Unusual response of anaesthetised pigs to asphyxia

The effects of vagosympathectomy, asphyxia, hypoxia and hypercapnia on the breathing of anaesthetised pigs are described. Vagosympathectomy caused changes in cardiovascular variables and in the pattern of breathing characteristic of the loss of stretch receptor activity. After vagosympathectomy the linear relationship between tI and tE was abolished. Hypoxia in intact animals produced changes in minute ventilation by peripheral chemoreceptor drive. When this drive was removed by vagosympathectomy the central depressing effects of hypoxia were revealed as a slowing of breathing and reduction in minute volume. The central depressing effect of hypoxia on respiration was very potent in the pig and very clearly seen in asphyxia. Vagosympathectomy caused a reduction in frequency of breathing and respiratory arrest occurred when a dead space of only moderate size was used. Breathing slowed from the moment of connection of the dead space to produce respiratory arrest within 2 min. The pig lung has been considered similar to the human lung on morphometric and physiological grounds but these results show that there are very important species differences in response to asphyxia.