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Biomedical subjects

T Thien

Publications and source records attributed to T Thien.

At least 181 records · Page 10Linked to original sources
PubMed1991

Double-blind placebo-controlled crossover study of oral nicardipine in the treatment of Raynaud's phenomenon.

The purpose of this study was to measure the efficacy and side effects of oral nicardipine in the treatment of Raynaud's phenomenon (RP). The study consisted of a 3-week baseline period followed by a double-blind, randomized, two-period placebo-controlled, balanced crossover design. Both treatment periods of 3 weeks with either oral nicardipine (3 x 30 mg) or matching placebo were interrupted by a 2-week washout period. Twenty-five patients with either primary (n = 16) or secondary (n = 9) RP participated. Twelve of them had taken part in a previous study on the acute effects of i.v. nicardipine to find out whether long-term efficacy could be predicted by the acute circulatory effects. No statistically significant differences were found between nicardipine and placebo for number, duration, or severity of vasospastic attacks or for any of the microcirculatory parameters (finger skin temperature and laser Doppler flux) measured during a finger cooling test. In patients with primary RP, heart rate significantly increased during nicardipine treatment (mean +/- SD: 9 +/- 6 beats/min; p less than 0.05). The long-term effects could not be predicted by the outcome of the i.v. study. Plasma nicardipine concentrations varied considerably, but in general were on the low side (17.4 +/- 3.7 ng/ml; range, 0-55.4 ng/ml). The adverse effects reported with nicardipine were similar to those with placebo, and required withdrawal of two patients on nicardipine and one on placebo. In conclusion, the results show that oral nicardipine does not significantly alter the course of RP.(ABSTRACT TRUNCATED AT 250 WORDS)

Administration, Oral↗
PubMed1991

Poikilothermia in man: pathophysiology and clinical implications.

Poikilothermia, the inability to maintain a constant core temperature independent of ambient temperature, markedly influences both the mental and physical function of affected patients; furthermore, prolonged hypothermia can induce numerous complications. To establish the pathophysiology of thermoregulation underlying poikilothermia in man, we compared 4 women with acquired poikilothermia, with 9 female control subjects. The activity of the main thermoregulatory effector mechanisms was assessed in a thermoneutral environment, and during subsequent cold stress and heat exposure. At thermoneutrality the patients had a significantly lower rectal temperature and resting metabolic rate compared with the controls; no patient showed peripheral vasoconstriction or shivering. Cooling revealed markedly reduced peripheral vasoconstriction in 3 patients and failure of the metabolic response in 2 patients; unlike controls, no patient exhibited shivering. Heat challenge revealed severely reduced capacity for heat dissipation in all patients. We conclude that in patients with poikilothermia, the mechanisms for both heat conservation and heat dissipation are seriously attenuated. Careful monitoring of the core temperature and adequate measures to maintain normothermia are of great importance in patients with poikilothermia in order to provide adequate treatment, improve the quality of life, and prevent serious complications.

Adipose Tissue↗
PubMed1991

Adenosine attenuates the response to sympathetic stimuli in humans.

The effect of adenosine on the forearm vasoconstrictor response to alpha-adrenergic and sympathetic stimulation was studied in healthy volunteers. During a predilated state achieved by infusion of sodium nitroprusside into the branchial artery, subsequent infusion of norepinephrine induced a mean increase in forearm vascular resistance of 571%, whereas this response was only 270% when an equipotent vasodilator dose of adenosine was used instead of sodium nitroprusside (nitroprusside versus adenosine, p less than 0.05, n = 6). A comparable difference was found when the endogenous release of norepinephrine was stimulated by the local infusion of tyramine, with tyramine-induced increments in forearm vascular resistance of 438% during nitroprusside versus 93% during adenosine (n = 6, p less than 0.05). During these tyramine infusions a similar increase in the calculated forearm norepinephrine overflow occurred in the adenosine and the nitroprusside tests. In a third experiment, we demonstrated that adenosine also reduced the vasoconstrictor response to lower body negative pressure, an endogenous stimulus, of the sympathetic nervous system. During nitroprusside, lower body negative pressure induced an increase in forearm vascular resistance of 135%, whereas this was 39% during adenosine (n = 6, p less than 0.05). We conclude that adenosine attenuates the response to sympathetic nervous system-mediated vasoconstriction in humans, and that this effect may at least partly be explained by a postsynaptic inhibition of alpha-adrenergic vasoconstriction. Therefore, we think that adenosine may be an important endogenous modulator of sympathetic nervous system activity in humans.

Adenosine↗
PubMed1991

Boiled coffee and blood pressure. A 14-week controlled trial.

The question of whether long-term elimination of coffee from the diet lowers blood pressure has not been settled. Consumption of Scandinavian-style "boiled coffee" is associated with coronary heart disease. However, little is known about the effect of brewing method on the blood pressure-raising potential of coffee. We have studied the effects on blood pressure and heart rate of total elimination of coffee and tea in comparison with drinking boiled coffee consumed as such, or boiled coffee consumed after filtration through paper filter. Thirty-one women and 33 men first consumed 6 cups/day of boiled and filtered coffee for 17 days. Then they were randomly divided into three groups, which for the next 79 days received either unfiltered boiled coffee (caffeine content 860 mg/l), boiled-and-filtered coffee (887 mg caffeine/l), or no coffee, the latter being replaced by fruit juice and mineral water. Total elimination of coffee did not significantly affect blood pressure or heart rate relative to boiled-and-filtered coffee. In subjects who drank boiled coffee, mean ambulant systolic blood pressure rose significantly relative to those who consumed boiled-and-filtered coffee (mean difference +/- SEM, 3.1 +/- 1.1 mm Hg, p = 0.006). This response showed a tendency to be stronger for women (4.5 +/- 1.8 mm Hg) than for men (1.7 +/- 1.2 mm Hg). We conclude that elimination of filtered coffee has no substantial long-term effect on blood pressure, but consumption of unfiltered boiled coffee may cause a slight but significant rise in systolic blood pressure.

Adult↗
PubMed1991

Attenuated forearm vasodilator response to atrial natriuretic factor in the elderly.

The vasodilator potency of human atrial natriuretic factor-(99-126) was investigated in the forearm vascular bed of 10 young and 10 elderly normotensive volunteers with venous occlusion strain gauge plethysmography. Atrial natriuretic factor was infused at six increasing dose steps into the brachial artery from 0.001 up to 0.3 microgram/min/100 ml of forearm volume. This induced a mean +/- SEM increase in blood flow from 1.4 +/- 0.2 up to 6.0 +/- 1.0 ml/min/100 ml in the young and from 1.4 +/- 0.2 up to 3.9 +/- 0.6 ml/min/100 ml in the elderly. The dose-response curves of forearm blood flow and of forearm vascular resistance after increasing infusion rates of atrial natriuretic factor were shifted to the right in the elderly when compared with the young subjects. The mean percent decrease in forearm vascular resistance, induced by atrial natriuretic factor, during this dose-response curve averaged -31 +/- 3% in the elderly versus -56 +/- 3% in the young subjects (p = 0.0002). The calculated forearm spillover of the second messenger of atrial natriuretic factor, cyclic guanosine monophosphate, significantly increased from baseline values of 1.2 +/- 1.1 and 0.7 +/- 0.5 pmol/min/100 ml in young and elderly subjects, respectively, up to 23.2 +/- 5.0 and 30.5 +/- 7.0 pmol/min/100 ml during the highest dose of atrial natriuretic factor (both p less than 0.01 versus baseline). There were no significant differences in the increments of the forearm spillover of this second messenger between both age groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1991

Pathophysiology of thermoregulation in patients with poikilothermia.

To investigate the thermoregulatory mechanisms underlying poikilothermia in man, we have studied 4 female patients (age 28-37 yr) with poikilothermia, most probably of hypothalamic origin, as well as 4 female volunteers of similar age. In a climatic chamber the participants were subjected to cold stress (16.5 degrees C) and subsequent heat exposure (40 degrees C). In the volunteers cold stress did not influence the rectal temperature; cooling induced a marked shivering response and an immediate peripheral vasoconstriction. Subsequent heat challenge induced a slight rise in the rectal temperature (from 36.3 +/- 0.2 to 37.0 +/- 0.3 degrees C) and a marked sweat secretion in all control subjects. All patients were hypothermic at the start of the experiment. Cooling induced a decrease in the rectal temperature of 0.3-0.9 degrees C. Three patients showed neither peripheral vasoconstriction nor a shivering response to cold stress. In contradistinction to the control subjects, in all patients an afterdrop of the rectal temperature of 0.3-0.5 degrees C was observed once heating of the environment had started; thereafter a progressive rise in core temperature occurred up to 38.5 (38.0) degrees C. In none of the patients sweat secretion was clinically visible. These results reveal that in these patients with poikilothermia the disorder of thermoregulation is accompanied by inadequate cutaneous vasomotor adjustment and disturbed sweat response and likely reduced metabolic response to cold stress.

Adult↗
PubMed1991

The value of tests predicting renovascular hypertension in patients with renal artery stenosis treated by angioplasty.

The aim of this study was to evaluate tests predicting renovascular hypertension. This was done by relating the results of renal vein renin tests, the captopril test, and renal scintigraphic tests to the blood pressure outcome 12 months after relief of renal artery stenosis by percutaneous transluminal renal angioplasty in 31 patients. Cure was seen in eight (26%). Improved blood pressure was obtained in 12 patients (39%), and in 11 patients (35%), the result for blood pressure was a failure. The accuracies of the two mathematical models used to analyze the renal vein renin assays were 44% and 60%. The captopril test showed a sensitivity of 36% and an accuracy of 43%. Renal captopril technetium Tc 99m-labeled pentetic acid scintigraphy gave a sensitivity of 60%. Stepwise logistic regression analysis of clinical variables in relation to blood pressure response revealed age as the only factor significantly related to blood pressure outcome. We conclude that the tests used are unfit for helping select patients for percutaneous transluminal renal angioplasty and that age may have an important influence on outcome.

Adolescent↗
PubMed1991

False-negative dipyridamole-thallium-201 myocardial imaging after caffeine infusion.

The vasodilator effect of intravenously administered dipyridamole may be caused by an increase in endogenous plasma adenosine levels. We evaluated the effect of caffeine, an adenosine receptor antagonist, on the diagnostic results of dipyridamole-201Tl myocardial imaging in eight patients with coronary artery disease. Caffeine infusion significantly attenuated the dipyridamole-induced fall in blood pressure and the accompanied increase in heart rate. The infusion of dipyridamole alone resulted in chest pain and ST-segment depressions on the electrocardiogram in four patients, whereas none of these problems occurred when the tests were repeated after caffeine. In six of eight patients, caffeine was responsible for false-negative dipyridamole-201Tl tests. Semiquantitive scores of the dipyridamole-induced 201Tl perfusion defects were decreased by caffeine from 9.0 +/- 0.9 to 2.0 +/- 1.1 points (p less than 0.05). Computerized analysis revealed a caffeine-mediated reduction in the percent reversibility of the images from 46% +/- 16% to 6% +/- 10% (p less than 0.05). We conclude that the use of caffeinated products prior to dipyridamole-201Tl testing may be responsible for false-negative findings.

Caffeine↗
PubMed1991

Laser Doppler evaluation of skin vasomotor reflexes during sympathetic stimulation in normals and in patients with primary Raynaud's phenomenon.

Laser Doppler flux measurements were used to determine skin blood flow in 12 patients with primary Raynaud's phenomenon and in 12 healthy age and sex matched control subjects. The vasoconstrictor response to standing, the Valsalva maneuver and a deep breath were used to diagnose local abnormalities of peripheral nerve sympathetic function and were found normal together with a normal catecholamine response to standing upright. However, baseline laser Doppler measured skin blood flow was lower in patients with primary Raynaud's phenomenon (p less than 0.01 in all 3 tests) while resting norepinephrine levels were higher (2.25 +/- 0.33 nmol/l) than in normals (1.31 +/- 0.11 nmol/l; p less than 0.01). These results are consistent with the existence of an elevated sympathetic nervous system activity at rest and a decreased baseline skin blood flow without signs of an excessive sympathetic and skin vascular responsiveness to sympathetic nervous system stimulation.

Humans↗
PubMed1990

Hemodynamic effects of atrial natriuretic factor in young and elderly subjects.

Because levels of plasma atrial natriuretic factor (ANF) increase with advancing age, a diminished hemodynamic responsiveness to ANF in the elderly has been hypothesized in the literature. Therefore hemodynamic effects after two infusion rates (0.25 and 2.0 micrograms/min) of atrial natriuretic factor (99-126) were investigated in young (n = 8) and elderly (n = 9) volunteers in a double-blind, randomized, and placebo-controlled protocol. After low-rate infusion, ANF concentrations increased to the upper normal range, and only minor effects were observed. In contrast, high-rate infusion resulted in a decrease in blood pressure and forearm vascular resistance, whereas an increase in heart rate was observed in both groups. Between young and elderly subjects, a significant difference was observed in the ANF-induced decrease in systolic blood pressure (mean +/- SD, -4% +/- 4% versus -12% +/- 7%, p less than 0.05) and mean arterial pressure (-6% +/- 5% versus -11% +/- 4%, p less than 0.05) during the high rate infusion. When compared with the concentrations of the young subjects, the ANF concentrations reached at both ANF dosages were higher in the elderly subjects; this was the result of a diminished ANF clearance in the elderly subjects. After correction of the changes of systolic blood pressure and mean arterial pressure for the higher ANF levels reached within this elderly group, no difference between young and elderly subjects remained. We conclude that a diminished cardiovascular responsiveness to ANF with advancing age could not be demonstrated. In contrast, the high-rate infusion of ANF induced an increased hemodynamic response in the elderly subjects, but this seems to be the result of the higher ANF levels reached within this group.

Adult↗
PubMed1990

Caffeine and theophylline attenuate adenosine-induced vasodilation in humans.

In this study the local vasoactive effects of adenosine were explored in the human forearm. Adenosine (15 micrograms/100 ml forearm/min) infused into the brachial artery (n = 6) increased forearm blood flow by 572% +/- 140%, versus - 0.5% +/- 5.8% during placebo infusion (p less than 0.01). Lower adenosine infusion rates (5 micrograms/100 ml forearm/min, three times) induced forearm blood flow increments to 330% +/- 94%, 339% +/- 67% and 330% +/- 79%, respectively (n = 8). These forearm blood flow responses were reduced (p = 0.02) during concomitant intra-arterial infusion of two doses of caffeine (30 and 90 micrograms/100 ml forearm/min) to 150% +/- 45% and 98% +/- 28%, respectively. Theophylline (30 micrograms/100 ml forearm/min; n = 6) also significantly attenuated the adenosine-induced increase in forearm blood flow. Enprofylline (30 micrograms/100 ml forearm/min), a related xanthine with a low affinity to adenosine receptors in vitro, did not change the response to adenosine. Nonspecific vasodilation by sodium nitroprusside infusion (50 ng/100 ml forearm/min) was not inhibited by caffeine compared with placebo (forearm blood flow responses were 202% +/- 21% versus 216% +/- 40%; n = 6). This study demonstrated that caffeine and theophylline specifically reduce adenosine-induced vasodilation in humans, supporting the existence of functional human vascular adenosine receptors.

Adenosine↗
PubMed1990

Changes in skin blood flow during the menstrual cycle: the influence of the menstrual cycle on the peripheral circulation in healthy female volunteers.

1. It is known that females have a lower skin perfusion than males. In women there are also differences in blood flow at different reproductive stages of their lives. As an initial investigation of the possible contribution of sex hormones to these differences, we studied skin and forearm blood flow during the natural changes in hormone levels which occur during the menstrual cycle. 2. Thirty-one healthy female volunteers were studied. The effect of a standardized finger cooling test (immersion of a gloved hand in a 16 degrees C water bath) on finger skin temperature and on laser Doppler flux in the finger, and forearm blood flow (strain gauge venous occlusion plethysmography) was assessed at four different times during one cycle: during menstruation, 1 day before ovulation, 2 days after ovulation and at the mid-luteal phase. Test days were determined by daily measurements of basal body temperature and were confirmed afterwards by determinations of serum luteinizing hormone, follicle-stimulating hormone, 17 beta-oestradiol and progesterone. 3. Peripheral skin circulation varied significantly within one menstrual cycle. The extremes were a mean finger skin temperature of 25.9 +/- 3.0 degrees C in the luteal phase compared with 28.4 +/- 3.7 degrees C in the pre-ovulatory phase (P = 0.002). The respective values for the mean laser Doppler flux were 18.4 +/- 10.9 compared with 29.2 +/- 16.4 arbitrary units (P = 0.003). 4. Baseline forearm muscle blood flow also varied significantly (P = 0.04) within one menstrual cycle, with low values in the menstrual phase compared with the other phases.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗