Characterization of ultrasound-induced pulmonary capillary hemorrhage in rats

Routine pulmonary ultrasound for diagnosis of disease or injury relies on interpretation of image features, such as comet-tail artifacts, which can also be indicative of the poorly understood phenomenon of ultrasound-induced pulmonary capillary hemorrhage (PCH). Evans blue extraction and bronchoalveolar lavage (BAL) were evaluated for assessment of PCH induced by ultrasound scanning. Rats anesthetized with ketamine with or without xylazine received sham or scanning for 5 min with a 7.6 MHz linear array. Evans blue extraction and BAL albumin measurements failed to demonstrate significant increases for scanning, even though the induction of comet-tail artifacts was significant. BAL cell counts had an insignificant increase relative to shams at a near-threshold mechanical index (MI) of 0.52 (P = 0.07), but a highly significant increase at MI = 0.9 (P = 0.001). The possibility of xylazine-induced elevated albumin was tested, but no significant decrease was found for sham or scanned rats with ketamine-only anesthesia. Interestingly, without xylazine, the widths of comet-tail artifacts in the ultrasound images were significantly smaller (P = 0.001) and cell counts in BAL fluid also were reduced (P = 0.014). The BAL cell-count method provides a valuable additional means of PCH quantification.