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Biomedical subjects

J Myers

Publications and source records attributed to J Myers.

At least 163 records · Page 9Linked to original sources
PubMed1990

Characterization and tissue distribution of H3 histamine receptors in guinea pigs by N alpha-methylhistamine.

We have used [3H]N alpha-methylhistamine to characterize H3-binding in the guinea pig brain and to study its tissue distribution. Kinetic and equilibrium binding experiments indicate a single class of high affinity sites in membranes isolated from guinea pig brain tissue (Kd = 0.4 nM, Bmax = 41 fmol/mg of protein). Competition binding experiments have confirmed that this ligand associates with H3-receptors and, under the conditions used in these experiments, does not bind to H1- or H2-receptors. Although there was some binding in the ileum and large intestine, H3-binding was found primarily in the central nervous system.

Animals↗
PubMed1990

Occupational health in developing countries: review of research needs.

Over the past two decades, industrial activity has increased rapidly in developing nations. Industrial growth has also increased the health risks facing workers in these countries both by intensifying existing health problems and by introducing new hazards. Inadequate information about occupational hazards creates major obstacles to effective prevention of occupational diseases in many developing countries. This brief report reviews the occupational health determinants of developing nations and suggests current research needs and objectives. Our purpose is to stimulate discussion and initiate debate among health professionals worldwide who confront growing problems in occupational health.

Developing Countries↗
PubMed1990

The effect of complete and incomplete revascularization on exercise variables in patients undergoing coronary angioplasty.

To investigate the effects of complete and incomplete revascularization on the response to exercise, 25 patients underwent symptom-limited exercise testing with continuous assessment of gas exchange a mean of 5 +/- 4 days prior to and 18 +/- 12 days following percutaneous transluminal coronary angioplasty. All antianginal medications were discontinued for testing. Revascularization was considered complete if all stenoses were reduced to less than 50% diameter (13 patients), and incomplete if one or more stenoses remained (12 patients). Consistent improvements in ST-segment depression were observed after angioplasty at matched submaximal exercise levels (mean range 0.5-0.8 mm; p less than 0.05), and were accompanied by a reduction in angina. Significant increases in heart rate and systolic blood pressure were observed at peak exercise following angioplasty in both groups. Gas exchange variables were significantly improved at maximal exercise, with a similar increase in oxygen uptake observed in both groups following angioplasty (mean increase 3.3-3.7 ml/kg/min; p less than 0.01). Thus, incomplete revascularization following coronary angioplasty resulted in hemodynamic, electrocardiographic, symptomatic, and gas exchange responses to exercise that were comparable to complete revascularization.

Adult↗
PubMed1990

Effect of fructose 1,6-diphosphate on exercise capacity in patients with peripheral vascular disease.

Exogenous fructose 1,6-diphosphate (FDP), a glycolytic intermediate, increases blood ATP and 2,3 diphosphoglycerate levels, facilitates the dissociation of oxygen from hemoglobin, and increases red blood cell flexibility. These mechanisms explain why it has been effective in enhancing energy production in a variety of ischemic conditions. The present study was undertaken to determine whether FDP could enhance oxygen supply and thus improve exercise performance in patients with peripheral vascular disease. Ten male patients (mean age 63 +/- 5 years) with peripheral vascular disease performed symptom-limited exercise testing after randomized, double blind infusion of either 200 mg/kg body weight FDP or placebo. Data were evaluated at rest, at a matched submaximal workload (2-3 MPH/0% grade), and at peak exercise, defined as the occurrence of moderately severe claudication. No differences were observed in heart rate, blood pressure, gas exchange data, time to the onset of claudication or peak exercise, or lactate and 2,3 diphosphoglycerate levels. In contrast to previous studies performed among patients with peripheral vascular disease and other studies using more severe hypoxic conditions, FDP did not affect the respiratory gas exchange or exercise capacity of patients with exertional claudication.

Aged↗
PubMed1990

Effect of sampling on variability and plateau in oxygen uptake.

To evaluate the effect of the gas exchange sampling interval on variability and plateau in O2 uptake (VO2), 10 subjects underwent steady-state treadmill exercise at 50% maximal VO2 and 6 subjects underwent maximal testing using a ramp protocol. During steady-state exercise, gas exchange data were acquired by using 10 different sampling intervals. The variability in VO2 was greater as the sampling interval shortened (SD = 4.5 ml.kg-1.min-1 for breath-by-breath vs. 0.8 ml.kg-1.min-1 for 60-s samples). The breath-by-breath data suggested a Gaussian distribution, and most of the variability was attributable to tidal volume (51%). During ramp testing, the slope of the change in VO2 (for each sample) was regressed with time. Considerable variability in the slopes was observed throughout exercise, and in each subject the slopes varied about zero, demonstrating both positive and negative values throughout submaximal effort. These observations were made despite the use of large sampling intervals. Shortening the sample resulted in even greater variability. We conclude that 1) the sampling interval can have a major impact on gas exchange data during exercise and 2) considerable variability exists in the slope of the change in VO2 with a consistent change in external work regardless of the sample used, suggesting that a plateau (defined as the slope of a VO2 sample at peak exercise that does not differ significantly from a slope of zero) in VO2 is not a reliable physiological marker for maximal effort.

Adult↗
PubMed1990

Optimizing the exercise test for pharmacological investigations.

Exercise trials in cardiology are often hindered by inconsistent approaches to exercise testing. These inconsistencies include the choice of exercise protocol, exercise end points, points of analysis, and absence or misuse of gas exchange data. Gas exchange techniques greatly enhance the accuracy with which cardiopulmonary function is assessed by exercise. Commonly used protocols are not always appropriate for all patients or all studies. Both cardiovascular disease and the exercise protocol can have an important impact on the relation between changes in work rate and oxygen uptake. Ramp protocols appear to offer the greatest promise for assessing cardiopulmonary function. Analyzing hemodynamic and gas exchange responses at several points submaximally, in addition to those at peak exercise, can add important information concerning the efficacy of a drug. A great deal of confusion continues to hinder the application of the gas exchange anaerobic threshold, and many of the commonly used testing end points are not reliable.

Anaerobic Threshold↗
PubMed1990

Prognostic factors among 185 adults with newly diagnosed advanced Hodgkin's disease treated with alternating potentially noncross-resistant chemotherapy and intermediate-dose radiation therapy.

The initial promising results with alternating chemotherapy regimens (mechlorethamine, vincristine, procarbazine, and prednisone/doxorubicin, bleomycin, vinblastine, and dacarbazine [MOPP/ABVD]; lomustine, melphalan, and vindesine [CAD] plus MOPP plus ABV) combined with intermediate-dose radiation therapy (RT) have been sustained with further follow-up; 82.2% of patients (152 of 185) achieved a complete remission (CR), and overall survival is 71.7% +/- 4.4% at 8 years (median follow-up is 55 months among the survivors). No statistically significant differences were found in CR percentage, CR duration, or survival between stages IIB, IIIB, and IV patients. For that reason, stepwise Cox regression analyses to identify the important prognostic factors were performed on overall survival, tumor mortality, freedom from disease progression, and survival following disease progression. Pretreatment characteristics were also tested for association with the probability of achieving CR, CR duration, and death due to other causes. Characteristics that were consistently associated with an independently unfavorable prognosis were low hematocrit, high serum lactic acid dehydrogenase (LDH), age more than 45 years, inguinal node involvement, mediastinal mass greater than .45 of the thoracic diameter, and bone marrow involvement. Patients with two or more unfavorable characteristics were much more likely to fail treatment (median survival, 62.4 months) than those with none or only one unfavorable factor (greater than 95% survival). This striking difference between the low- and high-risk groups remained even if the comparison was restricted to patients less than or equal to 45 years of age. These results provide a basis for selecting the young patients at high risk of failure for more intensive initial treatment with either autologous bone marrow rescue or hematopoietic growth factors.

Adult↗
PubMed1990

Directions for the future of Menninger children's services: summary of group discussions.

As part of the planning process for a new facility for children and adolescents at Menninger, a working conference on the Future of Mental Health Services for Children and the Role of Psychiatric Hospitalization in the Treatment of Emotionally Disturbed Children was convened August 24-25, 1989, at The Menninger Clinic. Four discussion groups met during the conference, and the authors summarize the central ideas emerging from those groups. They focus on the understanding of the Menninger mission, the need for both a continuum of care and continuity of care, physical requirements of the new facility, economic issues, and the critical role of research.

Adolescent↗
PubMed1990

Effect of fructose 1,6-diphosphate infusion on the hormonal response to exercise.

Exogenous fructose 1,6-diphosphate (FDP), a glycolytic intermediate, has recently been demonstrated to accelerate ATP production, prevent glycogen breakdown, stimulate glycogen synthesis, and synthesize free fatty acids in animals and humans. To assess the effects of FDP on the hormonal and metabolic response to exercise, ten trained males (34 +/- 7 yr) underwent 1 h of continuous exercise at 70% VO2max followed by 20 W.min-1 increments to exhaustion. Two hundred fifty mg.kg-1 body weight FDP or placebo was infused in randomized, double-blind, crossover fashion. No differences were observed in heart rate, blood pressure, gas exchange data, perceived effort, or glucose, insulin, free fatty acid, lactate, beta-hydroxybutyrate, glycerol, and glucagon concentration at rest, during exercise, or upon exhaustion. In contrast to the previously reported bioenergetic effects of FDP under conditions in which glycolysis is impeded (acidosis, hypoxia, and ischemia), FDP did not affect the gas exchange, hormonal, or substrate response to moderately high intensity exercise in healthy normals.

Adult↗
PubMed1989

Optimal sampling interval to estimate heart rate at rest and during exercise in atrial fibrillation.

To investigate the ideal sampling interval for the estimation of heart rate (HR) at rest and during exercise in atrial fibrillation (AF), maximal exercise testing with continuous electrocardiographic acquisition was performed in 10 patients with chronic AF (mean age 66 +/- 4 years) and 10 subjects in normal sinus rhythm (mean age 31 +/- 6 years). Measurements of HR were obtained at 9 different sampling intervals (1, 2, 3, 6, 10, 15, 20, 30 and 60 seconds) at rest and 7 different sampling intervals (1, 2, 3, 6, 10, 15 and 20 seconds) during the last 30 seconds of each minute during exercise. The HR obtained from each interval was compared with true HR (determined by a 4-minute sample at rest and by the last 30 seconds of each minute during exercise). Among patients with AF, large differences were observed between the HR obtained and true HR, both at rest and during exercise, using small sampling intervals. The mean of these differences ranged between 16 +/- 11 beats/min (range 14 to 22) using 1-second sampling intervals and 2.2 +/- 2.0 beats/min (range 1.6 to 4.4) using 20-second sampling intervals during progressive exercise. Variability of the HR obtained from a given random sample was also high when short sampling intervals were used among patients with AF. These observations were contrasted by subjects in normal sinus rhythm, among whom neither variability nor measurement error were influenced remarkably by changing the sampling interval or increasing HR.

Adult↗
PubMed1989

The effect of cardioversion on maximal exercise capacity in patients with chronic atrial fibrillation.

To evaluate the effect of cardioversion on exercise capacity, 11 male patients (59 +/- 8 years) with chronic atrial fibrillation underwent maximal exercise testing using gas exchange techniques before and after successful cardioversion to normal sinus rhythm. Testing was conducted 1 day prior to and a mean of 39 (range 10 to 95) days following cardioversion. Heart rate, blood pressure, and respiratory gas exchange responses were evaluated at rest, at a standard submaximal workload (3.0 mph/0% grade), at the gas exchange anaerobic threshold, and at maximal exertion. Cardioversion resulted in a mean decrease in resting heart rate of 37 beats/min (113 +/- 16 versus 76 +/- 10 beats/min, p less than 0.001). While mean heart rate was approximately 50 beats/min lower following cardioversion at both submaximal stages of exercise p less than 0.001), oxygen uptake was not different. At maximal exercise, heart rate was markedly reduced (192 +/- 24 to 144 +/- 21 beats/min, p less than 0.001) and maximal oxygen uptake was higher (1.86 +/- 0.5 to 2.06 +/- 0.5 L/min, p less than 0.05) after cardioversion. In addition, an improved efficiency of ventilation was observed at exercise levels exceeding 60% of maximal oxygen uptake.

Aged↗
PubMed1989

Increased exercise capacity after digoxin administration in patients with heart failure.

Failure to objectively assess the effect of digitalis on exercise capacity has resulted in controversy regarding its use in patients with chronic congestive heart failure. To clarify this situation, maximal treadmill testing with respiratory gas exchange analysis was performed on 11 patients (mean age 57 +/- 9 years) with chronic congestive heart failure with and without digoxin therapy. Ten of the 11 had a consistent third sound gallop, and the mean ejection fraction of the group was 24 +/- 10%. Rest heart rate was significantly higher (91 +/- 16 versus 102 +/- 16 beats/min; p less than 0.05) and rest systolic blood pressure was significantly reduced in the absence of digoxin (130 +/- 23 versus 121 +/- 15 mm Hg; p less than 0.05). No differences in heart rate or blood pressure were observed during exercise. Significant increases in ventilatory oxygen uptake were observed with digoxin submaximally (3.0 mph, 0% grade), at the gas exchange anaerobic threshold and at maximal exercise (mean increase of 2.6 ml/kg per min; p less than 0.02). An improvement in the estimated ratio of ventilatory dead space to tidal volume (VD/VT), an index of physiologic efficiency, occurred throughout exercise during digoxin therapy, and there was a significant negative correlation between the change in maximal oxygen uptake and change in maximal estimated VD/VT (r = -0.63; p less than 0.05). Thus, digoxin therapy is associated with a significant improvement in exercise capacity in patients with chronic heart failure, most likely due to an improved matching of ventilation to perfusion.

Adult↗