Pressure support versus assisted controlled noninvasive ventilation in neuromuscular disease

Introduction: Noninvasive ventilation (NIV) is being increasingly used in patients with chronic neuromuscular disorders, but the optimal ventilation mode remains unknown. We compared physiological short-term effects of assist/controlled ventilation (ACV) and two pressure-limited modes (pressure-support ventilation [PSV] and assist pressure-controlled ventilation [ACPV]) in patients with neuromuscular disease who needed NIV. Methods: Tidal volume was 10 to 12 mL/kg. The ACPV mode used the same respiratory cycle timing as the volume-limited mode. The level of inspiratory support was set to achieve the same tidal volume during the other ventilatory modes. Results: Thirteen patients with neuromuscular disease who met international criteria for NIV were included. The three ventilatory modes increased alveolar ventilation and decreased respiratory effort indices. However, no difference in breathing or respiratory effort was found among the three modes, with the exception that inspiratory peak flow and percentage of triggered cycles were higher during PSV than volume-limited ventilation. Interestingly, no relationship was observed between subjective patient preference and inspiratory effort indices or percentage of triggered cycles. Conclusion: In chronic, stable patients with neuromuscular disease, both noninvasive ACV, ACPV, and PSV had similar effects on alveolar ventilation and respiratory muscle unloading, despite some differences in the pattern of breathing and percentage of triggered cycles.     

Assessing the health of future physicians: an opportunity for preventive education

INTRODUCTION: Research shows that physicians who model prevention are more likely to encourage preventive behaviors in their patients. Therefore, understanding the health of medical students ought to provide insight into the development of health promotion programs that influence the way these future physicians practice medicine. A university-based General Clinical Research Center (GCRC) provides a venue well suited to the health assessment and education of medical students. This research explores the utility of a GCRC in a program measuring the prevalence of clinical risk factors and related health behaviors in first-year medical students. METHODS: A 6-year cross-sectional study of first-year medical students measured clinical and behavioral variables associated with metabolic syndrome. Statistical testing was used to determine the prevalence of risk factors and the influence of gender in these variables. RESULTS: This group of medical students displayed better health indicators than did the general young adult population; however a small proportion of medical students exhibited early risk factors for chronic disease. There were significant gender differences in mean values for clinical risk factors, with males displaying higher cardiovascular risk overall. Males and females demonstrated significant differences in dietary intake and exercise programs. DISCUSSION: A GCRC can be used to provide a health assessment of medical students. Moreover, some students may benefit from health promotion programs incorporated into medical school curricula. This study provides a foundation for further research on the health of future physicians and the development of health promotion programs for this population. It also begins to explore the use of a GCRC as a teaching resource for medical students.     

Occupational exposure to crystalline silica and risk of systemic lupus erythematosus: a population-based,case-control study in the southeastern United States

OBJECTIVE: Crystalline silica may act as an immune adjuvant to increase inflammation and antibody production, and findings of occupational cohort studies suggest that silica exposure may be a risk factor for systemic lupus erythematosus (SLE). We undertook this population-based study to examine the association between occupational silica exposure and SLE in the southeastern US. METHODS: SLE patients (n = 265; diagnosed between January 1, 1995 and July 31, 1999) were recruited from 4 university rheumatology practices and 30 community-based rheumatologists in 60 contiguous counties. Controls (n = 355), frequency-matched to patients by age, sex, and state of residence, were randomly selected from driver's license registries. The mean age of the patients at diagnosis was 39 years; 91% were women and 60% were African American. Detailed occupational and farming histories were collected by in-person interviews. Silica exposure was determined through blinded assessment of job histories by 3 industrial hygienists, and potential medium- or high-level exposures were confirmed through followup telephone interviews. Odds ratios (ORs) and 95% confidence intervals (95% CIs) were estimated by logistic regression. RESULTS: More patients (19%) than controls (8%) had a history of medium- or high-level silica exposure from farming or trades. We observed an association between silica and SLE (medium exposure OR 2.1 [95% CI 1.1-4.0], high exposure OR 4.6 [95% CI 1.4-15.4]) that was seen in separate analyses by sex, race, and at different levels of education. CONCLUSION: These results suggest that crystalline silica exposure may promote the development of SLE in some individuals. Additional research is recommended in other populations, using study designs that minimize potential selection bias and maximize the quality of exposure assessment.     

EMG amplitude in maximal and submaximal exercise is dependent on signal capture rate

This study analysed the effect of different electromyographic (EMG) capture rates during maximal voluntary contraction, submaximal and maximal dynamic cycling activity on EMG amplitude and signal characteristics. Ten healthy subjects participated in this study. Peak power output (PPO) and maximal isometric force output (MVC) were measured, followed by a progressive cycle ride on a cycle ergometer. Electromyographic (EMG) data were simultaneously captured during the MVC and cycling activities at frequencies of 32, 64, 128, 256, 512, 1024 and 1984 Hz. Significant differences in amplitude were found (p < 0.01) between MVC, submaximal (SUB) and maximal cycling activities (PWATT) for all capture rates. Asymptote values for IEMG amplitude occurred at EMG capture rates of 1604 +/- 235.6 Hz during MVC, 503.1 +/- 236.2 Hz during PWATT and 326.2 +/- 105.4 Hz during SUB cycling activity and were significantly different (p < 0.01). No significant differences were found for force/EMG ratios between PWATT and MVC at 1984 Hz capture rates (3.8 +/- 1.7 N/V vs 2.5 +/- 0.9 N/V) while significant differences occurred at 32 Hz capture rate (6.2 +/- 3.8 vs 16.0 +/- 8.0; p < 0.01). Low correlations were found between EMG activity captured at 1984 Hz during PWATT and lean thigh volume (r = 0.36) and MVC (r = 0.32). Asymptote values found on this study suggest that data captured below 326 Hz for SUB, 503 Hz for PWATT and 1604 Hz for MVC are not reliable. Therefore apparatus capturing EMG data at low frequencies from these values cannot be used for quantitative data analyses.     

Athletes with exercise-associated fatigue have abnormally short muscle DNA telomeres

INTRODUCTION/PURPOSE: Although the beneficial health effects of regular moderate exercise are well established, there is substantial evidence that the heavy training and racing carried out by endurance athletes can cause skeletal muscle damage. This damage is repaired by satellite cells that can undergo a finite number of cell divisions. In this study, we have compared a marker of skeletal muscle regeneration of athletes with exercise-associated chronic fatigue, a condition labeled the "fatigued athlete myopathic syndrome" (FAMS), with healthy asymptomatic age- and mileage-matched control endurance athletes. METHODS: Muscle biopsies of the vastus lateralis were obtained from 13 patients diagnosed with FAMS and from 13 healthy control subjects. DNA was extracted from the muscle samples and their telomeric restriction fragment (TRF) or telomere lengths were measured by Southern blot analysis. RESULTS: All 13 symptomatic athletes reported a progressive decline in athletic performance, decreased ability to tolerate high mileage training, and excessive muscular fatigue during exercise. The minimum value of TRF lengths (4.0 +/- 1.8 kb) measured on the DNA from vastus lateralis biopsies from these athletes were significantly shorter than those from 13 age- and mileage-matched control athletes (5.4 +/- 0.6 kb, P < 0.05). Three of the FAMS patients had extremely short telomeres (1.0 +/- 0.3 kb). The minimum TRF lengths of the remaining 10 symptomatic athletes (4.9 +/- 0.5 kb, P < 0.05) were also significantly shorter that those of the control athletes. CONCLUSION: These findings suggest that skeletal muscle from symptomatic athletes with FAMS show extensive regeneration which most probably results from more frequent bouts of satellite cell proliferation in response to recurrent training- and racing-induced muscle injury.     

Should patients with challenging anatomy be offered endovascular aneurysm repair?

OBJECTIVES: Treatment of abdominal aortic aneurysm is controversial in patients at high physiologic risk for open repair and high anatomic risk for endovascular repair. We compared outcome in patients at high risk because of anatomy (short or angulated neck), severe occlusive disease, or bilateral iliac aneurysms (group A) with outcome in patients at low risk (group B). MATERIAL AND METHODS: Patients at high anatomic risk who underwent treatment between October 1998 and March 2002 with the Zenith endovascular graft (group A) were compared with patients at low anatomic risk enrolled in a prospective multicenter trial (group B). Variables compared included overall mortality, need for secondary interventions, development of endoleak, and change in aneurysm sac diameter. The chi(2) test, Student t test, and proportions analysis were used to assess the data. RESULTS: Data for 493 patients (group A, 141; group B, 352) were evaluated. Mean follow-up was 9 months (range, 1-24 months). Perioperative mortality was similar for groups A and B (0.7% vs 1%). Frequency of endoleak was higher in patients with high-risk anatomy (25% vs 11%), but not significantly so (P >.06). The rate of aneurysm shrinkage, even in the absence of endoleak, was slower in group A (P <.05). CONCLUSIONS: In physiologically challenged patients at higher anatomic risk for endovascular aneurysm repair, initial mortality rate is similar to that in patients at lower risk. Short-term technical results are acceptable. Decreased long-term survival (largely unrelated to the procedure), slightly higher frequency of endoleak, and a lower rate of sac shrinkage may temper enthusiasm for endovascular repair in this subgroup. Risks of repairing aneurysms in this patient population must be viewed in the context of expected results of intervention or medical observation.