J. R. GILLESPIE AND W. S. TYLER 
227 
ACKNOWLEDGMENT 
We wish to thank Miss J. A. Nowell, Depart- 
ment of Anatomy, University of California, 
Davis, for the scanning electron micrographs. 
These studies were supported in hand by NIH 
grants ES AP 00628 and FR 06138. 
REFERENCES 
1. Gillespie, J. R. and Tyler, W. S. Chronic alveolar 
emphysema in the horse. Adv. Vet. Sci. Comp. Med. 
13:59-99, 1969. 
2. Tyler, W. S. and Gillespie, J. R. Structural and 
functional alterations in horses with emphysema. 
Proc. Symp. Animal Models for Biomedical Re- 
search II, Nat. Acad. Sci., 1969. 
3. Stoomer, 0., Uber das chronische vesiculare 
Emphysema namentlich der Pferde lunge. Deutsche 
Zeitschrift furr Thiermedizin und Vergleichende 
Pathologie. 13:97-127, 1887. 
4. Foley, P. D. and Lowell, F. C. Equine centrolob- 
ular emphysema with further observations on the 
pathology of heaves. Am. Rev. Resp. Dis. 93:17-21, 
1966. 
5. Tyler, W. S., Gillespie, J. R. and Nowell, J. A. 
Symposium on pulmonary and cardiac function, I. 
modern function morphology of the equine lung. 
Eg. Vet. J. 3:1-11, 1970. 
6. Weibel, E. R. Airways and respiratory surface in 
the lung. Eds. A. A. Liebow and D. E. Smith. 
Williams and Wilkins Co., Baltimore, p. 5, 1968. 
7. Gillespie, J. R. and Tyler, W. S. Quantitative 
electron microscopy of the interalveolar septa of 
horse lung. Am. Rev. Resp. Dis. 95:477-483, 1967. 
8. Gillespie, J. R. and Tyler, W. S. Capillary and 
cellular changes in alveolar walls of emphyse- 
matous horse lungs. Am. Rev. Resp. Dis. 95:484- 
489, 1967. 
9. Leith, D. E. and Gillespie, J. R. Respiratory 
mechanics of normal horses and one with chronic 
obstructive lung disease. (Abstract) Fed. Proc, 
April, 1971. 
10. Nowell, J. A., Gillespie, J. R. and Tyler, W. S. 
Scanning electron microscopy of chronic pulmonary 
emphysema: A study of the equine model. (Ab- 
stract) Proc. 4th SEM Symp. IIT Res. Inst., 
Chicago, April, 1971. 
11. Pratt, P. C. and Kilburn, K. H. A modern concept 
of the emphysemas based on correlation of structure 
and function. Human Path. 1:443-463, 1970. 
DISCUSSION 
H. Calderwood, University of Florida, 
Gainesville: I'd like to know your opinion on 
the role that allergic alveolitis might play in the 
clinical picture of heaves in the horse. 
Dr. Gillespie : Well, I don't really believe it 
has been shown that there's a marked alveolitis 
in these animals. For example, if you compare 
the reaction in the horse having bronchiolitis 
and the sheep having frank alveolitis, the re- 
sponse is quite different. In other words, you 
do not see the hypertrophy of the alveolar lin- 
ing cells, particularly the type II cells, in the 
horse as you do in the sheep. So, the correlation 
between those two diseases is not good. I have 
never seen a reaction that I felt was an inflam- 
matory alveolitis in a horse with heaves, or with 
emphysema, or with bronchiolitis. 
Dr. Calderwood: I'd also like to know how 
you do your maximum forced expiratory rates 
in the horses. 
Dr. Gillespie: These horses are suspended 
in a body sling and anesthetized. Through a 
tracheal cannula, the animal's lung is inflated 
to total lung capacity, or 30 cm of water. He 
then expires into a bank of evacuated drums. 
Sung S. Park, Yeshiva University, Bronx, 
N.Y. : The forced expiratory flow rate at FRC 
is reduced in the horse with emphysema. I 
guess the cause of this flow limitation could be 
related to a narrowing of small airways, or per- 
haps the collapsability of the large airways. 
Can you comment on this ? 
Dr. Gillespie: I think your surmise is cor- 
rect as far as what is the limiting factor in the 
maximum expiratory flow rate. We found that 
there's a marked deviation or variation in the 
amount of membranous tissue in the trachea of 
even normal horses, and so it's not terribly 
clear to us yet as to where the most important 
limitation is. The hypothesis is that the limiting 
point along the airways moves toward the al- 
veoli. There's a greater or increasing loss of 
elasticity of the lung, but we've not established 
where the equal pressure point is or where the 
closing point is along the airway. 
Dr. Park : What is the incidence of bronchitis 
in the horse with emphysema? 
Dr. Gillespie : We find that in the horse with 
emphysema there may or may not be bronchitis, 
or there may or may not be evidence of bron- 
chiolitis. The two diseases do co-exist very fre- 
quently, but we have often seen emphysema 
without evidence of active bronchitis or bron- 
chiolitis. 
