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Biomedical subjects

J Melin

Publications and source records attributed to J Melin.

At least 19 recordsLinked to original sources
PubMed2001

Comparison of denuder and impinger sampling for determination of gaseous toluene diisocyanate (TDI).

An air-sampling method employing denuders coated inside with a chemisorptive stationary phase has been evaluated for analysis of the hazardous gaseous 2,4 and 2,6 isomers of toluene diisocyanate (TDI). The denuder stationary phase consisted of polydimethylsiloxane (SE-30) to which dibutylamine (DBA) was added as a reagent for derivatization of TDI. The accuracy and precision of sampling by means of denuders were shown to differ only slightly from those of the established impinger method. The denuder method was, however, also shown to be suitable for long-term measurements (up to 8 h). The limit of determination (LOD) of the method, including LC-APCI-MS-MS analysis, was found to be 1.9 microg m(-3) and 1.2 microg m(-3) for 2,4- and 2,6-TDI, respectively, for short-term measurements (15 min). Significant lower LOD was obtained for long-term measurements. This is well below the Occupational Safety and Health Administration (OSHA) 8-h TWA (time-weighted average) exposure limit, which is 40 microg m(-3) for the sum of the TDI isomers. The denuder method was also found to be robust and easy to handle. The samplers can be prepared several days before sampling with no loss in performance. The contents of denuders should, on the other hand, be extracted immediately after sampling to prevent degradation of the isocyanate derivatives formed.

Journal Article↗
PubMed2001

Characterization of thermally generated aerosols from polyurethane foam.

Isocyanates constitute a group of highly reactive chemicals used on a large scale for the production of flexible polyurethane (PUR) foam. Exposure to isocyanates is known to produce irritation of the mucous membranes and the eyes. Isocyanates also have strong sensitizing properties and may cause occupational asthma. It is therefore important to monitor isocyanate emissions at workplaces. To obtain information for the improvement of isocyanate samplers and for health risk assessments of exposure, the emitted aerosol from two types of flexible PUR foam subjected to thermal degradation was characterized. Particle size distribution and toluene diisocyanate (TDI) concentration in the emitted aerosols were measured. Thermal degradation of flexible PUR foam at temperatures from 250 to 300 degrees C produced an aerosol with a geometric mean particle diameter of 30-50 nm. Between 5% and 9% of the PUR foam was emitted as TDI, and 2% to 6% of TDI monomers were found in the particle phase under the experimental conditions used. The 2,6-TDI isomer was more abundant in the gas phase than in the particle phase.

Aerosols↗
PubMed2001

Cerebral blood flow and glucose metabolism in hypothyroidism: a positron emission tomography study.

Hypothyroidism is often associated with defective memory, psychomotor slowing, and depression. However, the relationship between thyroid status and cognitive or psychiatric disturbances remains unclear. Using psychometric scales, 10 patients who had undergone total thyroidectomy for thyroid carcinoma were evaluated for depression, anxiety, and psychomotor slowing; they were examined both when euthyroid and hypothyroid after thyroid hormone withdrawal. Positron emission tomography was used, with oxygen-15-labeled water and fluorine-18F-labeled 2-deoxy-2fluoro-D-glucose as the tracers, to correlate the regional cerebral blood flow and cerebral glucose metabolism with the mental state in patients. Two different image analysis techniques (regions of interest and statistical parametric maps) were applied. In hypothyroidism, there was a generalized decrease in regional cerebral blood flow (23.4%, P < 0.001) and in cerebral glucose metabolism (12.1%, P < 0.001) and there were no specific local defects. Patients were also significantly more depressed (P < 0.001), anxious (P < 0.001) and psychomotor slowed (P < 0.005) in hypo than in euthyroid status. These results indicate that the brain activity was globally reduced in severe hypothyroidism of short duration without the regional modifications usually observed in primary depression.

Adult↗
PubMed2000

The effect of labor pain relief medication on neonatal suckling and breastfeeding duration.

We examined the relationship of labor pain relief medications with neonatal suckling and breastfeeding duration in 129 mothers delivering vaginally. Suckling was measured using the Infant Breastfeeding Assessment Tool (IBFAT). Controlling for infant age, birthweight, and gender, infants of unmedicated mothers had higher IBFAT suckling scores than those of medicated mothers (x = 11.1 vs. x = 8.2 respectively, P = .001). IBFAT suckling scores for intravenous and epidural groups were similar (x = 8.5) while those who received a combination of both intravenous and epidural medications were lower (x = 6.4 +/- 2.96, P = .001). Mothers evaluated their breastfeeding similarly to nurse evaluators (Z = 9.39, P = .001). Breastfeeding duration did not differ between unmedicated and medicated groups; however, dyads with low IBFAT scores weaned earlier than those with medium or high scores. Labor pain relief medications diminish early suckling but are not associated with duration of breastfeeding through 6 weeks postpartum.

Adult↗
PubMed2000

Required response time for variable air volume fume hood controllers.

This paper describes results from tests made with the aim of investigating how quickly the exhaust air flow rate through fume hoods needs to be controlled in order to prevent contaminants from leaking out of the fume hood and putting the safety of the laboratory personnel at risk. The measurements were made on a laboratory fume hood in a chemical laboratory. There were no other fume hoods in the laboratory, and the measurements were made without interference from persons entering or leaving the laboratory or walking about in it. A tracer gas method was used with the concentration of dinitrogen oxide (N(2)O) being recorded by a Foxboro Miran 101 infra-red gas analyser. In parallel with the tracer gas measurements, the air velocity through the face opening was also measured, as was the control signal to the damper controlling the air flow rate. The measurements show an increased outward leakage of tracer gas from the fume hood if the air flow rate is not re-established within 1-2 s after the sash is opened. If the delay exceeds 3 s the safety function is temporarily defeated. The measurements were made under virtually ideal conditions. Under more typical conditions, the fume hood could be exposed to various other external perturbations, which means that the control system should re-establish the correct exhaust flow more quickly than indicated by the measurement results obtained under these almost ideal conditions.

Air Movements↗
PubMed1999

Cardiological applications of nuclear medicine.

Cardiovascular mortality is falling in most industrialised nations. Primarily responsible for this encouraging trend are preventive measures such as risk-factor modification but improved medical and surgical management have helped too. Clinical decision making in the patient with coronary heart disease demands techniques that not only describe coronary anatomy but also provide functional indices for early detection and to monitor the severity and extent of disease. Nuclear medicine methods can characterise non-invasively myocardial function, perfusion, and metabolism. Novel radiopharmaceuticals, improvements in imaging equipment, and extensive validation have contributed to the growing clinical acceptance of these techniques and to their cost-effective integration in the workup of patients with cardiovascular disease.

Coronary Disease↗
PubMed1999

Improvement of myocardial blood flow to ischemic regions by angiotensin-converting enzyme inhibition with quinaprilat IV: a study using [15O] water dobutamine stress positron emission tomography.

OBJECTIVES: This study was designed to analyze the effects of acute angiotensin-converting enzyme (ACE) inhibition on myocardial blood flow (MBF) in control and ischemic regions. BACKGROUND: Although animal studies indicate an improvement of MBF to ischemic regions after ACE inhibition, this effect has not been conclusively demonstrated in patients with coronary artery disease. METHODS: Myocardial blood flow was analyzed in ischemic and nonischemic regions of 10 symptomatic patients with coronary artery disease using repetitive [15O] water positron emission tomography at rest and during maximal dobutamine stress before and after ACE inhibition with quinaprilat 10 mg i.v. To exclude the possibility that repetitive ischemia may cause an increase in MBF, eight patients underwent the same protocol without quinaprilat (placebo patients). RESULTS: Rate pressure product in control and quinaprilat patients was comparable. In placebo patients, repetitive dobutamine stress did not change MBF to ischemic regions (1.41 +/- 0.17 during the first stress vs. 1.39 +/- 0.19 ml/min/g during the second stress, p = 0.93). In contrast, MBF in ischemic regions increased significantly after acute ACE inhibition with quinaprilat during repetitive dobutamine stress (1.10 +/- 0.13 vs. 1.69 +/- 0.17 ml/min/g, p < 0.015). Dobutamine coronary reserve in ischemic regions remained unchanged in placebo patients (1.07 +/- 0.11 vs. 1.10 +/- 0.16, p = 0.92), but increased significantly after quinaprilat (0.97 +/- 0.10 vs. 1.44 +/- 0.14, p < 0.002). Total coronary resistance decreased after ACE inhibition (123 +/- 19 vs. 71 +/- 10 mm Hg x min x g/ml, p < 0.02). CONCLUSIONS: Angiotensin-converting enzyme inhibition by quinaprilat significantly improves MBF to ischemic regions in patients with coronary artery disease.

Adult↗
PubMed1998

Comparison of dipyridamole stress echocardiography and perfusion scintigraphy for cardiac risk stratification in vascular surgery patients.

Dipyridamole single-photon emission computed tomography (SPECT) has a high negative predictive value for perioperative cardiac events, but events are infrequent in patients with a positive test. In contrast, dipyridamole echocardiography is more selective for detection of multivessel disease and thus may have a greater specificity for cardiac events. We therefore compared the ability of dipyridamole SPECT and echocardiography to predict perioperative and long-term cardiac events in 133 patients referred for vascular surgery. The group was also evaluated based on clinical features and ejection fraction. Four patients had surgery cancelled because of high risk and were excluded from further analysis. Among the 129 remaining patients, 21 had coronary revascularization (n=12) or an early cardiac end point (n=9). The sensitivity of SPECT for the prediction of early events (90%) was not significantly different from that of echocardiography (66%, p=NS). The specificity of SPECT (68%) was less than that of echocardiography (88%, p <0.001%), as was the accuracy (72% vs 84%, p=0.02). These findings were replicated after exclusion of patients with treatment end points. During long-term follow-up, 12 patients experienced > or = 1 event: 6 died from cardiac causes, 4 underwent revascularization, and 3 had myocardial infarction. Thus, the specificity of SPECT and echocardiography for late events were 58% and 80%, respectively (p <0.001). The 3-year survival of patients without ischemia during echocardiography or at SPECT was not different (93% vs 94%, p=NS).

Adult↗
PubMed1997

Ischemia causes rapidly progressive nephropathy in the diabetic rat.

We examined the influence of renal ischemia in rats with diabetes mellitus (DM). Male Wistar rats were rendered diabetic by streptozotocin treatment. Two weeks later, 30 minutes of complete ischemia was induced in the left kidney of DM and non-DM animals. Both groups were evaluated functionally and morphologically four or eight weeks post-ischemia. In non-DM animals renal function and morphology showed almost complete recovery. In the DM animals, however, this comparatively short period of ischemia caused a substantial loss of renal function. Four weeks post-ischemia inulin clearance in the DM kidneys rendered ischemic was only 20% of that in the corresponding non-DM kidneys, and after eight weeks the DM kidneys were completely anuric. Extensive inflammation and tubulointerstitial fibrosis were evident in DM kidneys four weeks after ischemia and seemed to increase over time. After eight weeks, tubular atrophy was found in the ischemic DM kidneys, resulting in a substantial loss of kidney mass. We conclude that in diabetic rats renal ischemia causes rapidly progressive kidney damage that in several respects resembles diabetic nephropathy in humans. Since advanced renal lesions similar to those seen in human diabetic nephropathy never develop in the rat solely as a result of DM, the present study may provide an experimental model for further studies on renal failure in diabetes mellitus.

Animals↗
PubMed1997

[Cardiac decompensation: mechanism of reversibility].

Chronic regional left ventricular dysfunction in patients with coronary artery disease is a frequent cause of congestive heart failure. Chronic dysfunction might be reversed by restoration of myocardial blood flow. This condition has been referred to as myocardial hibernation. Until now, elucidation of the exact mechanisms leading to hibernation has remained difficult, owing mainly to the lack of relevant animal models. Therefore, we performed the present studies in patients with chronic left ventricular ischemic dysfunction undergoing coronary revascularization. The hibernating myocardium was characterized by : 1) a normal resting perfusion and oxidative metabolism; 2) a blunted coronary reserve; 3) a preserved contractile reserve with inotropic stimulation; 4) morphologic ultrastructural alteration, with aspects of cellular dedifferentiation; 5) a slow recovery of function overtime, inversely related to the severity of ultrastructural abnormalities. Further work should focus on designing appropriate animal models and on elucidating cellular and molecular bases of this phenomenon.

Coronary Circulation↗
PubMed1996

Radiographic skeletal survey and radionuclide bone scan in Langerhans cell histiocytosis of bone.

BACKGROUND: The lack of a consensus in the literature on the imaging strategy in Langerhans cell histiocytosis (LCH) bone lesions in childhood. OBJECTIVE: To evaluate the relative value of radionuclide bone scan (RBS) and radiographic skeletal survey (RSS) in the detection of LCH bone lesions, both in the initial work-up of the disease and during the follow-up period. MATERIALS AND METHODS: Ten children with bone lesions evaluated by means of RSS and RBS in a retrospective study (1984-1993). RESULTS: Fifty radiologically and/or scintigraphically abnormal foci were detected: 27 anomalies in the initial work-up (12 by both RSS and RBS, 8 by RSS only and 7 by RBS only) and 23 additional anomalies during follow-up (10 by both RSS and RBS, 10 by RSS only and 3 by RBS only). RSS+/RBS- lesions (n = 18) are more frequently encountered in the skull (P = 0.038), and more frequently lack radiologic signs of osteoblastic activity (P = 0.020), than RSS+/RBS+ lesions (n = 22). RSS-/ RBS+ abnormalities (n = 10) were most frequently insignificant. CONCLUSION: In the initial work-up both RSS and RBS should be carried out, while in the follow-up only RSS should be performed.

Adolescent↗
PubMed1996

Left ventricular failure and pulmonary edema in acute multiple sclerosis.

We describe a young woman who developed left ventricular failure and pulmonary edema during fulminant onset of multiple sclerosis. One of the numerous plaques was located in the left inferior cerebellar peduncle near the dorsal motor vagal and solitary tract nuclei. Within two days pulmonary edema had cleared, and within three days left ventricular function was normal. To our knowledge, left ventricular failure has not earlier been verified in acute multiple sclerosis.

Adult↗