Search PubMed⌕ Search

Biomedical subjects

J C Davis

Publications and source records attributed to J C Davis.

At least 109 records · Page 6Linked to original sources
PubMed1984

Dissociation of atrial electrograms by right and left atrial pacing in patients with atrioventricular reciprocating tachycardia.

Seventeen patients had atrioventricular (AV) reciprocating tachycardia incorporating an AV bypass tract as the retrograde limb of the tachycardia circuit. High right atrial pacing during tachycardia dissociated the low septal right atrial electrogram in four of seven patients with a left free wall bypass tract, neither of two patients with a right free wall bypass tract, four of six patients with a posteroseptal bypass tract and both patients with an anteroseptal bypass tract. Pacing from the coronary sinus during tachycardia dissociated the atrial electrogram recorded at the os of the coronary sinus in no patient with a left free wall bypass tract, both patients with a right free wall bypass tract, two patients with a posteroseptal bypass tract and one patient with an anteroseptal bypass tract. These findings suggest two distinct inputs to the AV node, with the left-sided input being part of the tachycardia circuit in patients with a left free wall bypass tract and the right-sided input being part of the tachycardia circuit in patients with a right free wall bypass tract. However, in some patients with a septal bypass tract, neither the right- nor the left-sided atrial input appears to be a necessary link in the tachycardia circuit.

Adult↗
PubMed1984

Clinical features and prognosis of patients with out of hospital cardiac arrest and a normal electrophysiologic study.

Nineteen patients survived a cardiac arrest not associated with an acute myocardial infarction, and had a normal electrophysiologic study with no inducible ventricular tachycardia despite programmed stimulation with one to three extrastimuli at two or more ventricular sites. Among 14 patients who had obstructive coronary artery disease, cardiac arrest occurred during exertion or an episode of angina pectoris in 11; 24 hour ambulatory electrocardiographic recordings demonstrated infrequent or no premature ventricular complexes in 10 and an ischemic response occurred during stage I or II (Bruce protocol) in 6 of 9 patients who underwent exercise testing. Treatment of these patients consisted of myocardial revascularization (eight patients) or antianginal medications (six patients). Only three patients were also treated with an antiarrhythmic drug. Over a follow-up period of 26 +/- 15 months (mean +/- standard deviation), only one patient died suddenly. Two patients who had coronary artery spasm were treated with coronary vasodilator medications and had no recurrence of cardiac arrest over 7 and 36 months of follow-up, respectively. Three patients who had cardiomyopathy or no identifiable structural heart disease were treated with nadolol or amiodarone and had no recurrence of cardiac arrest over 3 to 27 months of follow-up. Among patients who survive a cardiac arrest and have a normal electrophysiologic study, those with obstructive coronary artery disease or coronary artery spasm generally have an excellent prognosis with treatment directed primarily at the underlying heart disease. The clinical features of these patients suggest that cardiac arrest was related to ischemia rather than a primary arrhythmia.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1984

Potential uses of human pancreatic growth hormone-releasing factor 1-44 amide.

A family of growth hormone releasing peptides have been isolated and characterized from human pancreatic islet cell tumours. We have compared the growth hormone release in normal volunteers and patients with various hypothalamo-pituitary disorders, following direct stimulation of the pituitary using 50 micrograms of the most potent homologue, hp GRF 1-44 amide i.v. with that following indirect stimulation using oral clonidine 0.15 mg/m2, which depends on intact hypothalamic mechanisms. These tests both produced a wide variation in GH response in normal volunteers, considerable GH release following hp GRF 1-44 amide but little after clonidine in idiopathic GH deficiency, and indistinguishable, negligible responses in patients with craniopharyngiomas and pituitary tumours associated with GH deficiency. Two untreated acromegalics showed GH increments in the normal range despite elevated basal levels. It is concluded that hp GRF 1-44 amide is of limited diagnostic value by itself, but may be of considerable therapeutic use in patients with idiopathic GH deficiency.

Acromegaly↗
PubMed1984

A prospective comparison of triple extrastimuli and left ventricular stimulation in studies of ventricular tachycardia induction.

One hundred and one patients with sustained unimorphic ventricular tachycardia underwent programmed ventricular stimulation with one of two protocols. Fifty patients underwent programmed stimulation with protocol A, which consisted of burst overdrive pacing, single, double, and triple extrastimuli at the right ventricular apex, right ventricular outflow tract, or septum, and then at the left ventricular apex. Fifty-one patients underwent programmed stimulation with protocol B, which consisted of burst overdrive pacing, single and double extrastimuli at the right ventricular apex, right ventricular outflow tract or septum, and at the left ventricular apex, followed by triple extrastimuli at these sites. The stimulation protocol was continued until sustained ventricular tachycardia or rapid, polymorphic ventricular tachycardia greater than 10 sec in duration was induced. With protocol A, clinical and nonclinical ventricular tachycardia was induced in 76% and 36% of patients, respectively; with protocol B, clinical and nonclinical ventricular tachycardia was induced in 85% and 38% of patients, respectively. Direct-current countershock for sustained polymorphic ventricular tachycardia was required in 10% of patients studied under protocol A, compared with in 2% of patients studied under protocol B. With protocol A, near-maximal yield of induced clinical (72%) and nonclinical ventricular tachycardia (30%) was attained after the use of triple extrastimuli at the first stimulation site. The yield of stimulation at a second right ventricular site and of left ventricular stimulation was only an additional 2% each. With protocol B, triple extrastimuli increased the yield of induced clinical ventricular tachycardia from 61% to 85%.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1984

Existential issues in the management of the demented elderly patient.

Four major existential themes are explored, as they relate to the predicament of the relative supporting a demented elderly dependent at home. These issues, namely, death, isolation, freedom, and meaning are discussed with respect to their dynamic impact on the stressed supporter as well as their implications for anxiety management.

Aged↗
PubMed1984

Factitious decompression sickness.

The diagnosis of decompression sickness is made largely by history; there are few physical findings and no radiographic or laboratory tests to support the diagnosis. We present three cases of factitious decompression sickness in which patients fabricated an appropriate history and underwent compression therapy. Due to the potential severity of decompression sickness and the relative safety of compression therapy, the initiation of therapy must not be delayed in a case of decompression sickness. Once therapy is begun, investigation into the particulars of a suspicious case can be made.

Adult↗
PubMed1983

Desmethylimipramine and imipramine on left ventricular function and the ECG: a randomized crossover design.

Sixteen severely depressed patients participated in a double-blind randomized, crossover study to compare the effects of desmethylimipramine and imipramine on left ventricular function and the electrocardiogram. Following a drug-free week, patients had 3 weeks of therapy each with desmethylimipramine and imipramine. During each treatment period systolic time intervals, echocardiograms and high-fidelity electrocardiograms were recorded. There was no difference between desmethylimipramine and imipramine on (1) systolic time intervals, (2) shortening fraction or mean velocity of circumferential shortening, or (3) the electrocardiogram. There was a difference between the drug-free period and desmethylimipramine or imipramine on the PEPc (P less than 0.05) and the PEP/LVET ratio (P less than 0.05); on the R-R (P less than 0.05), PR (P less than 0.05), QRS (P less than 0.05), and QTc (P less than 0.05) intervals; but no difference on the LVETc or shortening fraction or the mean velocity of circumferential shortening. Drugs such as desmethylimipramine and imipramine which prolong intraventricular conduction can probably be expected to prolong the PEP and PEP/LVET. For this reason systolic time intervals have limitations in assessing myocardial function and the echocardiogram more reliably estimates myocardial performance in patients receiving tricyclic antidepressants.

Adult↗
PubMed1983

Plasma progesterone levels as an index of ovulation.

Plasma progesterone levels were measured in three groups of untreated women. (1) Nine women with follicle rupture, proved by laparotomy or laparoscopy, had values of greater than or equal to 40 nmol/l on days 18-24 (days-10- -5 from the next period); thus a value of less than 40 nmol/l should not be taken as evidence of ovulation. (2) Nineteen healthy women with normal menstrual histories had hormone assays on alternate days during one cycle. In five of them all values were less than 38 nmol/l. (3) Forty women had a single progesterone assay on days 20-29 of a conceptual cycle. Eight of them had a level less than 40 nmol/l. Ovulation had certainly occurred in all of them, but it is difficult to assess whether the sample timing was optimal since there was no following menstrual period. Progesterone levels in drug-induced conceptual cycles were in general higher than those in spontaneous pregnancy cycles. Women with luteinization of the unruptured follicle frequently had values of greater than 40 nmol/l. Conversely, a secretory endometrium was not uncommon in cycles with values of less than 38 nmol/l.

Adult↗
PubMed1982

Electrophysiologic effects of procainamide on sinus function in patients with and without sinus node disease.

To compare the effects of procainamide on sinus node (SN) function in the presence (seven patients) and absence (nine patients) of SN dysfunction, sinus cycle length (SCL), maximal corrected sinus recovery time (maximal CRST), paced cycle length yielding peak SN suppression (PCLp), and indirect sinoatrial conduction time (SACT) were determined before and after intravenous administration of 10 to 15 mg/kg procainamide in each patient. Plasma procainamide concentration was in the therapeutic range in all patients. The mean SCL did not change significantly in either group (-24 +/- 58 and -73 +/- 171 msec for patients with normal and abnormal SN function, respectively). The maximal CSRT shortened 136 +/- 112 msec (p less than 0.01) in the group with normal SN function (nine of nine patients)( but tended to lengthen 85 +/- 95 msec (p less than 0.10) in the group with SN dysfunction (six of seven patients). PCLp shortened in only two of nine of the normal group but tended (NS) to shorten in five of seven patients with SN dysfunction. We conclude that in the absence of SN disease, procainamide does not adversely affect SN function. In apparent contrast in patients with SN dysfunction, procainamide tended (NS) to prolong CSRT and seemed (NS) to enhance conduction in the sinoatrial junction (PCLp and SACT both declined). The occasional lengthening of CSRT implies that procainamide might prolong post-tachycardia pauses and thus could worsen symptoms in certain patients with the bradycardia-tachycardia syndrome.

Adult↗
PubMed1982

Evidence for a spin-coupled binuclear iron unit at the active site of the purple acid phosphatase from beef spleen.

The purple acid phosphatase from beef spleen, which contains two iron atoms per molecule, is EPR silent in its native (oxidized) purple form. Treatment with mild reducing agents results in conversion to a pink, enzymatically active form, which exhibits an unusual EPR signal centered at g approximately equal to 1.77; double integration of the EPR spectrum gives one spin per two iron atoms. A similar EPR spectrum is observed for enzyme reduced anaerobically by one electron, using sodium dithionite. Variable-temperature magnetic susceptibility measurements show that the oxidized and reduced proteins are both antiferromagnetically coupled systems, with S = 0 and 1/2 ground states, respectively. Replacement of one of the iron atoms by zinc produces an FeZn enzyme with full catalytic activity. The FeZn enzyme exhibits a highly temperature dependent g = 4.3 EPR signal, and magnetic susceptibility data are consistent with an S = 5/2 paramagnet. Treatment of the FeZn enzyme with phosphate, a competitive inhibitor, results in sharpening of the EPR spectrum; double integration at 77 K gives one spin per iron. These results strongly suggest the presence of a spin-coupled bimetallic unit at the active site of the enzyme.

Acid Phosphatase↗
PubMed1982

Entomophthorales infection of the maxillofacial region.

Phycomycosis infections caused by the fungi Rhizopus and Mucor are commonly termed mucormycosis. Mucormycosis infections exhibit a rapidly progressive course characterized by angioinvasion and necrosis. The rhinocerebral form has been described thoroughly in the literature. However, there exists another order of Phycomycetes, the Entomophthorales, which rarely cause clinical disease. Their infection is indolent and is associated with granulomatous inflammation and a protracted clinical course. Presented here is a rare case of suspected Canidiobolus coronato infection occurring in the maxillofacial region of a previously healthy male. The authors believe this to be the first reported case occurring in the United States. Because of the poorly documented natural history of this infection and the patient's relative intolerance to parenteral antifungal therapy, a multidisciplinary therapeutic approach was designed. It consisted of long-term, low-dosage amphotericin-B, hyperbaric oxygen and sequential surgical debridements. This unusual disease entity must now be considered in the differential diagnosis of granulomatous disorders of the head and neck.

Amphotericin B↗
PubMed1981

Kinetics and optical spectroscopic studies on the purple acid phosphatase from beef spleen.

A new purification scheme has been developed for the purple acid phosphatase from beef spleen; typical yields are 8 mg of homogeneous enzyme per kg of spleen in only five steps. Kinetics studies have shown that the enzyme is strongly inhibited by fluoride, phosphate, and [p-(acetylamino)-benzyl]phosphonate, a nonhydrolyzable substrate analogue; the last two of these show simple competitive inhibition. In contrast, cyanide, azide, tartrate, and p-nitrophenol show no inhibition at concentrations up to 10 mM. Molecular weight estimations by gel electrophoresis and gel permeation chromatography give a value of 40 000 for the native enzyme, which is shown to consist of two subunits of apparent molecular weight 24 000 and 15 000. Careful metal analyses indicate the presence of 2.1 +/- 0.1 iron atoms per enzyme molecule, and less than 0.1 copper, zinc, nickel, or manganese atom per enzyme. The purple enzyme (lambda max 550 nm) is reversibly converted to a pink, active form (lambda max 505 nm) upon treatment with mild reducing agents (dithioerythritol or ascorbate). Addition of competitive inhibitors to the pink form causes rapid reversion to the purple form. Electron paramagnetic resonance spectroscopy at several temperatures showed only weak g = 4.3 signals (less than 0.1 spin/molecule) for the native, reduced, and inhibited forms of the enzyme.

Acid Phosphatase↗
PubMed1981

Isolation from bovine spleen of a green heme protein with properties of myeloperoxidase.

A novel green heme protein from bovine spleen has been purified to apparent homogeneity. The visible spectrum, with unusually long wavelength absorptions due to alpha-, beta-, and gamma-porphyrin bands, the EPR g values of 6.81, 4.99, and 1.94, and the peroxidase activity are similar to those of myeloperoxidase (EC 1.11.1.7). The observed molecular mass of 57,000 daltons (established by gel permeation chromatography and sodium dodecyl sulfate-polyacrylamide gel electrophoresis studies) clearly distinguishes it from myeloperoxidase, as does the observed substrate specificity (e.g. oxidation of iodide but not ascorbate). Optical spectra of ferric and ferrous forms of the enzyme in the native state, complexed with ligands (CN-, CO, NO, N3-) and as the pyridine hemochromogens, are presented and compared to those of the corresponding derivatives of myeloperoxidase.

Animals↗
PubMed1981

Sinus node dysfunction caused by methyldopa and digoxin.

Symptomatic sinus bradycardia developed in two patients while they were taking methyldopa and digoxin. In one patient, bradycardia did not occur with either digoxin or methyldopa alone. The other patient, who had never taken methyldopa alone, did not demonstrate bradycardia with digoxin alone. In each patient, normal sinus node function was demonstrated after methyldopa and digoxin therapy was discontinued. Both patients continued to receive digoxin without recurrence of bradycardia.

Aged↗