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Biomedical subjects

T G Pickering

Publications and source records attributed to T G Pickering.

At least 163 records · Page 9Linked to original sources
PubMed1991

Clinical applications of ambulatory blood pressure monitoring: the white coat syndrome.

The estimation of an individual's true blood pressure by conventional clinical measurement is subject to a number of errors, stemming partly from the inherent variability of blood pressure, and also from the white coat syndrome, which is an elevation of blood pressure limited to the clinic setting. This may occur in about 20% of patients with mild hypertension, and is hypothesized to be a learned or conditioned response. Ambulatory monitoring may help to identify such patients. Other potential clinical applications of the technique include evaluation of patients with resistant hypertension, with excessively labile blood pressure, or with autonomic insufficiency, which may be characterized not only by hypotensive episodes, but also by hypertensive episodes during the night. An unresolved question is the definition of the upper limit of normal ambulatory pressure, which is required before ambulatory monitoring finds wide clinical acceptance.

Blood Pressure Determination↗
PubMed1991

The role of laboratory testing in the diagnosis of renovascular hypertension.

The diagnosis of renovascular hypertension depends heavily on laboratory tests. There is no universally applicable screening test, and it should be actively sought only in patients with clinical clues suggested by the history, physical examination, and routine laboratory testing. Hyperreninemia is a characteristic finding, and acute blockade of the renin system forms the basis of diagnostic tests such as the oral captopril test and captopril renography. Other abnormal laboratory findings include hypokalemia, proteinuria, and azotemia exacerbated by angiotensin-converting enzyme inhibitors.

Captopril↗
PubMed1991

Clinic and ambulatory blood pressure measurements for the evaluation of borderline hypertension in smokers and non-smokers.

Hypertension can be diagnosed only by blood pressure measurement, but conventional clinic measurement is subject to two major sources of error, first from the inherent variability of blood pressure, and second from the white coat effect, that is the increase of pressure that occurs in the presence of a physician. Ambulatory monitoring avoids both of these problems. Although smoking has been shown to raise blood pressure acutely, population studies have failed to show a sustained effect. To resolve this paradox, we compared clinic and ambulatory pressures in smokers and non-smokers. Clinic pressures were the same, but smokers had significantly higher daytime ambulatory pressures, than non-smokers, particularly in subjects over the age of 50. No differences in nighttime pressures were observed.

Adult↗
PubMed1991

Diagnosis and evaluation of renovascular hypertension. Indications for therapy.

Renovascular hypertension is caused by two distinct conditions with different causes, fibromuscular dysplasia and atheroma. Diagnosis of the former is both simpler and more rewarding, whereas atheromatous lesions of the renal artery may be secondary to essential hypertension. It is therefore important to establish existence of functional renal ischemia as well as an anatomical lesion. Universal screening of all hypertensive patients is not recommended because of the relatively low prevalence of the disease and insufficient accuracy of available screening tests. When renovascular hypertension is clinically suspected, an oral captopril test is the most reliable office screening test. After this, digital subtraction angiography with renal vein renins or captopril renography are appropriate steps. However, the latter procedure, while promising, requires further evaluation. Duplex scanning of the renal arteries also comes into this category. Arteriography is done last, so that if renal ischemia is indicated, angioplasty can be attempted at the same time as arteriography.

Angiography, Digital Subtraction↗
PubMed1990

The relationship between 'job strain,' workplace diastolic blood pressure, and left ventricular mass index. Results of a case-control study.

To determine whether "job strain" (defined as high psychological demands and low decision latitude on the job) is associated with increased workplace diastolic blood pressure and the left ventricular mass index, we conducted a case-control study at seven urban work sites of 215 employed men aged 30 to 60 years without evidence of coronary heart disease. After comprehensive blood pressure screening of male employees (N = 2556) at the work site, 87 cases of hypertension and a random sample of 128 controls were studied. In a multiple logistic regression model, job strain was significantly related to hypertension, with an estimated odds ratio of 3.1, after adjusting for age, race, body-mass index, type A behavior, alcohol intake, smoking, work site, 24-hour urine sodium excretion, education, and physical demand level of the job. Controlling for the above variables in subjects aged 30 to 40 years with job strain, we found that the echocardiographically determined left ventricular mass index was, on average, 10.8 g/m2 greater than in subjects without job strain. We conclude that job strain may be a risk factor for both hypertension and structural changes of the heart in working men.

Adult↗
PubMed1990

Winter-summer differences in the effects of emotion, posture and place of measurement on blood pressure.

The purpose of this study was to assess whether the effects of emotional state, posture, situation of measurement, and sex on daily blood pressure variation were different in subjects measured during summer months (May-September) and winter months (November-March). The subjects of the study were 157 patients from the Hypertension Center of New York Hospital-Cornell Medical Center in New York, who had ambulatory blood pressure monitoring performed between February 1984 and April 1985. Individual pressures taken with the monitor over the day in each subject were transformed to z-scores using the subject's daily mean pressure and standard deviation in order to assess differences in intraindividual variation. The zeta-scores were examined in separate but identical analyses of variance models (one for the winter months and one for the summer months) which included emotional state (happy, angry, anxious), posture (sitting, standing), situation of measurement (home, work, elsewhere) and sex as factors. The results showed that more factors had greater effects (as reflected in R2) on blood pressure during the winter months than summer months. In particular, the relative effect of anxiety, sitting, and being at work or home on blood pressure was significantly greater (P less than 0.05) in the winter months than summer months. In addition, pressure elevation during happiness was also more accentuated in winter than summer for diastolic pressure (P less than 0.05). These findings may have important implications for the interpretation of population studies examining the relationship between blood pressure and psychosocial stressors.

Adult↗
PubMed1990

A validation study of the instromedix Baro-Graf QD home blood pressure monitor.

The purpose of this study was to assess the accuracy of the Instromedix Baro-Graf QD home blood pressure monitor. Forty subjects were divided among three blood pressure (BP) groups: low (BP less than 110/70, N = 11); medium (BP 110/70 to 140/90, N = 17) and high (BP greater than 140/90, N = 12). Five seated readings were taken per subject. We examined the differences between simultaneous auscultatory and machine readings and assessed the machine's accuracy using ANOVA and correlation analysis. The results show that the device, while highly accurate, tended to become less so as pressure increased. However, its accuracy was superior compared to most other devices we have tested, and because of features, such as a computer memory that stores events and blood pressure over time, this monitor will likely be a useful tool for clinical trials of long term blood pressure change.

Analysis of Variance↗
PubMed1990

The effect of work environments on blood pressure: evidence from seven New York organizations.

The prevalence of hypertension defined according to National Health and Nutrition Examination Survey II (NHANES II) criteria (140/90 mmHg and/or taking antihypertensive medication) was analyzed cross-sectionally at seven worksites in New York City (n = 4274; 2616 men and 1648 women), in order to assess whether exposure to different work environments and occupations contributes to blood pressure variation. The prevalence of hypertension across worksites was 26% among men and 12% among women. Blood pressure was significantly different across worksites even after controlling for known risk factors using analysis of covariance. Of the variation in systolic pressure, 34% was predicted significantly by eight variables; after adjusting for upper-arm circumference, age and body mass index, higher pressures were associated with worksite differences (9.0 mmHg), being male (7.2 mmHg), lacking a high-school education (4.3 mmHg), having a clerical occupation (2.9 mmHg) and being unmarried (1.8 mmHg). Similar results for diastolic pressure suggest that researchers should consider worksite and job characteristics as important predictors of blood pressure differences in working populations.

Adult↗
PubMed1990

Relation of left ventricular hemodynamic load and contractile performance to left ventricular mass in hypertension.

The weak relation of systolic blood pressure to left ventricular mass in hypertensive patients is often interpreted as evidence of nonhemodynamic stimuli to muscle growth. To test the hypothesis that left ventricular chamber size, reflecting hemodynamic volume load and myocardial contractility, influences the development of left ventricular hypertrophy in hypertension, we studied actual and theoretic relations of left ventricular mass to left ventricular diastolic chamber volume, pressure and volume load, and an index of contractility. Data were obtained from independently measured M-mode and two-dimensional echocardiograms in 50 normal subjects and 50 untreated patients with essential hypertension. Two indices of overall left ventricular load were assessed: total load (systolic blood pressure x left ventricular endocardial surface area) and peak meridional force (systolic blood pressure x left ventricular cross sectional area). A theoretically optimal left ventricular mass, allowing each subject to achieve mean normal peak stress, was calculated as a function of systolic blood pressure and M-mode left ventricular end-diastolic diameter. Left ventricular mass measured by M-mode echo correlated better with two-dimensional echocardiogram derived left ventricular end-diastolic volume (r = 0.56, p less than 0.001) than with systolic blood pressure (r = 0.45, p less than 0.001) and best with total load or peak meridional force (r = 0.68 and 0.70, p less than 0.001). In multivariate analysis both end-diastolic volume and blood pressure were independent predictors of systolic mass (p less than 0.001) and explained most of its variability (R = 0.75, p less than 0.001). Theoretically optimal left ventricular mass was more closely related to end-diastolic volume (r = 0.72, p less than 0.001) than to systolic blood pressure (r = 0.46, p less than 0.001); thus, the relatively weak correlation between blood pressure and optimal mass reflected the influence of left ventricular cavity size, rather than a lack of proportionality between load and hypertrophy. Actual and theoretically optimal left ventricular mass were closely related (r = 0.76, p less than 0.001), indicating that left ventricular hypertrophy in most cases paralleled hemodynamic load. Left ventricular mass was positively related to stroke index and inversely to contractility (as estimated by the end-systolic stress/volume index ratio), the main determinants of left ventricular chamber volume. In multivariate analysis, systolic blood pressure, stroke index, and the end-systolic stress/volume index ratio were each independently related to left ventricular mass index (all p less than 0.001, multiple R = 0.81) and accounted for 66% of its overall variability.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗
PubMed1990

Body fat and its distribution in relation to casual and ambulatory blood pressure.

This study was undertaken to evaluate the associations of body fat and its distribution with casual and ambulatory blood pressure in nonobese men. One hundred and thirty-five normotensive or mildly hypertensive (but untreated) men employed at three work sites were studied. Casual blood pressure was measured at the work site at initial screening and on a second occasion by a nurse. Ambulatory blood pressure was measured noninvasively for 24 hours on a workday and analyzed as work, home, and sleep blood pressure measurements. Anthropometric measurements included height, weight, and waist and hip circumferences. Blood pressure was highest while at work; home blood pressure was higher than screening blood pressure or nurse blood pressure, and sleep blood pressure was lowest. Weight and both waist and hip circumferences (but not their ratio) were all significantly correlated with screening, nurse, and sleep blood pressures but not with work or home blood pressures. Stepwise regression analysis showed that waist circumference was the best overall predictor of blood pressure. We suggest that in situations where blood pressure is the dependent variable, correlations with other variables may be closest for "basal" measures of blood pressure and may be obscured by the effects of daily activities on blood pressure.

Adipose Tissue↗
PubMed1990

Can ambulatory blood pressure monitoring improve the diagnosis of mild hypertension?

Hypertension is usually defined, and treatment initiated, when blood pressure exceeds a certain threshold level. This level is usually determined by a limited number of clinic measurements, which may give a poor estimate of the true level of blood pressure, because of both the inherent variability of blood pressure and the white coat effect. Another way of defining the need for treatment is the threshold decision-making approach, which describes two threshold levels, the treatment and the testing thresholds. When the pressure is between these two, further testing is indicated. Ambulatory monitoring and self-monitoring avoid the inherent limitations of clinic pressure, by increasing the number of readings and taking readings outside the clinic setting. What evidence there is indicates that ambulatory pressures do give a better measure of prognosis, and hence of the need for treatment, but better criteria are needed to define the upper normal limit. While it may be premature to recommend the widespread application of ambulatory monitoring, there are good prospects that it will provide the basis for a more rational diagnosis.

Blood Pressure↗
PubMed1990

The role of behavioral factors in white coat and sustained hypertension.

Studies using ambulatory monitoring of blood pressure have indicated that patients with persistently elevated clinic pressures may be subdivided into two groups, those in whom ambulatory pressure is also elevated (persistent hypertension), and those in whom it is normal (white coat hypertension). The role of behavioral factors in contributing to these two types is discussed. Studies of white coat hypertension suggest that it is not characterized by any generalized physiological abnormality, and that target-organ damage is mild and the prognosis relatively benign. It may represent a conditioned response to the physician. Behavioral factors can significantly influence the diurnal profile of blood pressure, as shown by a comparison of ambulatory pressures recorded on working and non-working days, and in women who experience varying levels of occupational and domestic stress. The role of behavioral factors in the development of sustained hypertension (defined as an upward resetting of the diurnal profile), however, is much less clear. A cross-sectional study of normotensive and hypertensive men has shown that men employed in high-strain jobs are more likely to show a sustained elevation of blood pressure.

Behavior↗
PubMed1990

Relationship between ambulatory or exercise blood pressure and left ventricular structure: prognostic implications.

Left ventricular mass can be accurately measured by echocardiography, and this measurement has been shown to be a stronger predictor of cardiovascular morbid events or of death than blood pressure levels or all other conventional risk factors except age. Echocardiographic left ventricular mass is thus a useful 'bioassay' that can determine the effects on the heart of various measures of blood pressure. All available studies have shown a closer relationship between left ventricular mass or left ventricular wall thickness and blood pressure as measured by ambulatory monitoring over 24 h or during specific time periods, such as the working day, compared with casual pressure measurements. Similarly, blood pressure at the end of maximal or submaximal exercise predicted left ventricular mass better than causal pressures in each study of this topic. Thus there is a closer parallel between prognostically important measures of left ventricular structure and blood pressure during physical or mental activity than with clinic measurements of blood pressure. Although the mechanisms underlying these relationships are not fully understood, it has been proposed that the blood pressure levels measured during activity may be more closely related to left ventricular structure than conventional clinic measurements, that these levels appear to be free from any alerting reaction to the physician taking the measurement and that there may be a fundamental biological link between the stimuli to blood pressure levels during activity and cardiovascular hypertrophy.

Blood Pressure↗
PubMed1990

Does psychological stress contribute to the development of hypertension and coronary heart disease?

The role of mental stress in the development of hypertension and coronary heart disease remains uncertain. Its effects are likely to depend on an interaction of at least three factors: the nature of the stressor, its perception by the individual, and the individual's physiological susceptibility. This type of interaction is supported by animal studies. Most experimental studies in man have measured the cardiovascular response to acute laboratory stressors, on the assumption that subjects showing greater reactivity are at higher risk of developing cardiovascular disease. Experimental support for this "reactivity hypothesis" is limited, and the technique suffers from a number of limitations, such as an emphasis on acute rather than chronic effects, and a doubtful relevance to real-life stressors. It is possible, however, that transient surges of autonomic activity occurring in response to behavioral stimuli could trigger acute cardiac events. The role of environmental stressors can be studied by ambulatory monitoring techniques. Using the Karasek Job Content Survey (a known predictor of coronary heart disease), we have found that men in high strain jobs (defined by a combination of high demands and low control) are more likely to be hypertensive, and to show left ventricular hypertrophy than men in less stressful jobs.

Animals↗
PubMed1989

Assessment of the effects of alpha- and beta-blockade in hypertensive patients who smoke cigarettes.

A 24-week, crossover, comparison study was conducted to observe the effects of alpha-blockade with prazosin and beta-blockade with propranolol on blood pressure and plasma lipoprotein levels in 15 hypertensive cigarette smokers. Before treatment, mean sitting blood pressure was 140/100 mm Hg and rose to 147/105 mm Hg after the patients smoked two cigarettes. Treatment with prazosin and propranolol lowered sitting blood pressure to 127/89 mm Hg and 129/91 mm Hg, respectively (not significant), and did not alter the pressor response to smoking. The total cholesterol level at baseline was 207.3 +/- 11.0 mg/dl. This increased to 210.5 +/- 10.2 mg/dl with propranolol treatment and decreased to 201.0 +/- 11.1 mg/dl with prazosin treatment. The low-density lipoprotein cholesterol level was 132.5 +/- 8.1 mg/dl at baseline, 136.9 +/- 8.3 mg/dl with propranolol treatment, and 129.4 +/- 9.0 mg/dl with prazosin treatment (0.05 less than p less than 0.10 between-group comparison). The data indicated that whereas prazosin and propranolol are equally effective in controlling blood pressure in hypertensive cigarette smokers, effects on plasma lipoproteins also may need to be considered when selecting a first-step antihypertensive agent in this coronary-prone population.

Adult↗