Circulatory Control via Vagal Afferents

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Abstract
Castenfors, J., E. Knutssonand T. Sjöstrand. Circulatory control via vagal afferents. II. Effects of hemorrhage on afferent discharges via the laryngeal communicans in the rat. Acta physiol. scand. 1972. 84. 355–365.Recordings were made of afferent impulses passing through the communicating branch between the superior and inferior laryngeal nerves and in the recurrent nerve after section of the vagus. Two types of discharges varying with changes of the blood volume were recorded.1. Continuous nerve impulses which are increased in frequency on hemorrhage.2. Repetitive burst of spikes with a heart rhythm which starts at the first heart sound, proceeds until shortly after the P wave and ceases with the IV sound. This activity appears to correspond to the inflow of blood to the heart. On hemorrhage the activity diminishes and disappears entirely after a given loss of blood, returning on reinfusion.The slowing of the heart rate on hemorrhage, described in the preceding paper, is assumed to be a result of an increase of the impulse flow through the laryngeal communicans. It is also assumed that the allied receptors are located on the low‐pressure side. The receptors firing synchronously with the heart rhythm are assumed to belong to the earlier described group of atrial receptors of type B. Their function is postulated to be opposite to that of the former receptors, thus increasing the heart rate with increasing central blood volume.