- Email: [email protected]
Growth potential of porcine reduced-size mature pulmonary lobar transplants
Growth potential of porcine reduced-size mature pulmonary lobar transplants The use of mature pulmonary lobes for pediatric lung transplantation has recently been described. Successful application of this technique could help alleviate the pediatric donor lung shortage. Whether an already mature lobe can grow by forming new alveolar units after transplantation into a developing recipient is not known. We therefore measured functional residual capacity, fixed lung volume and weight, alveolar size and air space volume percent, and total number of alveoli in mature left lower lobe porcine lung transplants 12 weeks after transplantation into growing piglets. Comparisons were made with nontransplanted mature left lower lobes to determine if functional or morphologic growth had occurred after transplantation. The transplanted and control lobes were all taken from 6-month-old animals (mean body weight 105 ± 4 kg). Recipients of the transplanted lobes were 9 weeks old and weighed 22 ± 2 kg. By the end of the 12-week holding period, the recipient animals increased their body weight approximately fourfold (85 ± 4 kg). No significant differences were seen in functional residual capacity or morphologic analysis of total alveolar number and alveolar size between the transplanted and nontransplanted lobes (p = not significant). Although the reduced-size mature porcine lobar transplants did not display a significant increase in either functional residual capacity or total alveolar number, there was significant growth of the transplanted mature lobes as determined by fixed volume and total lobar weight (p :::5 0.05 versus control animals). (J THORAC CARDIOVASC SURG 1992; 104:1329-32)
John A. Kern, MD (by invitation), Curtis G. Tribble, MD (by invitation), Terry L. Flanagan, MPH (by invitation), Barry B. K. Chan, MD (by invitation), Walter W. Scott, MD (by invitation), David C. Cassada, BA (by invitation), and Irving L. Kron, MD, Charlottesville, Va.
A
major unresolved issue preventing the Widespread application of successful pediatric and neonatal lung transplantation is the lack of size-matched immature donor organs. The method of reduced-size lung transplantation, in which a lobe or segment of a more mature donor organ is sized down to fit the immature recipient's chest, could potentially augment the pediatric donor lung pool.'? Both short- and long-term functional studies of reduced-size mature lobar transplantation in animal Fromthe Division of Thoracic and CardiovascularSurgery, University of Virginia Health Sciences Center, Charlottesville, Va. Supported in part by funds from the AHA- VirginiaAffiliateand grant 92009290 AHA. Readat the Seventy-second Annual Meeting of The American Association forThoracicSurgery, LosAngeles,Calif.,April 26-29,1992. Address for reprints: Irving L. Kron, MD, Box 310, Department of Surgery,Universityof VirginiaHealth SciencesCenter, Charlottesville, VA 22908.
12/6/40974
models have recently been reported.P" Pulmonary vascular resistance of transplanted mature lobes functioning as whole lungs has been reported by us" and others/ to be normal both short and long term, even under conditions of high lobar blood flow." In addition, long-term gas exchange provided by lobar transplants in animal models also appears adequate.b 4 No data exist concerning longterm function of this type of clinical lung transplantation in children. The growth potential of reduced-size mature lobar transplants is an important, related issue. To provide adequate function after transplantation into an infant or neonate, reduced-size lung transplants, it would seem, need to undergo compensatory growth in proportion to the recipient's somatic growth. To date no studies have been done examining the growth potential of reduced-size mature pulmonary transplants. To examine this issue we designed this study in a chronic model of reduced-size lung transplantation to determine whether mature por-
1329
The Journalot Thoracic and Cardiovascular Surgery
I 3 3 0 Kern et al.
12 Week
Left Lower Lobes From 6 Month Old Animals
/
\
Transplanted (n=6)
f---
Growth
-
Studied
Period
Controls (n=6)
-
Studied
Fig. 1. Diagrammatic representation ofthe experimental design. Note that both transplanted and control lobes were obtained from mature animals of similar ages. cine lobes can undergo functional compensatory growth after transplantation into growing immature piglets.
Materials and methods Animal model. The domestic swine was chosen because of our knowledge of its rapid postnatal lung development'"? and because of our familiarity with its tolerance of thoracotomy and lung transplantation. All experimental protocols were reviewed and approved by an institutional animal use committee. The guidelines used by this committee conform to the "Principles of Laboratory Animal Care" formulated by the National Society for Medical Research and the "Guide for the Care and Use of Laboratory Animals" prepared by the National Academy of Sciences and published by the National Institutes of Health (NIH publication No. 85-23, revised 1985). Operative technique. At approximately 6 months of age, a total of 12 pigs were designated as either control animals or donors (Fig. I). Six control animals (102 ± 8 kg) underwent left upper lobectomy and determination of functional residual capacity of the isolated left lower lobes, as described later herein, and the lower lobes were then harvested, weighed, and prepared for further morphologic study. The upper lobes from these animals were used for determination of lung water content.f The remaining six animals (107 ± 5 kg) were donors of mature left lower lobes that were transplanted into 8- to 10-week-old recipients (22 ± 2 kg) after left pneumonectomy. The lobes were weighed and preserved with ice-cold physiologic saline solution infused through the pulmonary artery until the venous effluent became clear. The lobes were immediately transplanted. The vascular anastomoses were performed with running 7-0 absorbable monofilament sutures for the vein and 6-0 absorbable monofilament sutures for the artery. The bronchial anastomoses were performed with running 4-0 absorbable monofilament sutures for the posterior wall and interrupted figure-of-eight sutures for the front wall, utilizing a telescoping technique.? The transplant animals were then allowed to recover and grow for 12 weeks. Immunosuppression. Recipient animals received cyclosporine (18 mg/kg per day orally). In addition, recipient animals received methylprednisolone (500 mg intravenously) at the time of transplantation, and daily thereafter for 5 days, and azathioprine, I mg/kg intravenously at the time oftransplantation and I mg /kg orally daily thereafter.
Calculation offunctional residual capacity. At the time of final study of the transplanted lobes and before harvesting the control lobes, the left lower lobes were isolated in vivo by using intrabronchial balloon catheters to occlude the contralateral right main and epiarterial airways. Functional residual capacity (FRC) of the isolated left lower lobes was then calculated with use of the helium dilution technique.!" Preparation of lung tissue and morphometric techniques. After the recipient animals increased their body weight by approximately fourfold (85 ± 4 kg) during the 12-week holding period, the transplanted left lower lobes were harvested (after determination of FRC) and wet weights were again obtained. A small sample was taken for calculation of fractionallung water content. The control and transplanted lobes were fixed in exactly the same fashion. After the lobes were weighed, they were fixed through the airways with 10% formalin under 25 to 30 em water pressure for several hours. The airways were then clamped at this pressure and the lobes were fixed for several days in formalin. After several days of fixation, fixed volume of the lobes was assessed by water displacement technique, and each lobe was cut into I em thick parallel slices. Each slice was point counted with a I em grid for separating larger vessels and airways from the parenchyma. Block sections were selected from the peripheral slices, and microscopic point counting was done to further separate out smaller vessels and airways from the lung parenchyma, which at this time was considered to be made up predominantly of alveolar components. Microscopic point counting was based on the method described by Dunnill'! and was also used to determine alveolar air space volume percent of the true parenchyma. The total number of alveoli in each lobe was calculated according to the principle of Weibel and Gomez.F Statistical analysis. Values are reported as the mean ± standard error of the mean. Student's t statistic was used to compare unpaired and paired samples. A probability value less than or equal to 0.05 was taken to indicate a significant difference between the values.
Results Initial body weight of the animals from which all lobes were harvested was similar between the two groups (p = not significant). Initial weight of the left lower lobes was slightly lower in the transplanted group versus the
Volume 104 Number 5 November 1992
Growth potential of mature porcine lobar transplants
133 1
Table I. Gross parameters of lobar growth Group
Initial lobar weight (gm)
Final lobar weight (gm)
Fractional lung water content
Fixed volume (ml)
Transplanted lobes Control lobes
155 ± 8 181 ± 8t
298 ± 30*
0.91 ± 0.01 0.92 ± 0.01
863 ± 66 696 ± 39t
*p :oS 0.05 versus initial lobar weight; paired t test. t p :oS 0.05 versus transplanted lobes; unpaired t test.
Table II. Functional and morphologic assessment oflobar growth Group
Functional residual capacity (ml)
Mean alveolar diameter (um]
Alveolar air space volume % (%)
Total alveolar number (X](!)
Transplanted lobes Control lobes
600 ± 40 606 ± 100
72 ± 3 71 ± 2
56 ± I 66 ± 1*
107.4 ± 16.0 95.1 ± 10.7
*P :oS 0.05 versus transplanted
lobes; unpaired t test.
control group (p = 0.051; Table I), but it increased significantly (p :s 0.05) in the transplanted lobes during the 12-week postoperative period (see Table I). Fractionallung water content was similar between the two groups (p = not significant). Fixed lung volume was also increased in the transplanted lobes after 12 weeks of additional growth (p :s 0.05 versus control animals; see Table I). FRC, however, was nearly identical between the two groups and was not increased in the transplanted lobes to more than control values (Table 11). The total number of alveoli in the left lower lobes was not significantly different between the transplanted lobes and the control lobes (p = not significant; Table 11). While alveolar diameter was nearly identical between the two groups, alveolar air space volume percent of the true parenchyma was significantly lower in the transplanted lobes compared with the control lobes (p :s 0.05; see Table 11). Discussion
Growth potential of transplanted immature whole lungs in animal models has recently been reported to be norma!. 13, 14 Hislop and colleagues'" reported normal growth and alveolar number in transplanted immature rat lungs after a period of somatic growth. Both pulmonary function and development of the distal airways of transplanted immature lungs has been reported by us and other investigators, however, to be abnormal in other animal models of immature lung transplantation. IS, 16 Growth potential of mature reduced-size lobar transplants has not been reported previously. Compensatory growth oftransplanted mature lung tissue functioning as a whole lung in a pediatric patient may be crucial for adequate long-term function. In our porcine model, transplanted mature lobes increased in size as determined by gross weight and fixed lung volume when compared
with pretransplant values and control lobes. However, no increase in either functional capacity or total alveoli was observed. The increases in fixed volume and weight, along with a normal total number of alveoli, similar alveolar size, and smaller parenchymal alveolar air space volume percent of the transplanted lobes, indicate that the transplanted lobes most likely grew through an increase in connective tissue and cellular components of the lung parenchyma and not through an increase in alveolar number. Correspondingly, functional residual capacity was nearly identical between the two groups. Acute and chronic function of reduced-size mature lobar transplants has only recently been studied in animal models.r" Such models are technically feasible and the transplanted lobes appear capable of supporting the animal.' However, correlation of pulmonary function of transplanted mature lobes to growth of the lobes during an extended period of time has not been reported. Our results indicate that mature lobar transplants do not form a significant number of new functional alveolar units, but, instead, increase in size through other mechanisms. Whether this compensatory growth can provide total pulmonary function for the growing recipient during an extended period of time is presently unknown. REFERENCES 1. Goldsmith MF. Mother to child: first living donor lung
transplant. JAMA 1990;264:2724. 2. Crombleholme TM, Adzick NS, Longaker MT, et al. Reduced-size lungtransplantation in neonatalswine: technique and short-term physiologic response. Ann Thorac Surg 1990;49:55-60. 3. BackerCL, Ohtake S, Zales VR, LoCicero J III, Michaelis LL, Idriss FS. Living-related lobar lungtransplantation in beagle puppies. J Pediatr Surg 1991;26:429-33. 4. KernJA, TribbleCG, Chan BBK, FlanaganTL, Kron IL.
I 3 3 2 Kern et al.
5.
6.
7.
8.
9.
10. 11. 12.
13.
14.
15.
16.
Reduced-size porcine lung transplantation: long-term studies of pulmonary vascular resistance. Ann Thorac Surg 1992;53:583-9. Rendas A, Branthwaite M, Reid L. Growth of pulmonary circulation in normal pig-structural analysis and cardiopulmonary function. J Appl PhysioI1978;45:806-17. Winkler GC, Cheville NF. The neonatal porcine lung: ultrastructural morphology and postnatal development of the terminal airways and alveolar region. Anat Rec 1984;210:303-13. Winkler GC, Cheville NF. Morphometry of postnatal development in the porcine lung. Anat Rec 1985;211:42733. Cowan GSM, Staub NC, Edmunds LH. Changes in the fluid compartments and dry weights of reimplanted dog lungs. J Appl Physiol 1976;40:962-70. Calhoon JH, Grover FL, Gibbons WJ, et al. Single lung transplantation. Alternative indications and technique. J THoRAc CARDIOVASC SURG 1991;101:816-25. Levitzky MG. Alveolar ventilation. In: Pulmonary physiology. New York: McGraw-Hili, 1982:51-79. Dunnill MS. Quantitative methods in the study of pulmonary pathology. Thorax 1962;17:320-8. Weibel ER, Gomez DM. A principle for counting tissue structures on random sections. J Appl Physiol1962; 17:3438. Haverich A, Dammenhayn L, Demertzis S, Kemnitz J, Reimers P. Lung growth after experimental pulmonary transplantation. J Heart Lung Transplant 1991;10:288-95. Hislop AA, Odom NJ, McGregor CGA, Haworth SG. Growth potential of the immature transplanted lung: an experimental study. J THORAC CARDIOVASC SURG 1990;100:360-70. Kern JA, Kron IL, Flanagan TL, et al. Denervation of the immature porcine lung impairs normal airway development. J Heart Lung Transplant [In press]. Kottmeier PK, Cheng C, Fitzgerald J, Hochman R, Emmanuel GE. Growth and function of the replanted lung in young dogs. J Pediatr Surg 1969;4:66-76.
Discussion Dr. R. Morton Dolman III (Minneapolis. Minn.}. In light of this study and the data presented yesterday by the Pittsburgh group showing the efficacy of lung replacement in children, I think potential applicability of this technique is great.
The Journal of Thoracic and Cardiovascular Surgery
I assume that these 6-month-old pigs are truly mature and no further growth would be expected in the host before transplantation. Could you give us any idea of how you selected the lobes that you selected to transplant. Did you do FRC determinations of donor-recipient before the transplant in an attempt to decide which lobe to replace? What other combinations might be applicable? At the end of this 12-week period or even later, will these lobes support life after growth in the recipient? Have you performed any preliminary studies, or do you have any plans to perform contralateral pneumonectomy or balloon occlusion of the pulmonary artery and airway to assess the functional capacity of these lobes at a distance after implantation? Dr. Kern. I will answer your last question first, because that really is the clinically relevant question: Will these isolated lobes support life over the long term? Our own studies and most studies by other investigators looking at function of these transplanted mature lobes have all been done in well-controlled settings with the animals intubated and breathing supplemental oxygen. Although we have not performed contralateral pneumonectomies on our animals, we have functionally excluded the contralateral normal lung by clamping the hilar vessels,and the animals have generally done very well with just the one-lobe ventilation. Again, these functional studies were done with the animals at rest; the ability of an isolated mature lobar transplant to meet ventilatory requirements during exercise is not known. Having said this, we have no reason to doubt that these lobes will adequately support life. We chose the left lower lobe in this particular animal model simply because it is technically the easiest lobe to isolate and transplant. In the pig the left lower lobe, with only one main lower lobe artery and one large lower lobe pulmonary vein, is very easy to dissect free from the upper lobe. Sometimes the pig pulmonary vasculature, especially on the right side, can be difficult to sort out. The left lower lobe, however, is quite uniform and easy to study long term. The question of maturity of a 6-month-old pig is a very good one because pigs can certainly grow much larger beyond this age. Much beyond 6 months, however, domestic pigs get too difficult to handle because of their large size. Having said this, it turns out that pig lung development has been well studied by other investigators, and by 6 months the porcine lung is for the most part already functionally and morphologically mature. Total alveolar number, for example, reaches adult levels by as early as 12 weeks. Nevertheless, we plan to develop the same model of reduced-size lung transplantation in a different species, specifically a miniature pig, which at full maturity weighs roughly 100 kg. Studies in this species would allow for more long-term analysis of mature lobar transplants.
John A. Kern, MD (by invitation), Curtis G. Tribble, MD (by invitation), Terry L. Flanagan, MPH (by invitation), Barry B. K. Chan, MD (by invitation), Walter W. Scott, MD (by invitation), David C. Cassada, BA (by invitation), and Irving L. Kron, MD, Charlottesville, Va.
A
major unresolved issue preventing the Widespread application of successful pediatric and neonatal lung transplantation is the lack of size-matched immature donor organs. The method of reduced-size lung transplantation, in which a lobe or segment of a more mature donor organ is sized down to fit the immature recipient's chest, could potentially augment the pediatric donor lung pool.'? Both short- and long-term functional studies of reduced-size mature lobar transplantation in animal Fromthe Division of Thoracic and CardiovascularSurgery, University of Virginia Health Sciences Center, Charlottesville, Va. Supported in part by funds from the AHA- VirginiaAffiliateand grant 92009290 AHA. Readat the Seventy-second Annual Meeting of The American Association forThoracicSurgery, LosAngeles,Calif.,April 26-29,1992. Address for reprints: Irving L. Kron, MD, Box 310, Department of Surgery,Universityof VirginiaHealth SciencesCenter, Charlottesville, VA 22908.
12/6/40974
models have recently been reported.P" Pulmonary vascular resistance of transplanted mature lobes functioning as whole lungs has been reported by us" and others/ to be normal both short and long term, even under conditions of high lobar blood flow." In addition, long-term gas exchange provided by lobar transplants in animal models also appears adequate.b 4 No data exist concerning longterm function of this type of clinical lung transplantation in children. The growth potential of reduced-size mature lobar transplants is an important, related issue. To provide adequate function after transplantation into an infant or neonate, reduced-size lung transplants, it would seem, need to undergo compensatory growth in proportion to the recipient's somatic growth. To date no studies have been done examining the growth potential of reduced-size mature pulmonary transplants. To examine this issue we designed this study in a chronic model of reduced-size lung transplantation to determine whether mature por-
1329
The Journalot Thoracic and Cardiovascular Surgery
I 3 3 0 Kern et al.
12 Week
Left Lower Lobes From 6 Month Old Animals
/
\
Transplanted (n=6)
f---
Growth
-
Studied
Period
Controls (n=6)
-
Studied
Fig. 1. Diagrammatic representation ofthe experimental design. Note that both transplanted and control lobes were obtained from mature animals of similar ages. cine lobes can undergo functional compensatory growth after transplantation into growing immature piglets.
Materials and methods Animal model. The domestic swine was chosen because of our knowledge of its rapid postnatal lung development'"? and because of our familiarity with its tolerance of thoracotomy and lung transplantation. All experimental protocols were reviewed and approved by an institutional animal use committee. The guidelines used by this committee conform to the "Principles of Laboratory Animal Care" formulated by the National Society for Medical Research and the "Guide for the Care and Use of Laboratory Animals" prepared by the National Academy of Sciences and published by the National Institutes of Health (NIH publication No. 85-23, revised 1985). Operative technique. At approximately 6 months of age, a total of 12 pigs were designated as either control animals or donors (Fig. I). Six control animals (102 ± 8 kg) underwent left upper lobectomy and determination of functional residual capacity of the isolated left lower lobes, as described later herein, and the lower lobes were then harvested, weighed, and prepared for further morphologic study. The upper lobes from these animals were used for determination of lung water content.f The remaining six animals (107 ± 5 kg) were donors of mature left lower lobes that were transplanted into 8- to 10-week-old recipients (22 ± 2 kg) after left pneumonectomy. The lobes were weighed and preserved with ice-cold physiologic saline solution infused through the pulmonary artery until the venous effluent became clear. The lobes were immediately transplanted. The vascular anastomoses were performed with running 7-0 absorbable monofilament sutures for the vein and 6-0 absorbable monofilament sutures for the artery. The bronchial anastomoses were performed with running 4-0 absorbable monofilament sutures for the posterior wall and interrupted figure-of-eight sutures for the front wall, utilizing a telescoping technique.? The transplant animals were then allowed to recover and grow for 12 weeks. Immunosuppression. Recipient animals received cyclosporine (18 mg/kg per day orally). In addition, recipient animals received methylprednisolone (500 mg intravenously) at the time of transplantation, and daily thereafter for 5 days, and azathioprine, I mg/kg intravenously at the time oftransplantation and I mg /kg orally daily thereafter.
Calculation offunctional residual capacity. At the time of final study of the transplanted lobes and before harvesting the control lobes, the left lower lobes were isolated in vivo by using intrabronchial balloon catheters to occlude the contralateral right main and epiarterial airways. Functional residual capacity (FRC) of the isolated left lower lobes was then calculated with use of the helium dilution technique.!" Preparation of lung tissue and morphometric techniques. After the recipient animals increased their body weight by approximately fourfold (85 ± 4 kg) during the 12-week holding period, the transplanted left lower lobes were harvested (after determination of FRC) and wet weights were again obtained. A small sample was taken for calculation of fractionallung water content. The control and transplanted lobes were fixed in exactly the same fashion. After the lobes were weighed, they were fixed through the airways with 10% formalin under 25 to 30 em water pressure for several hours. The airways were then clamped at this pressure and the lobes were fixed for several days in formalin. After several days of fixation, fixed volume of the lobes was assessed by water displacement technique, and each lobe was cut into I em thick parallel slices. Each slice was point counted with a I em grid for separating larger vessels and airways from the parenchyma. Block sections were selected from the peripheral slices, and microscopic point counting was done to further separate out smaller vessels and airways from the lung parenchyma, which at this time was considered to be made up predominantly of alveolar components. Microscopic point counting was based on the method described by Dunnill'! and was also used to determine alveolar air space volume percent of the true parenchyma. The total number of alveoli in each lobe was calculated according to the principle of Weibel and Gomez.F Statistical analysis. Values are reported as the mean ± standard error of the mean. Student's t statistic was used to compare unpaired and paired samples. A probability value less than or equal to 0.05 was taken to indicate a significant difference between the values.
Results Initial body weight of the animals from which all lobes were harvested was similar between the two groups (p = not significant). Initial weight of the left lower lobes was slightly lower in the transplanted group versus the
Volume 104 Number 5 November 1992
Growth potential of mature porcine lobar transplants
133 1
Table I. Gross parameters of lobar growth Group
Initial lobar weight (gm)
Final lobar weight (gm)
Fractional lung water content
Fixed volume (ml)
Transplanted lobes Control lobes
155 ± 8 181 ± 8t
298 ± 30*
0.91 ± 0.01 0.92 ± 0.01
863 ± 66 696 ± 39t
*p :oS 0.05 versus initial lobar weight; paired t test. t p :oS 0.05 versus transplanted lobes; unpaired t test.
Table II. Functional and morphologic assessment oflobar growth Group
Functional residual capacity (ml)
Mean alveolar diameter (um]
Alveolar air space volume % (%)
Total alveolar number (X](!)
Transplanted lobes Control lobes
600 ± 40 606 ± 100
72 ± 3 71 ± 2
56 ± I 66 ± 1*
107.4 ± 16.0 95.1 ± 10.7
*P :oS 0.05 versus transplanted
lobes; unpaired t test.
control group (p = 0.051; Table I), but it increased significantly (p :s 0.05) in the transplanted lobes during the 12-week postoperative period (see Table I). Fractionallung water content was similar between the two groups (p = not significant). Fixed lung volume was also increased in the transplanted lobes after 12 weeks of additional growth (p :s 0.05 versus control animals; see Table I). FRC, however, was nearly identical between the two groups and was not increased in the transplanted lobes to more than control values (Table 11). The total number of alveoli in the left lower lobes was not significantly different between the transplanted lobes and the control lobes (p = not significant; Table 11). While alveolar diameter was nearly identical between the two groups, alveolar air space volume percent of the true parenchyma was significantly lower in the transplanted lobes compared with the control lobes (p :s 0.05; see Table 11). Discussion
Growth potential of transplanted immature whole lungs in animal models has recently been reported to be norma!. 13, 14 Hislop and colleagues'" reported normal growth and alveolar number in transplanted immature rat lungs after a period of somatic growth. Both pulmonary function and development of the distal airways of transplanted immature lungs has been reported by us and other investigators, however, to be abnormal in other animal models of immature lung transplantation. IS, 16 Growth potential of mature reduced-size lobar transplants has not been reported previously. Compensatory growth oftransplanted mature lung tissue functioning as a whole lung in a pediatric patient may be crucial for adequate long-term function. In our porcine model, transplanted mature lobes increased in size as determined by gross weight and fixed lung volume when compared
with pretransplant values and control lobes. However, no increase in either functional capacity or total alveoli was observed. The increases in fixed volume and weight, along with a normal total number of alveoli, similar alveolar size, and smaller parenchymal alveolar air space volume percent of the transplanted lobes, indicate that the transplanted lobes most likely grew through an increase in connective tissue and cellular components of the lung parenchyma and not through an increase in alveolar number. Correspondingly, functional residual capacity was nearly identical between the two groups. Acute and chronic function of reduced-size mature lobar transplants has only recently been studied in animal models.r" Such models are technically feasible and the transplanted lobes appear capable of supporting the animal.' However, correlation of pulmonary function of transplanted mature lobes to growth of the lobes during an extended period of time has not been reported. Our results indicate that mature lobar transplants do not form a significant number of new functional alveolar units, but, instead, increase in size through other mechanisms. Whether this compensatory growth can provide total pulmonary function for the growing recipient during an extended period of time is presently unknown. REFERENCES 1. Goldsmith MF. Mother to child: first living donor lung
transplant. JAMA 1990;264:2724. 2. Crombleholme TM, Adzick NS, Longaker MT, et al. Reduced-size lungtransplantation in neonatalswine: technique and short-term physiologic response. Ann Thorac Surg 1990;49:55-60. 3. BackerCL, Ohtake S, Zales VR, LoCicero J III, Michaelis LL, Idriss FS. Living-related lobar lungtransplantation in beagle puppies. J Pediatr Surg 1991;26:429-33. 4. KernJA, TribbleCG, Chan BBK, FlanaganTL, Kron IL.
I 3 3 2 Kern et al.
5.
6.
7.
8.
9.
10. 11. 12.
13.
14.
15.
16.
Reduced-size porcine lung transplantation: long-term studies of pulmonary vascular resistance. Ann Thorac Surg 1992;53:583-9. Rendas A, Branthwaite M, Reid L. Growth of pulmonary circulation in normal pig-structural analysis and cardiopulmonary function. J Appl PhysioI1978;45:806-17. Winkler GC, Cheville NF. The neonatal porcine lung: ultrastructural morphology and postnatal development of the terminal airways and alveolar region. Anat Rec 1984;210:303-13. Winkler GC, Cheville NF. Morphometry of postnatal development in the porcine lung. Anat Rec 1985;211:42733. Cowan GSM, Staub NC, Edmunds LH. Changes in the fluid compartments and dry weights of reimplanted dog lungs. J Appl Physiol 1976;40:962-70. Calhoon JH, Grover FL, Gibbons WJ, et al. Single lung transplantation. Alternative indications and technique. J THoRAc CARDIOVASC SURG 1991;101:816-25. Levitzky MG. Alveolar ventilation. In: Pulmonary physiology. New York: McGraw-Hili, 1982:51-79. Dunnill MS. Quantitative methods in the study of pulmonary pathology. Thorax 1962;17:320-8. Weibel ER, Gomez DM. A principle for counting tissue structures on random sections. J Appl Physiol1962; 17:3438. Haverich A, Dammenhayn L, Demertzis S, Kemnitz J, Reimers P. Lung growth after experimental pulmonary transplantation. J Heart Lung Transplant 1991;10:288-95. Hislop AA, Odom NJ, McGregor CGA, Haworth SG. Growth potential of the immature transplanted lung: an experimental study. J THORAC CARDIOVASC SURG 1990;100:360-70. Kern JA, Kron IL, Flanagan TL, et al. Denervation of the immature porcine lung impairs normal airway development. J Heart Lung Transplant [In press]. Kottmeier PK, Cheng C, Fitzgerald J, Hochman R, Emmanuel GE. Growth and function of the replanted lung in young dogs. J Pediatr Surg 1969;4:66-76.
Discussion Dr. R. Morton Dolman III (Minneapolis. Minn.}. In light of this study and the data presented yesterday by the Pittsburgh group showing the efficacy of lung replacement in children, I think potential applicability of this technique is great.
The Journal of Thoracic and Cardiovascular Surgery
I assume that these 6-month-old pigs are truly mature and no further growth would be expected in the host before transplantation. Could you give us any idea of how you selected the lobes that you selected to transplant. Did you do FRC determinations of donor-recipient before the transplant in an attempt to decide which lobe to replace? What other combinations might be applicable? At the end of this 12-week period or even later, will these lobes support life after growth in the recipient? Have you performed any preliminary studies, or do you have any plans to perform contralateral pneumonectomy or balloon occlusion of the pulmonary artery and airway to assess the functional capacity of these lobes at a distance after implantation? Dr. Kern. I will answer your last question first, because that really is the clinically relevant question: Will these isolated lobes support life over the long term? Our own studies and most studies by other investigators looking at function of these transplanted mature lobes have all been done in well-controlled settings with the animals intubated and breathing supplemental oxygen. Although we have not performed contralateral pneumonectomies on our animals, we have functionally excluded the contralateral normal lung by clamping the hilar vessels,and the animals have generally done very well with just the one-lobe ventilation. Again, these functional studies were done with the animals at rest; the ability of an isolated mature lobar transplant to meet ventilatory requirements during exercise is not known. Having said this, we have no reason to doubt that these lobes will adequately support life. We chose the left lower lobe in this particular animal model simply because it is technically the easiest lobe to isolate and transplant. In the pig the left lower lobe, with only one main lower lobe artery and one large lower lobe pulmonary vein, is very easy to dissect free from the upper lobe. Sometimes the pig pulmonary vasculature, especially on the right side, can be difficult to sort out. The left lower lobe, however, is quite uniform and easy to study long term. The question of maturity of a 6-month-old pig is a very good one because pigs can certainly grow much larger beyond this age. Much beyond 6 months, however, domestic pigs get too difficult to handle because of their large size. Having said this, it turns out that pig lung development has been well studied by other investigators, and by 6 months the porcine lung is for the most part already functionally and morphologically mature. Total alveolar number, for example, reaches adult levels by as early as 12 weeks. Nevertheless, we plan to develop the same model of reduced-size lung transplantation in a different species, specifically a miniature pig, which at full maturity weighs roughly 100 kg. Studies in this species would allow for more long-term analysis of mature lobar transplants.