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Biomedical subjects

J Verburg

Publications and source records attributed to J Verburg.

9 recordsLinked to original sources
PubMed1992

The effect of decrease in body temperature with Nembutal on meiosis and ovulation after induction by gonadotrophin-releasing hormone and luteinizing hormone in adult rats.

Sodium pentobarbital (Nembutal) is often used to block the pro-oestrous luteinizing hormone (LH) surge in rats. Nembutal is also known to lower body temperature. This study was designed to investigate whether Nembutal affected the time course of meiosis and timing of ovulation induced by exogenous hormones, and whether the possible effects of Nembutal on these processes were related to temperature. Gonadotrophin-releasing hormone (GnRH), the GnRH-analogue Ovalyse, or rat luteinizing hormone (LH) were administered to trigger resumption of meiosis and ovulation; Nembutal (35 mg kg-1 body weight) or saline was given 10 or 60 min later. Plasma profiles of LH were measured and Graafian follicles were studied histologically for meiotic progress and ovulation. Nembutal suppressed the spontaneous surge of LH at pro-oestrus and caused a long-lasting decrease in body temperature. If 1000 ng GnRH was given 2 h before the pro-oestrous LH surge, most of the oocytes had extruded a polar body 10 h later and most follicles had ovulated 14 h later. Nembutal given 1 h after GnRH delayed extrusion of the polar body and ovulation by about 2 h. Nembutal caused a similar delay in ovulation when it was administered after 100 ng of Ovalyse, and it also delayed meiosis when given after 1000 ng of LH. This effect of Nembutal was prevented if body temperature was maintained at 37 degrees C. The delaying effect of Nembutal on meiosis and ovulation induced by exogenous GnRH or LH is related to a long-lasting decrease in body temperature.

Animals↗
PubMed1990

Determinants of the occurrence of vortex rings in the left ventricle during diastole.

This study employs classical inviscid fluid dynamics theory to investigate whether LV diastolic inflow volume and the size of the LV play a role in vortex ring formation. Fluid injection across an orifice into a large container results in the generation of a vortex ring having a constant size and speed. Relations between the vortex size and speed and the injection were obtained by applying conservation laws regarding kinetic energy, impulse and vorticity; the initial state was computed using a bolus injection model, and the final state by using the Kelvin vortex model. An important parameter in the equations is the relative injection length, i.e., the ratio of the length of the injected bolus and the radius of the orifice (L/R). Its estimated highest value in man, L/R = 15, produces a rather thick vortex ring (relative thickness 0.77). Comparable results following from the Hill vortex model convinced us that the Kelvin vortex model can be applied in the whole range of injection lengths in the human left ventricle. In an in vitro model it is shown experimentally that vortex rings can be generated for L/R in the range from 2 to 16. The measured traveling speed of the vortex ring is in fair agreement with the theory, as well as the ring radius for large injections. A vortex ring located in a narrow channel cannot reach its proper traveling speed. The method of images is used to estimate the speed reduction of vortex rings within a cylinder. It turns out that propagation of vortex rings is possible when the ratio of orifice to cylinder radius is less than about 0.5.(ABSTRACT TRUNCATED AT 250 WORDS)

Biomechanical Phenomena↗
PubMed1988

A physical model of the intrathoracic stomach.

To determine whether duodenogastric reflux into the thoracic stomach could be caused by the transmission of negative intrapleural pressure fluctuations into the gastric lumen, a physical model is described and an equation calculated Pm + Pa - Pmb - (Sv.Pmb.Vmb/Pm) = Ppl - Sv.Vmb where Pm is intragastric pressure, Pa is atmospheric pressure, Pmb is end-expiratory gastric base pressure, Vmb is corresponding gastric volume, Sv is stiffness of gastric wall, and Ppl is intrapleural pressure. The validity of the model is demonstrated in six anesthetized mongrel dogs (18-31 kg) in which a thoracic stomach was constructed. The transmission of the intrapleural pressure fluctuations across the gastric wall proved to be greatly influenced by the gastric stiffness. The latter parameter varied from 0.05 to 1.97 cmH2O/ml, corresponding with a pressure transmission of 100 and 60%, respectively. Because high degrees of gastric stiffness are only present for large gastric volumes or when gastric peristalsis is present, it is concluded that, in general, the intrapleural pressure fluctuations are transmitted into the thoracic stomach. For this reason, respiratory efforts may play an important role in inducing duodenogastric reflux into the thoracic stomach.

Animals↗
PubMed1987

Forces acting on the patella during maximal voluntary contraction of the quadriceps femoris muscle at different knee flexion/extension angles.

From knee extension moments measured with a dynamometer, the quadriceps muscle force, the patellar ligament force and the reaction force in the patellofemoral joint at various knee angles (0-90 degrees) were estimated. The information needed to calculate the combined effect of both patellofemoral and tibiofemoral joint on the mechanical advantage of the muscle was obtained from lateral-view radiographs of autopsy knees. The results show that the smallest quadriceps force (2,000 N) is exerted at maximal extension, and the largest force (8,000 N) at about 75 degrees of flexion. The patellar ligament force reaches a maximum (5,000 N) at 60 degrees. The reaction force in the patellofemoral joint is the smallest (1,000 N) at extension and is of the same values as the muscle force in a range from 75 to 90 degrees. Especially at large flexion angles, the value of the estimated forces is considerably larger (by 100%) than reported in the literature. This difference is attributed to the influence of the patellofemoral joint on the mechanical advantage of the muscle, which has not been taken into account in other studies.

Biomechanical Phenomena↗
PubMed1986

A mathematical model of the patellofemoral joint.

A mathematical model of the patellofemoral joint taking into account movements and forces in the sagittal plane is described. The system parameters of the model are the locations of the attachments of the quadriceps muscle and the patellar ligament, the length of the patellar ligament, the dimensions of the patella and the geometry of the articulating surfaces. They were obtained from ten autopsy knees. The model enables calculation of the relative position of the patella, patellar ligament and quadriceps tendon, the location of the patellofemoral contact point and the magnitude of the patellofemoral compression force and the force in the patellar ligament as a function of the location of the tibial tuberosity at different flexion-extension angles of the knee. The model is validated by comparing model data with experimentally determined data.

Biomechanical Phenomena↗