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Biomedical subjects

K S Woo

Publications and source records attributed to K S Woo.

At least 55 records · Page 3Linked to original sources
PubMed1997

Chinese adults are less susceptible than whites to age-related endothelial dysfunction.

OBJECTIVES: We sought to assess the effects of aging on the endothelial physiology of a group of Chinese adults. BACKGROUND: Several studies have documented an association between aging and progressive arterial endothelial dysfunction in white subjects. We hypothesized that age-related endothelial dysfunction, an important event in atherosclerosis, might be less marked in southern Chinese subjects, in whom the prevalence of coronary heart disease is only approximately 20% of that in industrialized countries. METHODS: We studied endothelial function in 76 healthy adults aged 16 to 70 years: 38 Chinese from a village of 3,000 people in southern China and 38 white subjects from Sydney, Australia. In each ethnic group, there were 19 younger persons (16 to 40 years) and 19 older adults (55 to 70 years). None had evidence of diabetes, hypertension or clinical vascular disease or had ever been regular cigarette smokers. With the use of high resolution external vascular ultrasound, brachial artery diameter was measured at rest, after flow increase (causing endothelium-dependent dilation) and after sublingual nitroglycerin (an endothelium-independent dilator). RESULTS: Endothelium-dependent dilation was similar in young Chinese (mean +/- SD 8.3 +/- 2.5%), young whites (7.9 +/- 2.0%) and older Chinese (6.8 +/- 2.9%), but it was significantly impaired in older whites (1.8 +/- 2.5%, p < 0.001 by analysis of variance). On multivariate analysis, older age was associated with impaired endothelium-dependent dilation (p < 0.001) (independent of the effects of serum cholesterol, gender and vessel size) in the white but not in the Chinese subjects (p = 0.83). Nitroglycerin-induced dilation was not significantly different with aging in either ethnic group. CONCLUSIONS: Endothelium-dependent dilation is similar in the arteries of healthy young Chinese and white adults. With older age, however, Chinese subjects are less susceptible to impaired endothelial function.

Adolescent↗
PubMed1996

Lack of association between insertion/deletion polymorphism of the angiotensin-converting enzyme gene and end-stage heart failure due to ischemic or idiopathic dilate cardiomyopathy in the Chinese.

Homozygosity for the deletion allele of the angiotensin-converting enzyme gene (DD) has been associated with a variety of cardiovascular diseases, including ischemic and idiopathic dilated cardiomyopathy, in Caucasians. In this study of 104 Chinese patients with end-stage heart failure due to idiopathic dilated or ischemic cardiomyopathy, the DD genotype frequency was low (12% and 11%, respectively) and was not seen more often than in a control group of 183 subjects without cardiac disease (13%). Therefore, in the Chinese, the DD genotype is less common than in Caucasians and does not appear to be associated with the development of either ischemic or idiopathic dilated cardiomyopathy.

Adult↗
PubMed1996

Right ventricular diastolic dysfunction in heart failure.

BACKGROUND: Left ventricular (LV) diastolic dysfunction is common in heart failure and is an important predictor of prognosis and mortality. Less attention has been paid to right ventricular (RV) diastolic function. In this study, we compared RV diastolic function in a large cohort of patients with heart failure (HF) with two groups: patients with pulmonary hypertension and normal LV function (the PHT group) and normal subjects. METHODS AND RESULTS: Transtricuspid and pulmonary artery flow were assessed by two-dimensional Doppler echocardiography at maximum inspiration and expiration in 185 subjects: 114 symptomatic HF patients (ejection fraction < 0.5), 31 PHT patients (pulmonary artery systolic pressure > 40 mm Hg), and 40 normal subjects. A subset was matched for age and heart rate. The results showed a high prevalence of RV diastolic abnormalities: HF patients had lower tricuspid E-A ratios, lower peak E-wave velocity, and prolonged RV isovolumic relaxation time (all P< .0001). Tricuspid E-wave deceleration time was significantly shorter only in those who had an LV restrictive filling pattern. The PHT group had similar findings. Compared with a normal range, more than half of the patients had lower tricuspid E-A ratios (HF, 55%; PHT, 69%), and 61% of HF and 58% of PHT patients had a prolonged RV isovolumic relaxation time. In the PHT group, RV diastolic parameters (E-wave deceleration time, E-A ratio, and isovolumic relaxation time) correlated significantly with pulmonary artery systolic pressure (P< .05). In the HF group, however, only tricuspid E-wave deceleration time correlated significantly with pulmonary artery systolic pressure, and HF patients with normal pulmonary artery systolic pressures had significantly lower tricuspid E-A ratios and prolonged RV isovolumic relaxation times compared with normal subjects. A close correlation existed between individual RV and LV diastolic parameters, suggesting that LV diastolic dysfunction may directly affect RV function, but there was no relation between LV size or systolic function and RV diastolic dysfunction. CONCLUSIONS: RV diastolic function is frequently abnormal in HF patients, and this is not related to elevated pulmonary artery systolic pressure alone, although high pulmonary artery pressure by itself also is associated with impaired RV diastolic function. Assessment of the role of right ventricular diastolic function in determining the symptoms and prognosis of heart failure is warranted.

Diastole↗
PubMed1996

Somatostatin reduces gastric mucosal blood flow in patients with portal hypertensive gastropathy: a randomized, double-blind crossover study.

Agents which decrease gastric mucosal blood flow (GMBF) are postulated to have beneficial effects in arresting gastrointestinal bleeding in cirrhotic patients with portal hypertension. Our objective was to test the hypothesis that in a dose that significantly lowers wedged hepatic venous pressure (WHVP), a bolus injection of somatostatin will significantly decrease GMBF in patients with portal hypertensive gastropathy (PHG). In this placebo-controlled, double-blind, crossover study, 20 cirrhotic patients with PHG were randomly assigned to receive either somatostatin followed by placebo (Group A) or placebo followed by somatostatin (Group B). Wedged hepatic venous pressure was monitored. GMBF in the antrum and corpus was assessed by reflectance spectrophotometry. Indices of hemoglobin concentration (IHb) and indices of oxygen content (ISO2) were recorded. Nine patients were assigned to Group A, and 11 to Group B. Mild PHG was seen in 16 patients, and severe PHG in 4 patients. Baseline WHVP, IHb, and ISO2 were similar in both treatment groups. Wedged hepatic venous pressure (WHVP) was significantly lowered [median, 17.6%; interquartile range (-27.0,-12.6%); P = 0.0008] after a 250-microg bolus injection of somatostatin. This dose of somatostatin significantly reduced IHb both in the antrum [-10.2% (-23.4, 0.4%)] and in the corpus [-5.8% (-16.6, 5.6%)] compared to placebo (P = 0.02 and 0.04, respectively). Intravenous bolus injection of 250 microg somatostatin significantly reduces WHVP and GMBF in patients with PHG. Whether this ability to decrease the GMBF in PHG makes somatostatin an effective treatment in acute gastrointestinal bleeding in PHG deserves to be studied.

Aged↗
PubMed1996

Impact of changes in respiratory frequency and posture on power spectral analysis of heart rate and systolic blood pressure variability in normal subjects and patients with heart failure.

1. Autonomic dysfunction is a major feature of congestive cardiac failure and may have an important role in determining progression and prognosis. The low-frequency/high-frequency ratio derived from power spectral analysis of heart rate variability has been proposed as a non-invasive method to assess sympatho-vagal balance. However, the effects of different respiratory rates or posture are rarely accounted for, but may be relevant in patients with heart failure in whom clinical improvement is accompanied by a fall in respiratory rate and an increased proportion of the day in the upright position. 2. We have assessed the effect of controlled respiration at different rates (10, 15, 20 breaths/min or 0.17, 0.25 and 0.33 Hz), while supine and standing, on power spectral analysis of heart rate and blood pressure variability in 11 patients with heart failure and 10 normal subjects. 3. Heart rate variance and low-frequency power (normalized units) were reduced in patients with heart failure (absent in six). During controlled breathing while supine, the power of the high-frequency component was significantly greater at 10 breaths/min than at 20 breaths/min in patients with heart failure, whether expressed in absolute units (P = 0.005) or percentage of total power (P = 0.03). 4. On standing, controlled breathing in patients with heart failure produced less change in high-frequency power (P = 0.054), but the low-frequency/high-frequency ratio at lower respiratory rates was reduced (P = 0.05). In normal subjects, as expected, respiratory rate had a highly significant effect on high-frequency power. Also, in normal subjects there was the expected increase in heart rate low-frequency power (P = 0.04) moving from supine to standing with an increase in the low-frequency/high-frequency ratio (P = 0.003), while in the patients with heart failure this was absent, reflecting blunted cardiovascular reflexes. 5. Systolic blood pressure low- and high-frequency components and their ratio were significantly affected by respiration (P < 0.03) and change in posture (P < 0.03) in both patients with heart failure and normal subjects, with a significant increase in the low-frequency/high-frequency ratio (P = 0.03) on standing in patients with heart failure, indicating that autonomic modulation of blood pressure is still operating in heart failure. 6. Thus, respiratory rate and changes in posture have a significant effect on measurements derived from spectral analysis of heart rate and blood pressure variability. Studies that use power spectral analysis as a measure of sympatho-vagal balance should control for these variables.

Adult↗
PubMed1996

Diastolic dysfunction and natriuretic peptides in systolic heart failure. Higher ANP and BNP levels are associated with the restrictive filling pattern.

BACKGROUND: Left ventricular diastolic dysfunction is common in patients with systolic heart failure and the restrictive type of filling pattern appears to be associated with increased cardiac mortality. Both artrial and brain (or ventricular) natriuretic peptides are also proven markers of the severity of heart failure. The aim of this study was to determine in a large cohort of patients with systolic heart failure whether diastolic abnormalities, and in particular the restrictive filling pattern of transmitral flow velocity, correlate with plasma atrial and brain natriuretic peptide levels. METHODS: Sixty-eight consecutive patients with symptomatic systolic heart failure (ejection fraction < 0.5) underwent two-dimensional Doppler echocardiography of left ventricular systolic and diastolic function, together with measurement of atrial and brain natriuretic peptides. RESULTS: The restrictive filling pattern was present in 62%, the abnormal relaxation pattern in 31% and only 7% were normal. Atrial and brain natriuretic peptide (ANP/BNP) levels were significantly higher in the restrictive compared to the abnormal relaxation group (ANP: 202.2 +/- 31.7 vs 102.5 +/- 22.1 pg.ml-1, P = 0.012; BNP: 277.8 +/- 27.7 vs 162.4 +/- 21.9 pg.ml-1, P = 0.002). In addition, a restrictive filling pattern was associated with lower ejection fractions (P = 0.026), higher pulmonary artery systolic pressure (P < 0.001), larger left atrial size (P = 0.044), and were more likely to be in New York Heart Association class III or IV than those with an abnormal relaxation pattern (P = 0.007). Both atrial and brain natriuretic peptides correlated inversely with ejection fraction (P < 0.001), fractional shortening (P < 0.001), and positively with pulmonary artery pressure (P = 0.004 and 0.001 respectively). There were no significant correlations between single diastolic parameters and atrial or brain natriuretic peptide levels for the total patient group except between mitral peak A wave velocity and brain natriuretic peptides (r = -0.3, P = 0.01). For those with abnormal relaxation pattern mitral, valve E-wave deceleration time correlated significantly with both atrial and brain natriuretic peptide levels (P < 0.01). CONCLUSIONS: This study confirms that the restrictive filling pattern of transmitral flow velocity is a marker of more severe heart failure, as indicated by its association with higher atrial and brain natriuretic peptide levels, lower ejection fraction and higher pulmonary artery pressure. Thus, this easily obtained Doppler-derived marker of diastolic dysfunction is useful for identifying those patients with more severe heart failure.

Aged↗
PubMed1996

Factors determining the maintenance dose of warfarin in Chinese patients.

Chinese patients are reportedly more sensitive than Caucasians to the anticoagulant effect of warfarin. We examined warfarin dose requirements and their determinants in 151 Chinese out-patients on stable maintenance dose of warfarin with international normalized ratio of 2 to 2.5. Mean daily warfarin requirement was 3.3 +/- 1.4 mg, much lower than reported doses in Caucasian patients. The most important determinant was age (r = -0.43, p < 0.001), with progressively lower warfarin requirement with increasing age (p = 0.0001). There was a weaker association with body weight (r = 0.20, p = 0.01). Patients with chronic rheumatic heart disease tended to require a smaller dose than those with heart valve replacements (2.94 +/- 1.24 vs. 3.69 +/- 1.42 mg, p < 0.01). We confirm that Chinese patients require a smaller dose of warfarin for the same degree of anticoagulation. Age is the most important factor affecting dose requirement, although body weight and underlying disease also play a role.

Adult↗
PubMed1996

The effect of transcutaneous electrical nerve stimulation on coronary and systemic haemodynamics in syndrome X.

BACKGROUND: Neurostimulation techniques have been shown to be beneficial in patients with angina and syndrome X but the mechanism remains unclear. We examined the effect of transcutaneous electrical nerve stimulation (TENS) on coronary artery blood flow in a group of patients with syndrome X. METHODS: Coronary blood flows were measured in 11 patients with angiographically normal coronary arteries, positive results from exercise tests and angina (syndrome X) using intracoronary Doppler catheters combined with quantitative coronary angiography. RESULTS: The mean coronary flow velocity did not increase in any patient during TENS therapy; in fact, there was a fall from 5.2 +/- 2.8 to 4.3 +/- 1.9 cm/s (P = 0.02) and the coronary blood flow index fell from 47 +/- 22 to 38 +/- 16 cm/s per mm2 (P = 0.007). This was associated with a fall in the rate x pressure product from 0.92 +/- 0.22 to 0.83 +/- 0.18 mmHg/min (P = 0.038). The coronary vascular resistance rose from 2.4 +/- 1.1 to 3.0 +/- 1.6 mmHg/cm per s per mm2 (P = 0.041). There were no major changes in the epicardial coronary artery diameter during TENS and there was no significant effect on the response to the cold-pressor test. CONCLUSIONS: In this group of patients with syndrome X, TENS produced a small but significant fall in coronary artery blood flow associated with a reduction in the rate x pressure product. TENS had no significant effect on coronary vasomotion during sympathetic stimulation by the cold-pressor test. Thus, TENS is unlikely to have a direct effect on coronary artery vasomotion or haemodynamics in syndrome X but reduces the rate x pressure product and thus myocardial oxygen consumption.

Blood Flow Velocity↗
PubMed1996

Hyperhomocysteinaemia and premature coronary artery disease in the Chinese.

OBJECTIVES: To examine the prevalence of hyperhomocysteinaemia and compare it with the classic risk factors and vitamin status in Hong Kong Chinese patients with premature atherosclerotic coronary artery disease. DESIGN: Case-control study. SETTING: General hospital and community. SUBJECTS: Forty five patients (39 males) with significant coronary artery disease confirmed by angiography (32 post myocardial infarction) and 23 healthy volunteers (17 male), all aged less than 55 years. INTERVENTION: Standardised methionine-loading test. MAIN OUTCOME MEASURES: Coronary artery disease, risk factors. RESULTS: More patients than controls had fasting hyperhomocysteinaemia (10/45 v 2/23, P = 0.122), post-methionine hyperhomocysteinaemia (17/45 v 1/23, P = 0.008), and an abnormal response to methionine (15/45 v 1/23, P = 0.015). A history of smoking was more frequent in patients (3/23 v 25/45, P = 0.002). Sixteen of 17 patients with hyperhomocysteinaemia but only nine of 28 with normohomocysteinaemia were smokers (P = 0.0002). Fasting plasma cholesterol concentrations (mean (SD)) were higher in hyperhomocysteinaemic patients (6.41 (1.58) mmol/l) than in controls (5.53 (0.90) mmol/l) (P = 0.042). Serum vitamin B-12 was not reduced and serum folate was higher in hyperhomocysteinaemic patients (35 (4) nmol/l) than normohomocysteinaemic patients (26 (9) nmol/l) (P = 0.009). CONCLUSIONS: Although the prevalence of hyperhomocysteinaemia in Hong Kong Chinese is similar to that in white subjects, hyperhomocysteinaemia is not an independent risk factor for coronary artery disease and is associated with smoking. This may be of some consequence in view of the change to a more Western diet with more animal protein, and therefore methionine, coupled with a high frequency of cigarette smokers in this region. The causes of the hyperhomocysteinaemia are multifactorial but in this pilot study a deficiency of folate and/or vitamin B-12 did not seem to be one of them.

Adult↗
PubMed1995

The effect of transcutaneous electrical nerve stimulation (TENS) on autonomic cardiovascular reflexes.

Transcutaneous electrical nerve stimulation (TENS) has been shown to have an anti-ischaemic effect in patients with angina and peripheral vascular disease that appears to be additional to any analgesic action. The mechanism for this anti-ischaemic effect is not known but it is possible that TENS interferes with the autonomic responses to ischaemia. To determine if TENS has any direct action on autonomic reflexes we have assessed the effect of high frequency TENS on a variety of standard tests of autonomic cardiovascular reflexes in 10 normal subjects. Tests were done on four consecutive days at the same time and TENS therapy or placebo was randomly allocated on 2 days each. Results of the tests were assessed by one person 'blinded' to the randomization order. These showed that TENS was associated with a significant reduction in the rise of the diastolic blood pressure (21.8 +/- 2.3 v. 17.6 +/- 17 mmHg; p < 0.05) during isometric exercise, using sustained Handgrip. There was no significant effect discernible on the changes of heart rate and blood pressure during the Valsalva manoeuvre, cold face stimulus or head-up tilt. Transcutaneous electrical nerve stimulation appears, therefore, to have a mild inhibitory action on those reflexes mediated predominantly by the sympathetic nervous system and this is more apparent when the stimulation may be greater, as during isometric exercise.

Adult↗
PubMed1995

The aetiology of heart failure in the Chinese population of Hong Kong--a prospective study of 730 consecutive patients.

Heart failure is a common and serious condition in many parts of the world and is a frequent cause for hospital admission in the Chinese population of Hong Kong. There is no published information on the epidemiology of heart failure in this community or from mainland China. Therefore, a prospective study of consecutive patients admitted with the clinical diagnosis of heart failure has been carried out to identify the main risk factors or possible causes, and other clinical data. Seven-hundred thirty consecutive patients with cardiac failure were identified and studied. Standard clinical criteria were used for diagnosis and identification of the main or most likely aetiologies and echocardiography was done in 30%. The data analysis of the 730 patients showed the following. The majority were females (56%) and the prevalence of heart failure increased with age (mean age 73.5 +/- 11.7 years) with 76% of the women > 70 years old. In contrast, the men were younger with 40% < 70 years old. The main identifiable risk factors were hypertension (37%), ischemic heart disease (31%), valvular heart disease (15%), cor pulmonale (27%), idiopathic dilated cardiomyopathy (4%), and miscellaneous (10%). In women, hypertension was the commonest cause at all ages but in men aged < 70 years ischemic heart disease was equal in frequency to hypertension (36% and 35%, respectively). Twenty-one percent had diabetes compared to a community rate of 10% for this age group (odds ratio 2.25, P < 0.0001). There was considerable overlap between diabetes, hypertension and ischemic heart disease. The estimated incidence rate was 3.8/1000 women and 3.0/1000 men aged > 45 years old.(ABSTRACT TRUNCATED AT 250 WORDS)

Age Factors↗
PubMed1995

Reproducibility of angiotensin converting enzyme inhibitor induced cough: a double-blind randomised study.

1. The reproducibility of angiotensin converting enzyme inhibitor induced cough was examined in a double-blind cross over study in patients previously shown to have exhibited this side effect. 2. Ninety-seven patients who had experienced angiotensin converting enzyme inhibitor cough within the last 2 years were challenged with enalapril 20 mg daily for 4 weeks to establish eligibility. Eighty-eight of 97 (91%) patients experienced a repeat of their cough symptoms. Sixty-four patients entered the double-blind part of the study where they were treated with enalapril 20 mg and a renin inhibitor for up to 4 weeks in random order. These periods were separated by a minimum 4 week placebo wash out. 3. Of 59 evaluable patients who received enalapril a second time, 37 (62.7%) experienced cough again. Of 62 patients on the renin inhibitor 16 (25.8%) experienced cough, however as it was not equi-efficacious to enalapril no valid comparison could be made. 4. Angiotensin converting enzyme inhibitor cough is not reproducible within patients, as other factors are involved in the aetiology. Objective testing with blinded assessment together with symptom reporting, would give a more accurate measure of the incidence, and mechanism of this side effect.

Adult↗
PubMed1995

The effects of Danshen (Salvia miltiorrhiza) on warfarin pharmacodynamics and pharmacokinetics of warfarin enantiomers in rats.

The effects of Danshen (Salvia miltiorrhiza), a popular traditional Chinese medicinal herb on the pharmacokinetics and pharmacodynamics of R- and S-warfarin stereoisomers were studied in rats. After a single oral dose of racemic warfarin (2 mg kg-1), treatment with oral Danshen extract (5 g kg-1, twice daily) for 3 days significantly altered the overall pharmacokinetics of both R- and S-warfarin and increased the plasma concentrations of both enantiomers over a period of 24 h and the prothrombin time over 2 days. At steady-state levels of racemic warfarin (0.2 mg kg-1 day-1 for 5 days) the 3-day treatment of Danshen extract (5 g kg-1, twice daily) not only prolonged the prothrombin time but also increased the steady-state plasma concentrations of R- and S-warfarin. The results indicate that Danshen extracts can increase the absorption rate constant, area under plasma concentration-time curves, maximum concentrations and elimination half-lives, but decreases the clearances and apparent volume of distribution of both R- and S-warfarin. The pharmacokinetic and pharmacodynamic interactions of warfarin during co-treatment with Danshen extract observed in this study indicate an explanation for the clinically observed incidents of exaggerated warfarin adverse effects when traditional Chinese medicinal herbs or herbal products such as Danshen and Danggui (observed in a previous study) were co-administered.

Acenocoumarol↗