Abstract
Cooling the vagus nerve is often used to study respiratory reflexes mediated by pulmonary receptors (2,5). Its use is based on the finding that at low temperatures (e.g. 4°C) unmyelinated fibres still transmit impulses whereas transmission in myelinated fibres is fully blocked. This allows distinguishing reflex effects caused by C-fibres from those caused by slowly and rapidly adapting pulmonary receptors (SAR and RAR) (2). The aim of the present study was to investigate whether vagal cooling can also be used to distinguish between reflex effects caused by SAR and RAR. Cooling a nerve fibre increases its refractory period in the cooled area. During this period an afferent impulse in this fibre cannot pass the cold block. As a consequence, the frequency of impulses arriving at the brain stem respiratory centres is reduced. SAR have higher discharge frequencies than RAR. Therefore, the relative reduction in impulse frequency by cooling is larger for SAR than for RAR (5). Our hypothesis is that during vagal cooling the effects of stimulating SAR start to disappear at a higher temperature than the effects of stimulating RAR. In the present study two clearly distinct temperature ranges were identified. It is argued that in the first range (14–10°C) the reflex effects caused by SAR were strongly reduced and in the second (8–4°C) the reflex effects caused by RAR.KeywordsVagus NerveUnmyelinated FibreAfferent ImpulseReflex EffectHigh Discharge FrequencyThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.
Published Version
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