Flow through a Collapsible Tube: Experimental Analysis and Mathematical Model

Flow through thin-wall axisymmetric tubes has long been of interest to physiologists. Analysis is complicated by the fact that such tubes will collapse when the transmural pressure (internal minus external pressure) is near zero. Because of the absence of any body of related knowledge in other sciences or engineering, previous workers have directed their efforts towards experimental studies of flow in collapsible tubes. More recently, some attention has been given towards analytical studies. Results of an extensive series of experiments show that the significant system parameter is transmural pressure. The cross-sectional area of the tube depends upon the transmural pressure, and changes in cross-section in turn affect the flow geometry. Based on experimental studies, a lumped parameter system model is proposed for the collapsible tube. The mathematical model is simulated on a hybrid computer. Experimental data were used to define the functional relationship between cross-sectional area and transmural pressure as well as the relation between the energy loss coefficient and cross-sectional area. Computer results confirm the validity of the model for both steady and transient flow conditions.     

Potentials of spinal motoneurons in cats with experimental tetanus

Potentials of motoneurons of the lower segments of the spinal cord were recorded with the aid of intracellular microelectrodes in experiments on cats with induced tetanus produced by injection of tetanus toxin (1500–2000 mouse LD₅₀) into the extensor muscles of the left shin. Neither afferent volleys of impulses in cutaneous and muscle nerves, nor antidromic volleys in the corresponding ventral roots, produced IPSPs in motoneurons of the extremity into which toxin was injected. The form both of antidromic peak potentials and of monosynaptic EPSPs in motoneurons in which IPSPs were blocked by tetanus toxin did not differ from the form of corresponding potentials of motoneurons in normal cats. The values of threshold depolarization for peak discharges during synaptic and direct stimulation were equal in tetanus and control motoneurons. Resistance and time constant values of the membrane in "tetanus" motoneurons did not differ from the corresponding values for "control" motoneurons.N. I. Pirogov Second Medical Institute, Moscow. Translated from Neirofiziologiya, Vol. 1, No. 1, pp. 25–34, July–August, 1969.     

Corticofugal influences on neurons of the main trigeminal sensory nucleus

The effects of stimulation of the ipsilateral sensomotor cortex were studied on 88 neurons in the region of the main trigeminal sensory nucleus of a cat. The cortex was stimulated via a coaxial electrode by single impulses. Stimulation of the cortex caused the appearance of EPSPs and action potentials in these neurons; a small number of these responses were monosynaptic. The polarity of the impulse applied to the cortex had a significant effect on the magnitude of the latent period of the response and the postsynaptic reaction, which is apparently caused by the stimulation of different types of cortex neurons. Apparently, corticofugal pulsation regulates the level of sensitivity of the trigeminal sensory neurons.A. A. Bogomolets' Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 1, No. 1, pp. 47–53, July–August, 1969.