Biomedical subjects
Publications and source records attributed to G Johnsson.
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Explore the source record for details and available documents.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
The pharmacokinetics of metoprolol and propranolol in 6 healthy volunteers were compared after an intravenous dose of 10 mg of each drug. The mean t1/2, beta was 3.6 hr for both drugs, but due to a larger volume of distribution, the total body clearance was significantly higher for metoprolol (1.20 liters/min) than for propranolol (0.81 liters/min). The individual pharmacokinetic data were used to calculate the doses required to increase the amount of each drug in the body to 10 and 20 mg at 90 and 180 min respectively after an initial intravenous dose of 5.0 mg. The effect on exercise heart rate was determined 30 min after each dose. After identical doses, the two drugs had similar beta-blocking effects in terms of reducing exercise-induced tachycardia. These effects increased with the dose administered. The plasma levels of propranolol were twice as high as those of metoprolol for identical degrees of beta-blockade. The slope of the regression line for the relationship between the beta-blocking effect and log plasma concentrations was the same for the two drugs.
We studied the hemodynamic effects of the selective beta 1-adrenoceptor agonist prenalterol in healthy subjects before and after intravenous infusion of the nonselective beta-adrenoceptor blocker propranolol or the beta 1-selective adrenoceptor blocker metoprolol. Intravenous infusions of 0.1, 0.25, and 0.5 mg prenalterol induced a dose-dependent decrease in total electromechanical systole and pre-injection period, whereas left ventricular ejection time remained unchanged. Stoke volume as determined by impedance cardiography was not changed, but a dose-dependent increase in cardiac output due to an increase in heart rate was observed. Systolic blood pressure was significantly increased, but diastolic blood pressure remained unchanged. After intravenous administration of either 10 mg propranolol or 20 mg metoprolol, prenalterol was infused in a 10 times higher dose than before. The hemodynamic effects were similar to those observed before the beta-blockers. Whether propranolol or metoprolol was administered did not influence the effects induced by prenalterol. It is suggested that prenalterol might be a useful drug to counteract undesired hemodynamic effects of beta-adrenoceptor blockers.
The pharmacokinetics of metoprolol have been studied in a group of patients with varying degrees of renal impairment and in healthy subjects after administration of 20 mg of metoprolol tartrate intravenously and 50 mg orally in a single dose and during steady-state conditions. There were no significant differences in the extent of bioavailability or rate of elimination of the drug between the 2 groups. The fraction of the oral dose systemically available during steady-state was 59 +/- 9% in the renal patients and 55 +/- 7% in the control group. Total body clearance in the patients with renal failure was 1.0 +/- 0.1 L/min and in the healthy subjects it was 0.8 +/- 0.1 L/min. The corresponding values for the elimination half-life were 4.6 +/- 1.2h and 4.1 +/- 1.0h, respectively. The beta-adrenoceptor blocking effect of metoprolol (determined as percent reduction of exercise heart rate) did not differ significantly between the 2 groups during steady-state conditions. The effect on exercise heart rate was linearly related to the log of the plasma concentration of metoprolol. The relationship was identical for the single dose and during steady-state conditions, indicating that accumulation of metabolites in patients with renal failure does not influence the beta-blocking properties of metoprolol.
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This paper describes the implementation of a multiplying digital-to-analogue (D/A) converter as a programmable waveform generator to be used in an electrical impedance tomography (EIT) system. Different digital techniques of generation waveforms are considered and the advantages and disadvantages of the chosen slope-plus-pedestal technique are presented. A wire-wrapped prototype system has been designed, and from measured frequency spectra the total harmonic distortion can be calculated to values between 1.1 and 2.9% depending on frequency.