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Biomedical subjects

T G Pickering

Publications and source records attributed to T G Pickering.

At least 109 records · Page 6Linked to original sources
PubMed1994

Autogenic-feedback training: a potential treatment for orthostatic intolerance in aerospace crews.

Postflight orthostatic intolerance has been identified as a serious biomedical problem associated with long-duration exposure to microgravity in space. High priority has been given to the development of countermeasures for this disorder that are both effective and practical. A considerable body of clinical research has demonstrated that people can be taught to increase their own blood pressure voluntarily, and that this is an effective treatment for chronic orthostatic intolerance in paralyzed patients. The current pilot study was designed to examine the feasibility of adding training in control of blood pressure to an existing preflight training program designed to facilitate astronaut adaptation to microgravity. Using an operant conditioning procedure, autogenic-feedback training (AFT), three men and two women participated in four to nine training (15-30-minute) sessions. At the end of training, the average increase in systolic and diastolic pressure, as well as mean arterial pressures, that the subjects made ranged between 20 and 50 mm Hg under both supine and 45 degrees head-up tilt conditions. These findings indicate that AFT may be a useful alternative treatment or supplement to existing approaches for preventing postflight orthostatic intolerance. Furthermore, the use of operant conditioning methods for training cardiovascular responses may contribute to the general understanding of the mechanisms of orthostatic intolerance.

Adult↗
PubMed1994

Anticipatory and residual effects of an active coping task on pre- and post-stress baselines.

This study examined several issues concerning baseline measurement in cardiovascular reactivity testing: effects of anticipation of stress on baseline, point at which initial baseline stabilizes, effects of a stressful task on a succeeding baseline, and gender differences in baseline patterns. Ten males and ten females sat for a 30-min initial baseline period, a 2-min stressor (mental arithmetic), and a 15-min post-stress period. An additional ten males and ten females participated only in the 30-min initial baseline (no stressor). There was no difference in initial baseline between the stress and no-stress conditions; nor were there interactions between this factor and gender. Initial baseline stabilized at resting levels after approximately one minute. Post-stress rest levels were significantly higher than initial baseline levels for blood pressure (5.8 and 4.8 mmHg for systolic and diastolic pressure, respectively), but not for heart rate. Implications of recovery of baseline are discussed.

Adaptation, Psychological↗
PubMed1994

Multicenter assessment of the QuietTrak ambulatory blood pressure recorder according to the 1992 AAMI guidelines.

To clinically evaluate the QuietTrak ambulatory blood pressure (BP) recorder (Tycos-Welch-Allyn, Arden, NC), we assessed the device according to the performance criteria set out by the 1992 Association for the Advancement of Medical Instrumentation (AAMI) guidelines. The QuietTrak is a portable, noninvasive recorder that uses an auscultatory measuring system. As recommended in the 1992 AAMI guidelines, a large, heterogeneous population was recruited for the study using three clinic sites to assess accuracy and clinical performance. In addition, observer agreement and the effects of age, arm circumference, heart rate, posture, and blood pressure level on the observer-device differences were analyzed. There were 1098 simultaneous, same arm BP measurements performed in 122 subjects by the QuietTrak recorder versus two skilled clinicians per site using a teaching stethoscope and 24-h blood pressure recordings performed in 46 subjects to assess reliability of the monitor. The differences in observers for all sites were 0.7/-0.5 +/- 3.8/3.5 mm Hg with 89% of the BPs within 5 mm Hg. The mean difference between observer average and the device (all positions) was 0.3/-1.5 +/- 5.0/7.5 mm Hg. The agreement between the QuietTrak and mercury column determinations was within 10 mm Hg for 92 to 94% of systolic readings and 91 to 93% of diastolic readings, depending on the posture. The limits of agreement (2 standard deviations about the mean difference) between observers and the device for systolic BP tended to be lower for the sitting position (-11 to 10 mm Hg) compared to supine (-14 to 13 mm Hg) and standing (-14 to 14 mm Hg) positions.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1994

Nighttime dosing of doxazosin has peak effect on morning ambulatory blood pressure. Results of the HALT Study. Hypertension and Lipid Trial Study Group.

In this study the effects of a single daily dose (average 8.9 mg) of doxazosin (an alpha-adrenergic blocker) given at night were evaluated in 111 patients with mild hypertension. Patients were studied first on no medication, and a second time after being treated for up to 16 weeks with doxazosin. Blood pressure was measured by noninvasive ambulatory monitoring at the beginning and end of the study. There was a sustained reduction of both systolic and diastolic pressure throughout the day and night, but the greatest reduction occurred in the morning hours. Since the peak treatment effect was later than predicted from previous pharmacokinetic studies, it is suggested that the timing of the peak effect may depend on the prevailing level of alpha-adrenergic tone, as well as on the pharmacokinetics of the drug.

Adult↗
PubMed1994

Differential effects of doxazosin on clinic and ambulatory pressure according to age, gender, and presence of white coat hypertension. Results of the HALT Study. Hypertension and Lipid Trial Study Group.

In this study the effects of a single daily dose of doxazosin (an alpha-adrenergic blocker) given at night were evaluated in 112 patients with mild hypertension. Patients were studied first on no medication, and a second time after being treated for up to 16 weeks with doxazosin. Blood pressure (BP) was measured by noninvasive ambulatory monitoring at the beginning and end of the study. Before treatment, the white coat effect (clinic-ambulatory BP) was greater in women than in men (significant for systolic pressure but not diastolic), and greater in elderly (aged over 65 years) than in younger patients (significant for both systolic and diastolic pressure). Clinic and ambulatory BP were reduced to a similar extent in men and women by doxazosin, but in the elderly the fall in clinic BP was associated with a much smaller fall of ambulatory BP. In patients with white coat hypertension (elevated clinic but normal ambulatory BP) doxazosin lowered clinic but not ambulatory BP, while in those with sustained hypertension it lowered both.

Adult↗
PubMed1994

Hypertension in blacks.

In the United States, blacks have higher blood pressure levels than whites at all ages, a finding that cannot be explained solely by differences in body habitus. A European population survey reported similar differences. Several physiologic mechanisms have been evaluated, including sodium sensitivity and insulin resistance. Although it is often stated that blacks show a greater blood pressure reactivity than whites, recent data are conflicting, and such differences may be attributable to family history of hypertension. The physiologic mechanisms underlying any reactivity differences could be structural changes in the resistance vessels. Blacks tend to show smaller falls of nocturnal blood pressure than whites, and this could be related to the observation of a greater degree of left ventricular hypertrophy seen in blacks for a given level of clinic blood pressure. Severe left ventricular hypertrophy may be associated with functional myocardial ischemia, even in the absence of epicardial coronary artery disease. Renal damage is also more pronounced in blacks than in whites.

Black People↗
PubMed1994

How should diastolic blood pressure be defined during pregnancy?

Controversy exists concerning the most accurate method for defining diastolic blood pressure in pregnancy. Both disappearance (phase V) and muffling (phase IV) of Korotkoff sounds have been advocated. We previously reported an objective noninvasive method for measuring blood pressure, called K2 analysis, which in nonpregnant subjects was not different from intra-arterial diastolic blood pressure and was more accurate than the auscultatory technique. For determination of the relation of diastolic blood pressure (using K2) in pregnancy with muffling and disappearance of Korotkoff sounds, 58 women (42 hypertensive, 16 normotensive) underwent 556 blood pressure evaluations in the supine position at various stages of pregnancy. K2 analysis was compared with simultaneous auscultation by two observers, A1 (n = 461 observations; 364 hypertensive, 97 normotensive) and A2 (n = 415; 316 hypertensive, 99 normotensive). Overall, muffling was detected by observer A1 52.9% (244/461) and by observer A2 44.3% (184/415) of the time. When evaluated by clinical classification, muffling was found by both observers to be present less often in the hypertensive group (A1: 47.5%; A2: 37.3%) compared with the normotensive group (A1: 73.2%; A2: 66.7%) (P < .0001). When both observers were present (n = 348), they agreed that muffling was present only 112 times. Disappearance of sound was detected by both observers 98.3% (A1: 453/461; A2: 408/415) of the time. Muffling overestimated K2 diastolic pressure by 7 to 10 mm Hg, whereas there was no statistically significant difference between disappearance and K2 diastolic pressure for hypertensive subjects and a 2.5-mm Hg underestimation of K2 diastolic pressure for normotensive subjects.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1994

Augmentation of calf blood flow by epinephrine infusion during lumbar epidural anesthesia.

Lower rates of deep vein thrombosis after hip surgery performed under epidural anesthesia were noted in patients who received intravenous epinephrine infusion. To determine whether this effect could be mediated by enhanced lower extremity blood flow, 12 patients were studied immediately preoperatively. Calf blood flow increased from 3.7 +/- 1.6 to 5.0 +/- 2.2 mL.100 mL-1.min-1 with an intravenous epinephrine infusion (1.9 +/- 0.5 microgram/min). After epidural anesthesia calf blood flow increased to 6.3 +/- 3.3 mL.100 mL-1.min-1 with epinephrine infusion (2.7 +/- 1.0 micrograms/min) but was reduced to 2.6 +/- 1.5 mL.100 mL-1.min-1 when norepinephrine (0.8 +/- 0.7 microgram/min) was infused. Calf vascular resistance decreased from 27.7 +/- 13.5 to 7.9 +/- 4.6 mmHg.mL-1.100 mL-1.min-1 after epidural anesthesia with epinephrine (2.7 +/- 1.0 micrograms/min) but was unchanged when norepinephrine (0.8 +/- 0.7 microgram/min) was infused. The augmentation of lower extremity blood flow when epinephrine is used in conjunction with epidural anesthesia may in part explain the low frequency of deep vein thrombosis with conduction anesthesia.

Aged↗
PubMed1994

Association between ambulatory blood pressure and alternative formulations of job strain.

OBJECTIVES: The goal of the study was to determine whether alternative formulations of Karasek & Theorell's job-strain construct are associated with ambulatory blood pressure and the risk of hypertension. METHODS: Full-time male employees (N = 262) in eight worksites completed a casual blood pressure screening, medical examinations, and questionnaires and wore an ambulatory blood pressure monitor for 24 h on a workday. Cases of hypertension were ascertained from casual blood pressure readings for a case-referent analysis. A cross-sectional analysis was also conducted, ambulatory (continuous) blood pressure measurements being used as the outcome. RESULTS: All formulations of job strain exhibited significant associations with systolic blood pressure at work and home, but not with diastolic blood pressure. Employees experiencing job strain had a systolic blood pressure that was 6.7 mm Hg (approximately 0.89 kPa) higher and a diastolic blood pressure that was 2.7 mm Hg (approximately 0.36 kPa) higher at work than other employees, and the odds of hypertension were increased [odds ratio (OR) 2.9, 95% confidence interval (95% CI) 1.3-6.6]. Using national means for decision latitude and demands to define job strain increased the systolic and diastolic blood pressure associations to 11.5 mm Hg (approximately 1.53 kPa) and 4.1 mm Hg (approximately 0.54 kPa), respectively. Adding organizational influence to the task-level decision latitude variable produced a stronger association for hypertension with job strain (OR 3.7, 95% CI 1.6-8.5). Adding social support to the job-strain model also slightly increased the hypertension risk. CONCLUSIONS: The impact of job strain, at least on systolic blood pressure, is consistent and robust across alternative formulations, more restrictive cut points tending to produce stronger effects.

Adult↗
PubMed1994

Ambulatory blood pressure and prognosis.

PROGNOSTIC INFORMATION: Ambulatory blood pressure monitoring provides three kinds of information, all of which might have prognostic significance: blood pressure level, amplitude of diurnal variation and short-term variability. BLOOD PRESSURE LEVEL: Existing data support the hypothesis that patients whose ambulatory blood pressure is low in comparison with clinic blood pressure (white-coat hypertension) have a relatively low risk of morbidity. AMPLITUDE OF DIURNAL RHYTHM OF BLOOD PRESSURE: While there is limited support for the hypothesis that patients with small diurnal variations may carry a higher risk (particularly women), opposing hypotheses are also plausible. SHORT-TERM BLOOD PRESSURE VARIABILITY: It is hypothesized that increased variability will be associated with increased morbidity. Preliminary data from the Cornell prospective study are consistent with this hypothesis.

Blood Pressure↗
PubMed1994

Response to the captopril test is dependent on baseline renin profile.

OBJECTIVE: To determine prospectively the relationship between the renin-sodium profile and the renin response to captopril challenge in patients with essential hypertension. DESIGN: A standard captopril test was performed in 108 uncomplicated, untreated hypertensive subjects with normal renal function and urinary sodium excretion in the range 50-240 mmol/day. The subjects were selected from a working population with a low expected prevalence of renovascular disease. METHOD: The captopril test was considered positive if the captopril-induced rise in plasma renin activity met all three criteria established by Müller et al. Patients with a positive test and those meeting only one or two of the three criteria were further investigated for renovascular hypertension by measuring renal venous renins and by digital subtraction intravenous angiography. Renin responses were analyzed according to baseline renin-sodium profile. RESULTS: Nine of 108 subjects had a false-positive captopril test result. Among the subjects with a low or normal renin-sodium profile, 1% (one of 82) had a false-positive result. In contrast, false-positive results were seen in 31% (eight of 26) of high-renin subjects. False-positive test results were not related to urinary sodium excretion or to excessive decrease in blood pressure. The magnitude of the renin response to captopril was strongly and directly related to the baseline plasma renin activity. CONCLUSION: An exaggerated renin response to captopril challenge is common in patients with high-renin essential hypertension. Therefore, in a population with a low probability of renovascular hypertension, caution is recommended in interpreting a positive test result in patients with a high baseline renin.

Adult↗