Search PubMed⌕ Search

Biomedical subjects

T G Pickering

Publications and source records attributed to T G Pickering.

At least 181 records · Page 10Linked to original sources
PubMed1989

Renovascular hypertension: etiology and pathophysiology.

Evidence from animal studies demonstrates that the renin-angiotensin (ANG II) system and sodium retention play major roles in experimental renovascular hypertension (RVH). Two basic models have been described. In the first, one-clip two-kidney Goldblatt hypertension, the ischemic kidney secretes renin, which leads to increased ANG II formation and hence elevation of blood pressure (BP). As BP rises, sodium excretion by the intact contralateral kidney increases (pressure natriuresis); therefore, there is no sodium retention. In the second, one-clip one-kidney Goldblatt hypertension, the contralateral kidney is removed. In this case the pressure natriuresis can no longer occur, and sodium retention occurs. The ensuing expansion of plasma volume inhibits renin secretion, so that in this model the renin level is normal or low. Following the clipping of the renal artery, renal blood flow and pressure are maintained distal to the stenosis by an ANG II-mediated vasoconstriction. This acts preferentially on the efferent glomerular arterioles, so that the ratio of preglomerular to postglomerular resistance is reduced, which helps to maintain glomerular filtration despite the reduced renal perfusion pressure. In the contralateral kidney the afferent arteriolar resistance is increased, probably as a direct result of exposure to the higher intrarenal arterial pressure. ANG II constricts the efferent arterioles in the same way as in the ischemic kidney, so that the ratio of preglomerular to postglomerular resistance is unchanged. When an angiotensin converting enzyme (ACE) inhibitor is given, the efferent arterioles vasodilate. In the ischemic kidney this may produce a reduction of glomerular filtration rate (GFR), which is not seen in the contralateral kidney. Unilateral RVH in humans corresponds closely to the animal model of one-clip two-kidney hypertension. Plasma renin activity is usually high, and converting enzyme inhibitors lower BP effectively. The increased renin is due exclusively to increased secretion of renin by the ischemic kidney, and is completely suppressed in the contralateral kidney. It is not clear whether bilateral RVH corresponds to the one-clip one-kidney model, but there is circumstantial evidence to suggest that both renin and volume factors may be involved. The majority of cases of human RVH are caused by atheroma, which is commonly bilateral, or by fibromuscular dysplasia. The former tends to be associated with atheroma elsewhere in the arterial tree, and often progresses to complete occlusion and renal failure. The latter occurs in younger patients, and almost never progresses to complete occlusion.

Animals↗
PubMed1989

A comparison of two ambulatory blood pressure monitors, the Del Mar Avionics Pressurometer IV and the Spacelabs 90202.

The purpose of this study was to evaluate the accuracy of two noninvasive ambulatory blood pressure (BP) monitors, the new Del Mar Avionics Pressurometer IV (PIV) and the second generation Spacelabs 90202. Two sets of comparisons were made between two trained observers and the monitors on 17 normotensive and 28 hypertensive subjects. The result of the first comparison showed that the average difference between observers and the PIV was 1.2/-2.2 mm Hg for systolic and diastolic BP. Comparisons of both monitors to the observers showed differences of 0.9/1.0 mm Hg for the PIV and 0.3/0.8 mm Hg for the 90202 (systolic/diastolic). Correlations between the average observer reading and the monitors over both sets of comparisons ranged from 0.90 (diastolic 90202 vs observer) to 0.98 (systolic PIV vs observer). The percentage of readings within 5 mm Hg between observer and monitor over all comparisons ranged from a low of 68% (90202, systolic and diastolic) to a high of 83% (PIV, diastolic). In general, both devices are satisfactory and reliable machines for ambulatory BP monitoring, but each has a slightly different bias compared to auscultatory readings.

Adult↗
PubMed1989

Parity and perceived job stress elevate blood pressure in young normotensive working women.

This study examined the effect of physiological, behavioral, and psychosocial stressors on blood pressure measured in the work environment, home environment, and during sleep in a sample of 50 normotensive working women (average age = 30.2 +/- 7.4 years; average education = 4.3 years college). The results of separate stepwise regression analyses performed on the pressures measured in each environment showed that perceived job stress (P less than .05) and body fat or mass (P less than .05) significantly elevated systolic pressure in all situations, whereas home stress (P less than .05) and number of children (P less than .05) had the most marked effect on diastolic pressure variation over the day. These results suggest that the daily variation of systolic pressure in working women is related to stress on the job, and that diastolic pressure variation is associated with home stress, which may include stress arising from child care.

Adult↗
PubMed1989

Some implications of the differences between home, clinic and ambulatory blood pressure in normotensive and hypertensive patients.

Three different techniques are now available to measure blood pressure in patients - clinic measurements, self-monitoring by the patient at home and ambulatory monitoring. Clinic measurements are susceptible to a number of biases which make them frequently unrepresentative of pressures at other times. The differences between pressures measured in the clinic and elsewhere tend to be much greater in hypertensive than in normotensive subjects, whereas the diurnal variability of blood pressure is only slightly greater in hypertensives, implying that the traditional diagnosis of hypertension on the basis of clinic pressures may cause a bias in subjects who show an enhanced pressor response to the clinic situation ('white coat effect'). We conclude that all three techniques should be used. Ambulatory monitoring provides information about the diurnal profile of blood pressure, and is particularly suited to the initial evaluation of patients, while home monitoring is ideal for observing the effects of treatment.

Antihypertensive Agents↗
PubMed1989

The role of ambulatory monitoring in reducing the errors associated with blood pressure measurement.

The measurement of blood pressure for the clinical evaluation of hypertensive subjects is subject to three types of error. First is the error due to the measurement procedure itself. Although noninvasive methods are less accurate than invasive ones, they are preferred for clinical use both because of their convenience and safety, and because they form the basis of our knowledge of the risks associated with hypertension. Most automatic recorders use either the Korotkoff sound or oscillometric techniques, which generally provide an acceptable accuracy (to within 5 mmHg), although a new method (the K2 technique) may be the most accurate. The second error arises from the spontaneous variability of blood pressure, such that single clinic readings may vary by as much as 20 mmHg. This error can be reduced by multiple readings, e.g. obtained with ambulatory monitoring. The third type of error arises from a spurious elevation of blood pressure in the clinic (the white coat effect), which also may be as much as 20 mmHg. This can be reduced by including readings taken outside the clinic, e.g., by self- or ambulatory monitoring.

Blood Pressure Monitors↗
PubMed1988

Recurrent pulmonary oedema in hypertension due to bilateral renal artery stenosis: treatment by angioplasty or surgical revascularisation.

11 patients with atheromatous renovascular hypertension had a history of multiple episodes of pulmonary oedema. 7 had stenosis of both renal arteries, 2 had stenosis of the artery to a solitary kidney, and 2 had unilateral stenosis with an intact contralateral kidney. Successful revascularisation (by angioplasty in 8, and surgery in 3) improved blood pressure and renal function, and virtually eliminated pulmonary oedema. In a second series of 55 consecutive patients with azotaemia and renovascular hypertension, pulmonary oedema occurred in 13 (23%). Blood pressure and renal function were not significant predictors of pulmonary oedema, but coronary heart disease and bilateral (vs unilateral) renal artery stenosis were. Bilateral renal artery stenosis may be a specific and treatable predisposing factor to pulmonary oedema in azotaemic hypertensive patients.

Acute Disease↗
PubMed1988

How common is white coat hypertension?

Twenty-one percent of 292 patients with untreated borderline hypertension (clinic diastolic blood pressures persistently between 90 and 104 mm Hg) were found to have normal daytime ambulatory pressures (defined from a population of normotensive subjects). These patients were defined as having "white coat" hypertension, and they were more likely to be female and younger, to weigh less, and to be more recently diagnosed than patients whose pressure was elevated both in the clinic and during ambulatory monitoring. Patients with white coat hypertension did not show a generalized increase of blood pressure lability, nor an exaggerated pressor response while at work. The phenomenon is more pronounced when blood pressure is measured by a physician than by a technician. In such patients, the pressor response may be relatively specific to the physician's office and lead to significant misclassification of hypertension.

Adult↗
PubMed1988

Relationship between ambulatory and exercise blood pressure and cardiac structure.

Recent research using automated ambulatory blood pressure recorders and echocardiography has revealed a closer relationship between LV structure and blood pressure during usual activity than with physician measurements of blood pressure. Because increased LV mass is a strong predictor of an adverse prognosis, this suggests that ambulatory blood pressure may also be more predictive of prognosis than casual readings, a view supported by preliminary evidence. Ambulatory blood pressure monitoring has already proved useful to identify patients with "white coat" hypertension or "office" hypertension, whose hearts appear normal by echocardiography. Further research is needed to determine the relative predictive value and comparative cost-effectiveness of ambulatory blood pressure monitoring and echocardiography for identification of patients in whom hypertension does or does not constitute a cardiovascular disease that requires antihypertensive therapy.

Blood Pressure↗
PubMed1988

The influence of daily activity on ambulatory blood pressure.

Studies of ambulatory monitoring of blood pressure have found that blood pressure shows large variations over a 24-hour period and that in many subjects clinic pressures are a poor guide to the level of pressure at other times. Many of the variations in blood pressure that are observed during a normal day are predictable and can be attributed to factors such as physical activity, the sleep-wakefulness cycle, eating and drinking, and mental stress. In general, hypertensive persons show patterns of change similar to those of normotensive persons, but their diurnal profiles of pressure are reset at a higher level.

Activities of Daily Living↗
PubMed1988

Ambulatory blood pressure monitoring and cardiovascular reactivity testing for the evaluation of the role of psychosocial factors and prognosis in hypertensive patients.

This article reviews the contributions of laboratory-based reactivity testing and ambulatory blood pressure monitoring in the evaluation of the role of psychosocial factors in hypertension. Reactivity testing is ideally suited for evaluating individual differences in susceptibility to the acute effects of stressors but cannot resolve the question regarding whether stressors in everyday life contribute to a sustained elevation of pressure. Although several associations between increased reactivity and hypertension have been demonstrated, they do not necessarily imply a primary role for behavioral factors. Ambulatory monitoring is ideally suited for studying the effects of everyday stressors and has shown that blood pressure may increase as a result of occupational stress. On the grounds that hypertension results from an interaction of genetic and environmental factors, it is argued that both techniques have their place and that the role of psychosocial factors can best be demonstrated by prospective studies of persons exposed to different levels of stress.

Ambulatory Care↗
PubMed1988

Sex differences in factors affecting the daily variation of blood pressure.

The purpose of this study was to examine whether the life experiences described by postural, situational, and emotional changes during the day have similar effects on the blood pressure of men and women. The subjects of the study were 137 men and 67 women from the clinical population of the Hypertension Center at The New York Hospital-Cornell Medical Center. There were 3023 individual pressure measurements available for study, 2072 from the men, and 951 from the women, which were taken using noninvasive ambulatory blood pressure monitoring techniques. Pressures were transformed to z-scores using the subject's daily mean pressure and standard deviation to assess the relative elevation during the various effects. Separate but identical ANOVA models were run for each sex. The results show that there were differences between men and women in the parameters associated with the level of systolic and diastolic pressure. Men's systolic pressure varied by situation of measurement (P less than 0.0001) and emotional state (P less than 0.0001), while that of women varied by posture (P less than 0.0005) and situation of measurement (P less than 0.0001). The diastolic pressure of men varied by emotional state as did that of women, except that men's diastolic pressure tended to be highest during reported anger while that of women tended to be highest during reported anxiety. Differences in occupation or environment, hormones, or in behavioral patterns related to the socialization process may all contribute to the differences between the sexes.(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of Variance↗
PubMed1988

Do laboratory tests of blood pressure reactivity predict blood pressure changes during everyday life?

This study was undertaken to examine whether blood pressure reactivity measured in the controlled setting of a laboratory could be correlated with blood pressure changes occurring during daily life. The subjects were 164 untreated hypertensives with mild hypertension, all of whom had a 24-hour ambulatory blood pressure recording, during which their activities were unrestricted. One hundred thirteen performed a treadmill exercise test, and 51 performed two active coping tasks (playing a video game or mental arithmetic). Blood pressure was monitored at baseline and during the tasks. Significant correlations were observed between the absolute levels of pressure measured during the laboratory tests and ambulatory monitoring, but these were higher for the active coping tasks (r = 0.53 to 0.75) than the exercise testing (r = 0.26 to 0.46) and were no higher for pressures measured during the tasks than at baseline. Correlations between the changes of blood pressure during the laboratory tasks and the changes occurring during ambulatory monitoring were analyzed in three ways, using simple, multiple, and canonical correlations. In no case were these correlations substantively significant. We conclude that blood pressure reactivity measured in the laboratory may not be readily generalized to changes of pressure in everyday life, as measured by noninvasive ambulatory recorders.

Adult↗
PubMed1988

Wideband external pulse recording during cuff deflation: a new technique for evaluation of the arterial pressure pulse and measurement of blood pressure.

Analysis of the external brachial pulse recorded during standard blood pressure cuff deflation with use of a transducer with a wide frequency response has revealed a reproducible pattern with three distinct components that we have labeled K1, K2, and K3. K1 is a low-amplitude, low-frequency signal that is present with cuff pressures above systolic pressure. K2 is a triphasic signal appearing at systolic pressure and disappearing at diastolic pressure, which approximately corresponds to the audible Korotkoff sound. K3 appears with cuff pressure between systolic and diastolic pressure and continues to be present below diastolic pressure. Intra-arterial pressure recordings made with a high-fidelity Millar catheter-tip manometer revealed K2 and K3 analogs. K3 resembles the intra-arterial pressure waveform and when calibrated according to the pulse pressure, noninvasive dK3/dt determinations correlated well with intra-arterial dP/dt measurements. The appearance/disappearance property of K2 was designated as the "K2 algorithm" and represents a new, objective noninvasive method for measurement of blood pressure. The K2 algorithm compares favorably with intra-arterial measurements, is more accurate than the auscultatory technique, and may be especially useful in clinical situations in which the auscultatory technique does not work well.

Adolescent↗
PubMed1988

Blood pressure monitoring outside the office for the evaluation of patients with resistant hypertension.

Although severe hypertension is associated with a poor prognosis, there exists a substantial number of patients who have persistently elevated blood pressures, but no signs of target organ damage, and nearly normal life expectancy. In such cases, measurement of blood pressure outside the clinic may give readings that are as much as 30 mm Hg lower than the clinic readings. The first step recommended in the identification of such patients is to use home blood pressure monitoring. If home blood pressures are low, 24-hour ambulatory blood pressure recording is indicated. If this also gives low readings, it is appropriate to treat patients according to their level of home blood pressure. Because of the unreliability of clinic pressures, ambulatory and home blood pressure monitoring may also be of value in assessing the response to treatment.

Ambulatory Care↗
PubMed1988

The reproducibility of average ambulatory, home, and clinic pressures.

The reproducibility of ambulatory, home, and clinic blood pressures was compared in 13 untreated mildly hypertensive and 14 normotensive subjects. Each subject had two sets of daily ambulatory recordings, home self-measured readings (over 6 days), and clinic measurements taken 2 weeks apart. Comparisons over the 2 weeks within and among the methods of measurements were made using a repeated-measures analysis of variance. The results showed that there was no consistent average change in the ambulatory or home pressures and no change in clinic diastolic pressures, but the clinic systolic pressure of the hypertensive subjects dropped 6 mm Hg (p less than 0.05), while that of the normotensive subjects showed no significant change. Test-retest correlations of each of the three methods were similar in magnitude, indicating a similar level of reliability. Test-retest correlations of the ambulatory standard deviations, however, were low, indicating a low reliability of this measure of daily pressure variability. These results suggest that the reproducibility of ambulatory pressures may be as good or better than that of home or clinic measurements. They also suggest that the average ambulatory pressure may be preferable as the measurement in clinical trials, since it may be less influenced by measurement anxiety, particularly in hypertensive subjects.

Activities of Daily Living↗
PubMed1987

Proteinuria in renovascular hypertension and the effects of renal angioplasty.

In 46 patients with renovascular hypertension who underwent renal angioplasty, proteinuria (more than 150 mg/24 hours) was more pronounced than in patients with essential hypertension. The highest levels were seen in patients in whom 1 renal artery was totally occluded. There was no difference between patients with unilateral vs bilateral renal artery stenosis. Proteinuria could not be correlated with serum creatinine level, and in 28% of the patients with renovascular hypertension, proteinuria was present despite a normal creatinine level. Renal angioplasty produced a significant diminution in proteinuria when it resulted in a cure of the hypertension, but no diminution was achieved if blood pressure did not decrease.

Angioplasty, Balloon↗