By J. F. Nunn
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Ngai, Katz and Farhie (1965) showed that, in midcollicular decerebrate cats, the marked tachypnoea produced by trichloroethylene was not prevented by bilateral vagotomy and carotid denervation. It would, therefore, seem that there is no solid foundation for the oft repeated view that trichloroethylene causes tachypnoea as a result of sensitization of the pulmonary stretch receptors. Generations of medical students have been brought up with the unquestioned belief in the role of the Breuer-Hering reflex in man.
The first is an extrapolation of the curve to intersect the X axis (zero ventilation) at a P c o 2 known as the apnoeic threshold P c o 2. If P c o 2 is depressed below this point, apnoea commonly results, particularly in the anaesthetized patient, and the extension of the curve is a graphical representation of Haldane's post-hyperventilation apnoea. The second type of extension is horizontal and to the left, like a golf club, representing the response of the subject who continues to breathe regardless of the fact that his P c o 2 has been reduced.
Apart from loss of swallowing and phonation, and the development of hypertension, there was no change in the pattern or sensation of breathing. End-tidal P c o 2 and respiratory rate were unchanged but there was a substantial increase in the duration of breath holding. Loss of ventilatory response to hypoxia produced by inhaling 8 per cent oxygen in nitrogen was also reported in another publication by the same team (Guz and his colleagues, 1966a). Bilateral vagal block was not found to influence ventilation in five anaesthetized patients (Guz and his colleagues, 1964).
Applied Respiratory Physiology. With Special Reference to Anaesthesia by J. F. Nunn