Postural effects on lung volumes and asynchronous ventilation in anesthetized horses.

The researchers investigated how different body postures affect lung capacity and breathing patterns in anesthetized horses. They found that shifting from prone to lateral or supine postures reduces various lung volume measures and increases asynchronous ventilation, suggesting that posture, not anesthesia, primarily impacts gas exchange in anesthetized horses.

Research Methodology

• The study involved quasi-static pressure-volume curves and single-breath nitrogen washouts conducted simultaneously on eight anesthetized horses. The horses used in the study had an average body weight of 485 kg.
• The horses were placed in various positions: left lateral, right lateral, prone, and supine positions. The sequence in which the horses were placed in these postures was randomized to eliminate bias and sequences’ effects.

Findings and Data Interpretation

• The results revealed that shifting the horse from a prone position to a lateral or supine position decreases various measures of lung volume: expiratory reserve volume (ERV), vital capacity (VC), residual volume (RV), functional residual capacity (FRC), and total lung capacity (TLC).
• The percentage of RV and FRC remained unaltered when expressed as %TLC, indicating that a substantial portion of the lung volume was not accessed by VC maneuvers in lateral and supine positions.
• The third phase slope of the nitrogen washout increased when horses were shifted from a prone to lateral or supine positions, indicating increased unevenness in ventilation distribution.
• The onset of phase IV did not significantly differ from FRC in prone or laterally recumbent animals, yet it surpassed FRC in supine horses, indicating a volume above which ventilation increases during expiration.

Conclusion and Implications

• The study concluded that posture predominantly affects impaired gas exchanges in anesthetized horses, rather than general anesthesia itself.
• The changes in lung volumes and regional asynchronous ventilation could be reversed by placing the horse in the prone position, which suggests potential practical implications for managing anesthetized horses in a clinical setting.
• However, the sequence of body positions had no effect on any outcomes, highlighting that any alterations induced by different postures could be reverted, showing the temporary and reversible nature of these effects.