Studies were performed on the dog heart in situ to determine the effects of diphenylhydantoin (DPH) on excitability and automaticity. DPH decreased automaticity in the His-Purkinje system, evidenced by an increase in the ventricular escape time both during vagal stimulation in intact dogs and after ventricular overdrive in dogs with heart block. The spontaneous ventricular rate of dogs with heart block was unaffected by doses up to 20 mg/kg. DPH had no significant effect on either atrial or ventricular diastolic threshold when this variable was tested with bipolar stimuli or with stigmatic anodal or cathodal stimuli. The effective refractory period of atrial and particularly of ventricular muscle was shortened by DPH (10 mg/kg); a leftward shift in the strength-interval curve occurred consistently. Multiple response threshold and fibrillation thresholds were elevated by DPH in both the ventricle and atrium (20 of 24 experiments). In anesthetized dogs, intraventricular conduction velocity increased minimally after DPH administration. DPH increased transmembrane threshold voltage and reduced the current required to stimulate isolated Purkinje fibers. The commercial solvent used clinically as a diluent for DPH was found to increase diastolic threshold and prolong the effective refractory period.
1. These studies demonstrate that ventricular fibrillation can be produced in anesthetized, mechanically ventilated dogs by a current as low as 35 microamperes and a voltage as low as 0.06 volt.
2. Analysis of circuits of medical electronic equipment which is usually considered safe indicates that such low current levels may exist in the heart during catheterization.
3. The safety procedures established for our laboratory to minimize the hazard of electric shock are presented.
The role of the Na-K pump in the control of cellular ion balance has long been appreciated. Recent studies suggest that the manner in which this ion transport system functions in hypertrophied failing (HF) cardiac muscle is markedly different from that seen in normal muscles. The ability of the sympathetic neurohormone, epinephrine, to modulate membrane potential changes thought to reflect the activity of the Na-K pump in normal and HF cardiac muscle was examined in this study. Specifically rate-related changes in membrane potential (Emax) thought to be associated with the Na-K pump were measured in intact functioning cat papillary muscles. The results of these studies demonstrate that the rate-related changes in Emax thought to be associated with Na-K activity were markedly altered in HF cardiac muscles. Emax in these muscles responded to periods of transient stimulation by first depolarizing and then slowly returning to a new steady state which was depolarized with respect to the initial predrive Emax. Emax in normal muscles also depolarized on drive, but returned to a new steady state more rapidly and eventually hyperpolarized. Epinephrine significantly affected these rate-related changes in Emax in normal muscles by causing all the rates of change in Emax to be increased. In HF muscles, on the other hand, epinephrine had no significant effect on these parameters at the concentration tested. These results suggest that under certain conditions HF cardiac muscle may be incapable of maintaining normal resting membrane potentials. In addition the modulating influence of epinephrine is markedly blunted.
(Am J Obstet Gynecol. 2018;218:616.e1–e8)
Hypertensive disorders of pregnancy contribute to maternal morbidity and mortality. Women with hypertension are at increased risk for cesarean delivery. The American College of Obstetricians and Gynecologists suggests avoiding the use of nonsteroidal antiinflammatory drugs (NSAIDS) in women with preeclampsia as they have been shown to increase blood pressure in nonpregnant adults. The purpose of this study was to evaluate the effect of ibuprofen compared with acetminophen on blood pressure control in the postpartum period in women diagnosed with preeclampsia with severe features. They hypothesized that NSAIDs would adversely affect postpartum blood pressure control in women with preeclampsia with severe features.
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