raises more questions than convincing answers. One should be cautious about taking immature preclinical concepts from the laboratory to the clinic without sophisticated scientific founda- tion [6]. Heike Mertsching, PhD General Thoracic Tissue Engineering Club (LEBAO) Department of Thoracic and Vascular Surgery Heidehaus Hospital Hannover Medical School Am Leineufer 70 D-30419 Hannover, Germany Thorsten Walles, MD Paolo Macchiarini, MD, PhD Department of Thoracic and Vascular Surgery Heidehaus Hospital Hannover Medical School Am Leineufer 70 D-30419 Hannover, Germany e-mail: pmacchiarini@compuserve.com References 1. Martinod E, Seguin A, Pfeuty K, et al. Long-term evaluation of the replacement of the trachea with an autologous aortic graft. Ann Thorac Surg 2003;75:1572–8. 2. Mathisen DJ. Long-term evaluation of the replacement of the trachea with an autologous aortic graft [Invited commentary]. Ann Thorac Surg 2003;75:1578. 3. Walles T, Herden T, Haverich A, Mertsching H. Influence of scaffold thickness and scaffold composition on bioartificial graft survival. Biomaterials 2003;24:1233–39. 4. O’Brien MF, Goldstein S, Walsh S, Black KS, Elkins R, Clarke D. The SynerGraft valve: a new acellular (nonglutaraldehyde- fixed) tissue heart valve for autologous recellularization. First experimental studies before clinical implantation. Semin Thorac Cardiovasc Surg 1999;11(4 Suppl 1):194 –200. 5. Walles T, Puschmanr C, Haverich A, Mertsching H. Acellular scaffold implantation—no alternative to tissue engineering. Int J Artif Organs 2003;26:225–34. 6. Simon P, Kasimir MT, Seebacher G, et al. Early failure of the tissue engineered porcine heart valve SYNERGRAFT in pe- diatric patients. Eur J Cardio-thorac Surg 2003;23:1002–6. Reply To the Editor: We thank Drs Mertsching and associates for their interest in our work on tracheal replacement using an autologous aortic graft and particularly for pointing out that the results of our study raise many intriguing questions about the regeneration of tra- cheal tissue from an aortic graft [1]. We understand their reluctance to believe what we ourselves observed with great surprise. However, when scientific findings are stubbornly du- plicated in repeated, carefully conducted experimentation, it is hard not to believe them. We will clarify some points. First, we did not say that the inflammatory process was linked to the presence of a stent. Rather, we found that the inflammation of the transplanted aortic segment was less important in the group with the silicone stent and that we obtained a complete regen- eration of a mucociliary epithelium after removal of the stent. Second, there is no question that a certain degree of ischemia of the aortic graft may play a role in triggering the tissue transfor- mation. However, it did not lead to a degenerative process but to a reconstructive process, which had not been observed until then. We think that this initial process of inflammation could have created favorable conditions for tracheal regeneration, as it has previously been observed with other tissues such as the liver [2]. We also stressed how “mysterious” the appearance of newly formed cartilage is, and this leads to hypotheses that should be investigated. Third, we have not found it necessary to quantify collagen II in the extracellular matrix because it is well known that collagen II is a major component of newly formed cartilage. We will certainly continue our investigation to try to clarify the mechanisms involved in this transformation. Fourth, the fact that previous work on guided tissue regeneration and tissue engineering has been associated with disappointing results up to now does not mean that with improved techniques and perseverance, they will not succeed 1 day. In any case, our approach has been quite different. Finally, we thank the discussants for the usual ethical recom- mendation concerning the clinical application of a new tech- nique. This was superfluous, as we have not yet tried the method in a clinical setting. However, we have now a 3-year follow-up with no complications in 14 sheep, and Hazekamp and Nijdam [3] have used aortic tissue to patch a long tracheal stenosis in 2 newborns and an autologous carotid artery patch in a 4-month- old girl; the results have been encouraging. Emmanuel Martinod, MD Service de Chirurgie Thoracique et Vasculaire Ho ˆ pital Avicenne 125 Route de Stalingrad 93000 Bobigny, France e-mail: emartinod@wanadoo.fr Alain F. Carpentier, MD, PhD Laboratoire d’Etude des Greffes et Prothe `ses Cardiaques Ho ˆ pital Broussais UPRES 264, Universite ´ Paris 6 96 Rue Didot 75014 Paris, France References 1. Martinod E, Seguin A, Pfeuty K, et al. Long-term evaluation of the replacement of the trachea with an autologous aortic graft. Ann Thorac Surg 2003;75:1572–8. 2. Libbrecht L, Desmet V, Van Damme B, Roskams T. Deep intralobular extension of human hepatic ‘progenitor cells’ correlates with parenchymal inflammation in chronic viral hepatitis: can ‘progenitor cells’ migrate? J Pathol 2000;192: 373–8. 3. Hazekamp MG, Nijdam N. Use of autologous arterial patches for tracheal reconstruction in young infants [Letter]. Ann Thorac Surg 2004;7:. The Importance of Obstructed and Unobstructed Segments to be Resected in Predicting Postoperative FEV 1 To the Editor: I have just read the article by Sekine and colleagues [1]. In the text, a modified formula for calculating the predicted postoper- ative (ppo) forced expiratory volume in 1 second (FEV 1 ) after lobectomy on the basis of the following equation was offered: ppo FEV 1 = preoperative FEV 1  1 - S  0.0526, where S is the number of resected bronchopulmonary segments [2]. For lobectomy there is a strong correlation between the 1133 Ann Thorac Surg CORRESPONDENCE 2004;78:1130 – 4 © 2004 by The Society of Thoracic Surgeons 0003-4975/04/$30.00 Published by Elsevier Inc MISCELLANEOUS