Pleural liquid pressure measured with rib capsules in anesthetized ponies.

This study, conducted on anesthetized ponies, investigated the pleural liquid pressure at the end of exhalation in different body positions and found specific trends based on the ponies’ spatial orientation, providing insights into how the position affects lung function.

Methods

• The researchers measured pleural liquid pressure in 11 anesthetized ponies in prone and supine positions.
• A liquid-filled capsule was implanted into a rib to measure the pressure with minimal distortion of the pleural space. This method was based on a protocol established by Wiener-Kronish et al.
• The position of the capsule relative to the lung height was tracked through thoracic radiographs taken in each position.

Results

• The study found that pleural liquid pressure becomes more negative in the upper regions of the lungs and least negative in the lower regions, regardless of the pony’s body position.
• When the ponies were lying on their backs (supine position), the vertical gradient in pleural liquid pressure was slightly less than 1 cmH2O/cm height.
• The pleural liquid pressure in the lower lung regions showed a low transpulmonary pressure over the region of the chest where most of the lung mass is located.
• When the ponies were lying on their bellies (prone position), the vertical gradient in pleural liquid pressure was not significantly different from 0 cmH2O/cm height.
• After the ponies had died, the mean transpulmonary pressure measured was similar to the estimated pleural liquid pressure at 50% lung height. This suggests that pleural liquid pressure is closely related to pleural surface pressure.

Conclusions

• The results align with previous findings of poor ventilation distribution and reduced lung volumes in anesthetized horses lying on their backs compared to those lying on their bellies. This suggests that the body position of an animal could affect measurement and understanding of their respiratory physiology.