- Email: [email protected]
Tracheal morphometrics in the Thoroughbred horse
Refereed
TRACHEAL MORPHOMETRICS IN THE THOROUGHBRED HORSE Rodrigo Ramos de Freitas, DVM1; Fabio Celidonio Pogliani1; Nivaldo Moretti, Jr1: Eduardo Toshio Irino1; Angelo João Stopiglia, DVM, PhD1; Romeu Macruz, DVM2; Denise Tabacchi Fantoni, DVM, PhD1; Fabio Biscegli Jatene, MD, PhD3
SUMMARY Equine tracheal lesions have been associated with the orotracheal intubation procedure. These lesions may occur because of differences in the dimensions of the endotracheal tube and the trachea. The importance of the dimensions of the trachea for studies on respiratory mechanics and the lesions produced by the endotracheal tubes encouraged us to determine the size of trachea of the Thoroughbred horse. This study determined and compared the length and internal diameters of the tracheas from 59 Thoroughbred horses, 35 males and 34 females, weighing between 400 kg and 500 kg, and free of signs of respiratory or cardiopulmonary diseases. The tracheas were removed from the horses between 2 and 12 hours after death. The internal diameters were measured in tracheal rings one, twenty, forty and the last before the carina. The length of each trachea was measured in both the normal and extended state. The number of tracheal rings was also determined. In the unstretched trachea, the width of the last tracheal ring and the number of tracheal rings were significantly greater in males than females. The results of this study provide information for better design and manufacturing of endotracheal tubes and as basic information for further studies on equine respiratory mechanics. INTRODUCTION The trachea has been widely studied with the purpose of better understandings of respiratory physiology1,2,3 and mechanics.4,5,6,7 It has been shown that the increase in the total pulmonary resistance during exercise in equines is due, Authors’ addresses : 1 Department of Surgery - School of Veterinary Medicine - University of Sao Paulo. 2 Jockey Club of Sao Paulo - Brazil - Pathology Service. 3 INCOR - Instituto do Coração - F.M. - USP.
240
in part, to extra and intrathoracic dynamic collapse of the trachea during inspiration and expiration.8 Lekeux and colleagues studied the effects of shape, age and extension on the compliance of the equine tracheal segments, and one of the conclusions was that hyperextension of the neck during exercise would partly facilitate respiration by elongating the trachea and by decreasing its collapsibility.9 Another important aspect are equine tracheal lesions associated with the orotracheal intubation procedure. Several studies have shown that these lesions were frequently related to pharyngeal trauma,10 retroversion of the epiglottis11 and lesions such as erythema and ulceration.12,13 In addition, it has been demonstrated that tracheitis and pressure necrosis can be caused by endotracheal tubes used for the delivery of inhalatory anesthetics.14 These lesions may occur because the size and the shape of the endotracheal tube does not fit correctly in the trachea. Lodge and collaborators studied the tracheal dimensions in horses and cattle in relation to endotracheal tube size.15 The tracheal ring 15 centimeters caudal to the cricoid cartilage was measured. The authors concluded that an endotracheal tube with external diameter of 31.5 to 50.0 millimeters would satisfy the requirements for adult horses. The lesions produced by endotracheal tubes and the importance of the trachea size and extension patterns for the studies on respiratory mechanics encouraged us to perform studies to determine the size of trachea of the Thoroughbred. This paper reports the length and diameter of the trachea in male and female Thoroughbred horses weighing between 400 kg and 500 kg. MATERIALS AND METHODS Animals Fifty-nine Thoroughbred horses, 35 males and 24 JOURNAL OF EQUINE VETERINARY SCIENCE
females, weighing between 400 kg and 500 kg were used. There were no significant differences between the weights and ages (Table 1). All horses were from the Necropsy Service of the Jockey Club of Sao Paulo - Brazil. The animals were euthanized due to fractures that occurred during races. Signs of respiratory or cardiopulmonary diseases were absent in all horses. METHODS The tracheas were removed from the horses between 2 and 12 hours after death, in order to standardize the contraction state of the muscles and to minimize the variability due to any post-mortem changes. The tracheas of the horses examined in this study were divided in three regions. The first was from ring 1 to 19, the second from ring 20 to 39 and the third from ring 40 to the last tracheal ring before the carina. The first, the twentieth, the fortieth and the last tracheal ring before the carina (Figure 1) were selected to establish relations between them and to standardize the measurements of the entire trachea.
Figure state.
Figure 1. The anatomical position of the trachea of a Thoroughbred horse. The arrows indicate the tracheal rings measured in this study.
3.
Photograph of the trachea of a horse in the extended
The internal diameters, height and width, were measured in each tracheal ring (Figure 2 and Figure 3). The length of the trachea in the unstretched and extended state, as well as the number of the tracheal rings, were also determined for all equines. With the help of two assistants, each trachea was extended to its maximum length and securely fixed to a table with three nails (Figure 3). All measurements were made by the same person using a caliper ruler. a Statistics Statistical analysis of the data was performed using the Student t test. Statistical significance was determined at p < 0.05. For the relations between the tracheal rings, the Anderson-Darling test, the non-parametric Friedman’s test and the Wilcoxon test were used. RESULTS
Figure 2. Photograph of the cross-section of tracheal ring (20) of the horse. Volume 21, Number 5, 2001
Tracheal measurements and the relations between 241
Table 1. Measurements of the internal diameters of the tracheal rings from male and female Thoroughbred horses weighing between 400 kg and 500 kg (Mean ± SD). Variables Weight (Kg)
Sex Males (35)
Females (24)
445.61±23.56
444.78± 24.04
Age (months) 50.72±21.27 Normal length (cm) 78.28±4.03 Width of tracheal ring 5.04±0.58 1 (cm) Height of tracheal 4.26±0.49 ring 1 (cm) Width of tracheal ring 5.84±0.40 20 (cm) Height of tracheal 3.49±0.48 ring 20 (cm) Width of tracheal ring 5.99±0.46 40 (cm) Height of tracheal 3.54±0.58 ring 40 (cm) Width of the last 5.50±0.64 tracheal ring (cm) Height of the last 4.34±0.54 tracheal ring (cm) Number of tracheal 52±2.36 rings
Signific. ns
49.75± 24 .12 ns 75.39±5.27 p < 0.025 5.05±0.49 ns 4.39±0.54
ns
5.54±0.95
ns
3.48±0.69
ns
5.57±0.45
ns
3.52±0.40
ns
4.98±0.60 4.28±0.40 50.31±2.62
p < 0.0028 ns p < 0.0124
ns: not significant
Table 2. Correlations between the width of the 1, 20, 40 and last tracheal ring of Thoroughbred horses (males and females) weighing between 400 kg and 500 kg. Ring 1 Ring 1 Ring 20 ns Ring 40 ns Last ns tracheal ring ns: not significant
Ring 20 – – 0.451 ns
Ring 40
last tracheal ring
– ns
–
Table 3. Correlations between the height of the 1, 20, 40, and last tracheal ring of Thoroughbred horses (males and females) weighing between 400 kg and 500 kg. Ring 1 Ring 20 Ring 40 Last tracheal ring
Ring 1 – ns ns 0.603
Ring 20 – 0.720 ns
Ring 40 – ns
last tracheal ring
–
ns: not significant
tracheal rings are shown in Tables 1, 2 and 3. The unstretched length of the trachea, the width of the last tracheal ring and the number of tracheal rings in male horses were significantly greater than in the females (p < 0.025, p < 0.0028, p < 0.0124, respectively - Table 1). Comparing the width and height of rings 1, 20, 40 and the last tracheal ring, the first and last tracheal rings 242
were similar in height and rings 20 and 40 were similar in both height and width. No significant similarities were observed when comparing the height and width of either the first or last tracheal ring with those of rings 20 and 40 (Tables 2 and 3). DISCUSSION No significant differences in tracheal measurements were found between the males and females when the trachea was extended. This may be due to the differences in the compliance of trachea of the female. The difference in the length of the trachea in the unstretched state was probably due the greater number of tracheal rings in males (p < 0.0124). In horses, the shape of the trachea is an important factor modulating the mechanical properties of the trachea.9 During intense exercise when high levels of ventilation are required, horses having an ellipsoidal trachea may be at a disadvantage compared to those having a more circular trachea.9 In all tracheal rings measured (first, twentieth, fortieth and the last), the internal diameters indicated a predominance of an elliptic shape of the tracheas of the horses examined in this study. It was also observed that the tracheal rings were significantly different, showing similarities only with the ring 20 and ring 40 (height and width) and with the ring 1 and the last tracheal ring (height). With regard to tracheal lesions,12,13 we believe that the occurrence of these lesions following orotracheal intubation in horses is mainly related to the elliptical shape of the trachea. Almost all endotracheal tubes are designed in a circular shape, which probably influences the occurrence of these lesions. The results of this study suggest that endotracheal tubes should be manufactured to fit the shape of the trachea. Additionally, the use of endotracheal tubes made of compliant silicone material may also help to prevent these lesions.10 CONCLUSION Comparisons of the measurements of the tracheas of male and female Thoroughbreds, significant differences were found in the unstretched tracheal length, in the number of tracheal rings and the width of the last tracheal ring. Comparing the height and width of ring 1, 20, 40 and last tracheal ring, similarities were identified between ring 20 and 40 (height and width) and ring 1 and the last tracheal ring (height). We believe that the results of this study provide some very important information for better design and manufacturing of endotracheal tubes and basic information for further studies on the respiratory mechanics in horses.
JOURNAL OF EQUINE VETERINARY SCIENCE
FOOTNOTES a
Mitutoyo Metrology Center, IN, USA.
REFERENCES 1. Leith DE: Mammalian Tracheal Dimensions: Scaling and Physiology. Journal Applied Physiology: Respiratory Environment Exercise Physiology 1982;55(1):196-200. 2. Mead J: Expiratory Flow Limitation: A Physiologist Point of View. Federation Proc 1980;39:2771-2775. 3. Turino GM, Lourenco RV, McCracken GH: Role of Connective Tissues in Large Pulmonary Airways. Journal of Applied Physiology 1968;25(6):645-653. 4. Bennet FM and Tenney SM: Comparative Mechanics of Mammalian Respiratory System. Respiration Physiology 1982;49:31-140. 5. Leith DE, Lowe R, Gillespie JR: Mechanics of Baleen Whale’s Lungs. Federation Proc 1972;31:335-337. 6. Art T, Lekeux P: Mechanical Properties of Isolated Equine Trachea. Research in Veterinary Science 1991;50(1):55-60.
Volume 21, Number 5, 2001
7. Art T, Anderson LS, Robert CA, Woakes AJ, Butler PJ, Snow DH and Lekeux P: Mechanics of Breathing During Strenuous Exercise in Thoroughbred Horses. Respiration Physiology 1990;82(3):279-294. 8. Art T, Serteyn D, Lekeux P: Effect of Exercise on Partitioning of Equine Respiratory Resistence. Equine vet J 1988;20:268-273. 9. Art T and Lekeux P: The Effect of Shape, Age and Extension on the Compliance of Equine Tracheal Segments. Veterinary Research Communications 1991;15(2):135-146. 10. Brock KA: Pharyngeal Trauma From Endotracheal Intubation in a Colt. JAVMA 1985;187(9):944-946. 11. Dodman NH, Koblik PD, Court MH: Retroversion of the Epiglottis as a Complication of Endotracheal Intubation in the Horse. Veterinary Surgery 1986;15(3):275-278. 12. Heath RB, Steffey EP, Thurmon JC, et al: Laringotracheal Lesions Following Routine Orotracheal Intubation in the Horse. Equine Vet J 1989;21(6):434-437. 13. Freitas RR, et al: Lesões das Vias Aéreas Superiores Após a Intubação Endotracheal em Equinos. Brasilian Journal of Veterinary Research and Animal Science 1997;34(2):92-98. 14. Freeman DE: Trachea. In: Equine Respiratory Disorders (Beech J. ed) Philadelphia, PA: Lea & Febiger, 1991;pp 389-402. 15. Lodge D: A Survey of Tracheal Dimensions in Horses and Cattle in Relation to Endotracheal Tube Size. The Veterinary Record 1969;85:300-303.
243
TRACHEAL MORPHOMETRICS IN THE THOROUGHBRED HORSE Rodrigo Ramos de Freitas, DVM1; Fabio Celidonio Pogliani1; Nivaldo Moretti, Jr1: Eduardo Toshio Irino1; Angelo João Stopiglia, DVM, PhD1; Romeu Macruz, DVM2; Denise Tabacchi Fantoni, DVM, PhD1; Fabio Biscegli Jatene, MD, PhD3
SUMMARY Equine tracheal lesions have been associated with the orotracheal intubation procedure. These lesions may occur because of differences in the dimensions of the endotracheal tube and the trachea. The importance of the dimensions of the trachea for studies on respiratory mechanics and the lesions produced by the endotracheal tubes encouraged us to determine the size of trachea of the Thoroughbred horse. This study determined and compared the length and internal diameters of the tracheas from 59 Thoroughbred horses, 35 males and 34 females, weighing between 400 kg and 500 kg, and free of signs of respiratory or cardiopulmonary diseases. The tracheas were removed from the horses between 2 and 12 hours after death. The internal diameters were measured in tracheal rings one, twenty, forty and the last before the carina. The length of each trachea was measured in both the normal and extended state. The number of tracheal rings was also determined. In the unstretched trachea, the width of the last tracheal ring and the number of tracheal rings were significantly greater in males than females. The results of this study provide information for better design and manufacturing of endotracheal tubes and as basic information for further studies on equine respiratory mechanics. INTRODUCTION The trachea has been widely studied with the purpose of better understandings of respiratory physiology1,2,3 and mechanics.4,5,6,7 It has been shown that the increase in the total pulmonary resistance during exercise in equines is due, Authors’ addresses : 1 Department of Surgery - School of Veterinary Medicine - University of Sao Paulo. 2 Jockey Club of Sao Paulo - Brazil - Pathology Service. 3 INCOR - Instituto do Coração - F.M. - USP.
240
in part, to extra and intrathoracic dynamic collapse of the trachea during inspiration and expiration.8 Lekeux and colleagues studied the effects of shape, age and extension on the compliance of the equine tracheal segments, and one of the conclusions was that hyperextension of the neck during exercise would partly facilitate respiration by elongating the trachea and by decreasing its collapsibility.9 Another important aspect are equine tracheal lesions associated with the orotracheal intubation procedure. Several studies have shown that these lesions were frequently related to pharyngeal trauma,10 retroversion of the epiglottis11 and lesions such as erythema and ulceration.12,13 In addition, it has been demonstrated that tracheitis and pressure necrosis can be caused by endotracheal tubes used for the delivery of inhalatory anesthetics.14 These lesions may occur because the size and the shape of the endotracheal tube does not fit correctly in the trachea. Lodge and collaborators studied the tracheal dimensions in horses and cattle in relation to endotracheal tube size.15 The tracheal ring 15 centimeters caudal to the cricoid cartilage was measured. The authors concluded that an endotracheal tube with external diameter of 31.5 to 50.0 millimeters would satisfy the requirements for adult horses. The lesions produced by endotracheal tubes and the importance of the trachea size and extension patterns for the studies on respiratory mechanics encouraged us to perform studies to determine the size of trachea of the Thoroughbred. This paper reports the length and diameter of the trachea in male and female Thoroughbred horses weighing between 400 kg and 500 kg. MATERIALS AND METHODS Animals Fifty-nine Thoroughbred horses, 35 males and 24 JOURNAL OF EQUINE VETERINARY SCIENCE
females, weighing between 400 kg and 500 kg were used. There were no significant differences between the weights and ages (Table 1). All horses were from the Necropsy Service of the Jockey Club of Sao Paulo - Brazil. The animals were euthanized due to fractures that occurred during races. Signs of respiratory or cardiopulmonary diseases were absent in all horses. METHODS The tracheas were removed from the horses between 2 and 12 hours after death, in order to standardize the contraction state of the muscles and to minimize the variability due to any post-mortem changes. The tracheas of the horses examined in this study were divided in three regions. The first was from ring 1 to 19, the second from ring 20 to 39 and the third from ring 40 to the last tracheal ring before the carina. The first, the twentieth, the fortieth and the last tracheal ring before the carina (Figure 1) were selected to establish relations between them and to standardize the measurements of the entire trachea.
Figure state.
Figure 1. The anatomical position of the trachea of a Thoroughbred horse. The arrows indicate the tracheal rings measured in this study.
3.
Photograph of the trachea of a horse in the extended
The internal diameters, height and width, were measured in each tracheal ring (Figure 2 and Figure 3). The length of the trachea in the unstretched and extended state, as well as the number of the tracheal rings, were also determined for all equines. With the help of two assistants, each trachea was extended to its maximum length and securely fixed to a table with three nails (Figure 3). All measurements were made by the same person using a caliper ruler. a Statistics Statistical analysis of the data was performed using the Student t test. Statistical significance was determined at p < 0.05. For the relations between the tracheal rings, the Anderson-Darling test, the non-parametric Friedman’s test and the Wilcoxon test were used. RESULTS
Figure 2. Photograph of the cross-section of tracheal ring (20) of the horse. Volume 21, Number 5, 2001
Tracheal measurements and the relations between 241
Table 1. Measurements of the internal diameters of the tracheal rings from male and female Thoroughbred horses weighing between 400 kg and 500 kg (Mean ± SD). Variables Weight (Kg)
Sex Males (35)
Females (24)
445.61±23.56
444.78± 24.04
Age (months) 50.72±21.27 Normal length (cm) 78.28±4.03 Width of tracheal ring 5.04±0.58 1 (cm) Height of tracheal 4.26±0.49 ring 1 (cm) Width of tracheal ring 5.84±0.40 20 (cm) Height of tracheal 3.49±0.48 ring 20 (cm) Width of tracheal ring 5.99±0.46 40 (cm) Height of tracheal 3.54±0.58 ring 40 (cm) Width of the last 5.50±0.64 tracheal ring (cm) Height of the last 4.34±0.54 tracheal ring (cm) Number of tracheal 52±2.36 rings
Signific. ns
49.75± 24 .12 ns 75.39±5.27 p < 0.025 5.05±0.49 ns 4.39±0.54
ns
5.54±0.95
ns
3.48±0.69
ns
5.57±0.45
ns
3.52±0.40
ns
4.98±0.60 4.28±0.40 50.31±2.62
p < 0.0028 ns p < 0.0124
ns: not significant
Table 2. Correlations between the width of the 1, 20, 40 and last tracheal ring of Thoroughbred horses (males and females) weighing between 400 kg and 500 kg. Ring 1 Ring 1 Ring 20 ns Ring 40 ns Last ns tracheal ring ns: not significant
Ring 20 – – 0.451 ns
Ring 40
last tracheal ring
– ns
–
Table 3. Correlations between the height of the 1, 20, 40, and last tracheal ring of Thoroughbred horses (males and females) weighing between 400 kg and 500 kg. Ring 1 Ring 20 Ring 40 Last tracheal ring
Ring 1 – ns ns 0.603
Ring 20 – 0.720 ns
Ring 40 – ns
last tracheal ring
–
ns: not significant
tracheal rings are shown in Tables 1, 2 and 3. The unstretched length of the trachea, the width of the last tracheal ring and the number of tracheal rings in male horses were significantly greater than in the females (p < 0.025, p < 0.0028, p < 0.0124, respectively - Table 1). Comparing the width and height of rings 1, 20, 40 and the last tracheal ring, the first and last tracheal rings 242
were similar in height and rings 20 and 40 were similar in both height and width. No significant similarities were observed when comparing the height and width of either the first or last tracheal ring with those of rings 20 and 40 (Tables 2 and 3). DISCUSSION No significant differences in tracheal measurements were found between the males and females when the trachea was extended. This may be due to the differences in the compliance of trachea of the female. The difference in the length of the trachea in the unstretched state was probably due the greater number of tracheal rings in males (p < 0.0124). In horses, the shape of the trachea is an important factor modulating the mechanical properties of the trachea.9 During intense exercise when high levels of ventilation are required, horses having an ellipsoidal trachea may be at a disadvantage compared to those having a more circular trachea.9 In all tracheal rings measured (first, twentieth, fortieth and the last), the internal diameters indicated a predominance of an elliptic shape of the tracheas of the horses examined in this study. It was also observed that the tracheal rings were significantly different, showing similarities only with the ring 20 and ring 40 (height and width) and with the ring 1 and the last tracheal ring (height). With regard to tracheal lesions,12,13 we believe that the occurrence of these lesions following orotracheal intubation in horses is mainly related to the elliptical shape of the trachea. Almost all endotracheal tubes are designed in a circular shape, which probably influences the occurrence of these lesions. The results of this study suggest that endotracheal tubes should be manufactured to fit the shape of the trachea. Additionally, the use of endotracheal tubes made of compliant silicone material may also help to prevent these lesions.10 CONCLUSION Comparisons of the measurements of the tracheas of male and female Thoroughbreds, significant differences were found in the unstretched tracheal length, in the number of tracheal rings and the width of the last tracheal ring. Comparing the height and width of ring 1, 20, 40 and last tracheal ring, similarities were identified between ring 20 and 40 (height and width) and ring 1 and the last tracheal ring (height). We believe that the results of this study provide some very important information for better design and manufacturing of endotracheal tubes and basic information for further studies on the respiratory mechanics in horses.
JOURNAL OF EQUINE VETERINARY SCIENCE
FOOTNOTES a
Mitutoyo Metrology Center, IN, USA.
REFERENCES 1. Leith DE: Mammalian Tracheal Dimensions: Scaling and Physiology. Journal Applied Physiology: Respiratory Environment Exercise Physiology 1982;55(1):196-200. 2. Mead J: Expiratory Flow Limitation: A Physiologist Point of View. Federation Proc 1980;39:2771-2775. 3. Turino GM, Lourenco RV, McCracken GH: Role of Connective Tissues in Large Pulmonary Airways. Journal of Applied Physiology 1968;25(6):645-653. 4. Bennet FM and Tenney SM: Comparative Mechanics of Mammalian Respiratory System. Respiration Physiology 1982;49:31-140. 5. Leith DE, Lowe R, Gillespie JR: Mechanics of Baleen Whale’s Lungs. Federation Proc 1972;31:335-337. 6. Art T, Lekeux P: Mechanical Properties of Isolated Equine Trachea. Research in Veterinary Science 1991;50(1):55-60.
Volume 21, Number 5, 2001
7. Art T, Anderson LS, Robert CA, Woakes AJ, Butler PJ, Snow DH and Lekeux P: Mechanics of Breathing During Strenuous Exercise in Thoroughbred Horses. Respiration Physiology 1990;82(3):279-294. 8. Art T, Serteyn D, Lekeux P: Effect of Exercise on Partitioning of Equine Respiratory Resistence. Equine vet J 1988;20:268-273. 9. Art T and Lekeux P: The Effect of Shape, Age and Extension on the Compliance of Equine Tracheal Segments. Veterinary Research Communications 1991;15(2):135-146. 10. Brock KA: Pharyngeal Trauma From Endotracheal Intubation in a Colt. JAVMA 1985;187(9):944-946. 11. Dodman NH, Koblik PD, Court MH: Retroversion of the Epiglottis as a Complication of Endotracheal Intubation in the Horse. Veterinary Surgery 1986;15(3):275-278. 12. Heath RB, Steffey EP, Thurmon JC, et al: Laringotracheal Lesions Following Routine Orotracheal Intubation in the Horse. Equine Vet J 1989;21(6):434-437. 13. Freitas RR, et al: Lesões das Vias Aéreas Superiores Após a Intubação Endotracheal em Equinos. Brasilian Journal of Veterinary Research and Animal Science 1997;34(2):92-98. 14. Freeman DE: Trachea. In: Equine Respiratory Disorders (Beech J. ed) Philadelphia, PA: Lea & Febiger, 1991;pp 389-402. 15. Lodge D: A Survey of Tracheal Dimensions in Horses and Cattle in Relation to Endotracheal Tube Size. The Veterinary Record 1969;85:300-303.
243