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Biomedical subjects

J Chambers

Publications and source records attributed to J Chambers.

At least 73 records · Page 4Linked to original sources
PubMed1998

Pulmonary response of normal human subjects to inhaled vasodilator substances.

1. Inhaled vasodilators such as nitric oxide and epoprostenol (prostaglandin I2) are now widely employed as supportive therapies to improve oxygenation and reduce pulmonary vascular resistance in patients with acute and chronic pulmonary hypertension. However, few data exist concerning their effects in normal individuals. The aim of this study was to characterize the response of the pulmonary circulation in normal individuals to inhaled nitric oxide and nebulized prostaglandin I2.2.Eight healthy volunteers were exposed to inhaled nitric oxide (0, 20 and 40 p.p.m.) and nebulized prostaglandin I2 (10 microgram/ml). Changes in effective pulmonary blood flow and diffusing capacity of the lung for carbon monoxide (TLCO) were measured using respiratory mass spectrometry. Bicycle ergometry was used to increase effective pulmonary blood flow as a positive control.3. Exercise produced significant increases in both effective pulmonary blood flow and TLCO, but neither nitric oxide nor prostaglandin I2 produced significant changes in either parameter.4.No significant change in pulmonary haemodynamics was demonstrated in response to inhaled nitric oxide or nebulized prostaglandin I2, using doses known to be effective in patients with acute and chronic pulmonary hypertension. These data suggest that the normal pulmonary vascular bed is not amenable to vasodilatation by inhaled drugs. The study further suggests that the normal pulmonary vasodilatation seen on exercise is not mediated pharmacologically, but is a secondary consequence to the mechanical effects of a rise in pulmonary blood flow. This study thus supports the view that there is no resting vasoconstrictor tone in the pulmonary vascular bed.

Administration, Inhalation↗
PubMed1998

Atypical chest pain: looking beyond the heart.

Chest pain is common, and tends to be overinvestigated. Patients with normal coronary anatomy have a low mortality, but remain significantly incapacitated. We discuss ways of improving the management of such patients. An early diagnosis of a non-cardiac cause of pain should be made, ideally by the general practitioner, taking account of risk factors for cardiac as well as psychological disorders, the quality of the pain, the patient's concerns and worries and the presence of stressful life events. The minimum of investigation should be performed. Cardiological referral should be considered for patients with a high a priori risk of ischaemic heart disease. Otherwise referral, if necessary, should be to a gastroenterologist, psychiatrist or clinical psychologist, as appropriate. Treatment options are medications with musculoskeletal or oesophageal activity, simple or repeated reassurance, cognitive therapy, psychiatric drugs, and respiratory retraining. We suggest that a multidisciplinary chest-pain clinic may improve the care of such patients.

Chest Pain↗
PubMed1998

The use of routine duplex scanning in the assessment of varicose veins.

BACKGROUND: Clinical assessment has been shown to compare poorly with results of hand-held Doppler examination or venography in the evaluation of varicose veins. Although the use of duplex scanning has been well described in the assessment of varicose veins, there are few data comparing clinical and Doppler assessment with results of duplex scans. METHODS: A total of 188 patients were referred with varicose veins to a sole specialist vascular surgeon over a 1-year period. After clinical and Doppler assessment, all patients were referred for a duplex scan which was performed by a trained vascular technician. The results of the duplex scan were compared retrospectively with the clinical and Doppler findings. RESULTS: A total of 315 legs were assessed over this period, with 38.7% having recurrent disease and 31.4% having trophic skin changes or ulceration. On duplex scanning, 198 legs (62.9%) had saphenofemoral junction incompetence, 61 legs (19.4%) had saphenopopliteal junction incompetence, 94 legs (29.8%) had perforator incompetence and 24 legs (7.6%) had deep venous incompetence. The respective sensitivity of clinical and Doppler assessment at these sites was 71.2, 36.1, 43.6 and 29.2%. If patients who were felt to have sole saphenofemoral junction incompetence clinically were treated by high ligation, stripping to the knee and stab avulsions, 28.9% would have had sites of reflux untreated. CONCLUSIONS: Clinical and Doppler assessment is unreliable. Routine duplex scanning is likely to reduce recurrence by identifying sites of reflux with greater accuracy.

Adult↗
PubMed1998

How often do we operate too late in aortic stenosis?

The management of asymptomatic severe aortic stenosis remains controversial. Despite a good outcome in terms of mortality, the left ventricle may not recover fully after aortic valve replacement and patients may have impaired exercise ability. Routine assessment of the left ventricle is dominated by transverse systolic function to the relative neglect of long-axis and diastolic function. Long-axis dysfunction develops earlier than transverse dysfunction and may correlate with exercise ability. Reported symptoms can be unreliable and exercise testing reveals significant limitation in many apparently asymptomatic patients. Exercise testing and echocardiographic markers of early LV systolic dysfunction may help to refine the timing of surgery in patients with apparently asymptomatic severe aortic stenosis.

Aortic Valve Stenosis↗
PubMed1998

Early postoperative echocardiographic hemodynamic performance of the On-X prosthetic heart valve: a multicenter study.

BACKGROUND AND AIMS OF THE STUDY: This study aimed to investigate the early postoperative Doppler-derived hemodynamic results from the first patients receiving the On-XR prosthetic heart valve, a new bileaflet, pyrolytic carbon valve. METHODS: Data were derived from 111 patients included in a 10-center international trial between September 1996 and December 1997. RESULTS: The effective orifice area (EOA) for the valve, when implanted in the aortic position, ranged from 1.5 to 2.7 cm2 in 19 mm to 25 mm valves. The corresponding mean pressure gradients ranged from 11.8 to 7.6 mmHg. Mitral EOA was 2.3 cm2 for all sizes, these values being combined because the housing was identical for all mitral valves used in this study. The mitral mean gradient was 4.7 mmHg. CONCLUSIONS: Early results of the study show the good hemodynamic performance of the On-X valve when implanted in the aortic or mitral positions.

Adult↗
PubMed1997

Dyspnoea and exercise intolerance during cardiopulmonary exercise testing in patients with univentricular heart. The effects of chronic hypoxaemia and Fontan procedure.

BACKGROUND: Patients with univentricular hearts have decreased exercise tolerance and may demonstrate exertional dyspnoea. It is not known if chronic hypoxaemia exacerbates exercise intolerance and contributes to symptomatic limitation. The extent to which surgical correction of a right-to-left shunt by a Fontan-type procedure can increase exercise tolerance by reducing arterial deoxygenation is not well documented. The cardiopulmonary exercise responses and the symptomatic status in two groups of univentricular patients, those who are cyanotic and those who are acyanotic with Fontan-type circulation, were compared. METHODS AND FINDINGS: Cardiopulmonary exercise testing was performed in 10 univentricular patients with rest or stress-induced cyanosis (age 30.5 +/- 2.3 [SE] years; 5 men) who had palliative or no surgery and eight patients (age 29.4 +/- 1.5 years; 4 men) with Fontan-type circulation. Peak oxygen consumption was comparable in both groups of univentricular patients (21.7 +/- 2.5 vs 21.0 +/- 1.9 ml.kg-1.min-1, P = 0.85) but was less than an age-matched group of 10 healthy subjects (34.7 +/- 1.9 ml.kg-1.min-1, P < 0.001 for both). Arterial oxygen saturation was 90.6% at rest in the cyanotic patients compared with 95.1% in the Fontan patients (P < 0.001) and at peak exercise, 66.2% compared with 90.5% (P < 0.001). Using a modified Borg scale (0-10), the symptoms of dyspnoea and fatigue were also assessed during exercise in the patient groups. The Borg scores for dyspnoea in the cyanotic and the corrected univentricular patients were, respectively, as follows: Stage 1: 0.5 vs 1.7; P= 0.04; Stage 2: 1.8 vs 2.3, P = 0.5; Stage 3: 3.0 vs 3.5, P = 0.7; Peak Exercise: 4.9 vs 4.8, P = 0.9. In addition, the Borg scores for fatigue were: Stage 1: 0.4 vs 1.6, P = 0.08; Stage 2: 2.0 vs 2.2, P = 0.9; Stage 3: 3.0 vs 4.3, P = 0.5; Peak Exercise: 4.9 vs 5.4, P = 0.5. The major limiting symptom at peak exercise was dyspnoea in four cyanotic patients compared with one in the Fontan group (Chi-square 0.982, P > 0.10). The arterial oxygen desaturation at peak exercise in the cyanotic patients limited by dyspnoea was not different from those limited by fatigue (67.5 +/- 10.1% vs 66.7 +/- 13.7%, P = 0.92). Exercise tolerance was also not related to the arterial oxygen saturation at peak exercise (r = 0.47, P = 0.17) in these patients. CONCLUSIONS: Despite correction with Fontan-type surgery, the exercise tolerance and symptoms of these univentricular patients remained similar to those who were cyanosed. Cyanotic patients have adjusted to chronic hypoxaemia and it does not appear to determine the exercise tolerance or the genesis of dyspnoea in these patients. Further randomized prospective studies are required to investigate the long-term benefits of Fontan-type procedures in these patients on exercise tolerance, symptoms and prognosis.

Adult↗
PubMed1996

The potential role of external beam radiation in preventing restenosis after coronary angioplasty.

The potential role of radiation in the prevention of coronary artery restenosis after angioplasty has generated much recent interest. Animal research and pilot clinical efforts have focused primarily on intraluminal methods of radiation delivery. This article reviews the experience to date with external beam radiation in restenosis prevention and suggests issues that should be considered from the standpoint of both external beam and intravascular radiotherapy. External beam radiation can certainly play an effective role in clinical studies of coronary artery restenosis, and a multicenter randomized trial of external beam radiation after coronary angioplasty has been initiated.

Angioplasty, Balloon, Coronary↗
PubMed1996

Genomic organization of a mouse MHC class II region including the H2-M and Lmp2 loci.

The region encompassing the Ma, Mb1, Mb2, and Lmp2 genes of the mouse class II major histocompatibility complex (MHC) was sequenced. Since this region contains clusters of genes required for efficient class I and class II antigen presentation, it was interesting to search for putative additional genes in the 21 kilobase gap between the Mb1 and Lmp2 genes. Computer predictions of coding regions and CpG islands, exon trapping experiments, and cross-species comparison with the corresponding human sequence indicate that no additional functional gene is present in that stretch. However, computer analysis revealed the possible existence of an alternative 3' exon for Mb1. Except for the fact that the mouse MHC contains two Mb genes, the genomic organization of the H2-M loci was found to be almost identical to the organization of the human HLA-DM genes. The promoter regions of the Ma and Mb genes also resemble classical class II promoters, containing typical S, X, and Y boxes. Like the human genes, the three H2-M genes displayed very limited polymorphism when we compared the cDNA sequences from six haplotypes. Finally, comparison of DMB with Mb1 and Mb2, both at the genomic level and in their coding regions, suggests that the Mb gene was recently duplicated, probably only in certain rodents.

Animals↗