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Biomedical subjects

R T Smith

Publications and source records attributed to R T Smith.

At least 73 records · Page 4Linked to original sources
PubMed1985

The use of exercise testing in children to evaluate abnormalities of pacemaker function not apparent at rest.

The purpose of this study was to evaluate the use of exercise testing in identifying abnormalities of pacemaker function and in confirming set parameters not apparent at rest in children with implanted atrial synchronous physiologic pacemakers. Maximal exercise tests were performed on 24 children (15 boys, 9 girls) from 4.5 to 18 years of age (median = 15) with physiologic pacemakers. The lower rate limit was observed before or following testing in 19 of 24 cases. In each case this correlated with the set lower rate limit. The upper rate limit was reached in 10 of 24 cases and was found to be lower than that programmed in one case in which a long atrial refractory period had limited the upper rate limit. Six children reached the maximum upper rate limit to which their pacemaker could be programmed. No abnormalities of atrial capture or ventricular capture occurred during exercise testing. Ventricular sensing was normal in each case. Atrial sensing was observed to be normal in 15 of the 24 cases. Two patients had decreased atrial sensing with exercise. Reversion to the "noise rate" due to myopotential inhibition was found in seven other cases. Subsequent tests on two of these children showed normal sensing.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1985

Effects of chronic exercise during aging on muscle and end-plate morphology in rats.

Terminal sprouting, myofiber atrophy, and fiber type changes were studied in soleus and distal gastrocnemius muscles of 21- and 26-mo-old rats and in rats who performed treadmill running from 21 to 26 mo. End-plate structure and muscle fiber types were demonstrated by staining for acetylcholinesterase and myosin ATPase activity. Terminal sprouting was expressed as the percentage of end plates with growth configurations. Fiber atrophy was assessed as percentage of small-diameter fibers. In all three groups, the percentage of small-diameter fibers was significantly smaller and the percentage of growth configurations significantly larger in the soleus than in the gastrocnemius. The exercised-soleus group had a significantly higher percentage of growth configurations than the 26-mo controls, which had a higher percentage than the 21-mo controls. Percentages among gastrocnemius groups were not different. Fiber type was similar among gastrocnemius groups. However, the exercised-soleus had significantly more slow-twitch fibers than the controls. These data suggest that the soleus responds differently to chronic exercise during aging than does the gastrocnemius.

Aging↗
PubMed1984

Stress testing for comparison of synthetic patch aortoplasty with resection and end to end anastomosis for repair of coarctation in childhood.

Excellent clinical results have been achieved by both resection with end to end anastomosis and synthetic patch aortoplasty for the repair of coarctation of the aorta in older children. Increasing experience with exercise stress testing in the postoperative evaluation of patients with coarctation has allowed the discovery of less obvious differences between the two procedures. To evaluate these differences further, the stress tests of 50 postoperative patients who underwent coarctation repair were reviewed: 26 patients with end to end anastomosis and 24 with synthetic patch aortoplasty. Twenty normal control subjects were similarly exercised. Systolic blood pressure in the arm and leg was evaluated before and after the test. Heart rate, electrocardiogram and arm blood pressure were monitored during the test. The mean arm systolic blood pressure was higher at all points of measurement in the patients who underwent repair by end to end anastomosis than in the group who underwent patch aortoplasty. These systolic pressure differences reached statistical significance only for standing arm blood pressure before exercise (p less than 0.05) and for supine arm systolic blood pressure immediately after exercise (p less than 0.01). There was no difference in arm-leg pressure gradient between the two study groups before exercise; however, after exercise the group with end to end anastomosis had significantly higher arm-leg pressure gradients (p less than 0.001). Significant differences between the two types of repair not apparent at rest were found immediately after exercise. The long-term prognostic importance of an exercise-induced arm-leg blood pressure gradient remains to be determined. However, exercise stress testing is sensitive in demonstrating these differences.

Adolescent↗
PubMed1984

An evaluation of the referral and rehabilitation process among the minority handicapped.

This study examines factors believed to be predictive of the referral and rehabilitation process in this country. Using the Fiscal Year 1978 data from the Rehabilitation Services Administration, the study examines two general hypotheses found in the literature: (1) that minority status is likely to be a key determinant in the referral and rehabilitation process, and (2) that selected socio-demographic factors along with social supports and disability condition are likely to reveal direct influences on the referral and rehabilitation process. Multiple regression was used for the analysis. The analysis of the study revealed that the independent variables, for the most part, had either a direct or indirect effect on the outcome of referral and rehabilitation. More specifically, the results suggest that bias exist in the referral and rehabilitation process.

Adult↗
PubMed1984

Regulation of TCGF production in T cells. II. Early membrane events after anti-Thy-1 binding by the TCGF-producing T lymphoma EL-4 G-12.

The T cell lymphoma line EL-4 G-12 produces large quantities of TCGF (IL 2) shortly after exposure to anti-Thy-1 and cross-linking reagents. Early surface events that initiate nonconstitutive synthesis and secretion have been examined by fluorescent microscopy, EM analysis, flow cytometry of anti-Thy-1, and measurements of membrane polarization. The data show that anti-Thy-1 binding leads to immediate and rapid endocytosis and shedding of the antibody molecules, but with no change in membrane potential. Cross-linking of the anti-Thy-1 results in stabilization and accumulation of the antibody on the surface, and rapid hyperpolarization. The data suggest that cross-linking of ligand antibody interactions at the surface is a regulatory event involved in initiation of the signal for TCGF synthesis and secretion.

Animals↗
PubMed1983

Heterogeneity of an anti-H-2 I-A response as determined by cloned T cell reactivity.

T lymphocytes activated against the I-Aq gene product in primary mixed leukocyte culture (MLC) exhibit an unusually strong cross-reactivity against all third-party stimulating strains tested in secondary MLC. Through the development of anti-I-Aq clones, this cross-recognition has been shown to result from the activation of a heterogeneous T lymphocyte population bearing receptors that recognize the I-Aq gene product differently, yet specifically. The determination of functional activities of the anti-I-Aq cloned cells, e.g., lymphokine production and ability to induce lethal graft-vs-host disease, suggested even further heterogeneity in T cells grouped according to their similar cross-reactive pattern.

Animals↗
PubMed1982

Mechanisms controlling TCGF production by cloned sublines of EL-4 azgr in response to stimulation by anti-Thy-1 antibody.

The effect of xenogeneic anti-Thy-1 antibody on T cell growth factor (TCGF) production by T lymphoma cell lines has been examined as a model system for T cell activation. EL-4 G12 (a cloned subline of the producer EL-4 azgr cell line) produced TCGF when stimulated by a high concentration of anti-Thy-1, but none was induced by low concentrations of anti-Thy-1. Large amounts of TCGF were produced when these cells were cultured with Fc-receptor positive (FcR+) accessory cells. TCGF production by EL-4 G12 showed dose response kinetics similar to TCGF production by anti-Thy-1-stimulated, purified normal spleen T cells. Goat anti-rabbit IgG (GaRIG) and protein A substituted for this accessory helper effect, but neither FcR+ cells nor Protein A worked when (Fab')2 anti-Thy-1 was used instead of IgG anti-Thy-1. Anti-T-200 monoclonal antibody inhibited anti-Thy-1-induced TCGF production by EL-4 G12 and accessory cells. Phorbol myristic acetate and lymphocyte-activating factor also substituted in part for the accessory cell help. The data suggest there are at least 2 different accessory cell help mechanisms in anti-Thy-1-induced TCGF production, anti-Thy-1-bound membrane aggregation either by GaRIG, Protein A or FcR, and a LAF-dependent mechanism.

Animals↗
PubMed1981

Anti-Thy-1-mediated T cell activation. Role of soluble factors and expression of interleukin 2 receptors on T cells.

Rabbit anti-Thy-1 antibody bound to T cells induces the appearance of T cell growth factor (interleukin 2, IL2) receptors and the production of IL2. IL2 receptors induction by this means occurs within a short time span, and independent of any demonstrable accessory cell. A source of exogenous or endogenous IL2 is apparently the only requirement for proliferation after these receptors are expressed. IL2 production, on the other hand, is accessory cell-dependent, and this help is mediated via Fc receptors on the accessory cell. IL2 production in this model is demonstrable at 4-6 h, or earlier, and is proliferation-independent. X-irradiation actually augments apparent IL2 production. The data are consistent with the hypothesis that a differentiated subset of T cells in any mixed population is responsible for IL2 production.

Animals↗
PubMed1981

Immune response to chemically induced tumours: correlation of responding cell class with in vivo inhibition of tumour growth.

Lymphoid cells stimulated by soluble tumour antigens in the MCA-induced murine fibrosarcoma system have been identified by subclass and protective capacity in adoptive syngeneic hosts. Lymph-node or spleen cells taken at weekly intervals after inoculation of syngeneic chemically induced fibrosarcomas were enriched by 3 methods in T, B, and "null" cell subclasses, and assayed for proliferative kinetics in response to soluble membrane antigens. The stimulated subpopulations were found to be heterogeneous, their composition varying with time and tumour burden. Initial proliferative responses after tumour inoculation were limited to the T-enriched subpopulation. Later during tumour growth, T, B and null cell fractions were vigorously and equally stimulated by tumour antigen. The ability of the same T, B or null-cell subpopulations to inhibit tumour growth was measured in adoptive hosts by a modified Winn assay. Only the T-cell subpopulation responding to tumour antigen in vitro effectively and consistently retarded tumour growth in vivo. In contrast to the shared specificities on syngeneic tumours identified by the proliferative assay, tumour-growth inhibition was limited to the specific tumour borne by the cell donor.

Animals↗
PubMed1981

Hypoxemia and pulmonary gas exchange during hemodialysis.

With measured values of arterial blood gas tensions, of expired respiratory gas fractions, and volume of the expired ventilation, the determinants of alveolar oxygen tension (PAO2) were used to evaluate their influence on the development of the arterial hypoxemia that occurs in spontaneously breathing patients undergoing hemodialysis using an acetate dialysate. Dialysis produced no significant changes in the alveolar-arterial O2 tension gradient (AaDO2). The extracorporeal dialyzer removed an average of 30 ml.m-2.min-1 of CO2. Accordingly the pulmonary gas exchange ratio (R) dropped from a mean predialysis value of 0.81 to 0.62 (P less than 0.001). The arterial CO2 tension remained constant throughout, whereas the minute ventilation, both total (P less than 0.01) and alveolar (P less than 0.01), decreased during dialysis. This decrease in ventilation accounts for more than 80% of the fall in PAO2. During dialysis there was a decrease (P less than 0.001) in arterial oxygen tension (PaO2), which varied among the individuals from 9 to 23% of control. During the postdialysis hour PaO2 returns to control values concomitant with increase in ventilation. The quantitative gas exchange relationships among R, alveolar ventilation, and AaDO2 predict the PaO2 values actually measured.

Adult↗
PubMed1980

Mitogen-initiated synthesis and secretion of T cell growth factor(s) by a T-lymphoma cell line.

Of 12 T-lymphoma cell lines investigated, one line, EL-4 azgr (Thy-1+, Lyt-1+, Lyt-2-3-,Ia-, T-200+, sIg-, and FcR-) and, to a lesser extent, the parental cell line, EL-4, produced T cell growth factor(s) (TCGF) when stimulated by the T-cell mitogen concanavalin A (Con A). Induced production of TCGF-E was detected by 6 h and maximal at 18-24 h. Purified TCGF-E from this source had an approximately 30,000 mol wt and the biological activity of TCGF produced by whole spleen cells, including: augmentation of T cell-mitogen responses, cytotoxic T lymphocyte (CTL) proliferation support dependence, augmented generation of CTL, lack of strain specificity, and failure to stimulate resting T cells. TCGF-E is neither synthesized or secreted by this lymphoma cell line unless stimulated by Con A. X-irradiation up to 7,000 rad failed to inhibit synthesis and secretion. These observations have a practical application in providing a relatively homogeneous clonal cell product for T cell culture support and for structural and functional studies of the TCGF molecule(s). They suggest also a model for examining mechanisms of triggering production and secretion of a regulatory molecule that controls T cell functions.

Animals↗
PubMed1980

Use of social resources by the disabled: primary and secondary group influences.

Use of social resources by the disabled in the rehabilitation and recovery process has been viewed primarily as those derived from formal agencies and services. However, the more typical rehabilitation model suggests a negotiated process in which the active patient utilizes not only the formal service system of support (secondary group resources) but other resources that may be available to him, including his personal assets and those sources derived from his informal social network (primary group resources). This study examines the influence of primary and secondary group resources on need levels, i.e., severity of disability, among adult disabled males using data obtained from a national survey in the U.S.A. The availability and use of primary social resources will likely have a positive effect on the disabled's status--on the assumption that these resources mitigate the adverse effects of chronic health conditions. Use of secondary social resources will tend to reflect need and thus more likely be associated with increased severity of disability. The findings are suggestive in that selective personal and social resources of the individual continue to play a role; however, family and kin ties as part of the socially supportive network are less clearly identified from this study. Secondary social resources as formal service supports tend to play a limited role in disability. The implications of these findings are discussed in terms of effective utilization of primary social resources that are supportive of an individual's need, and appear to enhance recovery.

Adult↗
PubMed1980

Effect of in vitro hemolysis on assay of plasma catecholamines and DOPA.

I analyzed for free and sulfate-conjugated catecholamines and DOPA (3,4-dihydroxyphenylalanine) in four aliquots of a single plasma pool with use of Upjohn's "Cat-A-Kit" (catecholamines radioenzymatic assay kit [3H]. One aliquot was a clear plasma control; the others were supplemented with different concentrations of lysed human erythrocytes, to investigate possible interference by hemolysis with analysis for norepinephrine, epinephrine, dopamine, or DOPA in plasma. I observed no statistically significant difference that could be attributed to the degree of hemolysis between control and treatment groups for DOPA or any catecholamine fraction. Hemolysis in plasma from improper collection or processing techniques apparently does not preclude accurate and precise quantitation of free or sulfate-conjugated catecholamines or DOPA with the Cat-A-Kit.

Blood Specimen Collection↗