Use of flow-volume loops to evaluate upper airway obstruction in exercising standardbreds.

This study investigated the utility of tidal breathing flow-volume loops (TBFVL) in detecting upper airway obstruction in Standardbred horses at rest and during exercise. The results indicated that TBFVL, particularly from exercising horses, provided a reliable, non-invasive, and quick diagnostic tool for upper airway obstruction.

Relevance of Tidal Breathing Flow-Volume Loops (TBFVL)

• In this study, TBFVLs were evaluated at rest and during exercise, specifically at 75% of maximum heart rate and at maximum heart rate.
• The researchers utilized a pulmonary function computer to analyze the TBFVLs. The computer determined indices related to airflow rate and the ratio between expiratory and inspiratory airflow for individual loops.
• Traditional variables of upper airway function, including peak airflow, peak pressure, and both inspiratory and expiratory impedances, were also measured alongside TBFVL indices.
• The researchers found TBFVL shape and indices to be variable when horses were at rest. However, when the horses were exercising, TBFVL shape was consistent suggesting exercising horses provide more dependable airflow patterns for analysis.

Observations after Left Recurrent Laryngeal Neurectomy (LRLN)

• The study included measuring changes both before and after the LRLN, a surgical procedure implemented to induce left laryngeal hemiplegia – a common cause of upper airway obstruction in horses.
• Post-surgery, TBFVL from exercising horses exhibited noticeable limitation in inspiratory airflow, with the expiratory airflow curve remaining unaffected.
• Additionally, the researchers observed significant decreases in the peak inspiratory flow rate and inspiratory flow at 50 and 25% of tidal volume post-LRLN.
• The experiment also recorded a significant increase in both the ratio of peak expiratory to inspiratory airflow and the ratio of mid-tidal volume expiratory and inspiratory airflow rates.
• Inspiratory impedance was likewise noted to have increased after the surgical procedure.

Potential Diagnostic Tool

• Based on the findings, TBFVL, while not particularly useful in horses at rest, proved promising as a diagnostic tool for upper airway obstruction in exercising horses.
• The evaluation of TBFVL allowed for objective, specific, and repeatable detection of the condition.
• Given its non-invasive nature, speed, and tolerance by horses, the study concludes TBFVL to be a potentially valuable clinical diagnostic test.