Double pulsed field gradient diffusion MRI to assess skeletal muscle microstructure.

PURPOSE: Preliminary study to determine whether double pulsed field gradient (PFG) diffusion MRI is sensitive to key features of muscle microstructure related to function. METHODS: The restricted diffusion profile of molecules in models of muscle microstructure derived from histology were systematically simulated using a numerical simulation approach. Diffusion tensor subspace imaging analysis of the diffusion signal was performed, and spherical anisotropy (SA) was calculated for each model. Linear regression was used to determine the predictive capacity of SA on the fiber area, fiber diameter, and surface area to volume ratio of the models. Additionally, a rat model of muscle hypertrophy was scanned using a single PFG and a double PFG pulse sequence, and the restricted diffusion measurements were compared with histological measurements of microstructure. RESULTS: Excellent agreement between SA and muscle fiber area (r2 = 0.71; p < 0.0001), fiber diameter (r2 = 0.83; p < 0.0001), and surface area to volume ratio (r2 = 0.97; p < 0.0001) in simulated models was found. In a scanned rat leg, the distribution of these microstructural features measured from histology was broad and demonstrated that there is a wide variance in the microstructural features observed, similar to the SA distributions. However, the distribution of fractional anisotropy measurements in the same tissue was narrow. CONCLUSIONS: This study demonstrates that SA-a scalar value from diffusion tensor subspace imaging analysis-is highly sensitive to muscle microstructural features predictive of function. Furthermore, these techniques and analysis tools can be translated to real experiments in skeletal muscle. The increased dynamic range of SA compared with fractional anisotropy in the same tissue suggests increased sensitivity to detecting changes in tissue microstructure.

The morphology of the masticatory apparatus facilitates muscle force production at wide jaw gapes in tree-gouging common marmosets (Callithrix jacchus).

Common marmosets (Callithrix jacchus) generate wide jaw gapes when gouging trees with their anterior teeth to elicit tree exudate flow. Closely related cotton-top tamarins (Saguinus oedipus) do not gouge trees but share similar diets including exudates. Maximizing jaw opening theoretically compromises the bite forces that marmosets can generate during gouging. To investigate how jaw-muscle architecture and craniofacial position impact muscle performance during gouging, we combine skull and jaw-muscle architectural features to model muscle force production across a range of jaw gapes in these two species. We incorporate joint mechanics, resting sarcomere length and muscle architecture estimates from the masseter and temporalis to model muscle excursion, sarcomere length and relative tension as a function of joint angle. Muscle excursion from occlusion to an estimated maximum functional gape of 55 deg. was smaller in all regions of the masseter and temporalis of C. jacchus compared with S. oedipus except the posterior temporalis. As a consequence of reduced muscle excursion distributed over more sarcomeres in series (i.e. longer fibers), sarcomere length operating ranges are smaller in C. jacchus jaw muscles across this range of gapes. This configuration allows C. jacchus to act on a more favorable portion of the length-tension curve at larger gapes and thereby generate relatively greater tension in these muscles compared with S. oedipus. Our results suggest that biting performance during tree gouging in common marmosets is improved by a musculoskeletal configuration that reduces muscle stretch at wide gapes while simultaneously facilitating comparatively large muscle forces at the extremes of jaw opening.

Atrial fibrillation in the setting of acute myocardial infarction: the GUSTO-I experience. Global Utilization of Streptokinase and TPA for Occluded Coronary Arteries.

OBJECTIVES: We examined the clinical predictors and angiographic and clinical outcomes associated with atrial fibrillation in the setting of acute myocardial infarction (MI). BACKGROUND: This condition has been studied primarily in prethrombolytic era small trials. METHODS: We compared baseline clinical characteristics, short-term clinical and angiographic outcomes and 1-year mortality of patients enrolled in the Global Utilization of Streptokinase and TPA for Occluded Coronary Arteries (GUSTO-I) trial with atrial fibrillation on admission electrocardiography (n = 1,026 [2.5%]) or after enrollment (n = 3,254 [7.9%]) and those without atrial fibrillation (n = 36,611 [89.6%]). Univariable and multivariable analyses were used to assess relations between baseline factors and the development of atrial fibrillation. RESULTS: Patients with any atrial fibrillation more often had three-vessel coronary artery disease and initial Thrombolysis in Myocardial Infarction (TIMI) grade < 3 flow than those without the arrhythmia. In-hospital stroke was increased in patients with atrial fibrillation (3.1% vs. 1.3%, p = 0.0001), mainly ischemic stroke (1.8% vs. 0.5%, p = 0.0001). Significant multivariable predictors of later atrial fibrillation included advanced age, higher peak creatine kinase levels, worse Killip class and increased heart rate. The unadjusted mortality rate was significantly higher at 30 days (14.3% vs. 6.2%, p = 0.0001) and at 1 year (21.5% vs. 8.6%, p < 0.0001) in patients with atrial fibrillation. The adjusted 30-day mortality rate remained significantly higher with any (odds ratio [OR] 1.3, 95% confidence interval [CI] 1.2 to 1.4) or later (OR 1.4, 95% CI 1.3 to 1.5) atrial fibrillation but not with baseline atrial fibrillation (OR 1.1, 95% CI 0.88 to 1.3). CONCLUSIONS: Atrial fibrillation in the setting of acute MI independently predicts stroke and 30-day mortality. More aggressive treatment strategies in this subgroup may be warranted and deserve further study.

Efficacy and safety of a hemostatic puncture closure device with early ambulation after coronary angiography. Angio-Seal Investigators.

A collagen hemostatic puncture closure device has been developed as an alternative to traditional manual pressure techniques for achieving effective femoral arterial hemostasis after coronary angiography. The purpose of the current study was to determine if patients receiving this device can ambulate safely at 1 hour compared with patients receiving traditional manual pressure and bed rest after sheath removal for diagnostic cardiac catheterization. Patients (n = 304) were randomized to either the device group (n = 202) with ambulation at 1 hour after sheath removal or to the manual pressure control group (n = 102) with ambulation at 4 to 6 hours after sheath removal. The device group achieved earlier time to hemostasis (0.9 +/- 3 vs 17.0 +/- 8 minutes, p = 0.0001) and faster time to outpatient discharge (5.0 +/- 4 vs 7.7 +/- 4 hours, p = 0.0001) compared with the control group. There were bleeding or vascular complications in 19 patients (9%) in the device group and in 6 patients (6%) in the manual pressure group (p = 0.397). In patients undergoing diagnostic coronary angiography, this device, compared with traditional techniques for achieving hemostasis after sheath removal, allows for faster time to effective hemostasis with resultant earlier discharge from the hospital.

Effects of thrombolytic regimen, early catheterization, and predischarge angiographic variables on six-week left ventricular function. The TAMI Investigators. Thrombolysis and Angioplasty in Acute Myocardial Infarction.

The Thrombolysis and Angioplasty in Acute Myocardial Infarction phase 5 (TAMI-5) trial randomized patients to 1 of 3 thrombolytic regimens (alteplase, urokinase, or both), then further randomized them to acute or deferred catheterization. The group of patients randomized to acute catheterization had improved infarct zone but not global left ventricular function on predischarge left ventriculography. To better explore the late effects of these strategies on global and regional left ventricular function, a subset of patients (n = 296) were prospectively evaluated at 6 weeks by multiple uptake gated acquisition (MUGA) radionuclide ventriculography scan. Of these patients, 219 had interpretable studies with paired predischarge and late left ventriculographic data for comparison. At 6 weeks, choice of thrombolytic regimen had no impact on either global or infarct-zone left ventricular function. Further, catheterization strategy (acute vs deferred) did not influence global or infarct-zone function at 6 weeks. In patients randomized to acute catheterization, those undergoing rescue angioplasty had worse infarct-zone wall motion at 6 weeks than patients with a patent infarct vessel not requiring rescue angioplasty (p = 0.002). The early benefit on regional left ventricular function of triage to acute catheterization after thrombolysis for acute myocardial infarction did not persist at 6 weeks, which is most likely attributable to a high incidence of reocclusion. The worse infarct-zone regional wall motion in patients undergoing rescue angioplasty in the acute-catheterization group likely reflects failed reperfusion and illustrates the difficulty in identifying and consequences of early thrombolytic failures.

Simultaneous powering of forearm pronation and key pinch in tetraplegia using a single muscle-tendon unit.

This study clinically assessed the concept that both thumb flexion and forearm pronation can be restored by brachioradialis (BR)-to-flexor pollicis longus (FPL) tendon transfer if the BR is passed dorsal to the radius. Six patients [two women and four men, mean age 32.3 years (SD 4.9, range 23-56)] underwent BR-to-FPL transfer dorsal to the radius and through the interosseous membrane (IOM). Lateral key pinch strength and pronation range of motion (ROM) were measured 1 year after surgery. A group of six patients [two women and four men, mean age 31.2 years (SD 5.0, range 19-52)] who underwent traditional palmar BR-to-FPL was included for comparison. Postoperative active pronation was significantly greater in the dorsal transfer group compared to the palmar group [149 (SD 6) and 75 (SD 3), respectively] and pinch strength was similar in the two groups [1.28 (SD 0.16) kg and 1.20 (SD0.21) kg, respectively]. We conclude that it is feasible to reconstruct lateral key pinch and forearm pronation simultaneously using only the BR motor.

Industrial vision revisited.

With the Occupational Safety and Health Act of 1970 and other government agencies addressing the protection of employees from occupational hazards at their work place, there has been a reemphasis in the industrial eye care field. Industrial vision programs are reviewed and an overview of the Army's occupational vision program is presented. If optometry is to continue progress in this sphere of public health, optometrists must become more involved in and knowledgeable of the visual requirements of the local industrial community, and the profession should consider the establishment of a certification program for occupational doctors of optometry.

Long-term performance of a gas chromatography/tandem mass spectrometry assay for tebufelone in plasma.

An automated gas chromatography/tandem mass spectrometry (GC/MS/MS) based method for the rapid determination of tebufelone (TE) in animal and human plasma has been routinely applied in our laboratory to more than 3000 samples over a 2-year period. The selectivity of MS/MS conducted on a triple quadrupole instrument, combined with the use of a stable-isotope-labeled internal standard, results in excellent analytical figures of merit, as well as minimal sample preparation, rapid analysis, and high assay reliability. The work described here goes beyond initial method development and validation studies by evaluating the long-term performance of quantitative GC/MS/MS. Electron ionization produces M.+ ions for TE and the [13C, 18O]TE internal standard, which are selected in Q1 and undergo collisionally activated dissociation in Q2. Quantitation is based on monitoring daughter ions at m/z 248 and 251, respectively, in Q3. A linear range of 1-3000 ng of TE/sample (20 pg to 60 ng injected) provides access to an effective concentration range of 0.5-30,000 ppb TE in plasma (0.1-2-g samples). The assay shows no bias and less than 10% relative standard deviation over this range. In the automated mode, less than 7 min elapse from injection to report printout and more than 70 plasma samples are routinely prepared and analyzed in a day. Such performance is consistently maintained throughout long-term application.