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 panting respiratory rate 199±14 x min“1 in all anaesthetized rabbits. Significant correlations between BT and frequency of breathing (positive), heart rale (positive) or tidal volume (negative) were found. Cooling was accompanied by considerable arterial hypotension. Duration of the Hering-Breuer reflex (HB) was reduced by the rise of BT. Intensity of the reflex (assessed as the ratio of the apnoeic pause to the mean duration of the previous 5 breaths) was unchanged up to the body temperature eliciting panting (41.15±0.08 °C) when it was greatly diminished. Defensive airway reflexes were also changed in hyperthermia. The duration as well as the intensity of nasal apnoca (Kratschmer’s reflex) and laryngeal chemoreflex apnoea were decreased. The intensities 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 from the airways are diminished during hyperthermia and panting in anaesthetized rabbits.
In experiments on 51 healthy anaesthetized and paralyzed rabbits the changes in parameters of mechanics of breathing during high frequency jet ventilation (HFJV) were determined and the mechanisms responsible for these changes were investigated. In the first series of experiments with two groups of animals ventilated by HFJV with relative inspiratory time ti = 0.5 and ti = 0.7 airway resistance (Raw) after 5 h of HFJV in the ti = 0.5 group increased from 1.14±0.05 to 2.31±0.09 kPa.l_1.s (P<0.001), in the ti = 0.7 group from 1.22±0.04 to 1.78±0.08 kPa.l-1.s (P<0.01). Dynamic compliance (Cdyn) decreased in the ti = 0.5 group from 0.041 ±0.004 to 0.017±0.001 l.kPa-1 (P<0.01) and in the ti = 0.7 group from 0.034± 0.003 to 0.022± 0.002 l.kPa-1 (P<0.01). In the second series of experiments a group of animals was ventilated by HFJV after cervical vagotomy. The deterioration of Raw and Cdyn was significantly reduced in vagotomized rabbits in comparison to the controls without vagotomy. Finally, the study of phospholipid content in bronchoalveolar lavage fluid revealed no significant differences after 5 h of artificial ventilation or spontaneous breathing. These data indicate that HFJV results in changes in the parameters of mechanics of breathing in healthy lungs, which may be attenuated, but not fully eliminated, by bilateral cervical vagotomy. The decrease in Cdyn and increase in Raw are probably not due to changes in the pulmonary surfactant content.