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Biomedical subjects

A Versprille

Publications and source records attributed to A Versprille.

At least 73 records · Page 4Linked to original sources
PubMed1985

Hemodynamic effects of PEEP applied as a ramp in normo-, hyper-, and hypovolemia.

Nonlinear hemodynamic responses on positive end-expiratory pressure (PEEP) have been attributed to a rise of mean central venous pressure (Pcv), to compensatory cardiovascular control mechanisms, and to the occurrence of a lung stretch depressor reflex above a threshold lung stretch. We tested the hypothesis that the contribution of each of these mechanisms is dependent on the preexisting volemic load. PEEP was applied as a continuous rise (ramp) in piglets in three different volemic loads. In the normovolemic circulation cardiac output (CO) decreased nonlinearly in three phases during the PEEP ramp up to 15 cmH2O. CO decreased gradually in phase I, followed by a sharp decrease in phase II between a PEEP of 3 and 9 cmH2O and again a more gradual decrease in phase III up to a PEEP of 15 cmH2O. Heart rate (HR) and mean aortic pressure (PaO) also decreased during phase II, indicating the predominance of a lung stretch depressor reflex. In the hypervolemic circulation (loading 15 ml . kg-1 dextran) only phases I and II were observed with the onset of phase II at a higher level of PEEP (6 cmH2O). More lung stretch appeared to be necessary to elicit the lung stretch depressor reflex. In the hypovolemic circulation (hemorrhage 15 ml . kg-1) CO decreased linearly, Pao was stable after an initial decrease, and HR increased continuously, indicating a predominance of cardiovascular compensatory mechanisms.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1984

M-mode ultrasound recording of perinatal geometry and dynamics of the cardiac interventricular septum.

Fetal and early neonatal cardiac interventricular septal geometry and dynamics were studied by the M-mode ultrasound technique in a cross-sectional study between 28 and 40 wk of gestation (n = 193) and a longitudinal antenatal-early neonatal study up until 48 h following delivery (n = 15). Antenatally the interventricular septal diameter shows a linear increase of about 30%. There is no measurable change in septal diameter during systole, suggesting no-involvement in the process of ventricular contraction. In over 50% of the fetuses no measureable septal motion during systole was observed. Paradoxical septal movement only occurred in about 10% of the cases studied. Postnatally there is a further increase in septal thickness of 46% during the end-systolic phase without any significant change during the end-diastolic phase of the cardiac cycle, indicating active involvement of the septum in ventricular contractility. The septal motion pattern is nearly always non-paradoxical.

Cross-Sectional Studies↗
PubMed1984

Contribution of lung stretch depressor reflex to nonlinear fall in cardiac output during PEEP.

The hypothesis that lung stretch reflexes elicit negative cardiovascular effects during positive end-expiratory pressure (PEEP) application in a ramp procedure up to 15 cmH2O was tested in piglets under steady-state anesthesia and muscle relaxation. The effects of lung stretch on hemodynamics were studied by comparing the differences in responses during PEEP application with two different tidal volumes. In both ventilatory conditions cardiac output and aortic pressure decreased nonlinearly in three phases with the rise of PEEP: a gradual decrease in phase I, a sharp decrease in phase II, and again a more gradual decrease in phase III. Heart rate decreased significantly in phase II. In the series with the larger tidal volume, implying more lung stretch during insufflation, phase II was between a PEEP of 2.6 and 9 cmH2O. In the series with the smaller tidal volume, phase II occurred between 5.7 and 10.5 cmH2O. To assess the contribution of lung stretch reflexes to the decrease in cardiac output we also related cardiac output to the changes in central venous pressure. Again a nonlinear response was observed, indicating that an additional effect besides the rise in mean central venous pressure was involved in the decrease in cardiac output. During ventilation with the smaller tidal volume, phase II of the decrease in cardiac output was also shifted to higher values of mean central venous pressure, which only could be ascribed to the differences in lung stretch at insufflation. It appeared that under circumstances of artificial ventilation the onset of the reflex is determined by a characteristic threshold of lung stretch.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1983

Functional development of the parasympathetic innervation of the sino-auricular node in newborn rabbits, cats and guinea pigs.

The effects of supramaximal vagus nerve stimulation on heart rate were studied in newborn rabbits, cats and guinea pigs. The analysis of the stimulus-effect curve revealed that the earlier proposed relationship: log If/IO = H.f (IO is the steady state PP-interval before and If during stimulation, f is the stimulus frequency, and H the slope of the line) accurately summarizes the relation in rabbits, while with minor deviations it also holds for newborn cats and guinea pigs. Thus, the vagus effect for each nerve and animal is characterized by the slope of the line, H. In rabbits and cats the vagus effect decreased during the first postnatal week to about 1/3 and 1/5 of the initial value at birth. Guinea pigs, however, did not show such a postnatal change of the vagus effect. In comparison with rabbits and cats these animals are born at a relatively late ontogenetic stage. Therefore, we hypothesized that the decrease in vagus effect is related to the stage of development and occurs mainly before birth in this species.

Aging↗
PubMed1983

Model studies on the influence of nonstationary flow on the mean flow estimate with the indicator-dilution technique.

The applicability of the indicator-dilution technique for the estimate of the mean flow under circumstances of nonstationary flow is investigated by model studies. The studies comprise experiments using a hydrodynamical model as well as calculations with a compartmental approach. The main conclusions are: (1) The influence of nonstationary flow on the mean flow estimate with the indicator-dilution technique can be described accurately by a mathematical model based on a mixing-chamber approach. (2) The relative error in the mean flow estimate by a single measurement is dependent on the system parameters (number and time constant of mixing chambers) and the flow parameters (relative amplitude and relative frequency of flow variation and the phase with respect to the variation at the moment of injection). (3) Errors due to cyclic nonstationarities of the flow can be reduced strongly by averaging over two measurements with injection at two points of time with phases pi radians apart.

Cardiac Output↗
PubMed1983

Attenuation of the negative chronotropic effect of myelinated fibers by nonmyelinated fibers in the vagus nerve of the rabbit.

In the adult rabbit, both myelinated and nonmyelinated efferent fibers travel from the cervical vagus nerve to the sinoauricular node. The myelinated fibers convey the negative chronotropic effect. The influence of the nonmyelinated fibers was studied. Stimulation (4/sec) of the myelinated fibers, while the compound action potential was monitored continuously, caused a slowing of the heart rate. Subsequent activation of the non-myelinated fibers attenuated this negative chronotropic effect. Stimulation of adrenergic fibers was excluded, based on data from histochemical studies and the effects of blockade of beta- and muscarinic receptors. The lengthening of the RR interval during activation of the myelinated fibers alone was about 3.5 times larger than during activation of all fiber groups. When the conduction of the myelinated fibers was blocked (anodal block), activation of the nonmyelinated fibers did not show any effect on heart rate. It was concluded that the negative chronotropic effect is conducted via small myelinated fibers and that the nonmyelinated fibers modulate the effect of these cardiomotor fibers, without having an effect on heart rate on their own. This modulation is effected either via a presynaptic mechanism on preganglionic fibers or via an interaction with postganglionic neurons. The nonmyelinated fibers constitute a novel peripheral system to modulate heart rate.

Adrenergic Fibers↗
PubMed1982

Developmental morphometry and physiology of the rabbit vagus nerve.

The morphological and physiological features of the rabbit vagus nerve were studied at different ages after birth. The total fibre count is about 37,500 of which at birth 1-2% and in the adult animal approximately 10% are myelinated. In the postnatal period the cross-sectional area of the vagus grows to 5 times its perinatal size due to an increase of endoneural collagen, fibre growth and myelinization. The myelinization is most pronounced in the first 2 weeks after birth, axonal growth is predominant thereafter. The available data suggest that the begin of myelinization as well as the subsequent development of the myelin sheath are not dependent on axonal size. There seems to be no fundamental difference between the morphological development of the vagus and other peripheral nerves, e.g. the sciatic nerve of the rat. At birth the vagus nerve contains 2 fibre groups as can be measured from the compound action potential with conduction velocities of 11.4 and 0.9 m.s-1 respectively. Upon subsequent development the conduction velocity of these fibres increases to 31.9 and 1.2 m.s-1 in full-grown animals. THe compound action potential of the adult nerve implies 2 additional fibre groups with conduction velocities of 12.3 and 4.6 m.s-1 respectively. These two fibre populations develop gradually from 1 to 2 weeks after birth and arise probably from the slowest conducting, non-myelinated or C-fibres. It is concluded that the functional innervation of the sinoauricular node may be operational at birth as far as the cervical vagus nerve is concerned.

Action Potentials↗
PubMed1982

Hemodynamic effects of positive end-expiratory pressure applied as a ramp.

Hypotheses on the decrease in cardiac output due to positive end-expiratory pressure (PEEP) were tested during positive-pressure ventilation by application of PEEP from 0 to 15 cmH2O as a ramp input function, i.e., a continuous rise. Yorkshire pigs (n = 47, 5-7 wk old) were used under steady-state anesthesia (pentobarbital) and muscle relaxation. Cardiac output decreased nonlinearly in three distinct phases, I up to PEEP 3 cmH2O, II from 3 to 10 cmH2O, and III above 10 cmH2O, with the sharpest decline occurring in phase II. This three-phase cardiac output decrease was more pronounced when the individual responses were normalized to the inflection points between the phases. Heart rate did not change when related to PEEP, but when normalized to the inflection points a significant increase was observed in the phase I and III, whereas in phase II a decrease was evident. Based on a diversity of hemodynamic responses myocardial depression and right ventricular afterload were rejected as major causal mechanisms for the decrease of cardiac output. We hypothesized that the nonlinear response of cardiac output on PEEP is due to a combination of three types of mechanisms. First, the rise of central venous pressure with PEEP decreases cardiac output linearly. Second, the concomitant fall of arterial pressure elicits compensatory mechanisms, which flatten the slope of this venous return curve. Finally, above 3 cmH2O PEEP a lung stretch reflex is elicited, which performs an inhibitory effect on the circulation, causing the steeper fall in cardiac output as well as the decrease in heart rate in phase II.

Animals↗
PubMed1981

Thermodilution technique for measurement of cardiac output during artificial ventilation.

The feasibility of using the thermodilution method to monitor cardiac output during artificial ventilation was studied in anesthetized pigs. Normal saline (0.5 ml) at room temperature was injected into the left ventricle or the right atrium. The dilution curves were detected in the aortic arch and the pulmonary artery, respectively. The ventilation rate was 10 cycles/min at end-expiratory pressures of 0, 5, 10, and 15 cmH2O. For each level, 50 measurements of cardiac output were performed at regular intervals over the ventilatory cycle. The order of measurements were randomly selected. The average of each series of 50 measurements showed excellent correlation with the estimates of cardiac output based on the direct Fick method for oxygen. The maximum difference between the values of cardiac output randomly measured by the thermodilution method was 40% for the left side of the heart and 70% for the right side. However, when the values of cardiac output were sorted according to the specific phases of the respiratory cycle, there was a systematic variation with a small random error. For the left side of the heart, a satisfactory moment of injection for estimation of mean cardiac output appeared to be at the end of the spontaneous expiration. On the other hand, the analysis of cardiac output values at the right side did not reveal any satisfactory moment for injectate administration under changing circumstances, e.g., positive end-expiratory pressure.

Animals↗
PubMed1978

A non-invasive determination of lung perfusion compared with the direct Fick method.

In 5 young pigs (7--9 kg each) data on effective lung perfusion were obtained using a sinusoidal forcing function in the inspired halothane concentration. These data were compared with the cardiac output measured by the direct Fick method for oxygen, corrected for venous admixture. To produce different levels of cardiac output during each experiment the respiratory and circulatory conditions were changed. For the 5 experiments taken together, the mean of the ratios between the non-invasively obtained effective lung perfusion and the venous admixture corrected Fick data was 1.01 (SD = 0.14, n = 55) with r = 0.92.

Animals↗
PubMed1977

The left ventricle in congenital isolated pulmonary valve stenosis. A morphological study.

The wall thickness of the left ventricle was measured in the hearts of 16 children and 2 adults who died of congenital pulmonary valve stenosis. A right-to-left shunt through a patent foramen ovale had existed in 12 cases and was excluded in the other 6. The thickness of the left ventricular wall and the interventricular septum was increased in the majority of hearts, especially in the older patients. There was a good correlation between wall thickness and histological appearance of the left ventricular myocardium; in 2 cases there was also evidence of left ventricular myocardial fibrosis. The coronary arteries appeared normal in all cases. A direct interaction between the ventricles was thought to be a possible mechanism.

Adolescent↗
PubMed1975

The negative inotropic effect of secobarbital on the heart of reserpinised newborn and adult guinea pigs.

The negative inotropic effect of different concentrations of secobarbital was studied on isolated hearts of reserpinised newborn and adult guinea pigs. This effect was expressed as the percentage reduction of contraction height, from which the sensitivity of the heart was obtained as the reciprocal of the secobarbital concentration X1/2 needed to yield a 50% reduction (i.e. 1/X1/2). It was found that in adults depletion of catecholamines increased this sensitivity, but not in newborns. Possible interpretations are discussed and it is concluded that the age effects are not due to an effect of reserpine on contractility.

Aging↗