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J Thorac Cardiovasc Surg 2000;119:191-192
© 2000 Mosby, Inc.


LETTERS TO THE EDITOR

In vivo estimation of septal lung tissue volume and correlation with diffusing capacity in lung volume reduction surgery

Shin-ichi Takeda, MD

First Department of Surgery, Osaka University Medical School, 2-2 Yamada-oka, Suita City
Osaka 565-0871, Japan

Aaron S. Estrera, MD, Connie C. W. Hsia, MD

Departments of Surgery and Internal Medicine, University of Texas Southwestern Medical Center
Dallas, TX 75235-9034

To the Editor

We read with great interest the recent paper by J. C. Chen and associatesGo 1 about the diffusing capacity limitations of the extent of lung volume reduction surgery (LVRS) in animal models of emphysema. The authors induced diffuse emphysema by aerosol elastase, a model similar to the homogenous type of human emphysema. However, patients with emphysema who are good candidates for LVRS tend to have heterogeneous targeted areas for resection,Go 2 as Cooper has mentioned.Go 1 In these patients, improvement in respiratory system compliance is prominent even after resection of a large volume of the lung. In contrast, diffusing capacity deteriorated when the resected volume exceeded a threshold. In the setting of major lung resection, diffusing capacity may predict the postoperative morbidity and mortality.Go 3 We believe that the importance of diffusing capacity in LVRS needs to be emphasized. The goal of LVRS should be a balance between improving mechanical function of the lung and diaphragm without excessive loss of diffusing capacity or of the pulmonary vascular bed. We congratulate Chen and associates for raising this important issue.

In Dallas, weGo Go 4,5 have performed extensive studies to determine the diffusion limitation after major lung resection at rest and during exercise. Here, we would like to introduce a method of assessing the diffusing capacity and septal lung tissue volume in vivo using combined radiologic and physiologic techniques. We believe this approach has potentially important applications in LVRS. With the use of an acetylene and a carbon monoxide rebreathing method, lung air volume, tissue volume, diffusing capacity, and cardiac output can be simultaneously and noninvasively measured.Go 4 In addition, tissue volume and air volume were also separately estimated by computed tomographic (CT) scan, from which topologic distribution of tissue and air volumes are obtained.Go 6 We compared tissue volume measured by these 2 techniques in immature dogs at different ages. Half the dogs had undergone resection of the right lung; the other half had undergone thoracotomy without lung resection. WeGo 6 found significant correlations (P < .01) between tissue volume measured by CT and rebreathing and between tissue volume and diffusing capacity in both groups (Fig 1, A and B). These data suggest that tissue volume is an anatomic correlate of gas exchange capacity.



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Fig. 1. Measurement of tissue volume and diffusing capacity by computed tomography and rebreathing. Vt, Tissue volume; RB, rebreathing; CT, computed tomography; DLCO, diffusing capacity of carbon monoxide.

 
The article by Chen and associates reinforces the point that the key functional parameter of gas exchange is not total lung volume, but diffusing capacity and tissue volume. Measurement of diffusing capacity and tissue volume may aid the functional evaluation of patients with emphysema, although their predictive value in the setting of LVRS requires further investigation. For example, preoperative measurement of diffusing capacity and tissue volume by the rebreathing method could identify patients with insufficient gas exchange reserves who would not benefit from LVRS regardless of improvements in mechanical lung and respiratory muscle function. In addition, one could potentially use CT scan to map out the topologic distribution of tissue volume and to target regions with a low tissue volume (high air/tissue volume ratio) for resection.

References

  1. Chen JC, Serna DL, Powell LL, Huh J, McKenna R Jr, Fischel RJ, et al. Diffusing capacity limitations of the extent of lung volume reduction surgery in an animal model of emphysema. J Thorac Cardiovasc Surg 1999;117:728-35.[Abstract/Free Full Text]
  2. Weder W, Thurnheer R, Stammberger U, Burge M, Russi EW, Bloch KE. Radiologic emphysema morphology is associated with outcome after lung volume reduction. Ann Thorac Surg 1997;64:313-20.[Abstract/Free Full Text]
  3. Ferguson MK, Reeder LB, Mick R. Optimizing selection of patients for major lung resection. J Thorac Cardiovasc Surg 1995;109:275-83.[Abstract/Free Full Text]
  4. Carlin JI, Hsia CCW, Cassidy SS, Ramanathan M, Crifford PS, Johnson RL. Recruitment of lung diffusing capacity with exercise before and after pneumonectomy in dogs. J Appl Physiol 1991;70:135-42.[Abstract/Free Full Text]
  5. Johnson RL, Hsia CCW. Functional recruitment of pulmonary capillary. J Appl Physiol 1994;76:1405-7.[Free Full Text]
  6. Takeda S, Wu EY, Epstein RH, Estrera AS, Hsia CCW. In vivo assessment of changes in air and tissue volumes after pneumonectomy. J Appl Physiol 1997;82:1340-48.[Abstract/Free Full Text]



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