Awareness hazard using a Tec 6 vaporiser.
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Anesthesia, Inhalation↗
Biomedical subjects
J C Chambers
Publications and source records attributed to J C Chambers.
Should we screen hospice inpatients for orthostatic hypotension?
Orthostatic hypotension (OH) is defined as a reduction in systolic blood pressure of at least 20 mm Hg or a reduction in diastolic blood pressure of at least 10 mm Hg within three minutes of standing, with a reported prevalence of 40% in the hospice setting. Dizziness, falls and fractures have been attributed to OH and some cases of symptomatic OH might be reversible. This study explored the case for screening hospice inpatients for OH. Fifty-nine patients were screened up to five times and, whilst the detection rate was 27%, in no case was it reproducible. There was no statistical association between orthostatic symptoms and the detection of OH, and no patients benefited from the screening process. On closer examination of the literature, the current definition of OH might benefit from revision, sphygmomanometry is an unsatisfactory screening method and there is currently no case for screening hospice inpatients for OH.
Adult↗
Tamoxifen for retroperitoneal fibrosis.
Retroperitoneal fibrosis is characterised by diffuse inflammatory proliferation of fibroblasts and the deposition of collagen fibrils throughout the retroperitoneum, especially in perivascular sites. This results in blockage of the ureters and other tubular retroperitoneal structures such as the vasculature and lymphatic channels. Left untreated, it typically follows a progressive and fatal course. The condition responds favourably to tamoxifen and several case reports describe an improvement in renal function on this therapy. This case report describes a subjective and objective functional improvement of lymphoedema secondary to retroperitoneal fibrosis with the use of tamoxifen.
Antineoplastic Agents, Hormonal↗
Investigation of relationship between reduced, oxidized, and protein-bound homocysteine and vascular endothelial function in healthy human subjects.
Previous studies investigating homocysteine and vascular disease have relied on total plasma homocysteine as the sole index of homocysteine status. We examined the dynamic relationship between vascular endothelial function and concentrations of total, protein-bound oxidized, free oxidized, and reduced homocysteine to identify the homocysteine form associated with endothelial dysfunction in humans. We investigated 14 healthy volunteers (10 men, 4 women). Brachial artery flow-mediated dilatation was measured at baseline and at 30, 60, 120, 240, and 360 minutes after oral (1) L-methionine (50 mg/kg), (2) L-homocysteine (5 mg/kg), and (3) placebo. Plasma concentrations of total, protein-bound oxidized, free oxidized, and reduced homocysteine were measured at each time point, and nitroglycerin-induced dilatation at was assessed at 0, 120, and 360 minutes. Flow-mediated dilatation fell, and concentrations of total, protein-bound oxidized, free oxidized, and reduced homocysteine increased after oral homocysteine and oral methionine (all P<0.05 for difference in time course compared with placebo). Flow-mediated dilatation showed a reciprocal relationship with reduced homocysteine during both homocysteine and methionine loading. In both loading studies, peak reduction in flow-mediated dilatation coincided with maximal reduced homocysteine concentrations. In contrast, there was no consistent relationship between flow-mediated dilatation and free oxidized homocysteine, protein-bound oxidized homocysteine, or related species. Nitroglycerin-induced dilatation was unchanged by oral homocysteine and oral methionine (P>0.10 compared with placebo). Reduced homocysteine is closely associated with endothelial dysfunction during oral methionine and oral homocysteine loading. Our observations support the hypothesis that reduced homocysteine is the deleterious form of homocysteine for vascular function in vivo and suggest a less important role for other homocysteine species.
Administration, Oral↗
C-reactive protein, insulin resistance, central obesity, and coronary heart disease risk in Indian Asians from the United Kingdom compared with European whites.
BACKGROUND: Indian Asians in the United Kingdom have increased coronary heart disease (CHD) mortality compared with European whites, but the causes are not well understood. Increased circulating concentrations of C-reactive protein (CRP) are an independent risk factor for CHD. Therefore, we investigated this marker of inflammation in healthy UK Indian Asian and European white men. Methods and Results-- We measured serum CRP concentrations and conventional CHD risk factors in 1025 healthy male subjects (518 Indian Asians and 507 European whites) aged 35 to 60 years who were recruited at random from general practitioner lists. The geometric mean CRP concentration was 17% higher (95% confidence interval, 3% to 33%) in Indian Asians compared with European whites. CRP values were strongly associated with conventional CHD risk factors, measures of obesity, and metabolic disturbances associated with insulin resistance in both racial groups. The difference in CRP concentrations between Indian Asians and European whites remained after adjustment for conventional CHD risk factors but was eliminated by an adjustment for central obesity and insulin resistance score in Asians. On the basis of these results, we estimate that the processes underlying elevated CRP and/or increased CRP production itself are associated with an approximately 14% increase in population CHD risk among Indian Asians compared with European whites. CONCLUSIONS: CRP concentrations are higher in healthy Indian Asians than in European whites and are accounted for by greater central obesity and insulin resistance in Indian Asians. Our results suggest that inflammation or other mechanisms underlying elevated CRP values may contribute to the increased CHD risk among Indian Asians.
Adult↗
Association of maternal endothelial dysfunction with preeclampsia.
CONTEXT: Preeclampsia is believed to result from release of placental factors that damage maternal vascular endothelium. However, because most studies have been conducted during pregnancy, it has not been possible to separate maternal from placental mechanisms underlying endothelial dysfunction in preeclampsia. OBJECTIVE: To determine whether endothelial function is impaired in nonpregnant women with previous preeclampsia and whether endothelial dysfunction is mediated by oxidative stress. DESIGN AND SETTING: Case-control study conducted at 3 hospital maternity units in London, England, between July 1997 and June 2000. PARTICIPANTS: A total of 113 women with previous preeclampsia (n = 35 with recurrent episodes; n = 78 with a single episode) and 48 women with previous uncomplicated pregnancies, all of whom were at least 3 months (median, 3 years) postpartum. MAIN OUTCOME MEASURES: Brachial artery flow-mediated (endothelium-dependent) and glyceryl trinitrate-induced (endothelium-independent) dilatation were compared between previously preeclamptic women and controls. To investigate oxidative stress, these measurements were repeated after administration of ascorbic acid, 1 g intravenously, in 15 cases and 15 controls. RESULTS: Mean (SD) flow-mediated dilatation was lower in women with previous preeclampsia compared with controls (recurrent group, 0.9% [4.1%]; single-episode group, 2.7% [3.5%]; and control group, 4.7% [4.3%]; P<.001). In contrast, glyceryl trinitrate-induced dilatation was similar in the 3 groups (recurrent, 19.5% [5.9%]; single-episode, 21.0% [8.0%]; and control, 21.0% [8.3%]; P =.65). Impaired flow-mediated dilatation in previously preeclamptic women was not accounted for by recognized vascular risk factors. Ascorbic acid administration increased flow-mediated dilatation in previously preeclamptic women (baseline, 2.6% [3.3%]; after administration, 5.6% [3.0%]; P =.001) but not in controls (baseline, 6.2% [3.3%]; after administration, 6.7% [5.0%]; P =.72). CONCLUSIONS: Our results indicate that endothelial function is impaired in women with previous preeclampsia and is not explained by established maternal risk factors but is reversed by antioxidant ascorbic acid administration.
Adult↗
Vascular endothelial function and oxidative stress mechanisms in patients with Behçet's syndrome.
OBJECTIVES: We sought to test the hypothesis that vascular endothelial function is impaired in Behçet's syndrome and reflects increased levels of oxidative stress. BACKGROUND: Behçet's syndrome is a multisystem inflammatory disorder commonly complicated by vascular thrombosis and arterial aneurysm formation. The precise mechanisms underlying vascular disease in Behçet's syndrome are not known. METHODS: We studied 19 patients with Behçet's syndrome (18 to 50 years old, 9 men) and 21 healthy volunteers (18 to 50 years old, 10 men). Brachial artery flow-mediated dilation (endothelium-dependent), and nitroglycerin (NTG)-induced dilation (endothelium-independent) were measured. To investigate oxidative stress mechanisms, vascular studies were repeated 1 h after administration of vitamin C (1 g, intravenous) in 12 patients and 12 control subjects. RESULTS: Flow-mediated dilation was reduced in patients with Behcet's syndrome as compared with control subjects (0.7 +/- 0.9% vs. 5.7 +/- 0.9%, p = 0.001). In contrast, there were no significant differences in the brachial artery diameter (4.2 +/- 0.2 vs. 4.0 +/- 0.2 mm, p = 0.47) or NTG-induced dilation (19.7 +/- 1.9% vs. 19.7 +/- 1.2%, p = 0.98). In regression analysis, Behçet's syndrome was associated with impaired flow-mediated dilation independent of age, gender, brachial artery diameter, blood pressure, cholesterol and glucose. Vitamin C increased flow-mediated dilation in Behçet's syndrome (0.2 +/- 0.7% to 3.5 +/- 1.0%, p = 0.002), but not in control subjects (4.3 +/- 0.6% to 4.7 +/- 0.4%, p = 0.51). In both groups, NTG-induced dilation and brachial artery diameter were unchanged after vitamin C treatment. CONCLUSIONS: Vascular endothelial function is impaired in Behcet's syndrome and can be rapidly improved by vitamin C treatment. Our results support a role for oxidative stress in the pathophysiology of Behçet's syndrome and provide a rationale for therapeutic studies aimed at reducing vascular complications in this disorder.
Adolescent↗
Homocysteine--an innocent bystander in vascular disease?
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Arteriosclerosis↗
Homocysteine: a novel risk factor for coronary heart disease in UK Indian Asians.
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Biomarkers↗
Homocysteine--a novel risk factor for vascular disease.
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Adult↗
Improved vascular endothelial function after oral B vitamins: An effect mediated through reduced concentrations of free plasma homocysteine.
BACKGROUND: Hyperhomocysteinemia is an independent risk factor for coronary heart disease (CHD). Dietary supplementation with B vitamins lowers plasma homocysteine by up to 30%. However, little is known about the potential beneficial effects of homocysteine lowering on vascular function in patients with CHD. METHODS AND RESULTS: We investigated 89 men with CHD (aged 56 [range 39 to 67] years). Brachial artery flow-mediated dilatation (endothelium dependent) and nitroglycerin-induced dilatation (endothelium independent) were measured before and 8 weeks after treatment with either (1) folic acid (5 mg) and vitamin B(12) (1 mg) daily (n=59) or (2) placebo (n=30). Total, protein-bound, and free plasma homocysteine, serum folate, and vitamin B(12) were measured at baseline and at 8 weeks. Flow-mediated dilatation improved after treatment with B vitamins (2.5+/-3.2% to 4.0+/-3.7%, P:=0.002) but not placebo (2.3+/-2.6% to 1.9+/-2.6%, P:=0.5). Vitamin therapy lowered plasma concentrations of total homocysteine (from 13.0+/-3.4 to 9.3+/-1.9 micromol/L, P:<0.001), protein-bound homocysteine (from 8.7+/-2.8 to 6.2+/-1.4 micromol/L, P:<0.001), and free homocysteine (from 4.3+/-1.2 to 3.0+/-0.6 micromol/L, P:<0.001) and raised concentrations of serum folate (from 10.3+/-4.3 to 31.2+/-10.8 ng/mL, P:<0.001) and vitamin B(12) (from 314+/-102 to 661+/-297 pg/mL, P:<0.001). In regression analysis, improved flow-mediated dilatation correlated closely with the reduction in free plasma homocysteine (r=-0.26, P:=0.001), independent of changes in protein-bound homocysteine, folate, and vitamin B(12). Nitroglycerin-induced dilatation was unchanged after both B vitamins and placebo. CONCLUSIONS: Folic acid and vitamin B(12) supplementation improves vascular endothelial function in patients with CHD, and this effect is likely to be mediated through reduced concentrations of free plasma homocysteine concentrations. Our data support the view that lowering homocysteine, through B vitamin supplementation, may reduce cardiovascular risk.
Adult↗
Plasma homocysteine concentrations and risk of coronary heart disease in UK Indian Asian and European men.
BACKGROUND: Reasons for the increase in mortality due to coronary heart disease (CHD) in UK Indian Asians are not well understood. In this study, we tested the hypotheses that elevated plasma homocysteine concentrations are a risk factor for CHD in Indian Asians, and explain part of their increased CHD risk, compared with Europeans. METHODS: We undertook two parallel case-control studies, one in Europeans and one in Indian Asians. We recruited 551 male cases (294 European, 257 Indian Asian) and 1025 healthy male controls (507 European, 518 Indian Asian). Fasting and post-methionine load homocysteine, vitamin B12 and folate concentrations, and conventional CHD risk factors were measured. FINDINGS: Fasting homocysteine concentrations were 8% higher (95% CI 3-14) in cases compared with controls, in both ethnic groups. The odds ratio of CHD for a 5 micromol/L increment in fasting plasma homocysteine was 1.3 (1.1-1.6) in Europeans and 1.2 (1.0-1.4) in Indian Asians. The association between fasting plasma homocysteine and CHD was independent of conventional CHD risk factors in both ethnic groups. Post-load homocysteine concentrations were not significantly different in cases compared with controls. Among the controls, fasting homocysteine concentrations were 6% (2-10) higher in Indian Asians than in Europeans. From the results we estimate that elevated homocysteine may contribute to twice as many CHD deaths in Indian Asians, compared with Europeans. The differences in homocysteine concentrations between the two ethnic groups were explained by lower vitamin B12 and folate levels in Asians. INTERPRETATION: Plasma homocysteine is a novel and independent risk factor for CHD in Indian Asians, and may contribute to their increased CHD risk. Raised homocysteine concentrations in Indian Asians may be related to their reduced vitamin B12 and folate levels, implying that the increased CHD risk in this group may be reduced by dietary vitamin supplementation.
Case-Control Studies↗
CD4 T lymphocyte activation in BLV-induced persistent B lymphocytosis in cattle.
Bovine leukemia virus (BLV) is an oncogenic retrovirus in the human T cell leukemia virus family. BLV infects B lymphocytes and induces a nonmalignant persistent lymphocytosis (PL) and leukemia/lymphoma in cattle. There is evidence that CD4 T lymphocytes are activated during BLV infection and promote the development of PL. How CD4 T lymphocytes are activated by BLV infection is not known. We observed that CD4 T lymphocytes from PL cattle proliferated in the presence of autologous, irradiated peripheral blood mononuclear cells (PBMC), whereas no proliferation occurred in cell cultures from BLV-infected non-PL cattle. Proliferation required direct contact with metabolically active irradiated PBMC but was not associated with viral protein expression or inhibited by antibodies to BLV. Unexpectedly, B lymphocytes alone failed to account for the irradiated PBMC stimulation of CD4 T lymphocytes. These observations and the magnitude of the proliferative response suggest that activation is polyclonal and involves mechanisms other than BLV antigen-specific stimulation.
Animals↗
Methylenetetrahydrofolate reductase 677 C-->T mutation and coronary heart disease risk in UK Indian Asians.
Plasma homocysteine concentrations are elevated in UK Indian Asians and may contribute to twice as many coronary heart disease (CHD) deaths in this group compared with European whites. The mechanisms underlying elevated homocysteine concentrations among Indian Asians are not well understood. In this study, we have investigated the extent to which the methylenetetrahydrofolate reductase (MTHFR) 677 C-->T mutation accounts for elevated plasma homocysteine and increased CHD risk in Indian Asians compared with European whites. We investigated 454 male cases (with myocardial infarction or angiographically proven CHD: 224 Indian Asians, 230 European whites) and 805 healthy male controls (381 Indian Asians, 424 European whites). Fasting homocysteine concentrations, MTHFR 677 C-->T genotype, and conventional CHD risk factors were measured. The prevalence of homozygous MTHFR 677T in Indian Asian controls was less than one third that in European white controls (3.1% versus 9. 7%, P<0.001). In Indian Asians, the TT MTHFR genotype was not associated with homocysteine concentrations and was not present in any of the Asian controls with hyperhomocysteinemia (>15 micromol/L). In contrast, among European whites, the TT MTHFR genotype was strongly related to elevated plasma homocysteine concentrations and was found in 27% of the European controls with hyperhomocysteinemia. Elevated homocysteine in Indian Asian compared with European white controls was accounted for by their reduced levels of B vitamins but not by the MTHFR 677T genotype. However, neither the TT MTHFR genotype nor B vitamin levels explained the elevated homocysteine concentrations in CHD cases compared with controls. TT MTHFR was not a risk factor for early-onset CHD in Indian Asians (odds ratio, 0.5; 95% confidence interval, 0.1 to 2.4; P=0.39), unlike in European whites (odds ratio, 2.1; 95% confidence interval, 1.1 to 4. 1; P=0.02). We conclude that the MTHFR 677T: mutation does not contribute to elevated plasma homocysteine concentrations or increased CHD risk in Indian Asians compared with European whites. Our results suggest that novel genetic defects and/or environmental factors influence homocysteine metabolism in Indian Asians residing in the United Kingdom.
Adult↗
Demonstration of rapid onset vascular endothelial dysfunction after hyperhomocysteinemia: an effect reversible with vitamin C therapy.
BACKGROUND: Hyperhomocysteinemia is a major and independent risk factor for vascular disease. The mechanisms by which homocysteine promotes atherosclerosis are not well understood. We hypothesized that elevated homocysteine concentrations are associated with rapid onset endothelial dysfunction, which is mediated through oxidant stress mechanisms and can be inhibited by the antioxidant vitamin C. METHODS AND RESULTS: We studied 17 healthy volunteers (10 male and 7 female) aged 33 (range 21 to 59) years. Brachial artery diameter responses to hyperemic flow (endothelium dependent), and glyceryltrinitrate (GTN, endothelium independent) were measured with high resolution ultrasound at 0 hours (fasting), 2 hours, and 4 hours after (1) oral methionine (L-methionine 100 mg/kg), (2) oral methionine preceded by vitamin C (1g/day, for 1 week), and (3) placebo, on separate days and in random order. Plasma homocysteine increased (0 hours, 12.8+/-1.4; 2 hours, 25.4+/-2.5; and 4 hours, 31. 2+/-3.1 micromol/l, P<0.001), and flow-mediated dilatation fell (0 hours, 4.3+/-0.7; 2 hours, 1.1+/-0.9; and 4 hours, -0.7+/-0.8%) after oral L-methionine. There was an inverse linear relationship between homocysteine concentration and flow-mediated dilatation (P<0. 001). Pretreatment with vitamin C did not affect the rise in homocysteine concentrations after methionine (0 hours, 13.6+/-1.6; 2 hours, 28.3+/-2.9; and 4 hours, 33.8+/-3.7 micromol/l, P=0.27), but did ameliorate the reduction in flow-mediated dilatation (0 hours, 4. 0+/-1.0; 2 hours, 3.5+/-1.2 and 4 hours, 2.8+/-0.7%, P=0.02). GTN-induced endothelium independent brachial artery dilatation was not affected after methionine or methionine preceded by vitamin C. CONCLUSIONS: We conclude that an elevation in homocysteine concentration is associated with an acute impairment of vascular endothelial function that can be prevented by pretreatment with vitamin C in healthy subjects. Our results support the hypothesis that the adverse effects of homocysteine on vascular endothelial cells are mediated through oxidative stress mechanisms.
Adult↗
Abnormalities of vascular endothelial function may contribute to increased coronary heart disease risk in UK Indian Asians.
OBJECTIVE: To test the hypothesis that abnormalities of endothelial function are present in Indian Asians and may contribute to their increased coronary heart disease risk. SETTING: Single centre in west London. PATIENTS: 26 Indian Asian and 18 European white healthy male subjects, aged 35 to 61 years recruited from general practice lists. DESIGN: Brachial artery diameter responses to reactive hyperaemia and sublingual glyceryl trinitrate were compared using high resolution ultrasound. RESULTS: Mean (SEM) flow mediated, endothelium dependent dilatation was reduced in Indian Asians compared with European whites, at 3.2 (0.8)% v 5.9 (1.0)%, p = 0.03. In contrast, there were no significant differences in baseline brachial arterial diameter (4.6 (0.1) v 4.6 (0.1) mm, p = 0.65) or glyceryl trinitrate induced dilatation (18.8 (1.5)% v 18.5 (1.7)%, p = 0.90) between Indian Asians and European whites, respectively. Univariate analysis showed that Indian Asian race was significantly associated with impaired flow mediated dilatation (regression coefficient = -2.8 (1.3)%, p = 0.03), and in multivariate analysis, this relation was independent of both conventional coronary heart disease risk factors and markers of insulin resistance. CONCLUSIONS: Endothelial function is impaired in healthy UK Indian Asians compared with European whites, and the defect is not accounted for by major coronary heart disease risk factors. Endothelial function may be modulated by novel risk factors in Indian Asians.
Adult↗
Physiological increments in plasma homocysteine induce vascular endothelial dysfunction in normal human subjects.
We hypothesized that physiological increments in plasma homocysteine after low-dose oral methionine or dietary animal protein induce vascular endothelial dysfunction and that there is a graded, inverse relationship between homocysteine concentration and endothelial function. We studied 18 healthy volunteers aged 18 to 59 years. Brachial artery flow-mediated and glyceryltrinitrate-induced dilatation were measured after 1) oral L-methionine (10, 25, and 100 mg/kg), 2) dietary animal protein (lean chicken 551+/-30 g, comprising 3.2+/-0.2 g methionine), and 3) methionine-free amino acid mix (100 mg/kg). Methionine (10, 25, and 100 mg/kg) induced a dose-related increase in homocysteine (9.4+/-1.3 to 12.2+/-2.1, 17. 6+/-2.6, and 26.1+/-4.2 micromol/L, respectively; P<0.001) and a reduction in flow-mediated dilatation (4.1+/-0.8 to 2.1+/-0.8, 0. 3+/-0.8, and -0.7+/-0.8%, respectively; P<0.001) at 4 hours. Compared with usual meal, animal protein increased plasma homocysteine (9.6+/-0.8 to 11.2+/-0.9 micromol/L, P=0.005) and reduced flow-mediated dilatation (4.5+/-0.7% to 0.9+/-0.6%, P=0.003). Methionine-free amino acid mix did not induce any changes. Glyceryltrinitrate-induced dilatation was unchanged throughout. In this study, small physiological increments in plasma homocysteine after low-dose methionine and dietary animal protein induced vascular endothelial dysfunction. We propose that protein intake-induced increments in plasma homocysteine may have deleterious effects on vascular function and contribute to the development and progression of atherosclerosis.
Administration, Oral↗
Acute hyperhomocysteinaemia and endothelial dysfunction.
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Adult↗