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Biomedical subjects

T G Pickering

Publications and source records attributed to T G Pickering.

At least 199 records · Page 11Linked to original sources
PubMed1987

A quantitative analysis of the effects of activity and time of day on the diurnal variations of blood pressure.

The effects of activity and time of day on blood pressure (BP) were analyzed in 461 patients with untreated hypertension who wore a noninvasive portable BP recorder which took readings every 15 minutes for 24 hours. Patients recorded activity and location in a diary. The data were analyzed separately for two groups of patients: the 190 who stayed at home and the 271 who went to work. The effects of 16 different activities on BP were estimated by relating the BP to the associated activity and to the individual's clinic BP. Blood pressure was higher at work than at home, but the increment of BP for individual activities was similar in the two locations. The overall effect of activities on BP variability was computed using a one-way analysis of covariance model. For the patients who went to work this model accounted for 40% of the observed variation (R2) for systolic and 39% for diastolic BP. A similar model using time of day instead of activity accounted for 33% of variability in both systolic and diastolic BP. Combining activity and time of day was little better than activity alone (41% for both). After allowing for the effects of activity on BP, where sleep is one of the activities, there was no significant diurnal variation of BP. We conclude that there is no important circadian rhythm of BP which is independent of activity.

Adolescent↗
PubMed1987

Left ventricular hypertrophy in hypertension. Prevalence and relationship to pathophysiologic variables.

In less than a decade since development of echocardiographic measurement of left ventricular muscle mass, studies using this technique have provided considerable information about the prevalence and pathophysiology of left ventricular hypertrophy in human hypertension. Increased left ventricular mass has been found in a significant minority of patients with systemic hypertension, with the exact prevalence dependent both on how a population is selected and on the sex, race, and possibly age composition of its members. All published studies have reported that left ventricular hypertrophy is more closely related to blood pressure recorded in the patient's natural setting during normal activity or exercise-whether measured by portable recorder or home manometer-than to blood pressure measured by the physician. In addition, studies indicate that the classic hypertensive abnormalities of concentric left ventricular hypertrophy and increased peripheral resistance are interrelated, while left ventricular hypertrophy is absent in a subgroup of patients with mild essential hypertension who exhibit high cardiac output and evidence of supernormal myocardial contractility. Conversely, the left ventricular functional response to exercise is inversely related to the degree of hypertrophy. High levels of blood viscosity, which would tend to blunt the reduction in peripheral resistance expected during sleep or exercise, have also been associated with left ventricular hypertrophy in patients with essential hypertension. Echocardiographic studies have provided evidence both for and against the hypothesis that activity of the sympathetic or reninangiotensin systems plays a direct role in causing hypertensive cardiac hypertrophy. These findings demonstrate the useful role that echocardiographic assessment of left ventricular structure and function may play in hypertension research.

Age Factors↗
PubMed1987

Pathophysiology of exercise hypertension.

The blood pressure is not a fixed entity but rather a parameter subject to substantial situational fluctuations. Studies based on ambulatory blood pressure measurement as well as exercise testing have shown that the highest blood pressure values in an individual can be recorded during physical exercise. During exercise in healthy subjects, in association with an increase in cardiac output and decrease in peripheral resistance, there is an increase in systolic arterial pressure with nearly constant diastolic pressure. In contrast to normotensive individuals, during dynamic exercise hypertensive patients demonstrate excessive pressure increases due to impaired vasodilatation. The mechanism responsible may be structural changes in the arteriolar walls but age is also an important determinant. The extent of blood pressure increase is more dependent on the mass of contracting muscle than on the mode of contraction. During isometric exercise, there is an increase in both systolic and diastolic blood pressure, predominantly reflex-induced, which is more marked in patients with manifest hypertension at rest than in those with borderline hypertension or in normotensive subjects. During dynamic exercise in a subgroup of patients with coronary artery disease, in contrast to normal subjects in whom the diastolic pressure remains constant, an increase in up to 15 mm Hg in this parameter may be found as a result of ischemia induction with left ventricular dysfunction, inadequately increased cardiac output and reflex vasoconstriction. During dynamic exercise, there is an increase in norepinephrine, more marked in hypertensive than normotensive subjects together with an increase in plasma renin activity; plasma aldosterone changes are in parallel with those of renin activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Antihypertensive Agents↗
PubMed1987

Relation of renin-angiotensin system activity to left ventricular hypertrophy and function in experimental and human hypertension.

This article examines available data concerning the hypothesis that the renin-angiotensin system directly stimulates cardiac hypertrophy and dysfunction in hypertension. Several experiments support a direct effect of angiotensin on myocardial protein synthesis and suggest that this may be independent of adrenergic influences. However, the role played by the renin system in the pathogenesis of hypertensive cardiac hypertrophy may be small, for left ventricular (LV) muscle mass is not systematically greater in high-renin as opposed to low-renin forms of experimental or human hypertension. In animal studies, regression of LV hypertrophy is more consistently observed in response to drugs that inhibit as opposed to those that stimulate renin-angiotensin system activity (i.e., converting enzyme inhibitors or beta-adrenoceptor blockers vs. diuretics or direct vasodilators), although the difference is more quantitative than absolute. Similarly, significant reductions in LV mass occurred in 13 of 16 human trials with converting enzyme inhibitors or beta blockers as opposed to 2 of 10 trials with diuretics or vasodilators (mean = 7.11; p less than 0.01). However, uncertainties regarding the degree of reduction in angiotensin II and adrenergic effects, possible interactions between these systems, and incomplete characterization of induced changes in hemodynamic load on the heart all limit the interpretation of available studies. Preliminary data suggest that an inverse relation exists between renin-angiotensin system activity and LV systolic performance in primary and secondary human hypertension, a possibility that merits further study.

Angiotensin II↗
PubMed1987

Strategies for the evaluation and treatment of hypertension and some implications of blood pressure variability.

The distinction between normotension and hypertension, which is traditionally based on measurements of blood pressure made in the clinic, is arbitrary. The situation is further clouded by the fact that blood pressure varies greatly from moment to moment in any one individual, as shown by ambulatory recordings. The fundamental pattern of diurnal blood pressure variations is governed by the sleep-wakefulness cycle, on which the effects of different activities are superimposed. Although hyperreactivity of blood pressure to behavioral stimuli could in theory contribute to the elevation of blood pressure in hypertensive subjects, this would not by itself explain the sustained elevation of blood pressure that is usually seen throughout the day and night in such patients. It is not known how blood pressure variability contributes to the vascular changes associated with hypertension; three possibly relevant factors are the average level of pressure over time, the peaks of pressure, and the shape of the pressure waveform (dP/dt). Hyperreactivity of blood pressure occurring in the doctor's office may be of considerable practical importance in the evaluation of patients with mild hypertension and may confound the relationship between clinical and overall blood pressure and also the evaluation of the response to antihypertensive treatment. Recordings of blood pressure made outside the clinic may help to overcome these problems.

Behavior↗
PubMed1987

Exercise and hypertension.

The cardiovascular response to dynamic exercise is generally normal in patients with mild hypertension, but the response to isometric exercise may be increased, with a greater degree of vasoconstriction. The exercise-induced rise of pressure is affected little by most antihypertensive medications; with beta blockers, the response to dynamic exercise may be diminished, but to isometric exercise it may be enhanced. There is increasing evidence that regular dynamic exercise may attenuate the development of hypertension and lower blood pressure in patients with mild hypertension. For patients with mild, uncomplicated hypertension, the benefits of exercise appear to out-weigh the risks.

Animals↗
PubMed1986

Pathophysiology of systemic hypertension.

Systemic hypertension can be regarded as a quantitative disorder of blood pressure regulation. No single cause of hypertension has been identified, and it is likely that different mechanisms may be dominant in different individuals. In patients with sustained hypertension, there is usually increased peripheral resistance and normal cardiac output. The hemodynamic pattern of hypertension appears to vary according to the subject's age. Factors that may increase peripheral resistance are a decrease in the number of arterioles, changes in the caliber of the arterioles and increase in blood viscosity. Possible components of increased vascular tone in hypertensive patients include elevation of levels of circulating catecholamines and angiotensin II, increased number/affinity of receptors, changes in membrane permeability and increased excitation-contraction coupling. The major hormonal component that mediates vasoconstriction is the renin-angiotensin-aldosterone system. Genetic, environmental and psychologic factors may also play a role in hypertension.

Behavior↗
PubMed1986

Cardiac structure and function in renovascular hypertension produced by unilateral and bilateral renal artery stenosis.

To evaluate cardiovascular status in human renovascular hypertension, quantitative echocardiographic findings were compared in 42 patients with arteriographically documented renovascular hypertension and 46 age- and sex-matched patients with essential hypertension. Left ventricular (LV) fractional shortening, a measure of systolic performance at rest, was subnormal (less than 26%) in 8 of 42 renovascular hypertensive patients (19%), 0 of 42 essential hypertensive patients (p less than 0.005) and 1 of 79 normal subjects (1%) (p less than 0.005). Fractional shortening was equally reduced in patients with arteriosclerotic and nonarteriosclerotic causes of renal artery stenosis (32 +/- 9% vs 32 +/- 6%, both p less than 0.025 compared with 36 +/- 5% in patients with essential hypertension). The depressed function in renovascular hypertension appeared to be a result of greater LV dilation (p less than 0.02) and septal but not LV free wall hypertrophy (p less than 0.01) that failed to offset the pressure load, allowing end-systolic stress, a measure of myocardial afterload, to increase to abnormal levels (101 +/- 47 X 10(3) dynes/cm2, p less than 0.001 vs 68 +/- 19 in essential hypertension). These data indicate that human renovascular hypertension is associated with more adverse cardiac involvement than essential hypertension of similar severity. In addition, the 14 patients with bilateral renovascular stenosis had a higher cardiac index (3.9 +/- 1.1 liters/min/m2) than the 28 with unilateral stenosis (3.2 +/- 1.1 liters/min/m2, p less than 0.05). This result supports the proposition that bilateral renovascular disease is analogous to 1-clip 1-kidney experimental renovascular hypertension, while unilateral renovascular disease resembles the 1-clip 2-kidney model.(ABSTRACT TRUNCATED AT 250 WORDS)

Blood Pressure↗
PubMed1986

The captopril test for identifying renovascular disease in hypertensive patients.

To develop a screening test for identifying renovascular hypertension, the blood pressure and plasma renin activity responses to an oral test dose of captopril were studied in 246 quietly seated hypertensive patients. The following criteria were developed that exploit the hyperresponsiveness of renin secretion in renovascular hypertensive patients: a 60-minute post-captopril plasma renin activity of 12 ng/ml per hour or more and an absolute plasma renin activity increase of 10 ng/ml per hour or more, along with a 150 percent increase in plasma renin activity (or a 400 percent increase if the baseline plasma renin activity was below 3 ng/ml per hour). Retrospectively, the test identified, among 200 hypertensive patients without evidence of renal dysfunction, all 56 patients with proved renovascular disease. In this group, false-positive results occurred only in two of 112 patients with essential hypertension and in six with secondary hypertension. Nine untreated patients had blood pressure levels of less than 160/100 mm Hg. The test was neither as sensitive nor specific in the 46 patients with renal insufficiency. This study demonstrates that the renin response to oral captopril is a useful screening test for identifying patients with unilateral or bilateral renovascular disease. Since the test also characterizes the renin dependency of the hypertension, it may have other diagnostic and therapeutic uses.

Blood Pressure↗
PubMed1986

Behavioral determinants of 24-hour blood pressure patterns in borderline hypertension.

Borderline hypertension is a heterogeneous condition; only a minority of patients will progress to fixed essential hypertension or suffer cardiovascular damage. Ambulatory blood pressure monitoring can detect the subgroup of borderlines with sustained blood pressure elevation outside the office setting and can also provide a measure of blood pressure variability. Patients in the former group may be at greatest risk for cardiovascular complications while the latter have been theorized to be at risk for progression to fixed hypertension. Evidence we have gathered utilizing ambulatory monitoring does not support the contention that there is a subgroup of borderline hypertensives with excessive blood pressure variability in natural settings. Such recordings have been of benefit in identifying patients with excessive pressor responses to office visits. Future studies employing ambulatory monitoring may be useful in the detection of clinically important subgroups of borderline hypertension.

Behavior↗
PubMed1986

Differing patterns of renal vein renin secretion in patients with renovascular hypertension, and their role in predicting the response to angioplasty.

The correlation between the arteriographic appearance and functional significance of renal artery stenosis in hypertensive patients is poor. Measurements of renal vein renin in patients with unilateral renal artery stenosis undergoing renal angioplasty show that before angioplasty there is lateralization of renin secretion to the ischemic kidney, with suppression from the contralateral kidney. Following angioplasty this pattern returns to normal, with both kidneys showing similar increments of renin in the renal veins. The prediction of therapeutic outcome from renal vein renin measurements is more reliable (sensitivity 74%, specificity 100%) when expressed as the increment of renin for each renal vein over the inferior vena caval value than as the ratio between the two renal veins (sensitivity 62%, specificity 60%), but there is a high false-negative rate with both methods. Renal vein renin patterns cannot reliably distinguish between unilateral and bilateral renal artery stenosis, and in patients with bilateral stenoses tend to show lateralization to the more ischemic kidney.

Angioplasty, Balloon↗
PubMed1986

Technical aspects of percutaneous transluminal angioplasty in renovascular disease.

Technical aspects of percutaneous transluminal angioplasty in renovascular hypertension include knowledge about the pathophysiology of dilation, certain radiological and physiological markers, criteria for patient selection, and, finally, the catheter technique. Important factors for a successful procedure are overdilation and adequate pressure and time of balloon inflation. Radiological markers are inflation and deflation profiles of the balloon as well as determination of the pressure gradient across the stenosis. Main criteria for patient selection are renin-dependent hypertension and less frequent improvement of kidney function. Following dilation the most common adjunct medical therapy is low-dose application of aspirin for a period of 6 months.

Adult↗
PubMed1986

Value of echocardiographic measurement of left ventricular mass in predicting cardiovascular morbid events in hypertensive men.

To assess whether echocardiographic and electrocardiographic detection of left ventricular hypertrophy could predict cardiovascular morbid events in patients with uncomplicated essential hypertension, we followed 140 men for a mean of 4.8 years. Initial echocardiographic measurements of left ventricular mass were normal (less than 125 g/m2 body surface area) in 111 patients and revealed hypertrophy in 29 patients. Morbid events occurred in more patients with hypertrophy on echocardiography (7 of 29, 4.6/100 patient-years) than with normal ventricular mass (7 of 111, 1.4/100 patient-years; p less than 0.01). Electrocardiography showed hypertrophy in too few patients to be of predictive value. Multiple logistic regression analysis showed that left ventricular mass index had the highest independent relative risk for future events and that systolic and diastolic pressures and age had slightly lower relative risks. In men with mild uncomplicated hypertension, left ventricular hypertrophy detected by echocardiography identifies patients at high risk for cardiovascular morbid events and is a significant risk factor for future morbid events independent of age, blood pressure, or resting ventricular function.

Adolescent↗
PubMed1985

Should studies of patients undergoing coronary angiography be used to evaluate the role of behavioral risk factors for coronary heart disease?

Several studies have attempted to assess the contribution of behavioral factors to coronary heart disease by relating the Type A behavior pattern to the extent of coronary artery disease (CAD) in patients undergoing coronary angiography. Although the earlier studies gave positive results, more recent results have been negative; overall the results are confusing. These differences cannot be easily explained by differences in study design. Possible confounding factors which may limit the usefulness of such studies include biased subject selection (approximately 70% of subjects were classified as Type A, and 70% had CAD) and the effects of beta blockers. Furthermore, other studies of similar design which have attempted to relate the three major risk factors to CAD have also yielded conflicting results: an association has been demonstrated consistently with cholesterol, less consistently with smoking, and not at all with hypertension. It is argued that such studies are not well suited to investigating relationships between behavioral factors and coronary heart disease.

Adrenergic beta-Antagonists↗
PubMed1985

Relationship of blood pressure response and the renin-angiotensin system to first-dose prazosin.

It has been reported that the first-dose response to prazosin is more common in patients who are salt-depleted or already receiving beta blockers. The relationship between the first-dose blood pressure and plasma renin responses to oral administration of 1 mg prazosin in 13 (seven male, six female) patients with essential hypertension (average blood pressure = 150/100 +/- 5/2 mm Hg) was studied. Eight of 13 patients experienced marked orthostatic decreases in blood pressure associated with nausea and dizziness. The degree of the orthostatic depressor response was inversely correlated with the baseline plasma renin activity (p less than 0.005). This unique sensitivity of low-renin essential hypertension to prazosin may reflect an underlying increased alpha tone and/or an attendant blunted renin reactivity in this form of human essential hypertension.

Blood Pressure↗