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Biomedical subjects

R B Smith

Publications and source records attributed to R B Smith.

At least 289 records · Page 16Linked to original sources
PubMed1982

Ventilation at high respiratory frequencies. High frequency positive pressure ventilation, high frequency jet ventilation and high frequency oscillation.

This paper reviews the development of different methods of ventilation at respiratory rates higher than 60 per minute (1 Hz) along with data on experimental and clinical uses of the techniques. The definitions and terms that have been used for these high rates at the present time are confusing. An attempt to clarify the terms has been made. Whereas high frequency positive pressure ventilation (HFPPV) refers to respiratory rates between 60-110 per minute (1-1.8 Hz), high frequency jet ventilation (HFJV) usually refers to rates between 110-400 per minute (1.8-6.7 Hz) and high frequency oscillation (HFO) refers to rates above 400 and up to 2400 per minute (40 Hz). It should be recognised that this differentiation in terminology is rather arbitrary and does not necessarily represent a sudden switch to different physiological methods of ventilation. In view of the various techniques which are involved in ventilation methods utilising rates greater than 60 per minute (1 Hz), it is the purpose of the present work to review the literature. In so doing, the contrasting rates, mechanical equipment, and experimental and clinical uses of these different methods will be discussed in order to clarify their potential contribution to clinical medicine.

Animals↗
PubMed1982

Plasma and cerebrospinal fluid pharmacokinetics of acivicin in Ommaya reservoir-bearing rhesus monkeys.

Acivicin was administered iv to rhesus monkeys bearing Ommaya reservoirs, and serial blood and cerebrospinal fluid (CSF) samples were collected and analyzed to determine the time course of drug concentrations in these body fluids. After iv doses of 4 or 20 mg/kg (50 or 250 mg/m2), acivicin plasma concentrations demonstrated a rapid initial decline (distribution phase), and then declined exponentially with a terminal (elimination phase) half-life of 3--4 hrs. CSF concentrations increased over a period of 2--2.5 hrs, reaching peak values of 2.0--2.7 micrograms/ml at 20 mg/kg and 0.3--0.5 microgram/ml at 4 mg/kg; thereafter, CSF levels declined in parallel with plasma, with a CSF/plasma concentration ratio of 0.10--0.17. A three-compartment pharmacokinetic model gave a close fit of predicted and observed plasma and CSF concentration data. Significant and predictable CSF penetration by iv administered acivicin in monkeys is consistent with observation of CNS side effects in patients in the phase I clinical trial and suggests that acivicin should be evaluated in the treatment of CNS malignancies and metastases.

Animals↗
PubMed1981

Self-heard venous hums.

We describe two patients with symptomatic, self-heard venous hums. The venous hum was secondary to chronic anemia in one patient and was idiopathic in the other. The idiopathic hum was not heard in the neck but could be heard by auscultating the right auditory canal. Ligation of the right internal jugular vein abolished the idiopathic hum, which had been present for 14 years.

Adolescent↗
PubMed1981

Twenty-four-hour pH monitoring of esophageal function. Its use in evaluation in symptomatic patients after truncal vagotomy and gastric resection or drainage.

The incidence and character of gastrointestinal reflux after truncal vagotomy and gastric resection or drainage were studied prospectively in 42 symptomatic patients. Gastroesophageal reflux, proven by 24-hour pH monitoring, occurred in 31 patients. Initial symptoms of heartburn, regurgitation, or dysphagia were similar in patients with and without reflux. Eighteen patients had pure acid, nine had acid-alkaline, and four had pure alkaline reflux. Reflux occurred predominantly in the supine position. Esophagitis occurred only in patients with reflux and was not dependent on the pH of refluxed material. Reflux was eventually controlled by antireflux repair in 19 and by colon interposition in three patients. Twenty-four-hour esophageal pH monitoring is beneficial in evaluating symptoms after gastric surgery. It quantifies both acid and alkaline reflux, provides an objective assessment of the patient's subjective complaints, and gives a rational basis for management.

Drainage↗
PubMed1981

Lincomycin serum and saliva concentrations after intramuscular injection of high doses.

Serum and saliva levels of lincomycin were determined in 15 normal adult male volunteers after a single intramuscular injection of 600, 1000, or 1500 mg lincomycin in a three-way crossover study. The area under the serum concentration-time curve did not increase in proportion to the increase in dose. The increase in concentration of lincomycin in saliva was greater than expected for the increase in dose. There were not significant differences in elimination half-life between doses. These results suggest that the apparent clearance of lincomycin increases with increasing dose possibly because of a decrease in serum protein binding of lincomycin at high serum concentrations.

Adult↗
PubMed1981

First-pass metabolism of ethinyl estradiol in dogs and rats.

The contraceptive steroid ethinyl estradiol was extensively metabolized when given orally in solution to dogs. It was thought at first that metabolism occurred exclusively in the liver. However, use of standard equations to predict the oral bioavailability of drugs known to be metabolized by hepatic first pass resulted in significantly higher values than those obtained experimentally. To rationalize the data and to determine whether ethinyl estradiol also is metabolized in the gut wall during absorption, metabolism in rats was studied. The drug was administered in solution intraduodenally, intraportally, and intravenously as a bolus by first-order infusion. The results indicate that, in rats, 40% of the drug is metabolized by the gut wall and 79% of the drug in the portal blood is metabolized by the liver intraduodenal administration.

Animals↗
PubMed1981

Effect of vagotomy on exocrine pancreatic and biliary secretion in man.

The exocrine pancreatic and biliary secretion in response to vagal stimulation by insulin hypoglycemia was measured in preoperative patients with duodenal ulcer and in patients who underwent highly selective vagotomy, bilateral selective vagotomy with pyloroplasty, and truncal vagotomy with pyloroplasty. Significant stimulation of both biliary and pancreatic secretion occurred only in patients with an intact vagal nerve supply. No evidence of increased lithogenicity of human bile was found up to 2 years after truncal vagotomy.

Adult↗
PubMed1981

Synthesis of ubiquinone 9 by adult Brugia pahangi and Dirofilaria immitis: evidence against its involvement in the oxidation of 5-methyltetrahydrofolate.

Among various ubiquinone (Q) isoprenologues tested, only Q7 was more efficient than menadione in promoting the oxidation of 5-methyltetrahydrofolate (CH3FH4) by 5,10-methylenetetrahydrofolate reductase isolated from adult Brugia pahangi, whereas Q10 was the best cofactor in the same reaction catalysed by the analogous enzyme from adult Dirofilaria immitis. Menoctone (3-[1-cyclohexyloctyl] -2-hydroxy-1,4-naphthoquinone) was a strong competitive inhibitor of both these ubiquinone isoprenologues in the respective reactions. When incubated in the presence of D,L-[14C]-mevalonate, adult B. pahangi and D. immitis synthesized radiolabelled Q9 only, in addition to other isoprenoid derivatives in the neutral lipid fraction. In view of the inability of Q9 to promote the oxidation of CH3FH4 by 5,10-methylenetetrahydrofolate reductase from B. pahangi, it seems unlikely that this filaria uses Q9 as a cofactor in this reaction. Conceivably, D. immitis could use Q9 as a cofactor in its enzymatic oxidation of CH3FH4, since in this circumstance, it was a better cofactor than menadione.

Brugia↗
PubMed1981

Phenytoin-dexamethasone interaction: a previously unreported observation.

A possible drug interaction between phenytoin and dexamethasone was evaluated by comparing serum phenytoin concentrations in 23 patients receiving both drugs with those of a control group of 15 patients receiving phenytoin only. Serum phenytoin concentrations obtained 24 hours after a loading dose of 11 mg per kilogram body weight administered intravenously and 13 mg/kg given intramuscularly were examined. The total amounts of dexamethasone administered during the 24-hour period ranged from 16 to 150 mg. The average serum phenytoin concentration was 17.28 +/- 3.49 micrograms/ml in patients receiving both drugs, as compared to 12.48 +/- 3.52 micrograms/ml in patients receiving only phenytoin (p less than 0.001). Our results suggest that serum phenytoin concentrations should be monitored in patients receiving concurrent dexamethasone therapy.

Adult↗
PubMed1981

Intraocular and intracranial pressure during respiratory alkalosis and acidosis.

Intraocular and intracranial pressures (IOP and ICP) were measured at four different arterial carbon dioxide tensions by direct continuous techniques in Rhesus monkeys during anaesthesia with halothane and nitrous oxide. Increases in IOP correlated significantly with PaCO2 ranging from 2.66 to 10.24kPa (P less than 0.001). Increases in ICP correlated significantly (P less than 0.001) with PaCO2 between 2.66 and 7.71 kPa, but plateaued thereafter. When PaCO2 was decreased rapidly, PaCO2, IOP and ICP decreased exponentially with similar half-times. The fast changes in IOP and ICP can probably be explained by an alteration of intraocular and intracranial blood volumes. IOP usually remained within the normal range, even at maximum PaCO2.

Acidosis, Respiratory↗
PubMed1981

Long-term transtracheal high frequency ventilation in dogs.

Long-term effects of high frequency percutaneous transtracheal ventilation (HFTV) have not been studied. The purpose of this study is to evaluate the cardiopulmonary effects of 24 h transtracheal ventilation in dogs at a respiratory rate of 100/min. Four dogs were anesthetized with intermittent pentobarbital and paralyzed with pancuronium. Ventilation in the supine position was through a 14-gauge Angiocath introduced into the trachea through the cricothyroid membrane. A respiratory rate of 100/min was used at an FIO2 of 0.4 using a fluidic logic controlled ventilator. The inspiratory-expiratory ratio was 1:2 and tidal volume 70 ml. The driving pressure of the air-oxygen mixture was 50 psi. After 24 h, residual muscle relaxant was reversed and the animal allowed to recover. There was no significant change in the following parameters over 24 h compared to starting values: PaO2, PaCO2, pH, aortic, central venous, pulmonary artery and pulmonary artery wedge pressures, heart rate, cardiac index (CI), stroke index (SI), left ventricular stroke work (LVSW), systemic vascular resistance (SVR), pulmonary vascular resistance (PVR), C(a-V)O2, oxygen consumption (VO2), pulmonary shunt (Qs/Qt). A PEEP effect of 2.9 - 5.0 torr was maintained. All dogs recovered uneventfully. Three days after the experiment, blood gases of 2 dogs were normal. One dog was killed after 3 days; macroscopic and microscopic examinations of the upper and lower airway and pulmonary parenchyma were normal. Dogs can be ventilated for as long as 24 h using HFTV transtracheally at rates of 100/min without adverse cardiopulmonary effects.

Animals↗