PubMed Health⌕ Search

Biomedical subjects

M J Alexander

Publications and source records attributed to M J Alexander.

At least 37 records · Page 2Linked to original sources
PubMed1990

Peak torque values for antagonist muscle groups and concentric and eccentric contraction types for elite sprinters.

The purpose of this study was to provide descriptive strength estimates of the major muscle groups of the lower limbs for a group of elite sprinters by comparing both the eccentric and concentric and the agonist and antagonist peak torques. The peak torque values of the flexor and extensor muscle groups of the hip, knee, and ankle joints of the lower extremities were tested in a group of elite male and female sprinters. These values were measured both eccentrically and concentrically for each of the joint movements tested, using a Kin/Com isokinetic dynamometer. The peak torque values for the knee joint were found to be substantially larger than those reported for nonathletes, and comparable to those for other athletic populations. No comparable scores were located for the results of the hip and ankle scores. The flexion and extension ratios for the knee joint, at approximately .60, were similar to others reported, whereas the ratios for the hip joint were larger at .76. The concentric and eccentric ratios varied, depending on the speed of testing and the joint tested.

Adolescent↗
PubMed1990

Incidence of hepatitis B infection in Brunei Darussalam--analysis of racial distribution.

Brunei Darussalam has a mixed population with entirely different cultures and religions. The overall incidence of Hepatitis B virus (HBV) infection is 6%. A racial analysis of the incidence of HBV infection in Brunei shows a significantly higher incidence in Chinese compared to the other races. This is consistent with the incidence in the neighbouring countries.

Brunei↗
PubMed1990

A clinico-pathological profile of colonic polyps in Brunei Darussalam--a study of 25 cases treated by colonoscopic polypectomy.

Colonic polyps are not rare in Brunei Darussalam with an incidence of 13% in 193 colonoscopies performed over the last two years. Majority of the polyps were adenomatous. Incidence was higher in the Malays and had a male preponderance. Commonest age of presentation was above the age of 40 years and the pattern is comparable to the Western pattern. All the polyps were removed by colonoscopic polypectomy.

Adenocarcinoma↗
PubMed1989

Distribution of neurotensin/neuromedin N mRNA in rat forebrain: unexpected abundance in hippocampus and subiculum.

We have used in situ hybridization to determine the regional distribution of mRNA encoding the neurotensin/neuromedin N (NT/N) precursor in the forebrain of the adult male rat. Cells containing NT/N mRNA are widely distributed in the forebrain. These areas include the septum, bed nucleus of the stria terminalis, preoptic area, hypothalamus, amygdala, accumbens nucleus, caudate-putamen, and piriform and retrosplenial cortex. In general, the regional distribution of NT/N mRNA corresponds to the previously determined distribution of neurotensin-immunoreactive cell bodies; however, several notable exceptions were observed. The most striking difference occurs specifically in the CA1 region of the hippocampus, where intense labeling is associated with the pyramidal cell layer despite the reported absence of neurotensin-immunoreactive cells in this region. Analysis of microdissected tissue by S1 nuclease protection assay confirmed the abundance of authentic NT/N mRNA in CA1. A second major discrepancy between NT/N mRNA abundance and neurotensin-immunoreactivity occurs in the intensely labeled subiculum, a region that contains only scattered neurotensin-immunoreactive cells in the adult. These results suggest that, in specific regions of the forebrain, NT/N precursor is processed to yield products other than neurotensin. In addition, these results provide an anatomical basis for studying the physiological regulation of NT/N mRNA levels in the forebrain.

Animals↗
PubMed1989

Evidence that neurotensin participates in the central regulation of the preovulatory surge of luteinizing hormone in the rat.

Neurotensin (NT) has been implicated in the central regulation of LH and PRL secretion in the rat. We investigated the importance of NT release to the neural events that trigger the preovulatory LH surge and coincident PRL surge, using as our animal model ovariectomized (OVX) rats treated with estrogen and progesterone to induce reliable and robust surges. To interfere with the action of endogenous NT in the basal forebrain, we administered a NT antiserum (NTAS) in a series of bilateral microinjections aimed at the anterior border of the medial preoptic area. One week after OVX, rats bearing cerebral guide cannulae received Silastic capsules (3 x 15 mm; sc) containing 17 beta-estradiol. Two days later, beginning at 0830 h, conscious rats were administered either NTAS or control serum bilaterally in a series of four 100-nl injections spaced at 30-min intervals. After an initial blood sample, rats received progesterone (4 mg, sc) at 1200 h; blood samples were then taken at 1-h intervals from 1400-2100 h. Blood samples were obtained from conscious, freely moving rats via a chronic atrial catheter implanted previously. Plasma levels of LH and PRL were measured by RIA, and the location of microinjection sites was verified histologically. Administration of NTAS caused a 66% reduction in the magnitude of the LH surge without altering its timing, whereas the PRL surge was unaffected. These results provide strong evidence that NT in the basal forebrain participates in the steroid-induced LH surge and suggest that NT plays a role in the preovulatory LH surge.

Animals↗
PubMed1989

Estrogen induces neurotensin/neuromedin N messenger ribonucleic acid in a preoptic nucleus essential for the preovulatory surge of luteinizing hormone in the rat.

Ovarian steroids act on unidentified neurons to trigger preovulatory secretion of GnRH. In the rat, important steroid target cells reside in the anterior medial preoptic nucleus (AMPN), a sexually dimorphic structure essential for stimulatory effects of ovarian steroids on LH secretion. The AMPN contains neurotensin (NT)-immunoreactive neurons, and immunoneutralization of NT in the preoptic region markedly attenuates steroid-induced LH surges. Using probes derived from the rat gene that encodes NT and neuromedin N (NT/N), we investigated the ability of estrogen to influence NT/N mRNA levels in the AMPN. Ovariectomized rats were treated for 14 days with sham capsules or capsules that produce supraphysiological serum levels of 17 beta-estradiol (250 +/- 20 pg/ml). As determined by in situ hybridization, estradiol markedly altered the distribution of NT/N mRNA in the medial preoptic region, causing a striking increase in NT/N mRNA abundance specifically in the AMPN and adjacent medial preoptic nucleus (MPN). In contrast, estradiol caused no obvious changes in labeling in the lateral septum, diagonal band of Broca, bed nucleus of the stria terminalis, and lateral preoptic area. The distribution of NT/N mRNA in the AMPN of normal male rats closely resembled that in ovariectomized rats, where labeled cells were rarely observed. Microdissection and S1 nuclease protection analysis were used to quantitate the effect of estradiol on NT/N mRNA levels. Supraphysiological estradiol treatment for 14 days caused a 3.4-fold increase (P less than 0.0002) in NT/N mRNA levels in the combined AMPN/MPN, whereas levels in the central amygdaloid nucleus remained constant, providing further evidence of regional specificity. Forty-eight hours of estradiol treatment, at concentrations (60 +/- 1 pg/ml) similar to those observed on the morning of proestrus, caused a 1.8-fold increase (P less than 0.001) in NT/N mRNA levels in the AMPN/MPN, indicating that the time course of NT/N mRNA induction by estrogen is compatible with events of the normal estrous cycle. Together with previous findings, our results strongly suggest that NT neurons mediate, directly or indirectly, stimulatory effects of ovarian steroids on GnRH secretion.

Animals↗
PubMed1989

The relationship between muscle strength and sprint kinematics in elite sprinters.

Twenty-three elite sprinters, 9 females and 14 males, were filmed while performing a maximal sprint. Age, height, weight, and personal best 100 m time were also determined for each sprinter. Several kinematic variables were calculated for each athlete from the filmed sprint, including stride length, stride frequency, horizontal and vertical velocity of the CG, and the angular kinematics of the limbs. A Kin/Com isokinetic dynamometer was used to determine lower limb peak and average torque values. Correlation coefficients were calculated between each of the kinematic variables and each of the strength variables. Stepwise multiple regression analysis was also carried out for each set of kinematic and strength variables, to determine the best predictors of sprinting speed. Significant relationships were noted between sprinting times for the 100 m and peak torque scores (N.m/kg) for males for fast concentric knee extension and slow eccentric dorsiflexion, and for females for concentric dorsiflexion at both speeds, and slow eccentric dorsiflexion.

Adolescent↗
PubMed1988

Evidence that noradrenergic activity does not mediate the inhibition of luteinizing hormone secretion caused by vasoactive intestinal peptide.

We have recently shown that intracerebroventricular (i.c.v.) infusion of vasoactive intestinal peptide (VIP) in ovariectomized (OVX) rats causes a pronounced inhibition of pulsatile luteinizing hormone (LH) secretion. Since there is increasing evidence for an interaction between VIP- and norepinephrine-secreting systems in the brain, we tested the hypothesis that disruption of central noradrenergic activity would attenuate VIP-induced suppression of pulsatile LH release. Seven days prior to blood sampling, we administered either 6-hydroxydopamine (30 micrograms) or vehicle into the third cerebral ventricle of long-term OVX rats. This treatment reduced hypothalamic norepinephrine concentrations to 36% of control values. On the day of blood sampling, serial 300-microliter blood samples were taken from conscious, unrestrained animals at 5-min intervals for a total of 4 h. Each sample was replaced with an equal volume of a blood replacement mixture. Immediately following a control bleeding period of 2 h, VIP was administered i.c.v. to each animal for 2 h (at a dose of 1.8 nmol/h). The suppression of pulsatile LH secretion caused by VIP infusion was virtually identical in the 6-hydroxydopamine- and vehicle-pretreated groups. These results indicate that a substantial depletion of hypothalamic norepinephrine does not attenuate VIP-induced suppression of pulsatile LH secretion. This provides evidence that centrally administered VIP inhibits pulsatile LH secretion by a mechanism independent of noradrenergic transmission.

Animals↗
PubMed1986

An alternative to DRGs. A clinically meaningful and cost-reducing approach.

A statistical methodology based on the Cox proportional hazards model (a survival time analysis method), an alternative to the approach underlying DRGs, is presented. The method is used to obtain an estimate of the length-of-stay (LOS) distribution of a patient incorporating either patient-specific or hospital variables. A percentile of the distribution chosen to minimize prediction error serves as the assigned LOS. Absolute deviation is used as the loss function both to determine the choice of a predicted LOS and to examine how well the scheme works. Multiple assignment schemes may also be developed from this approach. The results of the method, tested on a national probability sample of 4,608 psychiatric patients treated in psychiatric units of general hospitals, suggest that with respect to average absolute deviation, the proposed methodology may provide a scheme that is superior to the present DRG scheme. For the sample, the average percent improvement obtained using the median of the estimated LOS distribution as the predicted LOS over the sample mean of the DRG group is 19%. A two assignment strategy results in average improvements over DRGs of 43%.

Cost Control↗
PubMed1985

Vasoactive intestinal polypeptide effects a central inhibition of pulsatile luteinizing hormone secretion in ovariectomized rats.

Recent studies implicate vasoactive intestinal polypeptide (VIP) as a neurotransmitter or neuromodulator, and several observations suggest that VIP, originating within the brain, may alter the secretion of GnRH. We have tested the hypothesis that VIP acts as a central nervous system regulator of pulsatile GnRH secretion, as reflected in pulsatile LH release, by assessing the effect of intraventricularly administered VIP on several parameters of LH secretion in ovariectomized (OVX) rats. To examine the possibility that centrally administered VIP alters pituitary responsiveness to GnRH, we challenged OVX rats with GnRH and compared the LH response in VIP-treated animals with that in control animals. Finally, we tested the hypothesis that exposure of the animal to gonadal steroids alters VIP's effect on LH secretion by assessing LH release during central administration of VIP in OVX rats pretreated with estrogen and progesterone. Unanesthetized rats with external jugular cannulae were bled at 5-min intervals for 2 h before infusion and for 2 h during continuous intraventricular infusion of either VIP (1.8 nmol/h) or saline. Blood samples (300 or 400 microliter) were replaced with an equal volume of a blood replacement mixture. VIP infusion significantly reduced LH pulse frequency by 80% (P less than 0.002) and mean LH levels by 60% (P less than 0.002), but did not significantly affect LH pulse amplitude. In contrast, saline infusion produced no significant change in any of these parameters. The plasma LH response to 2 ng GnRH, iv, in VIP-treated animals did not differ significantly from that in control animals. Finally, VIP infusion had no discernible effect on LH secretion in OVX rats pretreated with estradiol benzoate (50 micrograms) and progesterone (25 mg). These results demonstrate that VIP can profoundly inhibit pulsatile LH secretion in the OVX rat and provide evidence to suggest that this effect is not due to diminished pituitary responsiveness to GnRH. Based upon these observations, we argue that VIP, originating within the brain, may be an important inhibitory regulator of pulsatile GnRH secretion.

Animals↗
PubMed1985

Biomechanical aspects of lumbar spine injuries in athletes: a review.

One of the areas of the body which is very often injured by athletes is the lower lack, or the lumbar area of the spine. This problem is of some concern to physical educators, athletic therapists, coaches, athletes, and physicians. The type of injury which occurs in the lumbar spine is dependent on the direction, magnitude, and the point of application of the forces to the spine. This part of the body is susceptible to injury due to the large forces which must be supported, which include the body weight and any external weights, as well as the forces due to very high accelerations of the body parts. Since the lumbar spine is the only connecting column between the upper and lower parts of the body, all the forces must be transmitted via these structures. There are two general techniques of calculating the forces on the lumbar spinal structures, a static approach and a dynamic approach. The static approach may be useful to calculate compression and shear forces on the spine in stationary positions as may be seen in weightlifting. However, the dynamics approach should be used to calculate the effects of the various weights and inertial forces on spinal structures. The most common types of lower back injuries found in athletes were: muscle strains, ligament sprains, lumbar vertebral fractures, disc injuries, and neural arch fractures. The most common serious athletic injury to the lower back was found to be neural arch fractures at the pars interarticularis, or the isthmus between the superior and inferior articular processes. These fractures are known as spondylolysis, or defect in the pars interarticularis of one side of the vertebrae; and spondylolisthesis, a bilateral defect in the pars interarticularis, often accompanied by forward displacement of the vertebral body. The sports in which lower back injuries commonly occurred were also examined, and it was determined that gymnastics, weightlifting and football were the sports in which the lower back is at greatest risk. In order to help to reduce, the high incidence of injuries to this area of the body, athletes should attempt to increase the strength of the abdominal muscles, and to maximize the flexibility of the lower back.

Adolescent↗
PubMed1984

The current systems assessment and the clinical care process. A tool for clinical supervision and the design of clinical information systems.

A side benefit of a current systems assessment carried out prior to automation was the development of a systematic picture of the clinical care system as captured in the system flow chart. The results of this assessment provided clinical administrators with a blueprint identifying the current system's strengths and weaknesses, which could be used both to introduce improvements and to measure the effect of such changes totally apart from the initial question of automation.

Delivery of Health Care↗
PubMed1984

Evaluation of a computerized drug review system: impact, attitudes, and interactions.

A study was carried out across 11 psychiatric and mental retardation, and developmental disabilities facilities to investigate the impact of a computerized drug prescription monitoring system on clinicians' prescribing behavior, knowledge of pharmacotherapy, attitudes toward computers, and the relationships between their attitudes and changes in their prescribing practices. The results document that surveillance systems can improve prescribing practices. The tangible feedback provided by the exception report, although in the form of a surveillance mechanism, also increased user acceptance to computer technology. However, the findings also suggest that user acceptance is not necessarily required to see positive effects, which in environments where clinical and fiscal accountability are paramount, may override some clinicians' concerns. Attention to human factors components may help to alleviate some negativism.

Attitude↗
PubMed1984

Severe alcoholism in the mental health sector: II. Effects of service utilization on readmission.

A follow-up study of a cohort of suburban alcoholics who are comprehensively served by the public mental health sector used a Cox survival time analyses to examine the relationship of patient characteristics, receipt of outpatient services and readmission to inpatient care. Patients were followed up until their first readmission to inpatient care or for 2 yr subsequent to an inpatient episode. As expected, established chronicity was associated with short "survival" in the community, as were youth and living alone. For first admissions, the receipt of aftercare was associated with a decreased likelihood of readmission, especially in conjunction with inpatient stays of treatment that included rehabilitation services. Patients who had established a pattern of chronicity, however, appeared resistant to the effect of these services. The transition from inpatient to aftercare services was identified as a crucial point in treatment. Aftercare patients who did not receive services beyond 6 months in the community were likely to be readmitted, suggesting that this period is also an important focus for treatment planning.

Adult↗
PubMed1982

A kinematic analysis of an upper extremity ballistic skill: the windmill pitch.

The purposes of this study were (1) to determine the relative motions of the upper limb segments during the execution of the softball windmill pitch (2) to attempt to determine the effect of these motions on the performance of the skill. High speed motion picture film was used to calculate the kinematic parameters of the pitching arm segments during the pitch. Four highly-skilled pitchers were used as subjects. Each performed at least ten trials of the pitch, which were recorded by two motion picture cameras. The two trials with the fastest ball velocity for each of the four subjects were analyzed from a sagittal aspect only. The resulting kinematic analysis indicated that there was a definite proximal-to-distal sequence of these motions, with decelerations occurring in the proximal segments prior to release of the ball. It was concluded that one of the critical factors in highly-skilled performance of ballistic skills is the ability to decelerate such segments, which likely require very strong eccentric contractions of antagonistic muscle groups.

Arm↗