Blocking of impulse conduction in peripheral nerves by local cooling as a routine in animal experimentation.

Small thermodes, cooled by the Peltier effect and heated by transistor dissipation, were developed for reversible nerve blocking. Temperature control is achieved by an electronic feedback circuit for two thermodes independently. This enables simple operation of the cooling system during animal experimentation. Any nerve temperature between 0 and 37 degrees C can be obtained within 90 s and maintained within 0.2 degree C. The instrument can be used both as a stand alone apparatus or under computer control. Effects of local cooling of the cervical vagus nerve of the rabbit on the A-wave of the compound action potential and on spontaneous activity are given as examples of application of the cooling system in biological experiments.

Effect of graded vagal blockade and pulmonary volume on tonic inspiratory activity in rabbits.

Reflex respiratory responses to increased and decreased tracheal pressure have been studied at bilateral local vagus temperatures between 30 degrees C and 0 degrees C in anaesthetized spontaneously breathing rabbits. The temperature of each cervical vagus nerve was governed by separate thermodes, which were cooled by Peltier elements and heated by transistors. In this study, the lowest activity level of the diaphragm during expiration was considered to reflect tonic inspiratory activity. As an indicator for this level, the longest interspike interval in the electromyogram of the diaphragm during a breath was used. Tonic inspiratory activity at tracheal pressures below -1.2 kPa was higher with vagi intact than after vagotomy. This observation indicates that disinhibition, due to the decreased activity of pulmonary stretch receptors, occurring during the Hering-Breuer deflation reflex, is an insufficient explanation for the facilitation of tonic inspiratory activity. When local vagus temperatures are 8 degrees C, and tracheal pressure has been increased or decreased, tonic inspiratory activity is higher than it would be with vagi at 0 degrees C or cut. Two reflex mechanisms that might explain the observed high tonic inspiratory activity are discussed.

Relation between meteorological factors and pain in rheumatoid arthritis in a marine climate.

Reports indicate that weather conditions may affect some symptoms of rheumatoid arthritis (RA) but not the disease itself. Eighty-eight patients living in the marine climate of the Dutch coastal provinces scored their pain symptoms daily during a full year. Correlation analyses of monthly patient averaged pain scores against each of 6 weather factors indicated that RA pain associates positively and quite significantly (p less than 0.01) with temperature and with vapour pressure, negatively and significantly (p less than 0.02) with relative humidity and not with any of the other factors. The fact that the relation between the temperature/vapour pressure complex and RA pain is stronger in summer than in winter is discussed.

Effects of local nerve cooling on conduction in vagal fibres shed light upon respiratory reflexes in the rabbit.

In ten vagus nerves the effect of local cooling on the compound action potential was studied in the temperature range of 34 to 0 degrees C in spontaneously breathing, anaesthetized rabbits. The mean temperature at which the myelinated (A) fibres were completely blocked, was 10.2 +/- 2.4 degrees C (mean +/- S.D.). In nine nerves, local vagus cooling to 0 degrees C failed to block all non-myelinated (C) fibres. In one nerve, total blocking occurred at 2.0 degrees C. We conclude that in the rabbit, the earlier found increase in tonic activity of the diaphragm following lung inflation or deflation during bilateral local vagus cooling to a temperature between 8 and 0 degrees C is due to afferent impulses in vagal C fibres.