Anatomical and electrophysiological determinants of the human thenar compound muscle action potential

Clinical interpretation of the compound muscle action potential (CMAP) requires a precise understanding of its underlying mechanisms. We recorded normal thenar CMAPs and motor unit action potentials using different electrode configurations and different thumb positions. Computer simulations show that the CMAP has four parts: rising edge, negative phase, positive phase, and tail, which correspond to four distinct stages of electrical activity in the muscle: initiation at the end-plate, propagation, termination at the muscle/tendon junctions, and slow repolarization. The shapes of volume-conducted signals recorded beyond the muscle are also explained by these four stages. Changes in CMAP shape associated with thumb abduction are due to changes in termination times resulting from changes in muscle-fiber lengths. These findings demonstrate that the negative and positive phases of the CMAP are due to different mechanisms, and that anatomical factors, particularly muscle-fiber lengths, play an important role in determining CMAP shape. © 1996 John Wiley & Sons, Inc.     

Automatic wide complex tachycardia differentiation using mathematically synthesized vectorcardiogram signals

BackgroundAutomated wide complex tachycardia (WCT) differentiation into ventricular tachycardia (VT) and supraventricular wide complex tachycardia (SWCT) may be accomplished using novel calculations that quantify the extent of mean electrical vector changes between the WCT and baseline electrocardiogram (ECG). At present, it is unknown whether quantifying mean electrical vector changes within three orthogonal vectorcardiogram (VCG) leads (X, Y, and Z leads) can improve automated VT and SWCT classification.MethodsA derivation cohort of paired WCT and baseline ECGs was used to derive five logistic regression models: (i) one novel WCT differentiation model (i.e., VCG Model), (ii) three previously developed WCT differentiation models (i.e., WCT Formula, VT Prediction Model, and WCT Formula II), and (iii) one “all‐inclusive” model (i.e., Hybrid Model). A separate validation cohort of paired WCT and baseline ECGs was used to trial and compare each model''s performance.ResultsThe VCG Model, composed of WCT QRS duration, baseline QRS duration, absolute change in QRS duration, X‐lead QRS amplitude change, Y‐lead QRS amplitude change, and Z‐lead QRS amplitude change, demonstrated effective WCT differentiation (area under the curve [AUC] 0.94) for the derivation cohort. For the validation cohort, the diagnostic performance of the VCG Model (AUC 0.94) was similar to that achieved by the WCT Formula (AUC 0.95), VT Prediction Model (AUC 0.91), WCT Formula II (AUC 0.94), and Hybrid Model (AUC 0.95).ConclusionCustom calculations derived from mathematically synthesized VCG signals may be used to formulate an effective means to differentiate WCTs automatically.     

Anterior shear of spinal motion segments. Kinematics, kinetics, and resultant injuries observed in a porcine model.

STUDY DESIGN: A basic study of 56 porcine specimens in anterior shear loading. OBJECTIVES: To determine some modulators of the biomechanics of spinal motion segments exposed to acute shear loading and to identify the resultant injuries. SUMMARY OF BACKGROUND DATA: Most research on spinal injury mechanisms has focused on compressive loading, leaving a void in understanding of the effect of shear loading on origin of injury. METHODS: Cervical spines (n = 56) of domestic pigs (6 months old) were loaded to failure in a specially designed jig that restricted their motion to primarily the shear plane. The specimens were tested at load rates of 100 N/sec or 10,810 N/sec and either in a flexed or neutral posture. In addition, the function of the individual structures of the motion segment were determined by serial dissection forming three groups: whole specimens, specimens with no posterior ligaments, and specimens with no posterior ligaments or facet joints. Load-deformation curves were collected using analog-to-digital sampling rates of 50 and 100 Hz. The mode of failure was then documented through systematic dissection of the specimen and/or radiology techniques. Modeling approaches were then used to gain insight into the failure mechanisms. RESULTS: Dynamic loading (10,810 N/sec) and flexion of the specimens were found to increase the ultimate load at failure when compared with quasistatic loading (100 N/sec) and neutral postures. The disc resisted up to 70% of an applied load, with the pars interarticularis responsible for only 30% of the load. Nonetheless, the pars was the primary site of failure. Furthermore, higher load rates also caused endplate avulsion, specifically in the lateral borders of the anulus. CONCLUSIONS: The porcine model appears to reproduce injuries found in the data available on human lumbar material. Fractures in the pars interarticularis may not greatly weaken the joint, given the dominant role of the disc, but compromise its normal kinematics. Clinically, this may explain the occurrence of pars fractures, without total disability.     

Novel Atlantic bottlenose dolphin parainfluenza virus TtPIV-1 clusters with bovine PIV-3 genotype B strains

Parainfluenza virus 3 (PIV-3) is a common viral infection not only in humans, but also in many other species. Serological evidence suggests that nearly 100 % of children in the United States have been infected with PIV-3 by 5 years of age. Similarly, in cattle, PIV-3 is commonly associated with bovine respiratory disease complex. A novel dolphin PIV-3 (TtPIV-1) was described by Nollens et al. in 2008 from a dolphin that was diagnosed with an unknown respiratory illness. At that time, TtPIV-1 was found to be most similar to, but distinct from, bovine PIV-3 (BPIV-3). In the present study, similar viral growth kinetics and pro-inflammatory cytokine (IL-1β, IL-6, and CXCL8) production were seen between BPIV-3 and TtPIV-1 in BEAS-2B, MDBK, and Vero cell lines. Initial nomenclature of TtPIV-1 was based on partial sequence of the fusion and RNA polymerase genes. Based on the similarities we saw with the in vitro work, it was important to examine the TtPIV-1 genome in more detail. Full genome sequencing and subsequent phylogenetic analysis revealed that all six viral genes of TtPIV-1 clustered within the recently described BPIV-3 genotype B strains, and it is proposed that TtPIV-1 be re-classified with BPIV-3 genotype B strains.     

Characterization and Serologic Analysis of the Treponema pallidum Proteome

Treponema pallidum subsp. pallidum is the causative agent of syphilis, a sexually transmitted disease characterized by widespread tissue dissemination and chronic infection. In this study, we analyzed the proteome of T. pallidum by the isoelectric focusing (IEF) and nonequilibrating pH gel electrophoresis (NEPHGE) forms of two-dimensional gel electrophoresis (2DGE), coupled with matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) analysis. We determined the identity of 148 T. pallidum protein spots, representing 88 T. pallidum polypeptides; 63 of these polypeptides had not been identified previously at the protein level. To examine which of these proteins are important in the antibody response to syphilis, we performed immunoblot analysis using infected rabbit sera or human sera from patients at different stages of syphilis infection. Twenty-nine previously described antigens (predominantly lipoproteins) were detected, as were a number of previously unidentified antigens. The reactivity patterns obtained with sera from infected rabbits and humans were similar; these patterns included a subset of antigens reactive with all serum samples tested, including CfpA, MglB-2, TmpA, TmpB, flagellins, and the 47-kDa, 17-kDa, and 15-kDa lipoproteins. A unique group of antigens specifically reactive with infected human serum was also identified and included the previously described antigen TpF1 and the hypothetical proteins TP0584, TP0608, and TP0965. This combined proteomic and serologic analysis further delineates the antigens potentially useful as vaccine candidates or diagnostic markers and may provide insight into the host-pathogen interactions that occur during T. pallidum infection.Syphilis is a multistage progressive disease caused by the spirochete Treponema pallidum subsp. pallidum and is characterized by localized, disseminated, and chronic stages. Manifestations include the development of a localized lesion called a chancre during the primary stage and disseminated skin lesions and meningovascular syphilis during the secondary stage, followed by a period of latency lasting from months to decades. Chronic, debilitating symptoms develop during the tertiary stage, including granuloma-like lesions called gummas, neurosyphilis, and cardiovascular syphilis (38). Although syphilis can be successfully treated by antibiotics, it remains a significant public health problem, with an estimated 12 million new cases per year worldwide (41).Continued improvement of diagnostic tests (particularly point-of-care tests) as well as the development of an effective vaccine for syphilis would aid greatly in the control of syphilis (4, 6). T. pallidum research, including the identification of antigens, has been hindered by the inability to culture the bacterium continuously in vitro, necessitating the propagation of organisms by experimental rabbit infection (28). In addition, the fragility and low protein content of the T. pallidum outer membrane have complicated the identification of surface proteins potentially useful in vaccines (5, 28).The T. pallidum genome sequence (15) provides an additional tool for the analysis of potential antigens. The 1.14-Mb T. pallidum chromosome contains 1,039 open reading frames (ORFs) encoding predicted protein products, a smaller number than for any other spirochete genome sequenced to date (15). The average size of predicted proteins is 37,771 Da, ranging from 3,235 to 172,869 Da. Analysis of the translated genome of T. pallidum predicts an unusually basic proteome, with a mean pI of 8.1 and median pI of 8.5, with 66% of proteins having pIs of >7.0 (23). Small genome size and a predominance of basic proteins are more common in parasitic microorganisms, and the latter is thought to facilitate interaction of the organism with its host (20). Other pathogenic spirochetes also tend to have basic proteins; for example, the proteome of Borrelia burgdorferi has a mean pI of 8.36 and median pI of 9.03 (14, 29a), and 69% of Leptospira interrogans serovar Lai strain 56601 proteins have pIs greater than 7.0 (24, 33). A recent analysis of the T. pallidum genome indicates the presence of 46 putative lipoproteins, many fewer than the 127 predicted for B. burgdorferi (34).The availability of the genome sequence made it possible to examine predicted T. pallidum ORFs for potential suitability as diagnostic or immunization tools. McKevitt et al. (22) and Brinkman et al. (3) created a protein expression library of 900 of the 1,039 T. pallidum proteins predicted from the genome sequence and examined the serologic reactivity of these proteins by enzyme-linked immunosorbent assays (ELISAs). They identified 106 antigens reactive with rabbit sera and 34 antigens reactive with sera from syphilis patients. This set of antigens was termed the T. pallidum immunoproteome. This approach permits identification of low-abundance T. pallidum antigens, since they may be expressed as recombinant proteins in much larger quantities. Conversely, proteins that are poorly expressed in Escherichia coli or do not fold correctly may not be detected, leading to false-negative results.To provide a complementary set of data regarding the T. pallidum immunoproteome, we have performed proteomic analysis of T. pallidum proteins expressed during experimental rabbit infection. We used isoelectric focusing (IEF) and nonequilibrating pH gel electrophoresis (NEPHGE) forms of two-dimensional gel electrophoresis (2DGE) coupled with matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) analysis to identify T. pallidum polypeptides. Immunoblotting was subsequently used to identify antigens reactive with infected rabbit sera (IRS) and with human sera obtained at different stages of syphilis. This approach may permit identification of antigens that are not expressed well in E. coli and provides a more accurate picture of the level of protein expression in the intact organism. We have thereby characterized most of the major T. pallidum proteins expressed in infected tissue and identified a set of antigens reactive at all stages of infection, which could potentially be useful for the development of improved immunodiagnostic tests or for vaccines.