A Longitudinal Pulmonary Function Study of Children with Thoracic Insufficiency Syndrome (TIS) Treated with Vertical Expandable Prosthetic Titanium Rib (VEPTR)**

Objective: Surgical management of children with VEPTR is reported to produce clinical improvements (J Bone Joint Surg 85: 409, 2003). To date, however, effects of VEPTR on lung function have not been reported, due in part to difficulties to study young handicapped children. The forced deflation (FD) technique to obtain reproducible maximum expiratory flow-volume (MEFV) curves is a unique technique originally developed to study infants and children in the ICU (Am Rev Respir Dis 136: 50, 1987). The current study has been undertaken to evaluate the efficacy of VEPTOR under general anesthesia with pulmonary function tests (PFTs) using the FD technique.

Design and Methods: PFTs were performed in 10 children (1.8-9.8 years; median, 4.3 at the first test), with TIS of varying etiologies, 35 different occasions during before and immediately after the surgical insertion of VEPTRs. PFT was repeated every 6 to 12 months thereafter during the surgical expansion of VEPTR. The time span between the first and last test ranged 7-25 months. Forced vital capacity (FVC) and the maximum expiratory flow at 90% of FVC (MEF10/FVC, an index of lower airway conductance) were obtained from MEFV curves. Respiratory system compliance (Crs) and inspiratory capacity (IC) were obtained with passive lung deflation from static airway pressures of 10 and 40 cmH2O, respectively.

Results: 1). There were no significant differences in PFT indices before and right after VEPTR expansion, apparently due to prevention of immediate lung expansion by the stiff parietal pleura. 2). Not surprisingly, initial lung volume (FVC: 69 ± 13.4% pred.) was moderate to severely decreased. After VEPTR expansion, FVC in absolute terms markedly increased (26 ± 23.3% /year; p<.0001). 3). IC also increased markedly (16 ± 16.7%/year). There appears to be a trend of less increase in lung volumes among older children (> 6 years). 4). In terms of % pred. based on height (or arm span), however, increases in FVC (+3.4 ± 16.7%/year, ns) just kept up with increases in body size (or height). 5). MEF10/FVC, an index of lower airway conductance, was within normal range in most patients and was essentially unchanged with growth. 6). Crs was decreased, indicating the stiff thorax and did not change significantly with growth.

Discussion and Conclusion: VEPTR expansion of the thorax appears to help increase lung volumes and keeps up with subsequent body growth. The exact extent of clinical benefit by this procedure is difficult to judge but may be more than the numbers indicate, since there is no control group of children without surgical corrections, whose lung function would certainly deteriorate further with time with increasing scoliotic changes.

**The FDA has not cleared a drug and/or medical device the use described in this presentation (i.e., the drug or medical device is being discussed in an "off-label" use).