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Biomedical subjects

A G Logan

Publications and source records attributed to A G Logan.

At least 55 records · Page 3Linked to original sources
PubMed1991

Aldosterone, atrial natriuretic factor and sodium intake as determinants of the natriuretic response to head-out water immersion in healthy subjects.

1. The effect of sodium intake on the natriuresis and hormonal changes induced by head-out water immersion was studied in seven normal subjects during head-out water immersion and on a control day while successively on 20 mmol of sodium/day and 100 mmol of sodium/day diets. The effects of head-out water immersion were compared with those seen on the control day for both diets. 2. The natriuresis on the 100 mmol of sodium/day diet was significantly greater than on the 20 mmol of sodium/day diet (natriuretic peak: 10.3 +/- 2.2 versus 3.9 +/- 1 mmol of sodium/h; P less than 0.01). The total sodium excretion during the 3 h of head-out water immersion was 26.2 +/- 2.0 mmol on the 100 mmol of sodium/day diet and 9.9 +/- 0.9 mmol on the 20 mmol of sodium/day diet (P less than 0.01). In contrast, the increase in the plasma atrial natriuretic factor level was similar on both diets (peak plasma atrial natriuretic factor level 23.1 +/- 1.9 versus 26.2 +/- 1 pg/ml; not significant). As expected, the baseline serum aldosterone level was higher on the 20 mmol of sodium/day diet and, despite a significant suppression, remained significantly higher at the end of the third hour of head-out water immersion (peak serum aldosterone level: 495 +/- 130 versus 197 +/- 26 pmol/l, P less than 0.06). Furthermore, there was an inverse relationship between the serum aldosterone level and the urinary sodium excretion at the time of peak natriuresis (r = -0.59, P less than 0.01). 3. We conclude that the effect of sodium intake on the natriuresis induced by head-out water immersion is more dependent upon anti-natriuretic agents, such as aldosterone, than on natriuretic factors, such as atrial natriuretic factor.

Adult↗
PubMed1991

Renal and humoral responses to sustained cardiopulmonary baroreceptor deactivation in humans.

The renal and neurohumoral effects of prolonged cardiopulmonary baroreflex unloading and the relationship of these changes to urinary sodium excretion have not been well documented in humans. In this study, 12 normal males underwent lower body negative pressure at -15 mmHg for 90 min, a maneuver that deactivates cardiopulmonary baroreceptors. Glomerular filtration rate (GFR), effective renal plasma flow (ERPF), and filtration fraction (FF) were measured in eight of these subjects using inulin and p-aminohippuric acid clearance techniques. During reduction of central venous pressure, arterial blood pressure and heart rate did not change. Plasma concentrations of atrial natriuretic factor (ANF) decreased markedly (22 +/- 2 to 12 +/- 1 pg/ml, P = 0.0001) as did the second messenger of ANF's biological action, guanosine 3',5'-cyclic monophosphate, whereas renin and vasopressin were not significantly altered. There was a significant rise in plasma norepinephrine (1.6 +/- 0.2 to 2.4 +/- 0.4 nmol/l, P = 0.03). GFR (104 +/- 9 to 68 +/- 6 ml/min, P = 0.007) and FF (0.18 +/- 0.01 to 0.14 +/- 0.01, P = 0.007) decreased significantly, with maintenance of ERPF. There was a significant antinatriuresis without an antikaliuresis and a significant reduction in free water clearance. These changes in renal hemodynamics are unlike the known effects of renal vasoconstrictors, and the alterations in solute and free water clearance are consistent with the removal of the known actions of ANF from tubular target sites. Taken together, our findings suggest that a mechanism other than activation of vasoconstrictors, possibly the diminution of the influence of ANF on the kidney, may be operative in the renal adjustments to cardiopulmonary baroreflex deactivation in humans.

Adult↗
PubMed1991

Prevalence of Type A behavior in untreated hypertensive individuals.

Type A behavior has been associated with coronary heart disease as well as high cholesterol and smoking, major risk factors for coronary heart disease, but the data indicating a similar association with hypertension are inconsistent. Since past studies have usually based hypertension on a single blood pressure assessment or have often included treated hypertensive patients, this inconsistency is not surprising. The current study compared the prevalence of Type A behavior (assessed by Rosenman's structured interview) between 109 untreated hypertensive subjects and 109 age-, sex-, ethnic-, and occupation-matched normotensive subjects. Hypertension status was based on five repeated assessments over a 5-month period. Results indicated that Type A behavior is more prevalent in untreated, mildly hypertensive employed individuals than occupationally matched normotensive subjects. Type A component analysis confirmed the importance of hostility and certain vigorous voice stylistics in predicting cardiovascular conditions. These findings, taken together with the evidence linking Type A behavior with high cholesterol and cigarette smoking, further support the view that this behavior pattern is associated with increased risk of coronary heart disease.

Adult↗
PubMed1991

Treatment of mild-to-moderate hypertension: comparison between a calcium-channel blocker and a potassium-sparing diuretic.

In a multicenter study, 61 patients, 18-70 years of age, with mild-to-moderate hypertension [diastolic blood pressure (DBP) 95/114] completed a 28-week treatment. After initial placebo washout, patients were randomly allocated either to diltiazem or hydrochlorothiazide/triamterene. At the end of 12 weeks, the patients continued on the same medication if their goal blood pressure achieved (DBP less than 90; or 10 mm Hg below baseline). If not, the alternate agent was added (either diltiazem + hydrochlorothiazide/triamterene or hydrochlorothiazide/triamterene + diltiazem). At the end of 28 weeks, the intent-to-treat analysis showed that 90% on diltiazem alone, 73.7% on hydrochlorothiazide/triamterene alone, 71.4% on (diltiazem + hydrochlorothiazide/triamterene), and 57.1% on (hydrochlorothiazide/triamterene + diltiazem) achieved goal BP. End point mean values of BP and heart rate after adjusting for sex, baseline values, age, and weight showed no significant difference between groups. Forty-six percent on hydrochlorothiazide/triamterene alone and 24% on diltiazem alone reported one or more adverse events, possibly related to study medication. Patients with diltiazem as the first choice had better BP control than those on hydrochlorothiazide/triamterene alone (81.5% vs. 69.7%). Furthermore, among non-goal achievers at week 12, there was a greater response in the group when hydrochlorothiazide/triamterene was added to diltiazem than when diltiazem was added to hydrochlorothiazide/triamterene. This study suggests that in mild-to-moderate hypertension, diltiazem is better than hydrochlorothiazide/triamterene as first line therapy.

Adolescent↗
PubMed1991

Plasma atrial natriuretic factor concentrations in a canine model of right heart pressure overload.

Two studies were carried out in order to evaluate the plasma atrial natriuretic factor (ANF) concentrations, as well as hemodynamic and renal profiles in a chronic canine model of right heart pressure overload induced by pulmonary artery (PA) banding. In study I (n = 6), the animals were submitted to a gradual increase in pressure to clarify whether an increase in pressure or atrial distension was the main stimulus to ANF secretion. In study II (n = 6), right heart pressure overload was produced more rapidly, resulting in fluid retention and weight gain, thereby completing the model of right heart failure, and allowing an evaluation of the mechanisms involved in ANF resistance. In study I there were significant increases in right atrial pressure over baseline at 20 weeks, ANF levels at 24 weeks and right atrial area at 28 weeks following PA banding. In study II right heart pressures and ANF levels were higher than baseline at 12 weeks (p less than 0.0001), and fluid retention developed between 12-24 weeks in all dogs. The results suggest that increased right heart pressure, rather than atrial size, is a primary stimulus to ANF secretion in chronic right heart pressure overload. Despite the increases in right atrial pressure, clinical fluid retention occurred only with elevations of renin and aldosterone.

Aldosterone↗
PubMed1990

The response of atrial natriuretic factor and sodium excretion to dietary sodium challenges in patients with chronic liver disease.

Despite intensive investigation, the pathogenesis of sodium retention in patients with chronic liver disease is not fully known. We have studied 19 chronic liver disease patients, 13 without (group 1) and six with (group 2) histories of clinical sodium retention (ascites or edema) by varying dietary sodium intake. The patients were placed on a 20 mmol/day constant diet for 1 wk, followed by a constant 100 mmol/day sodium diet for 1 wk under strict metabolic conditions. After 5 days of equilibration on each diet, blood and urine samples were collected for plasma atrial natriuretic factor levels and urinary sodium excretion. Group 1 patients (n = 6) achieved near sodium balance in 5 days on both a 20-mmol (urinary sodium output = 17 +/- 3 mmol/day) and a 100-mmol sodium diet (urinary sodium output = 80 +/- 5 mmol/day). Atrial natriuretic factor levels in these patients tended to be elevated, but the increase was not significantly greater than that in normal control subjects (10 +/- 4 pg/ml to 19 +/- 4 pg/ml) on the same diets. In contrast, group 2 patients (n = 5) were in significant positive sodium balance on both the 20 mmol/day sodium diet (mean urinary sodium output = 9.5 +/- 3.3 mol/day) and the 100 mmol/day sodium diet (urinary sodium output = 37 +/- 13 mmol/day). This occurred despite significantly elevated baseline atrial natriuretic factor levels and a significant increase in plasma atrial natriuretic factor levels after sodium challenge (62 +/- 9 pg/ml, p less than 0.05) on a 100 mmol/day sodium diet.(ABSTRACT TRUNCATED AT 250 WORDS)

Ascites↗
PubMed1990

Assessing the clinical effectiveness of preventive maneuvers: analytic principles and systematic methods in reviewing evidence and developing clinical practice recommendations. A report by the Canadian Task Force on the Periodic Health Examination.

This paper examines a process for evaluating clinical effectiveness and developing recommendations in which systematic methods are used to review evidence from published clinical research and to reach sound conclusions about appropriate medical policy. The methodology addresses four important components of the analytic process: (1) the criteria that must be satisfied for a clinical practice to be considered effective; (2) proper methods for reviewing evidence from published clinical research to determine whether a clinical practice meets these criteria (including methods for performing comprehensive literature reviews, for judging the quality of individual studies, and for synthesizing or pooling the results of multiple studies); (3) theoretical and practical concerns in translating the results of the scientific review into sound clinical practice recommendations; and (4) the importance of documentation, guidelines, and other safeguards to minimize the effect the reviewers themselves have on the objectivity and consistency of the analytic methods.

Epidemiologic Methods↗
PubMed1988

Acute effects of peritoneovenous shunting on plasma atrial natriuretic peptide in cirrhotic patients with massive refractory ascites.

Plasma immunoreactive alpha-human atrial natriuretic peptide (ANP) was measured in six cirrhotic patients with massive refractory ascites, under strict metabolic conditions, while they were receiving a 20-meq sodium diet, both before and at two-hour intervals for eight hours following peritoneovenous shunting (PVS). The mean preoperative level of ANP was 75 +/- 18 pg/ml, which was found to be significantly higher than the normal range for this laboratory (8 to 24 pg/ml) (p less than 0.05). This value was also significantly higher than the value of 21 +/- 5 pg/ml (p less than 0.05) obtained in six patients with cirrhosis but without ascites. Following shunt insertion, an immediate natriuresis and diuresis were observed in five of the six cirrhotic patients with refractory ascites. In these five, right atrial pressure and ANP rose immediately, followed by a rise in the level of urinary cyclic guanosine monophosphate. The sixth subject had a delayed rise in right atrial pressure, and correspondingly the rise in ANP, the diuresis, and natriuresis were delayed. The changes in ANP following PVS were positively correlated with changes in right atrial pressure (p less than 0.05), urinary cyclic guanosine monophosphate (p less than 0.05), urinary sodium excretion (p less than 0.05), and urine volume (p less than 0.01). These results suggest that ANP may be important in mediating the acute response to PVS.

Aged↗
PubMed1988

Role of atrial natriuretic peptide in the natriuretic response to central volume expansion induced by head-out water immersion in sodium-retaining cirrhotic subjects.

PURPOSE: It is possible that abnormalities in atrial natriuretic peptide may be involved in the pathogenesis of sodium retention in edema states. We performed a study in a group of 12 sodium-retaining cirrhotic subjects to determine the role of this peptide in mediating differences in the natriuretic response to central volume expansion induced by head-out water immersion. PATIENTS AND METHODS: Each patient was maintained for seven days on a 20-mmol sodium intake, and then studied on both control and immersion days. On each day, measurements of the following were obtained: plasma atrial natriuretic peptide, hematocrit, electrolytes, creatinine, plasma renin activity, serum aldosterone, urinary cyclic guanosine monophosphate (cGMP), blood pressure, and pulse rate. RESULTS: In six subjects, immersion resulted in a marked natriuresis sufficient to induce negative sodium balance by the third hour, and these subjects were termed "responders." In these six patients, baseline pre-immersion levels of plasma renin activity and serum aldosterone were all below 3 ng/liter/second and 4 nmol/liter, respectively. In the other six subjects, the natriuretic response to immersion was markedly blunted and insufficient to induce negative sodium balance, and these subjects were termed "non-responders." In these subjects, baseline pre-immersion levels of plasma renin activity and aldosterone were all above 3.5 ng/liter/second and 5 nmol/liter, respectively, and were significantly elevated compared with the responders, and compared with the normal range for control subjects consuming the same sodium intake. In both groups of cirrhotic subjects, baseline levels of plasma atrial natriuretic peptide and cGMP excretion were significantly and comparably elevated compared with the normal range for control subjects ingesting the same sodium intake. Despite the marked difference in the natriuretic response to immersion in both responders and non-responders, there was a significant and comparable further elevation of plasma atrial natriuretic peptide and urinary cGMP excretion during immersion, compared with the control day. CONCLUSION: These results suggest that the relative resistance to the natriuretic action of atrial natriuretic peptide in the non-responders compared with the responders is mediated by anti-natriuretic factors acting at a level parallel with or beyond atrial natriuretic peptide release or coupling to its cGMP-linked receptors.

Adult↗
PubMed1988

Caffeine-containing beverages and the prevalence of hypertension.

Caffeine can produce a mild hypertensive effect for a few hours after use. Some epidemiological data relate chronic coffee intake to an increased risk of cardiovascular disease. We explored the possibility that a regular intake of caffeine-containing beverages (tea, coffee, cola) might produce a chronic increase in blood pressure and increase the likelihood of developing sustained hypertension. A random population survey of 2436 adults was made, with standardized blood pressure readings and a food-frequency questionnaire to determine the regular intake of various nutrients. We found evidence that caffeine intake was positively related to an increased diastolic blood pressure but the effect was small (less than 1 mmHg at usual caffeine intake). There was no evidence that a regular caffeine intake increases the risk of being classified as hypertensive.

Age Factors↗
PubMed1988

Hyperresponsiveness to water immersion in sodium retaining cirrhotics: the role of atrial natriuretic factor.

Cirrhotics do not respond uniformly to head-out water immersion (HWI). Some cirrhotics have an exaggerated natriuresis while others are unresponsive. We studied the humoral and urinary responses to HWI in 5 cirrhotics and compared this to 5 normals on the same 20 mM sodium intake. These cirrhotics had a documented tendency to salt and water retention but had minimal or no evidence of significant ascites. Plasma levels of atrial natriuretic factor (ANF) increased during immersion in both groups. However, the rise in plasma ANF from baseline during each hour of immersion was significantly greater in the cirrhotics (p less than 0.01), than in the normal volunteers. In these cirrhotics, HWI not only corrected the pre-immersion tendency to sodium retention, but by 3 hours had produced an exaggerated natriuretic response (p less than 0.05). It is possible that the greater risk of ANF in cirrhotics is responsible for this natriuretic response. However the reason for the larger rise in cirrhotics is unclear; presumably either a greater central redistribution of plasma volume occurs in cirrhotics following immersion, or there may be greater sensitivity of the ANF release system in cirrhotics.

Aldosterone↗
PubMed1987

Role of atrial natriuretic peptide and urinary cGMP in the natriuretic and diuretic response to central hypervolemia in normal human subjects.

The response of plasma atrial natriuretic peptide (ANP) and urinary cGMP excretion to central hypervolemia induced by water immersion was assessed twice in five healthy male subjects, once while immersed in water to the neck for 3 h and again on a control day. Plasma ANP and urinary cGMP were measured by radioimmunoassay. Compared with the control day, overall change in plasma ANP on the immersion day was significant (p less than 0.05). In response to water immersion, plasma ANP increased from a base-line level of 13.2 +/- 3.1 (mean +/- SEM) to 24.2 +/- 5.5 pg/mL by 0.5 h of immersion and was sustained at that level throughout the immersion period. Plasma ANP returned to the base-line level at 1 h postimmersion. Urinary cGMP excretion increased significantly by 1 h of immersion and was sustained at that level throughout water immersion and 1 h postimmersion (p less than 0.05). During water immersion urine flow, urinary sodium and potassium excretion, free water clearance, and osmolar clearance increased while plasma renin activity, serum aldosterone, and blood pressure fell; all changes were significant (p less than 0.05). Creatinine clearance and hematocrit did not show any significant changes. These data suggest that an increase in plasma ANP may contribute to the natriuretic and diuretic response to central hypervolemia, and that the measurement of urinary cGMP may be a valuable marker of ANP biological responsiveness.

Adult↗
PubMed1986

Sodium manipulation in the management of hypertension. The view against its general use.

Extreme changes in sodium intake do have an effect on blood pressure of both normotensive and hypertensive individuals. Cross-population correlates of average sodium intake and mean population blood pressure are discordant with the results of studies within single populations and cannot be used as sufficient evidence to justify a reduction of dietary sodium intake in the general population to prevent hypertension. Both explanatory and management trials of sodium restriction have yielded contradictory results, and convincing evidence on the nature and size of subgroups of hypertensives with enhanced sodium sensitivity is lacking. The proportion of patients who will follow a moderately restricted sodium diet is low, unless expensive and time-consuming programs of instruction and monitoring are introduced. In light of this evidence, it is premature to recommend diets that are low in sodium as a public health measure and as initial and sole treatment of hypertension.

Diet, Sodium-Restricted↗
PubMed1985

Hydrochlorothiazide-amiloride versus hydrochlorothiazide alone for essential hypertension: effects on blood pressure and serum potassium level.

In a double-blind randomized controlled trial the effects on the blood pressure and the serum potassium concentration of hydrochlorothiazide-amiloride hydrochloride (Moduret) and hydrochlorothiazide alone were compared in 266 adults who were normokalemic and had a diastolic blood pressure greater than 95 mm Hg at the time of entry into the study. The mean ages (52.2 and 53.8 years) and the proportions of men (66% and 56%) in the groups given the combination drug and hydrochlorothiazide alone respectively were similar. In the group given the combination drug the mean blood pressure, measured while the patients were supine, and the mean serum potassium level fell significantly, from 156/99 to 138/88 mm Hg and from 4.23 to 3.91 mmol/L, after 8 weeks of treatment. In the other group both measures also fell significantly, the blood pressure from 157/99 to 138/87 mm Hg and the potassium level from 4.16 to 3.69 mmol/L. The proportions of patients in the two groups with hypokalemia (14% and 29% respectively), defined as a serum potassium level below 3.5 mmol/L, differed significantly (p = 0.0026), whereas the proportions with a potassium level exceeding 4.5 mmol/L (4.5% and 3.9% respectively) were similar. Thus, the combination drug reduced the blood pressure to the same extent as hydrochlorothiazide alone but significantly less often caused hypokalemia. In light of growing concerns about the cardiovascular complications of hypokalemia, hydrochlorothiazide-amiloride appears preferable to hydrochlorothiazide alone for the treatment of some patients with hypertension.

Adolescent↗
PubMed1985

Alterations in health perception and lifestyle in treated hypertensives.

The effect of being treated for hypertension on health perception and life-style and the duration of any alterations after first diagnosis were assessed by administering a standardized interview schedule to employed treated hypertensive men and women, aged 40-64 years, who were either newly diagnosed (ND) (within 6 months of the interview) or previously diagnosed (PD) (1-3 years before the interview) and who were otherwise healthy. In both groups of 50 hypertensives, indices of health status and ability to participate in enjoyable activities were significantly lower while symptom score and index of worry about health were significantly higher compared with a group of 50 age and sex-matched normotensive controls (C) (p less than 0.001). The hypertensive groups did not differ from each other. Both hypertensive groups reported significant reductions in the time spent at work (p less than 0.005). Self-reported weight loss in the 2 months preceding the interview was significantly greater in ND hypertensives compared with PD and C individuals (p less than 0.01). Our data indicate that the diagnosis and treatment of hypertension had a significant and sustained negative impact on health perception and activities of daily living even among actively employed, relatively healthy, medicated hypertensives for whom there were no medical indications to restrict their life-style.

Absenteeism↗
PubMed1985

Role of paraprofessionals in improving compliance with antihypertensive treatment.

Community blood pressure (BP) surveys in the past indicated that less than 25% of the total hypertensive population was under good BP control. Over the past decade there has been a systematic attempt to involve paraprofessionals in community based hypertension control programmes. Highly successful model programmes have used either a health-care team or a physician with a specially trained nurse approach, with good BP control being achieved by the active involvement of paraprofessionals in the treatment process. Patients in these special programmes are more likely to be on antihypertensive medication, are more compliant with prescribed therapy and are less likely to drop out of care. On the other hand, the utilization of paraprofessionals to monitor the antihypertensive care of patients with uncontrolled hypertension at regular intervals does not significantly improve BP control, nor does it substantially alter medication compliance or lower the treatment drop out rate. Hypertension control programmes targeted at special groups, such as working men and women and designed to link identified individuals with uncontrolled hypertension to a source of medical care, are associated with a significant improvement in BP control, indicating the potential usefulness of such screening programmes.

Allied Health Personnel↗