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Biomedical subjects

H Purcell

Publications and source records attributed to H Purcell.

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

Potassium channel openers: clinical applications in ischemic heart disease--overview of clinical efficacy of nicorandil.

Nicorandil is a balanced arterial and venodilator that may also possess cardioprotective properties via its activation of ATP-sensitive potassium channels. It has a number of beneficial hemodynamic effects and has been shown to be effective in treating angina with similar efficacy as the currently available antianginal agents. In addition, it may have useful effects in unstable and variant angina. In this review we examine the hemodynamic effects of nicorandil and discuss the currently available data on its clinical efficacy, both in isolation and in comparison with other agents.

Angina Pectoris↗
PubMed1995

Detection of ambulatory ischaemia is not of practical clinical value in the routine management of patients with stable angina. A long-term follow-up study.

It has been reported that medically treated patients with stable angina and positive exercise test for ischaemia have an adverse 1-2 year outlook if they are shown also to have transient, and predominantly silent, ischaemic episodes detected by ambulatory ST segment monitoring during their daily activities: it has been suggested that this investigation could be used to identify patients more likely to benefit from early investigation and treatment. We assessed the long-term (up to 65 months) prognostic significance of transient ischaemic episodes during daily activities in 172 patients routinely attending cardiac outpatients with medically treated stable angina who had undergone exercise testing and 48 h of ambulatory ST segment monitoring between February 1988 and August 1989 for this purpose. A positive exercise test for ischaemia was not a prerequisite for inclusion. One hundred and four patients (60.5%) had a positive exercise test for ischaemia and 72 (42%) had transient ischaemia during daily activities (63 had both tests positive). Over a median 50-month follow-up period 54 patients suffered at least one cardiac event (primary event: cardiac death n = 7; non-fatal myocardial infarction n = 11; unstable angina n = 18; elective CABG/PTCA n = 18). Two further patients suffered non-cardiac death. Cardiac events, either objective (cardiac death or non-fatal myocardial infarction) or subjective (unstable angina or revascularisation) were no more likely to occur in those with transient ischaemia during daily life when compared with those without, at follow-up times up to 65 months.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1995

Circadian rhythms and the onset of myocardial infarction: clinical implications.

There is much current interest in the development of therapeutic strategies which may alter the circadian pattern of cardiovascular events such as myocardial infarction and sudden cardiac death. It is not known whether manipulating rhythmic processes and providing active medication at the most vulnerable periods during the day or night will protect patients and reduce the risk of death. This review examines the evidence from the limited available data and assess the feasibility of implementing such strategies.

Blood Pressure↗
PubMed1994

Nitrates in silent ischemia.

In recent years it has become clear that episodes of transient myocardial ischemia commonly occur in patients with coronary artery disease in the absence of chest pain or angina equivalent. These episodes of "silent myocardial ischemia" are particularly well documented during continuous ambulatory electrocardiographic monitoring in daily life. Evidence suggests that these episodes represent true ischemia, and appear to be a marker of unfavorable outcome. While the pathophysiology is not completely understood, it appears as though the mechanisms of angina and silent ischemia are the same. Both forms of ischemia respond to conventional antianginal medication. While long-acting nitrates are effective in reducing or preventing myocardial ischemia, because of their propensity to cause tolerance they should be used intermittently and in association with either beta-blockers or calcium antagonists. Nitrates are safe and comparatively inexpensive, and will continue to play an important role in the treatment and prevention of angina. However, in the light of current knowledge, there is no specific indication for the treatment of silent ischemia by nitrates.

Administration, Cutaneous↗
PubMed1993

Maturational changes in steroidogenesis in the inner and outer zones of the guinea pig adrenal cortex.

Studies were done to determine the effects of age on steroidogenesis in the inner (zona reticularis) and outer (zona fasciculata plus glomerulosa) zones of the guinea pig adrenal cortex. In 35-day-old animals, cortisol production by adrenal outer zone cells was approximately twice as great as that by inner zone cells. With aging, cortisol secretion by inner zone cells decreased to very low levels, but there was no detectable change in the capacity for cortisol production by the outer zone. However, the outer zone comprised a progressively decreasing fraction of the total adrenal mass in older animals. To determine the basis for the decline in cortisol production by inner zone cells with aging, the activities of several steroidogenic enzymes were determined. Microsomal 21-hydroxylase activity was greater in the inner than outer zone but was not significantly affected by age. By contrast, 17 alpha-hydroxylase activity was greater in the outer zone at all ages, and decreased with aging in the inner but not the outer zone. Mitochondrial cholesterol sidechain cleavage and 11 beta-hydroxylase activities were also higher in the outer than inner zone and declined in the inner zone only in older animals. The decrease in inner zone cholesterol sidechain cleavage activity with aging was proportionately greater than the age-dependent changes in other enzyme activities. The results indicate that the effects of aging on steroidogenesis are both zone- and enzyme-specific. The overall decline in cortisol secretion by the guinea pig adrenal cortex with aging is attributable to both a decrease in cortisol production by the cells of the zone reticularis and a disproportionate increase in the mass of the gland comprised by this zone. The decrease in cortisol secretion correlates closely with a decline in cholesterol sidechain cleavage activity in the zona reticularis, and may be causally related.

Adrenal Cortex↗
PubMed1993

Unstable and stable angina.

Treatment of both stable and unstable angina depends on initially defining the pathophysiological mechanisms. The goal of treatment is to prevent the development of angina pectoris and possibly also to improve the prognosis. beta-blockade is effective in treating effort-related angina, as are calcium antagonists, which are also effective in treating coronary spasm. Combination therapy may be synergistic, but evidence to support this is controversial. In unstable angina the main goal of treatment is the prevention of myocardial infarction and death. While calcium antagonists have not been shown to improve the prognosis, there is more evidence to support the use of beta-blockers, particularly in combination with a calcium antagonist. Aspirin and possibly heparin should be considered as routine treatment.

Adrenergic beta-Antagonists↗
PubMed1992

Effects of coronary artery bypass surgery and angioplasty on the total ischemic burden: a study of exercise testing and ambulatory ST segment monitoring.

To assess the effects of standard therapeutic interventions on the total ischemic burden, 86 patients with stable angina underwent 48 hours of ambulatory ST segment monitoring and treadmill exercise testing before and at a mean of 10 weeks after coronary artery bypass surgery (CABG) (group 1, N = 46) or percutaneous transluminal coronary angioplasty (PTCA) (group 2, N = 40). There were 72 male and 14 female patients with a mean age of 56.4 years. All patients had documented coronary artery disease (24, single-vessel; 28, two-vessel; 34, three-vessel disease). Both groups were characteristically similar apart from more severe coronary artery disease (p less than 0.001) and more previous myocardial infarctions (p less than 0.05) in group 1. Groups with CABG and PTCA had significant prolongation of exercise time after intervention (group 1: 7.6 to 9.8 minutes, p less than 0.0001; group 2: 8.1 to 10.0 minutes, p less than 0.001), and both interventions led to a significant reduction in ischemic responses (group 1: 33 to 4, p less than 0.001; group 2: 20 to 13, p less than 0.05) to exercise. During a total of 7643 hours of ST segment monitoring, 253 episodes of ischemia were recorded in 3768 hours before and 44 ischemic episodes in 3875 hours after intervention (group 1, 113 episodes in 24 patients and 21 episodes in 10 patients; group 2, 140 episodes in 13 patients and 23 episodes in six patients). Both interventions reduced the mean frequency of ischemia per 24 hours (group 1: 1.24 to 0.22 episodes per 24 hours; p less than 0.01; group 2: 1.9 to 0.3 episodes per 24 hours; p less than 0.05). Almost 28% (N = 24) of resting electrocardiographic findings were altered as a result of intervention.(ABSTRACT TRUNCATED AT 250 WORDS)

Activities of Daily Living↗
PubMed1991

Cellular distribution of H(+)-ATPase following acute unilateral ureteral obstruction in rats.

Unilateral ureteral obstruction for 24 h produces an acidification defect in the rat kidney that closely resembles the human disorder. We examined the role of renal vacuolar H(+)-ATPase distribution and content in the generation of the postobstructive abnormality in distal hydrogen ion secretion. Rats were subjected to unilateral ureteral obstruction for 24 h, and the obstructed and contralateral kidneys were removed at 3 h, 5 days, and 10 days after release of the obstruction. The postobstructed and contralateral kidneys and kidneys from sham-operated rats were analyzed for intercalated cell number and subtype and for the cellular distribution of ATPase staining by means of a monoclonal antibody specific for the 31-kDa subunit of the vacuolar H(+)-ATPase. No change in the number or distribution of subtypes was detected in the cortex nor in the outer or inner stripe of the outer medulla. Immunoreactive H(+)-ATPase increased in both the cortex and medulla at 3 h after obstruction, and thereafter it declined to control values. The major morphological changes in H(+)-ATPase staining detected were an alteration in the intracellular distribution of the enzyme, which we refer to as discontinuity of (or "gaps" in) apical staining, and a decrease in the percent of intercalated cells showing a rim (or plasma membrane) staining pattern in the inner medulla. The changes observed may be a morphological representation of the physiological abnormalities underlying the postobstructive acidification defect.

Animals↗
PubMed1991

Expression and distribution of renal vacuolar proton-translocating adenosine triphosphatase in response to chronic acid and alkali loads in the rat.

Renal hydrogen ion excretion increases with chronic acid loads and decreases with alkali loads. We examined the mechanism of adaptation by analyzing vacuolar proton-translocating adenosine triphosphatase (H+ ATPase) 31-kD subunit protein and mRNA levels, and immunocytochemical distribution in kidneys from rats subjected to acid or alkali loads for 1, 3, 5, 7, and 14 d. Acid- and alkali-loaded rats exhibited adaptive responses in acid excretion, but showed no significant changes in H+ ATPase protein or mRNA levels in either cortex or medulla. In contrast, there were profound adaptive changes in the immunocytochemical distribution of H+ ATPase in collecting duct intercalated cells. In the medulla, H+ ATPase staining in acid-loaded rats shifted from cytoplasmic vesicles to plasma membrane, whereas in alkali-loaded rats, cytoplasmic vesicle staining was enhanced, and staining of plasma membrane disappeared. In the cortical collecting tubule, acid loading increased the number of intercalated cells showing enhanced apical H+ ATPase staining and decreased the number of cells with basolateral or poorly polarized apical staining. The results indicate that both medulla and cortex participate in the adaptive response to acid and alkali loading by changing the steady-state distribution of H+ ATPase, employing mechanisms that do not necessitate postulating interconversion of intercalated cells with opposing polarities.

Acid-Base Equilibrium↗