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Biomedical subjects

N F Gordon

Publications and source records attributed to N F Gordon.

At least 37 records · Page 2Linked to original sources
PubMed1992

Cardiorespiratory fitness, glycemic status, and mortality risk in men.

OBJECTIVE: To determine the association of baseline cardiorespiratory fitness to all-cause mortality across the range of blood glucose levels. RESEARCH DESIGN AND METHODS: Data from a prospective study of 8715 men (average age 42 yr), followed for an average of 8.2 yr (range 1-15 yr), were analyzed. Cardiorespiratory fitness was assessed by maximal-exercise treadmill testing. Men with evidence of clinical vascular disease or who did not achieve 85% of their age-predicted maximum heart rate during exercise testing were excluded from analyses. RESULTS: Age-adjusted death rates increased with higher levels, of fasting blood glucose. Regardless of glycemic status, fit men had lower age-adjusted all-cause death rates than their less fit counterparts. For men with fasting blood glucose greater than or equal to 7.8 mM or physician-diagnosed non-insulin-dependent diabetes mellitus (NIDDM), the age-adjusted death rates per 10,000 person-yr of follow-up in unfit and fit subjects were 82.5 and 45.9, respectively. The age-adjusted relative risk of death due to all causes was significantly elevated in the lower-fitness group within each of three glycemic status levels: fasting blood glucose less than 6.4 mM; relative risk (RR) = 1.93 (95% confidence interval [95% CI] 1.15-3.26); fasting blood glucose 6.4-7.8 mM; RR = 3.42 (95% CI 2.27-5.15); and fasting blood glucose greater than or equal to 7.8 mM or with NIDDM, RR = 1.80 (95% CI = 1.25-2.58). Multivariate analyses, controlling for risk factors of mortality (age, resting systolic blood pressure, serum cholesterol, body mass index, family history of heart disease, follow-up interval, and smoking habit) showed a higher risk of death due to all causes for unfit compared with fit men. Multivariate risks of death associated with low fitness, compared with higher fitness (RR), in the three glycemic status groups were: fasting blood glucose less than 6.4 mM, RR = 1.38 (95% CI 1.09-1.74); fasting blood glucose 6.4-7.8 mM, RR = 1.61 (95% CI 0.91-2.86); and fasting blood glucose greater than or equal to 7.8 mM or with NIDDM, RR = 1.92 (95% CI 0.75-4.90).

Adult↗
PubMed1992

Musculoskeletal strength and serum lipid levels in men and women.

There currently is inconsistent information regarding the role that musculoskeletal strength (one component of musculoskeletal fitness) may have in lipid and lipoprotein metabolism, and consequently the risk of cardiovascular disease. Results of existing studies have been conflicting and have been influenced by several weaknesses. We provide cross-sectional analyses of the relation between muscular strength and serum lipid and lipoprotein status in a group of 1,193 women and 5,460 men. The large proportion of patients were not involved in formal weight training. As part of a preventive medical examination, patients were tested for maximal upper and lower body strength (one repetition maximum (1RM) bench and leg press). Fasting serum total cholesterol (TC), low-density lipoprotein cholesterol (LDLC), triglyceride (TG), and high density lipoprotein (HDLC) were evaluated for their relation to muscle strength, after adjusting for simultaneous associations with age, body composition, and cardiovascular fitness. Results showed no association between muscular strength and serum TC or LDLC for either men or women and a direct association between upper and lower body strength and TG in men. The direct association between strength and TG in women was not significant. A statistically significant inverse association was seen between muscular strength and HDLC in men only. These data suggest no beneficial effect, and perhaps an adverse association of muscular strength on lipid and lipoprotein status.

Adult↗
PubMed1992

Effect of macronutrient composition of an energy-restrictive diet on maximal physical performance.

Thirty-six sedentary, mildly obese (30-40% fat), premenopausal women (29-49 yr) were randomly assigned to one of two dietary regimens for an 8-wk double-blind, parallel study of the effect of moderate caloric restriction and macronutrient variation on maximal physical performance. Group 1 (N = 19) consumed 4186 kJ.d-1 (1000 kcal.d-1) with a diet composition of 40% fat, 40% carbohydrate (CHO), and 20% protein. Group 2 (N = 17) also consumed 4186 kJ.d-1 but varied the percent kilojoules to 20% fat, 60% CHO, and 20% protein. Maximal aerobic power was measured using a modified Balke protocol, strength was assessed using isotonic bench and leg press machines and a Cybex 340 isokinetic device during knee flexion and extension, and muscular endurance was taken as the number of sit-ups performed in 1 min. Pre- to post-testing revealed significant (P less than or equal to 0.05) reductions in body weight (group 1, -7.4 kg; group 2, -6.5 kg) within both groups. No significant changes were seen in maximal aerobic power within both groups. Strength measures for both groups showed a trend toward reduction but statistical significance was only evident in right knee extension for group 1 and left knee extension for group 2 (P less than or equal to 0.05). Sit-up number increased nonsignificantly for both groups. Between group differences were not found in any body weight, body composition, or physical performance index. We therefore conclude that in mildly obese women, maximal exercise performance is relatively unimpaired after 8 wk of caloric restriction with either of two diets differing moderately in their macronutrient content.

Adult↗
PubMed1991

Women walking for health and fitness. How much is enough?

OBJECTIVE: We studied whether the quantity and quality of walking necessary to decrease the risk of cardiovascular disease among women differed substantially from that required to improve cardiorespiratory fitness. DESIGN: A randomized, controlled, dose-response clinical trial with a follow-up of 24 weeks. SETTING: A private, nonprofit biomedical research facility. PARTICIPANTS: One hundred two sedentary premenopausal women, 20 to 40 years of age, were randomized to one of four treatment groups; 59 completed the study (16 aerobic walkers [8.0-km/h group], 12 brisk walkers [6.4-km/h group], 18 strollers [4.8-km/h group], and 13 sedentary controls). Eighty-one percent were white, 17% black, and 2% Hispanic. INTERVENTION: Intervention groups walked 4.8 km per day, 5 days per week at 8.0 km/h, 6.4 km/h, or 4.8 km/h on a tartan-surfaced, 1.6-km track for 24 weeks. MAIN OUTCOME MEASURES: Fitness (determined by maximal oxygen uptake) and cardiovascular risk factors (determined by resting blood pressure and serum lipid and lipoprotein levels). RESULTS: As compared with controls, maximal oxygen uptake increased significantly (P less than .0001) and in a dose-response manner (aerobic walkers greater than brisk walkers greater than strollers). In contrast, high-density lipoprotein cholesterol concentrations were not dose related and increased significantly (P less than .05) and to the same extent among women who experienced considerable improvements in their physical fitness (8.0-km/h group, +0.08 mmol/L) and those who had only minimal improvements in fitness (4.8-km/h group, +0.08 mmol/L). High-density lipoprotein cholesterol also increased among the 6.4-km/h group, but did not attain statistical significance (+0.06 mmol/L; P = .06). Dietary patterns revealed no significant differences among groups. CONCLUSION: Thus, we conclude that vigorous exercise is not necessary for women to obtain meaningful improvements in their lipoprotein profile. Walking at intensities that do not have a major impact on cardiorespiratory fitness may nonetheless produce equally favorable changes in the cardiovascular risk profile.

Adult↗
PubMed1991

Effect of beta-blockers on exercise physiology: implications for exercise training.

We conducted a series of studies aimed at investigating the effect of beta-blockers on exercise physiology. On the basis of these and other existing studies, it is possible to draw the following conclusions and to make the following tentative recommendations for patients engaged in exercise training who receive beta-blocker therapy: i) CAD patients treated with beta-blockers are capable of deriving the expected enhancement of cardiorespiratory fitness during training, irrespective of the type of drug used; ii) beta1-selective blockers are preferable to nonselective agents for hypertensive patients engaged in exercise training; iii) because beta1-selective blockers impair exercise tolerance in some hypertensive patients, physicians should look out for this adverse reaction and, if present, consider alternative antihypertensive therapy; iv) intrinsic sympathomimetic activity confers no advantage during exercise training; v) exercise intensity prescription for patients receiving beta-blockers should be in accordance with traditional guidelines and based on results of individualized exercise testing performed on medication; vi) exercise training is desirable during beta-blocker therapy in that it appears to offset adverse alterations in lipoprotein metabolism; and vii) nonselective beta-blockers may increase predisposition to exertional hyperthermia, and patients must therefore be encouraged to adhere strictly to accepted guidelines for heat injury prevention.

Adrenergic beta-Antagonists↗
PubMed1991

Exercise and mild essential hypertension.

The achievement of chronic blood pressure (BP) control in persons with mild hypertension is of central strategic concern in the prevention of hypertension-related morbidity and mortality. Epidemiologic and longitudinal studies suggest that regular participation in physical activity may be beneficial both in preventing hypertension and in lowering an already elevated BP. Moreover, preliminary analyses from our center suggest that cardiorespiratory fitness and, by inference, aerobic exercise may be of benefit in reducing mortality rates in hypertensive patients. When prescribing exercise with the intention of reducing an elevated BP and attenuating the risk for coronary artery disease, several factors must be considered to optimize the likelihood of a safe and effective response. These factors include specific safety aspects, and the type, frequency, intensity, and duration of exercise. In this respect, we recommend that aerobic exercise be performed at an intensity corresponding to 55 and 85% of the maximal heart rate and that the duration and frequency of training be modulated to achieve a weekly energy expenditure of between 14 and 20 kcal/kg of body weight. For those patients who require drug therapy, the interaction between the specific antihypertensive agent and exercise must also be considered.

Antihypertensive Agents↗
PubMed1991

The role of exercise in the primary and secondary prevention of coronary artery disease.

Over the past 30 years, mortality rates from coronary artery disease (CAD) have decreased by more than 30% in the United States. However, CAD remains the major public health problem in this country. There is now substantial evidence linking exercise training to a reduced risk for CAD and for mortality after myocardial infarction. The actual mechanism by which physical activity aids in reducing the risk for developing or dying from CAD has still to be elucidated. Several highly plausible mechanisms have been postulated, including decreased myocardial oxygen demand, increased myocardial oxygen supply, reduced propensity toward ventricular arrhythmias, reduced platelet aggregation, increased plasma fibrinolytic activity, and modification of multiple CAD risk factors. Irrespective of the precise mechanism, it now appears that lower levels of physical activity are needed to reduce the risk for CAD than are needed to optimize cardiorespiratory fitness. In this regard, we recommend that the type, frequency, intensity, and duration of exercise training be modulated to achieve a weekly energy expenditure of between 14 and 20 kilocalories per kilogram of body weight. Although aerobic activities should be emphasized, muscle strengthening and flexibility exercises should also be incorporated into the training program in order to promote musculoskeletal health.

Coronary Disease↗
PubMed1990

Flow-through particles for the high-performance liquid chromatographic separation of biomolecules: perfusion chromatography.

This paper reports a new technique for reducing resistance to stagnant mobile phase mass transfer without sacrificing high adsorbent capacity or necessitating extremely high pressure operation. The technique involves the flow of liquid through a porous chromatographic particle, and has thus been termed "perfusion chromatography". This is accomplished with 6000-8000 A pores which transect the particle. Data from electron microscopy, column efficiency, frontal analysis and theoretical modelling all suggest that mobile phase will flow through these large pores. In this manner, solutes enter the interior of the particles through a combination of convective and diffusional transport, with convection dominating for Peclet numbers greater than one. The implications of flow through particles on bandspreading, resolution and dynamic loading capacity are examined. It is shown that the rate of solute transport is strongly coupled to mobile phase velocity such that bandspreading, resolution of proteins and dynamic loading capacity are unaffected by increases in mobile phase velocity up to several thousand centimeters per hour. The surface area of this very large-pore diameter material is enhanced by using a network of smaller, 500-1500 A interconnecting pores between the throughpores. Scanning electron micrographs show that the pore network is continuous and that no point in the matrix is more than 5000-10,000 A from a through-pore. As a consequence, diffusional path lengths are minimized and the large porous particles take on the transport characteristics of much smaller particles but with a fraction of the pressure drop. Capacity and resolution studies show that these materials bind and separate an amount of protein equivalent to that of conventional high-performance liquid chromatography as well as low performance agarose-based media at greater than 10-100 times higher mobile phase velocity with no loss in resolution.

Chromatography, High Pressure Liquid↗
PubMed1990

An overview of continuous protein purification processes.

As the sphere of influence of recombinant technology moves away from the laboratory bench, towards product commercialization, development of manufacturing and large scale process technology is becoming a major challenge and determinant for commercial success. The challenge is particularly acute for protein purification process development where protein purification costs tend to dominate overall process economics. The primary objective for process scale purification is to minimize cost for a purified product which meets specifications. Continuous processes may be used to facilitate achievement of the overall objectives. This review critically examines the use of continuous processing for protein purification and recovery operations. The processes have been divided into three general areas: adsorptive and chromatographic, electrophoretic, and extractive. Consideration is given to the operational advantages and limitations of the reviewed processes.

Journal Article↗
PubMed1990

Effect of intrinsic sympathomimetic activity on the ability of hypertensive patients to derive a cardiorespiratory training effect during chronic beta-blockade.

The effect of intrinsic sympathomimetic activity (ISA) on the ability of patients with high blood pressure (BP) to derive a cardiorespiratory training effect during long-term beta-blocker therapy was studied. Fifty sedentary hypertensive subjects were randomly assigned to propranolol (n = 23) or pindolol (n = 27) therapy for a 22 week double-blind parallel study. Over the first 2 weeks, during which subjects remained sedentary, drug doses were titrated to produce equipotent, clinically significant BP reductions. Subjects subsequently continued drug therapy and completed 20 weeks of exercise training. Although pindolol tended to preserve submaximal exercise heart rates to a greater degree than propranolol, the initial 2 weeks of drug therapy resulted in equivalent reductions in maximal oxygen uptake with propranolol (6% reduction) and pindolol (8% reduction). Likewise, 20 weeks of training induced similar, statistically significant (P = .0001) increases in maximal oxygen uptake during propranolol (10% increase) and pindolol (11% increase) treatment. We therefore conclude that ISA does not confer any advantage to patients with high BP who receive chronic beta-blocker therapy and wish to improve their cardiorespiratory fitness by participating in exercise training.

Adrenergic beta-Antagonists↗
PubMed1990

Effect of a high carbohydrate diet on core temperature during prolonged exercise.

This study compared the effects of a high-carbohydrate and a mixed diet on core temperature responses to prolonged exercise in six male competitive cyclists (age = 22.2 +/- 1.9 years). This study, the first to investigate the effect of a high-carbohydrate diet on exercise core temperature in humans, therefore suggests that three days of increased dietary carbohydrate intakes do not evoke any deleterious thermoregulatory responses during prolonged submaximal exercise.

Adult↗
PubMed1990

Exercise and mild essential hypertension. Recommendations for adults.

Chronic essential hypertension is a major public health problem afflicting an estimated 15 to 30% of persons from most Western industrialised countries. Persons with mild hypertension (diastolic blood pressure between 90 and 104mm Hg and/or systolic blood pressure between 140 and 159mm Hg) represent the overwhelming majority of hypertensive individuals in the general population. The achievement of long term blood pressure control in these individuals is of central strategic concern in the prevention of hypertension-related morbidity and mortality. Epidemiological studies suggest that regular participation in physical activity may be beneficial in preventing hypertension. The findings of epidemiological studies are supported by a recent meta-analysis of 25 longitudinal aerobic training studies, in which the average sample-size-weighted reductions in resting systolic and diastolic blood pressures were 10.8mm Hg and 8.2mm Hg, respectively. Moreover, preliminary analyses from our centre suggest that cardiorespiratory fitness and, by inference, aerobic exercise training may be of benefit in reducing mortality rates in hypertensive patients. When compiling an exercise prescription with the intention of reducing an elevated blood pressure and attenuating the risk for coronary artery disease, several factors must be considered in order to optimise the likelihood of a safe and effective response. Specifically, the 5 basic components of the exercise prescription for patients with mild hypertension are safety aspects, the type of exercise to be performed, and the frequency, intensity and duration of exercise training. For those patients who require pharmacotherapy, the interaction between the specific antihypertensive agent and exercise responses must also be considered. We recommend that aerobic exercise training be performed at an intensity corresponding to 60 to 85% of the maximal heart rate and that the duration and frequency be modulated to achieve a weekly energy expenditure of between 14 and 20 kcal/kg of bodyweight.

Adult↗
PubMed1990

Optimization and simulation of continuous affinity-recycle extraction (care).

Simulation and optimization of continuous affinity recycle extraction (CARE), a protein purification unit operation based on protein adsorption to solid phase adsorbents, is described in this paper. Rather than packing conventional adsorbent particles in a fixed bed (column), solid/liquid contact is carried out in well-mixed reactors. Continuous operation is achieved by recirculation of the adsorbent particles between two or more contactors. The feasibility of this purification scheme was established with the recovery and isolation of the enzyme beta-galactosidase from E.coli, using the affinity support PABTG/Agarose. A mathematical model describing system performance was developed. The mathematical model was used to optimize several facets of the system design and operation. The base two-stage contractor design was modified by the addition of an intermediate wash stage as well as the incorporation of multiple adsorption stages. These design modifications serve to increase purification, concentration and recovery while utilizing the same amount of adsorbent. The methodology for defining and optimizing objective functions was developed and experimentally validated. Finally, optimum system start-up protocols, minimizing the time required to reach steady-state operation, were developed and experimentally validated. The impact of early introduction of adsorptive purification in a downstream processing sequence, with CARE, was evaluated and is described. Through the early introduction of a highly specific adsorptive step, significant purification is achieved simultaneously with clarification and concentration. In addition, purification performance in CARE was contrasted with that achievable in conventional column chromatography.

Chromatography, Affinity↗
PubMed1990

Effect of a practical neck cooling device on core temperature during exercise.

Previous studies have documented the effectiveness of combined head and neck cooling in reducing thermal stress during exercise. However, these studies investigated low intensity exercise and devices that are not practical for use on a widespread basis during recreational exercise. In the present study, we investigated the effect of a commercially available, practical neck cooling device on core temperature during strenuous exercise. In a randomized cross-over fashion, 10 male endurance athletes (age 29 +/- 2 yr) performed a 45-min submaximal run (Borg rating of perceived exertion approximately 15) at a constant speed, with and without neck cooling. Runs were conducted on an indoor track, where the ambient temperature was maintained at approximately 21 degrees C dry bulb and approximately 17 degrees C wet bulb. Exercise heart rates and subjective perception of effort were not significantly modified by neck cooling. In contrast, rectal temperature rises (by 0.21 degrees C or 9.5%, P less than 0.02) and sweat rates (by 92 ml.h-1 or 6.4%, P less than 0.02) were reduced by neck cooling. Our study therefore concludes that this practical neck cooling device is capable of inducing reductions in thermal stress during strenuous exercise that, although numerically small, are in a direction of potential benefit.

Adult↗
PubMed1990

An empirical evaluation of the ACSM guidelines for exercise testing.

The American College of Sports Medicine (ACSM) has published exercise guidelines identifying individuals who should have an exercise test prior to clearance for exercise participation and whether a physician should supervise the test. These age and health status criteria (apparently healthy, higher risk, and diseased) were developed using clinical judgement and opinion rather than empirical data. Thus, there is a need to validate the recommendations with actual data. We studied the results of 24,332 maximal treadmill tests in men (n = 18,076) and women (n = 5,626) as they associated with age and baseline health status. Commonly accepted criteria for abnormal exercise tests were used (i.e., 1 mm ST segment depression at 0.08 s, systolic blood pressure drop with exercise, complex ventricular ectopy, etc.). There were 895 and 183 abnormal exercise tests in men and women, respectively. Men and women who were apparently healthy had lower abnormality rates per 1,000 tests than those considered to be at higher risk for coronary heart disease and those who had preexisting disease. Further, when those who were at higher risk were considered, those men with only one risk factor had significantly lower abnormality rates than did men with more than one risk factor (95% confidence intervals (CI) per 1,000 tests: 1 risk factor = 36.1-46.4; greater than 1 risk factor = 47.5-62.5). Abnormality rates in women with 1 risk factor were also lower than those in their peers with greater than 1 risk factor, but not statistically so (95% CI per 1,000 tests: 1 risk factor = 24.9-43.0; greater than 1 risk factor = 25.3-54.4).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1989

Effect of opioid antagonism on the ability to tolerate maximal anaerobic exercise.

The effect of naloxone-induced endogenous opioid antagonism on the ability to tolerate maximal anaerobic exercise was studied in 11 young men. Volume-matched infusions of placebo or naloxone 4 mg were administered in a randomised double-blind crossover trial before a 30-second maximal cycle ergometer test (Wingate test). Mechanical power output was calculated for each 5 seconds of cycling and expressed as peak power (highest output during any 5-second period), average power (average output during the 30 seconds of cycling) and power decline (difference between peak power and the lowest 5-second power output divided by time). Naloxone did not significantly modify (P greater than 0.05) any index of anaerobic power. Similarly, the perception of leg pain during exercise was similar with placebo and naloxone. Therefore, insofar as naloxone may be used to examine the functional role of opioid-mediated mechanisms, these findings are not tenable with the hypothesis that endogenous opioids modulate the ability to tolerate maximal anaerobic exercise.

Adult↗
PubMed1988

Effect of opioid antagonism on esophageal temperature during exercise.

The effect of naloxone-induced endogenous opioid antagonism on core temperature control during exercise was studied in 8 competitive cyclists. Volume-matched infusions of placebo or 2 mg of naloxone were administered, in a randomized double-blind crossover fashion, prior to maximal graded cycle ergometer exercise testing. Esophageal (Tes), rectal (Tre) and oral (Tor) temperatures were measured before and after exercise, and Tes was continuously measured during exercise. Cardiorespiratory responses and maximal exercise duration were unaffected by naloxone. Naloxone did not significantly modify the Tes response or the highest Tre and Tor elicited by exercise testing. The rise in Tes (placebo: 2.2 +/- 0.4 degrees C; naloxone: 2.1 +/- 0.4 degrees C) and Tre (placebo: 1.1 +/- 0.2 degree C; naloxone: 0.9 +/- 0.4 degree C) was significant (p less than 0.001) with and without naloxone, whereas the rise in Tor was significant (p less than 0.05) with placebo (0.5 +/- 0.5 degree C) but not with naloxone (0 +/- 0.8 degree C, p greater than 0.5). These data indicate that although 2 mg of naloxone might alter heat exchange in the oral cavity during exercise, it does not modify the actual core temperature response. Therefore, insofar as this dosage of naloxone may be used to examine the functional role of opioid-mediated mechanisms, our findings are not tenable with the hypothesis that endogenous opioids play a role in maintenance of thermal homeostasis during exercise.

Adult↗