Effects of Nd:YAG laser irradiation on morphometry and lung function in elastase-induced emphysema in rats

Development of a canine model of pulmonary emphysema and imaging of the emphysematous lung with infrared thoracoscopy

BACKGROUND

The surgeon must use the results of preoperative computed tomography findings and scintigraphic studies to make a subjective decision during lung volume reduction surgery with regard to the best incision line.

OBJECTIVES

Our purpose was to develop an objective and real-time method of detecting areas of pulmonary emphysema by using infrared thoracoscopy.

METHODS

Pulmonary emphysema was developed in various lobes of the lung in the dog by injecting porcine pancreatic elastase through the bronchi. One month after the injection, chest computed tomography and lung biopsy were performed. Infrared thoracoscopic study was then performed to reveal the presence of the emphysematous lung tissue. Simultaneously, indocyanine green was injected intravenously, and the time taken for each type of lung tissue to stain blue was measured.

RESULTS

Chest computed tomography and histologic examinations revealed pulmonary emphysema-like areas in the porcine pancreatic elastase-injected lung. The computed tomography numbers of the porcine pancreatic elastase-injected lung tissue, normal lung tissue, and the tracheal lumen were -868.8 +/- 18.6, -752.2 +/- 32.5, and -1013 +/- 27.1, respectively. There were significant differences between the porcine pancreatic elastase-injected lung and the normal lung (P <.0001). The time for staining to begin was 10.7 +/- 4.8 seconds for normal lung tissue and 25.8 +/- 9.4 seconds for the emphysematous tissue; the onset of staining emphysematous lung tissue was significantly delayed (P =.003).

CONCLUSIONS

We developed a successful canine model of pulmonary emphysema by injecting porcine pancreatic elastase. Infrared thoracoscopic examination revealed that the staining of emphysematous lung using indocyanine green injection was significantly greater than of normal lung.

Myosin heavy chain and physiological adaptation of the rat diaphragm in elastase-induced emphysema

BACKGROUND

Several physiological adaptations occur in the respiratory muscles in rodent models of elastase-induced emphysema. Although the contractile properties of the diaphragm are altered in a way that suggests expression of slower isoforms of myosin heavy chain (MHC), it has been difficult to demonstrate a shift in MHCs in an animal model that corresponds to the shift toward slower MHCs seen in human emphysema.

METHODS

We sought to identify MHC and corresponding physiological changes in the diaphragms of rats with elastase-induced emphysema. Nine rats with emphysema and 11 control rats were studied 10 months after instillation with elastase. MHC isoform composition was determined by both reverse transcriptase polymerase chain reaction (RT-PCR) and immunocytochemistry by using specific probes able to identify all known adult isoforms. Physiological adaptation was studied on diaphragm strips stimulated in vitro.

RESULTS

In addition to confirming that emphysematous diaphragm has a decreased fatigability, we identified a significantly longer time-to-peak-tension (63.9 +/- 2.7 ms versus 53.9 +/- 2.4 ms). At both the RNA (RT-PCR) and protein (immunocytochemistry) levels, we found a significant decrease in the fastest, MHC isoform (IIb) in emphysema.

CONCLUSION

This is the first demonstration of MHC shifts and corresponding physiological changes in the diaphragm in an animal model of emphysema. It is established that rodent emphysema, like human emphysema, does result in a physiologically significant shift toward slower diaphragmatic MHC isoforms. In the rat, this occurs at the faster end of the MHC spectrum than in humans.

Sarcomeres are added in series to emphysematous rat diaphragm after lung volume reduction surgery

STUDY OBJECTIVES

The diaphragm adapts to its shortened state in experimental emphysema primarily by losing sarcomeres in series, thus reducing its optimal operating length. One would expect improved diaphragmatic function after lung volume reduction surgery (LVRS) only if the muscle can readapt to its elevated, lengthened postoperative position by either adding back sarcomeres or lengthening sarcomeres. We used a model of elastase-induced emphysema in rats to test the hypothesis that sarcomere addition occurs following LVRS.

DESIGN

A cohort of emphysematous rats was created by the intratracheal instillation of elastase. Five months after the instillation, one group of rats underwent measurement of in situ costal diaphragm length via laparotomy, the determination of optimal muscle fiber operating length (Lo) on stimulated diaphragm strips in vitro, and the measurement of sarcomere length by electron microscopy on strips fixed at Lo. Another group of rats underwent LVRS or sham sternotomy 5 months after the instillation, and 5 months following the operation these animals underwent the same series of diaphragmatic studies.

RESULTS

Lo was significantly greater in rats that underwent LVRS than those that underwent sternotomy (mean [+/- SE] Lo after LVRS, 2.50 +/- 0.08 cm; mean Lo after sternotomy, 2.27 +/- 0.06 cm; p = 0.013). There was no significant difference in sarcomere lengths between the two groups (2.95 +/- 0.04 vs 3.04 +/- 0.04 microm, respectively; p = 0.10). Using Lo as the length basis, the mean sarcomere number was calculated to be 8,712 +/- 192 in animals that had undergone LVRS and 7,144 +/- 249 in animals that had undergone sternotomy (p < 0.001).

CONCLUSION

Sarcomere length is not significantly altered but sarcomeres are added in series following LVRS in this experimental model of emphysema/LVRS. It is likely that this sarcomere addition is a prerequisite to the improvement in inspiratory muscle function that has been observed following LVRS in humans.