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Biomedical subjects

I Singer

Publications and source records attributed to I Singer.

At least 37 records · Page 2Linked to original sources
PubMed1988

Implanted automatic defibrillators: effects of drugs and pacemakers.

The automatic implantable cardioverter defibrillator is an effective device for prevention of sudden cardiac death. Patients who require the implantation of the device often require permanent pacing for symptomatic bradyarrhythmias and may require antiarrhythmic drug therapy. Antiarrhythmic drugs may alter the defibrillation thresholds, arrhythmia cycle length and frequency, pacing thresholds and postshock excitability. Interactions between the defibrillator and the pacemaker may result in sensing problems, leading to multiple counting and inappropriate shocks, or ventricular fibrillation nondetection, sensing or capture failure post defibrillation and pacemaker reprogramming induced by defibrillator discharge. The potential for interactions will increase as the new generation of programmable defibrillators become clinically available, combining features of permanent pacemakers, antitachycardia pacemakers and defibrillators.

Anti-Arrhythmia Agents↗
PubMed1988

The automatic implantable cardioverter defibrillator: T wave sensing in the newest generation.

The AICD uses an automatic gain control amplifier for detecting the small electrograms during ventricular fibrillation. The latest generation of the AICD appears to have a more sensitive lock on gain amplifier, as 6 of 76 patients implanted with the new AICD had double counting of the QRS-T wave complex resulting in asymptomatic discharges. Solutions to the problem of limiting these asymptomatic discharges are difficult and include slowing of the heart rate with beta blockers, changing the lead system, or replacement of the device. One of the six patients was treated with beta blockers. Three patients had their device changed, two patients requested the inactivation of their device until a rate programmable unit was available. The potential for T wave sensing in a lock on gain amplifier represents the unique dilemma between detecting small electrograms of ventricular fibrillation, and detecting diastolic events which occur shortly after the QRS complex.

Adult↗
PubMed1987

Infectious hepatitis in dialysis patients.

Infectious hepatitis is a major problem for patients with end-stage renal disease and for staff caring for these patients. Initially hepatitis B was the major cause of hepatitis in dialysis patients and staff. Patients had a tendency to develop chronic hepatitis or become chronic carriers of the virus while staff either developed typical acute hepatitis or a primary antibody response. The discovery of the hepatitis B surface antigen (HBsAg), the screening of transfused blood for HBsAg, and the institution of infection control measures including isolation techniques have resulted in a remarkable decrease in the incidence of this disease. Nonetheless, the problem of infectious hepatitis continues as non-A, non-B hepatitis has become more commonplace among dialysis patients. Unfortunately, no viral markers have been discovered, and blood products remain the major vehicle of transmission. The institution of infection control measures similar to those used to control hepatitis B has probably been effective in controlling the spread of this disease. It is hoped that the discovery of the etiologic agent(s), with the eventual goal of screening blood products and the development of a vaccine, will lead to full control of this disorder.

Dialysis↗
PubMed1979

Effects of tetracyclines on aldosterone- and insulin-mediated Na+ transport in the toad urinary bladder.

The effect of oxytetracycline and demethylchlortetracycline on aldosterone- and insulin-mediated Na+ transport (short-circuit current) were examined in toad urinary bladders mounted in modified Ussing chambers. Oxytetracycline had little or no effect on either basal or aldosterone-mediated Na+ transport. In contrast, demethylchlortetracycline markedly inhibited both basal and aldosterone-mediated Na+ transport. Furthermore, demethylchlortetracycline inhibited the aldosterone response significantly out of proportion to its effects on basal Na+ transport. Neither of the drugs had an effect on insulin-mediated Na+ transport. Consequently, the natriuresis observed in certain patients treated with demethylchlortetracyline may be related to drug-induced renal resistance to the effects of aldosterone.

Aldosterone↗
PubMed1979

Disposition of intravenous potassium in anuric man: a kinetic analysis.

The disposition of a constant-rate (0.3 mEq/kg/hr) intravenous potassium load was studied in anuric, chronic hemodialysis patients. Changes in plasma potassium concentration could be adequately described by a two-compartment kinetic model under both isohydric conditions and during acute metabolic alkalosis. From 63 to 92% of the infused potassium left the extracellular fluid (ECF) in isohydric studies, and from 73 to 97% left the ECF in alkalanizing studies. Cellular uptake of the infused potassium was less when the plasma potassium concentration was higher. Plasma aldosterone levels rose but insulin levels did not increase during infusions. In a juvenile-onset diabetic subject, the impairment of cellular potassium uptake at higher plasma potassium was magnified so that infused potassium was virtually confined to the ECF compartment until exogenous insulin was given. This implies a permissive rather than a regulatory role for endogenous insulin in facilitating cellular entry of excess potassium.

Anuria↗
PubMed1978

Superiority of demeclocycline over lithium in the treatment of chronic syndrome of inappropriate secretion of antidiuretic hormone.

We evaluated demeclocycline and lithium therapy in 10 patients with the syndrome of inappropriate secretion of antidiuretic hormone. Despite severe water restriction, all patients had hyponatremia (mean +/- S.E.M. serum sodium of 122 +/- 1.1 meq per liter) and elevated urine osmolality (744 +/- 59 mOsm per kilogram) before treatment. Demeclocycline (600 to 1200 mg daily) restored serum sodium concentration to 139 +/- 1.1 meq per liter within five to 14 days, permitting unrestricted water intake in all patients. In three patients given lithium carbonate (900 mg daily) the serum sodium concentration, urine osmolality and urine volume were unchanged; since two patients had adverse central-nervous-system symptoms during lithium therapy, further study of this agent was abandoned. A patient with an unusual 22-year history of the syndrome was unresponsive to lithium, whereas long-term treatment with demeclocyline was markedly effective. Demeclocycline is superior to lithium in the treatment of the syndrome and may obviate the need for severe water restriction.

Adult↗
PubMed1978

Tetracycline-induced inhibition of Na+ transport in the toad urinary bladder.

The effects of three tetracyclines, demethylchlortetracycline (DMC), minocycline (MNC), and oxytetracycline (OTC), on Na+ transport (measured as short-circuit current) were examined in toad urinary bladders mounted in modified Ussing chambers. During a 1-h incubation period serosal DMC (but not MNC or OTC) inhibited basal Na+ transport, whereas MNC (but not DMC or OTC) inhibited ADH-stimulated Na+ transport. MNC also inhibited cyclic AMP-stimulated Na+ transport. During longer incubation periods all three drugs inhibited basal Na+ transport. The DMC-induced inhibition of basal Na+ transport and the MNC-induced inhibition of ADH-stimulated Na+ transport were paralleled by an inhibition of the active conductance of the bladders. Thus, although all three drugs inhibit basal Na+ transport, only MNC inhibits ADH-stimulated Na+ transport. This effect does not correlate with the known effects of the tetracyclines on ADH-stimulated water flow or with drug-protein binding, and may be related to the greater lipid solubility of MNC.

Animals↗
PubMed1977

Insulin-mediated Na+ transport in the toad urinary bladder.

The characteristics of insulin-induced Na+ transport in the toad urinary bladder were determined and compared to those of aldosterone. Bladders were mounted in modified Ussing chambers, and standard short-circuit current techniques were employed to measure transepithelial Na+ transport. Insulin added to the serosal medium is much more effective than insulin added to the mucosal medium. Serosal insulin concentrations from 10(1) to 10(3) muU/ml increase both the initial rate and the final level of Na+ transport achieved, whereas concentrations from 10(3) to 10(5) muU/ml increase only the initial rate of Na+ transport. Insulin-induced Na+ transport probably does not require glucose. Both insulin- and aldosterone-induced Na+ transport are directly proportional to serosal (but not mucosal) K+ concentration over the physiologic range (2.0-7.0 meq/liter). However, cycloheximide abolishes aldosterone- but not insulin-induced Na+ transport. In addition, insulin stimulates Na+ transport after a maximal response to aldosterone, and aldosterone stimulates Na+ transport after a maximal response to insulin. Thus, although they have several similar characteristics, insulin and aldosterone have at least partially independent mechanisms of action on Na+ transport in the toad urinary bladder.

Aldosterone↗
PubMed1977

Guidelines for drug therapy in renal failure.

Five tables are presented that provide guidelines for drug usage in patients with renal insufficiency. The data are derived from the current medical literature. If specific information about a drug is unavailable, emphasis is given to normal pharmacokinetic variables in arriving at recommendations for therapy. Nephrotoxicity of adverse effects in patients with renal disease are noted and adjustments for dialysis suggested.

Acute Kidney Injury↗
PubMed1976

Hysterical polydipsia (compulsive water drinking) in children.

Two patients had entirely different clinical presentations of hysterical polydipsia: convulsions and coma in a 5-year-old boy with intrinsic renal disease and a single kidney, and abnormal behavior in a 3-year-old girl with normal kidneys. In neither case was the correct diagnosis made on initial evaluation. Physiological studies demonstrated primary polydipsia to be responsible for both clinical presentations. The differential diagnosis of polydipsia and polyuria is reviewed, and the nonuniform presentation of hysterical polydipsia is emphasized. In children with intrinsic renal disease, hysterical polydipsia may be life-threatening.

Child, Preschool↗
PubMed1976

Renal failure, hemodialysis, and nafcillin kinetics.

Nafcillin (N) pharmacokinetics was studied in 27 subjectswith and without renal failure (RF) (determined by endogenous creatinine clearance, Ccr). Elimination rate constants (K) were calculated from serial serum levels of N measured from 2 to 12 hr after a single 500-mg intramuscular injection. Only 4 of 9 hemodialysis patients had measurable levels of N at 24 hr. The K values for the groups with normal renal function,moderate RF, severe RF, and on hemodialysis were 0.477 hr(-1), 0.432 hr (1), 0.369 hr(-1), and 0.306 hr (-1), respectively...

Adult↗