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Biomedical subjects

M B Higginbotham

Publications and source records attributed to M B Higginbotham.

At least 19 recordsLinked to original sources
PubMed1995

Recovery of left ventricular function in acute nonischemic congestive cardiomyopathy.

The extent and time course of recovery of left ventricular function were investigated in 29 patients with no previous symptoms who had acute nonischemic congestive cardiomyopathy and left ventricular ejection fraction of 0.22 +/- 0.07. Improvement in left ventricular ejection fraction by at least 0.05 was observed in 24 of the 29 patients and was achieved within 6 months after the initial evaluation. Progressive improvement was seen, with a maximum ejection fraction of 0.45 +/- 0.17 being achieved within approximately 18 months. The degree of ejection fraction recovery was not related to the initial clinical or hemodynamic variables. However, the extent of fibrosis detected on endomyocardial biopsy correlated inversely with subsequent changes in ejection fraction (r = -0.65, p = 0.0003). Thus significant recovery is likely after an acute episode of nonischemic cardiomyopathy and may be progressive during the first year. Recovery is related to the extent of myocardial fibrosis detected on endomyocardial biopsy but cannot be predicted from the initial clinical or hemodynamic presentation.

Acute Disease↗
PubMed1995

Oxygen deficit during exercise testing in heart failure. Relation to submaximal exercise tolerance.

Measurements of oxygen deficit during submaximal exercise were correlated with the anaerobic threshold (as measured by gas exchange analysis), peak work rate on a ramp protocol, and the ability to perform constant work rate exercise in 10 male patients with New York Heart Association class 2 congestive heart failure and 12 age- and gender-matched normal controls. All subjects performed a maximal ramp exercise test for measurement of the anaerobic threshold. In addition, several 15-min constant work rate exercise sessions were conducted to evaluate oxygen deficit, measured as the area between the "ideal" square curve of oxygen consumption at the onset of constant work rate exercise and the actual exponentially shaped curve. Since the oxygen deficit significantly correlated with the plateau oxygen consumption during the 25-W constant work rate exercise (r = 0.61, p = 0.002), the oxygen deficit was normalized by the rectangular area of 15-min oxygen consumption above baseline. This normalized value significantly correlated with the inverse of the anaerobic threshold (r = 0.81, p < 0.0001). The logarithm of the normalized oxygen deficit significantly correlated with the maximum ramp work rate (r = -0.86, p < 0.0001) and the highest constant work rate sustained for 15 min (r = -0.82, p < 0.0001). In addition, the time to reach plateau oxygen consumption for the 25-W exercise significantly correlated with the inverse of the anaerobic threshold (r = -0.78, p < 0.0001), the maximum ramp work rate (r = -0.76, p < 0.0001), and the highest constant work rate sustained for 15 min (r = -0.74, p < 0.0001). Thus, the oxygen deficit seen in patients with heart failure during constant work rate exercise results from abnormally slow oxygen uptake kinetics and correlates with exercise capacity as measured by anaerobic threshold (via gas exchange analysis) and maximal and submaximal exercise tolerance. Oxygen deficit warrants further evaluation as a submaximal index of functional capacity in patients with heart failure.

Adult↗
PubMed1994

Central and peripheral limitations to upright exercise in untrained cardiac transplant recipients.

BACKGROUND: Functional capacity and quality of life are subjectively improved after cardiac transplantation. However, the objective improvement in exercise tolerance after transplantation has been disappointing. The extent to which allograft diastolic dysfunction contributes to this exercise intolerance has not been defined. METHODS AND RESULTS: Thirty cardiac transplant recipients between 3 and 16 months after transplantation and 30 age-matched normal control subjects underwent maximal symptom-limited graded upright bicycle exercise testing with simultaneous radionuclide angiography, invasive hemodynamic monitoring, and breath-by-breath gas analysis. Mean blood pressure was higher in the transplant group at supine rest (112.1 versus 97.7 mm Hg), normalized with upright posture, and became lower than normal at peak exercise (121.1 versus 133.2 mm Hg). Systolic function as measured by ejection fraction was normal in both groups. However, the cardiac transplant recipients had significantly lower exercise tolerance, achieving a mean maximal work rate of 390 kilopond-meters per minute (kpm/min), compared with 825 kpm/min in the normal subjects. Peak oxygen consumption was 12.3 mL.min-1.kg-1 in the transplant group, 46% lower than the normal group's value of 22.9 mL.min-1.kg-1. The transplant patients had a resting tachycardia (94 beats per minute) and a 79% reduction in exercise heart rate reserve compared with normal. Despite this chronotropic incompetence, stroke index response to exercise was consistently lower after transplantation, accounting for a 41% reduction in cardiac index at maximal exercise. The lower stroke index was accompanied by a 32% lower end-diastolic volume index at rest and a 14% lower end-diastolic volume index at peak exercise. Despite the smaller ventricular volumes after transplantation, pulmonary capillary wedge pressure was 35% higher than normal at supine rest and 50% higher at maximal exercise. Right atrial and mean pulmonary arterial pressures were similarly elevated. The ratio of pulmonary capillary wedge pressure to end-diastolic volume index was significantly higher during the postural change and exercise, suggesting allograft diastolic dysfunction. Arteriovenous oxygen difference was similar between groups at rest and with submaximal exercise but was 24% lower at maximal exercise in the transplant group, suggesting an abnormality in peripheral oxygen uptake or utilization. CONCLUSIONS: Exercise tolerance is severely limited during the first 16 months after cardiac transplantation despite preservation of allograft left ventricular systolic function. This intolerance is due to an inadequate cardiac index response from a combination of chronotropic incompetence and diastolic dysfunction limiting the appropriate compensatory use of the Starling mechanism. In addition, there is a peripheral abnormality in oxygen transport or utilization that may partially reflect the effects of deconditioning.

Adult↗
PubMed1993

Aerobic fitness, acute exercise and sleep in older men.

In the current study 12 aerobically fit and 12 sedentary older men underwent two nocturnal polysomnographic (PSG) studies. A control PSG was conducted following a day without aerobic activity, whereas a postexercise PSG study was conducted following an afternoon session of exhaustive aerobic exercise. In addition to deriving usual sleep parameters, a computer scoring program was used to count the number of individual electroencephalographic (EEG) slow waves in each PSG tracing. Multivariate and univariate analyses showed that the fit subjects had shorter sleep onset latencies, less wake time after onset, fewer discrete sleep episodes, fewer sleep stage shifts during the initial portion of the night, less stage 1 sleep, a higher sleep efficiency and more total slow waves during both PSGs than did the sedentary subjects. Although no main effects were found for the acute exercise challenge, post hoc analyses showed that high levels of body heating during exercise predicted increased sleep fragmentation for both fit and sedentary subjects. These findings provide initial support for the contention that exercise and fitness may have significant effects on the sleep of older men. However, results also suggest that high levels of body heating resulting from a single exercise challenge may have adverse effects. Implications of the study are discussed and suggestions for future research are provided.

Age Factors↗
PubMed1991

Age-related alterations of Doppler left ventricular filling indexes in normal subjects are independent of left ventricular mass, heart rate, contractility and loading conditions.

The purpose of this study was to determine whether age-related alterations in Doppler diastolic filling indexes occur independent of cardiovascular disease and confounding physiologic variables. Ten old (62 to 73 years) and 10 young (21 to 32 years) healthy male volunteers were rigorously screened for cardiovascular disease and underwent comprehensive Doppler echocardiography, radionuclide ventriculography and invasive measurements of right heart and left atrial pressures. There were no differences between the two groups in the physiologic variables of left ventricular mass, volumes, ejection fraction, end-systolic wall stress, left atrial size, heart rate and right atrial, pulmonary artery, pulmonary capillary wedge and systemic arterial pressures. However, there were marked differences in Doppler left ventricular filling indexes. Compared with the young group, the old group had reduced peak early diastolic flow velocity (56 +/- 13 vs. 82 +/- 12 cm/s, p = 0.0002) and increased atrial diastolic flow velocity (59 +/- 14 vs. 43 +/- 10 cm/s, p = 0.009) and had a peak atrial/early flow velocity (A/E) ratio twice that of the young group (1.09 +/- 0.29 vs. 0.54 +/- 0.15, p less than 0.0001). Similar results were obtained for the time-velocity integrals of the peaks. Subjects in the old group also had a markedly reduced peak filling rate (274 +/- 62 vs. 448 +/- 152 ml/s, p = 0.004). In univariate and multivariate regression analyses, peak early and atrial flow velocities were not related to any of the physiologic variables measured once age was accounted for, although peak filling rate, a volumetric measure flow, was related to body surface area as well as age.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1991

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)

Adult↗
PubMed1991

Effects of exercise training on cardiorespiratory function in men and women older than 60 years of age.

This study reports the physiologic effects of up to 14 months of aerobic exercise in 101 older (greater than 60 years) men and women. After an extensive baseline physiologic assessment (Time 1), in which aerobic capacity and blood lipids were measured, subjects were randomized to an aerobic exercise condition (cycle ergometry, 3 times per week for 1 hour), nonaerobic yoga (2 times per week for 1 hour), or a waiting list nonexercise control group for 4 months, and then underwent a second (Time 2) assessment. At the completion of the second assessment, all remaining subjects completed 4 months of aerobic exercise and were reevaluated (Time 3). Subjects were given the option of participating in 6 additional months of supervised aerobic exercise, and all available subjects completed a fourth assessment (Time 4) 14 months after their initial baseline evaluation. Results indicated that subjects generally exhibited a 10 to 15% improvement in peak oxygen consumption after 4 months of aerobic exercise training, and a 1 to 6% improvement in aerobic power with additional aerobic exercise training. On the other hand, subjects, especially men, continued to have improvements in submaximal exercise performance (i.e., anaerobic threshold). In addition, aerobic exercise was associated with an improved lipid profile; subjects participating in aerobic exercise for up to 14 months exhibited increased levels of high-density lipoprotein cholesterol. Maintenance of regular aerobic exercise for an extended time interval is associated with greater cardiovascular benefits among older adults than has been reported previously.

Aged↗
PubMed1991

Exercise intolerance in patients with heart failure and preserved left ventricular systolic function: failure of the Frank-Starling mechanism.

Invasive cardiopulmonary exercise testing was performed in 7 patients who presented with congestive heart failure, normal left ventricular ejection fraction and no significant coronary or valvular heart disease and in 10 age-matched normal subjects. Compared with the normal subjects, patients demonstrates severe exercise intolerance with a 48% reduction in peak oxygen consumption (11.6 +/- 4.0 versus 22.7 +/- 6.1 ml/kg per min; p less than 0.001), primarily due to a 41% reduction in peak cardiac index (4.2 +/- 1.4 versus 7.1 +/- 1.1 liters/min per m2; p less than 0.001). In patients compared with normal subjects, peak left ventricular stroke volume index (34 +/- 9 versus 46 +/- 7 ml/min per m2; p less than 0.01) and end-diastolic volume index (56 +/- 14 versus 68 +/- 12 ml/min per m2; p less than 0.08) were reduced, whereas peak ejection fraction and end-systolic volume index were not different. In patients, the change in end-diastolic volume index during exercise correlated strongly with the change in stroke volume index (r = 0.97; p less than 0.0001) and cardiac index (r = 0.80; p less than 0.03). Pulmonary wedge pressure was markedly increased at peak exercise in patients compared with normal subjects (25.7 +/- 9.1 versus 7.1 +/- 4.4 mm Hg; p less than 0.0001). Patients demonstrated a shift of the left ventricular end-diastolic pressure-volume relation upward and to the left at rest. Increases in left ventricular filling pressure during exercise were not accompanied by increases in end-diastolic volume, indicating a limitation to left ventricular filling.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1991

Long-term effects of exercise on psychological functioning in older men and women.

The purpose of this study was to determine the psychological, behavioral, and cognitive changes associated with up to 14 months of aerobic exercise training. For the first 4 months of the study, 101 older (greater than 60 years) men and women were randomly assigned to one of three conditions: Aerobic exercise, Yoga, or a Waiting List control group. Before and following the intervention, all subjects completed a comprehensive assessment battery, including measures of mood and cognitive functioning. A semi-crossover design was employed such that, following completion of the second assessment, all subjects completed 4 months of aerobic exercise and underwent a third assessment. Subjects were given the option of participating in 6 additional months of supervised aerobic exercise (14 months total), and all subjects, regardless of their exercise status, completed a fourth assessment. Results indicated that subjects experienced a 10-15% improvement in aerobic capacity. In general, there were relatively few improvements in cognitive performance associated with aerobic exercise, although subjects who maintained their exercise participation for 14 months experienced improvements in some psychiatric symptoms. However, the healthy subjects in this study were functioning at a relatively high level to begin with, and exercise training may produce greater improvements among elderly with concomitant physical or emotional impairments.

Affect↗
PubMed1989

A brief self-administered questionnaire to determine functional capacity (the Duke Activity Status Index).

To develop a brief, self-administered questionnaire that accurately measures functional capacity and assesses aspects of quality of life, 50 subjects undergoing exercise testing with measurement of peak oxygen uptake were studied. All subjects were questioned about their ability to perform a variety of common activities by an interviewer blinded to exercise test findings. A 12-item scale (the Duke Activity Status Index) was then developed that correlated well with peak oxygen uptake (Spearman correlation coefficient 0.80). To test this new index, an independent group of 50 subjects completed a self-administered questionnaire to determine functional capacity and underwent exercise testing with measurement of peak oxygen uptake. The Duke Activity Status Index correlated significantly (p less than 0.0001) with peak oxygen uptake (Spearman correlation coefficient 0.58) in this independent sample. The Duke Activity Status Index is a valid measure of functional capacity that can be obtained by self-administered questionnaire.

Activities of Daily Living↗
PubMed1989

Doppler left ventricular diastolic filling abnormalities in aortic stenosis and their relation to hemodynamic parameters.

Doppler mitral flow indexes and their relation to invasively measured hemodynamic diastolic indexes were assessed in 13 patients with isolated aortic stenosis (AS), and compared to Doppler indexes in 10 normal subjects matched for age, heart rate, left ventricular (LV) ejection fraction and LV load. Patients with AS showed no difference in Doppler early filling (E) indexes, but demonstrated greater Doppler atrial filling (A) indexes in comparison to normal subjects: atrial velocity (89 +/- 31 vs 56 +/- 7 cm/s), atrial integral (11.4 +/- 4.8 vs 5.7 +/- 1.6 cm), A/E velocity (1.69 +/- 0.89 vs 1.06 +/- 0.26) and A/E integral (3.53 +/- 6.64 vs 0.81 +/- 0.27) (all p less than 0.05). Doppler indexes in patients with AS did not correlate with hemodynamic indexes of LV relaxation or chamber stiffness. Significant correlations were observed between Doppler and angiographic peak filling rates (r = 0.70) and between Doppler atrial filling velocity and LV end-diastolic volume (r = -0.66), LV end-diastolic pressure (r = -0.48) and LV ejection fraction (r = 0.53) (all p less than 0.05). These data indicate that, compared to matched normal subjects, most patients with AS have an increased atrial contribution to LV filling. However, in patients with decreased LV function, atrial function may also be depressed, as indicated by a decreased atrial contribution to LV filling, resulting in "normalization" of the Doppler mitral flow pattern.

Aged↗
PubMed1989

Chronic stable angina monotherapy. Nifedipine versus propranolol.

A placebo-controlled, double-blind, crossover study was conducted to determine the effects of nifedipine (60 to 90 mg per day) monotherapy and propranolol (240 mg per day) monotherapy on symptoms, angina threshold, and cardiac function in patients with chronic stable angina. Following a two-week placebo period, patients were randomly assigned to receive either nifedipine or propranolol for a five-week treatment period, after which they crossed over to the alternative regimen. All 21 patients were men with chronic stable angina pectoris, 13 of whom had symptoms both at rest and on exertion. New York Heart Association functional class improved in patients taking either nifedipine or propranolol, and nitroglycerin consumption decreased with both treatments compared with placebo. Nifedipine significantly delayed the onset of chest pain and 1 mm of ST-segment depression during bicycle exercise; increases with propranolol were smaller and not statistically significant. Nine patients had a preferential clinical response to nifedipine compared with six patients to propranolol; this was unrelated to the presence or absence of pain at rest or to any baseline hemodynamic finding. Nifedipine and propranolol were equally effective in relieving exertional ischemia as shown by improvement in radionuclide ejection fraction at identical work loads. Exercise wall motion, assessed by a semiquantitative wall motion score, also improved with both drugs. Propranolol treatment decreased exercise cardiac output by 14 percent (p = 0.01) through its effect on heart rate. In contrast, nifedipine treatment had no effect on cardiac output. Thus, nifedipine is more effective on several measurements than propranolol when administered as single drug therapy in stable angina and has the advantage of preserving cardiac output during exercise.

Adult↗
PubMed1989

Exercise training in patients with chronic heart failure delays ventilatory anaerobic threshold and improves submaximal exercise performance.

We have recently demonstrated that exercise training can induce important hemodynamic and metabolic adaptations in patients with chronic heart failure due to severe left ventricular dysfunction. This study examines the accompanying changes in submaximal exercise performance and the ventilatory response to exercise in these patients. Before and after 16-24 weeks of exercise training, subjects underwent two symptom-limited bicycle exercise tests, one with an incremental graded workload, and one with a constant workload that represented 79 +/- 11% of the pretraining peak oxygen consumption. Breath-by-breath expired gas analysis was performed continuously during each test, and central hemodynamic, leg blood flow, and blood lactate measurements were obtained during the incremental protocol. The ventilatory anaerobic threshold was determined during the incremental exercise study from coplotted breath-by-breath ventilatory data with standard criteria by observers who were unaware of patient identity or training status. As previously reported, exercise training increased peak oxygen consumption by 23% from 16.8 +/- 3.8 to 20.6 +/- 4.7 ml/kg/min and reduced blood lactate levels during submaximal exercise. The training-induced decrease in lactate accumulation was accompanied by a decrease in carbon dioxide production, respiratory exchange ratio, and ventilation during submaximal exercise. The ventilatory anaerobic threshold was delayed from 284 +/- 43 to 352 +/- 91 seconds of exercise (p = 0.02), and it occurred at an increased oxygen consumption (10.1 +/- 1.2 vs. 12.1 +/- 2.6 ml/kg/min, p = 0.01). Exercise duration during the constant workload protocol increased from 938 +/- 410 to 1,429 +/- 691 seconds (p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1989

Relation between central and peripheral hemodynamics during exercise in patients with chronic heart failure. Muscle blood flow is reduced with maintenance of arterial perfusion pressure.

We studied the central hemodynamic, leg blood flow, and metabolic responses to maximal upright bicycle exercise in 30 patients with chronic heart failure attributable to severe left ventricular dysfunction (ejection fraction, 24 +/- 8%) and in 12 normal subjects. At peak exercise, patients demonstrated reduced oxygen consumption (15.1 +/- 4.8 vs. 32.1 +/- 9.9 ml/kg/min, p less than 0.001), cardiac output (8.7 +/- 3.2 vs. 18.6 +/- 4.4 l/min, p less than 0.001), and mean systemic arterial blood pressure (116 +/- 15 vs. 135 +/- 13 mm Hg, p less than 0.01) compared with normal subjects. Leg blood flow was decreased in patients versus normal subjects at rest and matched submaximal work rates and maximal exercise (2.1 +/- 1.9 vs. 6.4 +/- 1.4 l/min, all p less than 0.01). Mean systemic arterial blood pressure was no different in the two groups at rest or at matched submaximal work rates, whereas leg vascular resistance was higher in patients compared with normal subjects at rest, submaximal, and maximal exercise (all p less than 0.01). Although nonleg blood flow was decreased at rest in patients, it did not decrease significantly during exercise in either group. Peak exercise leg blood flow was related to peak exercise cardiac output in patients (r = 0.66, p less than 0.01) and normal subjects (r = 0.67, p less than 0.01). In patients, leg vascular resistance was not related to mean arterial blood pressure, pulmonary capillary wedge pressure, arterial catecholamines, arterial lactate, or femoral venous pH at rest or during exercise. Compared with normal subjects during submaximal exercise, patients demonstrated increased leg oxygen extraction and lactate production accompanied by decreased leg oxygen consumption. Thus, in patients with chronic heart failure compared with normal subjects, skeletal muscle perfusion is decreased at rest and during submaximal and maximal exercise, and local vascular resistance is increased. Our data indicate that nonleg blood flow and arterial blood pressure were preferentially maintained during exercise at the expense of leg hypoperfusion in our patients. This was associated with decreased leg oxygen utilization and increased leg oxygen extraction when compared to normal subjects, providing further evidence that reduced perfusion of skeletal muscle is important in causing early anaerobic skeletal muscle metabolism during exercise in subjects with this disorder.(ABSTRACT TRUNCATED AT 400 WORDS)

Aged↗
PubMed1988

The ventilatory threshold: quantitative analysis of reproducibility and relation to arterial lactate concentration in normal subjects and in patients with chronic congestive heart failure.

The present study evaluates optimal ventilatory criteria and exercise protocols for determining the ventilatory threshold, and assesses the day-to-day reproducibility of the ventilatory threshold and its relation to peak oxygen uptake VO2 and blood lactate concentration in normal subjects and patients with stable chronic congestive heart failure (CHF). Eighteen normal subjects and 18 patients underwent rapid (1-minute stage) and gradual (3-minute stage) bicycle exercise tests on consecutive days. The ventilatory threshold was determined from computer-generated printouts of expired gas variables measured breath by breath. Interobserver variability of ventilatory threshold was small in both normal (0.66 +/- 0.85 ml/min/kg) and CHF patients (0.50 +/- 0.46 ml/min/kg). Variability in the normal subjects was lower for the rapid exercise protocol (0.66 +/- 0.85 ml/min/kg) than the gradual protocol (1.72 +/- 1.63 ml/min/kg) (p less than 0.05), but both protocols produced similar results in the CHF group. Day-to-day reproducibility of ventilatory threshold was high (r = 0.91, standard error of the estimate 1.74 ml/min/kg) and was similar to that of peak VO2 (r = 0.95, standard error of the estimate 3.31 ml/min/kg). The use of co-plotted ventilatory equivalents for oxygen and carbon dioxide yielded ventilatory threshold values comparable to values obtained by using multiple parameters (r = 0.94, p less than 0.0001). Although the ventilatory threshold did not predict a precise lactate level for individual subjects, the lactate increment at the ventilatory threshold occurred within a narrow range in both normal subjects and patients with CHF; the increase was 7.5 +/- 4.5 mg/dl and 7.7 +/- 4.1 mg/dl, respectively, indicating a relation to initial increases in blood lactate.

Aged↗
PubMed1988

Increased exercise ventilation in patients with chronic heart failure: intact ventilatory control despite hemodynamic and pulmonary abnormalities.

This study was designed to determine the pathophysiologic basis of increased exercise ventilation in the presence of chronic heart failure. Sixty-four ambulatory patients with chronic heart failure and 38 age-matched normal control subjects performed exercise according to identical staged, symptom-limited bicycle exercise protocols with measurement of hemodynamic, ventilatory, and metabolic responses. Compared with normal subjects, ventilation and the ratio of ventilation to CO2 production (Ve/VCO2), and pulmonary capillary wedge pressure were elevated in patients at rest and during exercise. The ratio of pulmonary dead space to tidal volume (Vd/Vt) also was elevated in the heart failure group at rest and during exercise and was closely related to Ve/VCO2 (all r greater than .72, p less than .001). Rest and exercise arterial PCO2 regulation was normal in patients. Peak exercise Ve/VCO2 did not correlate with pulmonary vascular pressures, but was inversely related to cardiac output (r = -.49, p less than .001). Thus, neurohumoral ventilatory control mechanisms are intact in patients with chronic heart failure and act to maintain normal PaCO2 levels in the face of increased pulmonary dead space. Activation of abnormal reflexes due to hemodynamic derangements during exercise are not important in determining ventilation in the presence of chronic heart failure. The demonstration of a correlation between decreased cardiac output and increased ventilation in the patient group suggests that attenuated pulmonary perfusion may play a role in causing exercise hyperpnea in the presence of chronic heart failure by producing ventilation perfusion abnormalities and thereby increasing physiologic pulmonary dead space.

Exercise Test↗
PubMed1988

Exercise training in patients with severe left ventricular dysfunction. Hemodynamic and metabolic effects.

We studied the effects of exercise training in patients with chronic heart failure attributed to left ventricular dysfunction (ejection fraction, 24 +/- 10%). Twelve ambulatory patients with stable symptoms underwent 4-6 months of conditioning by exercising 4.1 +/- 0.6 hr/wk at a heart rate corresponding to 75% of peak oxygen consumption. Before and after training, patients underwent maximal bicycle exercise testing with direct measurement of central hemodynamic, leg blood flow, and metabolic responses. Exercise training resulted in a decrease in heart rate at rest and submaximal exercise and a 23% increase in peak oxygen consumption from 16.8 +/- 3.8 to 20.6 +/- 4.7 ml/kg/min (p less than 0.01). Heart rate, arterial lactate, and respiratory exchange ratio were unchanged at peak exercise after training. Maximal cardiac output tended to increase from 8.9 +/- 2.7 to 9.9 +/- 3.2 1/min and contributed to improved peak oxygen consumption in some patients, although this change did not reach statistical significance (p = 0.13). Rest and exercise measurements of left ventricular ejection fraction, left ventricular end-diastolic volume, and left ventricular end-systolic volume were unchanged. Right atrial, pulmonary arterial, pulmonary capillary wedge, and systemic arterial pressures were not different after training. Training induced several important peripheral adaptations that contributed to improved exercise performance. At peak exercise, systemic arteriovenous oxygen difference increased from 13.1 +/- 1.4 to 14.6 +/- 2.3 ml/dl (p less than 0.05). This increase was associated with an increase in peak-exercise leg blood flow from 2.5 +/- 0.7 to 3.0 +/- 0.8 l/min (p less than 0.01) and an increase in leg arteriovenous oxygen difference from 14.5 +/- 1.3 to 16.1 +/- 1.9 ml/dl (p = 0.07). Arterial and femoral venous lactate levels were markedly reduced during submaximal exercise after training, even though cardiac output and leg blood flow were unchanged at these workloads. Thus, ambulatory patients with chronic heart failure can achieve a significant training effect from long-term exercise. Peripheral adaptations, including an increase in peak blood flow to the exercising leg, played an important role in improving exercise tolerance.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗