PubMed Health⌕ Search

Biomedical subjects

R Mahmud

Publications and source records attributed to R Mahmud.

At least 19 recordsLinked to original sources
PubMed2005

Computed and conventional chest radiography: a comparison of image quality and radiation dose.

The aim of this study was to compare the image quality and entrance skin dose (ESD) for film-screen and computed chest radiography. Analysis of the image quality and dose on chest radiography was carried out on a conventional X-ray unit using film-screen, storage phosphor plates and selenium drum direct chest radiography. For each receptor, ESD was measured in 60 patients using thermoluminescent dosemeters. Images were printed on 35 x 43 cm films. Image quality was assessed subjectively by evaluation of anatomic features and estimation of the image quality, following the guidelines established by the protocols of the Commission of the European Communities. There was no statistically significant difference noted between the computed and conventional images (Wilcoxon rank sum test, P > 0.05). Imaging of the mediastinum and peripheral lung structures were better visualized with the storage phosphor and selenium drum technique than with the film-screen combination. The patients' mean ESD for chest radiography using the storage phosphor, film-screen combination and selenium drum was 0.20, 0.20 and 0.25 mGy, respectively, with no statistically significant difference with P > 0.05 (chi(2) tests).

Humans↗
PubMed2003

Surgical intervention in traumatic facial nerve paralysis.

A four years review from June 1998 to June 2002 of traumatic facial nerve paralysis from temporal bone fractures that required surgical intervention is presented. The aim of this clinical presentation was to determine the current pattern of cases with traumatic facial paralysis which required surgical intervention at our center. There were six cases, of which four (66%) were longitudinal fractures, one each (17%) had transverse fracture and fracture over the lateral wall of mastoid. Hearing loss (83%) was the commonest associated clinical symptom. All cases underwent decompression via the transmastoid surgical approach. Intraoperative findings revealed oedema of facial nerve involving vertical segment and horizontal segment in three cases each respectively. Two cases had concomitant bony impingement. The facial nerve functions in four cases (66%) and one case recovered to House Brackmann grade 2 and 4, 12 months and 3 months respectively postsurgery. The case with transverse fracture remained as House Brackmann grade 5 after two years.

Adolescent↗
PubMed1997

Structural basis for the haemotoxicity of dapsone: the importance of the sulphonyl group.

The structural basis of dapsone (4,4'-diaminodiphenyl sulphone) haemotoxicity has been determined by investigation of the in vitro bioactivation of a series of 4-substituted arylamines. In the presence of rat liver microsomes, dapsone (100 microM) was the most potent former of methaemoglobin in human erythrocytes (44.8 +/- 6.7%). Substitution of the sulphone group with sulphur (11.6 +/- 1.4% methaemoglobin), oxygen (4.5 +/- 1.1%), nitrogen (0.0 +/- 3.2%), carbon (13.6 +/- 0.8%) or a keto group (34.0 +/- 6.1%) resulted in a decrease in methaemoglobin formation. Only one compound, 4,4'-diaminodiphenylamine, generated significant (P < 0.001) amounts of methaemoglobin (25.6 +/- 2.5%) in the absence of NADPH. To assess further the role of the 4-substituent in methaemoglobinaemia, the toxicity of a series of 4-substituted aniline derivatives was also studied. Of the anilines studied, 4-nitroaniline caused the most methaemoglobin (36.5 +/- 8.0%), whilst aniline caused the least (0.3 +/- 0.5%). Overall, there was a significant correlation (r2 = 0.83) between the haemotoxicity and the Hammett constant, sigma(p), suggesting that it is the electron-withdrawing properties of the substituent that influence the methaemoglobin formation. In the presence of microsomes prepared from two human livers, dapsone was the most haemotoxic bis arylamine, whereas 4-iodoaniline was the most potent methaemoglobin former (60.6 and 73.6%) and aniline the least potent (1.1 and 2.4%). As a whole, these results indicate that the sulphonyl group, which is essential for the pharmacological activity of dapsone, is also largely responsible for the haemotoxicity seen with this drug.

Animals↗
PubMed1997

Ventriculoatrial conduction capability and prevalence of 1:1 retrograde conduction during inducible sustained monomorphic ventricular tachycardia in 305 implantable cardioverter defibrillator recipients.

Despite the advent of dual chamber ICDs, differentiation of VT (SMVT) with 1:1 VA conduction will remain a challenge. In this study, VA conduction capability and prevalence of inducible sustained monomorphic (SM) VT with 1:1 VA conduction was assessed in 305 ICD recipients. SMVT with a mean cycle length (CL) of 304 +/- 61 ms was induced in 161 (53%) patients. Twenty-six percent of the patients maintained 1:1 VA conduction to CL < or = 400 ms during incremental ventricular pacing, regardless of presenting tachyarrhythmia or presence of inducible SMVT. Among ten patients who had inducible SMVT with possible 1:1 VA conduction (based on SMVT CL comparable to the shortest CL associated with 1:1 retrograde conduction during ventricular pacing), all seven with available intracardiac tracings had documented 1:1 VA conduction during the induced SMVT--representing 4.4% of the patients with inducible SMVT (95% CI 1.2%-7.6%), and 2.3% of the entire ICD cohort (95% CI 0.6%-4.0%). We conclude that about one-fifth of ICD recipients possess 1:1 VA conduction to CL < or = 400 ms and that inducible SMVT with 1:1 VA conduction can be demonstrated in a small but nonnegligible proportion of ICD recipients. These data are relevant to the design of tachyarrhythmia-discrimination algorithms for dual chamber ICDs.

Adolescent↗
PubMed1997

Comparison of the metabolism and toxicity of dapsone in rat, mouse and man.

The metabolism and toxicity of dapsone was compared in vitro and in vivo in rat, mouse and man. Metabolism was assessed by high-pressure liquid chromatography-mass spectrometry and methemoglobin formation has been used as a toxic endpoint. The greatest toxicity in vitro was seen in microsomes prepared from male Wistar rats (36.6 +/- 1.5% methemoglobin), although toxicity was also seen in microsomes from the female rat (8.2 +/- 1.3%), male CD1 (4.2 +/- 1.6%) and human (10. 9 +/- 1.1%). The rank order of toxicity agreed with the formation of the hydroxylamine metabolite in vitro. All microsomes were also capable of catalyzing the reverse reaction, i.e., reduction of the hydroxylamine to dapsone. However, in vivo administration of dapsone resulted in significant (P < 0.05) methemoglobinemia only in male rats and humans. This species difference in the susceptibility to dapsone toxicity could not be attributed solely to the sensitivity of the target erythrocytes, because the order of sensitivity to dapsone hydroxylamine was human > mouse > rat. Analysis of bile and urine revealed the formation of dapsone hydroxylamine and its glucuronide in male rats and humans, but not in female rats or mice. This species difference in the metabolism and toxicity of dapsone has important implications in the safety evaluation of related compounds for man.

Acetylation↗
PubMed1994

Clinical experience with the implantable cardioverter defibrillator.

The implantable cardioverter defibrillator has played an increasingly greater role in the management of episodes of sudden cardiac-related death related to ventricular tachycardia or ventricular fibrillation. This study reviews the cases of 142 patients who underwent insertion of an implantable cardioverter defibrillator, 104 who received a device alone (group I) and 38 who underwent insertion of the device in combination with other cardiac surgical procedures (group II). The overall operative mortality was 3.5% and this did not differ between the two groups. The complication rate was higher for group II than for group I patients, and consisted primarily of an increased incidence of atrial arrhythmias (53% versus 13%; p < 0.001). Late complications included three device infections requiring removal of the defibrillator. The late mortality did not differ between the two groups and was primarily related to congestive heart failure. Sudden cardiac-related death was an uncommon late event, with an actuarial freedom from sudden cardiac-related death of 98%, 97%, and 87% at 1, 2, and 5 years, respectively. The morbidity and mortality rate are low in association with the insertion of an implantable cardioverter defibrillator, even when this is combined with other cardiac surgical procedures. Its insertion is also associated with a low subsequent rate of sudden cardiac-related death.

Adult↗
PubMed1994

Integration of absolute ventricular fibrillation voltage correlates with successful defibrillation.

Previous work has suggested that at higher absolute ventricular fibrillation voltages (AVFV), the heart is more amenable to defibrillation. This study investigated in a canine model whether voltage integration of the AVFV is associated with the defibrillation success rate. The moving-average filter was used to process the ventricular fibrillation (VF) waveform recorded from Lead II of the electrocardiogram (ECG). In seven animals, defibrillation trials were analyzed using a dc shock (DCS) successful approximately 50% of the time when delivered randomly. For each of a total of 84 DCS (40% successes, 60% failures), the fibrillation waveform just prior to DCS was analyzed. The integration of the AVFV waveform was performed over various sample sizes including 1, 4, 8, 16, 64, and 128 ms, as well as the time equal to the mean VF cycle length. The results suggest that dc shocks delivered at instants of higher values of integrated AVFV over the various window sizes are associated with successful defibrillation. Window sizes less than 16 ms appeared to offer the best discrimination. The integration of AVFV over the entire VF cycle length was significantly higher for successful rather than unsuccessful DCS. This interesting observation is consistent with the clinical observation that "coarse" VF (high AVFV) is easier to defibrillate than "fine" VF (low AVFV). The use of voltage integration of AVFV may have potential implications in the improvement of defibrillation success in implantable devices.

Analysis of Variance↗
PubMed1990

Changes in transmyocardial impedance during prolonged ventricular fibrillation. Implications for current flow and delivered energy during DC countershock.

Transthoracic resistance (TTR) and transmyocardial resistance (TMR) were measured during 10 minutes of uninterrupted ventricular fibrillation (VF) in a canine model. TMR was measured at 10- to 50-second intervals with two wire-mesh patch electrodes in 16 dogs. TTR was measured through two identical low-impedance electrodes. A monophasic exponentially truncated pulse with a duration of 5 msec was used for measurement of TMR as well as TTR. Low-energy pulses of 100 V were used for TMR measurements and pulses of 300 V for TTR measurements. TMR showed an increase of 22.8 +/- 5.14 omega (from 96.2 +/- 12.3 omega) after 600 seconds of uninterrupted VF (p less than 0.0006). TTR showed a change of 2.4 +/- 1.94 omega, which was not statistically significant in comparison with the initial value of 69.0 +/- 11.4 omega. A mathematical model was developed to predict energy delivered to the heart after a transthoracic shock. Observed values of TMR and TTR were used in this model. With the use of this model, the predicted fall in transmyocardial current after 600 seconds of uninterrupted VF and 19.3%, and the fall in energy delivered to the heart was 14%. Our study suggests that increase in TMR may contribute to the observed lack of successful defibrillation during prolonged VF.

Animals↗
PubMed1990

Genesis of sigmoidal dose-response curve during defibrillation by random shock: a theoretical model based on experimental evidence for a vulnerable window during ventricular fibrillation.

The sigmoidal dose-response curve (percent success vs shock energy) suggests a probabilistic nature of defibrillation. The mechanism is still largely unknown, however, random variation in the excitable state during ventricular fibrillation (VF) is suspected. A canine defibrillation study was designed to determine whether random variation in absolute VF voltage (AVFV) (a crude marker of number of excitable cells) was related to success of defibrillation, using a DC shock successful at the 50% level. The results were: (a) transmyocardial resistance (73.4 +/- 1.4 vs 73.6 +/- 1.5 ohms) and delivered energy (6.1 +/- 1.2 vs 6.2 +/- 1.2 joules) were similar; however, (b) AVFV 2 msec prior to DC shock was greater for successful as compared to unsuccessful attempts (0.5 +/- 0.1 vs 0.3 +/- 0.0 mV, P less than 0.01). A mathematical model was subsequently developed based on fluctuation in the number of excitable cells. Variation in the state of excitability resulted in a cyclic window potentially vulnerable to defibrillation. The vulnerable window occurred at a point when the number of excitable cells was low, i.e., a higher state of total depolarization, which was in agreement with the experimental finding. For a given VF pattern, duration of the vulnerable window was regulated by the shock energy. A larger shock energy generated a wider vulnerable window and, in turn, a higher success rate. Finally, the sigmoidal dose-response curve of defibrillation was theoretically constructed by calculating the variable chances of a random DC shock occurring either in a vulnerable window or elsewhere during VF. It is concluded that a vulnerable window susceptible to defibrillation can be demonstrated in the early stages (10 sec) of VF. The mathematical model provides a theoretical basis for the vulnerable window and helps elucidate the probabilistic nature of defibrillation.

Animals↗
PubMed1989

Electrophysiological determinants of antidromic reentry induced during atrial extrastimulation. Insights from a pacing model of Wolff-Parkinson-White syndrome.

The electrophysiology of antidromic reentry, a less common phenomenon than orthodromic reentry, remains a poorly understood aspect of the Wolff-Parkinson-White (WPW) syndrome. We used a pacing model of ventricular preexcitation in patients without WPW, so that electrophysiological events in the normal pathway during atrial extrastimulation (A1-A2 technique) could be precisely delineated without the obscuring effect of an actual accessory pathway. Ventricular preexcitation was simulated by an A1-V1 sequential basic drive with A2-V2 extrastimulation at progressively shorter A1-A2 (equal to V1-V2) coupling intervals. At each coupling interval tested within the zone of atrioventricular (A-V) nodal effective refractory period (since anterograde block of A2 was considered mandatory for manifestation of antidromic reentry), responses were assessed after A2 alone (method I), V2 alone (method II), and A2 plus V2 (method III, the complete preexcitation model). The entire pacing protocol was performed at two A-V intervals, short (50 msec) and long (150-180 msec), thereby simulating different proximities between the A pacing site and "accessory pathway" location. Of 47 consecutive unmedicated patients screened for the study protocol, 38 failed to meet minimal prerequisites for possible initiation of antidromic reentry because of failure in 18 (38% of total) to achieve anterograde A-V nodal block of A2, even though 1:1 ventriculoatrial conduction to cycle lengths less than or equal to 500 msec (less than or equal to 400 msec in 12) was present; and poor or absent ventriculoatrial conduction in the others. The nine remaining candidates underwent the full pacing protocol. Antidromic reentry (retrograde atrial response following V2 in method III) was observed in only two cases (4% of total), and both were associated with retrograde His-Purkinje system delays (documented by method II) occurring in tandem with a long A-V interval, thereby allowing for completion of retrograde A-V nodal recovery after penetration by A2. Indeed, such a prolonged recovery time prevented initiation of antidromic reentry in six of the nine patients (proven by intact ventriculoatrial conduction in method II). Retrograde A-V nodal block of V2, independent of A2, prevented an antidromic echo in one case. Findings in our model help to clarify the various factors, including specific anterograde and retrograde A-V nodal properties; anatomic relation between the accessory and normal pathways; and the retrograde His-Purkinje system delays, that must prevail in a concerted fashion to permit the initiation of antidromic reentry during the A1-A2 technique in patients with the WPW syndrome.

Atrioventricular Node↗
PubMed1989

Electrophysiologic characteristics of sudden QRS axis deviation during orthodromic tachycardia. Role of functional fascicular block in localization of accessory pathway.

We analyzed the effect of functional fascicular block (FFB) on ventriculoatrial conduction time (VACT) during orthodromic tachycardia (OT) in 32 patients with single accessory pathway (AP) of the Kent bundle type. The location of AP was left free wall (LFW-AP) in 21 patients, left posteroseptal in 6, right free wall in 2, and right anteroseptal in 3. FFB either alone or in combination with functional left or right bundle branch block (LBBB or RBBB) occurred predominantly at the onset of OT and was initiated with ventricular extrastimulus technique more often than with atrial extrastimulation. In patients with LFW-AP, isolated functional left anterior fascicular block (LAFB) produced significant prolongation in VACT (15-35 ms). A similar magnitude of VACT increase (20-35 ms) was also observed when LAFB was associated with RBBB. Although 25-45-ms prolongation in VACT occurred with functional LBBB and normal axis, an additional 20-55-ms VACT increase was seen when LAFB accompanied LBBB. Functional LAFB, alone or in combination with bundle branch block, however, did not prolong VACT in patients with other AP locations. Furthermore, left posterior fascicular block did not produce prolongation of VACT in any of the cases. It is concluded that in patients with the Wolff-Parkinson-White syndrome, evaluation of VACT during functional LAFB provides important information regarding AP localization and a clear separation of LFW-AP from all other locations.

Adolescent↗
PubMed1988

Absence of significant postdefibrillation bradyarrhythmias in patients with automatic implantable defibrillators.

Because postdefibrillation bradycardia or asystole is of clinical concern in patients with implanted automatic cardioverter defibrillators, we analyzed the cardiac rhythm after 157 intraoperative defibrillations in 50 patients undergoing implantation of the device. Factors that could influence the heart rhythm immediately after defibrillation were also analyzed. The postdefibrillation heart rate and the duration of postdefibrillation asystole did not correlate with age, conduction abnormalities, type or duration of arrhythmia before defibrillation, delivered energy, lead system, or left ventricular ejection fraction, but they did correlate with the resting preoperative heart rate and the concomitant performance of coronary artery bypass surgery at the time of defibrillator implantation. Temporary pacing (for prolonged asystole) was required in only two patients, both of whom had also undergone bypass surgery. Fourteen patients being treated with amiodarone had slower resting and postdefibrillation heart rates, but the mean duration of posdefibrillation asystole was similar to that seen in patients not receiving any antiarrhythmic medication. On follow-up, 25 monitored and 178 unmonitored automatic defibrillator discharges occurred in 24 patients, without evidence of symptomatic postdefibrillation bradyarrhythmias. Thus significant postdefibrillation bradyarrhythmias were uncommon, but when such a propensity existed it could not be predicted reliably on clinical grounds alone.

Adult↗
PubMed1988

Useful clinical criteria for the diagnosis of ventricular tachycardia.

Misdiagnosis occurs upon initial presentation to medical attention in a considerable number of patients referred for evaluation of wide QRS tachycardia. In order to improve diagnostic accuracy (ventricular versus supraventricular tachycardia), the answers to two key bedside questions were prospectively evaluated: (1) Had the patient experienced a prior myocardial infarction? (2) Did symptoms of tachyarrhythmia start only after the infarction? A patient presenting with a wide QRS tachycardia was considered to have ventricular tachycardia if he or she answered in the affirmative to both of these questions. Of 31 consecutive patients referred with electrocardiographically documented sustained wide QRS tachycardia that was reproduced in the electrophysiology laboratory, the diagnoses made when the patients first presented to medical attention were ventricular tachycardias in 17 patients and supraventricular tachycardias in 14 patients. Following electrophysiologic evaluation, 29 were diagnosed as having ventricular tachycardia and two as supraventricular tachycardia. If the diagnoses were made solely on the basis of responses to the bedside questions mentioned earlier, 28 of the 29 patients having a final diagnosis of ventricular tachycardia would have been correctly identified. It is concluded that the use of these two questions can be very helpful in improving the clinical diagnosis of ventricular tachycardia.

Adult↗
PubMed1988

Modulation of conduction and refractoriness in atrioventricular junctional reentrant circuit. Effect on reentry initiated by atrial extrastimulus.

The importance of activation sequence of an atrioventricular junctional reentrant (AVJRe) circuit, before delivery of an extrastimulus, has received little attention in studies concerned with clinical tachycardias. In this study a change in activation sequence was accomplished using bidirectional activation (V-A sequential pacing) during the basic drive (V1A1-V1A1). It was noted that, compared with an atrial extrastimulus (A2) after an atrial drive (A1-A1), earlier activation (by V1 impulse of the V1A1-V1A1 drive) consistently improved conduction, or decreased refractoriness, or both, in the anterograde as well as the retrograde pathway of the AVJRe circuit. In all patients, five with AV nodal reentry and six with Wolff-Parkinson-White syndrome, reentrant tachycardia could be prevented during V-A sequential pacing. In four of eleven patients, reentry was prevented despite achieving the so-called critical atrioventricular nodal delays that had previously caused reentry during control study. This finding suggested that conduction delay necessary for reentry was related to the site of block, which in turn was affected by V-A sequential pacing. We concluded that changing the activation sequence during basic drive modulates conduction and refractoriness in AVJRe circuits, and allows the study of a wide range of electrophysical factors that prevent or permit reentry.

Adult↗
PubMed1988

Behavior of postextrasystolic His-Purkinje system refractoriness after multiple premature beats.

Although the steady-state refractoriness of the human His-Purkinje system has been shown to be directly related to the cycle length of pacing, the effect that a varying number of premature beats would have on His-Purkinje system refractoriness of the first postextrasystolic beat has not been described. These effects were systematically investigated in 10 patients with normal intraventricular conduction. The His-Purkinje system relative refractory period (HPS-RRP) of the postextrasystolic beat and that of a comparable constant cycle length ventricular drive were measured by the ventricular extrastimulus technique. Results were as follows: the HPS-RRP of the postextrasystolic beat after one premature beat was longer than the HPS-RRP during a comparable constant ventricular drive. However, with the addition of each successive premature beat, the HPS-RRP of the postextrasystolic beat alternated between lower and higher values, in a manner dependent on whether there was an odd or even number of premature beats. In contrast, ventricular refractoriness of the postextrasystolic beats behaved in a cumulative manner, decreasing progressively with the addition of each premature beat.

Bundle of His↗
PubMed1987

Effects of abrupt changes in cycle length on atrial refractory periods in man.

While the electrophysiologic effects of sudden changes in cycle length on the His-Purkinje System and ventricular myocardial refractoriness are better known, the behavior of atrial myocardium in this regard is poorly understood. The effects of an abrupt long to short cycle length change (11 patients: group A) and/or short to long cycle length alteration (18 patients: group B) on the atrial effective and functional refractory period were assessed during electrophysiologic studies. The values thus obtained were compared to those observed during the scanning of both constant long and constant short cycle lengths of the same duration. In group A the effective and functional refractory periods of the right atrium measured 250 +/- 38 msec and 296 +/- 31 msec during a constant long cycle length of 709 +/- 80 msec, whereas the same parameters had values of 228 +/- 30 msec and 260 +/- 32 msec, respectively, at a constant short cycle length of 436 +/- 81 msec. With an abrupt change in cycle length from long to short (a change of 273 +/- 75 msec), the effective and functional atrial refractory periods were 225 +/- 29 and 267 +/- 29 msec in that order, and these values closely approximated those seen with a constant short cycle length. Similarly, the two atrial refractory period parameters in group B measured 218 +/- 16 msec and 262 +/- 19 msec during a constant short cycle length of 414 +/- 68 msec and were 236 +/- 17 msec and 284 +/- 21 msec, respectively, at a constant long cycle length of 689 +/- 92 msec.(ABSTRACT TRUNCATED AT 250 WORDS)

Cardiac Pacing, Artificial↗
PubMed1987

Effect of concealed anterograde impulse penetration on retrograde atrioventricular nodal conduction in man.

The manner in which concealed anterograde impulse penetration may affect retrograde atrioventricular nodal conduction was studied systematically in 12 patients with intact ventriculoatrial (VA) conduction. After the last beat of a basic atrial drive (A1), an extrastimulus (A2) was introduced 20 msec inside the effective refractory period of the atrioventricular node. A ventricular extrastimulus (Vp) was then introduced at a progressively shorter A1Vp coupling interval both in the presence (method I) and absence (method II) of A2. In two patients, Vp was never conducted retrogradely to the atria with method I despite the presence of VA conduction during method II. In the remaining 10 patients, the VpAp interval was longer with method I vs method II; moreover, retrograde block of Vp ultimately occurred at a mean A2Vp coupling interval of 359 +/- 153 msec (range 190 to 540 msec) during method I despite the persistence of VA conduction during method II at comparable A1Vp coupling intervals. Before onset of retrograde block in method I, the VpAp curve took one of the following three forms: (1) crescendo, a progressively increasing VpAp interval; (2) flat, a constant VpAp interval, (four cases); or (3) discontinuous, a marked jump in the VpAp interval before the onset of retrograde block (two cases). Our findings may serve to elucidate some poorly understood electrophysiologic phenomena.

Aged↗