Delayed cortical development in fetuses with complex congenital heart disease

Neurologic impairment is a major complication of complex congenital heart disease (CHD). A growing body of evidence suggests that neurologic dysfunction may be present in a significant proportion of this high-risk population in the early newborn period prior to surgical interventions. We recently provided the first evidence that brain growth impairment in fetuses with complex CHD has its origins in utero. Here, we extend these observations by characterizing global and regional brain development in fetuses with hypoplastic left heart syndrome (HLHS), one of the most severe forms of CHD. Using advanced magnetic resonance imaging techniques, we compared in vivo brain growth in 18 fetuses with HLHS and 30 control fetuses from 25.4-37.0 weeks of gestation. Our findings demonstrate a progressive third trimester fall-off in cortical gray and white matter volumes (P < 0.001), and subcortical gray matter (P < 0.05) in fetuses with HLHS. Significant delays in cortical gyrification were also evident in HLHS fetuses (P < 0.001). In the HLHS fetus, local cortical folding delays were detected as early as 25 weeks in the frontal, parietal, calcarine, temporal, and collateral regions and appear to precede volumetric brain growth disturbances, which may be an early marker of elevated risk for third trimester brain growth failure.

Improvement in cognitive function after right temporal arteriovenous malformation excision

A patient is presented in whom right temporal AVM excision led to improved cognitive function. Neuropsychological assessment showed a significant postoperative improvement in Performance IQ (p = < 0.05), Full Scale IQ (p = < 0.05), and clinically in visual memory (p = < 0.10). Reversal of vascular steal may lead to increases in cognitive function. We recommend that patients undergoing AVM excision have a complete neuropsychological evaluation.

Prophylactic chlorhexidine oral rinse decreases ventilator-associated pneumonia in surgical ICU patients

BACKGROUND

Pneumonia is one of the most common nosocomial infections in hospitalized patients. The risk of nosocomial pneumonia increases with age, severity of acute illness and preexisting co-morbid conditions. Ventilator-associated pneumonia (VAP) significantly increases morbidity, length of stay, resource utilization and mortality. The purpose of this study was to determine whether adherence to a ventilator weaning protocol (WP) and the use of chlorhexidine gluconate (CH) oral rinse for oral hygiene would decrease the incidence of VAP in surgical ICU patients.

METHODS

A prospective study was conducted over a period of 10 months (October 1998-July 1999) in surgical ICU patients requiring mechanical ventilation (n = 95). During the first 5 months, a WP was applied to all patients requiring mechanical ventilation. During the following 5 months, a CH 0.12% oral rinse administered twice daily was added to the protocol, initiated on ICU admission in all intubated patients. The data collection included age, gender, race, risk factors, co-morbid conditions, severity of the acute illness (APACHE II) at admission, duration of ventilation, ICU and total-hospital length of stay, and incidence of VAP and in-hospital mortality rates. Both WP and WP+CH groups were compared using the National Nosocomial Infection Surveillance (NNIS) and hospital databases as historic controls.

RESULTS

The institution of the WP alone led only to a slight decrease in the incidence of VAP but a significant reduction in the median duration of mechanical ventilation by 40% (4.5 days, p < 0.008). The addition of CH to the WP led to a significant reduction and delay in the occurrence of VAP (37% overall, 75% for late VAP, p < 0.05). The median duration of mechanical ventilation in this group was similar to that of the WP group. There was no significant difference in the overall hospital or ICU length of stay between the groups.

CONCLUSIONS

Improved oral hygiene via topical CH application in conjunction with the use of a WP is effective in reducing the incidence of VAP and the duration of mechanical ventilation in surgical ICU patients.

Systemic inflammatory response syndrome score at admission independently predicts infection in blunt trauma patients

BACKGROUND

Systemic inflammatory response syndrome (SIRS) score has been demonstrated to be an accurate predictor of outcome in critical surgical illness. To our knowledge, there is a paucity of data using SIRS score as a tool to predict posttraumatic infection. Our goal was to determine whether the severity of SIRS score at admission is an accurate predictor of infection in trauma patients.

METHODS

Prospective data were collected on 4,887 blunt trauma patients admitted to a primary adult resource center designated trauma center over an 18-month period. Patients were stratified by age and Injury Severity Score (ISS). SIRS score was calculated at admission. SIRS was defined as an SIRS score > or = 2. Each patient was screened for infection by an infectious disease specialist. Those at high risk for infection were then monitored daily throughout their hospitalization. Centers for Disease Control and Prevention guidelines were used to diagnose infection.

RESULTS

Of the 4,887 patients, 1,850 (38%) were admitted > 24 hours and evaluated for subsequent infection (mean ISS, 16 +/- 9; mean age, 43 +/- 19, SD). Thirty-one percent (577) of the patients acquired an infection. The mean hospital length of stay (20.2 days vs. 6.5 days) and mortality (7.8% vs. 2.7%) were significantly greater in the infected group (p < 0.001). Of the four SIRS variables (temperature, heart rate, white blood cell count, and respiratory rate), hypothermia and leukocytosis were the most significant predictors of infection (p < 0.001) when adjusted for age and ISS. SIRS scores of > or = 2 were increasingly predictive of infection when analyzed by multiple logistic regression analysis.

CONCLUSION

An admission SIRS score of > or = 2 is a significant independent predictor of infection and outcome in blunt trauma. Daily SIRS scores may be a meaningful method of assessing postinjury risk of infection, and may initiate earlier diagnostic intervention for determination of infection.

Metabolic adaptations in skeletal muscle overexpressing GLUT4: effects on muscle and physical activity

To understand the long-term metabolic and functional consequences of increased GLUT4 content, intracellular substrate utilization was investigated in isolated muscles of transgenic mice overexpressing GLUT4 selectively in fast-twitch skeletal muscles. Rates of glycolysis, glycogen synthesis, glucose oxidation, and free fatty acid (FFA) oxidation as well as glycogen content were assessed in isolated EDL (fast-twitch) and soleus (slow-twitch) muscles from female and male MLC-GLUT4 transgenic and control mice. In male MLC-GLUT4 EDL, increased glucose influx predominantly led to increased glycolysis. In contrast, in female MLC-GLUT4 EDL increased glycogen synthesis was observed. In both sexes, GLUT4 overexpression resulted in decreased exogenous FFA oxidation rates. The decreased rate of FFA oxidation in male MLC-GLUT4 EDL was associated with increased lipid content in liver, but not in muscle or at the whole body level. To determine how changes in substrate metabolism and insulin action may influence energy balance in an environment that encouraged physical activity, we measured voluntary training activity, body weight, and food consumption of MLC-GLUT4 and control mice in cages equipped with training wheels. We observed a small decrease in body weight of MLC-GLUT4 mice that was paradoxically accompanied by a 45% increase in food consumption. The results were explained by a marked fourfold increase in voluntary wheel exercise. The changes in substrate metabolism and physical activity in MLC-GLUT4 mice were not associated with dramatic changes in skeletal muscle morphology. Collectively, results of this study demonstrate the feasibility of altering muscle substrate utilization by overexpression of GLUT4. The results also suggest that as a potential treatment for type II diabetes mellitus, increased skeletal muscle GLUT4 expression may provide benefits in addition to improvement of insulin action.

Comparative effects of three beta blockers (atenolol, metoprolol, and propranolol) on survival after acute myocardial infarction

The beneficial impact of beta blockade after an acute myocardial infarction (AMI) is clear, but beta-adrenergic blockers differ in multiple characteristics, including lipophilicity and selectivity. The impact of these factors on the effects of beta blockade is unknown. We therefore compared the effects of different beta blockers on mortality after AMI. Charts of 201,752 patients with AMI were abstracted by the Cooperative Cardiovascular Project, a quality assurance program sponsored by the Health Care Financing Administration. Of the 69,338 patients prescribed beta blockers, we compared mortality of patients receiving different beta-adrenergic blockers using the Cox proportional-hazards model accounting for multiple factors that might influence survival. The mortality rates of the 2 selective agents, metoprolol and atenolol, were virtually identical (13.5% and 13.4% 2-year mortality, respectively). Compared with metoprolol, patients discharged on propranolol had a slightly increased mortality (15.9% 2-year mortality), which may be related to undetected differences at baseline. Survival with all of the drugs was superior to the 23.9% 2-year mortality seen in patients not receiving beta blockers. Beta blockade overall was associated with a 40% improvement in survival. Although the use of beta blockade after AMI has major prognostic importance, the present study suggests that the specific beta blocker chosen will have little influence on mortality.

Age, fatigue, and excitation-contraction coupling in masseter muscles of rats

The purpose of this study was to determine if masseter muscle endurance changes with increasing age and, if so, to examine mechanisms of fatigue. Characteristics of fatigue were measured under isometric conditions using high-frequency stimulation of anterior deep masseter (ADM) muscles of male Fischer 344 rats, 5 to 24 months old, and fed a hard (HD) or a soft (SD) diet. Potentiating effects of caffeine on ADM muscle performance in vitro were also examined. Fatigability increased by 48% with age in muscles of HD rats. Muscles of SD rats were highly fatigable at all ages. Increased HD fatigability was associated with significantly decreased concentrations of Na+/K+-adenosine triphosphatase (22%) and decreased responsiveness to caffeine postfatigue (29%). The pH levels decreased similarly in fatigued muscles of all groups. We conclude that the age-related increase in fatigability is associated with alterations in excitation-contraction coupling mechanisms. However, differences between SD and HD on ADM muscles represent possible fiber-type transitions.

Systemic inflammatory response syndrome score at admission independently predicts mortality and length of stay in trauma patients

BACKGROUND

Recent studies have documented that the systemic inflammatory response syndrome (SIRS) score is a useful predictor of outcome in critical surgical illness. The duration and severity of SIRS are associated with posttrauma multiple organ dysfunction and mortality. We sought to determine whether the severity of SIRS at admission is an accurate predictor of mortality and length of stay (LOS) in trauma patients.

METHODS

Prospective data of 4,887 trauma admissions to a Level I trauma center over a 18-month period (January 1997 to July 1998) were analyzed. Patients were stratified by age and Injury Severity Score (ISS), and a SIRS severity score (1 to 4) was calculated at admission (1 point for each component present: fever or hypothermia, tachypnea, tachycardia, and leukocytosis). The SIRS score was evaluated as an independent predictor of mortality and LOS by chi2 and multivariate logistic regression.

RESULTS

Trauma patients (n = 4,887, 83% blunt injuries, 72% male) had the following characteristics: 73.1% were age 18 to 45 years, 17.5% were age 46 to 65 years, and 9.4% were age > or =66 years; 77.7% had ISS less than 15, 18.8% had ISS 16 to 29, and 3.5% had ISS greater than 29. Analysis of variance adjusting for age and ISS determined that SIRS score of 2 was a significant predictor of LOS. Furthermore, the relative risk of death increased significantly with SIRS score of 2 when age and ISS were held constant.

CONCLUSION

Logistic regression analysis confirmed that a SIRS score of 2 was a significant independent predictor of increased mortality and LOS in trauma patients. These data suggest that admission SIRS scoring in trauma patients is a simple tool that may be used as a predictor of outcome and resource utilization.

Cognitive functioning after subthalamic nucleotomy for refractory Parkinson's disease

OBJECTIVE

To evaluate whether subthalamic nucleotomy produces adverse cognitive effects in patients with Parkinson's disease.

METHOD

Twelve patients with Parkinson's disease underwent stereotactic surgery to the subthalamic nucleus. Presurgical and postsurgical neuropsychological assessment of attention, memory, executive function, language, and verbal intellect were undertaken with a battery of tests designed to minimise potential contamination of cognitive effects by motor symptoms.

RESULTS

There was no statistically significant difference in the cognitive tests results after operation for the group as a whole. Reliable change indexes were generated for the cognitive tests. Reliable change postoperatively was found on specific tests of verbal memory, attention, and planning. Left sided operations were associated with greater incidence of deterioration postsurgery.

CONCLUSIONS

Preliminary data on the first reported cognitive changes after subthalamic nucleotomy suggested few adverse cognitive effects of the surgery although discrete neuropsychological changes were seen in some patients. These effects were consistent with current theories on the cognitive functions of the basal ganglia.

Lipoprotein (a) and the risk of ischemic stroke in young women

BACKGROUND AND PURPOSE

lipoprotein (a) (lp (a)) is a lipid-containing particle similar to LDL which has been found in atherosclerotic plaque. The role of lp (a) in ischemic stroke remains controversial, but some studies suggest lp (a) is particularly important as a risk factor for stroke in young adults. We investigated the role of lp (a) as a risk factor for stroke in young women enrolled in the Stroke Prevention in Young Women Study.

METHODS

subjects were participants in a population-based, case-control study of risk factors for ischemic stroke in young women. Cases were derived from surveillance of 59 regional hospitals in the central Maryland, Washington DC, Pennsylvania and Delaware area. Lp (a) was measured in 110 cases and 216 age-matched controls. Demographics, risk factors, and stroke subtype were determined by interview and review of medical records.

RESULTS

lp (a) values were higher in blacks than whites, but within racial groups, the distribution of lp (a) values was similar between cases and controls. After adjustment for age, race, hypertension, diabetes, cigarette smoking, coronary artery disease, total cholesterol and HDL cholesterol, the odds ratio for an association of lp (a) and stroke was 1.36 (95% CI 0.80-2.29). There was no dose-response relationship between lp (a) quintile and stroke risk. Among stroke subtypes, only lacunar stroke patients had significantly elevated lp (a) values compared to controls.

CONCLUSIONS

we found no association of lp (a) with stroke in a population of young women with ischemic stroke. Small numbers of patients limit conclusions regarding risk in ischemic stroke subtypes, but we could not confirm previous suggestions of an association of lp (a) with atherosclerotic stroke in young adults.

Analysis of the effects of growth hormone, voluntary exercise, and food restriction on diaphyseal bone in female F344 rats

The aim of this study is to examine the effects of growth hormone, exercise, and weight loss due to food restriction on tibial diaphyseal bone and on tibial muscle mass. Thirteen-month-old female F344 rats were divided into six groups: group 1, baseline controls (B); group 2, age-matched controls (C); group 3, GH treated (GH); group 4, voluntary wheel running exercise (EX); group 5, GH + EX; and group 6, food restricted (FR). The dose of GH was 2.5 mg recombinant human (rh) GH/kg body weight/day, 5 days per week, given in two divided doses of 1.25 mg at 9-10 A.M. and 4-5 P.M. Food-restricted rats were fed 60% of the mean food intake of the age-matched controls. All animals except the baseline controls were killed after 4.5 months. The baseline controls were killed at the beginning of the study. Growth hormone increased the body weight and tibial muscle mass of the rats markedly, while EX caused only a slight decrease in body weight and partially inhibited the increase caused by GH in the GH + EX group. Food restriction greatly decreased body weight below that of age-matched controls, but neither FR nor EX had a significant effect on the mass of the muscles around the tibia. Growth hormone and EX independently increased tibial diaphyseal cortical bone area (p < 0.0001, p < 0.0001), cortical thickness (p < 0.0001, p < 0.0001), cortical bone mineral content (p < 0.0001, p < 0.0001), periosteal perimeter (p < 0.0001, p < 0.0001), and bone strength-strain index (SSI) (p < 0.0001, p < 0.0001). The effects of GH were more marked and resulted in a greater increase in the weight of the mid tibial diaphysis (p < 0.0001). The combination of GH and EX produced additive effects on many of the tibial diaphyseal parameters, including bone SSI. GH + EX, but not GH or EX alone, caused a significant increase in endocortical perimeter (p < 0.0001). In the FR rats, cortical bone area and cortical mineral content increased above the baseline level (p < 0.001, p < 0.0001) but were below the levels for age-matched controls (p < 0.0001, p < 0.0001). In addition, marrow area, endocortical perimeter, and endocortical bone formation rate increased significantly in the FR rats (p < 0.01, p < 0.0001, p < 0.0001). Three-point bending test of right tibial diaphysis resulted in maximum force (Fmax) values that reflected the group differences in indices of tibial diaphyseal bone mass, except that GH + EX did not produce additive effect on Fmax. The latter showed good correlation with left tibial diaphyseal SSI (r = 0.857, p < 0.0001), and both indices of bone strength correlated well with tibial muscle mass (r = 0.771, Fmax; r = 0.700, SSI; p < 0.0001). GH increased serum IGF-I (p < 0.0001), and the increase was partially reduced by EX. Serum osteocalcin was increased by GH with or without EX (p < 0.01, p < 0.01), and FR or EX alone did not alter serum IGF-I and osteocalcin levels. The bone anabolic effects of GH with or without EX may relate, in part, to increased load on bone from tibial muscles and body weight, which were increased by the hormone. The osteogenic effect of EX with or without GH may relate, in part, to increased frequency of muscle load on bone as EX decreased body weight (p < 0.05), but had no significant effect on tibial muscle mass. The enhanced loss of endocortical bone by FR may relate, in part, to decreased load on bone due to low body weight (p < 0.0001), as FR did not cause a significant decrease in tibial muscle mass (p = 0.357). The roles of humoral and local factors in the bone changes observed remain to be established.

Homocyst(e)ine and risk of cerebral infarction in a biracial population : the stroke prevention in young women study

BACKGROUND AND PURPOSE

Genetic enzyme variation and vitamin intake are important determinants of blood homocyst(e)ine levels. The prevalence of common genetic polymorphisms influencing homocyst(e)ine levels varies by race, and vitamin intake varies by socioeconomic status. Therefore, we examined the effect of vitamin intake, race, and socioeconomic status on the association of homocyst(e)ine with stroke risk.

METHODS

All 59 hospitals in the greater Baltimore-Washington area participated in a population-based case-control study of stroke in young women. One hundred sixty-seven cases of first ischemic stroke among women aged 15 to 44 years were compared with 328 controls identified by random-digit dialing from the same region. Risk factor data were collected by standardized interview and nonfasting phlebotomy. Plasma homocyst(e)ine was measured by high-performance liquid chromatography and electrochemical detection.

RESULTS

Blacks and whites did not differ in median homocyst(e)ine levels, nor did race modify the association between homocyst(e)ine and stroke. After adjustment for cigarettes per day, poverty status, and regular vitamin use, a plasma homocyst(e)ine level of >/=7.3 micromol/L was associated with an odds ratio for stroke of 1.6 (95% CI, 1.1 to 2.5).

CONCLUSIONS

The association between elevated homocyst(e)ine and stroke was independent not only of traditional vascular risk factors but also of vitamin use and poverty status. The degree of homocyst(e)ine elevation associated with an increased stroke risk in young women is lower than that previously reported for middle-aged men and the elderly and was highly prevalent, being present in one third of the control group.

Distribution and correlates of elevated total homocyst(e)ine: the Stroke Prevention in Young Women Study

PURPOSE

To determine the distribution and correlates of elevated total homocyst(e)ine (tHcy) concentration in a population of premenopausal black and white women.

METHODS

Data from the Stroke Prevention in Young Women Study (N = 304), a population-based study of risk factors for stroke in women aged 15-44 years of age, were used to determine the distribution and correlates of elevated tHcy in black (N = 103) and white women (N = 201).

RESULTS

The mean tHcy level for the population was 6.58 micromol/L (range 2.89-26.5 micromol/L). Mean tHcy levels increased with age, cholesterol level, alcohol intake, and number of cigarettes smoked (all: p < 0.05). There were no race differences (mean tHcy 6.72 micromol/L among blacks and 6.51 micromol/L among whites; p = 0.4346). Regular use of multivitamins and increasing education was associated with significant reductions in tHcy concentration. Approximately 13% of the sample had elevated tHcy levels, defined as a tHcy concentration > or = 10.0 micromol/L. Multivariate-adjusted correlates of elevated tHcy included education > 12 vs. < or = 12 (odds ratio [OR] = 0.4, 95% confidence interval [CI] = 0.2-0.8); smoking > or = 20 cigarettes/day vs. nonsmokers (OR = 2.8, 95% CI = 1.1-7.3); and the regular use of multivitamins (OR = 0.4, 95% CI = 0.2-0.9).

CONCLUSIONS

These results suggest that a substantial proportion of healthy young premenopausal women have tHcy levels that increase their risk for vascular disease. A number of potentially modifiable behavioral and environmental factors appear to be significantly related to elevated tHcy levels in young women.

A randomized trial of surgical antimicrobial prophylaxis with and without vancomycin in organ transplant patients

BACKGROUND

Gram-positive organisms, including vancomycin-resistant enterococci (VRE), have emerged as major pathogens on the organ transplant service at our institution. We hypothesized that our use of vancomycin as part of routine surgical prophylaxis increased the risk of VRE colonization and infection; conversely, there was concern that failure to use vancomycin prophylaxis would increase peri-operative morbidity due to gram-positive organisms.

METHODS

Renal transplant recipients (n = 88) were randomized to receive either a) vancomycin/ceftriaxone or b) cefazolin; and pancreas transplants (n = 24) to receive either a) vancomycin/gentamicin or b) cefazolin/gentamicin. Stool samples or rectal swabs were obtained for culture for enterococci within 24 h of transplantation and weekly while hospitalized.

RESULTS

Enterococci were isolated on stool culture from 38 (34%) of 102 patients at the time of transplantation; 4 (11%) of the isolates were VRE. The percentage of patients who subsequently acquired VRE was low (1-7% per wk) but remained constant during hospitalization. There was no association between new VRE detection and vancomycin use for either prophylactic or therapeutic purposes. Forty-four patients (39%) had a post-operative infection with 46% of these infections due to gram-positive organisms; rates were unaffected by prophylactic vancomycin use. Pancreas transplant patients who did not receive vancomycin prophylaxis had a significantly longer initial hospitalization (p = 0.03); however, differences were not statistically significant when total length of stay (LOS) within the first 90 d of transplantation was compared.

CONCLUSIONS

Vancomycin surgical prophylaxis does not appear to have an effect on VRE colonization or infection, or on rates of infection with gram-positive bacteria. Elimination of vancomycin prophylaxis in renal transplant patients may be a reasonable part of an overall program to limit vancomycin usage, although as a single measure, its impact may be minimal. Vancomycin surgical prophylaxis may be of greater importance in pancreas transplants.

Additive effect of voluntary exercise and growth hormone treatment on bone strength assessed at four different skeletal sites in an aged rat model

The aim of the study was to assess the effect of growth hormone (GH), voluntary exercise (Ex), and the combination of GH and Ex on bone strength, mass, and dimensions in aged, intact female rats. In addition, the effect of food restriction (FR) was studied. Fourteen-month-old virgin F-344 rats were divided into 6 groups with 13 animals in each: (1) baseline (BSL); (2) control + solvent vehicle (CTRL); (3) GH 2.5 mg/kg/day (GH); (4) exercise, voluntary: 0.6-0.7 km/day (Ex); (5) GH treatment and voluntary exercise (GH + Ex); and (6) FR. Group 1 was killed at the beginning of the study and served as baseline. All the other groups were killed after 18 weeks' treatment. The effects of aging and treatment regimes were measured at four different skeletal sites: lumbar vertebrae, femoral cortical bone, femoral neck, and the distal femoral metaphysis. Aging in itself induced a decline in vertebral body strength and ash density. At the appendicular skeletal sites, bone mass and strength were unchanged or increased. Treatment with GH alone induced a significant increase in the biomechanical parameters at the vertebral body and the femoral diaphysis, but not at the femoral neck or the distal femoral metaphysis. Voluntary exercise on its own increased load values significantly over CTRL at the vertebral body site, but not at any of the appendicular skeletal sites. The combination of GH and voluntary exercise resulted in an additive effect at the vertebral site and at the femoral diaphysis, and a synergistic (potentiating) effect at the two femoral metaphyses. FR, on the other hand, had a negative effect on cortical bone area and strength at the femoral diaphysis, but no significant effect on the other sites tested. We conclude that GH treatment and voluntary exercise both have skeletal anabolic effects; however, these effects are exerted to differing degrees at different sites. Importantly, when dosed together, GH and Ex have either an additive or synergistic anabolic effect on all sites (axial and appendicular).

Elevated tissue plasminogen activator antigen and stroke risk: The Stroke Prevention In Young Women Study

BACKGROUND AND PURPOSE

Abnormalities in endogenous fibrinolysis are associated with an increased risk for stroke in men and older adults. We tested the hypothesis that elevated plasma tissue plasminogen activator (tPA) antigen, a marker for impaired endogenous fibrinolysis, is an independent risk factor for stroke in young women.

METHODS

Subjects were 59 nondiabetic females ages 15 to 44 years with cerebral infarction from the Baltimore-Washington area and 97 control subjects frequency-matched for age who were recruited by random-digit dialing from the same geographic area. A history of cerebrovascular disease risk factors was obtained by face-to-face interview. Plasma tPA antigen was measured by enzyme-linked immunosorbent assay.

RESULTS

Mean plasma tPA antigen levels were significantly higher in stroke patients than control subjects (4. 80+/-4.18 versus 3.23+/-3.67 ng/mL; P=0.015). After adjustment for age, hypertension, cigarette smoking, body mass index, and ischemic heart disease, there was a dose-response association between tPA antigen and stroke with a 3.9-fold odds ratio of stroke (95% CI, 1.2 to 12.4; P=0.03) for the upper quartile (>4.9 ng/mL) of tPA antigen compared with the lowest quartile. The dose-response relationship between tPA antigen and stroke was equally present in white and nonwhite women, and further adjustment for total and HDL cholesterol levels only modestly attenuated this association.

CONCLUSIONS

This population-based case-control study shows that elevated plasma tPA antigen level is independently associated with an increased risk for ischemic stroke in nondiabetic females 15 to 44 years of age. These findings support the hypothesis that impaired endogenous fibrinolysis is an important risk factor for stroke in young women.

Single muscle fiber discharge transformations: fibrillation potential to positive sharp wave

It is presently believed that a fibrillation potential (FP) can transform into a positive sharp wave (PSW) by displaying a number of individual transitional potentials with a high degree of morphological variation between different sets of independent transformations. Clinically obtained examples of FP-to-PSW transformations and a myotonic discharge transformation are simulated by a finite fiber computer model. The simulations demonstrate that the two clinical FP-to-PSW examples may well be the result of two independent muscle fibers synchronously firing for a short period of time such that their separate waveforms summate at the electrode to create a false impression of one potential changing into another through a specific series of transitional waveforms. The transition characterized by the myotonic discharge is substantiated through modeling to define the most reasonable transitional series of waveform morphologies for a single muscle fiber. The combination of clinical examples, histological needle electrode muscle penetration studies, and simulations of single muscle fiber discharge transitions support the hypothesis that a needle recording electrode is capable of inducing a variable degree of mechanical compression with a commensurate amount of action potential blockade. The degree of action potential blockade directly contributes to the clinically observed configuration for the single muscle fiber discharge in both innervated and denervated tissues.

Effects of fiber type on ischemia-reperfusion injury in mouse skeletal muscle

Tourniquets frequently used during surgery involve tissue ischemia followed by postoperative reperfusion. However, little information is available on the functional consequences of this procedure in skeletal muscle. The goal of this study was to use skeletal muscles of C57BL/6 adult male mice to assess functional, structural, and biochemical characteristics after hindlimb vessel occlusion. Experimental manipulation involved application of a tourniquet to the hindlimb for a 3-hour period (n = 65). Muscles were then excised after various periods of reperfusion. Soleus and extensor digitorum longus muscles were chosen as representative of slow oxidative and fast glycolytic muscle fiber types, respectively. The most striking functional change found after ischemia-reperfusion injury was markedly improved endurance of extensor digitorum longus muscles. These fast-twitch glycolytic muscle fibers became much more resistant to fatigue during recovery from ischemia-reperfusion injury. There was a progressive increase in force generation in both muscles during recovery; however, soleus muscles recovered function more quickly after ischemia-reperfusion than extensor digitorum longus muscles. Also, extensor digitorum longus muscles recovered mass more slowly than soleus muscles at 7 and 14 days after ischemia. Structurally, extensor digitorum longus muscles had more severely damaged mitochondria, sarcoplasmic reticulum, and myofibrils. Surprisingly, no differences in oxidative enzyme activity (citrate synthase) and oxidative damage (in protein and lipids) were found after ischemia-reperfusion. The results indicate that muscle fiber type has a significant impact on the nature of ischemia-reperfusion injury in skeletal muscle. Thus, muscle fiber composition would be expected to affect recovery from the clinical use of tourniquets and other ischemic procedures. Furthermore, the results suggest that damage to structures involved in energy transduction and excitation-contraction coupling may play a role in the effects.

Effect of beta-blockade on mortality among high-risk and low-risk patients after myocardial infarction

BACKGROUND

Long-term administration of beta-adrenergic blockers to patients after myocardial infarction improves survival. However, physicians are reluctant to administer beta-blockers to many patients, such as older patients and those with chronic pulmonary disease, left ventricular dysfunction, or non-Q-wave myocardial infarction.

METHODS

The medical records of 201,752 patients with myocardial infarction were abstracted by the Cooperative Cardiovascular Project, which was sponsored by the Health Care Financing Administration. Using a Cox proportional-hazards model that accounted for multiple factors that might influence survival, we compared mortality among patients treated with beta-blockers with mortality among untreated patients during the two years after myocardial infarction.

RESULTS

A total of 34 percent of the patients received beta-blockers. The percentage was lower among the very elderly, blacks, and patients with the lowest ejection fractions, heart failure, chronic obstructive pulmonary disease, elevated serum creatinine concentrations, or type 1 diabetes mellitus. Nevertheless, mortality was lower in every subgroup of patients treated with beta-blockade than in untreated patients. In patients with myocardial infarction and no other complications, treatment with beta-blockers was associated with a 40 percent reduction in mortality. Mortality was also reduced by 40 percent in patients with non-Q-wave infarction and those with chronic obstructive pulmonary disease. Blacks, patients 80 years old or older, and those with a left ventricular ejection fraction below 20 percent, serum creatinine concentration greater than 1.4 mg per deciliter (124 micromol per liter), or diabetes mellitus had a lower percentage reduction in mortality. Given, however, the higher mortality rates in these subgroups, the absolute reduction in mortality was similar to or greater than that among patients with no specific risk factors.

CONCLUSIONS

After myocardial infarction, patients with conditions that are often considered contraindications to beta-blockade (such as heart failure, pulmonary disease, and older age) and those with nontransmural infarction benefit from beta-blocker therapy.

Thermolabile methylenetetrahydrofolate reductase polymorphism (C677T) and total homocysteine concentration among African-American and white women

A polymorphism associated with a thermolabile variant (C677T) of the enzyme methylenetetrahydrofolate reductase has been associated with both elevated total homocysteine (tHcy) levels and risk for cardiovascular disease. Data from the Stroke Prevention in Young Women Study were used to determine the prevalence of the C677T genotype and to assess whether environmental factors modified the association between genotype and tHcy concentration. The C677T genotype prevalence was 80% -/-, 20% +/-, and 0% +/+ among 46 African-American women; and 39% -/-, 53% +/-, and 8% +/+ among 77 white women (P < 0.01). There was a trend toward higher tHcy levels in African-American women with the +/- genotype when compared with the -/- genotype (6.9 mumol/L vs 5.3 mumol/L respectively, p = 0.10); no association was found among the white women (6.0 mumol/L, -/-; 4.5 mumol/L, +/-; and 6.2 mumol/L, +/+; p = 0.67). Among African American women, those who smoked and were +/- genotype had the highest tHcy levels (8.0 mumol/L); while among white women, those who smoked and were -/- had the highest tHcy levels (8.1 mumol/L). Despite being hampered by a limited sample size, the thermolabile allele is significantly less common among African-American than white women. The association between genotype and tHcy concentration is influenced by smoking and multivitamin use.

Cerebral infarction in young adults: the Baltimore-Washington Cooperative Young Stroke Study

BACKGROUND

Few reports on stroke in young adults have included cases from all community and referral hospitals in a defined geographic region.

METHODS

At 46 hospitals in Baltimore City, 5 central Maryland counties, and Washington, DC, the chart of every patient 15 to 44 years of age with a primary or secondary diagnosis of possible cerebral arterial infarction during 1988 and 1991 was abstracted. Probable and possible etiologies were assigned following written guidelines.

RESULTS

Of 428 first strokes, 212 (49.5%) were assigned at least one probable cause, 80 (18.7%) had no probable cause but at least one possible cause, and 136 (31.8%) had no identified probable or possible cause. Of the 212 with at least one probable cause, the distribution of etiologies was cardiac embolism (31.1%), hematologic and other (19.8%), small vessel (lacunar) disease (19.8%), nonatherosclerotic vasculopathy (11.3%), illicit drug use (9.4%), oral contraceptive use (5.2%), large artery atherosclerotic disease (3.8%), and migraine (1.4%). There were an additional 69 recurrent stroke patients.

CONCLUSIONS

In this hospital-based registry within a region characterized by racial/ethnic diversity, cardiac embolism, hematologic and other causes, and lacunar stroke were the most common etiologies of cerebral infarction in young adults. Nearly a third of both first and recurrent strokes had no identified cause.

Platelet glycoprotein receptor IIIa polymorphism P1A2 and ischemic stroke risk: the Stroke Prevention in Young Women Study

BACKGROUND AND PURPOSE

Platelet glycoprotein IIb/IIa (GpIIb-IIIa), a membrane receptor for fibrinogen and von Willebrand factor, has been implicated in the pathogenesis of acute coronary syndromes but has not been previously investigated in relation to stroke in young adults.

METHODS

We used a population-based case-control design to examine the association of the GpIIIa polymorphism P1A2 with stroke in young women. Subjects were 65 cerebral infarction cases (18 patients with and 47 without an identified probable etiology) 15 to 44 years of age from the Baltimore-Washington region and 122 controls frequency matched by age from the same geographic area. A face-to-face interview for vascular disease risk factors and a blood sample for the P1A2 allele and serum cholesterol were obtained from each participant. Logistic regression was used to estimate the odds ratio for one or more P1A2 alleles after adjustment for other risk factors.

RESULTS

Among cases and controls, the prevalence rates of one or more P1A2 alleles were 21% and 22% among blacks and 36% and 28% among whites, respectively. This genotype was significantly associated with hypertension only in black control subjects but otherwise not with any of the established vascular risk factors. The adjusted odds ratio for cerebral infarction of one or more P1A2 alleles was 1.1 (confidence interval [CI], 0.6 to 2.3) overall, 0.5 (CI, 0.1 to 7.1) among blacks, and 1.4 (CI, 0.5 to 3.7) among whites. For the cases with an identified probable etiology, the corresponding odds ratios were 3.0 (CI, 0.9 to 10.4) overall, 0.7 (CI, 0.1 to 7.1) among blacks, and 12.8 (CI, 1.2 to 135.0) among whites.

CONCLUSIONS

No association was found between the P1A2 polymorphism of GpIIIa and young women with stroke. However, subgroup analyses showed that the P1A2 polymorphism of GpIIIa appeared to be associated with stroke risk among white women, particularly those with a clinically identified probable etiology for their stroke. Further work with an emphasis on stroke subtypes and with multiracial populations is warranted.

Use of renal allografts from donors positive for hepatitis B core antibody confers minimal risk for subsequent development of clinical hepatitis B virus disease

BACKGROUND

The risk associated with transplantation of renal allografts from hepatitis B virus core antibody-positive (HBcAb(+)), hepatitis B virus surface antigen-negative (HBsAg(-)) donors is not well defined.

METHODS

Over 4 years, we performed 45 kidney transplants from IgG HBcAb(+), IgM HBcAb(-), HBsAg(-) donors into recipients with a history of prior hepatitis B virus (HBV) infection or reported vaccination. We examined HBV-related outcomes in these 45 patients, in comparison with 45 recipients of allografts from HBcAb(-) donors (matched for transplant type, date, and pretransplant HBV antibodies). We sought evidence for HBV transmission by testing posttransplant sera for the presence of HBcAb, hepatitis B virus surface antibody, and HBsAg. Additionally, we analyzed alanine aminotransferase profiles and allograft survival rates for all patients.

RESULTS

No patient receiving an allograft from an HBcAb(+) donor developed clinical HBV infection. No patient receiving an allograft from an HBcAb(+) donor had HBsAg detected through retrospective testing of stored sera or through prospective routine clinical evaluation and care. However, among the HBcAb(+) kidney recipients, 27% developed new HBcAb and/or hepatitis B virus surface antibody after transplant; in contrast, only 4% of control patients developed new antibody responses (relative risk=4.94; confidence interval 1.07-22.83). Among the recipients of HBcAb(+) organs, 18% developed elevated transaminases after transplant, in comparison with 36% of the controls. No association was found between "seroconverter" status and elevated alanine aminotransferase profiles in either group.

CONCLUSIONS

Transplantation of renal allografts from HBcAb(+), HBsAg(-) donors was not associated with clinically detectable HBV disease or antigenemia. However, recipients had a significantly increased risk of HBV seroconversion, consistent with exposure to HBV antigen. These results suggest that HBcAb(+) kidneys can be safely used if transplanted into appropriate recipients, but highlight the need for effective HBV vaccination and vaccine-response monitoring in potential recipients.

Clostridium difficile infection is a risk factor for bacteremia due to vancomycin-resistant enterococci (VRE) in VRE-colonized patients with acute leukemia

A cohort study was conducted in a cancer center to identify risk factors for bacteremia with vancomycin-resistant enterococci (VRE) in neutropenic cancer patients colonized with VRE. There were 10 patients with VRE bacteremia among 56 colonized with VRE, of whose charts 51 were available for review. One hundred percent of patients with VRE bacteremia (10 of 10) vs. 56% of patients without VRE bacteremia (23 of 41) had acute leukemia (P = .01, Fisher's exact test). Four of the 10 patients with VRE bacteremia had a positive Clostridium difficile toxin assay within 6 days of their first positive VRE blood culture. Both C. difficile infection and antimicrobial (vancomycin and ciprofloxacin) use during VRE colonization were significant risk factors for VRE bacteremia in univariate analysis. When a Cox proportional hazards model was used to account for differences in follow-up time, C. difficile infection was the only statistically significant risk factor (risk ratio, 8.2; P = .007) for VRE bacteremia in VRE-colonized patients with acute leukemia.

Physical activity as a factor in the action of dietary restriction on aging: effects in Fischer 344 rats

Dietary restriction (DR) slows the rate of aging in laboratory rodents but the mechanism of action is unknown. DR is known to induce beneficial effects in a variety of tissues and organ systems. DR also maintains high levels of physical activity over the life span. We tested the hypothesis that lifelong physical activity is an important component of the anti-aging action of DR. Male specific pathogen-free Fischer 344 rats were divided into 4 groups at 6 weeks of age: A: fed old libitum; AE: fed ad libitum and in cages with running wheels; B: fed 60% ad libitum; BE: fed 60% ad libitum and in cages with running wheels. Running activity and spontaneous cage activity were measured over 24 hours and over the life span. Metabolic rate was measured indirectly by analysis of air entering and leaving cages. AE rats exhibited low levels of running activity and ran very little beyond 6 months of age. In contrast, BE rats sustained high running levels even after all A and AE rats had died. High levels of wheel running did not decrease spontaneous cage activity. Median life span (50% survival) was in the order A = AE < B < BE. Ten percent survival was in the order A = AE < B = BE. BE rats had greatest median life span and also highest specific metabolic rate. Exercise and DR altered pathology: At death BE rats had a high incidence of cardiomyopathy, whereas A and AE rats had high incidence of chronic nephropathy and pituitary tumors. The data indicate that increased physical activity is probably not an important factor in the action of DR on aging.

Elevated levels of albumin in soleus and diaphragm muscles of mdx mice

Muscle damage is often associated with an influx of extracellular fluid containing albumin into the muscle. Muscles affected by muscular dystrophy undergo severe muscle damage; therefore, the hypothesis was tested that muscles of dystrophic (mdx) mice contain elevated levels of albumin. Albumin levels in diaphragm (DIA) and soleus (SOL) muscles of control and mdx mice were measured at 3 months and 1 year of age. Albumin in mdx DIA at 1 year of age was twice that of control. In mdx SOL at 1 year of age albumin was increased 25% compared with control. The increase in albumin correlates well with the decline in function in mdx DIA and SOL muscles. Electron microscopy of muscles suggests that albumin is co-localized with transverse tubules of muscle fibers and thus may be mainly located in extracellular fluid. We conclude that albumin is elevated in muscles affected by muscular dystrophy and suggest that this may be of clinical importance in view of substances bound to albumin under physiological conditions.

Influence of age, exercise, and dietary restriction on oxidative stress in rats

This study was undertaken to investigate the effects of exercise, dietary restriction (DR) and aging on the formation of reactive oxidant species (ROS), antioxidant defenses, and membrane fluidity. Test were performed on hepatic microsomes, mitochondria, and cytosol from 9- and 20-month-old male Fischer 344 rats, which were divided into four groups: ad libitum fed, sedentary (AS); restricted, sedentary (RS); ad libitum fed, exercised (AE); and restricted, exercised (RE). Results show that both exercise and DR suppressed microsomal ROS production, but not mitochondrial ROS production, which increased with age in all groups. Exercise and DR increased catalase and glutathione peroxidase (GSH-Px) activities and maintained cytosolic ascorbic acid concentration at high levels. Exercise led to significantly higher levels of cytosolic glutathione (GSH). Activity of cytosolic superoxide dismutase (SOD) remained unchanged, whereas glutathione-s-transferase (GST) activity significantly increased with DR. The fluidity of the mitochondrial membrane from exercised and DR rats deteriorated less with age than the membrane from AS rats. Exercise alone was found to improve fluidity, but was more effective when coupled with DR. These results suggest for the first time that the combination of exercise training and DR is the most effective means of preserving membrane fluidity and suppressing microsomal ROS production.

The relationship of growth rate, plasma growth hormone (GH) concentration, and GH-binding protein

Growth hormone (GH)-binding protein (GHBP) and GH secretion are potential mediators of linear growth in children. To study the relationship between these variables, we measured GHBP activity, peak stimulated GH (PKGH), and 24-hour integrated GH concentration (ICGH) in 76 children referred for evaluation of growth. Linear growth was expressed as an age- and sex-specific growth rate standard deviation score (GRSD), which was calculated from sequential height measurements in the 6-month period immediately before GH testing. Using multiple regression models, we found that the relationship between GHBP and growth (GRSD) depended on height (height standard deviation [HGTSD] expressed as an age- and sex-specific z score) controlling for ICGH or PKGH. In further analysis of this relationship, we divided the subjects by HGTSD in subsequent analyses. In 19 children of normal stature (HGTSD > -2), GRSD increased with GH concentration (measured both as PKGH and ICGH: P <.013,R2 = .56) but decreased with higher levels of GHBP (P < .005,R2 = .62). In contrast, for 57 subjects with severe short stature (HGTSD < or = -2), GRSD could not be predicted from GHBP, GH secretion, HGTSD, or interaction involving these variables. These data suggest the hypothesis that under normal conditions, GHBP and GH level may be important predictors of growth rate in children.

Exercise and diet modulate cardiac lipid peroxidation and antioxidant defenses

Free radical metabolism can be altered by several interventions, including dietary restriction (DR) and exercise. Most of the previous work has focused on the liver and skeletal muscle. The following experiments were performed to determine whether long-term DR and chronic exercise affect free radical metabolism and change the status of the antioxidant defenses of the heart. Rats were subjected to DR and/or endurance exercise for 18.5 months and were sacrificed along with their ad lib fed and sedentary controls. Both DR and exercise decreased the malondialdehyde content of cardiac mitochondria, indicating a decrease in lipid peroxidation damage. The antioxidant enzymes in the cytosol, superoxide dismutase, selenium dependent glutathione peroxidase, and glutathione S-transferase were all increased by DR. Catalase activity was unaffected by DR but was increased by exercise. The following results demonstrate that long-term DR and exercise modulate the extent of free radical damage in the heart and enhance the antioxidant defense system.

Beneficial versus adverse effects of long-term use of clenbuterol in mdx mice

Long-term administration of the beta 2-adrenergic agonist clenbuterol in mdx mice was used to test the hypothesis that increasing contractile protein content in skeletal muscle will decrease the progression of muscular dystrophy. C57BL/10SNJ (control) and dystrophic (mdx) mice were given clenbuterol (1.0-1.5 mg/kg body weight/day) in the drinking water. Ventilatory function and morphological and functional characteristics of soleus (SOL) and diaphragm (DIA) muscles were evaluated. Clenbuterol administration was associated with increased SOL muscle weight, and SOL muscle weight to body weight ratio in control and mdx mice at both ages. There was a 22% increase in myosin concentration of mdx DIA at 1 year of age, correlating well with increased normalized active tension in mdx DIA at this age. Also, absolute tetanic tension increased in control and mdx SOL with clenbuterol at both ages. Ventilatory function was significantly impaired in mdx mice at both ages and clenbuterol administration did not alleviate this. Clenbuterol treatment was associated with a 30-40% increase in fatigability in DIA and SOL muscles of control and mdx mice at both ages. Furthermore, 1-year-old mdx mice receiving clenbuterol exhibited deformities in hindlimbs and spine. These results suggest that long-term clenbuterol treatment has a positive effect on muscle growth and force generation, but has adverse side effects such as increased muscle fatigability and development of deformities.

Role of caloric restriction in the prolongation of life

Restriction of caloric intake increases longevity, slows the rate of functional decline, and reduces incidence of age-related disease in a variety of species. Most laboratory rodent studies have initiated restriction before puberty, whereas ongoing studies in nonhuman primates utilize restriction in adulthood. The mechanism of action of caloric restriction remains unknown; however, data suggest that cellular functions are altered in such a way that destructive by-products of metabolism are reduced, and defense or repair systems are enhanced by this nutritional manipulation.

Enterococci resistant to multiple antimicrobial agents, including vancomycin. Establishment of endemicity in a university medical center

OBJECTIVES

To determine the distribution of and risk factors for colonization and infection with vancomycin-resistant enterococci; to evaluate the molecular epidemiology of these strains; and to assess the effect of interventions, including 1) strict adherence to infection control procedures and 2) restricted use of vancomycin.

DESIGN

Problem identification based on descriptive studies, point-prevalence surveys, and case-control studies and followed by specific interventions and evaluation of the response to these interventions.

SETTING

University medical center.

PARTICIPANTS

All patients hospitalized between May 1992 and June 1994 (59,196 admissions).

MAIN RESULTS

75 active infections attributed to vancomycin-resistant enterococci were identified. Thirty-one patients (41%) had bloodstream infections and 6 (8%) died. The incidence of active infection was highest in the organ transplantation unit (13.2 infections/1000 admissions). In the point-prevalence studies, vancomycin-resistant enterococci were isolated from 20% of a random sample of hospitalized patients in July, August, and September 1993 (adjusted prevalence, 16.9%). Case-control studies showed significant associations between colonization and infection and 1) receipt of antimicrobial agents, particularly vancomycin, and 2) severity of illness. Although several small case clusters had isolates with identical banding patterns on pulsed field gel electrophoresis, at least 45 different banding patterns were noted among medical center isolates. Interventions took place in November and December 1993. Vancomycin restriction policies resulted in a 59% decrease in intravenous vancomycin use and an 85% decrease in oral vancomycin use. Point-prevalence surveys done in April, May, and June 1994 showed a consistent 20% level of colonization with vancomycin-resistant enterococci strains (adjusted prevalence, 18.7%). No significant changes were seen in rates of vancomycin-resistant enterococci infection.

CONCLUSIONS

Vancomycin-resistant enterococci are an important cause of illness and death in the study institution, particularly among organ transplant recipients and other seriously ill persons; they have also become a common intestinal colonizer among hospitalized patients. The diversity of isolates (based on molecular typing studies) suggests that resistant organisms have been introduced from multiple sources. Interventions that effectively lower the overall level of colonization with vancomycin-resistant enterococci must still be identified.

Interrater reliability of an etiologic classification of ischemic stroke

BACKGROUND AND PURPOSE

Precise identification of the cause of stroke is critical to research and clinical practice. Published series of ischemic stroke show considerable variation in the proportion of cases classified as atherosclerotic large-vessel disease, lacunar infarct, cardioembolic stroke, stroke of other known cause, and stroke of undetermined etiology. We describe the development and use of an etiology-specific classification of ischemic stroke. The interrater reliability of the classification is then evaluated.

METHODS

A total of 160 cases of ischemic strokes in young adults were reviewed by paired neurologists who assigned cases to prioritized categories. The results of paired ratings were evaluated for each of the potential causes. Interrater agreement was assessed by means of kappa, which is the chance-adjusted percent agreement.

RESULTS

For standard pairs, kappa was fair to good for all causes except lacunar stroke (kappa = 0.31); however, pair-to-pair variation was greatest for lacunar strokes. Strokes of undetermined cause and hematologic/other cause were of borderline fair reliability.

CONCLUSIONS

The utility of a stroke classification system is dependent on its intended use. An etiologic classification is useful in studies of the epidemiology and pathophysiological basis of stroke. Fair to good reliability for an etiologic classification of stroke can be obtained when criteria are explicit.

Voluntary exercise decreases progression of muscular dystrophy in diaphragm of mdx mice

Effects of voluntary wheel running on contractile properties of diaphragm (DIA) and soleus (SOL) of dystrophic (mdx) and control (C57BL/10SNJ) mice were evaluated. In particular, we tested the hypothesis that daily voluntary running is not deleterious to muscle function in mdx mice. Both groups of mice ran extensively (control mice approximately 7 km/day, mdx mice approximately 5 km/day). Exercise increased maximal specific tetanus tension of mdx DIA from 1.02 +/- 0.04 to 1.33 +/- 0.06 kg/cm2 but did not restore it to the control level (2.55 +/- 0.17 kg/cm2). Maximal tetanus tension of sedentary mdx SOL (2.41 +/- 0.17 kg/cm2) was reduced compared with control (3.10 +/- 0.15 kg/cm2) and was not altered by running activity. Optimal length was significantly lower in DIA of mdx mice, and exercise did not change this. Fatigability and contractile properties of muscles measured in vitro were not altered by running activity with the exception of increased contraction time in mdx DIA. In conclusion, extensive wheel running is not deleterious to muscle function in mdx mice contrary to predictions of the "work overload" theory of muscular dystrophy. Rather, this exercise is beneficial for active tension generation of mdx DIA, the muscle most closely resembling muscles of patients with Duchenne muscular dystrophy.

Does muscular dystrophy affect metabolic rate? A study in mdx mice

In this study metabolic consequences of muscular dystrophy were investigated using the mdx mouse model. Measurements were performed on C57BL/10SNJ (control) and dystrophic (mdx) mice of ages 4-6 weeks (young) and 1 year (adult), i.e. at times when muscle degeneration and regeneration are known to be high (young) and low (adult). Whole body metabolic rate (MR) was measured indirectly under usual living conditions by recording O2 consumption and CO2 production over 24 h. Physical activity of mice was measured simultaneously. Oxygen consumption of soleus (SOL) and extensor digitorum longus (EDL) muscles of control and mdx mice was recorded in vitro, using polarographic O2 electrodes. MR in young mdx was significantly decreased compared to young control, but no differences were found in adults. Also, food consumption and physical activity of mdx were decreased significantly compared to control in young but not in adult mice. There was no difference in resting oxygen consumption of muscles from young mdx and control mice, but oxygen consumption of EDL from adult mdx was less than control. Results suggest that muscular dystrophy results in decreased rate of energy metabolism mainly as a consequence of decreased physical activity. The extensive muscular degeneration and regeneration characteristic of muscular dystrophy therefore do not appear to lead to an increase in whole body metabolism.

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.

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.

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.

Respiratory muscle stiffness is age- and muscle-specific

We investigated the possible contribution of respiratory muscles to the well documented increase in chest wall stiffness with age. Diaphragm and internal intercostal muscle strips were dissected from male Fischer 344 rats of 3, 6, 12, and 24 months of age. Muscles were subjected, in vitro, to stress-strain and yield point tests. Passive tension data from these tests were normalized to a reference length (Lr), which was defined in terms of absolute stress, 700 Pascals. In general, Lr of diaphragm was found to be 90% of the length (Lo) required for maximal tetanic tension. Within a range of stretch between Lr and 130% Lr, diaphragm muscles from adult rats (6-12 month) were more compliant than those of either young (3 month) or old (24 month) animals. In contrast, intercostal muscles from old rats were stiffer than those of young or adult rats. Yield strength of both muscles was constant with age, but diaphragm muscles were found to have a higher yield strength than intercostal muscles from any age. Thus, only some passive mechanical properties of respiratory muscles vary with age, and this variation in muscle-specific. A surprising finding of this study was that diaphragm muscles of adult animals were more compliant than those of either young or old rats.

Spatial memory in alcohol-dependent subjects: using a push-button maze to test the principle of equiavailability

The principle of equiavailability states that once the locations in a spatial array are learned, then all locations in the array are simultaneously available in memory (Levine, Jankovic, & Palij, 1982). To test the application of this principle, 21 nonamnesic, alcohol-dependent, male subjects and 20 demographic and ability-matched male control subjects were required to learn a series of push-button maze paths and to perform shortcut or retrace movements on the paths. The results for the control subjects conformed to the principle of equiavailability. In contrast, the alcohol-dependent subjects did not show equiavailability. This pattern of results is interpreted as evidence of a spatial memory deficit in the alcohol-dependent subjects.

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.

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.

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.

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.