Failure of subtotal arytenoidectomy to improve upper airway flow mechanics in exercising Standardbreds with induced laryngeal hemiplegia

James K. Belknap From the Department of Large Animal Clinical Sciences, Michigan State University, East Lansing, MI 48824-1214.

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Frederik J. Derksen From the Department of Large Animal Clinical Sciences, Michigan State University, East Lansing, MI 48824-1214.

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Frank A. Nickels From the Department of Large Animal Clinical Sciences, Michigan State University, East Lansing, MI 48824-1214.

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John A. Stick From the Department of Large Animal Clinical Sciences, Michigan State University, East Lansing, MI 48824-1214.

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N. Edward Robinson From the Department of Large Animal Clinical Sciences, Michigan State University, East Lansing, MI 48824-1214.

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 BVetMed, PhD

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SUMMARY

Upper airway flow mechanics and arterial blood gas measurements were used to assess the efficacy of subtotal arytenoidectomy for treatment of induced left laryngeal hemiplegia in horses. Measurements were collected with the horses at rest, and trotting or pacing on a treadmill (6.38° incline) at speeds of 4.2 and 7.0 m/s. Experimental protocols were performed after right common carotid artery exteriorization (baseline), after left recurrent laryngeal neurectomy (lrln), and after left subtotal arytenoidectomy.

At baseline, increasing treadmill speed progressively increased peak inspiratory and expiratory flow (Vimax and Vemax respectively), peak inspiratory and expiratory transupper airway pressure (PuI and PuE, respectively), respiratory frequency (f), tidal volume (VT), minute volume (VE), and heart rate. Inspiratory and expiratory times (TI and TE, respectively) and arterial oxygen tension (Pao2) decreased with increased treadmill speed; inspiratory and expiratory impedance (ZI and ZE, respectively) did not change.

After lrln, Vimax, f, and Pao2 significantly (P < 0.05) decreased at exercise, whereas PuI, TI, and ZI significantly increased. Minute volume decreased at exercise after lrln, but the changes were not significant; lrln had no effect on Vemax PuE, ZE, heart rate, arterial carbon dioxide tension (Paco2), or VT.

Subtotal arytenoidectomy did not improve upper airway flow mechanics or blood gas measurements impaired by laryngeal hemiplegia.

SUMMARY

Upper airway flow mechanics and arterial blood gas measurements were used to assess the efficacy of subtotal arytenoidectomy for treatment of induced left laryngeal hemiplegia in horses. Measurements were collected with the horses at rest, and trotting or pacing on a treadmill (6.38° incline) at speeds of 4.2 and 7.0 m/s. Experimental protocols were performed after right common carotid artery exteriorization (baseline), after left recurrent laryngeal neurectomy (lrln), and after left subtotal arytenoidectomy.

At baseline, increasing treadmill speed progressively increased peak inspiratory and expiratory flow (Vimax and Vemax respectively), peak inspiratory and expiratory transupper airway pressure (PuI and PuE, respectively), respiratory frequency (f), tidal volume (VT), minute volume (VE), and heart rate. Inspiratory and expiratory times (TI and TE, respectively) and arterial oxygen tension (Pao2) decreased with increased treadmill speed; inspiratory and expiratory impedance (ZI and ZE, respectively) did not change.

After lrln, Vimax, f, and Pao2 significantly (P < 0.05) decreased at exercise, whereas PuI, TI, and ZI significantly increased. Minute volume decreased at exercise after lrln, but the changes were not significant; lrln had no effect on Vemax PuE, ZE, heart rate, arterial carbon dioxide tension (Paco2), or VT.

Subtotal arytenoidectomy did not improve upper airway flow mechanics or blood gas measurements impaired by laryngeal hemiplegia.

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