Biomedical subjects
Publications and source records attributed to M Stafford.
Domestic pigeons were introduced into the Galapagos Islands in 1972 or 1973. There is a high prevalence of Trichomonas gallinae among them and some evidence of canker. Trichomonas gallinae can be found also in endemic Galapagos doves in the vicinity of Puerto Ayora on Santa Cruz Island. Doves examined on pigeon-free islands were not found infected.
In summary, the present examples illustrate how pacemaker malfunction can be simulated by the sources of artifact produced or detected by the monitoring equipment. This form of pseudopacemaker malfunction remains a common cause of mistaken diagnosis of pacemaker malfunction. A thorough understanding of the examples outlined above should help distinguish true pacemaker malfunction from pseudopacemaker malfunction produced by artifact.
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In summary, the application of principles of rehabilitation to athletic injury includes efforts directed at reducing swelling and pain while maintaining the range of motion. As the range of motion increases, efforts are made to regain strength while the patient is protected from reinjury and from the stresses of returning to function.
Twenty-four patients were allocated randomly into four groups for the study of the pharmacokinetics of, and effects on postoperative ventilation of, two doses of fentanyl (10 micrograms/kg or 25 micrograms/kg) administered at the start of general anesthesia in which ventilation was controlled at a fixed volume, but arterial PCO2 was adjusted to a range of either 38-42 torr, or 20-25 torr. During the first 2 hr after anesthesia, ventilatory depression (CO2 responsiveness decreased to less than 50% of awake values, PaCO2 greater than 48 torr) occurred only in patients who had received 25 micrograms/kg fentanyl, and was more marked in patients who were hyperventilated to a low PaCO2 during anesthesia. Plasma fentanyl concentrations associated with 50% depression of CO2 responsiveness were in the range 1.5-3.0 ng/ml, the lower values found in patients hyperventilated to a low PaCO2. Whole-body clearance of fentanyl was significantly decreased by hypocapnic hyperventilation.
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Transcutaneous PCO2 electrodes habe been constructed and evaluated on adults and children. Glass pH and silver reference electrodes were used at 44--45 degrees C, with either circulating water and a copper jacket, or with internal electrical heating. The skin surface PCO2 at 44 degrees C is about 1.33 times PaCO2 plus 3 mmHg when measured with electrodes calibrated in gas at 44 degrees C. Three temperature effects combine in this ratio: Heating raises blood PCO2 4.5%/degrees C, skin metabolism adds about 3 mmHg, and the cooling of the electrode active surface by skin increases electrode reading. Response time to step changes of PaCO2 was about 3 min to 63%, of which 1.2 min was sensor delay, the remainder skin CO2 washout. It was found important to use ethylene glycol-water mixtures rather than water for electrolyte to avoid bubble generation and drift. Heat transfer through the pH glass electrode has been increased by enlarging the internal silver electrode to virtually fill the entire glass electrode. Time required for initial vasodilation and stabilization is similar to that of tcPO2 electrodes, and accuracy of determination of PaCO2 appears to be better than +/- mmHg.
Seven subjects who underwent jejunoileal bypass surgery for massive obesity participated in a study to examine the relative bioavailability of digoxin before and one to two months after surgery. They were given a loading dose of 1 mg digoxin in divided oral doses followed by oral maintenance doses of 0.5 mg daily. There were no significant differences in the area under the serum concentration time curve, steady state serum levels or 24 hour steady state excretion of digoxin before and after surgery. We conclude that the bioavailability of digoxin from the Lanoxin tablets employed is not impaired in these patients, although urinary d-xylose and 24 hour fecal fat excretion indicated moderate to severe malabsorption after surgery.
A method for the analysis of volatile metabolites present in plasma, urine, breast milk and amniotic fluid collected from mother-infant pairs has been developed which requires only 100 mul of plasma, 3 ml of urine, 20 mul of breast milk and 500 mul of amniotic fluid. After extraction with diethyl ether, the volatile compounds were absorbed on glass wool in a special concentration tube and subsequently desorbed and transferred to a 100-m nickel capillary column for analysis by gas chromatography and gas chromatography-mass spectrometry. The separations, carried out by temperature programming, were complete in 90 min.
A strong correlation was found in a carefully selected homogenous population (n = 57) between antipyrine plasma half-life and the percent induction of aryl hydrocarbon hydroxylase by 3-methylcholanthrene in mitogen-stimulated lymphocytes from the same individual. The correlation coefficient of r = 0.923 indicates that antipyrine and benzo[a]pyrene share one or several common determinants that are responsible for the observed interindividual variation in the oxidation rates of the two compounds. When a heterogenous population (n = 80) was studied, the above correlation was not found (r = 0.425).
The bioavailability of digoxin (lanoxin) tablets, oral aqueous solution of digoxin, and capsules containing a solution of digoxin was compared with digoxin given intravenously over 1 and 3 hr. The mean peak serum concentration of digoxin after the 1-hr intravenous infusion was 5 ng/ml, after the 3-hr infusion, 3.5 ng/ml, and after the oral solution, 2.0 ng/ml. There was an equivalent bioavailability of the oral solution and reference tablets of digoxin. The digoxin in capsules tended to be better absorbed than the reference tablets. There was 21% more digoxin excreted over 6 days after the 3 hr iv infusion than after the 1 hr iv infusion. This indicates that the calculated bioavailability of an orally administered dose of digoxin may vary with the rapidity of injection of the intravenous standard. It is estimated that an oral tablet of digoxin of 0.5 mg has about the same bioavailability as 0.35 of digoxin given by slow intravenous infusion (or 0.4 mg if calculated against a rapid intravenous injection).
Pharmacokinetic studies involving plasma, urine, breast milk, saliva and liver homogenates have been carried out by selective ion detection with a gas chromatographic-mass spectrometric-computer system operated in the chemical ionization mode. Stable isotope labeled drugs were used as internal standards for quantification. The half-lives, the concentration at zero time, the slope (regression coefficient), the maximum velocity of the reaction and the apparent Michaelis constant of the reaction were determined by regression analysis, and also by graphic means.
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