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Biomedical subjects

D Mehta

Publications and source records attributed to D Mehta.

At least 127 records · Page 7Linked to original sources
PubMed1988

Limitations of rate response of an activity-sensing rate-responsive pacemaker to different forms of activity.

The responses of an activity-sensing rate-responsive system (Activitrax) to various forms of physiological activity were assessed in 15 individuals who had this pacemaker. Nine were patients with complete heart block and atrial arrhythmias; their mean age was 60 years (range, 41-85 years). Six were age-matched healthy volunteers who were exercised with an external Activitrax system attached firmly to the chest wall. The pacemaker was programmed to achieve a pacing rate of about 100 bpm at the end of the first stage of the Bruce protocol (pacemaker settings: rate = 70-150 bpm; threshold = low to medium; response = 6-9). In the activity-sensing ventricular pacing mode, all patients achieved a significant increase in treadmill time compared to constant-rate ventricular pacing (mean +/- SD, 8.0 +/- 3.3 vs 5.4 +/- 2.3 minutes; p less than 0.01), with a mean maximum pacing rate of 123 +/- 18 bpm. Jogging in place produced a prompt increase in pacing rate, with the maximum achieved at the end of the exercise. However, physiological activities such as hand-grip, the Valsalva maneuver and standing resulted in only minimal rate response. Pacing rate after ascending 4 flights of stairs was the same as that achieved after descending the same stairs (100 +/- 8 vs 105 +/- 4 bpm; p = 0.1). All 15 subjects were exercised from resting heart rate for 3 minutes on a treadmill at 1.2 mph and 2.5 mph with four gradients at each speed. Although the pacing rate increased with a faster treadmill speed (p less than 0.005), it did not respond appropriately to a change in gradient compared to the sinus rate. We conclude that although activity-sensing rate-responsive pacing gives a prompt increase in pacing rate and improves maximum exercise tolerance, further refinement is necessary because: (1) physiological activities not associated with significant movement are not detected by this pacing system; (2) detection of vibrations as an indicator of activities does not correlate well with the level of exertion.

Adult↗
PubMed1988

Comparative evaluation of chronotropic responses of QT sensing and activity sensing rate responsive pacemakers.

The rate responses of activity sensing (ATS) and QT sensing (QTS) rate responsive pacemakers to different forms and durations of exercises were compared. Nine patients with ATS and five with QTS were studied. All had complete heart block and atrial arrhythmias. At the onset, the pacemakers were programmed to achieve a pacing rate of 100-110 bpm by the end of stage 1 of the Bruce protocol, and to a pacing rate range of 70-150 bpm. With progressive exercise, using a treadmill (Bruce protocol), the maximum pacing rates in the two groups were not significantly different (mean +/- SD: 123 +/- 18 vs 129 +/- 23 bpm, ATS vs QTS). The time taken to return to the baseline pacing rate during recovery was significantly longer with QTS (178 +/- 70 vs 264 +/- 68 s, p less than 0.05). Brief exercise tests on a treadmill were performed for 3 min each with different combinations of treadmill speeds (1.2 and 2.5 mph) and gradients (0, 5, 10 and 15%). In both groups of patients, faster walking speed was associated with a faster pacing rate at each gradient. However, with increasing gradients, at each speed, there was a rise in the maximum pacing rate only in patients with QTS. During brief exercise tests, the maximum rate was achieved by the end of exercise in patients with ATS, but was delayed by 33 +/- 20 s after exercise in patients with QTS.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1988

Elimination of diffraction error in acoustic attenuation estimation via axial beam translation.

Optimized wideband attenuation estimations were performed on a tissue mimicking phantom in a water tank with and without axial beam translation (ABT), and the results were compared to those from standard substitution measurements. A -17 percent discrepancy between the results of the substitution method and the optimized estimation without ABT was noted in the far field. This discrepancy was eliminated when ABT was utilized.

Models, Structural↗
PubMed1988

Recurrent paroxysmal complete heart block induced by vomiting.

A woman had a 40-year history of vomiting associated with syncope. Spontaneous and induced vomiting was predictably associated with sinus bradycardia, paroxysmal atrioventricular block, and ventricular asystole. The clinical and laboratory studies carried out to illustrate the mechanism of this unusual complication of vomiting demonstrated it to be due to a vagovagal reflex initiated by distension of upper esophagus.

Bradycardia↗
PubMed1988

Mucoepidermoid carcinoma of the lung with intracranial metastases.

Discussed is the first roentgenographic and post-mortem description of a patient with mucoepidermoid carcinoma of the lung who presented with intracranial metastases. The patient's primary tumor eluded physical diagnosis and bronchoscopic delineation. The autopsy confirmed minimal tumor involvement of the bronchial wall despite bulky regional and distant metastases.

Aged↗
PubMed1987

Flecainide acetate in the treatment of tachycardias associated with Mahaim fibres.

Patients with Mahaim fibres are susceptible to tachycardias which can be refractory to conventional drug therapy, leading to treatment with surgery and catheter ablation. The effects of flecainide acetate were studied in 3 patients (61, 21 and 35 years of age) with Mahaim fibres presenting with tachycardias refractory to beta-blockers, quinidine and verapamil. One also had ophthalmic side-effects from amiodarone. Three types of tachycardias were induced: a reentrant tachycardia with left bundle branch block morphology (LBBBM) in all 3 patients, atrial flutter in one and atrial fibrillation in another. Intravenous flecainide acetate (2 mg kg-1) terminated reentrant tachycardia and abolished duality of atrioventricular conduction in patient 1. In patient 2, it abolished preexcitation during atrial flutter prior to termination. Atrial fibrillation could not be induced in patient 3 after flecainide acetate. In all patients, retrograde conduction was blocked, preexcitation was not present with atrial pacing and no tachycardia was induced after flecainide. All have remained asymptomatic on oral flecainide acetate (100 mg bd) for a mean follow-up period of 9 months. We conclude that (1) flecainide acetate is effective for the treatment of various tachycardias associated with Mahaim fibres; (2) since different mechanisms responsible for the tachycardia with LBBBM may be present in the same patient and difficult to determine in some, treatment with flecainide acetate which affects both the atrioventricular node and Mahaim fibre conduction may be appropriate for the condition and; (3) its use should be considered before more aggressive therapies.

Adult↗
PubMed1986

QT prolongation after ampicillin anaphylaxis.

Tall T waves and pronounced prolongation of the QT interval developed 24 hours after an apparently complete recovery from an acute anaphylactic reaction to oral ampicillin in a previously healthy woman of 29. These electrocardiographic abnormalities gradually subsided over five days. The prolongation of the QT interval has not previously been reported after anaphylaxis.

Adult↗
PubMed1986

Capillary remodeling in bleomycin-induced pulmonary fibrosis.

Lung fibrosis is a process in which collagen is laid down and the delicate capillary-alveolar relationship is disturbed. The architectural changes which occur in the capillaries, a main element of the oxygen transferring unit, are difficult to illustrate without a three-dimensional tool, such as scanning electron microscopy. Therefore, a scanning electron microscopic study was undertaken to show the capillary changes of lung fibrosis. Fibrosis was induced in rats by intratracheal instillation of bleomycin. After 30 days the rats were sacrificed, and the vascular tree of the lung was cast with methacrylate. The fibrosis was patchy. The intercapillary space became wider; and some capillaries had large, irregular dilatations. Occasionally giant capillaries (up to 19 mu in diameter) were noted. The pleural and alveolar capillary diameters increased (P less than 0.01), and the branching frequency decreased (P = 0.02). The center of the capillary rings, which has been suggested to be the site of contractile interstitial cells, increased in size (P = 0.03). The appearance of irregularly shaped capillaries and an increase in diameter without a change in density of alveolar capillaries, resulting in a loss of surface area and a decrease in branching, are the main scanning electron microscopic findings of the remodeling which occurs in pulmonary capillaries in lung fibrosis. These changes may partially explain the functional derangement of this disease.

Animals↗
PubMed1983

Carcinoma of the breast and meningioma. Association and management.

An association between carcinoma of the breast and meningioma has been recognized recently. Three more cases are added to the few previously reported in the literature. An awareness of this association together with modern techniques of investigation, particularly CAT scanning, may permit earlier diagnosis and treatment of more cases. Meningioma as well as carcinoma of the breast is more common in women and the incidence of both tumors reaches a peak in the fifth and sixth decades. Both are related to pregnancy and have an estrogen-receptor protein. Lesions of the central nervous system following the diagnosis and treatment of breast cancer are usually presumed to be metastatic. Therefore, these lesions may be irradiated without complete clinical investigation. If the clinician is aware of this association, appropriate diagnostic procedures could lead to the surgical removal of a benign meningioma. Skull x-rays, bone scan, brain scan, CAT scan, and cerebral angiograms are useful in making a diagnosis. Besides surgery, radiation therapy and hormonal therapy may play a role in the management.

Aged↗