Sex differences in musculoskeletal injury epidemiology and subsequent loss of tactical readiness during Marine Corps Officer Candidates School

INTRODUCTION

The US Marine Corps (USMC) Officer Candidates School (OCS) is a 10-week training course for Marine Officer Candidates (MOCs). OCS training is rigorous and demanding, which results in a high risk of musculoskeletal injuries (MSIs). The objective of this analysis was to describe MSIs among women and men during the USMC OCS at Quantico, Virginia, from September 2020 to November 2021.

METHODS

This prospective cohort study assessed MSIs that occurred among 736 MOCs (women: 17.8% of sample, men: 82.2%). Data for the study were derived from routinely collected injury data by athletic trainers and physical therapists embedded within the training units. Injury incidence, event at the time of injury occurrence, anatomic location, injury type and disposition following injury were described. Fisher's exact tests were used to compare proportions of injured women and men.

RESULTS

The cumulative injury incidence was higher among women (39.7%) compared with men (23.1%, p<0.001). When specific events associated with injuries were reported, most frequent events were the obstacle course (women: 20.9% of injuries, men: 12.9%) and the conditioning hike (women: 11.6%, men: 6.9%). Most injures affected the lower body (women: 67.4%, men: 70.8%). The most frequent body part injured was the lower leg (18.6%) in women and the knee (23.3%) in men. The most frequent injury type was strain (women: 39.5%, men: 24.3%), followed by sprain (women: 16.3%, men: 14.9%). A greater percentage of female (92.3%) compared with male MOCs (69.3%; p<0.001) were assigned light duty status following MSIs.

CONCLUSIONS

Mitigation of injuries during OCS events such as the obstacle course and the conditioning hike needs further investigation. The high risk of overuse lower leg injuries among women and the higher incidence of injuries among women compared with men underscore the need for further investigation of modifiable sex-specific injury risk factors.

Fluid regulation during physical work in the heat is not meaningfully modified by the menstrual cycle when fluids are freely available

We tested the hypothesis that women will be more dehydrated during physical work in the heat in the early follicular phase (EF), compared to the late follicular (LF) and mid-luteal (ML) phases of the menstrual cycle when allowed free access to drink. Twelve healthy, eumenorrheic, unacclimated women (26 ± 5 y) completed three trials (EF, LF, ML phases) involving 4 hours of exposure to 33.8 ± 0.8°C, 54 ± 1% relative humidity. Each hour, participants walked on a treadmill for 30 min at a rate of metabolic heat production of 338 ± 9 W. Participants drank a cool, flavor preferred non-caloric sport drink ad libitum. Nude body weight was measured pre- and post-exposure, and percent changes in body weight loss were interpreted as an index of changes in total body water. Total fluid intake and urine output were measured and sweat rate was estimated from changes in body mass corrected for fluid intake and urine output. Fluid intake was not different between phases (EF: 1609 ± 919 mL; LF: 1902 ± 799 mL; ML: 1913 ± 671; P=0.202). Total urine output (P=0.543) nor sweat rate (P=0.907) differed between phases. Percent changes in body mass were not different between phases (EF: -0.5 ± 0.9%; LF: -0.3 ± 0.9%; ML: -0.3 ± 0.7%; P=0.417). This study demonstrates that the normal hormonal fluctuations that occur throughout the menstrual cycle do not meaningfully alter fluid regulation during physical work in the heat.

High Intraindividual Variability in the Response of Serum Erythropoietin to Multiple Simulated Altitude Exposures

Baranauskas, Marissa N., Timothy J. Fulton, Alyce D. Fly, Bruce J. Martin, Timothy D. Mickleborough, and Robert F. Chapman. High intraindividual variability in the response of serum erythropoietin to multiple simulated altitude exposures. High Alt Med Biol. 23:85-89, 2022. Purpose: To evaluate within-subject variability in the serum erythropoietin (EPO) response to multiple simulated altitude exposures. Methods: Seven physically active men and women (age 27 ± 3 years, body mass index = 24.6 ± 4.0 kg/m²) were exposed to normobaric hypoxia (fraction of inspired oxygen [F_iO₂] = 0.14) for 12 hours on three separate occasions. Serum EPO concentrations were measured before exposure (0 hour), after 6 hours, and after 12 hours in hypoxia. The EPO response to hypoxia was calculated as percent change from 0 to 12 hours (ΔEPO_0-12). Results: Exposure time had a significant effect on EPO (p < 0.001) with concentrations increasing 3.2 ± 1.3 mIU/ml from 0 to 6 hours (p = 0.034) and 4.7 ± 1.2 mIU/ml from 0 to 12 hours (p = 0.001). Group mean ΔEPO_0-12 remained unchanged (p = 0.688) between the three exposures; however, there was considerable intraindividual variability in EPO responses. The intrasubject coefficient of variation for ΔEPO_0-12 was 61% ± 28% (range: 17%-103%) with intrasubject associations ranging r = 0.052 to r = 0.651 between repeated exposures. Conclusions: Athletes who routinely supplement training with simulated altitude methods (e.g., hypoxic tents) should expect inconsistent EPO responses to intermittent exposures lasting ≤12 hours.

Ventilatory Responsiveness during Exercise and Performance Impairment in Acute Hypoxia

INTRODUCTION

An adequate increase in minute ventilation to defend arterial oxyhemoglobin saturation (SpO2) during hypoxic exercise is commonly viewed as an important factor contributing to large inter-individual variations in the degree of exercise performance impairment in hypoxia. Although the hypoxic ventilatory response (HVR) could provide insight into the underpinnings of such impairments, it is typically measured at rest under isocapnic conditions. Thus, we aimed to determine whether 1) HVR at rest and during exercise are similar and 2) exercise HVR is related to the degree of impairment in cycling time trial (TT) performance from normoxia to acute hypoxia (∆TT).

METHODS

Sixteen endurance-trained men (V˙O2peak, 62.5 ± 5.8 mL·kg-1·min-1) performed two poikilocapnic HVR tests: one during seated rest (HVRREST) and another during submaximal cycling (HVREX). On two separate visits, subjects (n = 12) performed a 10-km cycling TT while breathing either room air (FiO2 = 0.21) or hypoxic gas mixture (FiO2 = 0.16) in a randomized order.

RESULTS

HVREX was significantly (P < 0.001) greater than HVRREST (1.52 ± 0.47 and 0.22 ± 0.13 L·min-1·%SpO2-1, respectively), and these measures were not correlated (r = -0.16, P = 0.57). ∆TT was not correlated with HVRREST (P = 0.70) or HVREX (P = 0.54), but differences in ventilation and end-tidal CO2 between hypoxic and normoxic TT and the ventilatory equivalent for CO2 during normoxic TT explained ~85% of the variance in performance impairment in acute hypoxia (P < 0.01).

CONCLUSION

We conclude that 1) HVR is not an appropriate measure to predict the exercise ventilatory response or performance impairments in acute hypoxia and 2) an adequate and metabolically matched increase in exercise ventilation, but not the gain in the ventilatory response to hypoxia, is essential for mitigating hypoxia-induced impairments in endurance cycling performance.

Influence of Zinc on the Acute Changes in Erythropoietin and Proinflammatory Cytokines with Hypoxia

Baranauskas, Marissa N., Joseph Powell, Alyce D. Fly, Bruce J. Martin, Timothy D. Mickleborough, Hunter L. Paris, and Robert F. Chapman. Influence of zinc on the acute changes in erythropoietin and proinflammatory cytokines with hypoxia. High Alt Med Biol. 22: 148-156, 2021. Background: Considerable, unexplained, interindividual variability characterizes the erythropoietin (EPO) response to hypoxia, which can impact hematological acclimatization for individuals sojourning to altitude. Zinc supplementation has the potential to alter EPO by attenuating increases in inflammation and oxidative stress. Yet, the application of such an intervention has not been evaluated in humans. In this proof-of-concept study, we aimed to evaluate the EPO and inflammatory responses to acute hypoxia in human participants following chronic zinc supplementation. Methods: Nine physically active participants (men n = 5, women n = 4, age 28 ± 4 years, height 176 ± 11 cm, mass 77 ± 21 kg) were exposed to 12 hours of normobaric hypoxia simulating an altitude of 3,000 m (F_iO₂ = 0.14) before and after 8 weeks of supplementation with 40 mg/day of elemental zinc from picolinate. Blood samples for subsequent analysis of serum zinc, EPO, superoxide dismutase (extracellular superoxide dismutase [EC-SOD]), C-reactive protein (CRP), and proinflammatory cytokines were obtained pre- and postsupplementation and exposure to hypoxia. Results: After zinc supplementation, EPO increased by 64.9 ± 36.0% (mean ± standard deviation) following 12 hours of hypoxia, but this response was not different from presupplementation (70.8 ± 46.1%). Considerable interindividual (range: -1% to +208%) variability was apparent in the acute EPO response. While most markers of inflammation did not change with hypoxia, interleukin-6 concentrations increased from 1.17 ± 0.05 to 1.97 ± 0.32 pg/ml during the final 6 hours. The acute EPO response at 12 hours was not related to changes in serum zinc, EC-SOD, CRP, or proinflammatory cytokines. Conclusions: Zinc supplementation does not influence the acute EPO or inflammatory response with short-term exposure to moderate levels of normobaric hypoxia (3,000 m) in apparently healthy young adults.

0242 Efficient Perception-Action Coupling Relates to More Slow Wave Sleep in Military Personnel

Introduction

The ability to adapt actions to perceptions of environmental constraints, perception-action coupling, may be compromised by military operational stress (caloric restriction, sleep disruption, physical exertion). Differences in sleep may influence susceptibility to these stressors. We investigated perception-action coupling during simulated military operational stress and the influence of sleep on perception-action coupling.

Methods

During a 5-day simulated military operational stress protocol, thirty-six (6 female) service members (25.8 ± 4.7 years) completed three trials of a perception-action coupling task (PACT) in the evening after a night of baseline sleep (BASE), two nights of sleep restriction (T1) and a night of recovery sleep (T2). Participants had 8-hr for baseline and recovery sleep (2300-0700) and 4-hr disturbed sleep on sleep restriction nights (0100-0300 and 0500-0700). Polysomnography was used to determine time spent in different sleep stages: stage 2 (N2), slow wave (SWS) and rapid-eye movement (REM). The tablet-based PACT requires participants make quick, accurate perceptual judgments and responses about the ability of virtual balls to fit through virtual apertures. Linear mixed models were used to assess interaction and main effects of study day and prior sleep on PACT response time (RT) and accuracy (ACC).

Results

No significant sleep x time interactions or significant main effect of time were found for RT or ACC. A significant main effect of SWS was found for RT (F1,88.307 = 4.331, p = .04). Higher SWS was related to lower (faster) RT. No significant main effects of other sleep stages were found.

Conclusion

Perception-action coupling was maintained during simulated military operational stress. Participants with more SWS across the study responded faster during the PACT but N2 and REM sleep did not relate to perception-action coupling performance, suggesting a specific effect of SWS on perception-action coupling abilities and behaviors.

Support

Department of Defense Award #W81XWH-17-2-0070 (PI: Nindl)

Evaluation of walking speed and functional ambulation categories in geriatric day hospital patients

Functional ambulation categories (0-5) were recorded on 105 patients on the first and last days of a day hospital physiotherapy programme. Walking speed was measured in patients capable of walking without physical support from another person (functional ambulation categories 3-5). Patients attended for a median of 10 therapy days. Ambulation categories improved in 26 patients, deteriorated in three patients and there was no change in 76 patients. Mean walking speed, measured in 61 patients who did not change walking aid, increased from 0.38 to 0.44 metres per second (p = 0.003). Forty-three patients who did not show improvement in functional ambulation category had an increase in mean walking speed from 0.37 to 0.43 metres per second (p = 0.015). Both measurements are valuable, complementary and suitable for routine use in day hospital practice. Together they provide a basis for assess ing effectiveness of therapy.

The effects of chiropody on the gait speed of a frail elderly population

There is a high incidence of foot deformities in the elderly population accompanied by difficulties in self-care. Chiropody is widely recommended but there have been no studies looking at its effects on mobility in the elderly. This study examined 55 elderly patients attending the Glasgow Eastern District Geriatric Services. Gait speed was measured before and after chiropody to see if there was any beneficial effect on mobility. There was no significant difference in gait speed before and after chiropody (medians 0.21 m/s versus 0.34m/s; 95% confidence interval for the difference between the medians, -0.17-0.08m/s). The subjective impression of the patients is that 60% thought that their foot condition had affected mobility and that their walking had been improved by chiropody. Although there has been no objective change in gait speed, this does not preclude other changes in mobility level which may be identified in further studies.

Patient outcomes using revised guidance NHS Continuing Care Eligibility Criteria, Scotland (CEL 2008)

AIM

To determine the efficacy of selection of patients for NHS (Scotland) continuing care using revised guidance eligibility criteria, CEL (2008).

METHODS

On September 2009, a census was conducted of 632 patients, distributed over 10 hospital sites in NHS Lanarkshire Older People's Directorate, to identify those patients who had future care needs assessed using revised NHSS CEL (2008) eligibility criteria during the previous 3 months. These patients were then assigned to one of four categories: (1) eligible for NHS continuing care; (2) likely destination care home; (3) likely discharge home with complex care package; and (4) outcome uncertain. 'Frailty' was recorded in a sub-group of patients using Rockwood's frailty index. The index records frailty on a scale 0-1, a higher score indicating greater frailty. Outcomes were recorded at 2-monthly intervals for 1 year. Patients undergoing acute assessment and/or specialist rehabilitation, those admitted before 1 April 2009 and already accepted for NHS continuing care and those with a planned discharge date were excluded.

RESULTS

Two hundred and eleven patients were identified as meeting the criteria for allocation to one of the four categories. Mortality at 1 year was as follows: NHS continuing care 40/45 (89%), likely Care Home destination 39/81 (48%), likely home discharge 22/61 (35%), outcome uncertain 13/24 (54%). Mean frailty scores were: NHS continuing care 0.4, likely care home 0.34, likely discharge home 0.29; p=0.0002 (ANOVA). Re-admission rates were high, 60% once and 40% twice or more, in patients discharged from hospital.

CONCLUSION

The revised guidance on Eligibility for NHS Continuing Care in Scotland, CEL (2008), is useful in identifying the frailest patients with complex needs and limited survival. However, hospital re-admission rates and mortality are high in all patients considered for eligibility to NHS continuing care in whom the guidance is applied.

Effect of acute caffeine ingestion on EPOC after intense resistance training

AIM

This study investigated the effect of acute caffeine (CAF) intake on postexercise oxygen consumption (EPOC) after intense resistance training.

METHODS

Fourteen strength-trained men (mean ± SD age and mass =23.1 ± 4.2 yr and 83.4 ± 13.2 kg, respectively) who were caffeine users initially completed one-repetition maximum testing (1-RM) of four exercises: bench press, leg press, lat row, and shoulder press. On each of two days separated by one week, they completed four sets of each exercise to fatigue at 70-80% 1-RM, which was preceded by ingestion of CAF (6 mg/kg) or placebo. Pre-exercise, indirect calorimetry was used to assess energy expenditure for 35 min; this was repeated for 75 min postexercise while subjects remained seated in a quiet lab. Two-way analysis of variance with repeated measures was used to examine differences in gas exchange variables across time and treatment.

RESULTS

Results revealed that EPOC was significantly higher (P<0.05) with CAF (26.7 ± 4.1 L) compared to placebo (22.8 ± 3.8 L). With CAF ingestion, oxygen uptake was significantly higher (P<0.05) from 10 min pre-exercise to 70 min postexercise. Respiratory exchange ratio was significantly different (P<0.05) with CAF versus placebo. Caffeine intake increased total energy expenditure by 15% (P<0.05), but the additional calories burned was minimal (+27 kcal).

CONCLUSION

Caffeine ingestion in individuals regularly completing rigorous resistance training significantly increases EPOC and energy expenditure pre-and post-exercise, yet the magnitude of this effect is relatively small.

Low mean level sustained and intermittent grip exertions: influence of age on fatigue and recovery

The goal of this study was to quantify localised muscle fatigue resulting from low mean levels of exertion in younger (< 40 years) and older (> 50 years) adults. Fatigue, elicited in the finger flexor muscles by intermittent (10% mean maximum voluntary contraction (MVC)) and sustained (8% MVC) handgrip exercises, was quantified by a muscle twitch force response before, immediately after and during 3 h following exercise. Despite greater mean loads, recovery time was shorter following intermittent than sustained contractions, which suggests that recovery from fatigue is more sensitive to rest within the work cycle than mean work. The more pronounced effects for younger than older individuals following the sustained exertion indicate that changes in muscle fibre type composition might predispose older individuals to be more resistant to fatigue resulting from sustained contractions of low level. Performing hand exertion tasks requiring low mean force levels contributes to similar long-lasting fatigue effects regardless of gender and age. Intermittent periods of complete rest reduce muscle fatigue. Since fatigue was not perceived during recovery from the tested sustained and intermittent contractions, subjective evaluations may not be a reliable indicator of localised muscle fatigue.

Ankylosing spondylitis: an Australian experience

BACKGROUND

The purpose of this study was to characterize an Australian cohort of ankylosing spondylitis (AS) patients and examine predictors of important disease outcomes.

METHODS

Cross-sectional study of first visit data among patients referred to the Austin Spondylitis Clinic from rheumatology or general practices. We obtained clinical and laboratory data and validated composite indices through self-reported questionnaire.

RESULTS

Delay in AS diagnosis averaged 8.1 years and was higher among women and younger-onset disease. Cervicothoracic mobility was better in women although they showed more entheseal tender points and greater impairment of quality of life. Those with long-standing AS had similar disease activity to recent onset disease but had greater functional disability. Current smoking was associated with worse outcomes although there was no association between cumulative exposure and AS outcomes.

CONCLUSION

The clinical expression of AS in this first-described Australian cohort is similar to previously described cohorts. We observed greater cervicothoracic mobility and a higher enthesitis index among women perhaps contributing to longer delay to diagnosis.

Predictors of perceived effort in the shoulder during load transfer tasks

The mechanism of muscular effort perception in the shoulder was examined in this experiment. Two shoulder biomechanical models and experimental muscle activity data were used to assess physical exposure for a series of reaching tasks. Effort perception was quantitatively correlated to these measures of physical loading, both at the resultant torque (r(2) = 0.50) and muscle activity model-based muscle force predictions (MFPs): r(2) = 0.42, electromyography (EMG): r(2) = 0.26) levels. Muscle data did not explain variation in effort perception more fully than torque data. The inclusion of subject and task variables improved the ability of each model to explain variability in effort perception (torque: r(2) = 0.74; MFP: r(2) = 0.67, EMG: r(2) = 0.64). These results suggest that effort perception may not be fully explained by only an image of the motor command, but is rather a complex integrative quantity that is affected by other factors, such as posture and task goals, which may be dependent on sensory feedback.

Expanding course goals beyond disciplinary boundaries: physiology education in an undergraduate course on psychoactive drugs

The topic of psychoactive drugs is one of inherent interest to college students. We used this insight to design and implement a multidisciplinary undergraduate course with psychoactive drugs as the central theme. The Medical Science of Psychoactive Drugs examines the biological mechanisms underlying all major effects of psychoactive drugs, including the effects on the brain and other organs and tissues. Physiological principles, molecular mechanisms, and genetic factors involved in drug-induced therapeutic and adverse effects are emphasized. The course is open to undergraduate students at all levels and carries no prerequisites, and enrollment is limited to approximately 50 students. Major teaching modes include lecture, short homework papers on topics related to the previous class meeting, small-group discussions at several points during each class, and whole class discussions. Because of the diversity of students' knowledge of basic science, we employ a variety of methods designed to help students grasp the necessary scientific concepts. Our methods are intended to be inquiry based and highly interactive. Our goals are 1) to foster the development of an organized knowledge base about psychoactive drugs that will have practical applicability in the daily lives of the students; 2) to promote the rational application of this knowledge in thinking about current medical, social, legal, and ethical issues involving psychoactive drugs; and 3) to cultivate science literacy, critical thinking, and communication skills among students.

A memory-based model for planning target reach postures in the presence of obstructions

Existing posture prediction and motion simulation models generally lack the capability of simulating human obstruction avoidance during target reach. This compromises the utility of digital human models for ergonomics, as many design problems involve interactions between humans and obstructions. To address this problem, this paper presents a novel memory-based posture planning (MBPP) model, which plans reach postures that avoid obstructions. In this model, the task space is partitioned into small regions called cells. For a given human figure, each cell is linked to a memory that stores various alternative postures for reaching the cell. When a posture planning problem is given in terms of a target and an obstruction configuration, the model examines postures belonging to the relevant cell, selects collision-free ones and modifies them to exactly meet the hand target acquisition constraint. Simulation results showed that the MBPP model is capable of rapidly and robustly planning reach postures for various scenarios.

Prostate Specific Antigen Isoforms and Human Glandular Kallikrein 2—Which Offers the Best Screening Performance in a Predominantly Black Population?

PURPOSE

Free prostate specific antigen, complexed PSA and human glandular kallikrein 2 have independently been tested against the gold standard of total PSA for prostate cancer screening in largely white populations. With the incidence of prostate cancer much higher in black men, we sought to evaluate these markers simultaneously in a predominantly black population.

MATERIALS AND METHODS

A total of 138 men, of whom 108 were black, underwent ultrasound guided biopsy of the prostate for tPSA levels greater than 2.5 ng/ml or an abnormal digital rectal examination. Sera were drawn before biopsy and analyzed for tPSA, fPSA, cPSA and hK2 concentrations using standard methods (hK2 assay is for research use only, not for use in diagnostic procedures). The areas under the receiver operator characteristic curves were determined for each marker as well as biomarker combinations. Additionally, each parameter's specificity, positive and negative predictive values, and theoretical screening efficiency were assessed at or above the 95% sensitivity level.

RESULTS

A total of 43 (31.1%) men had prostate cancer by biopsy. While the AUC for %fPSA was statistically the highest (0.822, p <0.001), cPSA offered the highest specificity (31.6%) and positive predictive power (31.7%) of any of the tested biomarkers at comparable sensitivity (greater than 95%). The calculated efficiency of cPSA (51.4%) was also higher than the other markers. Nearly 20% of biopsies would be avoided using cPSA vs standard tPSA screening methods.

CONCLUSIONS

Comparing the major PSA isoforms and hK2, cPSA alone appears to offer superior diagnostic discrimination for cancer detection in a predominantly black population.

Total synthesis of myxothiazols, novel bis-thiazole β-methoxyacrylate-based anti-fungal compounds from myxobacteria

Convergent total syntheses of myxothiazols A and Z are described. The syntheses are based on elaboration of the (S)-E,E-diene thioamide 22, conversion of 22 into the bis-thiazole 27 and Wittig reactions between 27c and the aldehyde 30. The substituted beta-methoxyacrylate aldehyde 30 was produced via an Evans asymmetric aldol protocol or via the 2H-pyran-2-one 31. An E-selective Wittig reaction between the ylide derived from the phosphonium salt 27c and the (+)-aldehyde 30 led to (+)-myxothiazol Z (1b), and a corresponding reaction with the (+/-)-acrylamide aldehyde 44 gave (+/-)-myxothiazol A (1a). Complementary studies led to synthesis of the ester 47b, corresponding to myxothiazol R and myxothiazol S.

Effects of low back disability status on lower back discomfort during sustained and cyclical trunk flexion

A laboratory study was conducted to determine the effects of back disability status on endurance time and perceived discomfort during trunk flexion. Eighty participants (40 with chronic or recurrent low back pain (CRLBP), 40 pain-free) were tested. The trunk was flexed to 15 degrees, 30 degrees, 45 degrees and 60 degrees under three conditions: 1) continuous static flexion; 2) cyclical flexion with 20% rest; and 3) cyclical flexion with 40% rest. Each condition was performed for up to 600 s or until the participant reached his/her pain tolerance limit. Dependent variables included time to distracting discomfort (TDD), total endurance time (TET) and perceived discomfort. For continuous exertions, CRLBP participants had lower TDD (p < 0.001), lower TET (p < 0.001) and greater discomfort (p < 0.001) compared to pain-free controls. In both groups, TDD and TET decreased and perceived discomfort increased as the flexion angle increased. For intermittent exertions, CRLBP participants reported greater discomfort than pain-free participants (p < 0.001). Increasing rest from 20 to 40% reduced discomfort in CRLBP participants, but produced no consistent benefit in pain-free participants. To accommodate persons with CRLBP, consideration should be given to reducing both the magnitude (angle) and duration of trunk flexion required by their jobs.

Early detection of prostate cancer in African-American men through use of multiple biomarkers: human kallikrein 2 (hK2), prostate-specific antigen (PSA), and free PSA (fPSA)

Recent studies have reported enhanced prostate cancer detection in Caucasians with serum human glandular kallikrein 2 (hK2) in combination with total- (tPSA) and free-prostate-specific antigen (fPSA). The purpose of this study is to validate these findings in an African-American patient cohort. A total of 137 African-American men were found by routine screening to have tPSA levels above 2.5 ng/ml or an abnormal digital rectal examination. Sera were drawn prior to biopsy of the prostate and Hybritech PSA, FPSA and hK2 (for research use only, not for use in diagnostic procedures) concentrations were determined on Beckman Coulter's Access immunoanalyzer. These independent variables and the ratios of percent fPSA (%fPSA), hK2/tPSA, hK2/fPSA, and hK2*tPSA/fPSA were compared between cancer and non-cancer groups. In all, 49 of 137 men had prostate cancer. hK2 and its calculated ratios outperformed tPSA on receiver operator characteristic (ROC) analysis, but %fPSA had statistically the highest area under the curve (AUC) at 0.801. When restricting the analysis to only the tPSA range of 4.0-10 ng/ml, hK2/fPSA yielded the highest AUC (0.721). The ratio of hK2/fPSA was also found to increase the positive predictive value (PPV) of the %fPSA ranges less than 10 and 10-25%. %fPSA offered the best performance and highest specificity in prostate cancer detection in African-American males over the entire range of tPSA. hK2/fPSA may offer modest improvement in the tPSA range of 4.0-10 ng/ml. Furthermore, hK2/fPSA can enhance the PPV of low %fPSA values. Therefore, the use of multiple biomarkers may ultimately increase the specificity of prostate cancer screening in African-American men.

cPSA and fPSA elimination in African-American men

In all, 22 African-American males undergoing radical prostatectomy for prostate adenocarcinoma had serum drawn for tPSA, cPSA, and total protein concentrations prior to, during, and after operation to determine the respective elimination rates. African-American cPSA was found to fit best a simple first-order exponential elimination kinetic, with a half-life of 44.6 h. fPSA followed a two-compartment elimination with an alpha-phase elimination of 0.50 h and a beta-phase half-life of 4.2 h. Our results suggest higher rates of elimination for both cPSA and fPSA in an African-American male population with respect to Caucasians and may account for differences in PSA values between races.

Outcome, functional recovery and unmet needs following acute stroke. Experience of patient follow up at 6 to 9 months in a newly established stroke service

OBJECTIVE

To assess outcome at six months post stroke and the unmet needs and adherence to the secondary prevention advice among survivors living at home.

SETTING

Stroke Rehabilitation Unit (SRU), Hairmyres Hospital and patients homes.

SUBJECTS

Survivors living at home who had been managed in the SRU.

RESULTS

Of 572 consecutive patients with confirmed acute stroke, 301 were managed in the SRU and 179 of these were reviewed at home between 6 and 9 months post acute stroke incident. One hundred and thirty seven (76%) survivors at home were living with a carer. Sixty-eight (38%) had had no personal contact with their General Practitioner since discharge from hospital, although 83 (46%) had attended or were attending day hospital. Thirty-two individuals (18%) had resumed smoking. One hundred and forty nine survivors (83%) still required assistance with daily living tasks. One hundred and fifteen patients (64%) required medication advice. One hundred and forty one (79%) had health concerns. Eight subjects had returned to paid employment. Issues raised by survivors included a feeling of being abandoned by the healthcare system, poor access to professional psychological support and a fear of further stroke.

CONCLUSION

There is a need for continuing patient education, improved support for stroke survivors and more active involvement of Primary Care Services in the care of stroke patients following hospital discharge.

Capillary density and retinal diameter measurements and their impact on altered retinal circulation in glaucoma: a digital fluorescein angiographic study

AIM

Normal pressure glaucoma (NPG) patients exhibit prolonged retinal arteriovenous passage times in fluorescein angiography and colour Doppler imaging suggests increased resistance downstream from the central retinal and posterior ciliary arteries. The aim of the study was to elucidate the morphological source of decreased perfusion and increased resistance of the ocular circulation in NPG.

METHODS

Retinal arteriovenous passage time (AVP) and peripapillary arterial and venous diameters were measured in digital scanning laser fluorescein angiograms. For estimation of retinal capillary density the area of the foveal avascular zone (FAZ) and the perifoveal intercapillary area (PIA) was quantified. 36 patients with NPG (mean age 57 (SD 13) years) and 21 healthy subjects (mean age 51 (13) years) were enrolled in the comparative study.

RESULTS

In NPG patients the AVP (2.55 (1.1) seconds) was significantly prolonged (p<0.001) when compared with healthy subject data (AVP: 1.70 (0.39) seconds). No differences for arterial or venous diameter, FAZ, and PIA were observed in NPG patients compared with healthy subjects. FAZ, PIA, arterial and venous diameter were not correlated with visual field indices (except venous diameter with PSD, r=0.35 (p<0.05)) or cup to disc ratios. AVP was significantly correlated (p<0.05) with the size of the optic nerve head (r=-0.28), visual field indices (MD: r=-0.3; PSD: r=0.3; CPSD: r=0.3), and contrast sensitivity (r=-0.34).

CONCLUSION

AVP times are significantly prolonged in NPG. The slowing of the retinal transit does not result from capillary dropout, or changes of peripapillary arterial or venous diameters with increased vascular resistance.

Mesenchymal stem cells: stealth and suppression

Human post-natal bone marrow contains mesenchymal stem cells (MSCs), which are capable of giving rise to multiple mesenchymal cell lineages. Large quantities of human MSCs can be readily obtained following a simple bone marrow aspiration procedure and subsequent expansion over a million-fold in culture. This extensive capacity for clinical scale expansion in vitro has facilitated the development of preclinical models as well as clinical studies designed to assess the safety, feasibility, and efficacy of transplanting allogeneic MSCs for a variety of indications. This review focuses on the rationale for performing clinical studies of MSC transplantation and will discuss the potential role that MSCs may have in the field of hematopoietic stem cell transplantation as well as for the repair or regeneration of bone, cartilage, and cardiac tissues.

Randomized controlled trial of quadriceps training after proximal femoral fracture

OBJECTIVE

To determine whether systematic progressive high-intensity quadriceps training increases leg extensor power and reduces disability in patients rehabilitating after proximal femoral fracture.

DESIGN

Open parallel group randomized controlled trial comparing the addition of six weeks quadriceps training (40 patients) with standard physiotherapy alone (40 patients). The training group exercised twice weekly, with six sets of 12 repetitions of knee extension (both legs), progressing up to 80% of their one-repetition maximum.

SETTING

Orthogeriatric unit, and community follow-up.

SUBJECTS

Eighty patients rehabilitating after proximal femoral fracture.

MAIN OUTCOME MEASURES

Measurements of leg extensor power (Nottingham Power Rig), functional mobility (elderly mobility score), disability (Barthel Index) and quality of life (Nottingham Health Profile) were made at baseline, after six weeks (at the end of the intervention) and at 16 weeks.

RESULTS

Leg extensor power increased significantly in the quadriceps training group (fractured leg mean improvement at six weeks 157% (standard error 16), nonfractured leg 80% (12)) compared with the control group (63% (11) and 26% (8) respectively, unpaired Student's t-test p = 0.007 and p = 0.01 for between-group comparisons). Significant benefits were maintained at 16 weeks. Quadriceps training resulted in a greater increase in elderly mobility scale score compared with standard rehabilitation (between-group difference of 2.5 (95% CI 1.1,3.8) at week 6 and 1.9 (0.4,3.4) at week 16). Barthel score increased significantly from week 0 to 6 in the quadriceps training group compared with controls (Mann-Whitney U-test p = 0.05). Patients in the quadriceps training group scored significantly better in the energy subscore of the Nottingham Health Profile at the end of follow-up (Mann-Whitney U-test p = 0.0185).

CONCLUSIONS

Progressive high-intensity quadriceps training in elderly proximal femoral fracture patients increased leg extensor power and reduced disability. This was accompanied by an increase in energy as measured by the Nottingham Health Profile. This intervention may provide a simple practical way of improving outcome in these patients.

A comparison of mobility assessments in a geriatric day hospital

OBJECTIVE

To assess the sensitivity of the Elderly Mobility Scale (EMS) to detect improvements in mobility after physiotherapy in comparison with the Barthel Index (BI) and Functional Ambulation Category (FAC) in routine clinical day hospital practice.

SUBJECTS

Eighty-three patients who completed a course of physiotherapy were studied.

METHODS

Each was assessed by an independent physiotherapist before and after a programme of physiotherapy, using the EMS, BI and FAC.

RESULTS

The mean age was 79 years (SD 7.7). Fifty-three out of 83 (64%) patients were female and 92% were community dwelling. The median number of physiotherapy sessions undergone by each patient was 9 (range 3-51). All three scales detected an improvement in mobility with physiotherapy (p < 0.001). However, using the EMS, 68 out of 82 (83%) patients had a detectable improvement in mobility compared with only 34 out of 80 (42%) using the BI and 28 out of 81 (35%) using the FAC. Using a matched-pairs comparison, the EMS was significantly more likely to detect an improvement in mobility following physiotherapy within the study group than the BI (p < 0.001) or the FAC (p < 0.001).

CONCLUSION

Although all three scales detected improvements in mobility, the EMS detected mobility improvements in a significantly greater number of patients.

Ocular perfusion and age-related macular degeneration

PURPOSE

To review the role of ocular perfusion in the pathophysiology of age-related macular degeneration (AMD), the leading cause of irreversible blindness in the industrialized world.

METHODS

Medline search of the literature published in English or with English abstracts from 1966 to 2000 was performed using various combinations of relevant key words.

RESULTS

Vascular defects have been identified in both nonexudative and exudative AMD patients using fluorescein angiographic methods, laser Doppler flowmetry, indocyanine green angiography, and color Doppler imaging.

CONCLUSION

Although these studies lend some support to the vascular pathogenesis of AMD, it is not possible to determine if the choroidal perfusion abnormalities play a causative role in nonexudative AMD, if they are simply an association with another primary alteration, such as a primary RPE defect or a genetic defect at the photoreceptor level, or if they are more strongly associated with one particular form of this heterogeneous disease. Further study is warranted.

Estrogen-replacement therapy: effects on retrobulbar hemodynamics

PURPOSE

Estrogen-replacement therapy causes vasodilation and increased blood flow in major peripheral arteries. We examined the role that estrogen may play in enhancing perfusion within the watersheds of several major and minor retrobulbar arteries.

METHODS

Postmenopausal women receiving estrogen-replacement therapy (n = 16) were compared with both age-matched women not receiving estrogen (n = 16) and with young women (n = 20). Studies involved color Doppler imaging analysis of flow velocities measured in the ophthalmic, central retinal, and nasal and temporal posterior ciliary arteries.

RESULTS

In the ophthalmic artery, young women and postmenopausal women receiving estrogen exhibited reduced resistance indexes as compared with postmenopausal women not receiving estrogen (each P <. 001). In contrast, flow velocities in the central retinal artery were similar among the three groups of women. In the posterior ciliary arteries, a different pattern emerged: young women, as compared with either group of postmenopausal women, showed greater peak systolic and end-diastolic velocities at similar resistance index (each P <.05).

CONCLUSIONS

Estrogen-replacement therapy in postmenopausal women apparently helps reduce vascular resistance distal to the ophthalmic artery to levels matching those of young women. However, estrogen replacement has little impact on flow velocities in the posterior ciliary arteries. In those vessels, aging per se may reduce perfusion, potentially contributing to the age-dependent risk of major eye diseases, such as glaucoma and age-related macular degeneration.

The effects of keyswitch stiffness on typing force, finger electromyography, and subjective discomfort

The effects of keyswitch stiffness and key action on typing force, electromyography (EMG), and subjective preference were examined. Each subject's own keyboard (with an audible key click and key activation force of 0.72 N) and three keyboards with no key click that were identical in design but had different key activation forces (0.28 N, 0.56 N, and 0.83 N) were used. Subjects (24 female transcriptionists) typed on each keyboard for 15 min while typing force and left hand surface EMG of the finger flexor and extensor muscles were monitored. Subjects then used one of the keyboards at their workstations for 7 workdays and were monitored again. This procedure was repeated for all four keyboards. Typing force and finger flexor and extensor EMG activity were highest for the 0.83 N keyboard. Lowest EMG values were for the 0.28 N and the 0.72 N audible key click keyboards. Baseline (10th percentile) and median (50th percentile) extensor EMG values were significantly higher than flexor EMG values. Peak (90th percentile) EMG values were comparable for flexors and extensors. Mean subjective discomfort was significantly higher for the 0.83 N keyboard at the fingers (36% higher), lower arm (40% higher), and overall (39% higher). Seventeen of 24 subjects preferred the 0.72 N keyboard, 4 the 0.28 N keyboard, and 3 preferred the 0.56 N keyboard. Results suggest that increasing make force causes typing force and EMG to increase but that the ratio of 90th centile typing force to make force decreases as make force increases. Subjective discomfort was significantly higher for the keyboard with 0.83 N make force. Buckling spring keyboards have better feedback characteristics, which may be responsible for a decrease in the amount of typing force and EMG produced.

Scanning laser ophthalmoscopy-based evaluation of epipapillary velocities: method and physiologic variability

PURPOSE

Scanning laser ophthalmoscopy is capable of producing high-resolution fluorescein angiograms. Measurements of capillary blood velocities in the fovea are well established. In this study, we used an identical technique to measure particle velocities in the superficial layers of the optic nerve head. We compared these data with simultaneous velocity measurements in the retinal and macular vasculature.

METHODS

Fluorescein angiograms were performed in 30 subjects (12 men, 18 women; mean age, 26 years; standard deviation [SD], 3 years). Off-line, the velocities of hypofluorescent particles through the microvasculature of epipapillary and macular vessels were measured by image-processing techniques. We also assessed the arteriovenous passage (AVP) time of the fluorescein dye front.

RESULTS

Epipapillary blood velocities ranged from 2.7 to 6.5 mm/sec (mean, 4.0 mm/sec; SD, 0.99 mm/sec) and differed significantly from macular capillary blood velocities (MCBVs), which ranged from 1.67 to 3.31 mm/sec (mean, 2.53 mm/sec; SD, 0.34 mm/sec). The AVP time in all subjects was 1.74 +/- 0.5 sec (mean +/- SD) and correlated with the MCBV (P < 0.05, r = -0.46). Epipapillary blood velocities showed no correlation with either AVP time or MCBV.

CONCLUSIONS

The scanning laser methodology, adapted to objectively assess velocities in the epipapillary vasculature, shows that these measurements are neither correlated with velocities in the perifoveal network, nor inversely correlated with overall retinal transit time. Epipapillary blood velocities were found to be substantially higher than those measured in macular capillaries. This result might be explained by the different anatomy of epipapillary vessels compared with macular capillaries.

Regional differences in retinal vascular reactivity

PURPOSE

Although glaucomatous visual field defects are more common in the superior field than in the inferior field, microaneurysms are more frequent in the superior than in the inferior retina in diabetic retinopathy. The authors hypothesized that differences in vascular hemodynamics in the two areas might contribute to these phenomena.

METHODS

The blood flow response to hyperoxia and hypercapnia was evaluated in peripapillary retinal tissue superior and inferior to the optic nerve head using confocal scanning laser Doppler flowmetry. In 14 young, healthy persons, blood flow was measured while breathing room air and during isocapnic hyperoxia (100% O2 breathing) and isoxic hypercapnia (PCO2 increased 15% above baseline). Histograms were generated from pixel-by-pixel analysis of retinal portions of superior and inferior temporal quadrants of the entire image.

RESULTS

Baseline blood flow in the inferior temporal quadrant was significantly greater than in the superior temporal quadrant (P < 0.05). However, the inferior region failed to increase in perfusion during hypercapnia and experienced significant mean blood flow reduction; flow reduction in the pixels at the 25th, 50th, 75th, and 90th percentile of flow; and an increased percentage of pixels without measurable flow, during hyperoxia (each P < 0.05). In contrast, in the superior temporal region, hyperoxia failed to reduce blood volume, velocity, or flow, whereas hypercapnia significantly increased mean flow; increased flow in the pixels at the 25th, 50th, 75th, and 90th percentile of flow; and reduced the percentage of pixels without measurable flow (each P < 0.05).

CONCLUSIONS

The inferior temporal quadrant of the peripapillary retina is, in comparison with the superior temporas region, less responsive to vasodilation and more responsive to vasoconstriction. These differences could contribute to different susceptibility to visual field defect or vascular dysfunction in the superior and inferior retina.

Color Doppler imaging discloses reduced ocular blood flow velocities in nonexudative age-related macular degeneration

PURPOSE

To study ocular perfusion defects in age-related macular degeneration.

METHODS

Twenty-five subjects with nonexudative age-related macular degeneration were compared with 25 age-matched control subjects in studies of flow velocities in several retrobulbar vessels. Color Doppler imaging, which was performed by an examiner who was masked to the subjects' assignment to the control or age-related macular degeneration group, measured peak systolic and end diastolic velocity in the ophthalmic, central retinal, and nasal and temporal posterior ciliary arteries of one eye. A resistive index was calculated from the peak systolic and end diastolic velocity.

RESULTS

Subjects with nonexudative age-related macular degeneration showed a consistent trend toward lower peak systolic and end-diastolic velocities in the posterior ciliary arteries. For example, in the nasal posterior ciliary artery, the mean end diastolic velocity measured 1.45 +/- 0.34 cm per sec in the age-related macular degeneration group compared with 1.96 +/- 0.66 cm per sec in the control group, yielding a 26% decrease in the age-related macular degeneration group, which represented the largest difference and was highly statistically significant (P = .0012). The resistive index was not significantly altered in the nasal or temporal posterior ciliary artery. Subjects with nonexudative age-related macular degeneration did not differ from control subjects in peak systolic velocity, end diastolic velocity, or resistive index in the ophthalmic artery. In the central retinal artery, the end diastolic velocity was lower (1.37 +/- 1.95 cm per sec vs 1.95 +/- 0.66 cm per sec), whereas the resistive index was higher (0.83 +/- 0.05 vs 0.76 +/- 0.06 cm per sec), in the age-related macular degeneration group; these results were highly statistically significant (P = .0007 and P < .0001, respectively).

CONCLUSIONS

Retrobulbar vascular changes in nonexudative age-related macular degeneration subjects include reduced flow velocities in the nasal and temporal posterior ciliary arteries. The reduced peak systolic velocity, combined with the reduced end diastolic velocity at a constant resistive index, seen in nonexudative age-related macular degeneration, is consistent with reduced bulk flow in these vessels, suggesting that choroidal perfusion is abnormal in this form of age-related macular degeneration. The changes in the central retinal artery suggest there may be a more generalized perfusion abnormality beyond the choroid in patients with age-related macular degeneration or that the central retinal artery exhibits a secondary autoregulatory response to a primary change elsewhere.

Post-effects of long-term hand vibration on visuo-manual performance in a tracking task

Movement precision and performance time were evaluated through a visuo-manual tracking task performed before and after 10-min hand vibration exposure. Constant displacement amplitude vibration of 0.2 and 0.3 mm peak to peak at 90, 150, 300 Hz were applied to the hand z-axis by a vertical handle. During exposure a grip force of 5% MVC was exerted for 5 s and then relaxed for 25 s while maintaining fingers-handle contact. The tracking task consisted in moving a ring (phi = 9 mm) attached to a thin rod held between the index finger and thumb along a zig-zagged wire (phi = 3.7 mm). Alterations of tracking errors (ring-wire contact) and tracking time were analysed as a function of the vibration parameters. The tasks were performed by ten healthy participants. Vibration induced a significant increase in tracking errors (ring-wire contact) and a significant decrease in tracking time. These impairments decayed with time after vibration exposure. The recovery period was > 5 min but < 10 min with the exception of 90 Hz vibration, for which recovery could be > 10 min. The number of tracking errors was neither influenced by vibration frequency nor by amplitude. The tracking time decreased as frequency increased and recovery was related to the displacement amplitude. The subjective rating of the performance on a visual analogue scale indicated that the subjects tended to perceive the task as being easier after vibration exposure. Vibration applied to the non-dominant hand while the participant performed the tracking task had no effect. These results show that vibration similar to hand-tool vibration affects precision and velocity control of visually guided hand movements. Furthermore, these performance decrements were not consciously perceived.

Venipuncture in the medical physiology laboratory

Medical physiology laboratories, traditionally devoted to animal experimentation, face unprecedented difficulties linked to cost, staffing, instrumentation, and the use of animals. At the same time, laboratory experiences with living creatures play a unique role in medical education. In this article we describe the use of venipuncture and subsequent blood analysis, with medical students serving as both subjects and experimenters, in a sequence of first-year physiology laboratories. These experiments are safe, robust, inexpensive, and time efficient, and they teach the principles of cardiovascular, respiratory, renal, nutritional, and gastrointestinal physiology. In addition, they enhance medical education in several other important dimensions. First, they teach safe venous blood collection and handling, a training appropriate for students at this level. Second, by serving each week as subjects as well as experimenters, students experience aspects of both sides of the doctor-patient relationship. Third, the laboratories can be used to teach fundamentals of research design and analysis. Finally, because blood analysis is central to medicine, and because the student's own blood data are discussed, students are enthusiastic and cooperative, and the clinical relevance of the data is clear.

The acute effect of topical beta-adrenoreceptor blocking agents on retinal and optic nerve head circulation

PURPOSE

Topical beta-blockers are the most common treatment for ocular hypertension in glaucoma, but their ocular hemodynamic effects are not well known. We investigated the acute effects of betaxolol (beta-1 selective antagonist), levobunolol (non-selective antagonist with active polar metabolite), and timolol (non-selective antagonist) on retinal and superficial optic nerve head circulation.

METHODS

Intraocular pressure (IOP), heart rate, blood pressure, and retinal circulation were evaluated in 12 healthy subjects (6F/6M; mean age=24+/-2 years) before and two hours after instillation of each drug on separate occasions at least two weeks apart. Macular capillary blood velocity (MCBV), epipapillary blood velocities (EBV), arteriovenous passage (AVP) times, and arterial and venous diameters were measured by digital image analysis of scanning laser fluorescein angiograms.

RESULTS

All drugs significantly (p<0.05) reduced IOP. There was no significant effect on blood pressure or calculated ocular perfusion pressure. Only levobunolol significantly lowered heart rate (p<0.05). Each drug produced a significant (p<0.01) decrease in AVP time of approximately 25%. MCBV was significantly (p<0.01) increased by approximately 20% in all three conditions; each drug also produced significant (p<0.01) increases in EBV. Arterial and venous diameters remained unaffected.

CONCLUSION

All three drugs, despite different beta-adrenergic properties, increased blood velocities in retinal and epipapillary capillaries. These changes, occurring as they do in concert with decreased retinal arteriovenous passage time at constant retinal arterial and venous diameter, may indicate improved retinal perfusion after drug treatment. Improved circulation, if it indeed occurs, in tandem with reduced IOP, might explain in part the beneficial effect of beta-adrenoreceptor blocking agents in glaucomatous patients.

Pyruvate augments calcium transients and cell shortening in rat ventricular myocytes

Pyruvate has been shown to be a metabolic inotrope in the myocardium. In millimolar concentrations, it has been shown to increase both myocardial phosphorylation potential and the cytosolic [NAD+]-to-[NADH] ratio. To determine if changes in these parameters can alter intracellular Ca2+ concentration ([Ca2+]i) and hence contractile function, Ca2+ transients and cell shortening (CS) were measured in isolated rat ventricular myocytes superfused with a physiological N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid buffer (11 mmol/l glucose) with and without additional pyruvate, L-lactate, acetate, or isoproterenol. The addition of 5 mmol/l pyruvate resulted in a 33% increase in CS and a 39% increase in systolic [Ca2+]i. These pyruvate effects were 70% of those observed with 100 nmol/l isoproterenol. The mitochondrial monocarboxylate transport inhibitor alpha-cyano-4-hydroxycinnamate (250 mumol/l) strongly inhibited pyruvate inotropy, suggesting a substantial obligatory coupling between pyruvate inotropism and its oxidation by the mitochondria. A possible role of the cytosolic [NAD+]-to-[NADH] ratio was assessed by comparing the effects of 20 mmol/l L-lactate to those of equimolar pyruvate. In contrast to 20 mmol/l pyruvate, excess L-lactate failed to appreciably increase CS or systolic [Ca2+]i. The findings imply that, at levels substantially above 5 mmol/l, a portion of pyruvate inotropism might be due to extreme cytosolic [NAD+]-to-[NADH] ratios. This study is the first evidence that augmented [Ca2+]i transients are most likely the mechanism of cardiac pyruvate inotropism.

The effect of keyboard keyswitch make force on applied force and finger flexor muscle activity

The design of the force-displacement characteristics or 'feel' of keyboard keyswitches has been guided by preference and performance data; there has been very little information on how switch 'feel' alters muscle activity or applied force. This is a laboratory-based repeated measures design experiment to evaluate the effect of computer keyboard keyswitch design on applied finger force and muscle activity during a typing task. Ten experienced typists typed on three keyboards which differed in keyswitch make force (0.34, 0.47 and 1.02 N) while applied fingertip force and finger flexor electromyograms were recorded. The keyboard testing order was randomized and subjects typed on each keyboard for three trials, while data was collected for a minimum of 80 keystrokes per trial. No differences in applied fingertip force or finger flexor EMG were observed during typing on keyboards with switch make force of 0.34 or 0.47 N. However, applied fingertip force increased by approximately 40% (p < 0.05) and EMG activity increased by approximately 20% (p < 0.05) when the keyswitch make force was increased from 0.47 to 1.02 N. These results suggest that, in order to minimize the biomechanical loads to forearm tendons and muscles of keyboard users, keyswitches with a make force of 0.47 N or less should be considered over switches with a make force of 1.02 N.

Effects of ischemia, preconditioning, and adenosine deaminase inhibition on interstitial adenosine levels and infarct size

In order to examine the relationship between local adenosine concentrations before, during, and after ischemia and the extent of ischemic myocardial damage, measurements of interstitial fluid (ISF) nucleosides were made using microdialysis probes implanted in the ischemic region of isoflurane anesthetized Micropigs undergoing 60' coronary artery occlusion (CAO) and 3 h of reperfusion (REP). Nucleoside concentrations in the dialysate collected from the microdialysis probes were used as an index of ISF levels. Dialysate nucleoside concentrations (ADO, inosine and hypoxanthine), myocardial infarct size, and myocardial blood flow (MBF) were determined in control animals (n = 6), animals preconditioned with a single 10' cycle of CAO and REP (PC, n = 6), and those treated with the adenosine deaminase inhibitor pentostatin (n = 6, 0.2 mg/Kg i.v. 30' prior to CAO). The brief PC occlusion resulted in a transient but significant increase in dialysate ADO (6.7 +/- 1.8 microM vs. 0.67 +/- 0.1 microM at baseline). Pentostatin administration had no significant effect on either dialysate nucleosides or MBF at baseline. During the 60' CAO, dialysate ADO increased in control animals. In PC animals, however, dialysate ADO during CAO was lower than control. Pretreatment with pentostatin resulted in a six-fold augmentation in dialysate ADO during the 60 min CAO when compared to the control values (110.62 +/- 30.2 microM vs. 16.31 +/- 2.1 microM at 60 min of ischemia). Pentostatin also resulted in a significant reduction in the accumulation of inosine and hypoxanthine, indicating inhibition of adenosine deaminase activity. There were no significant differences in MBF between groups at any time point. Following 3 h REP, infarct size was 35.4 +/- 5.5%, 8.1 +/- 1.5% and 8.3 +/- 1.8% of the region at risk in control, PC, and pentostatin groups, respectively. These data suggest that marked increase in ISF ADO during CAO, may be as effective in reducing INF as a modest increase in ISF ADO prior to prolonged CAO.

Infarct size reduction with the nucleoside transport inhibitor R-75231 in swine

Adenosine (Ado) has been reported to be cardioprotective in several models of myocardial ischemia. The nucleoside transport inhibitor R-75231 (R-75) has been reported to enhance local Ado concentrations and postischemic recovery of function, but little is known regarding its effects on myocardial infarct size. The purpose of the present study was to determine the effects of R-75 on infarct size and to measure myocardial regional Ado concentrations. Studies were conducted in pentobarbital-anesthetized swine undergoing 60 min of coronary artery occlusion and 2 h of reperfusion. Control pigs (n = 8) were compared with those receiving R-75 (0.1 mg/kg i.v.) 15 min before either occlusion (Pre R-75, n = 8) or reperfusion (Rep R-75, n = 8). Interstitial fluid (ISF) Ado, coronary venous Ado, and infarct size (% of the region at risk) were measured. In the Pre R-75 group, ISF Ado concentrations were significantly increased before and during ischemia, reaching a peak value of 71.8 +/- 8.6 microM (vs. 16.8 +/- 0.8 microM in control). ISF inosine and hypoxanthine concentrations were significantly reduced during ischemia in Pre R-75 animals. Infarct size was smaller in Pre R-75 compared with control (21.6 +/- 1.9 vs. 38.4 +/- 2.6%, P < 0.05). The Rep R-75 group had significantly elevated coronary venous Ado concentrations but no increases in ISF Ado or reduction in infarct size (33.5 +/- 3.5%). These data indicate that R-75 increases myocardial Ado and reduces infarct size when administered before coronary occlusion. The R-75-induced reduction in infarct size appears to be related to the augmentation of ISF Ado before ischemia rather than to increased plasma Ado during reperfusion.

Altered retrobulbar vascular reactivity in early diabetic retinopathy

AIM/BACKGROUND

In diabetic eye disease the factors leading to compromised circulation and the resulting loss of visual function are poorly understood. Although retinal circulation has been widely investigated, it accounts for only a fraction of total eye blood flow. Blood flow was investigated in the larger vessels feeding the eye in patients with early diabetic retinopathy.

METHODS

Eleven patients with early diabetes with minimal or no retinopathy and 11 healthy controls were evaluated for retrobulbar blood flow velocity using colour Doppler imaging for the ophthalmic and central retinal arteries. Patients and subjects were tested while breathing room air and again under conditions of isocapnic hyperoxia.

RESULTS

Hyperoxia induced a significant change in the central retinal artery end diastolic velocity (EDV) (p = 0.008) and resistance index (RI) (p = 0.032) in normal subjects, but not in diabetic patients. Consequently, during hyperoxia, the diabetic patients were significantly higher for EDV (p = 0.006) and significantly lower for RI (p = 0.002) compared with normal controls. Hyperoxia caused no significant change in either group in the ophthalmic artery; nevertheless, under isocapnic hyperoxia conditions the diabetic patients had lower peak systolic velocity (p = 0.05) and lower RI (p = 0.05) than normal subjects.

CONCLUSIONS

Imposition of isocapnic hyperoxia produces significant differences in the ophthalmic and central retinal artery blood flow velocities in diabetic patients with early disease when compared with normal subjects. These results demonstrate that diabetic patients with minimal or no retinopathy suffer from irregular ocular vascular function in the major vessels feeding the eye.

Erythrocyte magnesium in elderly patients: not a reliable guide to magnesium status

To assess body magnesium status in various illness states in older people by measurement of serum magnesium (S Mg) and erythrocyte magnesium (E Mg) and to explore the limitations of E Mg measurement. S Mg and E Mg were measured in 150 consecutive out-patients, mean age 77 years, and in 100 consecutive in-patient admissions, mean age 80 years. Results were analysed for different diagnostic groups S Mg was normally distributed for both in-patients and out-patients, mean values 0.79 mmol/l and 0.77 mmol/l respectively. In-patient E Mg concentrations were often higher but the distribution was considerably skewed, median 2.28 mmol/l, mean 2.35 mmol/l. Out-patient E Mg concentration followed a near normal distribution, median 2.32 mmol/l, mean 2.30 mmol/l. There was a significant correlation between E Mg and S Mg for out-patients, R = 0.29 (p < 0.001). In-patients with infections and pressure sores had significantly raised E Mg concentrations but normal or low S Mg. High E Mg concentrations in illness are likely to be due to alterations in characteristics of the erythrocytes themselves rather than an indication of body magnesium excess. E Mg concentrations in illness should be interpreted with caution.

A neural network model for simulation of torso muscle coordination

An artificial neural network (ANN) was created to simulate lumbar muscle response to static moment loads. The network model was based on an abstract representation of a motor control system in which muscle activity is driven primarily to maintain moment equilibrium. The network model parameters were obtained by an iterative method (trained), using a modification of the standard backpropagation algorithm and moment equilibrium constraints. In contrast to previous ANN models of muscle activity, patterns of muscle activity are not target (training) values, but rather emerge as a result of moment equilibrium constraints. Assumptions regarding the moment generating capacity muscles and competitive interactions between muscles were employed and enabled the prediction of realistic patterns of muscle activity upon comparison with experimental electromyographic (EMG) data sets (r2: 0.4-0.9). The success of the simulation model suggests that a motor recruitment plan can be mimicked with relatively simple systems and that 'competition' between responsive units (muscles) may be intrinsic to the learning process. Prediction of alternative recruitment patterns and differing magnitudes of co-contractile activity were achieved by varying competition parameters within and between units.