Esophageal and intrapleural pressures in the healthy conscious pony.

This study investigated the differences in pleural and esophageal pressures in six sedated, standing ponies. The research found significant changes in pleural pressure during respiration, mainly in the middle and ventral portions of the thorax, and less so in the dorsal portions and parts of the esophagus. These variations in pressure were noted to influence dynamic compliance calculations, with the potential to cause regional variations in lung inflation, similar to those observed in humans.

Methods and Experimentation

• The experiment involved six ponies in a sedated but conscious state, allowing the researchers to monitor pleural and esophageal pressures during normal respiration.
• Pleural pressure measurement was carried out using blunt needles attached to transducers, inserted into the 10th intercostal space level, and 10 and 20 cm above the point of the shoulder.
• Measurements of esophageal pressure were carried out via two balloons, a condom and an esophageal balloon, attached to transducers located in the cranial, middle, and caudal parts of the thoracic esophagus.
• To track the animals’ tidal volume, a pneumotachograph attached to an endotracheal tube, inserted through a tracheostomy, was used. This allowed the researchers to integrate a flow signal for tracking volume per respiration cycle.

Findings

• The changes in pleural pressure during respiration were greater in the middle and ventral parts of the thorax, and less in the dorsal section of the thorax and the middle and caudal parts of the esophagus.
• The cranial part of the thoracic esophagus experienced the least change in pleural pressure.
• The type of esophageal balloon deployed for measuring pressure did not affect the results, suggesting a consistent performance regardless of the balloon type used.
• Calculated dynamic compliance was affected by regional variations in esophageal or pleural pressure witnessed during respiration.

Implications

• The studies demonstrated pleural pressure gradients of 0.33 cm of water/cm of descent and 0.484 cm of water/cm of descent in the dorsal and ventral halves of the thorax, respectively. These pressure gradients may result in regional variations in lung inflation, paralleling phenomena witnessed in human lung function.