High-frequency ultrasound characterization of pulmonary arterial wall under normoxic and hypoxic conditions

Diagnosis of secondary pediatric pulmonary hypertension is often difficult because no single test permits complete evaluation. Improved understanding of the effects of hypertension on ultrasonic (US) properties of the wall of the pulmonary artery (PA) could lead to earlier detection. High-frequency US in vitro measurements were performed on fresh, excised PA walls from normoxic and hypoxic Long-Evans rat models to determine whether US properties differed between groups. Three population groups were studied: six normals, four normal hypoxics, and nine genetically modified (GM) hypoxics. The extrapulmonary artery system (main trunk, left and right branches) was excised following sacrifice and stored on ice in a nutritive solution until measurement. Ultrasonic measurements on the fresh specimens were performed by means of a 50 MHz acoustic microscope in a conventional double-transmission arrangement. The speed of sound (SOS) was determined from differences in times of flight between the reference and tissue measurements. Slope of attenuation was determined from the same signals using a log spectral subtraction technique. An expected increase (up to 10%) in SOS was observed for the normal hypoxic model compared to the normal model, but an unexpected decrease (by up to 6%) was observed for the GM hypoxic model. The slope of attenuation in both hypoxic models was greater (by up to 100%) than that of the normal model.