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101.
Wave-front curvature as a cause of slow conduction and block in isolated cardiac muscle 总被引:1,自引:0,他引:1
C Cabo AM Pertsov WT Baxter JM Davidenko RA Gray J Jalife 《Canadian Metallurgical Quarterly》1994,75(6):1014-1028
We have investigated the role of wave-front curvature on propagation by following the wave front that was diffracted through a narrow isthmus created in a two-dimensional ionic model (Luo-Rudy) of ventricular muscle and in a thin (0.5-mm) sheet of sheep ventricular epicardial muscle. The electrical activity in the experimental preparations was imaged by using a high-resolution video camera that monitored the changes in fluorescence of the potentiometric dye di-4-ANEPPS on the surface of the tissue. Isthmuses were created both parallel and perpendicular to the fiber orientation. In both numerical and biological experiments, when a planar wave front reached the isthmus, it was diffracted to an elliptical wave front whose pronounced curvature was very similar to that of a wave front initiated by point stimulation. In addition, the velocity of propagation was reduced in relation to that of the original planar wave. Furthermore, as shown by the numerical results, wave-front curvature changed as a function of the distance from the isthmus. Such changes in local curvature were accompanied by corresponding changes in velocity of propagation. In the model, the critical isthmus width was 200 microns for longitudinal propagation and 600 microns for transverse propagation of a single planar wave initiated proximal to the isthmus. In the experiments, propagation depended on the width of the isthmus for a fixed stimulation frequency. Propagation through an isthmus of fixed width was rate dependent both along and across fibers. Thus, the critical isthmus width for propagation was estimated in both directions for different frequencies of stimulation. In the longitudinal direction, for cycle lengths between 200 and 500 milliseconds, the critical width was < 1 mm; for 150 milliseconds, it was estimated to be between 1.3 and 2 mm; and for the maximum frequency of stimulation (117 +/- 15 milliseconds), it was > 2.5 mm. In the transverse direction, critical width was between 1.78 and 2.32 mm for a basic cycle length of 200 milliseconds. It increased to values between 2.46 and 3.53 mm for a basic cycle length of 150 milliseconds. The overall results demonstrate that the curvature of the wave front plays an important role in propagation in two-dimensional cardiac muscle and that changes in curvature may cause slow conduction or block. 相似文献
102.
N Romano FM Romano E Viviano F Vitale MR Villafrate AM Perna F Bonura R Guttadauro 《Canadian Metallurgical Quarterly》1996,34(6):1589-1591
We investigated by nested PCR the possible association of human herpesvirus 6 (HHV-6) and human papillomavirus (HPV) genomes in the cervixes of 109 women with normal and abnormal cytological smears. HPV DNA was detected in 8.33% of 24 women with normal cytologies and in 41.1% of 85 women with abnormal cytologies; the proportion of HPV DNA was directly related to the severity of the lesions. HHV-6 DNA was found in only one patient, who had a cytological pattern of koilocytosis. The HHV-6 genome was classified by restriction enzyme analysis as variant B. The study indicates that detection of the HHV-6 genome in the cervixes of women with a wide spectrum of gynecological complaints is a rare event and rules out the possible association between HHV-6 and HPV genomes in cervical cancer lesions. 相似文献
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SL Furth AM Neu B Case HM Lederman M Steinhoff B Fivush 《Canadian Metallurgical Quarterly》1996,128(1):99-101
We studied the antibody response to pneumococcal serotypes 3 and 14 after pneumococcal polysaccharide vaccine was administered to 41 children with renal disease. One month after vaccination, 76% and 61% of patients achieved at least a twofold titer rise to serotypes 3 and 14, respectively; this finding was comparable to historic control values. One year after vaccination, the majority of patients retained protective antibody levels. Achieving a titer > or = 1.0 microgram/ml IgG at 1 month was highly predictive of retaining a protective antibody level > or = 0.15 microgram/ml at 1 year. 相似文献
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The phosphorylation of glucose to glucose-6-phosphate, catalyzed by hexokinase, is the first committed step in glucose uptake into skeletal muscle. Two isoforms of hexokinase, HKI and HKII, are expressed in human skeletal muscle, but only HKII expression is regulated by insulin. HKII messenger RNA, protein, and activity are increased after 4 h of insulin infusion; however, glucose uptake is stimulated much more rapidly, occurring within minutes. Studies in rat muscle suggest that changes in the subcellular distribution of HKII may be an important regulatory factor for glucose uptake. The present studies were undertaken to determine if insulin causes an acute redistribution of HKII activity in human skeletal muscle in vivo. Muscle biopsies (vastus lateralis muscle) were performed before and at the end of 30 min insulin infusion, performed using the euglycemic clamp technique. Muscle biopsies were subfractionated into soluble and particulate fractions to determine if insulin acutely changes the subcellular distribution of HKII. Insulin decreased HKII activity in the soluble fraction from 2.20 +/- 0.31 to 1.40 +/- 0.18 pmoles/(min[chempt]micrograms) and increased HKII activity in the particulate fraction from 3.02 +/- 0.46 to 3.45 +/- 0.46 pmoles/(min[chempt]micrograms) (P < 0.01 for both). These changes in HKII activity were correlated with changes in HKII protein, as determined by immunoblot analysis (r = 0.53, P = 0.05). Insulin had no effect on the subcellular distribution of HKII activity, which was primarily restricted to the soluble fraction. These studies are consistent with the conclusion that, in vivo in human skeletal muscle, insulin changes the subcellular distribution of HKII within 30 min. 相似文献
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