Changes in pulmonary physiology after lung volume reduction surgery in a rabbit model of emphysema

Deficiency in pigment epithelium-derived factor accelerates pulmonary growth and development in a compensatory lung growth model

Children with hypoplastic lung disease associated with congenital diaphragmatic hernia (CDH) continue to suffer significant morbidity and mortality secondary to progressive pulmonary disease. Recently published work from our lab demonstrated the potential of Roxadustat (FG-4592), a prolyl hydroxylase inhibitor, as a treatment for CDH-associated pulmonary hypoplasia. Treatment with Roxadustat led to significantly accelerated compensatory lung growth (CLG) through downregulation of pigment epithelium-derived factor (PEDF), an anti-angiogenic factor, rather than upregulation of vascular endothelial growth factor (VEGF). PEDF and its role in pulmonary development is a largely unexplored field. In this study, we sought to further evaluate the role of PEDF in accelerating CLG. PEDF-deficient mice demonstrated significantly increased lung volume, total lung capacity, and alveolarization compared to wild type controls following left pneumonectomy without increased VEGF expression. Furthermore, Roxadustat administration in PEDF-deficient mice did not further accelerate CLG. Human microvascular endothelial lung cells (HMVEC-L) and human pulmonary alveolar epithelial cells (HPAEC) similarly demonstrated decreased PEDF expression with Roxadustat administration. Additionally, downregulation of PEDF in Roxadustat-treated HMVEC-L and HPAEC, a previously unreported finding, speaks to the potential translatability of Roxadustat from small animal studies. Taken together, these findings further suggest that PEDF downregulation is the primary mechanism by which Roxadustat accelerates CLG. More importantly, these data highlight the critical role PEDF may have in pulmonary growth and development, a previously unexplored field.

Computerized estimation of the lung volume removed during lung volume reduction surgery

RATIONALE AND OBJECTIVES

This study was designed to develop an automated method for estimating lung volume removed during lung volume reduction surgery (LVRS) using computed tomography (CT).

MATERIALS AND METHODS

The CT examinations of six patients who underwent bilateral LVRS were analyzed in this study. The resected lung tissue (right and left) was weighed during pathologic examination. An automated computer scheme was developed to estimate the lung volume removed using the CT voxel values and lung specimen weight. The computed fraction of lung volume removed was evaluated across a range of simulated surgical planes (ie, other than parallel to the CT image plane) and CT reconstruction kernels, and it was compared with the surgeons' postsurgical estimates.

RESULTS

The computed fraction of the lung volume removed during LVRS was linearly correlated with the resected lung tissue weight (Pearson correlation = 0.697, P = .012). The computed fraction of lung volume removed ranged from 12.9% to 51.7% of the total lung volume. The surgeons' postsurgical estimates of lung volume removed ranged from 30% to 33%. The percent difference between the surgeons' estimates and the computed lung volume removed as a percentage of the surgeons' estimates ranged from -72.3% to 57.0% with mean absolute difference of 29.7% (+/-20.7).

CONCLUSION

The preliminary findings of this study suggest that the proposed quantitative model should provide an objective measure of lung volume removed during LVRS that may be used to investigate the relationship between lung volume removed and outcome.

A New, Simple Stapling Technique for Pulmonary Emphysema: Its Effects and Safety for Improving Respiratory Function

PURPOSE

We performed lung volume reduction surgery (LVRS) in an experimental model using a simple stapling technique (SST) for pulmonary emphysema. The technique uses a stapler to isolate the affected lung from the remaining lung instead of removing it. We performed the present experiment using dogs to study the effects and safety of LVRS using the SST.

METHODS

Pulmonary emphysema was induced in 12 dogs with papain. They were divided into three groups: those operated on with SST composed the operation (Op) group; those receiving an experimental thoracotomy composed the sham-operation (Sham-op) group; and those not operated on composed the nonoperation (Non-op) group. Respiratory function was compared among the groups before induction of emphysema (baseline), after induction of emphysema (preoperation), and at 8 weeks after the operation (postoperation Op and Sham-op groups only). The lung was removed and histologically examined 8 weeks after the SST operation.

RESULTS

In the Op group, alteration in forced expiratory volume (FEV) 0.5%, airway resistance (Raw) and specific airway conductance (sGaw) showed significantly favorable results. Histologically, the isolated area was widely replaced by fibrous tissue with numerous blood vessels in the circumference in the Op group; no signs of infection such as polykaryoleukocytes or microabscesses were observed in any of the samples.

CONCLUSION

The LVRS for pulmonary emphysema using a simple stapling technique improved the expiratory flow and alleviated airway resistance. The isolated remaining lung was well organized without any infectious events or secondary adversity, thus demonstrating the safety of this technique. From these results, this technique is therefore suggested to be effective and applicable to clinical use.

Elastase-induced changes in lung function: relationship to morphometry and effect of drugs

Intratracheal administration of porcine pancreatic elastase (PPE) produced a dose related decline in lung function, as assessed by changes in dynamic lung compliance (C(dyn)) in New Zealand White rabbits. This occurred within 24 h of administration and persisted for 56 days (n=6). These lung function changes were accompanied by histological evidence of emphysema in the lungs and were not mimicked by intratracheal administration of the proteolytic enzyme trypsin. Neither the lung function nor the histological changes induced by elastase could be prevented or reversed by either the glucocorticosteroid, dexamethasone, or all trans retinoic acid (ATRA).Our data suggest that local administration of elastase to the lungs of rabbits may provide a convenient way to assess the effects of drugs on the changes induced by elastase in airways.

Effects of a novel implantable elastomer device for lung volume reduction surgery in a rabbit model of elastase-induced emphysema

OBJECTIVES

There is intense interest in lung volume reduction surgery (LVRS) for treatment of severe symptomatic emphysema. LVRS results in objective and subjective improvement in lung function in selected patients. However, LVRS is complicated by substantial morbidity, including prolonged pulmonary air leak associated with resection of emphysematous lung tissue. In this study, we investigated the use of a novel implanted silicone elastomer device that reduces lung volume without surgical resection, in a previously reported emphysematous animal model. The purpose of this investigation was to determine the applicability, physiologic effects, complications, and air-leak results of this lung volume reducer (LVR) approach.

DESIGN

Controlled, randomized, prospective animal study. Emphysema was induced in 20 New Zealand white rabbits with three nebulizations of 10,000 U of porcine elastase. After 6 weeks, the animals were randomized to control sham surgery (n = 10) vs implanted silicone elastomer LVR (n = 10) treatment groups. Lung function, including helium-dilution lung volumes, static respiratory system compliance curves, and diffusion capacity of the lung for carbon monoxide (DLCO), was measured at baseline, following emphysema induction (week 6), and when the animals were killed (1 week after LVR or sham surgery). Histologic evaluation was performed in all lung specimens after fixation.

RESULTS

Moderate emphysema developed after elastase nebulization, assessed by lung function and postmortem histology. Functional residual capacity (FRC) and an upward shift of lung compliance curves was observed with development of emphysema at 6 weeks (p < 0.05). Following LVR, FRC decreased (p = 0.005) and compliance curves shifted back downward (p = 0.002), without reduction in DLCO. There was no change in control sham animals. DLCO did not change in either group.

CONCLUSIONS

In this short-term, randomized, controlled animal model study, the implantable LVR approach produced safe and effective lung volume reduction without tissue resection in the treated animals. The implant procedure produced minimal morbidity, no mortality, and no observed air-leak complications in the treated animals. Limitations include the short-term follow-up and moderate degree of emphysema in this animal model. Further research is required to assess long-term effects and complications of this method for lung volume reduction.

Lung volume reduction surgery restores the normal diaphragmatic length-tension relationship in emphysematous rats

OBJECTIVE

Improved respiratory muscle function is a major effect of a lung volume reduction surgery. We studied length adaptation in rat diaphragmatic muscle in an attempt to elucidate the mechanism by which diaphragmatic function improves after this controversial operation.

METHODS

We developed a model of elastase-induced emphysema and bilateral volume reduction through median sternotomy in rats. Five months after emphysema induction, maximum exchangeable lung volume was determined in intubated and anesthetized control animals and animals with emphysema. Costal diaphragmatic length was measured in vivo, and the length at which maximal twitch force is generated was determined on muscle strips in vitro. Also 5 months after elastase administration, another cohort underwent volume reduction or sham sternotomy. Five months after the operation, these animals were similarly studied.

RESULTS

Lung volume was increased in emphysematous rats versus control rats (50.9 +/- 1.7 vs 45.4 +/- 1.3 mL, P =.001). Lung volume was decreased in emphysematous animals that had undergone volume reduction versus sham sternotomy (44.7 +/- 0.60 vs 49.4 +/- 1.0 mL, P =.001). In situ diaphragm length (1.99 +/- 0.04 vs 2.24 +/- 0.07 cm, P =.001) and the length at which maximal twitch force is generated (2.25 +/- 0.06 vs 2.48 +/- 0.09 cm, P =.038) were shorter in emphysematous than control animals. After volume reduction, in situ diaphragm length (2.13 +/- 0.06 vs 1.83 +/- 0.02 cm, P <.001) and the length at which maximal twitch force is generated (2.50 +/- 0.08 vs 2.27 +/- 0.06 cm, P =.013) were longer than in animals undergoing sham sternotomy.

CONCLUSIONS

In this experimental model of emphysema and lung volume reduction surgery, emphysema shortens the length at which maximal twitch force is generated and shifts the diaphragmatic length-tension curve to lower lengths; volume reduction returns the length at which maximal twitch force is generated toward normal and shifts the diaphragmatic length-tension curve back to longer lengths. This restoration toward normal physiology may enable the improvement in diaphragmatic function seen after lung volume reduction surgery. The mechanism by which these length adaptations occur merits further investigation.

Lung volume reduction surgery does not improve diaphragmatic contractile properties or atrophy in hamsters with elastase-induced emphysema

It is claimed that lung volume reduction surgery (LVRS) improves inspiratory muscle function. As diaphragm structure and function are not directly appraisable in patients, we studied the effects of LVRS on the diaphragm in vitro contractile properties and morphology in hamsters with elastase-induced emphysema. Four months after intratracheal instillation of elastase (40 U/100 g), hamsters underwent either bilateral LVRS (LVRS, n = 11) or a sham operation (SHAM, n = 8). Four animals died during the perioperative period in LVRS (n = 7). Hamsters instilled with saline served as control (CTL, n = 8). Animals were studied at the age of 9 mo. LVRS was associated with a significant 25% decrease in functional residual capacity compared to SHAM (p < 0.05). Compared with CTL, LVRS and SHAM showed a significant 18% and 14% reduction in diaphragm mass, respectively (p = 0.02). LVRS had a significantly decreased twitch tension compared to CTL and SHAM (p < 0.01). Both LVRS and SHAM showed increased resistance to muscle fatigue compared with CTL. The histochemical analysis revealed a significant shift from type IIx/b toward type IIa fibers in LVRS and SHAM compared with CTL. In conclusion, emphysema is associated with functional adaptations but LVRS does not appear to beneficially alter the diaphragm contractile and morphological characteristics in hamsters with elastase-induced emphysema.

Relationship between amount of lung resected and outcome after lung volume reduction surgery

BACKGROUND

Lung volume reduction surgery (LVRS) is being actively investigated for palliative treatment of severe emphysema. Considerable focus is directed toward patient selection and outcomes of LVRS. However, there is little information available regarding surgical methods to guide optimal extent of resection. We hypothesized that acute improvement and long-term survival after bilateral staple LVRS would be related to the extent of tissue resected.

METHODS

The relationship between acute improvement in forced expiratory volume in 1 second and forced vital capacity was examined as a function of the total grams of lung tissue resected in 237 patients who underwent bilateral staple LVRS by a single group of surgeons. Overall survival was assessed based on extent of resection by quartiles of tissue weight resected using Kaplan-Meier survival methods.

RESULTS

Improvement in forced expiratory volume in 1 second and forced vital capacity correlated with extent of tissue resected (p < 0.01), although there was considerable variability to individual response (r = 0.3). In contrast, there was no apparent relationship between the amount of tissue resected and overall postoperative survival (p = 0.7).

CONCLUSIONS

There is a correlation between the amount of tissue resected and improvement in forced expiratory volume in 1 second and forced vital capacity after bilateral staple LVRS, with generally greater postoperative improvement after larger volume resections. However, there does not appear to be greater long-term survival with larger volume resections despite greater improvement in spirometry. This study suggests that factors other than improvement in spirometric variables may govern optimal LVRS resection volumes and long-term outcome. Future studies will clearly be needed in this important area of LVRS emphysema research.

A surgical approach for patients with endstage emphysema

For patients with emphysema who experience deteriorating lung function and concomitant comorbidity, there has been little to offer apart from best supportive care and more recently pulmonary rehabilitation. The early promise of lung transplantation for these patients has failed to materialize--a shortage of donors has meant that younger patients are more likely to receive donor lungs. A renewed interest in lung volume reduction surgery (LVRS) appears to offer hope for selected patients. This article looks at the history of LVRS and illustrates its benefits with a case study. However, if LVRS is a clinically significant approach to the treatment of emphysemic patients, then it requires careful clinical trials so that its benefits and costs can be fully evaluated.

Diffusing capacity limitations of the extent of lung volume reduction surgery in an animal model of emphysema

OBJECTIVE

The purpose of this study was to investigate in an elastase-induced emphysema rabbit model the effects of increasing resection volumes during lung volume reduction surgery on pulmonary compliance, forced expiratory air flow, and diffusing capacity to assess factors limiting optimal resection.

METHODS

Emphysema was induced in 68 New Zealand White rabbits with 15,000 units of aerosolized elastase. Static respiratory system compliance, forced expiratory flow, and single-breath diffusing capacity were measured before the induction of emphysema, after the induction of emphysema, and 1 week after a bilateral upper and middle lobe lung volume reduction operation.

RESULTS

Static respiratory system compliance with 60 mL insufflation above functional residual capacity increased with emphysema induction and then decreased progressively with resection of larger volumes of lung tissue (P =.001 by analysis of variance). Expiratory flow improved after lung resection in the rabbits with large resection volumes. In contrast, diffusing capacity tended to deteriorate with larger resection volumes (P =. 18).

CONCLUSION

Improvements in respiratory system compliance and forced expiratory flow after lung volume reduction operations may account for the improvements seen clinically. Declines in diffusing capacity with extensive lung reduction may limit the clinical benefits associated with greater tissue resection volumes. Future investigations with animal models may reveal other physiologic parameters that may further guide optimal lung volume reduction procedures.