Biomedical subjects

T J Barstow

Publications and source records attributed to T J Barstow.

64 records · Page 4Linked to original sources

PubMed1989

Blood glucose turnover during high- and low-intensity exercise.

We hypothesized that whole body glucose uptake (Rd) during exercise is not related in a simple, linear manner to O2 uptake (VO2). To test this, seven healthy male subjects (age range 23-34 yr) were studied in the postabsorptive but not glycogen-depleted state. Three conditions were examined: 1) rest, 2) 40 min of constant exercise in which the work rates were carefully chosen to consist of low-intensity exercise (no elevated blood lactate, a mean of 40% maximal VO2), and 3) 40 min of high-intensity exercise (markedly elevated blood lactate, 79% maximal VO2). Gas exchange was measured breath by breath, and glucose uptake and production were measured using [6,6-2H2]glucose. Low-intensity exercise (n = 7) resulted in a small but not statistically significant increase in mean Rd [3.06 +/- 0.37 (SE) mg.min-1.kg-1] compared with resting values (2.87 +/- 0.39 mg.min-1.kg-1) despite a fourfold increase in the production of CO2 and VO2. By contrast, the high-intensity exercise Rd (n = 5, 6.98 +/- 0.67 mg.min-1.kg-1) was significantly greater than the resting value (3.03 +/- 0.56 mg.min-1.kg-1). Results of glucose production were virtually the same. Similarly, mean levels of epinephrine and norepinephrine increased significantly above resting values during high- but not low-intensity exercise. Our data demonstrate that whole body glucose dynamics and regulation during 40 min of exercise do not change in a simple linear manner with respect to metabolic rate.

Adult↗

PubMed1989

Changes in breath 13CO2/12CO2 consequent to exercise and hypoxia.

Because the natural enrichment of carbohydrate with 13C is greater than that of lipid, we hypothesized that the natural enrichment of exhaled CO2 with 13C (EN) could be used to gauge endogenous substrate utilization in exercising human subjects. To test this, EN and the respiratory exchange ratio (R) which equals the respiratory quotient (RQ) in the steady state, were measured simultaneously in seven subjects. Rest and exercise protocols, performed under conditions of room air (sea level) and hypoxic (inspired O2 fraction = 0.15) breathing, were chosen to cause a variety of patterns of oxidative substrate utilization. Work rates were performed both below and above the subject's lactate threshold (LT). Work above the LT was expected to cause the greatest increase in EN reflecting greater utilization of glucose. There was significant intersubject (P less than 0.05) but not intrasubject variability in resting EN. By 40 min of exercise, EN increased significantly (P less than 0.05) over resting values in all exercise protocols during both room air and hypoxia conditions. In the room air studies, we found no difference in EN during the below-LT work, even though there were significant increases in O2 uptake (VO2). In contrast, above-LT work resulted in significantly greater increases in EN by 20 and 40 min of exercise (P less than 0.05). Contrary to our expectations, we observed no separate effect by hypoxia on the EN during exercise. Both EN and R tended to increase from rest to exercise, but during exercise there was no overall correlation between R and the EN. EN reflects changes in endogenous substrate utilization over relatively long periods of time such as at rest, but delays in the appearance of 13CO2 at the mouth due to dilution in body CO2 pools, and possibly isotopic fractionation, preclude the usefulness of EN as an indicator of endogenous fuel mix during short-term exercise.

Adult↗

PubMed1989

Influence of work rate on ventilatory and gas exchange kinetics.

A linear system has the property that the kinetics of response do not depend on the stimulus amplitude. We sought to determine whether the responses of O2 uptake (VO2), CO2 output (VCO2), and ventilation (VE) in the transition between loadless pedaling and higher work rates are linear in this respect. Four healthy subjects performed a total of 158 cycle ergometer tests in which 10 min of exercise followed unloaded pedaling. Each subject performed three to nine tests at each of seven work rates, spaced evenly below the maximum the subject could sustain. VO2, VCO2, and VE were measured breath by breath, and studies at the same work rate were time aligned and averaged. Computerized nonlinear regression techniques were used to fit a single exponential and two more complex expressions to each response time course. End-exercise blood lactate was determined at each work rate. Both VE and VO2 kinetics were markedly slower at work rates associated with sustained blood lactate elevations. A tendency was also detected for VO2 (but not VE) kinetics to be slower as work rate increased for exercise intensities not associated with lactic acidosis (P less than 0.01). VO2 kinetics at high work rates were well characterized by the addition of a slower exponential component to the faster component, which was seen at lower work rates. In contrast, VCO2 kinetics did not slow at the higher exercise intensities; this may be the result of the coincident influence of several sources of CO2 related to lactic acidosis. These findings provide guidance for interpretation of ventilatory and gas exchange kinetics.

Adult↗

PubMed1989

Effect of hypoxia on ventilatory control during exercise in children and adults.

Little is known about maturation of peripheral chemoreceptor tone (PCT) during growth. We recently demonstrated that the increase in PCT was 49% greater during hypoxic (15% O2) exercise in children compared to adults. As the PCT is a major determinant of ventilatory (VE) response at the onset of exercise (measured by the time constant tau), we hypothesized that hypoxia would affect tau VE (and tau VCO2) to a greater extent in children. Nine healthy children (6-10 y old) and nine healthy adults (18-40 y old) performed multiple transitions from rest to constant work rate on the cycle ergometer. Studies were done breathing 21% O2 and 15% O2. Hypoxic breathing quickened the VE responses in all of the adults and children, but the magnitude of the hypoxic effect did not differ between the two groups (in children, tau VE was 50.9 +/- 9.9 s during 21% O2 breathing and 32.6 +/- 6.9 s during hypoxia; in adults, tau VE was 69.4 +/- 17.6 s, which fell to 50.9 +/- 18.4 s during hypoxia). The hypothesized greater ventilatory response to hypoxia in children compared to adults during exercise was not observed. During 21% O2 breathing, the data demonstrated that children stored relatively less CO2 (by 49%) than did adults in the transition between rest and exercise, possibly explaining the faster ventilatory kinetics. We speculate that there must be additional respiratory control differences between adults and children such that for a given increase in PCT-induced by hypoxia, the VE response at the onset of exercise is less in children than in adults.

Adolescent↗

PubMed1988

Comparison of daily and seasonal exposures of young monkeys to ozone.

Oxidant air pollution tends to occur in both seasonal and daily cycles of polluted and clean air. To compare the effects of these 2 cycles, we exposed 2 groups of 7-month-old male monkeys to 0.25 ppm (0.49 mg/m3) of ozone (UV photometric standard) 8 h/day either daily or, in the seasonal model, days of alternate months during a total exposure period of 18 months. This is a longer ozone exposure period than any previously reported. A control group breathed only filtered air. Young monkeys were studied as their lungs are similar to those of man and their lungs, like those of man, grow over a period of several years. Monkeys from the seasonal exposure model, but not those exposed daily, had significantly increased total lung collagen content, chest wall compliance, and inspiratory capacity. All monkeys exposed to ozone had respiratory bronchiolitis with significant increases in related morphometric parameters. The only significant difference between seasonal and daily groups was in the volume fraction of macrophages. Even though the seasonally exposed monkeys were exposed to the same concentration of ozone for only half as many days, they had larger biochemical and physiological alterations and equivalent morphometric changes as those exposed daily. Lung growth was not completely normal in either exposed group. Long-term effects of oxidant air pollutants which have a seasonal occurrence may be more dependent upon the sequence of polluted and clean air than on the total number of days of pollution. Estimations of the risks of human exposure to seasonal air pollutants from effects observed in animals exposed daily may underestimate long-term pulmonary damage.

Air Pollutants↗

PubMed1987

Effects of ozone on lung and somatic growth. Pair fed rats after ozone exposure and recovery periods.

Minor differences in lung growth and development during childhood have been considered as a potential cause of rapid decline in pulmonary function in adulthood. Inhalation of ozone commonly causes changes in both body weight and lung volumes, which complicates interpretation of any changes in lung growth. The effects of ozone on lung growth were studied in rats which were pair fed. This technique permitted comparison of ozone-exposed and filtered-air control rats of the same body weight and body size as well as age and sex. Exposure was to filtered air or to 0.64 or 0.96 ppm ozone (UV standard) 8 h/night for 42 nights. A second control group was fed ad libitum and exposed to only filtered air. Half the rats were studied at the end of the 42-night exposures, the rest after a 42-day post-exposure period during which all rats were fed ab libitum and breathed filtered air. Rats examined at the end of the exposure period had larger saline and fixed lung volumes. These larger lungs had greater volumes of parenchyma, alveoli and respiratory bronchioles. Some of these changes persisted throughout a 42-day post-exposure period. Ozone inhalation by young rats alters lung growth and development in ways likely to be detrimental and those changes persist after ozone inhalation stops.

Animals↗

PubMed1987

Simulation of pulmonary O2 uptake during exercise transients in humans.

Computer simulation of blood flow and O2 consumption (QO2) of leg muscles and of blood flow through other vascular compartments was made to estimate the potential effects of circulatory adjustments to moderate leg exercise on pulmonary O2 uptake (VO2) kinetics in humans. The model revealed a biphasic rise in pulmonary VO2 after the onset of constant-load exercise. The length of the first phase represented a circulatory transit time from the contracting muscles to the lung. The duration and magnitude of rise in VO2 during phase 1 were determined solely by the rate of rise in venous return and by the venous volume separating the muscle from the lung gas exchange sites. The second phase of VO2 represented increased muscle metabolism (QO2) of exercise. With the use of a single-exponential model for muscle QO2 and physiological estimates of other model parameters, phase 2 VO2 could be well described as a first-order exponential whose time constant was within 2 s of that for muscle QO2. The use of unphysiological estimates for certain parameters led to responses for VO2 during phase 2 that were qualitatively different from QO2. It is concluded that 1) the normal response of VO2 in humans to step increases in muscle work contains two components or phases, the first determined by cardiovascular phenomena and the second primarily reflecting muscle metabolism and 2) the kinetics of VO2 during phase 2 can be used to estimate the kinetics of muscle QO2. The simulation results are consistent with previously published profiles of VO2 kinetics for square-wave transients.

Computer Simulation↗

PubMed1985

In vivo 31P-NMR in human muscle: transient patterns with exercise.

Evaluation of dynamic changes in pH and concentrations of adenosine 5'-triphosphate (ATP), phosphocreatine (PCr), and inorganic phosphate (Pi) during the transition from rest to steady-state exercise in the human has been methodologically limited. Previous work has relied on muscle biopsy of exercising subjects at different times in different exercise bouts. Chemical evaluation of metabolites has been hampered by continuing change in metabolic concentration during the biopsy procedure. Recently, Fourier-transformed 31P nuclear magnetic resonance (31P-NMR), employing surface coils, has made evaluation of phosphorus metabolites possible by noninvasive atraumatic means in human muscle. Relative concentrations of PCr, Pi, and ATP, together with pH, have been obtained with 31P-NMR from the flexor digitorum superficialis muscle on two occasions in four adult men during the transition from rest to exercise. [PCr] rapidly fell and was mirrored by a rise in [Pi]. The former temporarily exceeded the latter with the discrepancy apparently being absorbed by a transient rise in [ATP], which was itself mirrored by alteration in [H+].

Adenosine Triphosphate↗

PubMed1978

Energy cost of circuit weight training.

The metabolic cost of circuit weight training was determined in a group of 20 men and 20 women, 17 to 36 years of age, who volunteered to participate in this study. Performing 3 circuits (10 stations/circuit), using a work (30-sec) to rest (15-sec) ratio of 2:1, and a total exercise time of 22.5 min, the energy expenditure was found to be highly related to body weight (r = 0.84 and r = 0.67 for men and women respectively). The average gross energy expenditure was 539.7 and 367.5 kcal/hr. (9.0 and 6.1 kcal/min) for the men and women respectively, but was 7.0 and 6.0 kcal/kg-hr when expressed relative to body weight, and 8.1 and 8.2 kcal/kg(LBW)-min when expressed relative to lean body weight. Thus, when body composition was considered, there were essentially no differences in the energy expenditure for males and females.

Adolescent↗

PubMed1978

Physiological alterations consequent to circuit weight training.

The efficacy of a 10-week program of circuit weight training to elicit specific physiological alterations was evaluated in a group of men (n = 16) and a group of women (n = 12), with an additional group of men (n = 10) and a group of women (n = 11) serving as controls. The circuit consisted of 10 stations performed on a Universal Gym, 3 circuits per day (approximately 22.5 min/day), 3 days/week. The subjects exercised at 40-55% of 1-RM, executing as many repetitions as possible in 30 sec on each of the lifts, followed by a 15 sec rest as the subject moved to the next station. Following the training program, the experimental groups demonstrated significant increases in lean body weight, flexed biceps girth, treadmill endurance time, VEmax (women only), Vo2max in ml/kg-min (women only), flexibility and strength. Significant decreases were found in selected skinfold measurements, and in resting heart rate (control group showed similar decreases). No change was found in body weight or in relative or absolute body fat. Generally, the women exhibited equal or greater changes when compared to the men for all variables assessed, which could be a function of their lower initial starting levels, or a more intense training program. It was concluded that circuit weight training is a good general conditioning activity, i.e., attends to more than one component of fitness.

Anthropometry↗