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Biomedical subjects

M A Creager

Publications and source records attributed to M A Creager.

At least 109 records · Page 6Linked to original sources
PubMed1989

Correlation between preoperative ischemia and major cardiac events after peripheral vascular surgery.

Patients who undergo peripheral vascular surgery are at increased risk for postoperative cardiac events and are difficult to assess preoperatively because of limitations on their activity. We prospectively studied 176 consecutive eligible patients undergoing elective vascular surgery to determine the value in predicting a postoperative cardiac event of preoperative electrocardiographic monitoring to detect myocardial ischemia. Of the 176 patients, 32 (18 percent) had 75 episodes of monitored ischemic ST-segment depression preoperatively (of which 73 were asymptomatic), and 13 (7 percent) met strict criteria for major postoperative cardiac events, including 1 with a fatal myocardial infarction, 3 with nonfatal infarctions, 4 with unstable angina, and 5 with ischemic pulmonary edema. Of the 32 patients with ischemia before their operations, 12 had postoperative events (univariate relative risk, 54; 95 percent confidence interval, 7.2 to 400). Only 1 postoperative event occurred among 144 patients who did not have preoperative ischemia. The sensitivity of preoperative ischemia was 92 percent, the specificity 88 percent, the predictive value of a positive result 38 percent, and the predictive value of a negative result 99 percent. In multivariate analyses, preoperative ischemia was the most significant correlate of postoperative cardiac events and remained a statistically significant independent correlate even after we had controlled for all other preoperative factors (multivariate relative risk, 24.4; 95 percent confidence interval, 6.8 to 88). These preliminary data suggest that preoperative electrocardiographic monitoring to detect episodes of myocardial ischemia is a useful method for assessing cardiac risk in patients who undergo elective vascular surgery. In particular, the absence of ischemia during monitoring indicates a very low risk.

Aged↗
PubMed1989

Effects of alpha- and beta-adrenergic antagonists on plasma apolipoproteins and forearm blood flow in patients with mild hypertension.

To study the mechanisms by which adrenergic antagonists affect blood pressure and plasma lipid levels, the effects of alpha-blockade with prazosin were compared with those of beta-blockade with propranolol in 23 normolipidemic, mildly hypertensive patients. Plasma lipoprotein composition, apolipoproteins, and some of the processes involved in lipid synthesis and clearance from plasma were investigated also. Patients entered an eight-week placebo period during which they were free of all antihypertensive medications. They were then randomly assigned under double-blind conditions to treatment with either prazosin (mean dose, 5 mg per day) or propranolol (mean dose, 133 mg per day) for eight weeks. Doses of both drugs were titrated to achieve either a decrease in diastolic blood pressure of 10 mm Hg or more or a reduction of diastolic blood pressure to less than 85 mm Hg, whichever was lower. Total plasma cholesterol decreased by 9 percent during prazosin treatment and increased by 7 percent during propranolol treatment (p less than 0.005 between treatments). Low-density lipoprotein cholesterol decreased by 12 percent with prazosin and increased by 12 percent with propranolol (p less than 0.005). Apolipoprotein B decreased by 17 percent with prazosin and increased by 15 percent with propranolol (p less than 0.005). There were no significant changes in total high-density lipoprotein cholesterol, its subfractions high-density lipoprotein2 or high-density lipoprotein3, or in apolipoprotein A1 and apolipoprotein A2. Plasma very low-density lipoprotein and low-density lipoprotein triglycerides were not significantly affected by either treatment. Plasma post-heparin lipase activities, which clear triglyceride and high-density lipoprotein cholesterol from plasma, were not altered significantly. Since regional blood flow could affect the clearance of plasma lipoproteins, measurements were taken of forearm blood flow, forearm vascular resistance, and maximal forearm vasodilatory potential during reactive hyperemia. The adrenergic antagonists had no effect on these measurements, nor did they affect cellular cholesterol synthesis as measured by the activity of 3-hydroxy-3-methylglutaryl coenzyme A reductase in blood mononuclear cells. The results of this study demonstrate differing actions between alpha- and beta-adrenergic antagonism. Alpha-blockade produced significantly lower levels of plasma low-density lipoprotein cholesterol and apolipoprotein B than beta-adrenergic antagonism without changes in high-density lipoproteins.

Adult↗
PubMed1989

Relation of atrial natriuretic factor to vasoconstrictor hormones and regional blood flow in congestive heart failure.

Plasma levels of both atrial natriuretic factor (ANF) and vasoconstrictor neurohormones are often increased in patients with congestive heart failure (CHF). It has been speculated that ANF is a counterregulatory hormone that influences regional blood flow and sodium balance in human patients by either direct vasorelaxation or by inhibiting the release of other vasoconstrictor neurohormones. The exact relation of increased ANF levels to regional vascular resistance and vasoconstrictor neurohormones has not previously been documented. Thus, we examined the relation between plasma ANF levels, levels of vasoconstrictor neurohormones, and forearm, splanchnic and renal blood flow in 20 normal subjects and in 17 patients with chronic CHF. The plasma ANF level was directly correlated with the plasma norepinephrine concentration (r = 0.83, p less than 0.01), plasma epinephrine concentration (r = 0.46, p less than 0.01), plasma renin activity (r = 0.50, p less than 0.01), plasma angiotensin II concentration (r = 0.79, p less than 0.01) and plasma vasopressin concentrations (r = 0.65, p less than 0.01). Positive correlations existed between plasma ANF levels and the calculated vascular resistances, i.e., between ANF and forearm vascular resistance (r = 0.41, p less than 0.05), splanchnic vascular resistance (r = 0.74, p less than 0.01) and renal vascular resistance (r = 0.66, p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1989

Mechanism of the attenuated peak heart rate response to exercise after orthotopic cardiac transplantation.

The mechanism responsible for attenuation of the peak heart rate response to exercise in patients after cardiac transplantation was studied. Because the donor heart is believed to be surgically denervated, the peak heart rate response to exercise is dependent primarily on 1) an increase in the circulating levels of the catecholamines norepinephrine and epinephrine at peak exercise, and 2) the end-organ responsiveness of the sinoatrial (SA) node to beta-adrenergic stimulation. To assess the former mechanism, the levels of plasma nonepinephrine and epinephrine were measured at rest and at peak exercise on a cycle ergometer in 23 transplant recipients an average of 7 +/- 1 months after transplantation and in 23 normal subjects matched for age. To assess the latter mechanism, the heart rate response to a graded infusion of isoproterenol was determined in six normal subjects with and without atropine pretreatment and in eight transplant recipients. In transplant recipients, both the absolute plasma levels of nonepinephrine and epinephrine at peak exercise and the increments from baseline to peak exercise were comparable with or greater than those in normal subjects. In transplant recipients, the isoproterenol dose that increased heart rate by 25 beats/min over baseline was not different from that in atropine-treated normal subjects (normal subjects 9 +/- 2 ng/kg per min; transplant recipients 11 +/- 1 ng/kg per min; p = NS). These data show that after cardiac transplantation, there is a normal or slight elevation of circulating catecholamines at peak exercise, and that the responsiveness of the SA node to beta-adrenergic stimulation is normal.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1989

International study of ketanserin in Raynaud's phenomenon.

PURPOSE: The effects of ketanserin on primary or secondary Raynaud's phenomenon due to connective tissue disease were studied in a large, international group of patients. PATIENTS AND METHODS: The study population consisted of 222 patients from 10 countries. After a run-in period of one month of placebo therapy, patients were randomly assigned in a double-blind manner to receive ketanserin 40 mg three times daily (n = 113) or placebo (n = 109) for three months. Total finger blood flow was measured in 41 patients in a warm and cool room before and during treatment. Vasospastic episodes were assessed by diaries and global evaluations. RESULTS: A significant reduction of 34% in frequency of episodes occurred with ketanserin, compared to 18% with placebo (p = 0.011). There was a 1% reduction in duration of episodes with ketanserin therapy, compared to a 2% increase with placebo therapy, but this finding was not statistically significant (p = 0.29). No difference was observed in severity of attacks. Global evaluations by investigators (p = 0.03) and patients (p less than 0.01) showed an overall benefit with ketanserin compared to that seen with placebo. Patients with primary or secondary Raynaud's phenomenon responded similarly to treatment. No changes in total finger blood flow were found. CONCLUSION: Ketanserin significantly improves the subjective symptoms of patients with primary or secondary Raynaud's phenomenon and is an appropriate agent to use in this disease when conservative measures fail.

Blood Pressure↗
PubMed1989

Regional vascular responses to prolonged lower body negative pressure in normal subjects.

The purpose of this study was to determine the effects of sustained unloading of baroreceptors in humans. The regional hemodynamic responses to lower body negative pressure (LBNP) were determined in 20 normal subjects. LBNP at -10 mmHg for 1 h decreased central venous pressure (CVP) without affecting blood pressure or heart rate, suggesting that only cardiopulmonary baroreceptors were unloaded. Forearm blood flow (FBF) and splanchnic blood flow (SBF) both decreased. Renal blood flow (RBF) did not change, but glomerular filtration rate (GFR) increased. Plasma renin activity rose slightly, whereas plasma norepinephrine levels did not change. Peak LBNP (either -20 or -40 mmHg for 1 h) caused a further decline in CVP and narrowed pulse pressure, thus unloading both arterial and cardiopulmonary baroreceptors. FBF returned to base-line values and SBF decreased further. RBF fell and the GFR remained increased. Plasma renin activity increased further, and plasma norepinephrine level rose. Thus the forearm and splanchnic circulations are sensitive to sustained unloading of cardiopulmonary baroreceptors; renal vasoconstriction occurs with additional unloading of arterial baroreceptors. Renin-angiotensin system activation during LBNP may be pertinent to the preservation of glomerular filtration.

Adult↗
PubMed1989

Impaired chronotropic response to exercise in patients with congestive heart failure. Role of postsynaptic beta-adrenergic desensitization.

The mechanism responsible for the attenuated heart rate (HR) response to exercise in patients with congestive heart failure (CHF) was investigated in 46 normal subjects and 59 patients with CHF stratified by peak exercise oxygen consumption (VO2). The peak exercise HR and the increment in HR from rest to peak exercise were decreased in CHF patients, and both correlated strongly with peak VO2 (r = 0.810, p less than 0.0001; r = 0.863, p less than 0.0001, respectively). Peak exercise norepinephrine level (NE) and the increment in NE from rest to peak exercise were not attenuated in CHF patients. Resting NE was elevated in CHF patients and correlated inversely with peak VO2 (r = -0.595, p less than 0.001). However, no significant correlation occurred between peak VO2 and either peak exercise NE or the exercise increment in NE. The ratio of the exercise increments in HR and NE, and indirect index of sinoatrial node sympathetic responsiveness, was markedly reduced in CHF patients and was inversely related to the severity of exercise impairment. Likewise, the HR response to a graded isoproterenol infusion was markedly reduced in CHF patients. Age-matching of normal subjects and CHF patients did not affect the foregoing observations. Infusion of CHF patients with the phosphodiesterase inhibitor milrinone caused a significant increase in the ratio of the exercise increments in HR and NE. These data strongly suggest that the attenuated HR response to exercise in CHF patients is due, at least in part, to postsynaptic desensitization of the beta-adrenergic receptor pathway.

Adult↗
PubMed1989

Vasopressin-mediated forearm vasodilation in normal humans. Evidence for a vascular vasopressin V2 receptor.

Arginine vasopressin (AVP) is a potent vasopressor and antidiuretic neurohormone. However, when administered intravenously to humans, AVP causes forearm vasodilation. This effect has been attributed to sympathetic withdrawal, secondary to AVP-induced sensitization of baroreceptors. The possibility that AVP also causes forearm vasodilation directly has not been examined. Accordingly, the direct effect of AVP was determined by studying the forearm blood flow (FBF) response to intraarterial (IA) AVP infusion (0.01-1.0 ng/kg per min). Infusion of IA AVP increased FBF (96%) in the infused arm, but not the control arm, in a dose-dependent manner. The role of specific AVP V1 receptors in mediating this FBF response was determined before and after pretreatment with a V1 antagonist (AVP-A). AVP-A alone had no effect on FBF, but coadministration of AVP and AVP-A potentiated the vasodilatory response (223%). IA infusion of the V2 agonist, 1-desamino[8-D-arginine] vasopressin, caused a dose-dependent increase in FBF. These findings suggest that AVP causes direct, dose-dependent vasodilation in the human forearm that may be mediated by V2 vasopressinergic receptors. In contrast, AVP infusion caused digital vasoconstriction that was blocked by AVP-A, whereas dDAVP did not affect digital blood flow. Thus, AVP induces regionally selective vascular effects, with concurrent forearm vasodilation and digital vasoconstriction.

Adult↗
PubMed1989

Progress in angiotensin-converting enzyme inhibition in heart failure: rationale, mechanisms, and clinical responses.

The pharmacology and mechanisms of action of angiotensin-converting enzyme (ACE) inhibitors are reviewed in this article together with discussions on their acute and hemodynamic effects; influence on regional blood flow and renal responses; clinical efficacy and adverse effects; and their impact on survival in severe congestive heart failure.

Angiotensin-Converting Enzyme Inhibitors↗
PubMed1988

Responsiveness of atrial natriuretic factor to reduction in right atrial pressure in patients with chronic congestive heart failure.

In patients with congestive heart failure, atrial natriuretic factor may serve as a counter-regulatory hormone, offsetting the vasoconstrictive and volume-retentive effects of the sympathetic nervous system, the renin-angiotensin-aldosterone system and vasopressin. Indeed, the plasma levels of atrial natriuretic factor and the vasoconstrictor hormones are often simultaneously elevated in these patients. It is not known, however, whether atrial natriuretic factor remains responsive to sudden reductions in atrial pressure in patients with chronic heart failure, or is unresponsive like the vasoconstrictor systems. To examine this issue, the plasma concentrations of atrial natriuretic factor and the vasoconstrictor hormones were measured in 20 normal subjects and 12 patients with chronic congestive heart failure during incremental lower body negative pressure, an intervention that lowers atrial pressure. In the normal subjects, incremental lower body negative pressure at -10, -20 and -40 mm Hg decreased central venous pressure and pulse pressure. At maximal lower body negative pressure, plasma atrial natriuretic factor levels decreased from 51 +/- 5 to 27 +/- 3 pg/ml (p less than 0.01), whereas increases occurred in plasma levels of norepinephrine (194 +/- 11 to 385 +/- 70 pg/ml, p less than 0.01), renin activity (1.4 +/- 0.2 to 3.9 +/- 0.1 ng/ml per h, p less than 0.01) and vasopressin (1.3 +/- 0.1 to 6.4 +/- 2.4 pg/ml, p less than 0.05). In the patients with congestive heart failure, lower body negative pressure also reduced central venous pressure. Baseline plasma atrial natriuretic factor levels were markedly elevated, averaging 438 +/- 138 pg/ml, and decreased to 317 +/- 87 pg/ml at maximal lower body negative pressure (p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1987

Comparison of intravenous milrinone and dobutamine for congestive heart failure secondary to either ischemic or dilated cardiomyopathy.

Milrinone and dobutamine are positive inotropic agents with beneficial hemodynamic effects in patients with congestive heart failure. This study was undertaken to compare the effects of intravenous milrinone and dobutamine in patients with stable New York Heart Association class III or IV congestive heart failure and to test the hypothesis that intravenous milrinone is at least as beneficial as dobutamine in this setting. Seventy-nine patients were randomized to either dobutamine therapy at incremental doses of 2.5, 5, 7.5, 10, 12.5 and 15 micrograms/kg/min, or milrinone as a bolus of 50 or 75 micrograms/kg followed by an infusion of 0.5 to 1.0 micrograms/kg/min. Both agents significantly increased heart rate, cardiac index and stroke volume index and decreased pulmonary artery wedge pressure and systemic vascular resistance compared with baseline levels (p less than 0.01). During sustained infusion for 48 hours, no difference in hemodynamic effects was observed between the 2 drugs. Ventricular tachycardia occurred in 5 patients (3 taking milrinone, 2 taking dobutamine); 1 patient taking milrinone had ventricular fibrillation. Milrinone and dobutamine elicited similar beneficial hemodynamic results with relatively few adverse effects.

Cardiomyopathy, Dilated↗
PubMed1987

Relationship of cardiac chamber volume to baroreflex activity in normal humans.

The objectives of this study were to examine the effect of incremental lower body negative pressure (LBNP) on cardiac chamber volume and assess the relationship between cardiac chamber volume and baroreflex activation of the neurohormonal axis. Accordingly, echocardiographic determination of cardiac chamber volume and neurohormonal responses were studied in 14 normal subjects during incremental LBNP. LBNP -10 mm Hg decreased left atrial diameter and left ventricular systolic volume index, but did not alter heart rate, systolic or pulse pressure, or stroke volume. During LBNP -10 mm Hg, plasma norepinephrine levels increased, suggesting activation of the sympathetic nervous system. LBNP -40 mm Hg caused a significant decrease in left atrial diameter and left ventricular systolic, diastolic, and stroke volume indices. During LBNP -40 mm Hg, heart rate increased, and systolic and pulse pressure fell. With this more negative level of LBNP, norepinephrine, angiotensin II, aldosterone, and arginine vasopressin concentrations and PRA all increased. The findings that left atrial diameter decreased and plasma norepinephrine concentration increased during LBNP -10 mm Hg suggest that the sympathetic nervous system is sensitive to changes in atrial receptor activity. At higher levels of LBNP (-40 mm Hg), activation of the renin-angiotensin system and release of vasopressin were associated with a fall in left ventricular diastolic volume as well as a decrease in the pressure input to the arterial baroreceptors. Under this condition, the differential contribution of the cardiopulmonary and arterial baroreceptors to the regulation of the renin-angiotensin system and vasopressin release cannot be distinguished.

Adult↗
PubMed1987

Clinical response to angiotensin-converting enzyme inhibition in cardiac failure.

The renin-angiotensin system plays a pivotal role in the pathophysiology of heart failure. ACE inhibitors block the production of angiotensin II and are efficacious in the therapy of patients with heart failure, ACE inhibitors have combined preload and afterload reducing effects. Cardiac index is augmented, cardiac filling pressures are reduced and renal function may improve with ACE inhibition. Long-term subjective and objective improvements have been reported. Preliminary data suggest that this class of vasodilators may favorably influence the prognosis of advanced heart failure.

Angiotensin-Converting Enzyme Inhibitors↗
PubMed1987

Baroreceptor function in congestive heart failure: effect on neurohumoral activation and regional vascular resistance.

A series of neurohumoral systems are activated in congestive heart failure that contribute to the increased vascular resistance and sodium retention that characterize this disorder. Abnormalities in baroreceptor function are intrinsic to the pathophysiology of heart failure and may subserve the vasoconstrictive and volume overloaded state that defines patient morbidity. Blunted baroreceptor responses to high cardiac filling pressures or depressed cardiac function reduce afferent signals that normally inhibit sympathetic efferent activity, vasopressin release, and indirectly, renin secretion. The resulting increase in neurohumoral activity mediates the redistribution of blood flow that occurs in this disorder. Limb blood flow is usually reduced and may be responsible for exercise intolerance. Decreased renal blood flow and altered intrarenal hemodynamics contribute to sodium retention. In addition, renal vasoconstriction and elevated circulating levels of angiotensin II and vasopressin may contribute to hyponatremia by influencing free water intake and excretion. Hence, baroreceptor dysfunction may be a principal mechanism that contributes to neurohumoral activation and subsequent alteration in vascular resistance and sodium and water balance in congestive heart failure. It may not be coincidental that two principal markers of an unfavorable prognosis in patients with heart failure, high plasma norepinephrine levels and hyponatremia, share baroreceptor dysfunction as a common theme.

Animals↗
PubMed1986

Contribution of vasopressin to vasoconstriction in patients with congestive heart failure: comparison with the renin-angiotensin system and the sympathetic nervous system.

Ten patients with advanced congestive heart failure were treated with an arginine vasopressin V1 antagonist during hemodynamic monitoring to determine the contribution of vasopressin to vasoconstriction in this disorder. The vasopressin antagonist caused a decrease in systemic vascular resistance in the three patients whose plasma vasopressin was greater than 4.0 pg/ml (average for the group was 2.4 +/- 0.6). Plasma vasopressin concentration correlated with the percent decrease of systemic vascular resistance (r = 0.70, p less than 0.025), serum sodium (r = 0.72, p less than 0.02) and serum creatinine (r = 0.85, p less than 0.005). To compare the relative roles of vasopressin, the renin-angiotensin system and the sympathetic nervous system, these patients also received captopril and phentolamine. Captopril decreased systemic vascular resistance by 20% (p less than 0.05), mostly in patients with high plasma renin activity. Levels of plasma renin activity ranged between 1 and 46 ng/ml per h (average 14.7 +/- 5.7) and correlated with serum sodium (r = 0.77, p less than 0.025), serum creatinine (r = 0.73, p less than 0.025) and right atrial pressure (r = 0.67, p less than 0.05). Phentolamine decreased systemic vascular resistance in all patients (average 34%, p less than 0.01), but the decrease did not correlate with the pretreatment norepinephrine concentration. Norepinephrine levels were elevated in all patients (694 +/- 110 pg/ml) and correlated with baseline stroke volume index (r = 0.75, p less than 0.025) and plasma renin activity (r = 0.67, p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1985

Acute and long-term effects of enalapril on the cardiovascular response to exercise and exercise tolerance in patients with congestive heart failure.

Enalapril is a recently developed angiotensin-converting enzyme inhibitor that improves cardiac function at rest in patients with congestive heart failure. This study investigated the acute effects of enalapril on the cardiovascular response to exercise, and then evaluated the long-term effects of enalapril on exercise capacity and functional status during a 12 week placebo-controlled trial in patients with heart failure. Ten patients underwent hemodynamic monitoring while at rest and during incremental bicycle exercise before and after 5 to 10 mg of enalapril orally. At rest, enalapril decreased mean blood pressure 13% (p less than 0.01) and systemic vascular resistance 20% (p less than 0.05) and increased stroke volume index 21% (p less than 0.01). During maximal exercise, enalapril decreased systemic vascular resistance and increased both cardiac and stroke volume indexes. Enalapril acutely increased exercise duration (p less than 0.05) and maximal oxygen consumption (p less than 0.001). These 10 patients and an additional 13 patients were then randomized to either placebo or enalapril treatment and followed up for 12 weeks. Of the 11 patients assigned to active treatment, 73% considered themselves improved compared with 25% of the patients assigned to placebo treatment (p less than 0.02). During long-term treatment, exercise capacity increased in patients receiving enalapril (p less than 0.001) but was unchanged in patients receiving placebo (intergroup difference, p less than 0.05). During long-term treatment, no adverse effects of enalapril occurred. Thus, enalapril improves cardiac function at rest and during exercise. Compared with placebo, maintenance therapy with enalapril results in symptomatic improvement and increased exercise capacity.

Adult↗
PubMed1985

The contribution of the renin-angiotensin system to limb vasoregulation in patients with heart failure: observations during orthostasis and alpha-adrenergic blockade.

1. In patients with congestive heart failure, both the sympathetic nervous system and renin-angiotensin system are often stimulated. In order to assess the contribution of the renin-angiotensin system to limb vascular resistance, the forearm haemodynamic response to captopril was studied in 13 patients with heart failure. 2. Seven subjects were studied while supine and during 60 degrees head-up tilt. To eliminate alpha-adrenergic effects, six additional patients with heart failure were pretreated with intra-arterial phentolamine and then given captopril. Venous occlusion plethysmography was used to determine forearm blood flow and forearm vascular resistance. 3. Tilt did not significantly increase pretreatment plasma renin activity or plasma noradrenaline concentration, nor did it decrease forearm blood flow. Furthermore, captopril did not alter forearm vascular resistance during supine or upright posture. During the phentolamine infusion, however, captopril reduced forearm vascular resistance by 19% (P < 0.05). 4. Despite increased plasma renin activity, captopril did not cause forearm vasodilatation during supine or upright posture in these patients with heart failure. When the contribution of the sympathetic nervous system was eliminated, captopril decreased forearm vascular resistance. Therefore, in patients with congestive heart failure, the sympathetic nervous system is important in limb vasoregulation, and the contribution of the renin-angiotensin system is apparent only after alpha-adrenergic blockade.

Adrenergic alpha-Antagonists↗