The effect of body cooling on respiratory system mechanics and hysteresis in rats

- Respiratory mechanics were measured at 36.6 ± 0.25 °C and after body cooling (32.1 ± 0.26 °C).
- Cooling induced no significant change in static and dynamic compliance.
- Cooling increased respiratory system resistance and hysteresis.
- Cooling increased the total and resistive components of the work of breathing.

Literature reports and theoretical considerations suggest that body cooling may affect respiratory mechanics in vivo. To examine this hypothesis, healthy rats were studied using the end-inflation occlusion method under control conditions and after total body cooling. Respiratory mechanics parameters, hysteresis areas, the inspiratory work of breathing, and its elastic and resistive components, were calculated. After body cooling (mean rectal temperature from 36.6 ± 0.25 to 32.1 ± 0.26 °C), the ohmic and the additional visco-elastic respiratory system resistances, the hysteresis, the total inspiratory work of breathing, and its resistive components, were all increased. No significant changes were detected for the static and dynamic respiratory system elastance mean values, and the related elastic component of the work of breathing. These data indicate that body cooling increases the mechanical inspiratory work of breathing by increasing the resistive pressures dissipation. This effect is evident even for limited temperature variations, and it is suggested that it may occur in the event of accidental or therapeutic hypothermia.