Conference: 2011 PH Professional Network Symposium
Release Date: 09.22.2011
Presentation Type: Abstracts
S. Walker MS, CRNP1; D. B. Frank, MD, PhD1; Z. Bshouty, MD 2; H.L. Meluskey, BS, BSN, RN 1; B.D. Hanna, MD, PhD 1
1. The Children's Hospital of Philadelphia, Division of Pediatric Cardiology, Department of Pediatrics, University of Pennsylvania, Philadelphia, PA
2. Respiratory Investigation Unit, University of Manitoba, Winnipeg, Manitoba R3E 0Z3, Canada
BACKGROUND: Pulmonary hypertension (PH), a progressive and lethal disease characterized by reversible and fixed vaso-occlusive lesions of the pulmonary vascular tree, is initially asymptomatic for years because pulmonary vascular resistance (PVR) and mean pulmonary arterial pressures (mPAP) do not change until significant loss of vascular bed. A computational model using pulmonary dimensions and hemodynamic data predicts pulmonary vascular capacity (PVC) in PH (Bshouty, 2009). We used this model to quantify PVC and determine whether PVC predicts outcomes in pediatric PH.
PURPOSE: We used the computational model to quantify PVC and validate whether PVC predicts outcomes in pediatric PH.
MATERIALS/METHODS: PVC was computed by a retrospective analysis of invasive hemodynamic data and chest x-rays from 35 pediatric PH patients aged 6-18 years. Univariate and multivariate mixed model analyses were performed comparing PVC, hemodynamic, and non-hemodynamic variables: age at event, disease duration, BMI, and gender. Outcome variables included actual mortality, estimated mortality (Clabby, 1997), B-type natriuretic peptide (BNP), and 6 minute Walk (6MW). Cox regression with time varying covariates was used to evaluate the effects of BNP, PVC, PVR, and RAP on time to survival, and Kaplan-Meier survival estimate curves were generated.
RESULTS: Values of PVC conform to theoretically modeled PH. PVC > 25% was seen on patients with mild PH whereas PVC < 25% was found in severe PH. PVC is a statistically significant predictor of the outcome variables, actual and estimated mortality, 6MW, and BNP. By Kaplan-Meier analysis, PVC predicted survival more accurately than previous mortality estimates.
CONLCUSIONS: For the first time, we quantified the progressive loss of pulmonary vessels. PVC is a significant predictor of clinical outcomes and survival. This confirms that hemodynamics change minimally until the PVC is < 25% normal. Pediatric PH is a silent disease until 70-75% of the pulmonary vasculature is lost; however, evaluation of other populations and the effect of PH directed therapy on PVC is needed.
The computational model to predict vascular capacity is an abbreviated five-generation branching system that represents 15 generations of arterial and venous vessels, bifurcating from the pulmonary artery (PA) to the left atrium (LA). The premise of the model is that the resistance of a given vessel in the model is dependent on vessel dimensions (length and cross-sectional area). Patient specific data including patient height, weight, lung height (P-A diameter at LA level), lung compliance (assumed to be 0.317 L/cm H2O), and lung volume are entered into the program. In addition, hemodynamic data entered includes LAP, CO, and mPAP at Pal of zero and a Ppl of -5 cm H2O reflecting end-expiration. Under standardized conditions including a transpulmonary pressure (Ptp) of zero and vessel transmural pressure (Ptm) of 35 cm H2O, the computer iterates until attaining a stable solution, and an estimate of vascular area (PVC), PVR, upstream (arterial), middle (capillary), and downstream (venous) resistances are generated.