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Postural effects on lung volumes and asynchronous ventilation in anesthetized horses
Summary
Posture significantly impacts lung function in horses. Changing from prone to lateral or supine positions reduces lung volumes and increases ventilation unevenness, suggesting posture, not anesthesia, impairs gas exchange.
Area of Science:
- Veterinary Medicine
- Respiratory Physiology
- Comparative Physiology
Background:
- General anesthesia can alter respiratory mechanics.
- Body positioning is known to affect lung volumes and gas exchange in various species.
Purpose of the Study:
- To investigate the effects of different body postures on lung volumes and ventilation distribution in anesthetized horses.
- To determine if posture or anesthesia is the primary factor affecting gas exchange.
Main Methods:
- Quasi-static pressure-volume curves and single-breath nitrogen washouts were performed simultaneously.
- Eight anesthetized horses were studied in left lateral, right lateral, prone, and supine postures.
- The sequence of postures was randomized to control for order effects.
Main Results:
- Lateral and supine postures decreased expiratory reserve volume (ERV), vital capacity (VC), residual volume (RV), functional residual capacity (FRC), and total lung capacity (TLC).
- RV and FRC as %TLC remained unchanged, indicating incomplete lung recruitment in lateral/supine positions.
- Phase III slope increased, and phase IV onset exceeded FRC in supine positions, signifying increased ventilation asynchronousity.
Conclusions:
- Posture significantly influences lung volumes and ventilation distribution in anesthetized horses.
- Impaired gas exchange in these horses is predominantly related to body posture rather than general anesthesia.
- Lung function changes were reversible upon returning to the prone posture.