A Preliminary Study on the Siphon Mechanism in Giraffe (Giraffa camelopardalis).

Simple Summary: Long-necked animals like giraffes face the challenge of adequately supplying blood to the brain. The heart of such tall animals must work harder to pump blood over a 2 m head-to-heart distance against the force of gravity compared to a short-necked animal. Does a mechanism exist to assist tall animals in overcoming this challenge? We found that there is a possibility of a mechanism that can enhance blood flow to the brain and a subsequent increase in oxygen supply, which will reduce the heart's workload to pump blood over a 2 m distance in a Giraffe. In short-necked animals, the workload on the heart is less to supply blood to the brain adequately; therefore, no additional mechanism is necessary. We, however, suggest that a similar mechanism might have been functional in dinosaurs with extremely long necks to help with adequate blood supply to the brain by comparing relevant giraffe physiology and anatomy with existing data on paleontology. Adult giraffes reach heights of 4.5 m with a heart-to-head distance of over 2 m, making cranial blood supply challenging. Ultrasound confirmed that the giraffe jugular vein collapses during head movement from ground level to fully erect, negating the possibility of a siphon mechanism in the neck. We showed that a short-length siphon structure over a simulated head-to-heart distance for a giraffe significantly influences flow in a collapsible tube. The siphon structure is determined according to brain case measurements. The short-length siphon structure in a shorter-necked ostrich showed no significant increase in flow. The shorter head-to-heart distance might be the reason for the lack of effect in ostriches. A siphon mechanism situated in the cranium is certainly possible, with a significant effect exerted on the amount of pressure the heart must generate to allow adequate cranial blood perfusion in a long-necked giraffe. The study validated that a cranial-bound siphon structure can operate and will be of significant value for adequate cranial blood perfusion in long-necked species such as giraffes and might also have existed in extinct species of long-necked dinosaurs. [ABSTRACT FROM AUTHOR]