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Biomedical subjects

R J McCarter

Publications and source records attributed to R J McCarter.

At least 55 records · Page 3Linked to original sources
PubMed1993

Cardiovascular reflex abnormalities in children and adolescents with diabetes mellitus.

OBJECTIVE: To assess the usefulness of specific cardiovascular reflex tests in childhood and to estimate the prevalence of cardiovascular reflex abnormalities among children with IDDM. In adults, abnormal cardiovascular reflexes are a frequent complication of diabetes, associated with increased morbidity and mortality. RESEARCH DESIGN AND METHODS: We measured heart-rate responses to deep breathing and standing in ambulatory children with and without IDDM between 6-19 yr of age. A subgroup of the IDDM patients was retested after 1 yr. RESULTS: We found the best techniques for detecting cardiovascular reflex abnormality in children were as follows: to record heart-rate responses to deep breathing either as the change in heart rate corrected for inspiratory heart rate or as the ratio of R-R intervals during expiration and inspiration; and to use the Maximum-minimum ratio for heart-rate responses to standing. HR-DBc was lower in diabetic than nondiabetic children (28.6 +/- 9.2% [n = 248] vs. 33.6 +/- 6.8% [n = 60]; P < 0.0005). Similarly, E:I was lower in children with IDDM than control subjects (1.42 +/- 0.19 [n = 248] vs. 1.52 +/- 0.15 [n = 60]; P < 0.0005). In the IDDM group, 21% of the children had abnormal HR-DBc or E:I responses. HR-STND M/m was lower in children with IDDM than control subjects (1.28 +/- 0.20 [n = 167] vs. 1.38 +/- 0.22 [n = 45]; P < 0.014). Among children with IDDM, 11.4% had abnormal HR-STND M/m responses. Overall, 29% of IDDM children tested abnormal in either HR-DBc or HR-STND M/m; 3% were abnormal in both tests. We found no correlation of HbA1c levels (n = 74) or duration of diabetes with either HR-DB, expiration to inspiration (n = 248), or HR-STND M/m (n = 167). In patients who were reevaluated after 1 yr we found a high correlation of the first and repeat HR-DBc tests (r = 0.47, n = 75, P < 0.0001), E:I (r = 0.53, n = 75, P < 0.0001), and HR-STND M/m (r = .49, n = 37, P < 0.002), but no evidence of an increased number of children with cardiovascular reflex abnormality. CONCLUSIONS: With easily performed HR-DB and HR-STND tests, we detected cardiovascular reflex abnormality in 29% of children with IDDM. We found no correlation of changes in HR-DB and HR-STND with HbA1c or duration of diabetes. These tests provide an objective clinical measurement to monitor autonomic neuropathy in children with diabetes.

Adolescent↗
PubMed1993

Effect of third-party reimbursement on use of services and indexes of management among indigent diabetic patients.

OBJECTIVE: To determine the effect of third-party reimbursement on the use of services and indexes of diabetes-related health management among inner-city diabetic patients. RESEARCH DESIGN AND METHODS: Adult diabetic patients (n = 158; 67% women, 33% men) from an inner-city diabetes clinic were categorized by level of third-party medical coverage: complete reimbursement for all services (full); partial reimbursement (part); and no reimbursement (none). Patients were followed for 13 mo. Use of billable medical services, diabetes clinic visits, emergency room visits, and hospital admissions were recorded. Use of a free, day-time diabetes telephone hot line was also documented. Indexes of diabetes-related health management, HbA1, blood pressure, and weight were compared from the beginning and the end of the study. Diabetes complications were scored and tabulated. RESULTS: Univariate analysis showed that patients with full reimbursement were more likely to use services than patients without reimbursement. When the combined effects of reimbursement status, age, sex, type of diabetes, and diabetes complications on use of services were analyzed together in a multivariate analysis, complications was the best predictor of admissions to the hospital and whether a patient called the hot line. IDDM patients and patients with full reimbursement were most likely to have an emergency room visit. Age was the best predictor of diabetes clinic attendance. No difference was noted in blood pressure or weight among the reimbursement groups at the beginning and end of study. However, the trend was toward (P < 0.05) an increase in HbA1 in the none group. CONCLUSIONS: Among inner-city diabetic patients, multiple factors influence use of medical services. Indigent diabetic patients without third-party reimbursement were observed to have a rise in HbA1. These factors should be taken into consideration when planning strategies to prevent diabetes complications and the most effective allocation of health-care resources.

Adult↗
PubMed1993

Black-white differences in stroke risk among young adults.

BACKGROUND AND PURPOSE: Little information is available regarding black-white differences in stroke incidence in young adults. METHODS: Cerebral infarction and intracerebral hemorrhage rates among adults 15 to 44 years of age were studied in Baltimore City and Baltimore County for 1988. Diagnoses were based on neurologist review of data obtained from medical records at 41 hospitals by neurological nurses. RESULTS: The cerebral infarction rates per 100,000 were 22.8 for black males, 10.3 for white males, 20.7 for black females, and 10.8 for white females. The intracerebral hemorrhage rates per 100,000 were 14.2 for black males, 4.6 for white males, 4.8 for black females, and 1.5 for white females. CONCLUSIONS: Blacks had significantly (P < .05) higher rates than whites for both cerebral infarction and intracerebral hemorrhage. Cerebral infarction rates are high in Baltimore compared with Florence, Italy, or Stockholm, Sweden.

Adolescent↗
PubMed1993

Shortening-length diagram: a new method of modeling skeletal muscle performance.

Muscle shortening is usually characterized in terms of force-velocity and length-active tension properties. We have examined a third relationship, that between shortening and initial length to further characterize muscle performance. This analysis shows that optimal shortening is achieved at a length (Ls) different from the length (Lo) of optimal tension development. Moreover, the analysis reveals discrepancies between results expected (using classical modeling) and experimental findings and these discrepancies increase with age. This effect of age on shortening has not been previously identified. Diaphragm muscle strips were dissected from male Fischer 344 rats of 3 and 24 months of age. Muscles were subjected, in vitro, to isotonic loads of either 30% or 50% of peak isometric tension (Po*) and shortened from initial lengths ranging from 80% to 130%Lo. The relationship between shortening and initial length was fitted by a second order polynomial using linear regression analysis. Results at 30% P/Po* indicate a difference in ability to shorten of 7% at Lo between muscles of young and elderly rats. The age-related change was enhanced under a load of 50% P/Po*, with a 46% difference in ability to shorten between young and old rats. The results show an age-related decrease in shortening of the diaphragm that is not predicted using classical muscle mechanics. Factors other than the length-tension relation and load must therefore be explored to explain decrements of shortening with age.

Aging↗
PubMed1993

Predictors of frequent middle school health room use.

Disproportionately high use of school health room (HR) services by small groups of users has been reported. This study investigated predictors of frequent HR use in two suburban middle schools involving 1089 students who made at least one HR visit during a single academic year. Subsets of high and low users were compared using logistic regression. Predictor variables included gender, grade, academic ability, and existence of a chronic health condition. Although demographic characteristics of the study schools varied significantly, a pattern of increasing HR use associated with progressive lowering of academic ability was demonstrated in both schools. Existence of a chronic health condition was associated with increased HR use, even when controlling for routine medication visits. Gender and grade were not predictive. These findings suggest that HR use reflects more than medical concerns. Patterns of HR use by students with chronic health conditions deserve additional study to determine whether current strategies to meet their needs are adequate.

Adolescent↗
PubMed1992

Differential expression of muscular dystrophy in diaphragm versus hindlimb muscles of mdx mice.

Contractile properties of diaphragm (DIA) from mdx and control mice were compared with those of hindlimb muscles [soleus (SOL) and extensor digitorum longus (EDL)] in vitro. Mice ranged in age from 2 weeks to 1.5 years. Muscles were directly stimulated and properties measured were: contraction time, half-relaxation time, active tension per unit area, fatigue index, and maximal velocity of shortening (Vmax). Active tension decreased significantly with age in mdx DIA but not in control DIA. SOL and EDL active tensions were less in mdx than control over the whole age range and did not decrease with age. Vmax was decreased in mdx DIA, but not in mdx SOL or EDL. These results demonstrate that DIA is more affected by muscular dystrophy than hindlimb muscles. Since many Duchenne patients exhibit respiratory distress, this differential expression of dystrophy in diaphragm, as compared to limb muscles, may have important clinical implications.

Animals↗
PubMed1992

Dietary restriction alters characteristics of glucose fuel use.

A longitudinal study of plasma glucose and insulin concentrations in ad libitum fed and dietary restricted male F344 rats was carried out. The life span diurnal pattern of plasma glucose concentration was such that through most of the day dietary restricted rats have significantly lower plasma glucose levels than ad libitum fed rats. Throughout the life span, dietary restricted rats maintain mean 24-hour plasma glucose concentrations about 15% below those of ad libitum fed rats. Plasma insulin levels are maintained in dietary restricted rats at about 50% of the levels in ad libitum fed rats. Although plasma glucose and insulin levels are lower, dietary restricted rats use glucose fuel at the same rate per unit of metabolic mass per day as rats fed ad libitum. While these findings are consistent with the glycation hypothesis of aging and with our hypothesis that dietary restriction retards the aging processes by altering the characteristics of fuel use, they do not establish the validity of either. It is possible that this effect of dietary restriction on carbohydrate metabolism plays no role in its antiaging action. Further studies are required to define the role of these altered characteristics of carbohydrate metabolism in the aging processes.

Animals↗
PubMed1992

Energy metabolism and aging: a lifelong study of Fischer 344 rats.

Metabolic rate is widely regarded as an important component of aging processes, but variation of metabolic rate with age has not been well characterized. The purpose of the present study was to measure daily metabolic rate under usual living conditions over the lifespan of barrier-maintained Fischer 344 rats. In addition, effects of life-prolonging food restriction were assessed. Metabolic rate was measured indirectly by analysis of gas entering and leaving standard rodent cages over a 24-h period. Group A rats were fed ad libitum. Group B rats were fed 60% of ad libitum intake from 6 wk of age. Both group A and group B rats exhibited variation of metabolic rate per unit lean mass over the lifespan, with metabolic rate decreasing from 6 to 18 mo and then increasing from 18 to 24 mo of age. Results show estimates of lifetime energy expenditure in rats should take account of variability of metabolic rate and confirm the life-prolonging action of food restriction is not a consequence of reduced metabolic rate per unit metabolic mass. Rather, restricted rats are able to sustain appropriate fluxes of nutrients and appropriate metabolic rate under conditions of fuel utilization which promote maintenance of cellular homeostasis.

Aging↗
PubMed1990

Maternal diabetes and cardiovascular malformations: predominance of double outlet right ventricle and truncus arteriosus.

Most studies on the relationship of maternal diabetes to cardiovascular malformations (CVM) have been prospective investigations of pregnancy outcome and therefore could not identify associations with rare cardiac lesions. The results of a retrospective study shed new light on the risks of specific cardiac defects in diabetic pregnancies. The Baltimore-Washington Infant Study, a population-based case-control investigation of CVM, provides information on maternal diabetes reported in personal interviews. Among 2259 mothers of cases, 35 (1.5%) reported diabetes present before pregnancy (called "overt") and 95 (4.2%) reported diabetes only during pregnancy (called "gestational"). Among 2,801 mothers of controls, 14 (0.5%) had overt diabetes and 83 (3.0%) had gestational diabetes. Malformation-specific risks were expressed as odds ratios (OR) with 99.5% confidence intervals (CI). The strongest associations with overt maternal diabetes were found with double outlet right ventricle (OR 21.33; 99.5% CI 3.34, 136.26), and truncus arteriosus (OR 12.81; 99.5% CI 1.43, 114.64). No significant diagnosis-specific associations were found with gestational diabetes. Non-cardiac malformations were present in 23% of infants with CVM whose mothers had overt diabetes and in 26% of infants with CVM whose mother had gestational diabetes, in 32% of infants with CVM whose mothers did not have diabetes, and in 4% of controls. Double outlet right ventricle and truncus arteriosus are malformations dependent upon neural-crest-cell-derived ectomesenchymal tissues; these are precisely the conotruncal abnormalities that result from experimental ablation of the neural crest in chick embryos. The association with diabetes suggests a further etiologic link between these two lesions.

Case-Control Studies↗
PubMed1990

Age-related changes in skeletal muscle function.

This review examines current evidence for the existence of aging processes in skeletal muscle fibers. Experimental data demonstrating changes with age in nerve-muscle interaction, excitation-contraction coupling, mechanical properties and muscle energetics are discussed, with emphasis on factors in addition to aging which might account for the observed results. The effects of dietary restriction, exercise and disease on age-related changes in muscle function are also discussed. Results of recent studies highlight the need to establish the health status of subjects and animals used for aging research as well as the need to obtain data from a wide variety of muscles. Although marked decline of muscle performance with age is documented by early studies, recent work indicates that at least some muscles of healthy individuals and animals do not show an age-related decline in function or an impaired ability to respond to exercise. Decreased physical performance in the elderly may be due to factors extrinsic to aged skeletal muscle fibers.

Aging↗
PubMed1990

Health care costs for employed hypertensives.

Health care insurance claims were used to track costs associated with hypertension for an employed population. Employees were classified as hypertensive (n = 373), high normal (n = 363), or normotensive (n = 2,411) on the basis of hypertension screening done at the worksite. Claims activity was monitored for the three groups during a three-year period, including periods before, during, and after the screening done at the worksite. The average amount claimed per employee was significantly higher for the hypertensives as compared with the normotensives or high normals, even after adjustment for age, race, sex, salary, marital status, and duration of insurance coverage. There was no significant difference in the average amount claimed per employee between high normals and normotensives. The health care costs for hypertensives are estimated to be about 80% more than those for normotensives. Hospital, physicians, and nursing care accounts for about 50 percentage points of this increment while the remaining 30 percentage points derive from drug costs.

Adult↗
PubMed1990

Metabolic effects of aminophylline in weanling rats.

Methylxanthines are commonly used to treat asthma and apnea in infants and children. A physiological effect of these compounds is an elevation of the metabolic rate, but the mechanism of this increase is unclear. We have investigated the hypothesis that this elevation of metabolic rate in young animals is in part due to increased physical activity. Metabolic rate and spontaneous physical activity of weanling Fischer 344 rats were measured before and during 2 days of aminophylline administration. Our results show increased metabolic rate measured over 23 h, concomitant with increased activity during treatment. Resting metabolic rate was not elevated. The results suggest that increased physical activity plays a major role in increasing metabolic rate during aminophylline treatment. Metabolic rate returned to control levels on the 2nd day of treatment despite a smaller but still significant elevation in physical activity. This suggests development of tolerance to the effects of aminophylline on activity together with adaptation to the metabolic effects of this drug.

Aminophylline↗
PubMed1989

Regional distribution of fiber types in developing baboon diaphragm muscles.

Fiber type distribution and mean fiber area were determined for seven sites in diaphragm muscles of premature (140 days gestation), full-term (180 days gestation), and adult baboons. Within a group, data did not differ significantly amongst the seven sites. The diaphragm of premature animals had a large proportion [56(+/- 2)%] of type IIc fibers, smaller proportions of type I, IIo, and IIh fibers [16(+/- 2), 21(+/- 1), and 7(+/- 2)%, respectively], and no type IIg fibers. Full-term animals had fewer type IIc [2(+/- 1)%] fibers, greater proportions of type I [46(+/- 2)%], IIh [23(+/- 1)%], and IIg [11(+/- 1)%] fibers, and a similar proportion of type IIo fibers [17(+/- 1)%]. Diaphragm from adult baboons had similar proportions of type IIh, IIg, and IIc fibers in females [39(+/- 4), 20(+/- 2), 1(+/- 1), 41(+/- 5), and 1(+/- 1)%] and males [48(+/- 2), 16 (+/- 1), 0(+/- 0), 36(+/- 2), and 3(+/- 2)%]. Fiber area for premature [143(+/- 9), 210(+/- 15), 231(+/- 15), and 156(+/- 16) microns2 for type I, IIo, IIh, and IIc fibers], newborn [317(+/- 32), 374(+/- 36), 468(+/- 42), 498(+/- 43), and 322(+/- 37) microns2 for type I, IIo, IIh, IIg, and IIc fibers], and for type I, IIo, IIg, and IIc fibers from adult female [1,759(+/- 130), 2,365(+/- 284), 5,026(+/- 742), and 1,843(+/- 111) microns2] and adult male [2,513(+/- 221), 3,987(+/- 267), 6,102(+/- 376), and 2,833(+/- 151) microns2] baboons indicated growth which correlated with body weight. Our results also show that metabolic and contractile enzymes develop normally, but growth of respiratory muscle fibers is arrested, during 10 days following premature birth.

Animals↗
PubMed1989

Metabolic rate and aging: effects of food restriction and thyroid hormone on minimal oxygen consumption in rats.

Metabolic rate (MR) is widely regarded as an important component of aging processes. Decreased MR has been suggested as a possible mechanism of the life-prolonging action of food restriction in rodents and recent reports show lowered plasma levels of tri-iodothyronine (T3), a regulator of MR, in food restricted rodents. In order to study the relationship between MR, food restriction, thyroid status and aging we measured the Minimal Oxygen Consumption (MOC) of barrier-raised Fischer 344 male rats fed ad libitum (Group A) or fed a diet restricted to 60% of ad libitum intake (Group R). Oxygen consumption (VO2) was also measured over 24 hr to establish the relationship between MOC and VO2 under usual living conditions. Results show: (i) MOC declines with age in both groups of rats; (ii) there is no difference in MOC of Groups A and R rats; (iii) MOC of Group R rats is significantly more sensitive to doses of injected T3 than MOC of Groups A rats at all ages; and (iv) MOC of both groups of rats is significantly lower than the lowest VO2 recorded under usual living conditions. The results indicate that a decrease in MR is not the mechanism by which food restriction retards aging processes in rodents. The results also suggest no change in thyroid status due to restriction of food although there is increased sensitivity to T3 in food restricted rats.

Aging↗