Regional blood flow during simulated diving in the conscious Weddell seal

TLDR

The study measured regional blood flow in conscious Weddell seals during simulated normobaric diving by injecting 25‑µm radioactive microspheres into the left ventricle before and 8–12 min after head immersion in iced seawater. Diving reduced cardiac output from 39.8 l/min to 5.6 l/min, heart rate from 52 to 15 bpm, splanchnic and peripheral flow by >90 %, cerebral flow remained unchanged, ventricular flow fell 85 %, adrenal flow dropped 39 %, and pulmonary microsphere fraction rose from 7.9 % to 29.9 %, indicating increased peripheral arteriovenous shunting or bronchial flow and that blood is redirected to metabolically demanding organs.

Abstract

Changes in regional blood flow during simulated normobaric diving were studied in the conscious Antarctic Weddell seal (Leptonychotes weddelli) by injecting 25-microns radioactive microspheres into the left ventricle. Injections were performed before and 8--12 min after submersion of the head in iced seawater. Diving was associated with a fall in cardiac output from a mean control value of 39.8 +/- 10.2 to 5.6 +/- 3.4 l/min (mean +/- SD) and in heart rate from 52 +/- 15 to 15 +/- 4 beats/min. Blood flow to the splanchnic and peripheral vascular bed was reduced by more than 90%, cerebral blood flow was unchanged, right and left ventricular blood flow decreased by 85%, and adrenal blood flow decreased by 39%. The pulmonary fraction of the injected microsphere dose increased from 7.9 to 29.9% during diving. This may signify a large increase of peripheral arteriovenous shunting during the dive and/or increased bronchial artery blood flow. It is concluded that blood flow during diving is directed to organs and tissues according to their metabolic requirements.