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Biomedical subjects

M C Limacher

Publications and source records attributed to M C Limacher.

At least 37 records · Page 2Linked to original sources
PubMed1995

Extreme blood pressure fluctuations in a patient with intact autonomic reflexes and intact sodium conservation.

A patient who had episodes of profound hypotension alternating with severe hypertension without an obvious precipitating cause is reported. The hypotensive episodes were accompanied by tiredness, syncope, bradycardia, and a low norepinephrine concentration while supine or standing. In contrast, the hypertensive episodes were associated with marked tachycardia, sweating, anxiety, abdominal pain, and very high levels of plasma norepinephrine concentration. Extensive investigations failed to support a diagnosis of pheochromocytoma. The testing of baroreceptor function and autonomic reflexes was normal. Blood pressure was not salt sensitive. It was concluded that this patient has a unique clinical syndrome of extreme fluctuation of blood pressure and sympathetic nervous activity yet intact cardiovascular reflexes and normal sodium conservation. The abnormal blood pressure regulation most likely has a central origin.

Aged↗
PubMed1994

Moderate- and high-intensity exercise lowers blood pressure in normotensive subjects 60 to 79 years of age.

To investigate the effects of exercise intensity on resting blood pressure (BP) in normotensive elderly subjects, 44 sedentary healthy subjects aged 60 to 79 years of age were studied during 6 months of walking exercise. Subjects were ranked according to maximal oxygen consumption and randomly stratified to groups that trained at 70% (n = 19) or 80% to 85% (n = 14) of maximal heart rate reserve, or to a control group (n = 11) that did not train. Initial BP was established during a 2- to 3-week control period. During the first 3 months, both exercise groups progressed to 70% of heart rate reserve for 40 minutes 3 times each week. The moderate-intensity group continued to train at 70% (45-minute duration) for an additional 3 months, whereas the high-intensity group progressed to training at 85% of heart rate reserve (35-minute duration). Maximal oxygen consumption increased (p < or = 0.05) during the initial 3 months in both exercise groups (25.2 to 28.1 ml.kg-1.min-1 and 26.3 to 29.3 ml.kg-1.min-1) and continued to increase (p < or = 0.05) after 3 additional months of training, but the increase was greater (p < or = 0.05) in the high-intensity group (28.1 to 29.4 ml.kg-1.min-1 and 29.3 to 32.8 ml.kg-1.min-1). Systolic BP decreased (p < or = 0.05) similarly at 6 months in both training groups (120 to 111 mm Hg and 120 to 112 mm Hg).(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1994

Does routine stress-thallium cardiac scanning reduce postoperative cardiac complications?

OBJECTIVE: Prophylactic cardiac revascularization in patients with ischemic myocardium could reduce postoperative cardiac complications after aortic reconstruction. However, the effectiveness of this approach has not been documented. SUMMARY BACKGROUND DATA: Stress-thallium scanning can identify patients with ischemic myocardium. Morbidity and mortality after aortic reconstruction appears to be largely caused by co-existent coronary artery disease, and patients who have had recent cardiac revascularization have few postoperative cardiac complications. METHODS: Preoperative stress-thallium scanning was evaluated prospectively in 146 patients undergoing aortic reconstruction. Patients with positive studies underwent coronary arteriography and cardiac revascularization, when appropriate. Postoperative cardiac complications and long-term survival in these patients were compared with results from 172 similar patients undergoing aortic reconstruction without stress-thallium scanning. Results also were analyzed to determine predictors of postoperative cardiac events. RESULTS: Forty-one per cent of patients undergoing stress-thallium testing underwent coronary arteriography, and 11.6% had cardiac revascularization. In contrast, 14.7% of patients treated without stress-thallium testing had coronary arteriography, and 4.1% had revascularization (p < 0.01). Despite this, cardiac mortality, serious cardiac complications, and long-term cardiac mortality were similar in both groups. Only advanced age and intraoperative complications (but not a positive stress-thallium test) predicted postoperative cardiac events. CONCLUSIONS: Preoperative stress-thallium testing confirmed a high incidence of significant coronary artery disease in patients undergoing aortic reconstruction, but prophylactic cardiac intervention does not reduce operative or long-term mortality. Thus, the risk and expense of routine stress-thallium testing and subsequent cardiac revascularization cannot be justified.

Aged↗
PubMed1994

Aging and cardiac function: influence of exercise.

Changes in cardiac structure occur with increasing age. Cardiac function is also altered, partially by the increase in blood pressure that accompanies aging. Diastolic left ventricular dysfunction, in particular, is more common in older individuals. In the elderly, maximal exercise produces a higher end-diastolic volume to achieve maximal increase in cardiac output, but the increase in ejection fraction is less than in younger subjects Also, a high proportion of apparently healthy elderly subjects, if carefully tested, are found to have occult coronary artery disease. Thus, exercise performance and testing have special considerations in the elderly. Older individuals who exercise regularly have a lower resting heart rate and blood pressure and improved fitness, balance, and gait. Those who maintain a pattern of routine exercise are at lower risk for cardiovascular events. In most cases, exercise can be recommended as an important strategy for promotion of cardiovascular health.

Aged↗
PubMed1994

Exercise testing in selected patient groups. Women, the elderly, and the asymptomatic.

Exercise testing for coronary artery disease (CAD) has been validated primarily for middle-aged men. For women and the elderly, full assessment of individual risk and estimation of the pre-test likelihood of CAD is important before deciding to perform an exercise study. Negative electrocardiographic (ECG) findings with an exercise test in women and the elderly are predictive of good prognosis and low risk of cardiovascular events. Positive ECG findings may be falsely positive, and additional testing, nuclear or echocardiographic imaging, or coronary angiography may be indicated. Consensus guidelines are not yet available for testing in asymptomatic patients with exercise, and individual management decisions are still required.

Aged↗
PubMed1993

Exercise-induced hypoxemia in heart transplant recipients.

OBJECTIVES: The purpose of this study was to determine whether heart transplantation has an adverse effect on pulmonary diffusion and to investigate the potentially deleterious effects of impaired pulmonary diffusion on arterial blood gas dynamics during exercise in heart transplant recipients. BACKGROUND: Abnormal pulmonary diffusing capacity is reported in patients after orthotopic heart transplantation. Abnormal diffusion may be caused by cyclosporine or by the persistence of preexisting conditions known to adversely affect diffusion, such as congestive heart failure and chronic obstructive pulmonary disease. METHODS: Eleven patients (mean age 50 +/- 14 years) performed pulmonary function tests 3 +/- 1 months before and 18 +/- 12 (mean +/- SD) months after heart transplantation. Transplant patients were assigned to groups with diffusion > 70% (n = 5) or diffusion < 70% of predicted values (n = 5). The control group and both subsets of patients performed 10 min of cycle exercise at 40% and 70% of peak power output. Arterial blood gases were drawn every 30 s during the 1st 5 min and at 6, 8 and 10 min. RESULTS: Significant improvements in forced vital capacity (17.4%), forced expiratory volume in 1 s (11.7%) and diffusion capacity (6.6%) occurred in the patients; however, posttransplantation vital capacity, forced expiratory volume and diffusion were lower (p < or = 0.05) compared with values in 11 matched control subjects. Changes in blood gases were similar among groups at 40% of peak power output. At 70% of peak power output, arterial blood gases and pH were significantly (p < or = 0.05) lower in transplant patients with low diffusion (arterial oxygen pressure 15 to 38 mm Hg below baseline) than in patients with normal diffusion and control subjects. Cardiac index did not differ (p > or = 0.05) between transplant patients with normal and low diffusion at rest or during exercise. Posttransplantation mean pulmonary artery pressure was significantly related to exercise-induced hypoxemia (r = 0.71; p = 0.03). CONCLUSIONS: Abnormal pulmonary diffusion observed in patients before heart transplantation persists after transplantation with or without restrictive or obstructive ventilatory defects. Heart transplant recipients experience exercise-induced hypoxemia when diffusion at rest is < 70% of predicted. Our data also suggest that abnormal pulmonary gas exchange possibly contributes to diminished peak oxygen consumption in some heart transplant recipients; however, direct testing of this hypothesis was beyond the scope of the present study. This possibility needs to be investigated further.

Adult↗
PubMed1993

The impact of diet on coronary heart disease.

The epidemiologic relationship between dietary intake and coronary heart disease (CHD) is reviewed by presenting the findings of the major large national and international cohort studies. There is considerable heterogeneity in the results from these studies because of the many differences in design, sample population, and analysis. Dietary intervention studies, which have numerous limitations, likewise have reported discrepant results, although short-term dietary changes do appear to reduce the likelihood of CHD progression. Although proof is lacking that the currently recommended prudent dietary patterns reduce the incidence or severity of CHD, healthy dietary choices are both inexpensive and safe and are supported by a foundation of sound biological principles.

Clinical Trials as Topic↗
PubMed1993

Emotional and coping responses to serial killings. The Gainesville murders.

Forensic experts have focused more on the psychological profile of a serial killer rather than on the pronounced effects on the community at large. Coping with a stressful event is thought to influence emotional states. However, little empirical understanding of this process exists. The present study examined changes in psychological factors 9 days after the occurrence of serial killings in a college community. Multivariate analyses of variance conducted on the variables of stress, anxiety, physical symptoms, and depression revealed a significant difference between the group tested after the murders and a cross-sectional cohort group. Univariate analyses revealed that the study class was significantly more depressed compared with the cohort group. The study class was also significantly more depressed compared with their own responses 1 year before the killings. For both classes, depression was significantly correlated with certain coping styles, including escape-avoidance and accept responsibility. Results have implications for certain coping behaviors (i.e., avoidant behaviors), such as that leaving the community may have been maladaptive and perhaps diverted attention from the more necessary active problem-solving behaviors (e.g., increasing security) in addition to increasing depression.

Adaptation, Psychological↗
PubMed1993

Blood gas dynamics at the onset of exercise in heart transplant recipients.

One hypothesis to explain the rapid neural component of exercise hyperpnea contends that afferent stimuli originating in the ventricles of the heart act reflexly on the respiratory center at the onset of exercise, ie, "cardiodynamic hyperpnea." Orthotopic cardiac transplantation (Tx) results in the loss of afferent information from the ventricles. Thus, Tx possibly results in transient hypercapnia and hypoxemia in deafferented heart transplant recipients (HTR) at the onset of exercise due to hypoventilation. To examine the cardiodynamic hypothesis, we collected serial arterial blood gas (ABG) samples during both the transient and the steady-state responses to moderate cycle exercise in 5 HTRs (55 +/- 7 years) 14 +/- 7 months post-Tx and 5 control subjects matched with respect to gender, age, and body composition. Forced vital capacity, forced expiratory volume in 1 s, total lung capacity, and diffusion capacity did not differ (p > or = 0.05) between groups. Resting arterial PO2, PCO2, and pH did not differ between groups (p > or = 0.05). The ABGs were drawn every 30 s during the first 5 min and at 6, 8, and 10 min of constant load square wave cycle exercise at 40 percent of the peak power output (watts). Absolute and relative changes in arterial PO2, PCO2, and pH were similar (p > or = 0.05) between HTR and the control group at all measurement periods during exercise. Heart rate (%HRmax reserve), rating of perceived exertion, and reductions in plasma volume (% delta from baseline) did not differ between HTR and control during exercise at 40 percent of peak power output (p > or = 0.05). Our results demonstrate that there is no discernible abnormality in ABG dynamics during the transient response to exercise at 40 percent of peak power output in patients with known cardiac denervation. These data do not support the cardiodynamic hyperpnea hypothesis of ventilatory control in humans. The absence of hypercapnia in HTRs is further evidence for the existence of redundant mechanisms capable of stimulating exercise hyperpnea.

Adult↗
PubMed1992

Abnormal neuroendocrine responses during exercise in heart transplant recipients.

BACKGROUND: Osmotic and neural factors stimulate neuroendocrine activity during exercise. In contrast to excitatory mechanisms, afferent information from cardiac mechanoreceptors inhibits integrative centers in the hypothalamus and medula oblongata, which serves to buffer neuroendocrine activity. Orthotopic cardiac transplantation results in the loss of afferent information from cardiac mechanoreceptors. Thus, transplantation possibly results in exaggerated neuroendocrine responses when patients are physically active. METHODS AND RESULTS: We measured the neuroendocrine response to moderate and strenuous exercise performed at the same relative intensity in 11 heart transplant recipients (50 +/- 14 years old) 18 +/- 12 months after transplantation and 11 control subjects matched with respect to sex, age, and body size. Plasma levels of norepinephrine, vasopressin, renin activity, atrial natriuretic peptide, angiotensin II, and aldosterone were measured at rest, during a maximal graded exercise test, and during submaximal exercise at 40% and 70% of peak power output on a cycle ergometer (W). Plasma renin activity and atrial natriuretic peptide were elevated at rest in heart transplant recipients (p < or = 0.05). Heart rate (%HRmax reserve), rating of perceived exertion, and reductions in plasma volume (% delta from rest) at the conclusion of the three exercise conditions did not differ between heart transplant recipients and control (p > or = 0.05). Relative changes in neuroendocrine hormones were similar (p > or = 0.05) in heart transplant recipients and control during exercise at 40% of peak power output. Relative changes in plasma norepinephrine, vasopressin, atrial natriuretic peptide, and plasma renin activity were greater (p < or = 0.05) in heart transplant recipients during exercise at 70% of peak power output and the graded exercise test. CONCLUSIONS: We interpret these data as a possible indication of ablation of cardiac mechanoreceptor afferents and unopposed neuroendocrine stimulation in heart transplant recipients. Furthermore, chronic neuroendocrine hyperactivity is likely in ambulatory heart transplant recipients. Although cyclosporine nephrotoxicity is implicated in the development of hypertension, our data suggest that chronic neuroendocrine hyperactivity, which alters renal volume regulation, also contributes to the incidence and severity of hypertension in heart transplant recipients.

Afferent Pathways↗
PubMed1992

Clinical features of coronary heart disease in the elderly.

Care of the elderly patient with CHD requires an understanding of the prevalence of disease and its variability of presentation. Sound application of the diagnostic and therapeutic maneuvers developed for younger patients remains the predominant basis for the clinical approach to older individuals with heart disease. As more research is directed toward age-related issues in cardiac disease, the approach may be refined with more specific guidelines than are currently available.

Aged↗
PubMed1989

Renal and hemodynamic responses to bumetanide in hypertension: effects of nitrendipine.

The effects of a calcium antagonist on the response to a loop diuretic were tested in eight hypertensive patients while they received 120 mmol.24 hr-1 of dietary Na. Nitrendipine (N; 20 mg) or placebo (P) was administered twice daily for five days and bumetanide (B; 1 mg, i.v.) for the last three days of each period. Cardiac index (CI) was measured during tilt. B alone significantly (P less than 0.05; N = 7) reduced CI and increased total peripheral resistance; N prevented these effects of B. Neither drug altered BP consistently. Although three days of B increased plasma renin activity (PRA) during P and N, it increased plasma aldosterone (PAldo) only during P (P, 4.4 +/- 1.3 to 7.6 +/- 1.0; P less than 0.05, N, 5.7 +/- 1.3 to 6.0 +/- 1.3; pg.liter-1; NS). B increased Na excretion without changing GFR or RPF; this was followed by 18 hours of decreased renal Na excretion. These actions were unchanged by N. N did not change the cumulative excretion of B (P, 268 +/- 35 vs. N, 217 +/- 21 micrograms) or the relationship between Na excretion and the log of B excretion. However, Na excretion was increased (P less than 0.05) by 40 to 60% in the six hour period following the first two doses of N. Therefore, the cumulative Na balance was more negative during five days of N (P, -47 +/- 17 vs. N, -108 +/- 24 mmol; P less than 0.05). The effect of N and B on Na balance were independent.(ABSTRACT TRUNCATED AT 250 WORDS)

Bumetanide↗
PubMed1987

Assessment of left ventricular diastolic filling by two-dimensional echocardiography.

Although two-dimensional echocardiography has provided accurate measurements of left ventricular ejection fraction, the technique has been limited in the evaluation of diastolic function. First half-filling fraction, representing the difference between mid-diastolic and end-systolic volumes divided by stroke volume, is a recently introduced index of diastolic function. We developed a method for determining half-filling fraction by two-dimensional echocardiography with the use of the average of left ventricular internal diameters measured at the base, middle, and apical third of the ventricular cavity in multiple longitudinal planes. In 27 patients with a wide range of ventricular function, we compared angiographic measurements of half-filling fraction to results obtained by two-dimensional echocardiography. Half-filling fraction measured angiographically averaged (mean +/- SD) 0.58 +/- 0.15 (range 0.26 to 0.77) and measured by two-dimensional echocardiography averaged 0.58 +/- 0.15 (range 0.35 to 0.90). A significant correlation was found between angiographic and echocardiographic half-filling fractions (r = 0.84, SEE = 0.08). Results were similar in the presence or absence of segmental wall motion abnormalities. All seven patients with half-filling fractions below 0.50 by echocardiography had depressed half-filling fractions by angiography; three of these patients had ejection fractions of greater than or equal to 0.55. Thus half-filling fraction can be derived with two-dimensional echocardiography providing a noninvasive assessment of diastolic function.

Adult↗
PubMed1986

Determination of regurgitant fraction in isolated mitral or aortic regurgitation by pulsed Doppler two-dimensional echocardiography.

Measurements of mitral and aortic valve flows were obtained with two-dimensional Doppler echocardiography in 25 patients with isolated mitral (n = 19) or aortic (n = 6) regurgitation and regurgitant fraction was calculated as the difference between the two flows divided by the flow through the regurgitant valve. Results were compared with measurements of regurgitant fraction determined by combined left ventricular angiography and thermodilution. Regurgitant fraction averaged 56 +/- 18% (range 19 to 79) by Doppler echocardiography and 48 +/- 17% (range 13 to 72) by angiography. A significant correlation was observed between the two methods (r = 0.91; SEE = 7%). In contrast, no significant correlation was found between regurgitant fraction measured by either method and the angiographic 1+ to 4+ qualitative classification of regurgitation. Doppler echocardiography appears to be an accurate method for the non-invasive quantification of severity of regurgitation in isolated left-sided valve lesions.

Adolescent↗
PubMed1986

Effect of propranolol on myocardial ischemia occurring during acute coronary occlusion.

In 16 patients undergoing angioplasty of the left anterior descending coronary artery, the clinical, electrocardiographic, and hemodynamic effects of short-term intravenous nonselective beta-adrenergic blockade with propranolol (0.1 mg/kg) were assessed during temporary occlusion of the artery. Myocardial ischemia during coronary occlusion was prevented, delayed in onset, or diminished in magnitude by propranolol in 10 of the 16 patients. Propranolol decreased values for indexes of myocardial oxygen demand, such as heart rate and blood pressure and their product, in all patients. Surprisingly, in patients who derived clinical benefit, propranolol did not change indexes of myocardial oxygen supply to the left ventricular region perfused by the occluded artery. For example, great cardiac vein flow (40 +/- 15 to 41 +/- 17 ml/min, p = NS) and coronary collateral resistance (2.1 +/- 1.0 to 2.1 +/- 1.1 mm Hg/ml/min, p = NS) were unchanged. In contrast, a worsening of supply occurred in patients who were not benefited: great cardiac vein flow (50 +/- 10 to 39 +/- 6 ml/min, p less than .05) decreased and coronary collateral resistance (1.6 +/- 0.5 to 2.0 +/- 0.6 mm Hg/ml/min, p less than .05) increased. Information obtained from this study demonstrates the value of this new experimental preparation in helping assess potential clinical effectiveness of drug interventions during the initial phase of acute coronary occlusion and providing insight into the mechanisms of drug effect.

Adult↗