Biomedical subjects
Publications and source records attributed to R S Reneman.
This paper describes a catheter-tip micromanometer for chronic left ventricular pressure measurements which can be calibrated in the animal after implantation. The calibration curves are linear, both in vitro and in vivo. Good zero-stability is reached after 1 week of implantation. The duration of function of the device is 3 to 6 months.
In this study the pressure wave velocity in the anterior descending branch of the left coronary artery (LADC) of the dog was measured by determining the delay time between pressure pulses along this artery. This method can only be applied if reflections of the pressure wave distal to the sites of pressure measurement are insignificant. From araldite casts of the coronary arteries the following relation between the diameter proximal to (dprox) and distal to (ddist 1, ddist 2) a bifurcation was found: dprox2.55 = ddist12.55 + ddist 22.55, indicating that reflections at a bifurcation areminimal. In dogs reflections were studied by inducing during diastole a pressure pulse in the aorta and measuring pressure and volume flow proximal to and pressure distal to a segment of the LADC at various levels of the coronary peripheral resistance. Reflection of high-frequency components (greater than 7 Hz) was found to be insignificant, allowing application of the above-mentioned method for measuring the wave-front velocity, which is insensitive to low-frequency reflection. At a pressure in the LADC of 13.3 kPa this velocity was 8.6 +/- 1.4 m.s-1 (mean +/- SD). The calculated dynamic cross-sectional stiffness (deltaP/(deltaA/A)) of the LADC was 97 +/- 11 kPa (mean +/- SE) at an arterial pressure of 13.3 kPa.
This review summarizes the principle, advantages, and limitations of Doppler ultrasound flowmeters, and discusses the possibilities of applying these systems in evaluating the functional state of the peripheral arterial circulation. This discussion is not limited to the assessment of blood flow velocity and poststenotic arterial pressure with Doppler flowmeters, but includes among other things the recordings of flow patterns, the determination of the transit time of velocity wave forms, and the imaging of the arterial circulation.
The present study was conducted so as to obtain more insight into the controversies concerning the alpha-adrenoceptor blocking properties of droperidol, a short-acting neuroleptic agent used in neuroleptanalgesia. The effect of droperidol on the vasoconstriction induced by norepinephrine, sympathetic nerve stimulation, histamine and potassium ions was studied on isolated, perfused ear arteries; its effect on norepinephrine-induced contraction was studied on isolated aorta, spleen and vas deferens. In addition, the onset and duration of action of droperidol was studied. Low doses of droperidol inhibit the vasoconstriction induced by norepinephrine and sympathetic nerve stimulation in the ear artery of the rabbit (3.3 X 10(-9) M and 1.3 X 10(-8) M respectively). At similar low doses, droperidol inhibits norepinephrine-induced contractions in the other tissues studied and has a potency comparable to that of phentolamine; its action is rapid in onset and of short duration. High doses of droperidol (10(-6) M) also inhibit the vasoconstriction of the ear artery induced by histamine and by potassium ions. These findings indicate that a low doses, droperidol has specific and competitive alpha-adrenoceptor blocking effects.
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A series of experiments, carried out to evaluate the histochemical method for the morphological diagnosis of early stages of myocardial ischaemis (HBFP) is reported. The experiments were performed on dog hearts in which ischaemia was induced by coronary artery ligation for different periods of time. The original procedure or modifications of the HBFP-technique, including different staining, rinsing, and differentiation times, the use of different commercial brands of chemicals and preparatory changes of routine histological procedures such as fixation, embedding, cutting, and mounting, did not give satisfactory results. False positive and negative staining was frequent. Very equivocal results were obtained on serial sections of ischaemic tissue samples. Therefore this method was regarded as unreliable and non-reproducible.
In the present study, several techniques for calculating cardiac output were evaluated in order to find an accurate technique suitable for on-line digital computation. The thermodilution method was evaluated by different calculation techniques and by comparing these techniques with electromagnetic flowmeter values. Comparison of thermal dilution curves, manually calculated by the log-normal and the exponential assumption, showed a correlation coefficient of 0.978 between the two methods, the former values being 11% higher. The exponential method correlated very well with the technique, using a correction factor for injection errors (r = 0.999). Since the exponential technique correlated well with the electromagnetic values (r = 0.84) and since it was less complicated than the technique, using correction factors, this technique was chosen for automation. Comparison of exponential calculated thermodilution values with a digital computer and manually, showed a correlation coefficient of 0.991. Therefore, it was concluded that on-line computation of thermodilution curves improves the applicability of the termodilution techniques as a means of measuring cardiac output.
In rats, stasis thrombosis of a renal vein was produced by the occlusion of a vascular segment after induction of systemic hypercoagulability by i.v. injection of ellagic acid. Prostaglandin E1, at doses which reduced platelet retention by glass beads (6 mug/min/300 g i.v.) only slightly reduced the thrombus size. The platelet release inhibitors suprofen and indomethacin, at doses which prolonged tail bleeding time in rats (50 mg/kg i.v.) had no effect on the thrombus size. Heparin (10 and 20 U/kg i.v.) produced a marked, dose-related reduction of venous thrombosis. The platelet-active compound VK774, at the dose levels of 50 to 10 mg/kg i.v., also reduced the thrombus size to about half that of controls. Lower doses (5, 2.5 mg/kg i.v.) had a progressively weaker effect. Binding to ellagic acid or induction of coagulation changes by VK774 are proposed as possible mechanisms of action. It is concluded that, in comparison with the contribution of plasma coagulation, the participation of the aspects of platelet function we measured in the development of venous stasis thrombosis is comparatively small.
On the basis of corrosion preparations and of microsphere studies, the following characteristics of the canine and feline cerebral circulation were observed. (1) In cats, a greater part of the vertebral arterial blood goes to the brain and it is more specifically restricted to the ponto-medullary and cerebellar structures. These structures received approximately 3 times more microspheres in cats than in dogs. (2) In dogs, an important amount of vertebral blood goes to the neck muscles, and the intracranial vertebral blood supply is spread over a greater area of the brain, including the thalamo-hypothalamic and posterior cortical zone. (3) In cats the thalamo-hypothalamic area receives a greater amount of blood via the common carotid artery than in dogs. (4) In both animal species, the vascular connections between the left and right side of the brain are more extensive in the vertebral than in the carotid bed. However, for either vascular bed, a more important left to right transmission was found in the dog.
In this study, we have tried to determine the magnitude of the inaccuracy of the radioactive microsphere method - due to variations in the diameter distribution of the spheres - for measuring regional myocardial blood flow after coronary artery occlusion. In 5 mongrel dogs, three types of 15 mum microspheres, labelled with 125I, 141Ce or 85Sr, were injected simultaneously after the descending branch of the left coronary artery had been ligated. Myocardial samples wert taken from the left ventricle and divided into four groups according to the number of spheres per sample. The radioactivity of the various isotopes per gram tissue was expressed as percentage of their activity per milliliter of the reference sample. The diameter distribution of microspheres, labelled with each of the isotopes, was determined light-microscopically in suspensions belonging to three different batches. The relative error, as determined from the difference in relative radioactivity of the various types of microspheres in the tissue samples, was higher than the theoretical error for each of the number of spheres per sample. It is very likely that this discrepancy is caused by the differences in diameter distribution of the various types of microspheres, resulting in non-random error. The smaller spheres tended to go to low flow areas and the larger ones to high flow areas. Because of the non-randomness, the error due to diameter variations in the spheres can be diminished by randomizing the order of injection of the various isotopes. The present study indicates that the relatively high degree of accuracy of the microsphere method for the determination of blood flow to large parts of the myocardium with an unimpeded coronary circulation, as was described in literature, cannot be extrapolated to the determination of regional myocardial blood flow after coronary artery occlusion, when the combination of small tissue samples, variations in the diameter distribution of the spheres and an unevenly distributed myocardial blood flow unfavourably affect the accuracy of the method.
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The effects of lidoplazine on K-metabolism were investigated in two types of experiments. (1) K and Na concentrations were measured in plasma, heart, diaphragm and erythrocytes in normo- and hypokalaemic rats with or without chronic (1 month) lidoplazine treatment. Total body weight, heart weight, dry weight/wet weight ratios and extracellular space were also determined. (2) Radioactive K influx in the heart was measured in acute in vitro experiments with or without lidoplazine. It is demonstrated that while lidoflazine has no effect on the Na and K distribution of normokalaemic animals, it has rather a K-saving effect in conditions of severe loss of intra- and extracellular K-ions. In normal in vitro preparations the unidirectional K-influx is not affected by lidoflazine.
Erythro-1-(1-[2-(1,4-benzodioxan-2-yl)-2-OH-ET]-4-piperidyl)-2-benzimidazolinone (R 28935), provokes marked antihypertensive effects lasting several hours in conscious SHR (0.63 to 40 mg/kg i.p.) and beagles with renal hypertension (1.25 mg/kg p.o.). In SHR, this compound induces much less bradycardia, compared to equiactive hypotensive doses of clonidine, guanethidine and propranolol. Significant postural hypotension during tilting, is induced by guanethidine and mecamylamine but not by R 28935. In anaesthetized beagles with renal hypertension, the lowering of the blood pressure by R 28935, (0.02-0.64 mg/kg i.v.) is associated with a considerable decrease in the total peripheral vascular resistance, whereas the myocardial function is not affected. R 28935 is considered a potent antihypertensive drug, with attractive haemodynamic characteristics.