Anatomy and physiology of bone perfusion in living and foss il birds as assessed by CT-scann ing, microsphere distribution, vascular contrast imaging and foramen measurement

Abstract

Artery sizes are determined by local blood flow rates, which are driven by local oxygen demand. Arteries that pass through bone foramina, leave the foramina as size representatives of the arteries. Therefore, measuring these foramina sizes without any presence of soft tissue can be a way to estimate blood flow rates. This ‘foramen technique’ can be a useful tool to estimate blood flow rates in ancient animals such as dinosaurs. However, the absolute blood flow passing though foramina needs to be calibrated at this stage, as the size relationship between the foramen and occupying vessel is unclear, especially in foramina with more than one vessel. The major aim of this thesis is to evaluate the foramen-artery size relationship, especially the relationship between the femoral nutrient foramen and nutrient artery, to improve the method of femoral bone blood flow estimation for further foramen studies. Chickens are chosen as the experimental animals. Studying blood flow in birds gives us an opportunity to get insight into blood flow rates in dinosaur bones, as birds are living dinosaurs. The thesis chapters involve several methods to measure foramen sizes or estimate regional bone blood flow rates. Microphotography is chosen to be the most practical foramen measurement method compared to micro-CT and impression material approaches. Chicken femoral bone blood flow rates estimated from infusion of fluorescent microspheres and vascular contrast imaging give similar results. Foramen-artery size relationships are evaluated in chicken femur bones, revealing that the morphologies of femoral nutrient arteries and nutrient foramina can vary among femora. The ‘foramen technique’ is used to estimate femoral bone blood flow in fossil cursorial birds.