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The reversibility of impaired mucociliary function after lung transplantation
J THoRAc
CARDIOVASC SURG 1991;102:908-12
The reversibility of impaired mucociliary function after lung transplantation Impairment of mucociliary function occurs after lung transplantation and may predispose patients to repeated pulmonary infections. The purpose of this study is to determine whether and how soon such mucociliary function may recover. Ten dogs underwent left lung autotransplantation. Within 3 weeks five of these dogs underwent study for proximal airway clearance by observation through a bronchoscope of the movement of carbon particles placed at different locations on the tracheobronchial mucosa. The mechanical properties of coUected mucus from specific sites were determined by magnetic rheometry. The right lung, which was not operated on, served as a paired control. Similar studies were conducted in the remaining five dogs at 12 weeks after autotransplantation. Lung autotransplantation caused significant depression of proximal airway clearance and a 35 % increase in mucous rigidity (p = 0.05) soon after operation. At 12 weeks after operation, there was a partial recovery of proximal airway clearance. Mucous changes were no longer consistent. Histologic and electron microscopic examinations initiaUy revealed focal denudation of ciliated ceUs and loss of the bronchial glands. At 12 weeks there was a regeneration of cilia and a reappearance of the bronchial glands. We conclude that the mucociliary function, observed to be depressed early after lung autotransplantation, recovers partiaUy during the late postoperative period. Thus the mucociliary functional recovery should be attributed to revascularization rather than to reinnervation, since the latter is unlikely to occur during this period.
Daniel Marelli, MD, Andreas Paul, MD, Dao M. Nguyen, MD, Hani Shennib, MD, Malcolm King, PhD, Nai-San Wang, MD, PhD, James A. Wilson, MD, David S. Mulder, MD, and Ray c.-J. Chiu, MD, PhD, Montreal, Quebec, and Edmonton, Alberta, Canada
MucOCiliary function has been reported to be impaired after lung transplantation. I, 2 This may lead to repeated pulmonary infections, which are considered one of the limiting factors in the survival of patients who undergo such transplantations. Understanding this dysfunction could conceivably lead to treatments aimed at From the Departments of Surgery and Pathology, McGill University, Montreal, Quebec, and the University of Alberta Pulmonary Defense Group, Edmonton, Alberta, Canada. Supported in part by a grant from the Quebec Thoracic Society and from the Alberta Lung Association. Presented at the Sixteenth World Congress on Diseases of the Chest, Boston, Mass. Oct. 30-Nov. 3,1989. Received for publication Feb. 23, 1990. Accepted for publication Aug. 31,1990. Address for reprints: Ray C.-J. Chiu, MD, PhD, The Montreal General Hospital, 1650 Cedar Ave., Room 947, Montreal, Quebec, Canada, H3G lA4.
12/1/26545
908
reducing the prevalence of pulmonary infections in recipients of lung and heart-lung transplants. M ucociliary clearance is a physiological defense mechanism resulting from an interaction between the cilia and mucus of the bronchial epithelium.v 4 Mucociliary function can therefore be impaired as a result of alterations in cilia structure and function, alterations in mucous viscoelastic properties, or a combination of these. We have previously reported that changes in mucous rheologic properties after lung autotransplantation and allotransplantation can impair mucociliary function in the early postoperative period and occur simultaneously with alterations in mucosal structures.P Others have noted that bronchial mucosa is normal 1 year after lung autotransplantation in a canine model." It can therefore be hypothesized that impairment of mucociliary function after lung transplantation may be partially reversible as progressive healing of the bronchial anastomosis occurs. The purpose of the present study was to test this hypothesis by assess-
Volume 102
Mucociliary function in lung transplantation
Number 6 December 1991
909
Table I. Proximal airway clearance rates after lung autotransplantation, in millimeters per minute Before operation * 3 wkafter operation 12 wkafter operation
Trachea
Left lung
Right lung
lOA ± 2.1
7.8 ± 2.0
10.5 ± 3.0 13.5 ± 1.5
5.0 ± 3.5
6.9 ± 0.8 8.3 ± 1.0 8.0 ± 2.0
ot
Values are mean ± standard deviation. 'Values represent the mean for all dogs undergoing operation, tp < 0.05 when compared to preoperative value,
ing mucociliary function in the late period after lung autotransplantation and comparing these observations with previous studies of the early postoperative period.
Material and methods Ten dogs (20 to 30 kg) underwent left lung autotransplantation by a previouslydescribed technique." The bronchial anastomosis was performed at the level of the distal main-stem bronchus with interrupted 5-0 polypropylene sutures and wrapped with an omental flap.s Ischemia times ranged from 40 to 60 minutes. Healing of the bronchial anastomosis was verifiedby bronchoscopicstudy and lung function was confirmed by ventilation/perfusion scintigraphy with technetium 99mlabeled sulphur and albumin particles. Proximal airway mucociliary clearance was measured before operation in 'al1 animals. Within 3 weeks after operation, five dogs underwent study for proximal airway clearance and mucousrheologicstudies. Mucociliaryclearance measurements were repeated and compared with preoperative values. The mechanical properties of mucus col1ected distal1y from specific sites in both main-stem bronchi were determined by magnetic microrheometry. The right lung, which was not operated on, servedas a paired control for these studies. Postmortem studies consistedof light and electron microscopy.Similar studies were conducted after 12 weeks in the other five dogs. Measurement of mucociliary function. As previously described.' the animals were allowed to breathe spontaneously after sedation with diazepam (5 mg administered intravenously and xylazine hydrochloride (I to 2 mg/kg administered intravenously). After endotracheal intubation was accomplished, a bronchoscopewas passed into the tracheobronchial tree. Proximal airway clearance was measured by observing the movement of the leading edge of a spot of carbon particles suspended in saline deposited on the airway mucosa through polyethylene tubing threaded through the biopsy channel of the bronchoscope. Mucociliary clearance was measured sequential1y in the trachea, right main-stem bronchus, and the left main-stem bronchus during three separate IS-minute observation periods. A starting point I to 2 ern distal to the bronchial anastomosis was chosen for postoperative studies. Results are expressed in millimeters per minute. Mucous viscoelastic properties were analyzed by magnetic microrheornetry.? Samples of mucus were col1ected from the right and left main-stem bronchi with a cytology brush passed through the biopsychannel of the bronchoscopeand were stored at -80 0 C until analysis. This analysis consisted of oscillating a steel bal1 in a droplet of the sample. The force applied was electromagneticand measured in radians per second. Displace-
ment of the bal1 was tracked by photocel1s and the resulting signals were displayed on an oscilloscope, enabling calculation of mucous elasticity and viscosity.The logarithm of the vectorial sum of these is defined as log G*. This can be regarded as the resistance of the mucus to flow and is considered an index of rigidity. Measurements were conducted at frequencies of I and 100 radians/sec, representing normal ciliary and cough activity, respectively.The values for the mucus from either lung were compared and differences were calculated and compiled for each group. Statistical analysis was done by Student's paired t test. Animal care in all experiments was performed according to guidelines set by the Canadian Council for Animal Care.
Results Serial bronchoscopy and ventilation/perfusion scanning confirmed satisfactory postoperative function in all transplanted lungs. All the anastomoses healed with minimal stenosis. Three weeks after operation, perfusion scanning showed mean relative distribution of the initial burden to be 68.1 % ± 5.8% for the right lung and 31.9% ± 5.8% for the transplanted left lung. Similarly, ventilation scanning revealed the mean relative distribution ofthe initial burden for the right and transplanted left lungs to be 56.6% ± 3.7% and 43.4% ± 3.7%, respectively. Proximal airway mucociliary clearance, determined during a l5-minute observation period after deposition of carbon particles, was found to be absent 3 weeks after lung autotransplantation. The results of these early postoperative observations have been previously presented.i At 12 weeks after operation, there was partial recovery of carbon particle clearance in the transplanted lungs and no statistically significant difference could be detected in clearance rate between late postoperative and preoperative measurements (Table I). The bronchial anastomosis was not found to be an obstacle to clearance of the carbon particles. Mucociliary clearance rate in the trachea was unchanged in all postoperative studies. Also, when left lung clearance rates at 12 weeks were compared with right lung rates, no significant difference could be detected (p = 0.5). In all postoperative studies, the mucosa distal to the
The Journal of
9 10Marelli et ai.
Thoracic and Cardiovascular Surgery
Fig. 1. Light microscopy shows bronchial anastomosis 3 (A) and 12 (B) weeks after left lung autotransplantation. Note the change in the mucosa distal to the anastomosis (right side). (Hematoxylin and eosin stain; originalmagnification X400.)
bronchial anastomosis in the transplanted lung was noted to be more friable than that of the untreated right lung. Left lung mucus was compared with mucus from the right lung. Three weeks after operation, under measurement conditions comparable to those of normal ciliary activity (l radian/sec), the resistance to movement of left lung mucus was 35% ± 3% greater than that for mucus from the right lung (p < 0.05). At a force comparable to that of cough (l00 radians/sec), the mean increase was 35% ± 7% (p = 0.1). Twelve weeks after operation, results were no longer consistent, with wide variations observed. Some samples showed greater mucous rigidity in the left lung, whereas others showed slightly decreased or relatively unchanged mucous rigidity in the left lung, when compared with that of the right lung; the mean increase in left lung mucous rigidity was 35% ± 60% at a force of I radian/sec and 33% ± 37% at a force of 100 radians/sec (p> 0.4). Histologic and electron microscopic studies in the early postoperative period revealed focal denudation of ciliated cells and disappearance of the bronchial glands and their associated ducts distal to the bronchial anastomosis. Twelve weeks after lung autotransplantation, the anastomosis was found to be well healed and the mucosa distal
to the suture line closely resembled the normal mucosa proximal to the suture line. There was also regeneration of the ciliated cells and reappearance of the bronchial glands and ducts (Figs. I and 2). Discussion Impairment of mucociliary function after lung transplantation may be caused by both bronchial denervation and devascularization. It is also possible that subclinical rejection can contribute to mucociliary dysfunction. We 5 have previously shown that mucociliary function is impaired in the early period after lung autotransplantation and allotransplantation but not after sleeve resection with preservation of a flap of peribronchial tissue. There was no difference between autotransplanted and allotransplanted lungs. The purpose of this study was to assess mucociliary function in the late postoperative period in the canine lung autotransplant model. This obviates the need for and eliminates the effects of immunosuppression required for allografts. The experimental model used in this study consisted of complete bronchial denervation and devascularization. The long-term aspect of the study protocol introduces the possibility of bronchial revascularization and reinnerva-
Volume 102 Number 6 December 1991
tion. The endpoints chosen consisted of assessing and comparing mucociliary function in the early and late postoperative periods after lung autotransplantation. Thus an attempt was made to evaluate the possible effects of progressive bronchial healing on long-term mucociliary function in transplanted lungs. This was achieved by separating this function into its two components. Airway clearance was determined by observing movement of carbon particles deposited at specific locations in the tracheobronchial tree. Rheologic properties of mucus were studied with an ex vivo microrheometry model that quantifies the viscoelastic properties of mucus. Both of these methods have been previously described and have shown reproducible results. 10, II This study shows that there is partial recovery of airway mucociliary clearance rate in the late period after lung autotransplantation and that there is simultaneous regeneration of mucosal structures related to this function. The importance of anatomic integrity for mucociliary function is thus highlighted. These findings, consistent with those of early studies carried out by Edmunds and coworkers.F support the concept that complete bronchial disruption affects mucociliary clearance rate and that these specific effects are reversible as the bronchial anastomosis heals. Since revascularization is probably among the first events to occur during healing of the bronchial anastomosis.P it can be hypothesised that revascularization would account for the first observable reversal of impaired mucociliary clearance rate after lung autotransplantation. Mucociliary transport itself depends on the interaction between cilia and mucus. 14 This is determined mainly by the thickness, elasticity, and viscosity of the mucus. Particle transport, shown to fail in the absence of mucus, can be restored by placing autologous or heterologous mucus on intact ciliated epithelium, demonstrating the importance of mucus for normallung mucociliary function. 15, 16 The rheologic studies of mucus in our experiments showed increased rigidity during the early postoperative period. This is an atropine-like effect, and one can therefore infer that this effect may be related to lung denervation.'? These changes were not consistently demonstrable in the late postoperative period. Nerve regeneration after complete lung denervation is not well defined.U:'? It is possible that partial nerve regeneration may occur as early as 3 months after lung reimplantation, thus explaining the inconsistent changes in rheologic properties of mucus observed in the course of our study 12 weeks after lung autotransplantation. If this is the case, then it is conceivable that at a l Z-month interval after operation the rheologic properties of mucus may revert to normal. This would mean that clinical observations of impaired muco-
Mucociliary function in lung transplantation
9 11
Fig. 2. Electronmicroscopy shows bronchialanastomosis 3 (A) and 12 (B) weeks after left lung autotransplantation. Note that after 12weeks the mucosadistal to the anastomosis (right side) cannot be distinguished from the mucosa of the proximal airway. (A, Original magnification X120. B, Original magnification X45.)
ciliary clearance rates carried out long after lung allotransplantation could be attributable to immunologic factors, to impaired healing as a result of immunosuppressive therapy, or to subclinical infection. Indeed, this last situation, which may be a result of prolonged animal housing, may explain the inconsistent results of the mucous rheologic study at 12 weeks after operation." Further clinical studies are needed to determine whether changes in the rheologic properties of mucus persist in long-term survivors of lung allotransplantation. If present, these changes need to be correlated with histologic examination of the mucus to determine whether they are in fact due to the persistent effects of lung denervation or
The Journal of Thoracic and Cardiovascular Surgery
9 12Marelli et al.
are due, alternatively, to any of the other possible causes mentioned above, including undetected low-grade rejection. In conclusion, the present study shows that, after early postoperative impairment, there is partial recovery of mucociliary clearance rate 12 weeks after lung autotransplantation. This is probably attributable to bronchial revascularization, since reinnervation is unlikely to be complete during this period.
9.
10.
II.
REFERENCES I. Dolovich M, Rossman C, Chambers C, et al. Muco-ciliary function in patients following single lung or lung/heart transplantation. Am Rev Respir Dis 1987;135:A363. 2. Mancini MC, Griffith BP, Tauxe WN. Assessment of ciliary function in the tracheobronchial tree of the heart-lung transplant recipient. Surg Forum 1987;38:300-1. 3. Newhouse M, Sanchis J, Bienenstock J. Lung defense mechanisms (first of two parts). N Engl J Med 1976; 295:990-8. 4. Wanner A. Mucociliary clearance in the trachea. Clin Chest Med 1986;7:247-58: 5. Paul A, Marelli D, Shennib H, et al. Mucociliary function in autotransplanted, allotransplanted, and sleeve resected lungs. J THORAC CARDIOVASC SURG 1989;98:523-8. 6. Fujimura S, Kondo T, Handa M, et al. Histologic assessment of bronchial anastomotic healing in canine lung transplantation. J THORAC CARDIOVASC SURG 1987; 94:323-30. 7. Veith FJ, Richards K. Improved technique for canine lung transplantation. Ann Surg 1970;171:553-8. 8. Lima 0, Goldberg M, Peters WJ, Ayabe H, Townsend E,
12.
13.
14.
15. 16. 17. 18.
19.
Cooper JD. Bronchial omentopexy in canine lung transplantation. J THORAC CARDIOVASC SURG 1982;83:418-21. King M, Macklem PT. Rheological properties of microliter quantities of normal mucus. J Appl Physiol 1977; 42:797-802. Jeanneret-Grosjean A, King M, Michoud MC, Liote H, Amyot R. Sampling technique and rheology of human tracheobronchial mucus. Am Rev Respir Dis 1988;137:70710. Pavia D, Bateman JRM, Sheahan NF, Agnew JE, Newman SP, Clarke SW. Techniques for measuring lung mucociliary clearance. Eur J Respir Dis 1980;61 (supp!):157-77. Edmunds LH Jr, Stallone RJ, Graf PD, Sagel SS, Greenspan RH. Mucus transport in transplanted lungs of dogs. Surgery 1969;66:15-22. Stone RM, Ginsberg J, Colapinto RF, Pearson FG. Bronchial artery regeneration after radical hilar stripping. Surg Forum 1966;17:109-10. Katz I, Zwas T, Baum GL, et al. Ciliary beat frequency and mucociliairy clearance-What is the relationship? Chest 1987;92:491-3. Eliezer N, Sade J, Silberberg A, et al. The role of mucus in transport by cilia. Am Rev Respir Dis 1970;102:48-52. van As A. Pulmonary airway clearance mechanisms: a reappraisal. Am Rev Respir Dis 1977;115:721-6. Secrist WL, Trummer MJ. Nerve regeneration following lung reimplantation. Ann Thorac Surg 1967;4:125-32. Nigro SL, Hirsch EF, Rams JJ, Hamouda E, Adams WE. Regression of the intrinsic nerves and other sequelae with reimplantation of the lung. J THORAC CARDIOVASC SURG 1967;54:815-21. . EdmundsLH, Jr, GrafPD, NadelJA. Reinnervationofthe reimplanted canine lung. J Appl Physiol 1971;31:722-7.
CARDIOVASC SURG 1991;102:908-12
The reversibility of impaired mucociliary function after lung transplantation Impairment of mucociliary function occurs after lung transplantation and may predispose patients to repeated pulmonary infections. The purpose of this study is to determine whether and how soon such mucociliary function may recover. Ten dogs underwent left lung autotransplantation. Within 3 weeks five of these dogs underwent study for proximal airway clearance by observation through a bronchoscope of the movement of carbon particles placed at different locations on the tracheobronchial mucosa. The mechanical properties of coUected mucus from specific sites were determined by magnetic rheometry. The right lung, which was not operated on, served as a paired control. Similar studies were conducted in the remaining five dogs at 12 weeks after autotransplantation. Lung autotransplantation caused significant depression of proximal airway clearance and a 35 % increase in mucous rigidity (p = 0.05) soon after operation. At 12 weeks after operation, there was a partial recovery of proximal airway clearance. Mucous changes were no longer consistent. Histologic and electron microscopic examinations initiaUy revealed focal denudation of ciliated ceUs and loss of the bronchial glands. At 12 weeks there was a regeneration of cilia and a reappearance of the bronchial glands. We conclude that the mucociliary function, observed to be depressed early after lung autotransplantation, recovers partiaUy during the late postoperative period. Thus the mucociliary functional recovery should be attributed to revascularization rather than to reinnervation, since the latter is unlikely to occur during this period.
Daniel Marelli, MD, Andreas Paul, MD, Dao M. Nguyen, MD, Hani Shennib, MD, Malcolm King, PhD, Nai-San Wang, MD, PhD, James A. Wilson, MD, David S. Mulder, MD, and Ray c.-J. Chiu, MD, PhD, Montreal, Quebec, and Edmonton, Alberta, Canada
MucOCiliary function has been reported to be impaired after lung transplantation. I, 2 This may lead to repeated pulmonary infections, which are considered one of the limiting factors in the survival of patients who undergo such transplantations. Understanding this dysfunction could conceivably lead to treatments aimed at From the Departments of Surgery and Pathology, McGill University, Montreal, Quebec, and the University of Alberta Pulmonary Defense Group, Edmonton, Alberta, Canada. Supported in part by a grant from the Quebec Thoracic Society and from the Alberta Lung Association. Presented at the Sixteenth World Congress on Diseases of the Chest, Boston, Mass. Oct. 30-Nov. 3,1989. Received for publication Feb. 23, 1990. Accepted for publication Aug. 31,1990. Address for reprints: Ray C.-J. Chiu, MD, PhD, The Montreal General Hospital, 1650 Cedar Ave., Room 947, Montreal, Quebec, Canada, H3G lA4.
12/1/26545
908
reducing the prevalence of pulmonary infections in recipients of lung and heart-lung transplants. M ucociliary clearance is a physiological defense mechanism resulting from an interaction between the cilia and mucus of the bronchial epithelium.v 4 Mucociliary function can therefore be impaired as a result of alterations in cilia structure and function, alterations in mucous viscoelastic properties, or a combination of these. We have previously reported that changes in mucous rheologic properties after lung autotransplantation and allotransplantation can impair mucociliary function in the early postoperative period and occur simultaneously with alterations in mucosal structures.P Others have noted that bronchial mucosa is normal 1 year after lung autotransplantation in a canine model." It can therefore be hypothesized that impairment of mucociliary function after lung transplantation may be partially reversible as progressive healing of the bronchial anastomosis occurs. The purpose of the present study was to test this hypothesis by assess-
Volume 102
Mucociliary function in lung transplantation
Number 6 December 1991
909
Table I. Proximal airway clearance rates after lung autotransplantation, in millimeters per minute Before operation * 3 wkafter operation 12 wkafter operation
Trachea
Left lung
Right lung
lOA ± 2.1
7.8 ± 2.0
10.5 ± 3.0 13.5 ± 1.5
5.0 ± 3.5
6.9 ± 0.8 8.3 ± 1.0 8.0 ± 2.0
ot
Values are mean ± standard deviation. 'Values represent the mean for all dogs undergoing operation, tp < 0.05 when compared to preoperative value,
ing mucociliary function in the late period after lung autotransplantation and comparing these observations with previous studies of the early postoperative period.
Material and methods Ten dogs (20 to 30 kg) underwent left lung autotransplantation by a previouslydescribed technique." The bronchial anastomosis was performed at the level of the distal main-stem bronchus with interrupted 5-0 polypropylene sutures and wrapped with an omental flap.s Ischemia times ranged from 40 to 60 minutes. Healing of the bronchial anastomosis was verifiedby bronchoscopicstudy and lung function was confirmed by ventilation/perfusion scintigraphy with technetium 99mlabeled sulphur and albumin particles. Proximal airway mucociliary clearance was measured before operation in 'al1 animals. Within 3 weeks after operation, five dogs underwent study for proximal airway clearance and mucousrheologicstudies. Mucociliaryclearance measurements were repeated and compared with preoperative values. The mechanical properties of mucus col1ected distal1y from specific sites in both main-stem bronchi were determined by magnetic microrheometry. The right lung, which was not operated on, servedas a paired control for these studies. Postmortem studies consistedof light and electron microscopy.Similar studies were conducted after 12 weeks in the other five dogs. Measurement of mucociliary function. As previously described.' the animals were allowed to breathe spontaneously after sedation with diazepam (5 mg administered intravenously and xylazine hydrochloride (I to 2 mg/kg administered intravenously). After endotracheal intubation was accomplished, a bronchoscopewas passed into the tracheobronchial tree. Proximal airway clearance was measured by observing the movement of the leading edge of a spot of carbon particles suspended in saline deposited on the airway mucosa through polyethylene tubing threaded through the biopsy channel of the bronchoscope. Mucociliary clearance was measured sequential1y in the trachea, right main-stem bronchus, and the left main-stem bronchus during three separate IS-minute observation periods. A starting point I to 2 ern distal to the bronchial anastomosis was chosen for postoperative studies. Results are expressed in millimeters per minute. Mucous viscoelastic properties were analyzed by magnetic microrheornetry.? Samples of mucus were col1ected from the right and left main-stem bronchi with a cytology brush passed through the biopsychannel of the bronchoscopeand were stored at -80 0 C until analysis. This analysis consisted of oscillating a steel bal1 in a droplet of the sample. The force applied was electromagneticand measured in radians per second. Displace-
ment of the bal1 was tracked by photocel1s and the resulting signals were displayed on an oscilloscope, enabling calculation of mucous elasticity and viscosity.The logarithm of the vectorial sum of these is defined as log G*. This can be regarded as the resistance of the mucus to flow and is considered an index of rigidity. Measurements were conducted at frequencies of I and 100 radians/sec, representing normal ciliary and cough activity, respectively.The values for the mucus from either lung were compared and differences were calculated and compiled for each group. Statistical analysis was done by Student's paired t test. Animal care in all experiments was performed according to guidelines set by the Canadian Council for Animal Care.
Results Serial bronchoscopy and ventilation/perfusion scanning confirmed satisfactory postoperative function in all transplanted lungs. All the anastomoses healed with minimal stenosis. Three weeks after operation, perfusion scanning showed mean relative distribution of the initial burden to be 68.1 % ± 5.8% for the right lung and 31.9% ± 5.8% for the transplanted left lung. Similarly, ventilation scanning revealed the mean relative distribution ofthe initial burden for the right and transplanted left lungs to be 56.6% ± 3.7% and 43.4% ± 3.7%, respectively. Proximal airway mucociliary clearance, determined during a l5-minute observation period after deposition of carbon particles, was found to be absent 3 weeks after lung autotransplantation. The results of these early postoperative observations have been previously presented.i At 12 weeks after operation, there was partial recovery of carbon particle clearance in the transplanted lungs and no statistically significant difference could be detected in clearance rate between late postoperative and preoperative measurements (Table I). The bronchial anastomosis was not found to be an obstacle to clearance of the carbon particles. Mucociliary clearance rate in the trachea was unchanged in all postoperative studies. Also, when left lung clearance rates at 12 weeks were compared with right lung rates, no significant difference could be detected (p = 0.5). In all postoperative studies, the mucosa distal to the
The Journal of
9 10Marelli et ai.
Thoracic and Cardiovascular Surgery
Fig. 1. Light microscopy shows bronchial anastomosis 3 (A) and 12 (B) weeks after left lung autotransplantation. Note the change in the mucosa distal to the anastomosis (right side). (Hematoxylin and eosin stain; originalmagnification X400.)
bronchial anastomosis in the transplanted lung was noted to be more friable than that of the untreated right lung. Left lung mucus was compared with mucus from the right lung. Three weeks after operation, under measurement conditions comparable to those of normal ciliary activity (l radian/sec), the resistance to movement of left lung mucus was 35% ± 3% greater than that for mucus from the right lung (p < 0.05). At a force comparable to that of cough (l00 radians/sec), the mean increase was 35% ± 7% (p = 0.1). Twelve weeks after operation, results were no longer consistent, with wide variations observed. Some samples showed greater mucous rigidity in the left lung, whereas others showed slightly decreased or relatively unchanged mucous rigidity in the left lung, when compared with that of the right lung; the mean increase in left lung mucous rigidity was 35% ± 60% at a force of I radian/sec and 33% ± 37% at a force of 100 radians/sec (p> 0.4). Histologic and electron microscopic studies in the early postoperative period revealed focal denudation of ciliated cells and disappearance of the bronchial glands and their associated ducts distal to the bronchial anastomosis. Twelve weeks after lung autotransplantation, the anastomosis was found to be well healed and the mucosa distal
to the suture line closely resembled the normal mucosa proximal to the suture line. There was also regeneration of the ciliated cells and reappearance of the bronchial glands and ducts (Figs. I and 2). Discussion Impairment of mucociliary function after lung transplantation may be caused by both bronchial denervation and devascularization. It is also possible that subclinical rejection can contribute to mucociliary dysfunction. We 5 have previously shown that mucociliary function is impaired in the early period after lung autotransplantation and allotransplantation but not after sleeve resection with preservation of a flap of peribronchial tissue. There was no difference between autotransplanted and allotransplanted lungs. The purpose of this study was to assess mucociliary function in the late postoperative period in the canine lung autotransplant model. This obviates the need for and eliminates the effects of immunosuppression required for allografts. The experimental model used in this study consisted of complete bronchial denervation and devascularization. The long-term aspect of the study protocol introduces the possibility of bronchial revascularization and reinnerva-
Volume 102 Number 6 December 1991
tion. The endpoints chosen consisted of assessing and comparing mucociliary function in the early and late postoperative periods after lung autotransplantation. Thus an attempt was made to evaluate the possible effects of progressive bronchial healing on long-term mucociliary function in transplanted lungs. This was achieved by separating this function into its two components. Airway clearance was determined by observing movement of carbon particles deposited at specific locations in the tracheobronchial tree. Rheologic properties of mucus were studied with an ex vivo microrheometry model that quantifies the viscoelastic properties of mucus. Both of these methods have been previously described and have shown reproducible results. 10, II This study shows that there is partial recovery of airway mucociliary clearance rate in the late period after lung autotransplantation and that there is simultaneous regeneration of mucosal structures related to this function. The importance of anatomic integrity for mucociliary function is thus highlighted. These findings, consistent with those of early studies carried out by Edmunds and coworkers.F support the concept that complete bronchial disruption affects mucociliary clearance rate and that these specific effects are reversible as the bronchial anastomosis heals. Since revascularization is probably among the first events to occur during healing of the bronchial anastomosis.P it can be hypothesised that revascularization would account for the first observable reversal of impaired mucociliary clearance rate after lung autotransplantation. Mucociliary transport itself depends on the interaction between cilia and mucus. 14 This is determined mainly by the thickness, elasticity, and viscosity of the mucus. Particle transport, shown to fail in the absence of mucus, can be restored by placing autologous or heterologous mucus on intact ciliated epithelium, demonstrating the importance of mucus for normallung mucociliary function. 15, 16 The rheologic studies of mucus in our experiments showed increased rigidity during the early postoperative period. This is an atropine-like effect, and one can therefore infer that this effect may be related to lung denervation.'? These changes were not consistently demonstrable in the late postoperative period. Nerve regeneration after complete lung denervation is not well defined.U:'? It is possible that partial nerve regeneration may occur as early as 3 months after lung reimplantation, thus explaining the inconsistent changes in rheologic properties of mucus observed in the course of our study 12 weeks after lung autotransplantation. If this is the case, then it is conceivable that at a l Z-month interval after operation the rheologic properties of mucus may revert to normal. This would mean that clinical observations of impaired muco-
Mucociliary function in lung transplantation
9 11
Fig. 2. Electronmicroscopy shows bronchialanastomosis 3 (A) and 12 (B) weeks after left lung autotransplantation. Note that after 12weeks the mucosadistal to the anastomosis (right side) cannot be distinguished from the mucosa of the proximal airway. (A, Original magnification X120. B, Original magnification X45.)
ciliary clearance rates carried out long after lung allotransplantation could be attributable to immunologic factors, to impaired healing as a result of immunosuppressive therapy, or to subclinical infection. Indeed, this last situation, which may be a result of prolonged animal housing, may explain the inconsistent results of the mucous rheologic study at 12 weeks after operation." Further clinical studies are needed to determine whether changes in the rheologic properties of mucus persist in long-term survivors of lung allotransplantation. If present, these changes need to be correlated with histologic examination of the mucus to determine whether they are in fact due to the persistent effects of lung denervation or
The Journal of Thoracic and Cardiovascular Surgery
9 12Marelli et al.
are due, alternatively, to any of the other possible causes mentioned above, including undetected low-grade rejection. In conclusion, the present study shows that, after early postoperative impairment, there is partial recovery of mucociliary clearance rate 12 weeks after lung autotransplantation. This is probably attributable to bronchial revascularization, since reinnervation is unlikely to be complete during this period.
9.
10.
II.
REFERENCES I. Dolovich M, Rossman C, Chambers C, et al. Muco-ciliary function in patients following single lung or lung/heart transplantation. Am Rev Respir Dis 1987;135:A363. 2. Mancini MC, Griffith BP, Tauxe WN. Assessment of ciliary function in the tracheobronchial tree of the heart-lung transplant recipient. Surg Forum 1987;38:300-1. 3. Newhouse M, Sanchis J, Bienenstock J. Lung defense mechanisms (first of two parts). N Engl J Med 1976; 295:990-8. 4. Wanner A. Mucociliary clearance in the trachea. Clin Chest Med 1986;7:247-58: 5. Paul A, Marelli D, Shennib H, et al. Mucociliary function in autotransplanted, allotransplanted, and sleeve resected lungs. J THORAC CARDIOVASC SURG 1989;98:523-8. 6. Fujimura S, Kondo T, Handa M, et al. Histologic assessment of bronchial anastomotic healing in canine lung transplantation. J THORAC CARDIOVASC SURG 1987; 94:323-30. 7. Veith FJ, Richards K. Improved technique for canine lung transplantation. Ann Surg 1970;171:553-8. 8. Lima 0, Goldberg M, Peters WJ, Ayabe H, Townsend E,
12.
13.
14.
15. 16. 17. 18.
19.
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