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Biomedical subjects

P A McElroy

Publications and source records attributed to P A McElroy.

16 recordsLinked to original sources
PubMed1990

Myocardial energetics and efficiency in patients with idiopathic cardiomyopathy: response to dobutamine and amrinone.

Nine consecutive patients having severe idiopathic dilated cardiomyopathy were studied for their response in ventricular function, coronary sinus blood flow and myocardial oxygen consumption, lactate extraction and efficiency following incremental doses of dobutamine, followed by the combination of dobutamine and the phosphodiesterase inhibitor amrinone. Results, presented as baseline and the response to the peak dose (15 micrograms/kg/min) of dobutamine and to the combination of dobutamine and amrinone (each at 15 micrograms/kg/min) (differences compared with baseline) were: wedge pressure decreased from 28 +/- 7 to 26 +/- 8 mm Hg (p = NS) and to 20 +/- 6 mm Hg (p less than 0.01); cardiac index rose from 1.47 +/- 0.44 L/min/m2 to 2.89 +/- 1.1 L/min/m2 (p less than 0.01) and to 3.64 +/- 1.05 L/min/m2 (p less than 0.001); myocardial oxygen consumption remained invariant (18 +/- 8, 17 +/- 5, and 19 +/- 5 ml/min) despite progressive increments in minute work from 2.96 +/- 1.1 to 6.98 +/- 3.9 kg - m/min (p less than 0.01) and to 9.38 +/- 4.3 kg - m/min (p less than 0.001); myocardial lactate extraction rose from 21 +/- 10% to 30 +/- 15% (p = NS) and to 35 +/- 10% with the addition of amrinone (p less than 0.01). No patient had net lactate efflux into the coronary sinus, and myocardial efficiency improved from 9.5 +/- 5% to 21.7 +/- 13.0% (p less than 0.01) and to 28.0 +/- 18.0% (p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Amrinone↗
PubMed1990

Long-term reproducibility of respiratory gas exchange measurements during exercise in patients with stable cardiac failure.

Present-day technology has greatly facilitated the monitoring of respiratory gas exchange in the clinical exercise laboratory. Despite the growing use of these techniques to assess the severity and progression of disease or therapeutic response in patients with heart failure, the long-term reproducibility of oxygen uptake (VO2), carbon dioxide production, minute ventilation, heart rate (HR), and blood pressure at rest and during incremental exercise in such patients, to our knowledge, has not been evaluated. Therefore, the purpose of this study was to quantify the reproducibility of these variables along with exercise duration, maximum VO2 (VO2max) and anaerobic threshold in a group of 16 patients (61 +/- 7 years, 14 male) with chronic, stable cardiac failure of varying severity and etiology who had five or more incremental treadmill exercise tests over a period of time that ranged from 3 to 22 months. For each variable, reproducibility was represented by the coefficient of variation (CVAR). Except for exercise duration, CVAR was not a function of the severity of heart failure and, for all variables, patient-to-patient variation in CVAR was approximately 9 percent. The maximum CVAR for HR, systolic blood pressure, VO2, and VO2max was generally below 10.5 percent and for exercise duration and anaerobic threshold it was less than 12.5 percent. Based on this retrospective analysis, it is concluded that reproducible respiratory gas exchange and HR exercise responses are obtainable over extended periods of time in patients with stable, chronic cardiac failure. Exercise duration, however, is less reproducible in patients with moderate to severe failure.

Aged↗
PubMed1989

Response in oxygen uptake and ventilation during stair climbing in patients with chronic heart failure.

To examine the level of muscular work and ventilatory response to stair climbing (mobile Stairmaster staircase, 1 step/2.5 s), respiratory gas exchange, ventilation, heart rate and arterial pressure were monitored in patients with chronic heart failure and their response compared with that of normal individuals. Aerobic capacity (maximal oxygen uptake) and anaerobic threshold during treadmill exercise were also determined and used to ascertain the metabolic cost of stair climbing. No differences were observed in the response of mean arterial blood pressure between the 12 patients and 10 normal subjects during exercise or recovery. However, the heart rate and oxygen consumption obtained during exercise were significantly lower in the patients with chronic heart failure than in the normal subjects (p less than 0.05). All patients with a maximal oxygen uptake less than 20 ml/min/kg during treadmill exercise had an oxygen uptake during stair climbing that exceeded their anaerobic threshold and, consequently, they attained a significantly (p less than 0.01) higher level of ventilation during exercise and recovery. This was not the case for those patients with greater aerobic capacity. Therefore, it is concluded that stair climbing for the 12 patients with heart failure and moderate to moderately severe impairment in aerobic capacity represents strenuous anaerobic exercise. The resultant excess ventilation may explain the limiting sensation of dyspnea that is frequently experienced by these patients during and after stair climbing.

Adult↗
PubMed1989

Safety and efficacy of low-potassium dialysate.

To evaluate the safety and efficacy of low-potassium dialysate, 11 patients with stable end-stage renal disease and with no history of arrhythmia or digitalis use were studied. All were treated with hemodialysis three times per week. Dialysates with potassium concentrations of 2 mEq/L, 1 mEq/L, or 0 mEq/L were compared. Each patient (exceptions noted in text) was studied once at each bath potassium concentration. Cardiac rhythm was recorded by Holter monitor during and for six hours following dialysis. Single PVCs and APCs were common with all potassium concentrations. Only one patient had high-grade ventricular ectopy. It was seen with each of the three potassium concentrations, but was most severe with the potassium-free dialysate. The potassium-free dialysate removed significantly more potassium (78.5 +/- 2.6 mEq) than the 1-K dialysate (62.9 +/- 5.1 mEq) or the 2-K dialysate (50.6 +/- 6 mEq), and the 1-K dialysate removed significantly more potassium than the 2-K dialysate. There were small but significant differences in serum potassium concentrations with the three different dialysates. It was concluded that (1) in all but one of our patients potassium-free dialysate did not produce new ectopy; (2) potassium-free dialysate was 24% more effective than 1-K dialysate and 50% more effective than 2-K dialysate in removing body potassium; and (3) 1-K dialysate was 20% more effective than 2-K dialysate in removing body potassium.

Adult↗
PubMed1989

Pathophysiology of the failing heart.

Cardiac (or myocardial) failure of acute onset or of chronic duration is the result of a structural and/or biochemical remodeling of the myocardium. This, in turn, compromises the contractile performance of the myocardium. The hypertrophic growth of myocytes and the architectural transformation of ventricular chamber size and shape--while initially useful compensatory responses--do not prevent the inevitable appearance of pump failure where oxygen delivery to the metabolizing tissues becomes inadequate. Indeed, the severity of cardiac failure can be judged from the level of oxygen consumption that elicits this state of impaired oxygen supply and demand. A better understanding of the mechanical behavior of the ventricular chamber, including its elastic and resistive properties, together with recent advances in our ability to measure instantaneous ventricular pressure and volume, may prove useful in identifying pathologic features of hypertrophy and dilatation in individual patients. In grading the severity of failure and comparing groups of patients, a normalization of the mechanical parameters by differences in chamber size, shape, and mass is necessary. Symptomatic cardiac failure, based invariably on inadequate oxygen delivery and/or pulmonary congestion, is more commonly the result of ventricular systolic dysfunction. Abnormalities in diastolic function, including ventricular relaxation and filling, while less common and often associated with preserved systolic pump function, do occur. Finally, it must be recognized that the failing ventricle carries an additional hydraulic load that arises from the arterial circulation to which it is coupled.(ABSTRACT TRUNCATED AT 250 WORDS)

Forced Expiratory Flow Rates↗
PubMed1988

Cardiopulmonary exercise testing in congestive heart failure.

Cardiopulmonary exercise testing includes the monitoring of respiratory gases and airflow to determine oxygen uptake, carbon dioxide (CO2) production, respiratory rate, tidal volume, and minute ventilation during a graded maximal exercise test. A plateau in oxygen uptake, which occurs despite an increase in work load, and which is termed maximal oxygen uptake (VO2 max), correlates with the maximal exercise cardiac output and can therefore be used to grade the severity of heart failure. The anaerobic threshold occurs at 60 to 70% of VO2 max and is another indicator of the severity of heart failure and, when attained, indicates that the patient is close to performing a maximal test. We have found VO2 max and anaerobic threshold to be objective measures of efficacy of both investigational and noninvestigational therapy in patients with heart failure. A pulmonary limitation to exercise can be identified by the failure to attain anaerobic threshold or VO2 max, as well as exhaustion of the ventilatory reserve, as estimated by maximal voluntary ventilation. Thus, cardiopulmonary exercise testing can be used to (1) grade the severity of heart failure, (2) objectively follow the response to therapy, and (3) differentiate a cardiac from a pulmonary limitation to exercise.

Carbon Dioxide↗
PubMed1988

Physiologic correlates of the heart rate response to upright isotonic exercise: relevance to rate-responsive pacemakers.

Rate-responsive cardiac pacing requires a sensitive physiologic variable that is closely correlated with the heart rate-oxygen uptake relation, particularly in patients with heart failure whose cardiac output response to exercise is more dependent on heart rate. Accordingly, the heart rate response to upright exercise was measured in 81 patients with heart failure or hypertension, or both, and in 27 normal subjects. Oxygen uptake (VO2), minute ventilation (VE), cardiac output, right heart pressures and the mixed venous temperature, oxygen saturation (SvO2) and pH were analyzed throughout exercise. Linear regression analysis of these variables with heart rate revealed the following: 1) There was a highly linear heart rate-VO2 relation in each subject (the average slope of this relation was greater [p less than 0.05] in patients with more severe failure). 2) VE was highly correlated with exercise heart rate, and its slope was not different between normal subjects and patients. 3) Mixed venous temperature and pH were poor predictors of exercise heart rate, particularly at low or moderate levels of work; however, SvO2 was highly correlated with heart rate for all levels of work. Thus, in normal subjects and patients with heart failure or hypertension, or both, heart rate increases linearly with isotonic leg exercise. Minute ventilation and mixed venous oxygen saturation are highly correlated with this response and may serve as potential sensors for rate-responsive pacemakers.

Adult↗
PubMed1988

Hemodynamic, ventilatory and metabolic effects of light isometric exercise in patients with chronic heart failure.

Light isometric exercise, such as lifting or carrying loads that require 25% of a maximal voluntary contraction, is frequently reported to cause dyspnea in patients with heart failure. The pathophysiologic mechanisms responsible for the appearance of this symptom, however, are unknown. Accordingly, hemodynamic, metabolic and ventilatory responses to 6 min of light isometric forearm exercise were examined and compared in 20 patients with chronic heart failure and abnormal ejection fraction (24 +/- 9%) and 17 normal individuals. In contrast to findings in normal volunteers, exercise cardiac index did not increase whereas exercising forearm and mixed venous lactate concentrations increased (p less than 0.05) above levels at rest in patients with heart failure; at 90 s of recovery, blood lactate concentration remained elevated (p less than 0.05). The venous lactate concentration of the nonexercising arm, unlike that of the exercising forearm, was not altered. Oxygen uptake, carbon dioxide production and minute ventilation increased similarly in patients and normal subjects during exercise, but only in patients did each increase further (p less than 0.05) during recovery. Thus, in patients with heart failure, light isometric forearm exercise represents an anaerobic contraction with lactate production. The subsequent increase in carbon dioxide production leads to a disproportionate increase in minute ventilation and oxygen uptake during recovery that may be perceived as breathlessness.

Adult↗
PubMed1988

Use of the cardiopulmonary exercise test to evaluate the patient with chronic heart failure.

Isotonic exercise testing imposes a physiological stress on the cardiopulmonary unit. Accordingly, monitoring of oxygen, carbon dioxide and air flow during an exercise test (i.e. a cardiopulmonary exercise test) can be used to assess heart function in patients with chronic heart failure. Specifically, an incremental treadmill cardiopulmonary exercise test represents a non-invasive means to determine aerobic capacity, or maximal oxygen uptake (VO2max ml min-1 kg-1), and anaerobic threshold (AT, ml min-1 kg-1). These objective measures of cardiopulmonary function are then used to grade the severity of failure and the functional capacity of the patient. In addition, they may be used to predict the cardiac reserve, or maximal cardiac index (CImax, l min-1 m-2) during exercise. That is, the severity is considered to be mild (class A) when AT greater than 14 or VO2max greater than 20, mild to moderate (class B) when AT falls between 11 and 14 or VO2max between 16 and 20, moderate to severe (class C) when AT ranges between 8 and 11 or VO2max between 10 and 16, and severe (class D) when AT less than 8 or VO2max less than 10. The predicted CImax for classes A, B, C and D are greater than 8, 6-8, 4-6 and less than 4, respectively. Finally, a major objective of medical therapy in patients with heart failure is to improve cardiac output and oxygen delivery to working skeletal muscle and thereby enhance effort tolerance. This therapeutic endpoint can be gauged by cardiopulmonary exercise testing from the response in AT and VO2max.

Anaerobic Threshold↗
PubMed1988

Monitoring physical activity in ambulatory patients with chronic cardiac failure.

Static or dynamic work in patients with chronic cardiac failure elicits a variety of pathophysiologic responses that impair the ability of the cardiopulmonary unit to sustain O2 delivery at a rate that is commensurate with the O2 requirements of working skeletal muscle. Regional abnormalities in the circulation of skeletal muscle may further compromise nutritive blood flow to muscle. As a result, the patient experiences a sense of fatigue during physical activity. Dyspnea, or an abnormal awareness of breathing, may also accompany exercise in these patients. This sense of breathlessness may be due to an abnormally elevated work of breathing secondary to decreased pulmonary compliance, a heightened chemical drive to ventilation, and a possible imbalance in the O2 supply and demand of the respiratory muscles. The ambulatory monitoring of physical activity in patients with chronic cardiac failure has not been systematically examined. Potential monitoring techniques that may provide accurate and reproducible results regarding the exercise response in these patients include the thoracic impedance principle to measure minute ventilation and portable O2 uptake sensors.

Activities of Daily Living↗
PubMed1987

Measurement and interpretation of maximal oxygen uptake in patients with chronic cardiac or circulatory failure.

Rapidly responding gas analyzers have simplified the monitoring of oxygen uptake (VO2) in the clinical exercise laboratory. An incremental, exhaustive, upright exercise test can be safely used to determine the plateau in oxygen uptake during exercise, or maximal VO2 (VO2max), in patients with chronic cardiac or circulatory failure. We define VO2max in these patients as an increase in VO2 of less than 1 ml/min/kg despite an increment in work load. The value for VO2max indicates the patient's aerobic capacity; it also predicts the maximal cardiac output during exercise and therefore serves as an estimate of cardiac reserve and of the severity of cardiac or circulatory failure. Symptom-limited VO2 during exercise, termed maximum oxygen uptake but more appropriately peak VO2, bears no relationship to VO2max. The two terms should not be used interchangeably.

Cardiac Output↗
PubMed1987

Cardiopulmonary exercise testing in clinical practice.

Cardiopulmonary exercise testing refers to the noninvasive measurement of respiratory gas exchange and air flow, together with heart rate, blood pressure, and the electrocardiogram. These data, obtained during an incremental exercise test, can be used to derive the aerobic capacity or VO2max, which is an objective measure of the severity of chronic cardiac and circulatory failure, as well as to predict the maximum cardiac output response to exercise. The additional monitoring of minute ventilation and arterial oxygen saturation can be used to distinguish ventilatory from cardiac or circulatory causes of exertional dyspnea. Finally, this information serves as an objective measure of functional capacity which can be monitored over time to assess the natural history of disease as well as its response to medical therapy.

Heart Function Tests↗
PubMed1987

Determination of aerobic capacity and the severity of chronic cardiac and circulatory failure.

The noninvasive determination of maximal oxygen uptake or VO2max, defined as a plateau in VO2 during incremental treadmill exercise, is an objective, reproducible, and negotiable measure of the severity of chronic cardiac or circulatory failure. Moreover, this noninvasive variable predicts the exercise cardiac output response and thereby the cardiac reserve. The lactate or anaerobic threshold has been validated in these patients from the response of mixed venous lactate to incremental exercise and has been shown to be another objective measure of the severity of chronic cardiac or circulatory failure. The anaerobic threshold can be reliably assessed from the response in breath-by-breath respiratory gas exchange by the use of multiple criteria, several of which can be monitored during the exercise test itself and the remainder of which can be measured during the recovery period. We find the breath-by-breath monitoring of respiratory gas exchange and air flow to provide the best means of assessing the anaerobic threshold and for identifying the plateau in VO2, or VO2max, in response to incremental treadmill exercise.

Aerobiosis↗
PubMed1986

Failure of nitroglycerin introduced after prolonged myocardial ischemia to improve collateral blood flow and function in tranquilized dogs.

This study investigated whether nitroglycerin can improve ischemic zone blood flow and function when its infusion is delayed following left anterior descending (LAD) occlusion. Nitroglycerin (200 micrograms/min, 11 dogs) or saline (six dogs) was infused for 2 hours starting 2 hours after occlusion. Regional myocardial blood flow (MBF) was measured (9 +/- 1 micron radioactive microspheres) before and at 2 and 4 hours after occlusion. Segmental contraction was determined by cineroentgenography of implanted tantalum markers. For all ischemic samples (defined as MBF less than or equal to 0.4 ml/min/gm), the average improvement in MBF in the epicardial half (EPI) was 0.05 +/- 0.02 ml/min/gm (mean +/- SEM) with nitroglycerin vs 0.06 +/- 0.06 with saline (p greater than 0.5). Improvement in the endocardial half (ENDO) averaged 0.03 +/- 0.03 ml/min/gm with nitroglycerin vs 0.09 +/- 0.08 with saline (p = 0.5). Contraction in the ischemic zone ceased following occlusion and was unaffected by nitroglycerin or saline. Control blood flows in the ischemic region were 22% less in the ENDO (p less than 0.001) and 19% less in the EPI (p less than 0.005) than in nonischemic myocardium. These results indicate that 2 hours after LAD occlusion in dogs, nitroglycerin was unable to improve ischemic zone collateral flow or contractile function compared to untreated controls. Lower ischemic zone control flows indicate that infarct volume expansion may occur within 4 hours after coronary occlusion.

Animals↗
PubMed1986

Cardio-pulmonary exercise testing in the evaluation of mitral and aortic valve incompetence.

Cardio-pulmonary exercise (CPX) testing can be used to discern the functional integrity of the right and left heart and pulmonary circulation in patients with chronic mitral or aortic valvular incompetence. The noninvasive determination of VO2 max and anaerobic threshold in these patients serves to assess the severity of chronic circulatory failure and to predict the maximum exercise cardiac output (or cardiac reserve). Invasive monitoring of right heart pressures and left ventricular filling (wedge) pressure identifies abnormalities in ventricular function and the pulmonary circulation that may not be otherwise apparent. Noninvasive and invasive CPX testing is therefore a valuable tool which can also be applied to the serial evaluation of these patients. CPX offers several advantages over traditional indices of ventricular function (e.g., resting cardiac output, filling pressure and ejection fraction) in that it objectively identifies the patients functional status, the heart's pumping reserve, and the integrity of the cardio-pulmonary unit. The utility of CPX, however, in assessing an early and subtle decline in left ventricular function and its ability to predict the appropriate timing for valve replacement in chronic mitral or aortic valvular incompetence remains to be elucidated.

Adult↗