Foramen Ovale and Ductus Arteriosus Patency in Neonatal Harbor Seal (Phoca vitulina) Pups in Rehabilitation

Twenty neonatal harbor seal (Phoca vitulina) pups in rehabilitation following maternal separation underwent serial echocardiographic studies to assess patency and subsequent age of functional closure of the ductus arteriosus (d.a.). B-mode, color-flow Doppler, and pulse and continuous wave Doppler were utilized to identify the d.a. and determine patency and directionality of blood flow. Seals were also evaluated for evidence of foramen ovale (f.o.) patency. B-mode ultrasound was used to evaluate the inter-atrial septum for abnormal (aneurismal) motion, a sign of f.o. patency in other species. In one harbor seal, this motion was confirmed as being consistent with f.o. patency by contrast echocardiography. Closure of the f.o. was not confirmed in any harbor seal prior to release back into the free-ranging population. Data acquired indicate that there is patency of the f.o. and d.a. after birth for a longer period in phocids than in described terrestrial mammals. The f.o. may be patent up to 7 wks of age, and the d.a. may be patent up to 6 wks of age without evidence of clinical consequence. This difference in ontogeny between terrestrial mammals and harbor seals is presumptively a diving adaptation. Such an adaptation is counterintuitive given that humans with f.o. patency are at increased risk of stroke following the introduction or formation of intravascular gas bubbles and suggests that concurrent protective mechanisms may be present.