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Year: 1998

Evaluation of the upper respiratory tract in the horse during treadmillexercise - A review Part ll: Measurement of upper airway flow mechanics

Kästner, Sabine Beate Rita ; Weishaupt, Michael A ; Townsend, Hugh G G

Abstract: Literature pertaining to the evaluation of the upper respiratory tract of the horse during exer-cise was reviewed. Articles were found by searching two databases. Videoendoscopy of the upper airwaysduring exercise is presented in part I of this review. Part II describes upper airway pressure and airflowmeasurements for objective assessement of the prescence of a respiratory limitation. Different measure-ment techniques and definitions of upper airway pressure as well as airflow measurement techniques aredescribed. Upper airway pressures and flow indices increase linearly with increasing exercise. Airflowresistance as caused by laryngeal hemiplegia grade IV increases negative upper airway pressure and limitsinspiratory flow. Dorsal displacement of the soft palate alters both inspiratory and expiratory pressures.

Posted at the Zurich Open Repository and Archive, University of ZurichZORA URL: https://doi.org/10.5167/uzh-72594Journal ArticlePublished Version

Originally published at:Kästner, Sabine Beate Rita; Weishaupt, Michael A; Townsend, Hugh G G (1998). Evaluation of theupper respiratory tract in the horse during treadmill exercise - A review Part ll: Measurement of upperairway flow mechanics. Pferdeheilkunde, 14(1):43-50.

Sabine B. R. Kästner et al

Pferdeheilkunde 14 (1998) 1 (Januar/Februar) 43-50

Evaluation of the upper respiratory tract in the horseduring treadmill exercise - A reviewPart ll: Measurement of upper airway flow mechanicsSabine B. R. Kästnerl, M. A. Weishauptl and H.G.G Townsend2

1 Veterinär-Chirurgische Klinik der Universität Zürich, Zürich, Schweiz2 Department of Veterinary Internal Medicine, Western College of Veterinary Medicine, University of Saskatchewan SK S7N sBC, Canada

Summary

Literature pertaining to the evaluation of the upper respiratory tract of the horse during exercise was reviewed. Articles were found by sear-ching two databases. Videoendoscopy of the upper airways during exercise is presented in part I of this review. Part ll describes upper air-way pressure and airflow measurements for objective assessement of the prescence of a respiratory limitation. Different measurement tech-niques and definitions of upper airway pressure as well as airflow measurement techniques are described.Upper airway pressures and flow indices increase linearly with increasing exercise. Airflow resistance as caused by laryngeal hemiplegiagrade lV increases negative upper ainvay pressure and limits inspiratory flow. Dorsal displacement of the soft palate alters both inspiratoryand expiratory pressures.

keywords: horse, airflow, upper ainrvay pressure, flow resistance, flow-volume loop

Beurteilung der oberen Luftwege des Pferdes während der Belastung auf dem Laufband - Eine Literaturstudie

Teil ll: Messung der Atemmechanik der oberen Luftwege

Die vorliegende Literaturstudie beschäftigt sich mit der Untersuchung der oberen Atemwege des Pferdes unter Belastung auf einem Lauf-band. lm ersten Teil wurde die Belastungsendoskopie beschrieben. lm vorlregenden zweiten Teil werden Druck- und Atemstromstärkemes-sungen in den oberen Atemwegen dargestellt. Die Literaturdatenbanken Index Medicus (Medline) und Commonwealth Agricultural Bureaux(CAB) wurden nach den Begriffen ,,horse" or ,,equine" und ,,treadmill" abgefragt. Die Adikel, welche die oberen Atemwege betrafen wurdenmanuell ausgesucht. Die Abfrage erfolgte für den Zeitraum von ,,1966 bis heute".Die einfachste objeKive Methode zur Überprüfung der Funktion der oberen Atemwege ist die Messung der Druckgradienten entlang deroberen Atemwege. Dazu wird ein Katheter perkutan oder nasotracheal im proximalen Teil der Trachea und/oder im Pharynx platziert und dieDruckdifferenzen zwischen Trachea und Pharynx beziehungsweise Trachea und atmosphärischem Druck gemessen. In Tabelle 1 sind dieDruckgradienten für gesunde Pferde bei steigender Belastung zusammengefasst. Die Dorsalverlagerung des weichen Gaumens führt zu ei-nem geringeren Inspirationsdruck in Trachea und Pharynx, einem geringeren Exspirationsdruck im Pharynx und einem verstärkten Exspirati-onsdruck in der Trachea. Die Hemiplegia laryngis Grad lV verursacht hauptsächlich einen stark erhöhten Unterdruck bei der Inspiration.Die Druckfluktuationen zwischen Ein- und Ausatmung in dgn oberen Luftwegen sind sowohl von der Atemstromstärke als auch vom Atem-wegswiderstand abhängig. Deshalb sind zur genaueren Beurteilung Messungen der Atemstromstärke notwendig. Zur Messung der Atem-stromstärke wird am häufigsten ein Fleisch Pneumotachograph venvendet, daneben existieren verschiedene Ultraschall Messgräe. Normal-werte für Pferde ohne Beeinträchtigung der Funktion der oberen Luftwege sind in Tabelle 2 dargestellt. Die Hemiplegia laryngis Grad lV führtin Ruhe zu nicht messbaren Veränderungen des Atemstromes. Hingegen können im submaximalen Belastungsbereich bereits erste signifi-kante Veränderungen verschiedener inspiratorischer Atmungsparameter gemessen werden. Die maximde inspiratorische Atemstromstärkeist signifikant niedriger als bei gesunden Pferden.Eine Methode die sich nur auf die Messung der Atemstromstärke stützt und dadurch wenig invasiv ist, ist die Darstellung und Auswertungvon sogenannten ,,Tidal Breathing Flow Volume Loops" ffBVFL). Eine konekte Auswertung dieser Schleifen ist jedoch nur möglich bei ange-strebter Maximalatmung. Dies wird beim Pferd durch die Belastungsuntersuchung errreicht. Eine Hemiplegia laryngis Grad lV fühd dazu,dass die höchste maximale Atemstromstärke sehr früh eneicht wird in Kombination mit einer Limitierung des Luftflusses (Plateaubildung).Hauptsächlich die inspiratorischen Indices der TBVFLs sind verändert.Die Kombination einer Belastungsendoskopie mit einer der hier beschriebenen Methoden gilt als das derzeitige Optimum zur Beurteilung derFunktion der oberen Atemwege des Pferdes unter Belastung.

Schlüsselwörter Pferd, Atemstromstärke, Trachealdruck, Atemwegswiderstand, Atemstrom-Volumen Schleife

lntroduction

The importance of the evaluation of the upper respiratorytract function during exercise lies in the fact that many func-tional disorders are not apparent at rest. On the other handabnormal findings at rest do not necessarily mean a respi-

Pferdeheilkunde 14

ratory limitation during exercise (Williams et al., 1990a,1990b, Morris and Seeherman, 1991). ln additon, somemethods are not sensitive enough to diagnose mild diseasestages at rest.

43

Evaluation of the upper respiratory tract in the horse during treadmill exercise - Part ll: Measurement of upper airway flow mechanics

There are different methods of assessing upper respiratoryfunction in exercising horses. These include endoscopy,upper airway pressure measurement and aidlow measure-ment (pneumotachography). Recently there have beenmany advances in the techniques and the knowledge aboutthe diagnostic value of these tests. The purpose of this re-view is to list the different techniques of upper respiratorytract evaluation in the horse during exercise, and describetheir indications, usefulness and diagnostic value.Part I described exercise endoscopy. In Part ll the mea-surement of airflow and upper airuuay pressures are presen-ted.

Materialand Methods

The methods used for localization of the literature pertai-ning to the evaluation of the upper airuuays during exerciseare given in part I of this review (Kästner et al., 1998).

Results

U pper airvvay pressure measurements

TechniquesThe simplest test of upper airway function is the measure-ment of the pressure gradient along the upper airuuay. Se-veral measurement techniques and definitions for upper air-way pressure have been used. A catheter (polyethylene,polytetrafluoroethylene, teflon tubing) is placed percuta-neously through the wall of the trachea into the cranial partof the trachea (Derksen et al., 1986; Shappell et al., 1988;Funkquist et al., 1988; Williams et al., 1990a; Lumsden etal., 1993; Roethlisberger-Holm, 1993) or nasotracheally(Williams et al., 1990a; Williams et al., 1990b; Ducharme etal., 1994; Rehder et al., 7995)into the pharynx and the cra-nial part of the trachea. Williams and assistants (f990a)have shown that the pressure recordings via a transnasalcatheter are not different from recordings made by a trans-tracheal catheter but less invasive and therefore more suitablefor clinical use. The static pressure is measured by differen-tial pressure transducers and the pressure changes are re-corded continously during the respiratory cycle. Several dif-ferent definitions for upper airway pressure are reported:lntratracheal pressure (Funkquist et al., 19BB; Roethlisberger-Holm, 1993), the pressure difference between the pressurerecordings in the trachea and pressure recordings at thehorse's mouth (Derksen et al., 1986, Shapell et al., 1988;Lumsden et al., 1993), the difference between trachealpressure and atmospheric pressure (Williams et al., 1990a),the difference between tracheal and pharyngeal pressure(Ducharme et al., 1994; Rehder et al., 1995) and the diffe-rence between pharyngeal and mask pressure (Bayly et al.,7994). Most studies use the measurement of peak statictracheal and pharyngeal pressures to evaluate the functionof the upper respiratory tract based on the assumption thatpeak pressures cause collapse or vibration of the proximal

44

part of the airways. A study on repeatability and normal va-lues for measurements of pharyngeal and tracheal pressu-res (Ducharme et al., 1994) has shown that mean pressuremeasurements have better repeatability than peak pressuremeasurements. At least 96% of all mean oressure measu-rements were within 5 cm HrO of the mean value for anyhorse. At least 96% of all peak pressure measurementswere within 10 cm HrO of the mean peak pressure measu-rements for any horse.

Pressure Measurement during Exercise

Normal Function of the Upper Airvvays

Several experimental studies have shown that pressurealong the upper respiratory tract increases with increasingexercise fl-able 1). Because of the different definitions forupper airuray pressure it is difficult to directly compare theresults from the different research groups. Similar pressuresin the upper respiratory tract as during exercise can beachieved during nasal occlusion (Holcombe et al., 1996).

Abnormal Function of the Upper Airuays

Laryngeal Hemiplegia (LH)

Studies on experimentally induced laryngeal hemiplegiagrade lV (neurectomy or anesthesia of the recurrent nerve)agree on significantly increased (negative) inspiratory upperainruay pressures (Derksen et al., 1986; Funkquist et al.,1988; Shappell et al., 1988; Williams et al., 1990a; Lums-den et al., 1994; Ducharme et al., 1994) compared tohealthy horses. Williams and assrstants (1990a) also obser-ved a significant increase in expiratory pressure. Horseswith complete laryngeal hemiplegia were readily identifiedby measurement of tracheal and pharyngeal pressures(Ducharme et al., 1994), but it still needs to be determinedhow sensitive and useful these measurements are in lesssevere grades of LH.

Dorsal Displacement of the soft Palate (DDSP)

To correctly identify the occurence of DDSP in the exerci-sing horse it is necessary to perform endoscopy duringexercise. lt has been shown that the prescence of a 9 mmendoscope in the upper respiratory tract does not interferewith pressure measurements in the trachea and thepharynx (Ducharme et aL, 1994). Compared with clinicallynormal horses, horses with intermittent DDSP did not haveexcessive negative inspiratory pressures before displace-ment during exercise (Rehder et al., 7995). Displacement ofthe soft palate occured during inspiration, expiration or afterswallowing. Some horses displaced the soft palate at theinitiation of exercise, some at peak speed and some whileslowing down (,Qehder, et al., 7995,). But the same horse

Pferdeheilkunde 14

seems to displace consistently at the same time in thebreathing cycle when subjected to the exercise test repea-tedly. After displacement the ainruay pressures were signifi-cantly altered. Pharyngeal and tracheal inspiratory pressu-res were decreased, pharyngeal expiratory pressuredecreased and tracheal expiratory pressure increased(Rehder et al., 1995), indicating mainly an impairment of ex-piration.

Tab. 1: Normal values for peak pressures in the upper airways in exercising horses.

Normalwerte für Maximaldrücke in den oberen Atemwegen von Pferden in der Bewegung

Other Abnormalities

Complicated epiglottic entrapment (thick membrane, ul-cers) produced modest increases, uncomplicted entrap-ment and pharyngeal lymphoid hyperplasia grade lV produ-ced slight increases in inspiratory (negative) pressure.Arytenoid chondropathy produced pressure changes simi-lar to LH grade lV (/Villiams et al., 1990b).

Airflow Measurement

Techniques

Pressure can be affected by changes in flow rate as wellas changes in resistance (impedance) of the upper air-

Pferdeheilkunde 14

Sabine B. R. Kästner eI al.

ways. Therefore airflow needs to be measured to correctlyassess a respiratory limitation. Upper ainrrray resistance isdefined as the ratio of peak upper airway pressure andpeak airflow rates for a given inspiration or expiration. Air-flow is measured by a pneumotachograph or an ultrasonicflow meter in addition (Robinson, 1992).Mostly Fleisch pneumotachographs are used to measureairflow in humans and animals. A pneumotachograph

measures the pressure difference over a tube with knowndiameter and resistance and along a laminar flow profile.This pressure difference is directly proportional to the flow.Integration over time equals the ventilated volume. Themeasurement accuracy of this system depends on the ab-solute pressure, temperature and humidity of the gas.Derksen and assrsfants (1986) used in their early experi-ments two No. 4 Fleisch pneumotachographs (Dynascien-ces, Blue Bell, Pa, USA) mounted on a facemask. Later apneumotachograph with a diameter of 15.2 cm was deve-loped for the use in exercising horses (Shappell et al.,19BB; Belknap, et aL, 1990; Lumsden et aL, 7994). Atightfitting fiberglass mask mounted with the pneumotacho-graph is placed over the horse's nose. The mask allowsfree movement of the nostrils. A rubber shroud is used toseal the mask against the face. Pressure differences

InspiratoryTrachealPressure

ExpiratoryTrachealPressure

InspiratoryPharyngealPressure

ExpiratoryPharyngealPressure

Speed Author

-12 to -24

mm Hg

;öi;-5öcm HrO

6to8

mm ng

rä toää

cm HrO

-2O Io-26

cm HrO

10 Io 24

cm HrO

7 m/s

14m/s

Funkquist et al., 1988

o ä ni u,lÄ "

ii ä.'.," r' öö; q

Inspiratory Tracheal

-Atmospheric PressureExpiratory Tracheal-

-Atmospheric PressureSpeed Author

-29 to -30,6 cm HrO

-29.7+4cmHrO

11 7 to 12,6 cm HrO

1 1.9 t 1.5 cm HrO

gallop

7.2 m/s

Wllliams et al,, 1990

Shappell et al., 1988

lnspiratory Tracheal-Mask (mouth)Pressure

Expiratory Tracheal

-Mask (mouth) PressureSpeed Author

H 1.94 t0.22cmHrO

t - l i ) .ze i r . rs cm urö. .^^;- ^^^( - ) Jö.Ci + 3.V3 Cm H2U

(-) 27.4ö r s.äo cm Hrö

(-) 40.82 r 3.92 cm HrO

7.85 + 1.51 cm HrO

e.O7 + r.OO Crt' HrO

standing:-^; ; , :/C7o HH max

HR m;,--^, . .^/57o HH max.

ii r"i.

Lumsden et a::: 1994

Ce,tiiie et a,i., lsös

Abbreviations: 75% HR max.'. 75o/o of the maximal heart rate; HR max.: Maximal heafi rate

45

Evaluation of the upper respiratory tract in the horse during treadmill exercise - Part ll: Measurement of upper airway flow mechanics

across the pneumotachograph are measured with a diffe-rential pressure transducer (Model DP 45-22, ValidyneSales, Northridge, Ca, USA) and recorded on a physio-graph (Model 8188, Gould Inc., Madison Hts, Mich., USA)(Shappell et al., 1988; Belknap, et al., 1990; Lumsden etal., 1994).Ultrasonic flowmeters measure the transmission time of ul-trasound signals through a given flow channel. The speedof the gas flow is calculated from the difference of abso-lute transmission time of ultrasound beams with andagainst the airstream. With the known diameter of the flowchannel the respiratory flow can be calculated. Integrationof the flow over time gives the ventilated volume. Severaldifferent systems are in use for equine respiratory researchlike the Spiroson@ (Figure 1) [Spiroson Scientific, lslerBioengineering AG, Zurich, Switzerland (Buess et al.,1986; Weishaupt et al., 1995)1, an ultrasonic phase-shiftflowmeter [British patent application 8608906 (VVoakes etal., 1987)l and a density corrected pneumotachometer[UF2O2, Novex Instruments Inc. Redmond, WA, USA(Beadle et al., 1995)1.

Fig. 1: Horse equipped with a facemask and an ultrasonic flow-meter (Spiroson@) during exercise on a treadmill.

Pferd mit Atemmaske und Ultraschallgerät zur Messungder Atemstromstärke (Spiroson@) während der Bewe-gung auf dem Laufband.

Upper Airway Flow Mechanics during Exercise

Normal Function of the Upper Airvvays

Different experimental studies (Derksen et al., 1986; Shap-pell et al., 1988; Belknap et al., 1990; Lumsden et al.,1993; Lumsden et al., 1994; Connally and Derksen, 1994,Petsche et al., 1994; Guthrie et al., 1995) give normalvalues for horses without dysfunctions of the upper airway

46

f-able 2). These studies have shown that increasing speedprogressively increased respiratory frequency (f), tidalvolume (Vf), minute ventilation (VE), peak inspiratory flow(PlF), peak expiratory flow (PED, mean inspiratory flow(MlF), mean expiratory flow (MEF), peak inspiratory pres-sure (Pui), and peak expiratory pressure (Pue). Inspiratoryresistance (Zi) and expiratory resistance (Ze) remained un-changed during exercise (Derksen et al., 1986; Shappelletal, 1988; Belknap et al., 1990).

Abnormal Function of the Upper Aintrays

After surgically induced laryngeal hemiplegia grade 4 (neu-rectomy) no significant changes were observed at rest.Peak rnspiratory pressure (Pui) and inspiratory resistance(Zi) were significantly increased at speeds 4.2 m/s andgreater. Peak inspiratory flow was significantly decreased atspeed 4.3 m/s (Derksen et al., 1986) or 7.2 m/s and greater(Shappell et al., 1988; Belknap et al., 1990; Weishaupt etal., 1995). This inspiratory limitation leads to an increasedinspiratory time reflected in a significantly decreased expira-tory: inspiratory time ratio fl-e/Ti) at speeds of 4.2 m/s andgreater. Weishaupt and asslsfants (1995) observed additio-nally a significant decrease in tidal volume, minute ventilati-on and peak expiratory flow at submaximal exercise levelsin a reversible laryngeal hemiplegia model (anesthesia of theleft recurrent nerve), reflecting an inspiratory as well as anexpiratory limitation.

90

45

-45

-90

Volume ( l )

Fig. 2: Tidal Breathing Flow Volume Loop from a horse withlaryngeal hemiplegia grade lV at a heart rate of 200P200). Note the early peak flow and the plateau formati-on during inspiration.

Tidal Breathing Flow Volume Loop von einem Pferd mit He-miplegia laryngis Grad lV bei einer Herzfrequenz von 200(V200). Während der Inspiration sind die frühzeitige Spitzen-atemstromstärke und die Plateaubildunq zu beachten.

c.o

äU)c

U):\

=o

LL

c.9

'aXLrJ

15100 20

I

I

Pferdeheilkunde 14

Tab. 2: Upper airway flow mechanics in normal horses, effect of exercise.

Atemmechanik der oberen Atemwege, Einfluss der Belastung.

Abbreviat ions: HR=heartrate, f=respiratoryfrequency,W=tidal volume,VE=minutevent i lat ion,plp=peakinspiratoryf low,PEF=peak expiratory flow, MIF = mean inspiratory flow, MEF = mean expiratory flow, Pui = inspiratory pressure (tracheal pressure - maskpressure), Pue = expiratory pressure (tracheal pressure - mask pressure), Zi = inspiratory impedance, Ze = expiratory impedance Ti = in-spiratory time, Te = expiratory time, TelTi = ratio expiratory time : inspiratory time.

Different surgical procedures for the treatment of LH andDDSP have been evaluated with this method. lt could beshown that laryngoplasty alleviated the flow limitations of in-duced LH (Derksen et al., 1986; Shappell et al., 1988).Ventriculocordectomy additionally did not fufther improveupper airway function (Tetens et al., 1996). No improve-ment could be observed after ventriculectomy (Shappell etal., 1988) and subtotal arytenoideclomy (Belknap et al.,7990). Parlial arytenoidectomy improved respiratory flow li-mitations at submaximal exercise but at near maximal exer-cise some inspiratory flow limitations remained (Lumsden etal., 1994).

Sabine B. R. Kästner et al.

ty, specificity and repeatability of the test depends on pati-ents cooperation for maximal inhalation and exhalation(Lumsden et al., 1993).In human neonates and infants tidalbreathing flow volume loops I|BFVL) have been evaluated.This variation of the test lacks sensitivity and has great flowvariability compared to maximal breathing (Abramson et al.,7982,). Qualitative and quantitaive analysis of flow-volume-loops and airflow rates at rest in Standardbreds has shownlarge intra- and interhorse variations for the TBFVL indices(Lumsden et al., 1.993) reflecting different breathing strate-gies in the individual horse. This limits the clinical usefulnessof TBFVLS obtained in resting horses. During high-speed

treadmill exercise airflow of horses are near maximal brea-thing (Belknap et al., 1990). The coefficients of variation forTBFVL indices progressively decreased with increasingexercise level indicating that respiratory patterns becameless variable (Lumsden et al., 1993).Evaluation of upper airway function by TBFVLS requiresthe same equipment and near maximal exercise proto-cols as airflow measurements described above. Specificcomputer software allows the analysis of loop shapeand quantitative TBFVL indices (Petsche et al., 1994),Loops are usually calculated by the means of 10breaths, loop closure is accepted as adequate if there isless than 5 % difference in expiratory and inspiratory vo-lume.

Myectomy of the sternothyrohyoid muscle is often used asa treatment for DDSP. But in healthy horses myectomy in-creased the negative inspiratory pressures and inspiratoryresistance in the upper respiratory tracl (Holcombe et al.,1994).

Tidal Breathing Flow Volume Loops (TBFVL)

The clinical use of upper airu,ray pressure and impedancemeasurement is limited (Stick and Derksen, 1989, Williamset al., 1990b) because of its invasive nature. Flow-volumeanalysis is a common test for respiratory function in hu-mans because it is noninvasive and sensitive. But sensitivi-

Pferdeheilkunde 14

At rest

Speed

4.2mls

-HR 75 max11 m/s

-HR max

rn (t/minlf !1/minlw (Llve ivmin)PIF (Usec)

pir tu"""lPui (cm of HrO)

puö tö' öi H,öi

2i räÄ öi H,ö/üil2ä iCÄ o+r,özvil- . , .rr (sec)

i" ir""ffef i i

30.8+ 1.1 to 50 + 9

15.6 r 3.1 to 33 + 3

s Ca ; o 3e i; 6.0, ; o.e,147 + 0.08 to 151 .41 t 15.01

+gio.s ioz.z iö.ä4.9t1to7.9t1.1

1.94 rQ.221o2.4 +0.4

1.5 ;ö. , to r .e i o.+ö.Ca * o.öa io o.os i o.oa0.1 4 t 0.03 to 0.43 * 0. 1 1

oi.iq i o.og i; 1.ee ; o.6s

0.92 t 0.1 1 1o 2.23 t O.77

oeeiöos

143.6 + 18,5 to 185. + 3

67 .2 t 3.5 to 97.3 t 9.7

11.6e + o.e4 to rä.rr iö.e

950.23 r 59.02 to 1256 + 63

38 x.4.7 to 56.3 t 1.0

40j x.4.2to 47.5 x.4.5

20e+3Btä ü: is i t . i i

7.3 + 0.5 to 9.5 t 2

0.37 + o.06 tö ö.sä ; 0.ö6

0.16; o.öztö ö.äs; ö.06

0.32 t 0.04 to 0.38 IO.OZ

0.33 r 0.04 to 0.39 + 0.03

o.e; * o.oä

217 . 17 + 2.37 Io 225.5 + 4.92

92.6 + 15.16 to 117 .4 19.25

ti.ei ,l.t;iti ti.zC *f.zi1295.97 + 127 .52 to 1B5B + 109

t i .zz *e.,elt" zs.sä. s.ää65.43 + 5.3 to 66.05 r 5.58

äe.sz * a.gsr r.äo iä.ar0.53 + 0.04

0.19 + 0.06

ö.zs r o.ozeO.28 tO.O24

0.98 10.05

47

Evaluation of the upper respiratory tract in the horse during treadmill exercise - Part ll: Measurement of upper airway flow mechanics

Normal Function of the Upper Airvvays

At rest four basic shapes occured. The inspiratory curvewas mono-, bi- or triphasic with PIF early or late in inspirati-on, the expiratory flow was biphasic with peak flow early inexpiration. During exercise inspiratory flow was monopha-sic, biphasic or a combination of both, predomaninantly abiphasic inspiratory shape occured. The expiratory curvewas mono- or biphasic. (Lumsden et al., 1993).Representative values for TBFVL indices in healthy horsesare given by Lumsden and assrstants (1993) and Petscheand assistants, (1 994).

Abnormal Function of the Upper Airways

After surgically induced LH grade 4 (LRLN) no changes inloop shape were seen at rest (Lumsden et al., 1993). Du-ring submaximal and near maximal exercise loop shapeswere markedly altered. The inspiratory limb shows a peakflow early in inspiration followed by a marked reduction inairflow [plateau formation] (Figure 2). The expiratory curve isapproximately the same as in normal horses.After induced LH grade lV mainly the inspiratory indiceswere altered. PEF/PIF, the expiratory flow at 50% of the vo-lume : inspiratory flow at 50% of the volume ratio (EF 50/lF50) and TilTtot increased and PIF decreased significantly atsubmaximal and near maximal exercise. lF 50, lF 25 andTelTi decreased significantly at near maximal exercise com-pared to normal horses (Lumsden et al., 1993, Lumsden etal., 1994).Flow measurements in horses with DDSP are presently dif-ficult to pedorm because it is almost impossible to deter-mine when the horse displaces the palate without a con-current videoendoscopy (Rehder et al., 7995). In addition,horses with DDSP tend to start mouth breathing. Mouthbreathing produces a high amount of saliva which can in-terfere with the flow measurement technioue.In conclusion, examination of the upper respiratory tractduring exercise on high-speed treadmills can be a usefultool in evaluation of upper respiratory tract disorders. lt hasbeen shown that many functional disorders only occur du-ring high intensity exercise. On the other hand some abnor-malities observed at rest do not produce a functional disor-der during exercise. An evaluation on the treadmill shouldnot be used as a routine diagnostic tool. A good history,careful physical examination and endoscopic examinationat rest are necessary before dynamic evaluation is indica-ted. Many horses with a functional upper airway obstructionduring exercise have a history of an abnormal respiratorynoise during exercise or suggestive diagnostic findings atexamination at rest. Videoendoscopy during treadmill exer-cise as a subjective technique already can accomplish agood assessment of the upper airuuay function. But a finaldiagnosis of the presence of a respiratory limitation can on-ly be made by the quantitative measurement of respiratorymechanics (airuray pressure and flow-volume measure-ment). Videoendoscopy coupled with these objective me-

48

thods is currently considered the optimum method to eva-luate upper airway function

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Art, T. and Lekeux, P. (1988): Respiratory airflow patterns in ponies atrest and during exercise. Can. J. Vet. Res.52, 299-303.

Bayly, W.M. Slocombe, R.F., Weidner, J.P. Schott, H.C. andHodgson, D,F. (199a): Influence of air movement, Facemask de-sign and exercise on upper ainvay, transpulmonary, and transdia-phragmatic pressures in Thoroughbred horses. Cornell Vet. 84,77-90.

Beadle, R.E., Guthrie, A.J. and Kou, A.H. (1995): Characterization of adensitiy-corrected ultrasonic pneumotachometer for horses. J. Ap-pl. Physiol. 78, 359-367.

Belknap, J.K., Derksen, F.J. Nickels, F.A. Stick, J.Ä. (1990): Failure ofsubtotal arytenoidectomy to improve upper airway flow mechanicsin exercising Standardbreds with induced laryngeal hemiplegia. Am.J. Vet. Res. 51,1481-1487.

Buess, C., Pietsch, P, Guggenbuehl, W. and Koller, EA (1986): Designand construction of a oulsed ultrasonic air flowmeter. IEEE Tran-sactions on Biomedical Engineering BME 33.

Connally, B.A. and Derksen, F.J. (199a): Tidal breathing flow-volumeloop analysis as a test of pulmonary function in exercising horses.Am. J. Vet. Res. 55, 589-594.

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Dr. Sabine Kästner, M Vet SciDr. M. A. Weishaupt

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