Physiologic limits of resection and intraoperative methods for determining optimal LVRS lung resection volumes for emphysema

Purpose: For lung volume reduction surgery (LVRS), the physiologic factors limiting the maximal extent of resectable lung tissue can only be assessed with animal models at this time. We measured physiologic response to LVRS in rabbits with elastase induced emphysema in order to determine which variables limit LVRS resection volumes. We hypothesized that spirometry and compliance would improve with progressively larger volume resections, but diffusion would limit maximal resections. Methods: We induced emphysema in 76 male New Zealand White rabbits by aerosolizing elastase through an endotracheal tube. LVRS was performed 4 weeks after emphysema induction and sacrifice 1 week postoperatively. Compliance, early forced expiratory flow (FEF33%), and diffusing capacity for carbon monoxide (DLCO) were measured prior to emphysema induction, surgery, and sacrifice. Rabbits were divided into 3 treatment groups (₁-sham surgery, ₂-less than, and ₃-greater than 3 grams lung resected). Results: Static respiratory system compliance with 60cc insufflation above FRC decreased witn progressively larger resection (ANOVA, p<0.001). Early forced expiratory flow (FEF33) decreased after sham surgery and small resection volumes and increased with large resection (p=0.31). DLCO worsened in all groups and most in rabbits with larger resection volumes. Conclusions: 1) This animal model provides a unique opportunity to address important questions concerning limits and optimization of LVRS. 2) The extent of LVRS in this model appears limited by diffusing capacity and pulmonary circulation. 3) With further refinement, intraoperative assessment of pulmonary circulatory physiology may help determine optimal resection volumes. Clinical Implications: Since some physiologic variables improve, while others deteriorate with increasing resection volumes, it may someday be possible to individualize the extent of resection based on relative preoperative impairment of specific variables. Further studies under resting and exercise conditions are clearly needed in this important field.