The influence of age and gender on left ventricular response to supine exercise in asymptomatic normal subjects

Women at Altitude: Sex-Related Physiological Responses to Exercise in Hypoxia

Sex differences in physiological responses to various stressors, including exercise, have been well documented. However, the specific impact of these differences on exposure to hypoxia, both at rest and during exercise, has remained underexplored. Many studies on the physiological responses to hypoxia have either excluded women or included only a limited number without analyzing sex-related differences. To address this gap, this comprehensive review conducted an extensive literature search to examine changes in physiological functions related to oxygen transport and consumption in hypoxic conditions. The review encompasses various aspects, including ventilatory responses, cardiovascular adjustments, hematological alterations, muscle metabolism shifts, and autonomic function modifications. Furthermore, it delves into the influence of sex hormones, which evolve throughout life, encompassing considerations related to the menstrual cycle and menopause. Among these physiological functions, the ventilatory response to exercise emerges as one of the most sex-sensitive factors that may modify reactions to hypoxia. While no significant sex-based differences were observed in cardiac hemodynamic changes during hypoxia, there is evidence of greater vascular reactivity in women, particularly at rest or when combined with exercise. Consequently, a diffusive mechanism appears to be implicated in sex-related variations in responses to hypoxia. Despite well-established sex disparities in hematological parameters, both acute and chronic hematological responses to hypoxia do not seem to differ significantly between sexes. However, it is important to note that these responses are sensitive to fluctuations in sex hormones, and further investigation is needed to elucidate the impact of the menstrual cycle and menopause on physiological responses to hypoxia.

Effects of aging and endurance exercise training on cardiorespiratory fitness and cardiac structure and function in healthy midlife and older women

Cardiovascular disease (CVD) remains the leading cause of morbidity and mortality in women in developed societies. Unfavorable structural and functional adaptations within the heart and central blood vessels with sedentary aging in women can act as the substrate for the development of debilitating CVD conditions such as heart failure with preserved ejection fraction (HFpEF). The large decline in cardiorespiratory fitness, as indicated by maximal or peak oxygen uptake (V̇o2max and V̇o2peak, respectively), that occurs in women as they age significantly affects their health and chronic disease status, as well as the risk of cardiovascular and all-cause mortality. Midlife and older women who have performed structured endurance exercise training for several years or decades of their adult lives exhibit a V̇o2max and cardiac and vascular structure and function that are on par or even superior to much younger sedentary women. Therefore, regular endurance exercise training appears to be an effective preventative strategy for mitigating the adverse physiological cardiovascular adaptations associated with sedentary aging in women. Herein, we narratively describe the aging and short- and long-term endurance exercise training adaptations in V̇o2max, cardiac structure, and left ventricular systolic and diastolic function at rest and exercise in midlife and older women. The role of circulating estrogens on cardiac structure and function is described for consideration in the timing of exercise interventions to maximize beneficial adaptations. Current research gaps and potential areas for future investigation to advance our understanding in this critical knowledge area are highlighted.

Comparison Between Treadmill and Bicycle Ergometer Exercises in Terms of Safety of Cardiopulmonary Exercise Testing in Patients With Coronary Heart Disease

Background

Cardiopulmonary exercise testing (CPET) is used widely in the diagnosis, exercise therapy, and prognosis evaluation of patients with coronary heart disease (CHD). The current guideline for CPET does not provide any specific recommendations for cardiovascular (CV) safety on exercise stimulation mode, including bicycle ergometer, treadmill, and total body workout equipment.

Objective

The aim of this study was to explore the effects of different exercise stimulation modes on the occurrence of safety events during CPET in patients with CHD.

Methods

A total of 10,538 CPETs, including 5,674 performed using treadmill exercise and 4,864 performed using bicycle ergometer exercise at Peking University Third Hospital, were analyzed retrospectively. The incidences of CV events and serious adverse events during CPET were compared between the two exercise groups.

Results

Cardiovascular events in enrolled patients occurred during 355 CPETs (3.4%), including 2 cases of adverse events (0.019%), both in the treadmill group. The incidences of overall events [235 (4.1%) vs. 120 (2.5%), P < 0.001], premature ventricular contractions (PVCs) [121 (2.1%) vs. 63 (1.3%), P = 0.001], angina pectoris [45 (0.8%) vs. 5 (0.1%), P < 0.001], and ventricular tachycardia (VT) [32 (0.6%) vs. 14 (0.3%), P = 0.032] were significantly higher in the treadmill group compared with the bicycle ergometer group. No significant difference was observed in the incidence of bradyarrhythmia and atrial arrhythmia between the two groups. Logistic regression analysis showed that the occurrence of overall CV events (P < 0.001), PVCs (P = 0.007), angina pectoris (P < 0.001), and VT (P = 0.008) was independently associated with the stimulation method of treadmill exercise. In male subjects, the occurrence of overall CV events, PVCs, angina pectoris, and VT were independently associated with treadmill exercise, while only the overall CV events and angina pectoris were independently associated with treadmill exercise in female subjects.

Conclusion

In comparison with treadmill exercise, bicycle ergometer exercise appears to be a safer exercise stimulation mode for CPET in patients with CHD.

Gender Differences in Hemodynamic Regulation and Cardiovascular Adaptations to Dynamic Exercise

Exercise is a major challenge for cardiovascular apparatus since it recruits chronotropic, inotropic, pre-load, and afterload reserves. Regular physical training induces several physiological adaptations leading to an increase in both cardiac volume and mass. It appears that several gender-related physiological and morphological differences exist in the cardiovascular adjustments and adaptations to dynamic exercise in humans. In this respect, gender may be important in determining these adjustments and adaptations to dynamic exercise due to genetic, endocrine, and body composition differences between sexes. Females seem to have a reduced vasoconstriction and a lower vascular resistance in comparison to males, especially after exercise. Significant differences exist also in the cardiovascular adaptations to physical training, with trained women showing smaller cardiac volume and wall thickness compared with male athletes. In this review, we summarize these differences.

Sex differences in cardiovascular function during submaximal exercise in humans

Differences in cardiovascular function between sexes have been documented at rest and maximal exercise. The purpose of this study was to examine the sex differences in cardiovascular function during submaximal constant-load exercise, which is not well understood.

Thirty-one male and 33 female subjects completed nine minutes moderate and nine minutes vigorous intensity submaximal exercise (40 and 75% of peak watts determined by maximal exercise test). Measurements included: intra-arterial blood pressure (SBP and DBP), cardiac index (Q_I), heart rate (HR), oxygen consumption (VO₂) and arterial catecholamines (epinephrine = EPI and norepinephrine = NE), and blood gases. Mean arterial pressure (MAP), stroke volume index (SV_I), systemic vascular resistance index (SVR_I), arterial oxygen content (CaO₂), arterial to venous O₂ difference (AVO₂) and systemic oxygen transport (SOT) were calculated.

At rest and during submaximal exercise Q_I, SV_I, SBP, MAP, NE, CaO₂, and SOT were lower in females compared to males. VO₂, AVO₂, EPI were lower in females throughout exercise. When corrected for wattage, females had a higher Q, HR, SV, VO₂ and AVO₂ despite lower energy expenditure and higher mechanical efficiency.

This study demonstrates sex differences in the cardiovascular response to constant-load submaximal exercise. Specifically, females presented limitations in cardiac performance in which they are unable to compensate for reductions in stroke volume through increases in HR, potentially a consequence of a female’s blunted sympathetic response and higher vasodilatory state. Females demonstrated greater cardiac work needed to meet the same external work demand, and relied on increased peripheral oxygen extraction, lower energy expenditure and improvements in mechanical efficiency as compensatory mechanisms.

Sex influence on myocardial function with exercise in adolescents

OBJECTIVES

Ventricular systolic functional response to exercise has been reported to be superior in adult men compared to women. This study explored myocardial responses to maximal upright progressive exercise in late pubertal males and females.

METHODS

Doppler echocardiographic techniques were utilized to estimate myocardial function response to a bout of progressive cycle exercise.

RESULTS

Systolic functional capacity, as indicated by ejection rate (12.5 +/- 2.8 and 13.1 +/- 1.0 [x10(-2)] ml s(-1) cm(-2) for boys and girls, respectively) and peak aortic velocity (208 +/- 45 and 196 +/- 12 cm s(-1), respectively) at maximal exercise, did not differ between the two groups. Similarly, peak values as well as increases in transmitral pressure gradient (mitral E flow velocity), ventricular relaxation (tissue Doppler imaging E'), and left ventricular filling pressure (E/E' ratio) as estimates of diastolic function were similar in males and females.

CONCLUSIONS

This study failed to reveal qualitative or quantitative differences between adolescent boys and girls in ventricular systolic or diastolic functional responses to maximal cycle exercise.

Sex differences in mechanisms of cardiac excitation-contraction coupling in rat ventricular myocytes

Components of excitation-contraction (E-C) coupling were compared in ventricular myocytes isolated from 3-mo-old male and female rats. Ca2+ concentrations (fura-2) and cell shortening (edge detector) were measured simultaneously (37°C). Membrane potential and ionic currents were measured with microelectrodes. Action potentials were similar in male and female myocytes, but contractions were smaller and slower in females. In voltage-clamped cells, peak contractions were smaller in females than in males (5.1 ± 0.7% vs. 7.7 ± 0.8% diastolic length, P < 0.05). Similarly, Ca2+ transients were smaller in females than in males and the rate of rise of the Ca2+ transient was slower in females. Despite smaller contractions and Ca2+ transients in females, Ca2+ current density was similar in both groups. Sarcoplasmic reticulum Ca2+ content, assessed with caffeine, did not differ between the sexes. However, E-C coupling gain (rate of Ca2+ release/Ca2+ current) was smaller in females than in males (157.0 ± 15.6 vs. 338.4 ± 54.3 (nM/s)/(pA/pF), P < 0.05). To determine whether the reduced gain in female cells was due to changes in unitary Ca2+ release, spontaneous Ca2+ sparks were evaluated (fluo-4, 37°C). Spark frequencies and widths were similar in both groups, but spark amplitudes were smaller in females than in males (0.56 ± 0.01 vs. 0.64 ± 0.01 ΔF/F0, P < 0.05). Spark durations also were shorter in females than in males (full duration at half-maximum = 14.86 ± 0.17 vs. 16.25 ± 0.27 ms, P < 0.05). These observations suggest that decreases in the size and duration of Ca2+ sparks contributes to the decrease in E-C coupling gain in female myocytes. Thus, differences in cardiac contractile function arise, in part, from differences in unitary Ca2+ release between the sexes.

Evidence for sex differences in cardiovascular aging and adaptive responses to physical activity

There are considerable data addressing sex-related differences in cardiovascular system aging and disease risk/progression. Sex differences in cardiovascular aging are evident during resting conditions, exercise, and other acute physiological challenges (e.g., orthostasis). In conjunction with these sex-related differences-or perhaps even as an underlying cause-the impact of cardiorespiratory fitness and/or physical activity on the aging cardiovascular system also appears to be sex-specific. Potential mechanisms contributing to sex-related differences in cardiovascular aging and adaptability include changes in sex hormones with age as well as sex differences in baseline fitness and the dose of activity needed to elicit cardiovascular adaptations. The purpose of the present paper is thus to review the primary research regarding sex-specific plasticity of the cardiovascular system to fitness and physical activity in older adults. Specifically, the paper will (1) briefly review known sex differences in cardiovascular aging, (2) detail emerging evidence regarding observed cardiovascular outcomes in investigations of exercise and physical activity in older men versus women, (3) explore mechanisms underlying the differing adaptations to exercise and habitual activity in men versus women, and (4) discuss implications of these findings with respect to chronic disease risk and exercise prescription.

Gender differences in athlete's heart: association with 24-h blood pressure. A study of pairs in sport dancing

BACKGROUND

Long term athletic training is associated with an increase in left ventricular diastolic cavity dimensions, wall thickness, and mass. These changes are described as the "athlete's heart". In comparison to men, athletic training in women athletes is not a stimulus for substantial increase in left ventricular wall thickness. Although many variables are related to these gender differences in cardiac morphology, some factors such as 24-h blood pressure and the level of training have not been studied yet. Therefore pairs in sport dancing, in which the level of training of both partners is the same, were chosen as models in order to evaluate whether 24-h blood pressure contributes to sex-related differences in an athlete's heart.

METHODS

Fifteen pairs in the national sport dancing team and 30 control subjects (15 males, 15 females) were studied. In all subjects casual and 24-h ambulatory blood pressures, echocardiography, and maximal stress testing were performed.

RESULTS

Female in comparison to male dancers had significantly lower M-mode (P<0.004) and 2-D left ventricular mass index (P<0.001), 24-h systolic blood pressure (P<0.003), day systolic blood pressure (P<0.002), casual systolic blood pressure (P<0.025), and achieved significantly lower peak systolic blood pressure at stress testing (P<0.004). Multiple stepwise regression analysis showed that the best predictors of 2-D left ventricular mass index are maximal work load and peak exercise systolic blood pressure, 24-h systolic blood pressure, day, and casual systolic blood pressure.

CONCLUSIONS

Lower left ventricular mass index in female dancers can be partly explained by lower systolic blood pressures during 24-h and at exercise.

Influence of cardiac functional capacity on gender differences in maximal oxygen uptake in children

OBJECTIVE

To examine the role of gender differences in cardiac functional capacity in explaining higher mean values for maximal oxygen uptake (VO(2)max) in boys than in girls.

DESIGN

Comparative group exercise testing.

SETTING

Pediatric exercise testing laboratory.

SUBJECTS

Twenty-five prepubertal boys (mean [+/- SD] age, 12 +/- 0.4 years) and 24 premenarcheal girls (mean age, 11.7 +/- 0.5 years).

INTERVENTIONS

Maximal incremental upright cycle exercise.

MEASUREMENTS AND RESULTS

Mean values for VO(2)max were the following: boys, 47.2 +/- 6.1 mL/kg/min; and girls, 40.4 +/- 5.8 mL/kg/min (16.8% difference; p < 0.05). The average maximal stroke index with Doppler echocardiography was 62 +/- 9 mL/m(2) for boys and 55 +/- 9 mL/m(2) for girls (12.7% difference; p < 0.05). No significant gender differences were seen in maximal heart rate or arterial venous oxygen difference. When VO(2)max and maximal stroke volume (SV) were expressed relative to lean body mass, gender differences declined but persisted, falling to 6.2% and 5.2%, respectively.

CONCLUSIONS

These findings indicate that differences in SV as well as in body composition contribute to gender-related variations in VO(2)max during childhood. Whether this reflects small gender differences in relative heart size or dynamic factors influencing ventricular preload and contractility during exercise is unknown.

Effects of gender on the sensitivity of rat cardiac muscle to extracellular Ca2+

Experiments were designed to determine if the inotropic response to increasing buffer calcium concentration differs in male and female cardiac muscle. Left atrial and papillary muscles were isolated from hearts of 3-4-month old male and female rats, bathed in Krebs-Henseleit solution (30 degrees C), and stimulated at 1.5 Hz. Isometric developed tension was monitored continuously as extracellular Ca2+ was increased in a cumulative fashion. When compared to male atrial muscle, female atrial preparations were more sensitive to the resulting positive inotropic action; EC50 values were 2.89 +/- 0.22 and 1.86 +/- 0.21 mM in male and female atria, respectively. Two-way analysis of variance (ANOVA) also indicated that there was a significant gender-associated difference in the Ca2+ dose-response curves in atrial muscle. In contrast, papillary muscle did not show a significant gender-related difference in EC50 values (0.88 +/- 0.07 and 0.74 +/- 0.06 mM in males and females); however, the Ca2+ dose-response curves obtained from male and female preparations were found to be significantly different when compared by ANOVA.

Echocardiographic parameters in training compared with non-training greyhounds

Echocardiographic parameters were compared between training and non-training greyhound dogs. When indexed to body weight there was a statistically significant increase (p < 0.05) in the interventricular septal thickness (systole) and when indexed to body surface area there were increased interventricular septal (systole) and left ventricular free wall measurements (systole) in training compared with non-training greyhounds. When each gender was analyzed separately and echocardiographic parameters were indexed to body size, both genders had an increase in the interventricular septal thickness (diastolic in the female, systolic in the male) in the training compared with non-training greyhounds. In male training greyhounds there was additionally an increase in the left ventricular internal dimension (systole) and free wall thickness (systole) when echocardiographic parameters were indexed to body surface area compared with non-training greyhounds (p < 0.05). The results indicate that certain training greyhound echocardiographic parameters are larger than non-training greyhound echocardiographic parameters. The potential effects of training, body size and gender should be considered when interpreting echocardiographic parameters in populations of greyhounds.

Changes in stroke volume with beta-blockade before and after 10 days of exercise training in men and women

We sought to determine whether 10 days of training would be a sufficient stimulus for cardiac adaptations that would allow a greater compensatory stroke volume during beta-blockade. We also sought to determine whether men and women had a similar cardiac reserve capacity for increasing stroke volume with beta-blockade during submaximal exercise. Eight men (age 29 +/- 2 yr, mean +/- SE) and eight women (25 +/- 2 yr) cycled at 65% of peak O2 consumption (unblocked) under placebo-control and beta-blockade (100 mg atenolol) conditions performed on separate days. These tests were repeated at the same power output after training (10 consecutive days, 1 h of cycling per day). Before training, beta-blockade significantly (P < 0.05) decreased heart rate (HR) and cardiac output and increased stroke volume in both men and women. After training, the increase in stroke volume and decrease in HR with beta-blockade was significantly less while cardiac output was reduced more. There were no gender differences in the effects of beta-blockade on HR, stroke volume, or cardiac output. These data indicate that, during exercise with beta-blockade, exercise training for 10 days does not enhance the compensatory increase in stroke volume and that men and women have a similar cardiac reserve capacity for increasing stroke volume.

Relation between gender, etiology and survival in patients with symptomatic heart failure

OBJECTIVES

This study investigated the relation between gender, etiology and survival in patients with symptomatic heart failure.

BACKGROUND

Previous work provides conflicting results concerning the relation between gender, clinical characteristics and survival in patients with heart failure.

METHODS

We examined the relation of these factors in 557 patients (380 men, 177 women) who had symptomatic heart failure, predominantly nonischemic in origin (68%) and typically associated with severe left ventricular dysfunction.

RESULTS

Follow-up data were available in 99% of patients (mean follow-up period 2.4 years, range 1 day to 10 years) after study entry, and 201 patients reached the primary study end point of all-cause mortality. By life-table analysis, women were significantly less likely to reach this primary end point than men (p < 0.001). A significant association was found between female gender and better survival (p < 0.001), which depended on the primary etiology of heart failure (p = 0.008 for the gender-etiology interaction) but not on baseline ventricular function. Women survived longer than men when heart failure was due to nonischemic causes (men vs. women: relative risk [RR] 2.36, 95% confidence interval [CI] 1.59 to 3.51, p < 0.001). In contrast, outcome appeared similar when heart failure was due to ischemic heart disease (men vs. women: RR 0.85, 95% CI 0.45 to 1.61, p = 0.651).

CONCLUSIONS

Women with heart failure due to nonischemic causes had significantly better survival than men with or without coronary disease as their primary cause of heart failure.

Gender-related differences in exercise ventricular function among healthy subjects and patients

Increasing numbers of women are undergoing noninvasive stress testing for coronary artery disease evaluation. Limited information is available regarding the presence, magnitude, and importance of gender-related differences in exercise ventriculography among the heterogeneous population of patients referred for noninvasive stress testing. Patients referred for exercise radionuclide ventriculography between 1979 and 1986 were evaluated, including 175 patients with a likelihood of coronary artery disease, 59 patients with angiographically normal coronary arteries, and 419 patients with coronary artery disease. Overall, women demonstrated higher resting left ventricular ejection fraction and lower delta left ventricular ejection fraction response to exercise compared with men. Although left ventricular response to exercise correlated with the underlying severity of coronary artery disease in both women and men, fewer women demonstrated a delta left ventricular ejection fraction >5 percent despite a lower prevalence of multivessel coronary artery disease compared with men. We conclude that gender-related differences in left ventricular response to exercise are present in a wide range of patients referred for testing.

The limited efficacy of exercise radionuclide ventriculography in assessing prognosis of women with coronary artery disease

Increasing numbers of women are undergoing stress testing for coronary artery disease evaluation. Limited study is available as to its efficacy in women. Four hundred nineteen patients with coronary artery disease (74 women and 345 men) referred for exercise radionuclide ventriculography between 1979 and 1986 were evaluated in a prospective cohort evaluation with 5-year follow-up. Exercise radionuclide ventriculographic variables were analyzed and compared between women and men. The prognostic efficacy of exercise radionuclide ventriculography was assessed separately for women and men among patients with coronary artery disease by Kaplan-Meier cumulative survival curves, univariate Cox regression analyses, and hierarchical stepwise Cox regression analyses. Overall, women demonstrated higher resting and peak left ventricular ejection fraction response to exercise than men. Ninety-six of 419 patients (23%) had cardiac events at 5-year follow-up. Although left ventricular response to exercise conveyed prognostic information in the combined and male populations (multivariate hierarchical analyses chi-square 11, p = 0.001 for delta left ventricular ejection fraction and chi-square 10, p = 0.002 for worsening exercise wall motion score), these variables were not found to be prognostically useful in women. Women with coronary artery disease demonstrated a worsened functional status, evidenced by greater compromise of exercise capacity, despite having less extensive anatomic disease than their male counterparts. We conclude that sex-related differences in left ventricular response to exercise limit the prognostic utility of exercise ventriculography in women with coronary artery disease.

Left ventricular ejection fraction during supine and upright exercise in patients with systemic hypertension and its relation to peak filling rate

In hypertensive patients with hypertrophy, abnormal peak filling rate (PFR) is related to a decline in left ventricular (LV) ejection fraction (EF) during supine exercise. Because an increased LV preload is more common during upright exercise, we determined this relation during upright and supine exercise. In 20 hypertensive patients, rest and exercise radionuclide angiography in the supine and upright positions, as well as echocardiography, were performed and compared with 20 age-matched controls. At rest in the supine and upright positions, blood pressure, LVEF, and PFR were 164 +/- 20/94 +/- 10 and 164 +/- 24/94 +/- 10 mm Hg, 65 +/- 8% and 65 +/- 6%, and 2.77 +/- 0.59 and 2.70 +/- 0.52 end-diastolic volumes/s, respectively. PFR was reduced compared with controls (3.29 +/- 0.3 and 3.27 +/- 0.27 end-diastolic volumes/s, supine and upright). LV mass index was normal (94 +/- 19 g/m2). LVEF increased during upright but not during supine exercise in the hypertensives. Four patients had a decline in each position versus none of the controls. There was no relation between the change in LVEF and rest PFR. In patients with mild to moderate hypertension without extensive hypertrophy, abnormal filling rates were present but did not correlate with the change in LVEF with exercise.

Cardiovascular responses to exercise. Effects of aging and exercise training in healthy men

BACKGROUND

Cardiac aging alters many of the acute responses to exercise stress, but the extent to which chronic exercise (ie, training) can alter or improve the effects of aging in humans is largely unknown.

METHODS AND RESULTS

Cardiovascular responses to graded supine exercise stress (beginning at 200 kpm and increasing by 200 kpm every 3 minutes till exhaustion) were assessed using radionuclide ventriculography in 13 older (age, 60 to 82 years) and 11 young (age, 24 to 32 years) rigorously screened healthy men before and after 6 months of endurance training. Repeated-measures ANOVA was used to test significance. During exercise, the old group had a lesser increase in heart rate (+105% old versus +166% young), a greater increase in mean blood pressure (+35% old versus +22% young), lesser increases in ejection fraction (+3 ejection fraction units old versus +11 units young) and peak ejection rate (+62% old versus +119% young), a greater increase in end-diastolic volume index (+8% old versus -10% young), a lesser fall in end-systolic volume index (-0% old versus -32% young), and a lesser increase in cardiac index (+135% old versus +189% young) (all P < .01 young/old versus exercise stage). Stroke volume index response to exercise was not different with aging (+14% old versus +6% young, P = NS). Exercise training increased maximal oxygen intake by 21% in the older group (28.9 +/- 4.6 to 35.1 +/- 3.8 mL.kg-1.min-1, P < .001) and by 17% in the young (44.5 +/- 5.1 to 52.1 +/- 6.3 mL.kg-1.min-1, P < .001) and increased peak workload by 24% in the old and 28% in the young. Exercise training had no differential effects on old versus young men. Among all subjects, training significantly reduced the resting heart rate by 12% (-8 beats per minute) and increased resting end-diastolic volume index by 13% (+9 mL/M2) and resting stroke volume index by 18% (+7 mL/M2) (all P < .01). At peak exercise, cardiac index increased by 16% (+1.07 L.M-2.min-1) compared with before training, which was the result of an increase in stroke volume of 18% (+7 mL/M2) (P < .001); peak heart rate was unchanged. The increase in stroke volume index at peak exercise was the result of both a 12% increase in end-diastolic volume index (+8 mL/M2) (P < .01) and an increase in ejection fraction (+3 ejection fraction units) (P < .05) at peak exercise. The increased ejection fraction at peak exercise occurred despite a 9% increase in systolic blood pressure (+18 mm Hg) (P < .01), suggesting an increase in contractility. Thus, both the young and old increased peak exercise cardiac output by use of the Frank-Starling mechanism (ie, cardiac dilatation) as well as an increase in ejection fraction.

CONCLUSIONS

We conclude that there is an age-associated decline in heart rate, ejection fraction, and cardiac output responses to supine exercise in healthy men. Although the stroke volume responses of the young and old are similar, the old tend to augment stroke volume during exercise more through cardiac dilatation, with an increase in end-diastolic volume (+8%) but without much change in ejection fraction (+3 ejection fraction units), whereas the young rely more on an increase in the ejection fraction (+11 ejection fraction units) with no cardiac dilatation (-10%). Despite the significant cardiovascular changes that occur in the response to a single bout of exercise with aging, adaptations to chronic exercise training were not different with aging and included improvements in maximal workload and increases in ejection fraction, stroke volume index, and cardiac index at peak exercise.

Left ventricular performance during prolonged exercise and early recovery in healthy subjects

The effect of semi-supine long lasting exercise to exhaustion [61 (SD 10) min] on left ventricular systolic performance was studied by echocardiography in 16 young healthy volunteers. During the incremental phase of exercise, the ejection fraction increased from 65.2 (SD 4.1)% to 80.1 (SD 4.8)% (P < 0.0001), then it levelled off up to the end of exercise [81.7 (SD 4.4)%, P < 0.0001 vs rest]. During recovery, the ejection fraction rapidly and steadily decreased to a value similar to that at rest [66.1 (SD 5.0)%, n.s.). A similar pattern was shown by the systolic blood pressure/end-systolic volume coefficient, which rose from 3.2 (SD 0.8) mmHg.ml-1 to 7.5 (SD 2.7) mmHg.ml-1 (P < 0.0001) in the initial phase and subsequently did not change until the end of exercise [7.0 (SD 2.2) mmHg.ml-1, P < 0.0001 vs rest], to fall sharply after the cessation of exercise [2.9 (SD 1.1) mmHg.ml-1 at the 10th min, n.s. vs rest]. Exercise and recovery indices of left ventricular performance were not correlated with exercise duration, maximal heart rate and increase in free fatty acids. The present results indicated that, after the initial increase, left ventricular performance remained elevated during prolonged high intensity exercise and that conclusions on exercise cardiac performance drawn from postexercise data can be misleading.

Exercise performance and diastolic filling in essential hypertension

OBJECTIVES

To investigate the relationship between arterial blood pressure, left ventricular mass, diastolic filling and maximal exercise capacity in patients with newly diagnosed essential hypertension.

DESIGN

Asymptomatic untreated patients with office blood pressure > 140/90 mmHg were studied prospectively after exclusion of associated disease.

METHODS

Twenty consecutive white patients (14 male, 6 female; age 43 +/- 12 years) with office blood pressure 164 +/- 23/103 +/- 10 mmHg, mean 24-h ambulatory blood pressure 142 +/- 25/89 +/- 15 mmHg and normal systolic cardiac function underwent an echocardiographic examination to determine left ventricular mass and diastolic filling parameters and performed a bicycle ergometer test to determine maximal voluntary exercise capacity.

RESULTS

In single regression analysis exercise time and maximal oxygen uptake were related to sex and age. A multiple regression showed that only age was related to exercise capacity, however. On subgroup analysis of male patients between 30 and 50 years (n = 10), exercise time (659 +/- 134 s) was significantly inversely related to mean 24-h ambulatory diastolic blood pressure (92 +/- 11 mmHg) (r = -0.67; p = 0.03) and positively to diastolic filling expressed as ratio of peak early to peak atrial filling velocity (Emax/Amax ratio; 1.34 +/- 0.40) (r = 0.65; p = 0.04) or as ratio of velocity time integral (VTI) of early filling phase to VTI of atrial filling phase (VTIE/VTIA ratio; 1.94 +/- 0.72) (r = 0.02). Maximal oxygen consumption (22.3 +/- 4.1 ml/kg/min) was significantly inversely correlated with mean 24-h ambulatory diastolic blood pressure (r = -0.67; p = 0.03), mean 24-h ambulatory systolic blood pressure (147 +/- 25 mmHg) (r = -0.82; p < 0.01), left ventricular mass (312 +/- 143 g) (r = -0.86; p < 0.01), left ventricular mass index (135 +/- 41 g/m2) (r = -0.76, p = 0.01) and positively with diastolic filling expressed as Emax/Amax ratio (r = 0.71; p = 0.02) or as VTIE/VTIA ratio (r = 0.70; p = 0.02).

CONCLUSION

This study shows the important interrelation between blood pressure, cardiac mass, diastolic filling and exercise capacity. High blood pressure entrains a larger cardiac mass but slows cardiac filling and decreases exercise capacity.

Stroke volume increases by similar mechanisms during upright exercise in normal men and women

To define the effects of gender on stroke volume control during upright exercise in normal subjects, we examined central hemodynamics in 34 men and 27 women during staged bicycle ergometry. Central hemodynamics were assessed by right-sided cardiac catheterization and simultaneous radionuclide angiography. Left ventricular end-diastolic and end-systolic volumes were calculated from the stroke volume (by direct Fick) and the corresponding left ventricular ejection fraction. Men were larger than women (1.85 +/- 0.11 vs 1.65 +/- 0.13 m2, p less than 0.001) but groups were matched for age (39 +/- 12 vs 36 +/- 9 years, p = 0.27). Oxygen consumption at peak exercise was higher in men than in women (2.51 +/- 0.50 vs 1.74 +/- 0.30 liters/min, p less than 0.001) but was not different when adjusted for body weight (31.5 +/- 8.1 vs 28.4 +/- 6.4 ml/kg/min, p = 0.14), indicating similar levels of overall fitness in the 2 groups. At rest and during submaximal and maximal exercise, stroke volume and left ventricular end-diastolic and end-systolic volumes were higher in men than in women, but there were no intergroup differences in stroke volume index, left ventricular ejection fraction, and left ventricular end-diastolic or end-systolic volume indexes. Comparison of derived regression equations of cardiac index, stroke volume index and left ventricular end-diastolic and end-systolic volume indexes revealed no differences in the time course or magnitude of changes with respect to oxygen consumption, expressed as percentage of peak oxygen consumption, in the 2 groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Unrecognized left ventricular dysfunction in an apparently healthy cocaine abuse population

To determine the frequency and severity of clinically unrecognized left ventricular (LV) dysfunction related to cocaine use, 84 asymptomatic cocaine abusers underwent cardiac evaluation which included chest x-ray, electrocardiography (ECG), and radionuclide angiography after a two-week abstinence from cocaine use. LV dysfunction was discovered in 6/84 (7%). Regional wall motion abnormalities suggesting a localized myocardial abnormality were found in 2, whereas an ejection fraction less than 50% suggesting a more global process was noted in 4. An abnormal chest x-ray was found in only 1 subject and none had abnormal ECGs. In each of these cases, repeated and protracted use of cocaine was documented and the suggestion of cardiac dysfunction was supported by at least one other independent abnormal finding. In these 6 cases, the dysfunction was clinically unrecognized and unsuspected after routine evaluation. The significance of subclinical LV dysfunction in this population has not been determined and requires long-term study.

The application of radionuclide ventriculography to cardiac screening

Screening asymptomatic individuals for latent coronary disease often requires sequential testing because exercise electrocardiography typically produces more false positive than true positive results in a population with a low prevalence of coronary disease. Cardiac scintigraphy is a technique that may be employed as a confirmatory test in lieu of coronary arteriography to further evaluate the significance of a positive exercise electrocardiogram. Radionuclide ventriculography was employed in 98 asymptomatic individuals who were considered to be at moderate risk of heart disease after risk factor analysis and exercise electrocardiography. Seventeen (17%) patients had an abnormal study and underwent cardiac catheterization. Seven had coronary artery disease, two had cardiomyopathy, and eight were normal. Eighty-one (83%) patients had a normal study. Because the sensitivity of radionuclide ventriculography is 63-80%, it was postulated that 2 to 5 individuals with disease were missed. Thus, from a population with an 11-14% prevalence of disease, two subsets were identified. A large subset in which a prevalence of 2-6% could be estimated was separated from a much smaller one in which a prevalence of approximately 50% was demonstrated.

Comparison of doxazosin and atenolol in mild hypertension, and effects on exercise capacity, hemodynamics and left ventricular function

The effects of once-daily therapy with doxazosin (1 to 8 mg/day) on exercise capacity, left ventricular performance and hemodynamics (radionuclide ventriculography) were compared with those of atenolol (50 to 100 mg/day) and placebo in a randomized, double-blind crossover trial in 16 patients (9 men) with mild hypertension. Both medications controlled blood pressure (BP) to a similar degree (mean BP was 150 +/- 12, 137 +/- 17 and 141 +/- 14 mm Hg for placebo, atenolol and doxazosin, respectively) but by different mechanisms. Changes during maximal semierect bicycle exercise were similar to those seen at rest. Doxazosin decreased total peripheral resistance and maintained cardiac output, whereas atenolol decreased cardiac output. Exercise capacity (136 +/- 56 watts with placebo) was maintained by doxazosin (135 +/- 56 watts) but decreased with atenolol (122 +/- 55 watts). Compared with atenolol, doxazosin slightly increased the left ventricular ejection fraction at rest and during exercise. The significance of this study is in the choice of a first-line antihypertensive agent. Both are once-a-day medications that control BP. However, doxazosin does so by improving the abnormal physiology of essential hypertension and, consequently, does not adversely affect exercise performance.

Acute elevation of blood carboxyhemoglobin to 6% impairs exercise performance and aggravates symptoms in patients with ischemic heart disease

Acute exposure to carbon monoxide has the potential to impair exercise capacity in patients with ischemic heart disease. The effect of sufficient inhalation of this compound to gradually produce a level of 6% carboxyhemoglobin was studied in 30 nonsmoking patients with obstructive coronary artery disease and evidence of exercise-induced ischemia. After an initial training session, subjects were exposed to air or carbon monoxide on successive days in a randomized double-blind crossover fashion. Cardiac function and exercise capacity were assessed during symptom-limited supine radionuclide ventriculography. On the carbon monoxide day, mean postexposure carboxyhemoglobin was 5.9 +/- 0.1% compared with 1.6 +/- 0.1% (p less than 0.01) after air exposure. The mean duration of exercise was significantly longer after air compared with carbon monoxide exposure (626 +/- 50 s for air versus 585 +/- 49 s for carbon monoxide, p less than 0.05). Actuarial methods suggested that subjects were likely to experience angina earlier during exercise on the day of carbon monoxide exposure (p less than 0.05). Both the level (62 +/- 2.4 versus 60 +/- 2.4%, p = 0.05) and change in left ventricular ejection fraction at submaximal exercise (1.6 +/- 1.6 versus -1.2 +/- 1.6%, p = 0.05) were greater on the air exposure day compared with the carbon monoxide day. The peak exercise left ventricular ejection fraction was not different for the two exposures (57 +/- 2.5% for both). These results demonstrate earlier onset of ventricular dysfunction, angina and poorer exercise performance in patients with ischemic heart disease after acute carbon monoxide exposure sufficient to increase blood carboxyhemoglobin to 6%.