HEAD'S PARADOXICAL REFLEX

¹ Department of Physiology, St. Bartholomew's Hospital Medical College, London, E.C.1, and the University Laboratory of Physiology, Oxford

Cold block of the vagus nerves of rabbits completely prevents conduction in pulmonary stretch fibres at temperatures close to or higher than those required to block the Hering-Breuer inflation reflex. These temperatures are several degrees higher than those required to block Head's paradoxical reflex. It is concluded that Head's paradoxical reflex cannot be due to pulmonary stretch fibre activity during cold block; that is, cannot be due to cold block of the vagus nerves being more effective for high-frequency discharges (during lung inflation) than for low-frequency discharges in pulmonary stretch fibres. This conclusion is supported by a consideration of the pattern of Head's paradoxical reflex, and by a summary of the published evidence that the reflex can be elicited when the nerves are not being cooled at all.

Note:

The experiments described were carried out at the Department of Physiology, St. Bartholomew's Hospital Medical College, in 1958-59. I am grateful to the American Physiological Society for permission to publish fig. 3, and to the Editors of the Journal of Physiology for permission to publish fig. 4. Part of the apparatus used was bought with a grant from the Central Research Fund, University of London.