Maximal cardiac output during upright exercise: approximate normal standards and variations with coronary heart disease

Diagnosis and assessment of pulmonary arterial hypertension

The diagnosis and assessment of pulmonary arterial hypertension is a rapidly evolving area, with changes occurring in the definition of the disease, screening and diagnostic techniques, and staging and follow-up assessment. The definition of pulmonary hypertension has been simplified, and is now based on currently available evidence. There has been substantial progress in advancing the imaging techniques and biomarkers used to screen patients for the disease and to follow up their response to therapy. The importance of accurate assessment of right ventricular function in following up the clinical course and response to therapy is more fully appreciated. As new therapies are developed for pulmonary arterial hypertension, screening, prompt diagnosis, and accurate assessment of disease severity become increasingly important. A clear definition of pulmonary hypertension and the development of a rational approach to diagnostic assessment and follow-up using both conventional and new tools will be essential to deriving maximal benefit from our expanding therapeutic armamentarium.

Assessing Muscle Vasodilation Using Near-Infrared Spectroscopy in Cardiac Patients

BACKGROUND

In patients with chronic heart failure, an inadequate increase in muscle blood flow resulting from impaired vasodilation plays a key role in their exercise intolerance. However, no non-invasive methods to assess muscle vasodilation during dynamic exercise were available. We investigated whether the changes in tissue hemoglobin and myoglobin content (total-Hb + Mb) determined by non-invasive measurement using near-infrared spectroscopy (NIRS) reflect vessel conductance of working muscle during exercise.

METHODS AND RESULTS

Sixteen patients (10 patients with normal cardiac systolic function, 6 with cardiac dysfunction) performed incremental bicycle exercise testing. Total-Hb + Mb from the right vastus lateralis muscle was monitored using NIRS. Leg blood flow (LBF) in the right femoral vein was measured using a thermodilution technique every 30-60 s. Leg vessel conductance was calculated as LBF/mean arterial pressure at each time of the measurement. In all cases except 1, the levels of total-Hb + Mb showed significant correlation with the leg vessel conductance (r=0.792 to 0.980). Intra-subject reproducibility of the NIRS measurement was also confirmed in 6 patients.

CONCLUSIONS

Total-Hb + Mb from NIRS reflected muscle vasodilation during sub-maximal dynamic exercise in patients with and without cardiac dysfunction, indicating that NIRS provides a valuable method to assess the working muscle vasodilation.

The effects of interval training on oxygen pulse and performance in supra-threshold runs

The aim of this study was to examine (i) the effects of a severe interval training period on oxygen pulse kinetics (O2-p, the ratio between VO2 and heart rate), and (ii) to study the consequences of these effects on the variation of performance (time to exhaustion) during severe runs. Seven athletes were tested before and after an eight-weeks period of a specific intermittent training at v Delta 50, i.e., the intermediate velocity between the lactate threshold (vLT) and the velocity associated with VO2max (vVO2max ). During the test sessions, athletes performed an incremental test and an all-out test at the pretraining v Delta 50. After the training period they also completed an additional all-out test at the posttraining v Delta 50 (v Delta 50bis). Results showed that after training there was i) an increase in the O2-p maximal value during the incremental test (22.7 +/- 1.5 mlO2.b-1 vs. 20.6 +/- 1.5 mlO2.b-1; p < 0.04), ii) a decrease in the time to reach the O2-p steady state (TRO2-p ) at the same absolute v Delta 50 (33 +/- 7 s vs. 60 +/- 27 s; p < 0.04) and iii) an increase in the O2-p steady state duration (TSSO2-p) at the same absolute v Delta 50 (552 +/- 201 s vs. 407 +/- 106 s; p < 0.04). However, there was no relationship between the improvement of these two O 2 -p kinetics parameters (TRO2-p and TSS O2-p) and those of the performance. This study found that after an individualised interval-training program conducted at the same absolute velocity, the O2-p kinetics reached a steady state quicker and for a longer duration than before training. This is however not related with the improvement of performance.

Effects of age on aortic blood velocity at rest and during exercise in patients with coronary artery disease

The effect of age on aortic blood velocity has been studied in 100 patients with angiographically-documented coronary artery disease, 500 of whom were receiving beta-adrenergic blocking agents. Using continuous-wave Doppler ultrasound, the aortic blood velocity signals, both at rest and at maximal-tolerated supine exercise, were obtained. From the Doppler signals the peak velocity (Vp), stroke distance (Sd; the velocity-time integral) and minute distance (Md = Sd x heart rate) were calculated. The measurements were repeated 6 weeks after coronary artery bypass grafting (CABG), performed in 30 patients. No relationship with age (p < 0.01) was found for any of the indices, either at rest or during exercise, except for the resting Md in patients not on beta-blockers, (p < 0.02). No difference in the slope of the relationship with age was found between patients on or not on beta-blockers, except for the resting Md (p < 0.02). Following CABG, a significant age relationship with Vp, Sd and Md was restored, during both resting and exercise, suggesting improvement of systolic left ventricular function following myocardial revascularization. In conclusion, the normal age relationships of the derivatives of aortic blood velocity Doppler ultrasound signals were not seen in patients with coronary artery disease, irrespective of whether they were on or off beta-blockers. The relationship changed following myocardial revascularization, suggesting their dependence on systolic left ventricular function.

[Cardiovascular evaluation in athletic children]

Although rare, sports related sudden cardiac deaths in children and adolescents justify the search for risk factors in any child or adolescent who wishes to practice sports. Each time that history and careful clinical cardiovascular examination point to a possible cardiovascular abnormality, an electrocardiogram and an echocardiography must be performed. Exercise testing is useful to appreciate the cardiovascular tolerance, either in normal subjects or in subjects with a cardiovascular abnormality; its interpretation requires good knowledge and understanding of hemodynamic responses to exercise. Indications, risks and procedures of exercise testing are discussed with reference to exercise physiology.

Prediction of stroke volume during upper and lower body exercise in men and women

In this study, regression equations were derived to predict cardiac stroke volume (SV, mL/beat), measured by carbon dioxide rebreathing, from oxygen pulse (O2 pulse, mL/beat) measurements in healthy men (n = 25) and women (n = 12) during upper and lower body exercise at the ventilatory threshold. The equations for upper body exercise were as follows: men, Y = 10.21X - 1.0, SE = 13.0; r = 0.85; women, Y = 12.70X - 4.8, SE = 15.4, r = 0.78. The equations for lower body exercise were as follows: men, Y = 5.22X + 53.0, SE = 17.9, r = 0.76; women, Y = 7.41X + 27.1, SE = 13.5, r = 0.78. No significant differences (p > .05) were observed between the exercise modes for the slopes and intercepts of the regression equations in both genders. The relationships between O2 pulse and SV were indirectly validated by using raw data from previous studies that had used the direct Fick method to determine cardiac output (Q) for each exercise mode and gender. Comparisons between the values of SV reported in several studies that used direct and indirect methods to determine Q and those predicted from the current equations indicated an error that was usually within 10% of the reported values. These observations suggest that the equations derived for predicting SV from O2 pulse measurements at the ventilatory threshold are quite accurate and can be generalized to a variety of techniques currently used to determine Q.

Variation of aortic blood velocity with age at rest and during exercise in normal subjects

The effect of age on aortic blood velocity signal and its derived indices of left ventricular function namely peak velocity, stroke distance (the velocity-time integral) and minute distance (stroke distance x heart rate) was studied at rest and at maximal-tolerated supine exercise using a 2-mHz continuous-wave Doppler ultrasound applied via the suprasternal notch in 66 normal healthy volunteers. The peak velocity, stroke distance and the minute distance, both at rest and at maximal exercise decreased with advancing age by 1-1.1% per annum between the ages of 20 and 70 years. Accordingly a method for age-adjustment of the peak velocity, stroke and minute distances was introduced for clinical use in assessing individual subjects. These results indicate that age is an important variable affecting aortic blood velocity and its derived variables as non-invasive measures of left ventricular function both at rest and with exercise. The relationship with age is an important consideration when assessing individual subjects.

Prediction of stroke volume from oxygen pulse measurements in untrained and trained men

This study examined the relationship of oxygen pulse (O2 pulse) to stroke volume (SV) and arterio-venous oxygen difference [(a-v)O2 diff] during submaximal cycle exercise in untrained (UG) and trained (TG) males. Fourteen volunteers in each group completed an incremental VO2 max test and a submaximal test at 60% VO2 max to determine cardiac output (Q) via CO2 rebreathing. VO2, Q, and heart rate (HR) were used to calculate SV and (a-v)O2 diff. There were no significant differences (p > .05) between the two groups for O2 pulse, SV, and (a-v)O2 diff during submaximal exercise. Stroke volume index (SVI) was significantly higher (p < .05) in the TG. O2 pulse was significantly related to SV and SVI (p < .05) but not to (a-v)O2 diff in both groups. Regression equations for predicting SV from O2 pulse for UG and TG were Y = 6.81X + 26.7, SE = 21.4, r = 0.84, and Y = 10.33X - 32.3, SE = 14.2, r = 0.71, respectively. These results suggest that O2 pulse can be used to predict SV during submaximal cycle exercise in untrained and trained men.

Nomogram based on metabolic equivalents and age for assessing aerobic exercise capacity in men

OBJECTIVES

The goal of this study was to create a nomogram, based on maximal exercise capacity (in metabolic equivalents [METs]) and age, for assessing a patient's ability to perform dynamic exercise to quantify the level of physical disability or relative capacity for physical activity.

BACKGROUND

Providing an estimation of exercise capacity relative to age is clinically useful. Such an estimate can be derived from measured or estimated maximal oxygen uptake (in METs) from treadmill exercise testing and age. It is an effective means of communicating to patients their cardiopulmonary status, encouraging improvement in exercise capacity and quantifying disability.

METHODS

Exercise test results of 1,388 male patients (mean age 57 years, range 21 to 89) free of apparent heart disease who were referred for exercise testing for clinical reasons were retrospectively reviewed. This referral group as well as subgroups of active (n = 346) and sedentary (n = 253) patients were analyzed to determine norms for age and for age by decades for exercise test responses, including METs, maximal heart rate and maximal systolic blood pressure. Regression equations were calculated from this information, and a nomogram for calculating degree of exercise capacity from age and MET level achieved by a patient was created. A similar analysis was performed in a separate group of 244 apparently healthy, normal male volunteers (mean age 45 +/- 14 years, range 18 to 72) who underwent exercise testing with direct measurement of expired gases.

RESULTS

Equations for predicted METs for age were derived for the entire clinical referral group (METs = 18.0-0.15[Age]) and for the subgroups of active (METs = 18.7-0.15[Age]) and sedentary (METs = 16.6-0.16[Age]) patients. All results achieved statistical significance, with p values < 0.001. In the volunteer group of normal men who performed exercise testing with ventilatory gas exchange, the decline in maximal heart rate and METs with age was not as steep as in the referral group. Although the normal group confirmed nomograms published previously among similar subjects, the equations derived from the patients differed from those previously reported; in contrast to previous studies using healthy volunteers, the equations and nomograms for the referral group are more appropriate for patients typically referred for testing in a hospital or office-based internal medicine practice.

CONCLUSIONS

Norms for METs based on age are presented as well as population-specific nomograms that enable physicians to assess patients' exercise capacity relative to their age group.

Usefulness of myocardial ischemia as predictor of training effect in cardiac rehabilitation after acute myocardial infarction or coronary artery bypass grafting

Exercise capacity increases to a variable degree in coronary patients during cardiac rehabilitation. The effect of baseline exercise-induced ischemia on the response to a 12-week conditioning program was evaluated in 106 coronary patients. The magnitude of exercise conditioning response was greater in nonischemic patients than in ischemic patients, with maximal exercise intensity increasing 69 versus 50% (7.2 to 12.1 vs 7.1 to 10.6 METs) (p less than 0.05) and maximal oxygen consumption increasing 28 versus 10% (23.1 to 29.6 vs 23.0 to 25.4 cc/kg/min) (p less than 0.05). Markers of conditioning during submaximal exercise such as heart rate and heart rate-systolic blood pressure product were similarly reduced in both groups. The groups did not differ by age, diagnosis, resting ejection fraction, incidence of beta-blocker use, maximal exercise capacity, maximal exercise heart rate, blood pressure or intensity of actual exercise training. These results suggest that exercise-induced ischemia alters the stimulus to adapt to exercise training.

Accuracy of cardiac output measured by continuous wave Doppler echocardiography during dynamic exercise testing in the supine position in patients with coronary artery disease

To estimate the accuracy of cardiac output measured by continuous wave Doppler echocardiography from the suprasternal notch and the utility of this method for evaluating left ventricular function during dynamic exercise, simultaneous thermodilution and Doppler cardiac output were measured in 34 patients with coronary artery disease during multistage ergometer exercise in the supine position. Cardiac output was measured at rest and during each stage of exercise. Twenty-five of the 34 patients whose thermodilution curves were adequate for analysis were studied during exercise. The correlation coefficient for the two methods was 0.85 at rest and 0.84 during exercise. Differences between the two methods were not significant at rest but were significant during exercise, with the thermodilution method giving the higher values. Underestimation by the Doppler method is probably due to technical problems and changes in aortic diameter during exercise. The 25 patients were classified into two groups according to pulmonary artery wedge pressure at peak exercise. There were 11 patients in Group 1 pressure (greater than or equal to 20 mm Hg at peak exercise) and 14 in Group 2 pressure (less than 20 mm Hg at peak exercise). There were significant differences in the change in cardiac index and in peak aortic velocity from rest to peak exercise between the two groups. A significant linear correlation between the percent change in peak aortic velocity and in pulmonary artery wedge pressure from rest to peak exercise was observed (r = -0.66, p less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Rebreathing method for the simultaneous measurement of oxygen consumption and effective pulmonary blood flow during exercise

This paper describes a rebreathing method for the simultaneous measurement of oxygen consumption (VO2) and effective pulmonary blood flow (QP. eff) at rest and during exercise. Subjects rebreathed a test gas consisting of 35% oxygen, 3.5% chlorodifluoromethane (freon-22), and 10% argon in nitrogen for 30 seconds or until the respired oxygen tension fell to below 13.3 kPa. Sixty normal subjects were studied on a motorized treadmill, the Bruce protocol being used. The rebreathing manoeuvre was performed at three minute intervals, and was initially practised sitting down. Measurements were then made with the subjects standing at rest, and subsequently during the last minute of each stage of the Bruce exercise protocol until the subjects were exhausted. Heart rate was recorded from the electrocardiogram. Oxygen uptake plotted against calculated power (watts) showed a discontinuity between resting and exercise values, probably because power output during treadmill exercise is underestimated. The arbitrary addition of 30 watts to the exercise power output abolished this discontinuity. There was good agreement between rebreathing estimates of oxygen consumption and values measured during a second exercise test by the conventional open circuit argon dilution method. Coefficients of variation of oxygen consumption and effective pulmonary blood flow measured by rebreathing were usually less than 10% even during maximal exertion. At rest mean (SD) effective pulmonary blood flow corrected for body surface area was 2.2 (0.46) l/min/m2. Effective pulmonary blood flow rose linearly with oxygen consumption. At rest the arteriovenous oxygen content difference for pulmonary blood (VO2/QP eff) was 9.1 (1.6) ml/dl, rising to a maximum of 16.4 (1.8) ml/dl. The stroke volume index was 27.5 (6.8) ml/m2, rising to a maximum of 46.5 (7.1) ml/m2 during exertion.

A Longitudinal Study of Cardiovascular Stability in Active Men Aged 45 to 65 Years

In brief: Cross-sectional studies of physical performance generally show a linear decline in maximum aerobic power (V O2 max) with increasing age (about 1% to 2% per year). In the study described in this article, 15 men were serially followed for 20 years. They performed exercises consisting of walking, running, swimming, and cycling for an average of 3.6 days per week and requiring an energy expenditure of 2,104 kcal per week. Over the 20 years, directly measured V O2 max declined 12% (from 44.4 to 38.9 ml· kg(-1)· min(-1), or 0.27 ml· kg(-1)· min(-1) per year). Essentially no differences were seen in resting heart rate or arterial blood pressure. The authors conclude that physical training forestalls the decline in V O2 max until at least age 65.

Measurement of cardiac output by CO2 rebreathing in unsteady state exercise

The ability to determine cardiac output (Q) noninvasively during a nonsteady state (NSS) incremental exercise test was assessed. Seven healthy subjects performed two maximal incremental cycle ergometer exercise tests (100 kpm/min increments every minute), and also steady state exercise (SS) at 25, 50, and 75 percent of their maximum power output. The Q was determined by the indirect CO2 Fick method; mixed venous PCO2 was calculated using the exponential CO2 rebreathing method. No significant differences were observed for the cardiac output/oxygen uptake relationship (Q/VO2) obtained between the two incremental exercise tests. During NSS, the Q/VO2 was linear (r = .89; intercept = 5.69 L/min; slope = 5.39). During the SS, Q/VO2 was linear (r = .90; intercept = 5.47 L/min; slope = 4.87). No significant difference was observed between the SS and NSS Q/VO2 relationships (p greater than 0.05), and the NSS relationship was similar to Q/VO2 values previously reported in the literature. Accurate and reproducible measurements of Q can be obtained noninvasively in healthy subjects using the exponential CO2 rebreathing method during incremental progressive exercise tests, with similar values at comparable VO2 to those obtained in the steady state.

Effect of propranolol and verapamil on oxygen utilization, acidosis and fatigue during exercise in stable angina pectoris

Oxygen utilization, arterial and venous blood gas levels, hemodynamic values and exercise tolerance were compared before and after administration of propranolol and verapamil in 10 patients with stable angina pectoris. During exercise, propranolol decreased cardiac output (CO) by 22%; O2 extraction was increased and O2 consumption (VO2) did not change. With verapamil treatment, CO modestly increased (7%), O2 extraction decreased and VO2 did not change. In contrast to O2 utilization, the drugs produced opposite changes in mixed venous and arterial blood gas levels. Propranolol decreased mixed venous pH, increased CO2 tension and decreased the pH of arterial blood. Verapamil increased venous pH and decreased CO2 tension; pH of arterial blood did not change. The drugs yielded similar levels of antianginal efficacy, but patients exercised longer during verapamil therapy and were less fatigued. The hemodynamic and metabolic differences suggest that muscle perfusion during exercise influences the onset of fatigue and may help determine the choice of therapy.

Exercise conditioning in the elderly coronary patient

We compared conditioning effects of a supervised exercise program in 100 elderly and younger patients with a recent coronary event. Twenty-one patients were greater than or equal to 62 years of age (mean, 65 years) and 79 were less than or equal to 61 years of age (mean, 48.7 years). While the elderly patients attained a lower peak exercise intensity on entry and on completion of the exercise protocol, they obtained a similar relative training benefit as the younger patients. Peak exercise intensity increased 68% in each group and submaximal (five METS) heart rate-blood pressure product decreased 27% in the older patients and 26% in the younger patients. Rate of entry into our program was substantially lower in the elderly patient group, 19% v 57% in younger patients (P less than 0.001) despite a similar inhospital recruiting effort. Thus, although elderly coronary patients obtain similar training benefits as younger patients, they are less likely to participate in a program designed to decrease cardiac disability.

Comparison of acute hemodynamic effects of nitroglycerin versus diltiazem and combined acute effects of both drugs in angina pectoris

Fifteen patients with exertional angina underwent hemodynamic monitoring and measurement of cardiac output during a control treadmill exercise test. They were then randomized to receive sustained-release nitroglycerin, 13 mg (group I) or placebo (group II). Repeat exercise testing revealed that in group I, both maximal oxygen consumption and cardiac output increased significantly. In group II neither maximal oxygen consumption nor cardiac output increased significantly. All patients then received diltiazem, 60 mg, and repeat testing was carried out 1 hour later. In group I maximal oxygen consumption and cardiac output were higher than control, but were no higher than after nitroglycerin. In group II, maximal oxygen consumption increased significantly, but the increase in cardiac output was not significant. Thus, sustained-release nitroglycerin, 13 mg, or diltiazem, 60 mg, both improve exercise performance, but the combination does not improve exercise performance to an extent greater than either drug alone.

Effects of the limiting symptom on the achievement of maximal oxygen consumption in patients with coronary artery disease

This study was conducted to determine if the limiting symptom in patients with coronary artery disease (CAD) influenced the pattern of oxygen consumption (VO2) over the final 90 seconds of a maximal exercise test. The pattern was classified according to the presence or absence of a plateau. Twenty-six normal persons and 55 patients with CAD were studied. They rated the severity of fatigue, dyspnea and angina at end exercise using the Borg scale and designated which symptom was the limiting factor. A plateau of VO2 over the final 90 seconds of exercise was observed in 77% of normal subjects and patients with CAD. Eighty percent of patients limited by angina achieved a plateau. In normal subjects and patients with CAD, peak VO2 was more reproducible than the pattern of VO2 over the final 90 seconds of exercise. There were no differences in the cardiac responses to exercise at maximal effort between patients who achieved a plateau of VO2 and those who did not. These results indicate that the limiting symptom of exercise, even angina pectoris, does not influence the ability to exercise maximally. Therefore, the peak value of VO2 during symptom-limited treadmill exercise is a valid measure of maximal cardiovascular capacity irrespective of the limiting symptom or the pattern of VO2 in the final 90 seconds of exercise.

Regulation of stroke volume during submaximal and maximal upright exercise in normal man

To characterize the hemodynamic factors that regulate stroke volume during upright exercise in normal man, 24 asymptomatic male volunteers were evaluated by simultaneous right heart catheterization, radionuclide angiography, and expired gas analysis during staged upright bicycle exercise to exhaustion. From rest to peak exercise, oxygen consumption increased from 0.33 to 2.55 liters/min (7.7-fold), cardiac index increased from 3.0 to 9.7 liters/min per m2 (3.2-fold), and arteriovenous oxygen difference increased from 5.8 to 14.1 vol% (2.5-fold). The increase in cardiac index resulted from an increase in heart rate from 73 to 167 beats/min (2.5-fold), and an increase in left ventricular stroke volume index from 41 to 58 ml/m2 (1.4-fold). During low levels of exercise, there was a linear increase in cardiac index due to an increase in both heart rate and stroke volume index; stroke volume index increased as a result of an increase in left ventricular filling pressure and end-diastolic volume index and, to a much smaller extent, a decrease in end-systolic volume index. During high levels of exercise, further increases in cardiac index resulted entirely from an increase in heart rate, since stroke volume index increased no further. Left ventricular end-diastolic volume index decreased despite a linear increase in pulmonary artery wedge pressure; stroke volume index was maintained by a further decrease in end-systolic volume index. The degree to which stroke volume index increased during exercise in individuals correlated with the change in end-diastolic volume index (r = 0.66) but not with the change in end-systolic volume index (r = 0.07). Thus, the mechanism by which left ventricular stroke volume increases during upright exercise in man is dependent upon the changing relationship between heart rate, left ventricular filling, and left ventricular contractility. At low levels of exertion, an increase in left ventricular filling pressure and end-diastolic volume are important determinants of the stroke volume response through the Starling mechanism. At high levels of exertion, the exercise tachycardia is accompanied by a decrease in end-diastolic volume despite a progressive increase in filling pressure, so that stroke volume must be maintained by a decrease in end-systolic volume.

Changes in cardiac functional capacity after coronary bypass surgery in relation to adequacy of revascularization

Seventy patients having aortocoronary vein bypass grafting surgery for angina pectoris underwent preoperative invasive exercise testing to symptom limits and again 6 to 14 months postoperatively. Cardiac output was measured using the direct Fick principle. Postoperatively at maximal exercise, there was a 3.11 liters/min (p less than 0.0001) increase in cardiac output in men (n = 61) and a 2.04 liters/min (p less than 0.01) increase in women (n = 9). Patients with complete revascularization showed a significantly greater improvement in cardiac output postoperatively than did those with incomplete revascularization (26 versus 6%, p less than 0.0001). The major reason for the increased maximal cardiac output was a marked increase in heart rate while stroke volume was maintained at the same preoperative level. These findings were true irrespective of preoperative use of beta-adrenergic blocking drugs.

Prediction of maximal cardiac output in preoperative patients with coronary artery disease

Of 100 patients (89 men, 11 women) studied preoperatively to determine their aerobic and hemodynamic profiles at rest and during upright treadmill exercise. The mean maximal cardiac output (CO), measured using the direct Fick principle, was 57 +/- 14% of average normal values. The reduction in maximal heart rate (63 +/- 13% of normal) was a greater factor in the reduction in CO than stroke volume (88 +/- 16% of normal). Maximal oxygen consumption (VO2max) was 48 +/- 15% of normal and the greater reduction in VO2max compared with CO was due to lower peripheral extraction in the coronary patients. Variables that correlated with maximal CO in a univariate analysis included angina severity (r = -0.45), VO2max (r = 0.67), maximal heart rate (r = -0.31), left ventricular dysfunction (r = -0.45), maximal systolic blood pressure (r = -0.31) and number of vessels with greater than or equal to 50% diameter reduction (r = -0.3). Resting ejection fraction did not correlate with maximal CO. In a multivariate analysis, 4 variables correlated significantly (r = 0.77) with maximal CO: in order, VO2max, number of vessels with greater than or equal to 50% stenosis, magnitude of ST depression and sex.

Psychosocial coping strategies and cardiac capacity before and after coronary artery bypass surgery

One hundred patients, eighty-nine men and eleven women, with chronic stable angina who were previously selected for aortocoronary bypass grafting gave informed consent for non-invasive and invasive testing of hemodynamic responses to symptom-limited maximal exercise before surgery. Psychosocial coping strategies were evaluated preoperatively by structured interviews and assessment of patients perceptions of symptoms (Cornell Medical Index) and life changes (Holmes and Rahe Schedule of Recent Experiences). Preoperatively forty-one patients were "compartmentalized," forty-two "generalized" and seventeen "vacillated" according to Josten's classification of coping strategies. The Berle Index of social assets was lower and the prevalence of psychiatric symptoms (Cornell categories M to R) was greater in the vacillators preoperatively. Despite less ischemic ST depression in vacillators, no other significant physiological differences were noted between these categories preoperatively. Postoperatively more of the vacillators refused follow-up evaluation, and of vacillators who returned, only one-half were adequately revascularized at operation. Of sixty-five reevaluated after surgery, eight improved, twelve worsened and forty-five did not change classification of coping strategies, yet physiological variables of cardiac function when invasively measured in sixty patients were significantly improved in all three groups. Amounts of improvement, both absolutely and relative to sex- and age-adjusted normal values, were least in vacillators with virtually normal cardiac capacity, and/or inadequate revascularization. Compartmentalized patients were more frequently working, yet only sixty-four in all psychosocial classifications worked before surgery. After this event only forty-five resumed working; none of the non-workers or retired returned to work. Both physiologic improvement and working status were independent of postoperative psychosocial status.

Determinants of variable exercise performance among patients with severe left ventricular dysfunction

The relation between bicycle exercise performance and determinants of central and peripheral cardiovascular function was assessed in 17 patients with class II to III heart failure and in 9 normal subjects. Proportional changes in oxygen consumption (VO2) from rest (R) to maximal exercise (Ex), or Mets, were used as an objective measure of the exercise capacity or functional reserve of the cardiovascular system. Left ventricular ejection fraction (EF) and proportional changes in end-diastolic volume, stroke volume, and cardiac output were determined from appropriate count data by equilibrium radionuclide angiography. Proportional changes in arteriovenous oxygen difference (A-VO2) were derived from the equation Ex/R A-VO2 = Ex/R VO2 divided by Ex/R CO, where CO = count output. Each subject exercised to an anaerobic endpoint. Maximal VO2 was significantly lower in patients than in normal subjects. Because Ex/R A-VO2 was comparable in normal subjects and patients, the lower exercise performance in patients resulted from a reduced count output response. The reduced CO response in patients resulted from failure of the ejection fraction to increase or from an attenuated heart rate response, or both. Exercise performance was variable in both groups. Multivariable analysis in the patient group identified changes in heart rate, count output, and A-VO2 with exercise as important predictors of Mets, but found no relation between Mets and changes in ejection fraction or stroke counts during exercise. Similarly, multiple regression analyses between Mets and determinants of cardiovascular function demonstrated significant correlations with Ex/R heart rate, Ex/R count output, and Ex/R A-VO2 in both groups. In patients, EF at rest ranged from 0.09 to 0.36, but it did not correlate with Mets, nor did changes in ejection fraction, stroke counts, or end-diastolic counts during exercise. The variable exercise performance among patients with severe left ventricular dysfunction was determined predominantly by a variable heart rate and A-VO2 response and not by rest or exercise indexes of left ventricular function.

Myocardial infarct size and cardiac performance at exercise soon after myocardial infarction

Infarct size was estimated from serial serum CK MB measurements in a series of 101 patients admitted less than 15 hours after the first acute myocardial infarction. A maximal symptom limited exercise test comprising impedance measurements for the estimation of stroke volume at rest and at different levels of exercise was performed early after admission by 26 patients. There was a slight, though not significant, negative correlation between infarct size and physical capability as measured by the duration of work. The rise in systolic blood pressure during exercise showed a significantly negative and the increase in heart a significantly positive correlation to infarct size. This suggests that the rise in blood pressure, which is less in patients with the larger infarcts, is compensated by an increase in heart rate, so that the same maximum of cardiac performance and myocardial oxygen consumption is reached. The increase in cardiac stroke volume during exercise was negatively correlated with infarct size. Stroke volume only increased during lower levels of exercise; the increase in cardiac output at higher levels of exercise was achieved entirely by an increase in heart rate. The magnitude of ST segment elevation during exercise showed a significantly positive correlation with infarct size, whereas the occurrence of arrhythmias during exercise was independent of it.

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.