate And Pyruvate ◽  
Low Levels ◽  
Pyruvate Ratio

The pattern of lactate increase and its relation to pyruvate and lactate-to-pyruvate (L/P) ratio were studied during exercise and early recovery in 10 normal subjects for incremental exercise on a cycle ergometer. Gas exchange was measured breath by breath. Lactate and pyruvate were measured by enzymatic techniques. Lactate and log lactate changed only slightly at low levels of O2 uptake (VO2) but both began to abruptly increase at approximately 40–55% of the maximal VO2. However, the point of abrupt increase in pyruvate occurred at higher work rates and the rate of increase was not as great as that for lactate. Thus L/P ratio increased at the same VO2 as the log lactate increase. Following the exercise, pyruvate continued to increase steeply for at least the first 5 recovery min, whereas at 2 min lactate increased only slightly or decreased. Thus arterial L/P ratio reversed its direction of change and decreased toward the resting value by 2 min of recovery. Lactate, as well as L/P ratios, decreased in all subjects by 5 min. This study demonstrates that lactate and pyruvate concentrations increase slightly at low levels of exercise without a change in L/P ratio until a threshold work rate at which lactate abruptly increases without pyruvate. The resulting increase in L/P ratio is progressive as work rate is incremented and abruptly reverses when exercise stops.

scholarly journals Sprint training reduces urinary purine loss following intense exercise in humans

2006 ◽  
Vol 31 (6) ◽  
pp. 702-708 ◽  
Author(s):  
Christos G. Stathis ◽  
Michael F. Carey ◽  
Alan Hayes ◽  
Andrew P. Garnham ◽  
Rodney J. Snow
Keyword(s):  
Uric Acid ◽  
Performance Test ◽  
Recovery Period ◽  
Rest Period ◽  
Cycle Ergometer ◽  
Sprint Training ◽  
Intense Exercise ◽  
Before And After ◽  
Exercise Induced ◽  
Male Subjects

The influence of sprint training on endogenous urinary purine loss was examined in 7 active male subjects (age, 23.1 ± 1.8 y; body mass, 76.1 ± 3.1 kg; VO2 peak, 56.3 ± 4.0 mL·kg–1·min–1). Each subject performed a 30 s sprint performance test (PT), before and after 7 d of sprint training. Training consisted of 15 sprints, each lasting 10 s, on an air-braked cycle ergometer performed twice each day. A rest period of 50 s separated each sprint during training. Sprint training resulted in a 20% higher muscle ATP immediately after PT, a lower IMP (57% and 89%, immediately after and 10 min after PT, respectively), and inosine accumulation (53% and 56%, immediately after and 10 min after the PT, respectively). Sprint training also attenuated the exercise-induced increases in plasma inosine, hypoxanthine (Hx), and uric acid during the first 120 min of recovery and reduced the total urinary excretion of purines (inosine + Hx + uric acid) in the 24 h recovery period following intense exercise. These results show that intermittent sprint training reduces the total urinary purine excretion after a 30 s sprint bout.

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