Diastolic function: modeling left ventricular untwisting as a damped harmonic oscillator.

Objective.We developed a method using cardiovascular magnetic resonance imaging to model the untwisting of the left ventricle (LV) as a damped torsional harmonic oscillator to estimate shear modulus (intrinsic myocardial stiffness) and frictional damping, then applied this method to evaluate the torsional stiffness of patients with resistant hypertension (RHTN) compared to a control group.Approach.The angular displacement of the LV during diastole was measured. Myocardial shear modulus and damping constant were determined by solving a system of equations modeling the diastolic untwisting as a damped, unforced harmonic oscillator, in 100 subjects with RHTN and 36 control subjects.Main Results.Though overall torsional stiffness was increased in RHTN (41.7 (27.1-60.7) versus 29.6 (17.3-35.7) kdyn*cm;p = 0.001), myocardial shear modulus was not different between RHTN and control subjects (0.34 (0.23-0.50) versus 0.33 (0.22-0.46) kPa;p= 0.758). RHTN demonstrated an increase in overall diastolic frictional damping (6.13 ± 3.77 versus 3.35 ± 1.70 kdyn*cm*s;p< 0.001), but no difference in damping when corrected for the overlap factor (74.3 ± 25.9 versus 68.0 ± 24.0 dyn*s/cm3;p = 0.201). There was an increase in the polar moment (geometric component of stiffness; 11.47 ± 6.95 versus 7.58 ± 3.28 cm4;p<0.001).Significance.We have developed a phenomenological method, estimating the intrinsic stiffness and relaxation properties of the LV based on restorative diastolic untwisting. This model finds increased overall stiffness in RHTN and points to hypertrophy, rather than tissue- level changes, as the major factor leading to increased stiffness.

Bilateral weighted radiographs are required for accurate classification of acromioclavicular separation: an observational study of 59 cases.

INTRODUCTION: Misinterpretation of the Rockwood classification system for acromioclavicular joint (ACJ) separations has resulted in a trend towards using unilateral radiographs for grading. Further, the use of weighted views to 'unmask' a grade III injury has fallen out of favour. Recent evidence suggests that many radiographic grade III injuries represent only a partial injury to the stabilising ligaments. This study aimed to determine (1) whether accurate classification is possible on unilateral radiographs and (2) the efficacy of weighted bilateral radiographs in unmasking higher-grade injuries. METHODS: Complete bilateral non-weighted and weighted sets of radiographs for patients presenting with an acromioclavicular separation over a 10-year period were analysed retrospectively, and they were graded I-VI according to Rockwood's criteria. Comparison was made between grading based on (1) a single antero-posterior (AP) view of the injured side, (2) bilateral non-weighted views and (3) bilateral weighted views. Radiographic measurements for cases that changed grade after weighted views were statistically compared to see if this could have been predicted beforehand. RESULTS: Fifty-nine sets of radiographs on 59 patients (48 male, mean age of 33 years) were included. Compared with unilateral radiographs, non-weighted bilateral comparison films resulted in a grade change for 44 patients (74.5%). Twenty-eight of 56 patients initially graded as I, II or III were upgraded to grade V and two of three initial grade V patients were downgraded to grade III. The addition of a weighted view further upgraded 10 patients to grade V. No grade II injury was changed to grade III and no injury of any severity was downgraded by a weighted view. Grade III injuries upgraded on weighted views had a significantly greater baseline median percentage coracoclavicular distance increase than those that were not upgraded (80.7% vs. 55.4%, p=0.015). However, no cut-off point for this value could be identified to predict an upgrade. CONCLUSIONS: The accurate classification of ACJ separation requires weighted bilateral comparative views. Attempts to predict grade on a single AP radiograph result in a gross underestimation of severity. The value of bilateral weighted views is to 'unmask' a grade V injury, and it is recommended as a first-line investigation.

Granuloma annulare arising in association with pulmonary coccidioidomycosis.

Granuloma annulare (GA) is a reactive process in the dermis, related to degeneration of collagen. It may occur as an idiopathic phenomenon or in conjunction with a myriad of systemic conditions, including infectious disease. We report an interesting case of GA precipitated by pulmonary coccidioidomycosis.

A Comparative Study of Haptic Stiffness Identification by Veterinarians and Students.

Palpation is an important clinical skill in both veterinary and medical health professions. The present study compares the ability of practicing veterinarians and veterinary students to identify the stiffness of virtual surfaces through palpation. An absolute identification paradigm was used where a force-feedback haptic device rendered virtual surfaces with five levels of stiffness within a "clinically relevant" range (0.2-0.5 N/mm). The mean information transfer was 0.97 bits (almost two perfectly identifiable stiffness levels) for 12 veterinarians and 0.58 bits (one correctly identified level) for 14 veterinary students. Although the difference between the two groups was significant (p <; 0.001), neither group was able to reliably identify more than two levels of stiffness, indicating that the success of veterinarians in clinical practice probably relies on additional properties such as size, shape, and texture. Analyses of force versus time and displacement versus time recordings suggest that the superior performance of the veterinarians may be partially attributable to motor strategy. Specifically, veterinarians used a greater mean maximum force (2.0 N) compared to students (1.6 N) (p <; 0.05). However, further studies are required to investigate motor strategy in more detail. The implications of our findings for veterinary education and quantitative skill assessment are discussed.

Femoral head viability after Birmingham resurfacing hip arthroplasty: assessment with use of [18F] fluoride positron emission tomography.

BACKGROUND: Total hip resurfacing has become increasingly popular over the last decade. There remains concern about the effect of the surgical approach on femoral head viability and the role of resurfacing in the management of established osteonecrosis. In view of these concerns, we examined femoral head viability following resurfacing through a modified anterolateral approach. METHODS: The viability of the femoral heads of ten patients who had undergone successful unilateral Birmingham hip resurfacing was assessed with use of positron emission tomography in conjunction with the injection of fluorine at a mean of twenty months after surgery. For each patient, in both the hip that had undergone resurfacing and the contralateral nonresurfaced hip, activity was measured in four regions of interest: the lateral aspect of the femoral head, the medial aspect of the femoral head, the lateral aspect of the femoral neck, and the proximal aspect of the femur. The uptake of fluorine in each area was converted to standard uptake volumes. RESULTS: No areas of osteonecrosis were seen in the femoral head of any patient. There were no significant differences in the standard uptake volumes as measured in the four regions of the nonresurfaced hips, whereas the median values were higher in all four regions of the resurfaced hips. The difference between the values in the resurfaced hips compared with those in the nonresurfaced hips was only significant (p < 0.05) in the lateral aspect of the femoral head. CONCLUSIONS: This study establishes positron emission tomography in conjunction with injection of fluorine as a possible modality for the assessment of femoral head viability after hip resurfacing. Viability following successful Birmingham hip resurfacing performed through a modified anterolateral approach has also been demonstrated. The increase in bone activity that was seen in the resurfaced hips in our study group may be related to bone remodeling or reperfusion of small areas of osteonecrosis. This technique offers the potential to study femoral head perfusion and viability following all types of resurfacing. LEVEL OF EVIDENCE: Diagnostic Level IV. See Instructions to Authors on jbjs.org for a complete description of levels of evidence.

Regulation of DNA synthesis and capacity for initiation in DNA temperature sensitive mutants of Escherichia coli I. Reinitiation and chain elongation.

The capacity for initiation and subsequent chain elongation was examined in several DNA temperature sensitive mutants of Escherichia coli after the mutants had been held at nonpermissive temperature for approximately 1.5 generation equivalents and then returned to permissive temperature in the presence of chloramphenicol. The results obtained indicate that 4-5 sets of replication forks can be initiated after return to permissive temperature in the presence of chloramphenicol but the forks apparently become stalled and fail to complete chromosomal replication in the presence of chloramphenicol. In temperature reversible dnaA mutants, once the chloramphenicol is removed the forks appear to be able to resume replication at the nonpermissive temperature. The relationship between premature initiation and premature chain termination is discussed.

Regulation of DNA synthesis and capacity for initiation in DNA temperature sensitive mutants of Escherichia coli. II. Requirements for acquisition and expression of initiation capacity.

This paper deals with the conditions that are necessary for the acquisition and expression of initiation potential in dnaA temperature sensitive mutants after they have been held for periods of time at nonpermissive temperature and then returned to permissive temperature in the presence of chloramphenicol. The following conditions were found to be essential: (1) 40-60 min at nonpermissive temperature during which time protein synthesis must occur; this period must be followed by (2) return to permissive temperature under which conditions active dnaA product is present, and (3) protein synthesis must be blocked during the first 10-20 min immediately after return to permissive temperature (when initiation takes place). In order for expression of the initiation potential (4) the chloramphenicol must be removed to allow the progression of the replication forks which had been initiated to occur and (5) the recA+ phenotype appears to be required for acquisition or expression (or both) of the initiation potential.

Regulation of DNA synthesis and capacity for initiation in DNA temperature mutants of Escherichia coli. III. Synthesis of the dnaA protein and of DNA-binding proteins.

The synthesis and action of the dnaA product with respect to DNA initiation and the synthesis of DNA-binding proteins in Escherichia coli was examined. Results indicate that when dnaA product is irreversibly denatured and must be synthesized before initiation can occur, its synthesis and action appear to be complete approximately 30 min before initiation takes place. However, in mutants whose dnaA product is temperature reversible the action of the dnaA product appears to occur near the time of initiation. Examination of the DNA-binding proteins from the mutants suggests that a 53 kd protein, possibly the dnaA product, may be synthesized at the time of initiation under normal conditions at permissive temperature. The presence of active dnaA product appears to trigger the synthesis of a 60-65 kd protein which may be responsible for preventing another immediate initiation event.

Effect of blocking protein synthesis at nonpermissive temperatures on temperature-sensitive deoxyribonucleic acid mutants of Escherichia coli.

When protein synthesis was blocked in temperature-sensitive deoxyribonucleic acid synthesis mutants of Escherichia coli at nonpermissive temperatures, it reduced the amount of apparent subsequent chain elongation to approximately half that observed in the mutants either at nonpermissive temperatures alone or when protein synthesis was blocked at the permissive temperature. Blocking protein synthesis at the nonpermissive temperatures for periods of 40 min caused the loss of ability to reinitiate deoxyribonucleic acid synthesis at the permissive temperature.