Hot‐Film Anemometer Velocity Measurements of Arterial Blood Flow in Horses

Blood velocity measurements were carried out using a constant-temperature hot-film anemometer system in both anesthetized and conscious horses. Catheter probes were used to measure velocity wave forms in conscious horses and L-shaped needle probes inserted by direct vessel puncture were used to measure the profiles in regions of the thoracic and abdominal aorta of anesthetized, open-chest horses. Both catheter and L-shaped probes were used for coronary velocity wave-form measurements. The flow conditions were characterized by peak Reynolds numbers of 200–10,000 and unsteadiness parameter of 2–30. These measurements indicate that in the thoracic aorta the flow at peak systole is largely inviscid with a thin-wall boundary layer; in the abdominal aorta the flow is more fully developed but skewed due to branching effects. Highly disturbed flows were observed in the thoracic aorta of both anesthetized and conscious horses, but not in the abdominal aortic region or in the coronary arteries. The results of this study indicate that the flow in the arterial system, although in many cases laminar and disturbance free, is extremely varied in character. It may be asymmetric and certainly is not representative of fully developed, Poiseuille flow.