Der Einflu� der Temperatur auf die CO2-Schwelle des Atemsystems

A respiratory drive in addition to the increase in CO2 production at raised body temperature in rats

“…Only when mean body temperature was raised to 39.9 ± 0.1°C did breathing reappear during hypocapnia, and the mean Pa,COµ level was 18.2 ± 1.5 mmHg. The lowest Pa,COµ level ever recorded at which breathing is still present at raised temperature is 5 mmHg (Pleschka et al 1965), but since Pleschka et al did not confirm that the same hypocapnia failed to restart breathing at normal temperature, the contribution of a reduction in Oµ availability at Pa,COµ levels of 5 mmHg must still be considered. At 39.9°C mean blood pressure fell by a further 15 mmHg (to 83 mmHg), but even this further fall cannot explain the reappearance of breathing in all rats.…”

“…Furthermore, the additional drive can sustain breathing even when mechanical ventilation is used to drive Pa,COµ levels below the lowered mean level seen at raised body temperatures. Thus, Pleschka et al (1965) made the remarkable observation that when body temperature was raised to 41°C, rhythmic phrenic activity persisted even when mechanical ventilation was used to drive the mean Pa,COµ level down to 5 mmHg in anaesthetised dogs. Thus, the greater increase in alveolar ventilation than COµ production, and the failure of hypocapnia to cause apnoea, reveal the presence of an additional respiratory drive in these species at raised temperatures.…”

The preoptic area in the hypothalamus is the source of the additional respiratory drive at raised body temperature in anaesthetised rats

“…The presence of this additional drive at raised body temperatures is even more clearly shown in these species when mechanical ventilation is used to drive Pa,COµ levels far below the lowered eupnoeic level. Thus in anaesthetised dogs at 41°C, rhythmic breathing is sustained even when mechanical ventilation is used to drive the mean Pa,COµ level down to 5 mmHg (Pleschka et al 1965). Although the thermoregulatory system in the hypothalamus mediates the onset of panting, we are not aware of any experimental demonstration (Plum & Leigh, 1981) that this additional respiratory drive at raised body temperature also originates from the thermoregulatory system in the hypothalamus.…”