Measurement of the elastic modulus of porcine septal cartilage specimens following Nd: YAG laser treatment.

Laser cartilage reshaping is a temperature-dependent process that results in stress relaxation with subsequent formation of a new and stable specimen geometry. The objective of this study was to quantitatively measure changes in the elastic moduli of porcine cartilage following laser heating. The elastic modulus of porcine nasal septal cartilage specimen (25 x 5 x 2 mm) was measured before and after Nd: YAG laser (lambda=1.32 Irvinem, 21.22 W/cm2) irradiation and following rehydration in saline solution. Specimens were secured in a single beam cantilever configuration and displaced using a calibrated thin beam load cell attached to a motorised micropositioner. Elastic modulus was calculated using elastic beam theory. Measurements were recorded before and immediately after laser heating, and following rehydration in saline solution (40 minutes, 25 degrees C). Specimens heated in saline (100 degrees C and then re-hydrated) were used as controls to determine the effect of total thermal denaturation. The calculated moduli before and after irradiation were 4.86 +/- .145 MPa and 1.166 +/- .055 MPa respectively. Following rehydration in saline, the modulus returned to near-baseline values (5.119 +/- .163 MPa). In contrast, elasticity remained lower in specimens boiled and re-hydrated (3.25 +/- .130 MPa). These findings suggest that cartilage matrix does not undergo complete thermal denaturation during laser reshaping, given the return in tissue properties with rehydration.

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.