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Biomedical subjects

M Akhtar

Publications and source records attributed to M Akhtar.

At least 433 records · Page 24Linked to original sources
PubMed1978

Study of the temporal effects on conduction and refractoriness of the His-Purkinje system in man.

Temporal effects on refractoriness within the His-Purkinje system (HPS) were studied in 14 patients in whom effective refractory period (ERP) of HPS could be determined, using His bundle electrograms, incremental atrial pacing, and atrial extrastimulus method. His-Purkinje conduction times (H-V interval) and relative (R), effective (E), and functional (F) refractory periods (RP) of HPS were measured during the control period and repeat measurements were made after a 30 minute interval. H-V intervals were unchanged from control in all patients. Although changes of the magnitude of 5 to 25 msec. in either direction from control values commonly occurred, on the average, no statistically significant changes were seen in RRP, ERP, or FRP of HPS. The results of the present study confirm the stability of refractoriness of HPS over a 30 minute period and provide baseline data for future investigations of cardiovascular drugs which act primarily on the distal part of the A-V conduction system.

Adult↗
PubMed1978

Effects of digitalis on ventricular myocardial and His-Purkinje refractoriness and reentry in man.

The effects of digitalis on retrograde conduction and refractoriness of the His-Purkinje system, ventricular myocardium and reentry within the His-Purkinje system were studied in 17 patients using the ventricular extrastimulus (V2) technique. Studies were performed, before and 30 minutes after intravenous administration of ouabain, 0.01 mg/kg. After treatment with ouabain, there was a significant decrease in the functional refractory period (266 +/- 19 to 254 +/- 18 msec, P less than 0.001), relative refractory period (253 +/- 17 to 240 +/- 16 msec, P less than 0.001) and effective refractory period (242 +/- 23 to 231 +/- 24 msec, P less than 0.005) of the ventricular muscle. In contrast, there was no significant change in retrograde His-Purkinje conduction and refractoriness. The phenomenon of reentry within the His-Purkinje system characterized by the reentrant beat (V3) at critical retrograde conduction delays in the His-Purkinje system (V2-H2) within a narrow range of V1-V2 intervals was seen in 10 of 17 patients. Ouabain increased and shifted to the left the zone of reentry within the His-Purkinje system in 7 of 10 patients (36 +/- 23 to 55 +/- 23 msec, P less than 0.001) and decreased it by 10 to 30 msec in the remaining 3 patients. The critical V2-H2 (186 +/- 29 to 193 +/- 27 msec, difference not significant [NS]) and V1-V2 (299 +/- 30 to 294 +/- 36 msec, NS) intervals for reentry did not significantly change after ouabain. However, the minimal V1-V2 intervals (266 +/- 26 to 253 +/- 25 msec, P less than 0.025) decreased significantly, whereas the maximal V2-H2 intervals (266 +/- 40 to 239 +/- 37 msec, P less than 0.01) increased significantly. Thus, in the intact human heart, digitalis (1) significantly decreased all measures of ventricular myocardial refractoriness, (2) had no significant effect on retrograde conduction and refractoriness of the His-Purkinje system, and (3) widened the zone of reentry within the His-Purkinje system due to shortening of the functional refractory period of the ventricular muscle with attainment of longer V2-H2 delays.

Adult↗
PubMed1978

Solitary primary amyloidosis of urinary bladder. Light and electron microscopic study.

A fifty-four-year-old white woman with a history of episodic gross hematuria was diagnosed as having solitary primary amyloidosis of the urinary bladder involving a large segment of the dome and anterior wall. A segmental resection of the bladder was performed with good results. Electron microscopic examination of the lesion revealed evidence to indicate that amyloid in this case was produced by the fibroblasts within the lamina propria of the bladder. The mode of amyloidogenesis is identical to that noted in some of the previously published electron microscopic studies on localized amyloidosis of skin. Solitary primary amyloidosis of the urinary bladder is a rare lesion with only 46 cases having been previously reported in the literature.

Amyloid↗
PubMed1978

Reentry within the His-Purkinje system. Elucidation of reentrant circuit using right bundle branch and His bundle recordings.

Routes of impulse propagation during reentry in the His-Purkinje system (Re-HPS) in 13 patients were studied using the right ventricular extra stimulus (V2) method and right bundle branch (RBB) recordings in addition to the conventional His (H) bundle recordings. The H-V and RB-V intervals during sinus rhythm averaged 44.2 and 27.6 msec respectively, with the average antegrade H-RB interval 16.6 msec. All 13 patients demonstrated Re-HPS in the form of V3 showing a left bundle branch block (LBBB) pattern, and two of the 13 patients also manifested V3 with a right bundle branch block (RBBB) pattern. During Re-HPS showing a LBBB pattern, the retrograde activation of the His bundle (H2) in response to V2 occurred via the left bundle branch (LBB), as indicated by inscription of retrograde H2 prior to RB2 in nine of 13 cases (average H2-RB2 = 9.4 msec), and simultaneous incription of retrograde H2 and RB2 in the remaining four. When V3 showed a RBBB pattern the retrograde RB2 preceded H2, suggesting H2 activation via the RBB. These findings suggest that circuit of Re-HPS incorporates both bundle branches and the bundle of His. The H-RB recordings were also useful in distinguishing sustained Re-HPS from atrioventricular nodal reentry when in both instances the QRS complex showed a LBBB pattern.

Adult↗
PubMed1978

Sub-unit assembly in the biosynthesis of neomycin. The synthesis of 5-O-beta-D-ribofuranosyl and 4-O-beta-D-ribofuranosyl-2,6-dideoxystreptamines.

The preparation of the deoxy- analogues of two pseudodisaccharide fragments of neomycin, 5-O-beta-D-ribofuranosyl-2,6-dideoxy-streptamine and 6-deoxyneamine is described. When added to the growth medium of a deoxystreptamine-idiotroph of Streptomyces rimosus forma paromomycinus only the latter was incorporated into antibiotic, suggesting an obligatory order for the assembly of sub-units. 4-O-beta-D-Ribofuranosyl-2,6-dideoxystreptamine was also prepared. When added to the growth medium of a deoxystreptamine-idiotroph of Streptomyces fradiae it was converted into the 6-deoxyneomycins, apparently after hydrolysis to 2,6-dideoxystreptamine. The structure of the protected derivatives of the ribofuranosyl 2,6-dideoxystreptamines, potentially useful intermediates for the synthesis of novel antibiotics, was shown by using 15C NMR spectroscopy.

Hexosamines↗
PubMed1978

Nephrotoxicity from cancer immunotherapy.

Because systemic intravenous immunotherapy with Corynebacterium parvum is an effective immunopotentiating and immunotherapeutic agent in animals, clinical studies of this agent have been undertaken. Toxicities in man have been noted, but most are treated symptomatically. Three patients with metastatic melanoma developed oliguria, edema, diffuse bilateral pulmonary infiltrates, azotemia, hypoalbuminemia and hypocomplementemia, while receiving intravenous C. parvum therapy. All had renal biopsies that showed a proliferative glomerulonephritis with subendothelial basement membrane deposits. Immunofluorescence showed glomerular IgG, IgA, IgM, and the C3 component of complement. A fourth patient was found in retrospective chart review of 87 patients registered on two C. parvum-containing protcols. The frequency of the complication in this group was 3/87. Renal failure resolved in all four patients spontaneously after the cessation of C. parvum immunotherapy. Serial evaluation of renal function should be carried out in all patients on systemic adjuvant immunotherapy.

Adult↗
PubMed1977

Ventricular septal motion and left ventriclular dimensions during abnormal ventricular activation.

To determine the effect of abnormal ventricular activation on ventricular septal motion, left ventricular endocardial motion and left ventricular dimensions, 12 patients with normal motion were studied with echocardiography during incremental pacing of the right ventricular apex, outflow and inflow regions. Three types of abnormal ventricular septal motion were seen: The type I pattern was characterized by an early rapid preejection posterior ventricular septal motion followed by another posterior systolic motion that lasted throughout ejection, both of which were associated with septal thickening. In the type II pattern an early rapid preejection posterior ventricular septal motion was followed by an anterior ejection motion; the latter was not accompanied by septal thickening. The type III pattern consisted of an early preejection posterior ventricular septal motion followed by a mid and late systolic posterior motion: the latter motion extended through diastole. During right ventricular apical pacing, 8 of 11 patients showed a type 1 pattern, 1 a type II pattern and 2 a normal septal motion. During right ventricular outflow pacing,seven of nine patients showed a type II pattern, one a type III pattern and one a type I pattern. During right ventricular inflow pacing, eight of nine patients showed a type II pattern and one a type III pattern. At faster pacing rates patterns of types I and III changed to a type II pattern (five patients). End-diastolic dimensions decreased significantly during incremental right ventricular pacing when compared with those during sinus rhythm. End-systolic dimensions decreased significantly only during right ventricular apical and outflow pacing at maximal rates. In the seven patients who had pacing from all three sites, the decrease in left ventricular dimensions did not significantly differ when the three pacing sites were compared. These findings suggest that (1) abnormal ventricular septal motion during right ventricular pacing (induced left bundle branch block patterns) is dependent on the sequence of ventricular activation; (2) ventricular septal motion during right ventricular outflow and inflow pacing is similar to that seen in spontaneous left bundle branch block, whereas the pattern of septal motion during right ventricular apical pacing is different from that of spontaneous left bundle branch block; and (3) changes in left ventricular dimension are dependent on ventricular pacing rate but independent of pacing site.

Adult↗
PubMed1977

Studies on the biosynthesis, assembly and secretion of vitellogenin, an oestrogen-induced multicomponent protein.

1. The process by which the egg-yolk protein precursor vitellogenin is biosynthesized, assembled and secreted by Xenopus laevis (South African clawed toad) liver was studied. It was previously shown in other laboratories that vitellogenin contains the two egg-yolk proteins lipovitellin (mol.wt. 140 000) and phosvitin (mol.wt. 35 000). 2. Evidence is presented which shows that Xenopus liver microsomal fractions synthesize precursors of vitellogenin. These precursors were solubilized from the membranes with detergent and analysed by sodium dodecyl sulphate/polyacrylamide-gel electrophoresis. This analysis indicated that there is only one precursor polypeptide, and this has mol.wt. approx. 200 000 +/- 20 000. This demonstrates that the egg-yolk proteins are translated as part of this larger polypeptide. 3. Experiments also demonstrate the existence of a microsomal proteinase which is able to cleave the precursor into smaller fragments. The nature of these fragments provided some indirect evidence that phosvitin and lipovitellin light chains are situated together within the precursor molecule. 4. These precursor data fit in well with structural studies on serum vitellogenin, since it has been shown that the latter protein consists of two identical subunits each with a mobility on sodium dodecyl sulphate/polyacrylamide gels identical with that shown by the microsomal precursor. This indicates that both the intracellular precursor and subunit of vitellogenin have similar (but not necessarily identical) molecular weights. 5. It was also shown that trypsin or chymotrypsin can cleave the serum vitellogenin into leucine- and serine-rich fragments which resemble lipovitellin and phosvitin respectively. Attention is, however, drawn to the fact that the serine-rich fragment is not identical with phosvitin, since it contains eight times more leucine than that expected for the authentic phosvitin molecule [Penning (1976) Ph.D. Thesis, University of Southampton].

Animals↗
PubMed1977

Ultrastructure of elastofibroma.

An elastofibroma from a 69-year-old white man was studied by light and electron microscopy. The lesion was comprised of abundant collagen fibers and numerous randomly disposed masses of amorphous elastinophilic material. Ultrastructurally, this material appeared to be derived from a markedly dense, finely fibrillar precursor secreted by fibroblasts and manifested a striking resemblance to young elastic tissue. Central cores of mature elastic tissue were recognized within some of these elastinophilic masses. This study demonstrates unequivocally that the abnormal elastic material in elastofibroma is derived from excessive production of young elastic tissue and not from elastotic degeneration of collagen, as suggested in some of the previous studies. This young elastic tissue manifests a marked retardation of maturation, the cause of which however is not clear. Another interesting finding in this case was the presence of prominent fibrous laminae within the nuclei of most of the fibroblasts. The significance othis finding is briefly discussed.

Aged↗
PubMed1977

Extrarenal Wilms' tumor: report of a case and review of the literature.

A case of an extrarenal Wilms tumor arising in the inguinal region of a 2-month-old boy is described. A review of the literature indicates that nine well-documented cases of extrarenal Wilms tumor have previously been described. Four of these tumors arose within teratomas. The remaining five cases, in which no teratomatous components were encountered, probably arose in embryologic rests of renal tissue.

Adult↗