Altered reactivity and nitric oxide signaling in the isolated thoracic duct from an ovine model of congenital heart disease with increased pulmonary blood flow.

We have previously shown decreased pulmonary lymph flow in our lamb model of chronically increased pulmonary blood flow, created by the in utero placement of an 8-mm aortopulmonary shunt. The purpose of this study was to test the hypothesis that abnormal lymphatic function in shunt lambs is due to impaired lymphatic endothelial nitric oxide (NO)-cGMP signaling resulting in increased lymphatic vascular constriction and/or impaired relaxation. Thoracic duct rings were isolated from 4-wk-old shunt (n = 7) and normal (n = 7) lambs to determine length-tension properties, vascular reactivity, and endothelial NO synthase protein. At baseline, shunt thoracic duct rings had 2.6-fold higher peak to peak tension and a 2-fold increase in the strength of contractions compared with normal rings (P < 0.05). In response to norepinephrine, shunt thoracic duct rings had a 2.4-fold increase in vascular tone compared with normal rings (P < 0.05) and impaired relaxation in response to the endothelium-dependent dilator acetylcholine (63% vs. 13%, P < 0.05). In vivo, inhaled NO (40 ppm) increased pulmonary lymph flow (normalized for resistance) ∼1.5-fold in both normal and shunt lambs (P < 0.05). Inhaled NO exposure increased bioavailable NO [nitrite/nitrate (NOx); ∼2.5-fold in normal lambs and ∼3.4-fold in shunt lambs] and cGMP (∼2.5-fold in both) in the pulmonary lymph effluent (P < 0.05). Chronic exposure to increased pulmonary blood flow is associated with pulmonary lymphatic endothelial injury that disrupts NO-cGMP signaling, leading to increased resting vasoconstriction, increased maximal strength of contraction, and impaired endothelium-dependent relaxation. Inhaled NO increases pulmonary lymph NOx and cGMP levels and pulmonary lymph flow in normal and shunt lambs. Therapies that augment NO-cGMP signaling within the lymphatic system may provide benefits, warranting further study.

B-type natriuretic peptide: prognostic marker in congenital diaphragmatic hernia.

BACKGROUND: B-type natriuretic peptide (BNP) has not been evaluated in newborns with congenital diaphragmatic hernia (CDH). We hypothesized that BNP and severity of pulmonary hypertension (PH) would predict clinical outcome in these infants. METHODS: We measured BNP levels and assessed severity of PH by echocardiography at 1 d and 1 wk of life. Outcome was classified by status at 56 d (or prior discharge): Good (n = 13) if alive on room air and Poor (n = 14) if expired or receiving respiratory support. We estimated area under the curve (AUC) and 95% confidence interval (CI). RESULTS: BNP levels were higher at 1 d in newborns with Poor outcome (median 220 pg/ml vs. 55 pg/ml, P < 0.01). At 1 wk, there was no significant difference in BNP level (median 547 pg/ml vs. 364 pg/ml, P = 0.70, for Poor and Good outcomes). At 1 d, BNP level predicted outcome (AUC = 0.91, 95% CI = 0.77-1.0), but this relationship dissipated by 1 wk (AUC = 0.55, 95% CI = 0.31-0.79). Severity of PH did not predict outcome at 1 d (AUC = 0.51, 95% CI = 0.27-0.74), but prediction improved at 1 wk (AUC = 0.80, 95% CI = 0.61-0.99). CONCLUSION: BNP is a strong predictor of clinical outcome in newborns with CDH at 1 d of life.