COMPARISON OF THE CIRCULATORY RESPONSE TO UPRIGHT EXERCISE IN 25 "NORMAL" MEN AND 9 DISTANCE RUNNERS

Cardiopulmonary parameters and organ blood flows for workers expressed in terms of VO2 for use in physiologically based toxicokinetic modeling

Minute ventilation rates (VE), alveolar ventilation rates (VA), cardiac outputs (Q), liver blood flow (LBF) and kidneys blood flows (KBF) for physiologically based toxicokinetic modeling and occupational health risk assessment in active workers have apparently not been determined. Minute energy expenditure rates (E) and oxygen consumption rates (VO₂) in workers during exertions and their aggregate daytime activities are obtained by using open-circuit wearable devices for indirect calorimetry measurements and the doubly labeled water method respectively. Hundreds of E (in kcal/min) and VO₂ (in L of O₂/min) were previously reported for workers. The oxygen uptake factors of 0.2059 ± 0.0019 and 0.2057 ± 0.0018 L of O₂/kcal during postprandial and fasting phases respectively enabled conversion of E into VO₂. Equations determined in this study based upon more than 25 000 published measurements enable the calculation of 15 parameters in the same worker only by using the VO₂ reflecting workload. These parameters, notably VE, VA, VE/VO₂ VA/Q, Q, LBF and KBF were found to be interrelated. Altering one of these changes the order of magnitude of the others. Q, LBF and KBF decrease when supine adults at rest switch to an upright position. This effect of gravity diminished when VO₂ increased. The fall in LBF and KBF during exertion might enhance muscle blood flow as reported previously. Taken together these equations and data may improve the accuracy of physiologically based toxicokinetic modeling as well as occupational health assessment studies in active workers exposed to xenobiotics.List of main abbreviations: AVOD: arterioveinous oxygen content difference.BMI: body mass index (in kg/m²).BSA: body surface area (in m²).BTPS: body temperature and saturated with water vapor.Bw: body weight (in kg).E: minute energy expenditure rate (in kcal/min).F_GE: organ blood flow factor for the gravitational effect on blood circulation.H: oxygen uptake factor, volume of oxygen (at STPD) consumed to produce 1 kcal of energy expended.KBF: kidneys blood flow (in ml/min).LBF: liver blood flow (in ml/min).P_BF: liver or kidneys blood flows expressed in terms of percentages (in %) of Q_{sup C} values: namely P_BF = (LBF or KBF/Q_{sup C}) x 100.Q: cardiac output (in L/min or ml/min).Q_{sup C:} cardiac output for the cohort of males or females in supination (in ml/min).STPD: standard temperature and pressure, dry air.sup: values measured when adults are in the supine position.up: values measured when adults are in the upright position.VDphys: physiological dead space at BTPS (in L).VT: tidal volume at BTPS (in L).VA: alveolar ventilation rate at BTPS (in L/min).VA/Q: ventilation-perfusion ratio (unitless).VE: minute ventilation rate at BTPS (in L/min).VO₂: oxygen consumption rate (i.e. the oxygen uptake) at STPD (in L/min).VQ: ventilatory equivalent for VO₂ (VE at BTPS /VO₂ at STPD).

Increased aortic stiffness and elevated blood pressure in response to exercise in adult survivors of prematurity

Objectives

Adults born prematurely have an increased risk of early heart failure. The impact of prematurity on left and right ventricular function has been well documented, but little is known about the impact on the systemic vasculature. The goals of this study were to measure aortic stiffness and the blood pressure response to physiological stressors; in particular, normoxic and hypoxic exercise.

Methods

Preterm participants (n = 10) were recruited from the Newborn Lung Project Cohort and matched with term‐born, age‐matched subjects (n = 12). Aortic pulse wave velocity was derived from the brachial arterial waveform and the heart rate and blood pressure responses to incremental exercise in normoxia (21% O₂) or hypoxia (12% O₂) were evaluated.

Results

Aortic pulse wave velocity was higher in the preterm groups. Additionally, heart rate, systolic blood pressure, and pulse pressure were higher throughout the normoxic exercise bout, consistent with higher conduit artery stiffness. Hypoxic exercise caused a decline in diastolic pressure in this group, but not in term‐born controls.

Conclusions

In this first report of the blood pressure response to exercise in adults born prematurely, we found exercise‐induced hypertension relative to a term‐born control group that is associated with increased large artery stiffness. These experiments performed in hypoxia reveal abnormalities in vascular function in adult survivors of prematurity that may further deteriorate as this population ages.

Left ventricular response to dynamic exercise in young cyclists

PURPOSE

The purpose of this study was to compare cardiac physiological and dimensional responses to exercise in highly trained young male cyclists (mean age 13.7 +/- 1.0 yr) with those of nontrained boys.

METHODS

Ventricular systolic and diastolic dimensions were measured by two-dimensional echocardiography, and stroke volume was estimated by Doppler echocardiography during a progressive maximal upright cycle test.

RESULTS

At rest, the cyclists demonstrated larger left ventricular dimensions relative to body size than the nonathletes. Maximal stroke index and cardiac index were significantly greater in the cyclists. The pattern of stroke volume response to exercise was similar in the two groups, with an early rise and then plateau to exhaustion. Left ventricular diastolic dimension increased slightly at onset of exercise and then gradually declined as workload increased in both groups.

CONCLUSION

Factors responsible for the greater maximal stroke volume in young endurance athletes involve those variables that contribute to resting left ventricular diastolic filling (preload).

Cardiac responses to exercise in competitive child cyclists

PURPOSE

Cardiovascular responses to exercise in highly trained child endurance athletes have not been well-defined. This study compared hemodynamic responses with progressive cycle exercise in seven competitive child cyclists (mean age 11.9 yr) compared with 39 age-matched untrained boys.

METHODS

Doppler echocardiography and gas exchange variables were utilized to assess cardiovascular changes during submaximal and maximal exercise.

RESULTS

Mean VO2max was 60.0 (+/-6.0) and 47.0 (+/-5.8) mL x kg(-1) x min(-1) in the cyclists and nonathletes, respectively. At rest and maximal exercise, the cyclists demonstrated greater stroke index than the untrained subjects (resting mean 59 (+/-6) vs 44 (+/-9) mL x m(-2); maximal mean 76 (+/-6) vs 60 (+/-11) mL x m(-2)), but the ratio of maximal:rest stroke index was similar in both groups (1.31 for cyclists, 1.41 for nonathletes). Both groups showed a plateau in stroke volume beyond low-intensity work levels. No significant difference was observed in maximal arteriovenous oxygen difference.

CONCLUSIONS

These findings indicate that 1) maximal stroke volume is the critical determinant of the high VO2max in child cyclists and 2) factors that influence resting stroke volume are important in defining VO2max differences between child endurance athletes and untrained boys.

Cardiac responses to progressive exercise in normal children: a synthesis

The cardiac responses to exercise are influenced by a complex interplay of changes in diastolic filling, intrinsic myocardial contractility, heart rate, and ventricular afterload.

PURPOSE

To characterize these responses in children, findings are reported from two studies utilizing Doppler echocardiographic assessment of stroke volume and cardiac output during maximal upright and semisupine cycle exercise.

METHODS

In study 1, stroke volume, heart rate, and peak aortic velocity were assessed during upright cycle exercise to exhaustion in 39 sixth-grade boys. In study 2, similar methods were used to examine cardiac responses to semisupine exercise with measurement of left ventricular dimensions by two-dimensional echocardiography.

RESULTS

The findings support patterns similar to that previously described in adults, with an initial rise in stroke volume reaching a plateau at mild-moderate exercise intensities.

CONCLUSIONS

The observations in these two studies also suggest 1) peripheral vasodilatation plays an important role in the early rise in stroke volume, 2) increasing heart rate acts to maintain a stable stroke volume and left ventricular diastolic dimension at high workloads, and 3) improvements in contractility serve to maintain stroke volume as the systolic ejection period shortens.

Cardiac responses to maximal upright cycle exercise in healthy boys and men

Previous investigations have indicated that children demonstrate a lower cardiac output at a given oxygen uptake during exercise compared with adults. This study compared cardiac responses with maximal upright cycle exercise in 15 boys (mean age 10.9 yr) and 16 men (mean age 30.7 yr) to determine whether this observation reflects differences in size or age-related influences on myocardial function. Stroke volume, aortic peak velocity, and systolic ejection time were measured to peak exercise in all subjects using Doppler ultrasound techniques. No significant differences were observed in resting, submaximal, or peak mean values for these variables relative to body size between the boys and men. Average values for peak stroke index, cardiac index, and peak aortic velocity were 59 (+/-11) mL.m-2, 11.33 (+/-2.32) L.min-1.m-2, and 152 (+/-30) cm.s-1, respectively, for the boys. Respective values for the men were 61 (+/-14) mL.m-2, 11.08 (+/-2.52) L.min-1.m-2, and 144 (+/-24) cm.s-1 (P > 0.05). This study failed to demonstrate evidence of impaired cardiac responses to maximal exercise in prepubertal boys compared with that in adult males.

Prevalence of feline immunodeficiency virus in submissions of feline serum to a diagnostic laboratory in Atlantic Canada

The purpose of this project was to identify the prevalence of feline immunodeficiency virus (FIV) in the Atlantic region of Canada, and to determine possible associations between FIV serological status and breed, sex, and age. Feline serum samples (671) submitted to the Prince Edward Island Diagnostic Services - Atlantic Veterinary College laboratory between January 1, 1988 and July 30, 1989 were considered eligible for this study. The majority of samples originated from Prince Edward Island (607). Testing was performed in duplicate using commercial 96-well enzyme-linked immunosorbent assay test kits for FIV antibody. Results included a seropositive rate of 7.6% for all submissions. Mean age of FIV-seropositive cats was eight years. There was an increasing risk of FIV-seropositive status associated with age. Prevalence of FIV among intact males was significantly higher (odds ratio = 2.59) than other gender categories. The principal conclusion of this study was that FIV is present in cats of the Atlantic provinces, and that its associations and prevalence are consistent with those found in other North American epidemiological studies.

Heritability of cardiac size: an echocardiographic and electrocardiographic study of monozygotic and dizygotic twins

Because of the uncertainty as to the extent to which cardiac size is determined by exercise training vs genetic endowment, this study investigated familial (genetic plus common family environment) vs nonfamilial influences on cardiac size. College-age monozygotic twins (group 1, 31 sets), dizygotic twins (group 2, 10 sets), siblings of like sex (group 3, six sets), and nonrelated subjects (group 4, 15 sets) underwent echocardiographic and electrocardiographic tests, measurement of maximum oxygen uptake (VO2max), and evaluation of pulmonary and body composition; mean intrapair differences of the four groups were compared. Mean intrapair differences in cardiac size varied as much for subjects in group 1 as for those in groups 2 and 3. However, subjects in groups 1, 2, and 3 had less variation (p less than .05) than those in group 4. After the initial testing, 14 pairs of monozygotic twins, five sets of dizygotic twins, and six sets of siblings underwent 14 weeks of exercise training (both members participated) and all tests were repeated. After exercise training, subjects in group 1 still had as much intrapair variability in cardiac size as those in groups 2 and 3. The data suggest cultural familial influences are more important in determining cardiac size than nonfamilial influences or even genetic influences alone.

Blood volume expansion among blacks: an hypothesis

Black persons are believed to have developed in a tropical environment and an expanded blood volume would have facilitated adaptation to such an environment. Throughout most of the first half of the life cycle blacks have slower heart rates than whites, and several lines of evidence suggest that heart rate is inversely related to blood volume. Review of blood volume studies in normotensive whites and normotensive blacks does not permit any conclusion concerning the blood volume hypothesis. Among patients with hypertension results of blood volume studies are inconsistent, but indirect evidence suggests that black patients with hypertension have greater plasma volume expansion than white patients with hypertension.

Noninvasive evaluation of exercise training in college-age men

The purpose of this study was to assess noninvasively the effects of intense aerobic training on cardiac structure and function in a group of healthy, college-age men (25 experimental and 11 control, mean age 22 years). Echocardiographic, electrocardiographic (ECG), and fitness measurements were obtained before and after a 3-month endurance training program and compared with similar measurements obtained in nonexercising subjects. The supervised training program consisted of 50-minute jogging sessions 5 days a week at 85% of maximal heart rate. Compared with the control group, echocardiography after training showed an increase in left ventricular (LV) end-diastolic dimension (p less than 0.05). LV posterobasal wall thickness, septal wall thickness and ejection fraction did not change significantly. ECG measurements revealed a decrease in resting heart rate (p less than 0.05) and an increase in R-wave voltage in leads V5 and V6 (p less than 0.01). The measured maximal oxygen consumption increased by 16% (p less than 0.001). These data indicate that intense aerobic training in college-age men results in a significant increase in resting LV end-diastolic dimension and volume. The increase in maximal stroke volume associated with exercise training may be partially explained by these changes in cardiac dimensions.

Approximate normal standards of maximal cardiac output during upright exercise in women

The observed normal ranges of age- and weight-adjusted maximal oxygen uptake and age-adjusted maximal heart rate during upright exercise using the Bruce protocol are shown for 104 asymptomatic women. Cardiac output was measured during upright exercise in 11 normal women with the use of the direct Fick method. On the basis of the relation between oxygen uptake and cardiac output in these 11 women, the cardiac output and stroke volume were estimated by regression in the 104 women to provide normal ranges of age-adjusted values for cardiac output and stroke volume. The potential usefulness of these age-adjusted normal ranges is illustrated by analysis of 21 observations of maximal cardiac output in 16 women with heart disease.

Hemodynamics of essential hypertension in young subjects

Cardiac output was determined in 42 young essential hypertensives (15 to 25 yrs); values ranged from 3.86 to 10.30 L./minute. These differences were not related to magnitude of volemia. Correlation of output to weekly blood pressure average (BPav) was not significant; its relationship to intraarterial pressure (BPia) was not significant in 21 patients aged 20 to 25 and of borderline significance in 13 aged 15 to 19. Blood pressure changes associated with the study (BPia--BPav) were also not consistently related to cardiac output. Six patients had systolic hypertension; only one had elevated stroke volume. These results outline as complex a picture in young essential hypertensives as in older subjects.

Heart rate and ventilation in relation to venous [K+], osmolality, pH, PCO2, PO2, [orthophosphate], and [lactate] at transition from rest to exercise in athletes and non-athletes

To evaluate to what metabolci event in contracting muscles heart rate (HR) and VE are related, time courses of femoral and cubital venous [K=], osomolality (OSM), pH, POC2, PO2, [lactate], and [orthophosphate] ([Pi]) at onset of exercise were studied in athletes (TR) and non-athletes (UT) and compared to time courses of HR and VE. During ischaemic work with the calf muscles it could be shown that most of these blood constituents were only released from contracting muscles. Thus their time courses reflected the metabolic events in working muscles being not essentially disturbed by non-working parts of the body. Ischaemic work induced, however, substantial increases of HR and VE. In the course of non-ischaemic bicycle work HR and VE rose more rapidly in TR than in UT but were lower in TR during the steady state. During non-ischaemic work only the increased of femoral venous [K=1 closely mimicked the cardiorespiratory transients in TR as well as in UT. None of the other femoral venous substances showed such a rapid change or such typical variations between TR and UT. Cubital venous [K=1 and [Pi] approached femoral venous concentrations only in second minute after start whereas pH, PCO2, and OSM increased mainly in venous outflow from contracting muscles. PO2 decreased in femoral venous blood of TR and UT, but in cubital venous blood it remained depressed only in UT. It was discussed that the cardiorespiratory adjustment during the initial stages of work was related to K+ release in working muscles and not to O2 consuming or H+ producing processes, nor to release of Pi or increase of OSM.

Comparative exercise-cardiorespiratory performance of normal men in the third, fourth, and fifth decades of life

The circulatory and respiratory responses to five levels of treadmill exercise were recorded for 75 normal males divided equally in the age groups 20 to 29, 30 to 39, and 40 to 49 years. Parameters studied included heart rate, cardiac output, stroke volume, intra-arterial blood pressure, minute ventilatory volume, oxygen uptake, and carbon dioxide elimination. Values for peripheral vascular resistance, left ventricular work, and stroke work indices were calculated. Intergroup and intragroup differences were analyzed by modified covariance technique using oxygen uptake per square meter of body surface area as the concomitant variable reflecting a specific midrange work level. Significant differences were observed between groups in cardiac output, stroke volume, systolic, diastolic, and mean arterial blood pressure as well as pressure-related variables with regard to absolute values and trend over the exercise spectrum. The results indicate that normal untrained males in the fourth and fifth decades of life react to moderate and heavy upright exercise with statistically significant systemic pressure elevations as compared to 20-year-olds. A tendency toward initially high cardiac output and stroke volume during light exercise was observed in the older men. Relatively small subsequent increments in cardiac output with resultant low absolute values during heavier work were also characteristic for this group as reflected in their decreasing stroke output at submaximal loads.

Hemodynamic Consequences of Physical Training after Myocardial Infarction

The hemodynamic effects of physical training, three periods weekly for 1 to 2 months, after myocardial infarction were assessed in seven patients by cardiac catheterization at rest and during exercise. The training was followed by reduction in exercise heart rate and tension-time index as determined from brachial artery pressures. Stroke volume during exercise was enhanced. No significant change occurred in the heart volume. Left ventricular function was improved, and a significant increase in the rate of rise of right ventricular pressure occurred. These were interpreted as indicating myocardial hypertrophy, which probably through reduced compliance also accounted for increased ventricular filling pressures. Lactate in arterial blood was reduced during exercise without any change in the arteriovenous oxygen difference. Small and not significant changes occurred in vital capacity, forced expiratory volume, fasting blood sugar, and serum lipids.

Concomitant with the hemodynamic changes exercise tolerance was improved. The data support the thesis that in some patients increased physical activity after myocardial infarction is followed by beneficial hemodynamic effects on the heart and possibly by increased coronary blood flow. The need for proper selection of patients and close medical supervision during training is illustrated and emphasized.

Hemodynamic responses to graded treadmill exercise in young untreated labile hypertensive patients

Twenty labile hypertensive patients and their age-matched controls were studied at rest and during five levels of treadmill exercise. Intra-arterial blood pressure, cardiac output, and various aspects of the pressure pulse wave were analyzed under these conditions. Exercise provoked diastolic hypertension in 30% of the patient group. Mean group pressure responses demonstrated an almost constant differential through all phases of the study. The validity of a previously suggested classification of labile hypertensive subjects based on resting cardiac output estimations is questioned. A differentiation of modes of adjustment to an increased pressure load was suggested from exercise measurements of arterial ejection time. Despite numerous factors affecting the measurement, first derivative of the peripheral arterial pulse correlated well with indices of ejection time and mean rate of left ventricular ejection.