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Biomedical subjects

J R Sutton

Publications and source records attributed to J R Sutton.

At least 91 records · Page 5Linked to original sources
PubMed1987

Operation Everest II: man at extreme altitude.

Rapid ascent to high altitude may cause serious problems for climbers, skiers, and aviators. In contrast, gradual ascent enables humans to function where the unacclimatized cannot. To examine changes in the O2 transport system that produce acclimatization, eight men were taken in a decompression chamber (without other stresses experienced on high mountains) to a simulated altitude of 8,840 m (29,028 ft, ambient PO2 = 43 Torr) in 40 days. Maximal O2 uptake fell to 1.2 l/min, and arterial PO2 and PCO2 were 30 and 11 Torr, respectively, with arterial pH of 7.56. Many sophisticated studies were done: Swan-Ganz catheterization and inert gas diffusion studies at three altitudes showed that normal cardiac function persisted, pulmonary vascular resistance increased and at extreme altitude was not lowered by O2, and pulmonary ventilation-perfusion mismatch increased, though variably. This appears to be an important factor limiting performance at extreme altitude. This paper presents the background, general approach, and a summary of major observations reported in detail in other papers.

Acclimatization↗
PubMed1987

Operation Everest II: pulmonary gas exchange during a simulated ascent of Mt. Everest.

Eight normal subjects were decompressed to barometric pressure (PB) = 240 Torr over 40 days. The ventilation-perfusion (VA/Q) distribution was estimated at rest and during exercise [up to 80-90% maximal O2 uptake (VO2 max)] by the multiple inert gas elimination technique at sea level and PB = 428, 347, 282, and 240 Torr. The dispersion of the blood flow distribution increased by 64% from rest to 281 W, at both sea level and at PB = 428 Torr (heaviest exercise 215 W). At PB = 347 Torr, the increase was 79% (rest to 159 W); at PB = 282 Torr, the increase was 112% (108 W); and at PB = 240 Torr, the increase was 9% (60 W). There was no significant correlation between the dispersion and cardiac output, ventilation, or pulmonary arterial wedge pressure, but there was a correlation between the dispersion and mean pulmonary arterial pressure (r = 0.49, P = 0.02). When abnormal, the VA/Q pattern generally had perfusion in lung units of zero or near zero VA/Q combined with units of normal VA/Q. Alveolar-end-capillary diffusion limitation of O2 uptake (VO2) was observed at VO2 greater than 3 l/min at sea level, greater than 1-2 l/min VO2 at PB = 428 and 347 Torr, and at higher altitudes, at VO2 less than or equal to 1 l/min. These results show variable but increasing VA/Q mismatch with long-term exposure to both altitude and exercise. The VA/Q pattern and relationship to pulmonary arterial pressure are both compatible with alveolar interstitial edema as the primary cause of inequality.

Acclimatization↗
PubMed1987

Environmental considerations for exercise.

Physical activity, whether at a competitive or a recreational level, is frequently affected by environmental conditions. With changes in the natural environment, the exercising individual invokes a series of complex physiologic responses that are directed at maintaining homeostasis. This article will focus on the nature of these responses, with special reference to their influence on cardiorespiratory function. Because alterations in ambient temperature and ascent to altitude are the most common and are the most extensively studied of man's adaptational abilities, these will provide the basis for this discussion.

Altitude Sickness↗
PubMed1987

Operation Everest II: Altitude decompression sickness during repeated altitude exposure.

The incidence of altitude decompression sickness (ADS) was studied in 23 altitude scientists during repeated altitude exposure to 15,000-29,000 ft (4572-8839 m) in a decompression chamber. Prior to each altitude exposure, a 30-60-mm pre-breathing period with 100% oxygen took place. Ascent was made to an altitude at a rate of 2000 ft X min-1. The altitudes studied ranged from 15,000-29,000 ft (4572-8839 m). Symptoms reported appear consistent with previous reports. Incidence of ADS at 26,000-29,000 ft (7925-8839 m) was 29.7%, during 274 chamber flights and 1264.6 h of altitude time. Incidence appeared related to frequency of exposure, severity of altitude, and physical activity. Incidence was not related to age, duration of exposure, or body index (weight/height 2). This high incidence of ADS reported in this study is similar to that reported by NASA.

Adult↗
PubMed1986

Activation of human muscle pyruvate dehydrogenase with activity and immobilization.

The activity of pyruvate dehydrogenase (PDH) was measured in samples of triceps muscle obtained in 15 males, before and after immobilization for 5 weeks and 5 months of strength training carried out in random order with cross-over of treatment. Although the total PDH activity was unchanged at 300 nmol min-1 g-1, the proportion in the active form increased after strength training (62 +/- 10.1%) and decreased after immobilization (12 +/- 2.3%) compared with control (36 +/- 3.4%). In six subjects measurements were repeated after 10 min maximal exercise (arm ergometer). The proportion of PDH in the active form increased least after immobilization (to 52 +/- 13.6%), compared with control (95 +/- 11.7%) and post-training (98 +/- 6.6%). After exercise muscle glycogen fell to the greatest extent and lactate rose the least in the post-training state, with opposite findings post-immobilization, suggesting that PDH activation contributes to the control of lactate formation in muscle during heavy exercise, and that the effects of training and immobilization are mediated at least in part through changes in the activation of this regulatory enzyme.

Adult↗
PubMed1986

Muscle power and metabolism in maximal intermittent exercise.

Muscle power and the associated metabolic changes in muscle were investigated in eight male human subjects who performed four 30-s bouts of maximal isokinetic cycling at 100 rpm, with 4-min recovery intervals. In the first bout peak power and total work were (mean +/- SE) 1,626 +/- 102 W and 20.83 +/- 1.18 kJ, respectively; muscle glycogen decreased by 18.2 mmol/kg wet wt, lactate increased to 28.9 +/- 2.7 mmol/kg, and there were up to 10-fold increases in glycolytic intermediates. External power and work decreased by 20% in both the second and third exercise periods, but no further change occurred in the fourth bout. Muscle glycogen decreased by an additional 14.8 mmol/kg after the second exercise and thereafter remained constant. Muscle adenosine triphosphate (ATP) was reduced by 40% from resting after each exercise period; creatine phosphate (CP) decreased successively to less than 5% of resting; in the recovery periods ATP and CP increased to 76 and 95% of initial resting levels, respectively. Venous plasma glycerol increased linearly to 485% of resting; free fatty acids did not change. Changes in muscle glycogen, lactate, and glycolytic intermediates suggested rate limitation at phosphofructokinase during the first and second exercise periods, and phosphorylase in the third and fourth exercise periods. Despite minimal glycolytic flux in the third and fourth exercise periods, subjects generated 1,000 W peak power and sustained 400 W for 30 s, 60% of the values recorded in the first exercise period.(ABSTRACT TRUNCATED AT 250 WORDS)

Acid-Base Equilibrium↗
PubMed1986

Supercompensation of muscle glycogen in trained and untrained subjects.

The purpose of this study was to determine whether or not trained athletes have the same capacity for supercompensation of muscle glycogen as untrained subjects. Muscle glycogen was measured in 4 highly trained cyclists and 4 untrained controls over a 6 day period of exercise and dietary manipulation. During the week prior to the investigation the trained group tapered their training load but maintained a high carbohydrate intake as they would in preparation for a major competition. Needle biopsies were taken from the vastus lateralis before and after exhaustive cycle ergometry at 73% VO2 max followed by several sprint intervals, after 3 days on a carbohydrate-restricted diet and after 2 and 3 days on a high carbohydrate diet. All food intake was quantified and plasma insulin and glucose were monitored daily. The mean initial glycogen concentration for the trained group was 115 mmol X kg-1 wet muscle weight and 92 mmol X kg-1 for the untrained group. Both groups showed similar post exercise depletion and recovery patterns when expressed as a % of their initial values. Following 3 days of high carbohydrate diet, the glycogen concentration for the trained cyclists reached 174 mmol X kg-1 or 152% of its initial value while the untrained-group reached 143 mmol X kg-1 or 155% of its initial value. It was concluded that a regimen of exhaustive exercise, followed by a period of carbohydrate restriction and a period of high carbohydrate intake, results in substantially higher muscle glycogen storage than can be achieved by a reduction in training in combination with high carbohydrate intake.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1985

Drugs and exercise.

In this article, we have examined some pharmacologic principles as they apply to drug use by healthy individuals. With the present emphasis on community activities, we have dealt with the impairment of thermoregulation by athletes and fun runners who may take normal over-the-counter medications for a variety of reasons. However, many of these drugs impair thermoregulation. Our additional focus has been on drug abuse, again by healthy people, often striving to enhance their performance. Here we have dealt principally with the anabolic and androgenic steroids and stimulants. Finally, we have reproduced the current list of medications permitted by the International Olympic Committee, but have also offered some suggestions of common medications that may be required by athletes for such illnesses as hay fever, upper respiratory tract infections, and other simple disorders (Table 2). These medications do not contain any ingredients prohibited by the International Olympic Committee regulations. It is important to remember that many of the compound medications often sold over-the-counter contain substances such as caffeine, codeine, and ephedrine, which the unwitting athlete, trainer or coach could prescribe for a legitimate indication but which could, and have in the past, cost such athletes Olympic medals.

Absorption↗
PubMed1985

Arterial blood pressure response to heavy resistance exercise.

The purpose of this study was to record the blood pressure response to heavy weight-lifting exercise in five experienced body builders. Blood pressure was directly recorded by means of a capacitance transducer connected to a catheter in the brachial artery. Intrathoracic pressure with the Valsalva maneuver was recorded as mouth pressure by having the subject maintain an open glottis while expiring against a column of Hg during the lifts. Exercises included single-arm curls, overhead presses, and both double- and single-leg presses performed to failure at 80, 90, 95, and 100% of maximum. Systolic and diastolic blood pressures rose rapidly to extremely high values during the concentric contraction phase for each lift and declined with the eccentric contraction. The greatest peak pressures occurred during the double-leg press where the mean value for the group was 320/250 mmHg, with pressures in one subject exceeding 480/350 mmHg. Peak pressures with the single-arm curl exercise reached a mean group value of 255/190 mmHg when repetitions were continued to failure. Mouth pressures of 30-50 Torr during a single maximum lift, or as subjects approached failure with a submaximal weight, indicate that a portion of the observed increase in blood pressure was caused by a Valsalva maneuver. It was concluded that when healthy young subjects perform weight-lifting exercises the mechanical compression of blood vessels combines with a potent pressor response and a Valsalva response to produce extreme elevations in blood pressure. Pressures are extreme even when exercise is performed with a relatively small muscle mass.

Adult↗
PubMed1985

Muscle performance and metabolism in maximal isokinetic cycling at slow and fast speeds.

To provide a description of the metabolic changes in muscle during maximal dynamic exercise, muscle biopsies were obtained in five healthy subjects before and after 30 s of isokinetic exercise at two pedaling frequencies (60 and 140 rpm) associated with contrasting fatigue characteristics. Higher peak power was attained at 140 rpm (1,473 + 185 W) (mean +/- SE) than at 60 rpm (1,122 +/- 70 W), but the decline in power during 30 s (fatigue index) was greater at 140 rpm (61.6 +/- 3.2 vs. 21.5 +/- 2.4%), total work in 30 s being similar (18.1 +/- 1.10 vs. 20.1 +/- 1.10 kJ). Changes in the concentration of muscle metabolites were similar; creatine phosphate concentration fell to approximately 50% of resting values, and the glycolytic intermediates glucose 6-phosphate, fructose 6-phosphate, and fructose 1,6-biphosphate increased up to 30-fold. Muscle lactate concentration ([La-]) was 29.0 +/- 3.98 and 31.0 +/- 4.31 mmol/kg wet wt immediately postexercise at 140 and 60 rpm, respectively. Even after only 10 s exercise (n = 2), large increases were measured in glycolytic intermediates and [La-]. In the two subjects, muscle [La-] increased to 17.2 and 15.1 mmol/kg at 140 rpm and to 14.3 and 14.2 mmol/kg at 60 rpm. In this type of exercise, glycogenolysis is activated very rapidly at both pedal speeds; the changes in glycolytic intermediates were consistent with rate-limiting steps at the phosphofructokinase and pyruvate dehydrogenase reactions. The greater fatigue at the higher speed is not accompanied by different biochemical changes than at 60 rpm.

Adenosine Triphosphate↗
PubMed1985

Endorphins: what are they? How are they measured? What is their role in exercise?

A generalized knowledge of opiates has been available for centuries, but it was not until 1975, following the isolation of the first endogenous opioids, that it was appreciated that their analgesic properties were mediated via specific receptors. Three general classes of opioids are now recognized: the endorphins, the enkephalins, and the dynorphins. Assaying of the endogenous opioid peptides has never been simple, and now radioimmunoassay has replaced the earlier bioassays. When coupled with immunohistochemical techniques, radioimmunoassay allows precise localization of opioids in various tissue sections. There is evidence that plasma concentration of endorphins, and possibly also met-enkephalin, increases with exercise. In addition, the opioid peptides have important implications for the effects of other hormonal functions, including the pituitary hormones and catecholamines. Few studies during exercise are available, and naloxone has been used widely as the agent to determine the role of endogenous opioids on hormonal secretions. Slightly conflicting results have been obtained, depending on the dosage of naloxone used. With high-dose naloxone, there appears to be overall endorphin inhibition of cortisol, prolactin, and growth hormone secretion. Endorphins do not appear to exert a major influence on the cardiovascular response to exercise, but in high-intensity exercise, they appear to partially inhibit the ventilatory response to exercise.

Adrenocorticotropic Hormone↗
PubMed1985

Heart rate response to facial immersion and apnea in quadriplegia.

Profound bradycardia is a common complication in the early posttraumatic period following cervical spinal cord damage. It is thought to be due to temporary inactivity of the sympathetic nervous system after separation from supraspinal control, coupled with unopposed parasympathetic dominance because of vagus nerve sparing. Hypoxia, underventilation, and tracheal suctioning appear to intensify the bradycardia. This study examined the effect of vagal stimulation using facial immersion and apnea on heart rate in patients with quadriplegia. Ten patients with quadriplegia (eight males and two females, mean age 25, age range 16-37) and ten healthy controls (eight males and two females, mean age 25, age range 15-37) underwent facial immersion during ECG monitoring. The patients with quadriplegia were studied at a mean of 9.4 months after injury (range, 4-26 months); cord level of injury ranged from C5 to C8; seven of the ten had had heart rates of less than 50 beats/min in the early period after injury and five of the ten had received treatment for this. No change in heart rate was seen in the quadriplegic group during facial immersion (delta = 1.5 +/- 2.7 beats/min, mean +/- SE), but a significant drop in heart rate was seen in the control group (delta = -12.2 +/- 3.7 beats/min, mean +/- SE; p less than 0.01). No significant decreases were seen in either group during apnea alone. Patients with chronic quadriplegia appear to have less sensitivity than controls to the vagal-stimulating maneuver of facial immersion and apnea.

Adolescent↗
PubMed1984

Muscle fiber number in biceps brachii in bodybuilders and control subjects.

Muscle fiber numbers were estimated in vivo in biceps brachii in 5 elite male bodybuilders, 7 intermediate caliber bodybuilders, and 13 age-matched controls. Mean fiber area and collagen volume density were calculated from needle biopsies and muscle cross-sectional area by computerized tomographic scanning. Contralateral measurements in a subsample of seven subjects indicated the method for estimation of fiber numbers to have adequate reliability. There was a wide interindividual range for fiber numbers in biceps (172,085-418,884), but despite large differences in muscle size both bodybuilder groups possessed the same number of muscle fibers as the group of untrained controls. Although there was a high correlation between average cross-sectional fiber area and total muscle cross-sectional area within each group, many of the subjects with the largest muscles also tended to have a large number of fibers. Since there were equally well-trained subjects with fewer than normal fiber numbers, we interpret this finding to be due to genetic endowment rather than to training-induced hyperplasia. The proportion of muscle comprised of connective and other noncontractile tissue was the same for all subjects (approximately 13%), thus indicating greater absolute amounts of connective tissue in the trained subjects. We conclude that in humans, heavy resistance training directed toward achieving maximum size in skeletal muscle does not result in an increase in fiber numbers.

Adult↗
PubMed1983

Characteristics that predicted recurrence of infarction within 3 years in the Ontario Exercise-Heart Collaborative Study.

Data on 13 baseline characteristics of 618 patients who had previously had a myocardial infarction and who had entered the Ontario Exercise-Heart Collaborative Study were analysed for their ability to predict recurrence of infarction within 3 years. These characteristics were age, serum levels of cholesterol and triglycerides, systolic and diastolic blood pressure, number of hours of competitive sports per week, number of hours of jogging per week, angina, type of occupation, smoking, cough and phlegm production, personality type and the number of previous infarctions. The characteristics showing independent statistical significance (p less than 0.05) were smoking and blue-collar occupation, with estimated adjusted relative odds of 2.3 and 2.1 respectively.

Adult↗
PubMed1983

Predictors of dropout from cardiac exercise rehabilitation. Ontario Exercise-Heart Collaborative Study.

The Ontario Exercise-Heart Collaborative Study was a multicenter randomized clinical trial of high intensity exercise for the prevention of recurrent myocardial infarction in 733 men. Of the 678 subjects who could have participated for at least 3 years, 315 (46.5%) dropped out. Stepwise multiple linear logistic regression analysis was carried out to examine the relation between subject characteristics and the probability of dropping out during the study. Analysis was performed on the entry group as a whole by considering those subjects who had reinfarction while complying with the program and also by excluding all subjects with reinfarctions. The consistent and statistically significant predictors of dropout in both analyses were smoking and a blue collar occupation. Angina was significantly associated with dropout only when reinfarctions were excluded. It may be important to consider these factors when investigating the potential for compliance-improving strategies in reducing dropout from exercise rehabilitation programs.

Adult↗