Elimination of abnormal respiratory noise in horses (Proceedings)

Sources of respiratory noise

• Laryngeal hemiplegia

• Dorsal displacement of the soft palate

• Pharyngeal collapse

• Alar fold flutter

• Epiglottic entrapment

• Axial deviation of aryepiglottic folds

• Lower airway inflammatory disease?

Sources of noise associated with inhalation

• Laryngeal hemiplegia

• Axial deviation of aryepiglottic folds

• Pharyngeal collapse

• Lower-airway inflammatory disease

• Epiglottic retroversion

• Alar fold flutter/collapse

Sources of noise associated with exhalation

• Dorsal displacement of the soft palate

• Alar fold flutter/collapse

• Epiglottic entrapment

• Lower-airway inflammatory disease?

Diagnosis of respiratory noise

• Can be a challenge!

• Not all pathologies have consistent noise production

o DDSP did not always produce an abnormal respiratory noise experimentally (Derksen et al AJVR 200l;(62) 659-664)

• Not all noises indicate pathology

• Resting endoscopy

• Treadmill endoscopy

• Sound analysis

o Treadmill

o Field

Sound analysis

• Acquisition of respiratory sounds

• Can be performed in the field or on treadmill with specialized microphone apparatus and recording device

• Recordings digitized and analyzed using computer-based spectrum analysis

• What sound recordings have been studied?

o Normal horse

o LLH-affected horse

o Dorsal displacement of soft palate

o Other pathologies?

o Alar fold flutter/collapse

• Both inhalatory and exhalatory with sharp spikes Cable et al AJVR 2002;(63)1707-13

o No other pathologies extensively studied

• Not easily reproduced experimentally

• Clinical prospectives necessary

Treatment for abnormal respiratory noise

• Identify source 1st!

• Source will dictate treatment

• Axial deviation of the aryepiglottic folds

o 52 racehorses with ADAF

• 83% had noise

• Laser resection had a more significant affect on noise reduction and return to racing

• Rest and anti-inflammatory therapy less effective

• Alar fold flutter/collapse

o Sound analysis moderate sensitivity and specificity in experimental alar fold collapse (Cable CS et al 2002 Dec;63(12):1707-13)

o In 22 race horses

• Manual elevation decreased noise in 11/11

• Clips or mattress sutures decrease noise in 8/8

• Surgical resection improved noise and performance in 71% (Hawkins JF et al JAVMA 1995 Jun 15;206(12):1913-6)

o FLAIR® nasal strips – will they be effective?

• Stabilize and tents external nares

• Decreases work of breathing (Holcombe SJ et al AJVR 2002 Aug;63(8):1101-5)

o Dorsal displacement of the soft palate

• Intermittent and often multifactoral etiology

• Don't always make a noise

• Difficult to diagnose

• Sternothyroideus tenectomy plus laser cautery of soft palate – 92% improved performance (Hogan et al AAEP Proc 2002;48:228-30) and 63% (Smith JJ, Vet Surg 2005;34:5-10)

• Tie-forward – 80% horses had improved performance (Woodie JB et al EVJ 2005;37:418-23)

• Anti-inflammatory therapy (steroids and throat spray)

o Other pathologies

• Lower airway inflammatory disease

• How much noise does mucus make?

• Steroid therapy (prednisolone or dexamethasone – decreasing doses)

o Often will have more than one problem!

Laryngeal hemiplegia and vocal fold collapse

• Most consistent source of abnormal respiratory noise is associated with laryngeal hemiplegia and vocal fold collapse

• Most widely studied

• Easily reproduced experimentally

• Experimental studies

o Bilateral ventriculocordectomy

o Prosthetic laryngoplasty

o Unilateral laser-assisted vocal cordectomy

o Unilateral laser-assisted ventriculocordectomy

• Experimental protocol

o Horses exercised on a treadmill at HRmax

o Respiratory sounds recorded and trans-upper airway pressures measured:

o Baseline

o 14 days after induction of LH by left recurrent laryngeal neurectomy

o 30, 60, 90 and 120 days following surgery

• Materials and Methods

o 6 standardbred horses

o Normal upper airway at rest and on treadmill exercising at HRmax

• Sound recordings

o Dynamic unidirectional microphone with cardioid pick-up pattern

o Respiratory sounds recorded on a audiocassette which were subsequently digitized for analysis

• Sound analysis

o Two different indices of sound measured with computer based spectrogram programa

o Sound level of inspiratory noise (dB)

o Sound intensity of characteristic formants (dB)

o Definitions

• Sound level

• 10 log (I/Is)

• Relative loudness of a sound

• Formant

• A region of concentration of sound energy prominent on a sound spectrogram that collectively constitute the frequency spectrum of a sound

• Trans-upper airway pressure

• Tracheal catheter with side holes

• Pressure transducer

• Difference between barometric and tracheal pressure

Bilateral ventriculocordectomy

• Often used in combination with laryngoplasty in LH-affected horses

• Removes the saccule and portion of vocal fold

• Stabilization of arytenoid via scar formation

• Surgical procedure

o General anesthesia via laryngotomy

o Saccule everted and excised with aid of sacculectomy burr

o 4 mm of vocal fold removed

o Axial free edge of vocal fold and abaxial free edge of saccule apposed

• Effect on respiratory noise

o Peak sound intensities of F2 and F3 to baseline values by 90 days following surgery

o Sound level improved, but not to baseline

• Effect on airway obstruction

o Inspiratory trans-upper airway pressures significantly improved from LH-values but remained different from baseline.

o 60-70% improvement in airway function

• Conclusions

o Bilateral ventriculocordectomy returns indices of sound to baseline

o Restores 60-70% of airway function

o Takes 90 days to be fully effective

Laryngoplasty

• First described by Marks

o Fixes arytenoid in abducted position

o "Gold Standard" for treatment of horses with laryngeal hemiplegia and exercise intolerance

• Procedure proven to return upper-airway mechanics to baseline (Derksen et al , AJVR 1986;47:16-20, Shappell et al, AJVR 1988;49:1760-65, Tetens et al, AJVR;57:1668-73)

• Proven an effective treatment for returning horses to racing (Hawkins et al, Vet Surg 1997;26:484-91, Russell et al, JAVMA 1994;8:1235-41, Spiers et al, Aust Vet J 1983;60:294-99, Strand et al, JAVMA 2000;217:1689-96)

• Improvement in respiratory sound production used as marker of success based on subjective measures (Marks et al, JAVMA 1970;157:157-63, Baker, Comp Cont Edu 1983;5:S61-S67, Spiers et al, Aust Vet J 1983;60:294-99, Hawkins et al, Vet Surg, 1997;26:484-91, Russell et al, JAVMA 1994;8:1235-41.)

• Degree of arytenoid abduction necessary for surgical success is debated

o Grading scale of arytenoid abduction following surgery was introduced by Russell et al JAVMA 1994; 204:1235-41

• Grade 5

• Arytenoid maximally abducted

• Caused depression in pharyngeal wall

• Grade 4

• Full abduction

• Contacting pharyngeal wall

• Grade 3

• Abduction just beyond intermediate position

• Not contacting pharyngeal wall

• Grade 2

• Arytenoid at intermediate position

• Grade 1

• Cartilage crossed midline of rima glottidis

• Effect on respiratory noise

o Laryngoplasty improved respiratory noise, but at no point did it return Formants or Sound Level to baseline values

o Improvement seen at 30 days post-operatively

o Degree of abduction positively correlated with noise production

• "Less is more" in regards to noise reduction in LH-affected horses

• Effect on airway obstruction

o Inspiratory trans-upper airway pressures returned to base-line at 30 days post-operatively

o Degree of abduction not correlated with upper airway pressure

• Conclusions

o Cannot predict the degree of remaining airway obstruction from noise in individual animals

o Therefore cannot predict surgical success based on residual sound following surgery

o The degree of arytenoid abduction did not correlate with Pui

o Eliminating LH-associated airway obstruction does not require maximal arytenoid abduction

Laser-assisted vocal cordectomy

• Used in conjunction with laryngoplasty

• Saccule remains

• Removal of vocal fold to increase the ventral diameter of the rima glottidis

• Performed in the standing sedated horse

o Decreases general anesthesia time

o No second incision

• Surgical Procedure

o As described by Ducharme et al (Ducharme NG et al Clin Tech in Eq Prac 2002;1:17-21)

• Effect on respiratory noise

o Formant 2 the only index of sound to improve from LH values, but remained significantly different from baseline

o Sound level, F1, and F3 remained significantly different from baseline and were not significantly improved from LH values at any time point

• Effect on airway obstruction

o Improved inspiratory pressures by 30 days post-operatively

o 40-50% improvement in obstruction

• Conclusions

o Not as effective as bilateral ventriculocordectomy or laryngoplasty in improving respiratory noise

o Improved airway obstruction, but to lesser degree than bilateral ventriculocordectomy

Laser-assisted ventriculocordectomy

• Used in conjunction with laryngoplasty

• Performed in the standing sedated horse

• No second incision compared to ventriculocordectomy performed through a laryngotomy

• Surgical procedure

o Sullins et al (AAEP Proceedings 2005 pg 312-16)

o Performed in standing sedated horse

o 980nm diode laser

o Trans-nasal sacculectomy burr to evert saccule

o Vocal fold & saccule excised

• Effect on respiratory noise

o Significantly improved all sound indices from LH values

o Sound level and formant 3 returned to baseline by 60 days after surgery (Robinson P, et al AAEP Proc 2005; 51:317-18)

• Effect on upper-airway pressures

o By 60 days after surgery inspiratory trans upper-airway pressures returned to baseline (Robinson P, et al AAEP Proc 2005; 51:317-18)

• Conclusions

o Removal of ventricle is necessary to eliminate noise

o As effective as BVC in noise improvement

o LAVC is as effective as laryngoplasty in alleviating airway obstruction

Clinical evaluations

• Laryngoplasty

o Often combined with vocal fold and ventricle surgery so difficult to make fair clinical assessments

o Studies utilize subjective data to evaluate noise and often increased performance

o Laryngoplasty plus ventricle/vocal fold surgery

• 106 Draft horses 72% reduction in noise (Kraus BM Vet Surg 2003532: 530-38)

• 48% noise reduction in 40 race horses

• The higher the degree of abduction, the more noise made. (Russell et al AP JAVMA 1994;204:1235-4)

• 75% had noise reduction in 168 racehorses, (80% had ventriculectomy) (Hawkins et al Vet Surg 1997;26:484-491)

• 73% noise elimination in mixed population of 200 horses (Dixon et al EVJ 2003;35:397-401)

• Laser-assisted ventriculocordectomy

o 23 horses with laryngeal hemiplegia treated with LAVC alone

o All had abnormal respiratory noise

o 48% had concurrent exercise intolerance

o 86% had complete resolution of abnormal noise

o 80% had resolution of exercise intolerance

Based on experimental and clinical evalutions which procedure is best?

• Which surgical procedure reduces sound more?

o Bilateral ventriculocordectomy and laser assisted ventriculocordectomy reduces some indices of sound to baseline levels

o With laryngoplasty sound indices improve but do not return to baseline

o Laser vocal cordectomy ineffective

• How long before improvement in sound noted?

o LAVC 60 days

o BVC 90 days

o Laryngoplasty 30 days

• How long before improvement in exercise intolerance?

o BVC - 90 days

o LAVC – 60 days

o Laryngoplasty – 30 days

• Which procedure is most effective in improving exercise intolerance?

o Laryngoplasty and LAVC equally effective in alleviating airway obstruction

• Will this hold true in the racehorse?

• Will this hold true over time?