CARDIORESPIRATORY PARAMETERS AND RESPIRATORY REFLEXES IN RABBITS DURING HYPERTHERMIA

The effects of different body temperature (BT) on the respiratory and cardiovascular parameters and respiratory reflexes were studied in 33 anaesthetized adult rabbits. Hyperthermia elicited panting with mean p anting respiratory rate 199+/-14 x min(-1) in all anaesthetized rabbit s. Significant correlations between BT and frequency of breathing (pos itive), heart rate (positive) or tidal volume (negative) were found. C ooling was accompanied by considerable arterial hypotension. Duration of the Hering-Breuer reflex (HE) was reduced by the rise of BT. Intens ity of the reflex (assessed as the ratio of the apnoeic pause to the m ean duration of the previous 5 breaths) was unchanged up to the body t emperature eliciting panting (41.15+/-0.08 degrees C) when it was grea tly diminished. Defensive airway reflexes were also changed in hyperth ermia. The duration as well as the intensity of nasal apnoea (Kratschm er's reflex) and laryngeal chemoreflex apnoea were decreased. The inte nsities of respiratory efforts in sneezing and laryngeal coughing were reduced. The expulsive reactions evoked by mechanical stimulation of the larynx were replaced by very shortlasting inhibition of breathing during panting. The results indicate that reflex control of breathing via the Hering-Breuer reflex and the ability to eliminate irritants fr om the airways are diminished during hyperthermia and panting in anaes thetized rabbits.