Haemodynamics and Circulation Quiz

Haemodynamics

• Haemodynamics is the study of the physical and physiological principles governing blood movement through the circulatory system.
• It describes the physical laws governing blood flow in blood vessels.
• The function of circulation is to supply nutrients to tissues and remove waste products.

Intended Learning Outcomes

• Define pulse pressure and mean arterial pressure, state their ranges and calculate their values in adults.
• Explain relationships between cardiac output, total peripheral resistance, and mean arterial pressure.
• Explain compliance and relationship between pulse pressure, stroke volume, and compliance.
• Discuss the importance of Poiseuille's law relating vessel radius and resistance to flow.
• Discuss the importance of Laplace's law relating vessel radius and pressure.

The Circulatory System

• Circulation functions to supply nutrients to tissues and remove waste products.
• Adequate cardiac output maintains tissue blood flow.
• Arterioles are like taps, controlling local blood flow.

Properties of Blood Vessels

• Arteries transport blood under high pressure to tissues (conducting vessels).

• Arterioles control blood flow to tissues (distributing vessels).

• Capillaries exchange fluids, nutrients, gases, and electrolytes with interstitial fluid.

• Venules collect blood from capillaries.

• Veins return blood to the heart and act as a reservoir.

• Details on vessel types (Aorta, large artery, medium-sized vein, muscular artery, arteriole, venule, continuous capillary, fenestrated capillary, large vein)

Blood Flow

• Flow (rate) = volume/time
• Blood flow is the volume of blood flowing through a vessel or organ over a period of time.
• Differences in blood pressure throughout the body, driving force for flow, high pressure areas (arteries) to low pressure areas (veins).
• Flow is proportional to pressure gradient and inversely proportional to resistance.

How Does Blood Flow in Circulation?

• Laminar flow is streamlined and smooth, observed at low velocities (parallel layers).
• Turbulent flow is random and chaotic, observed at high velocities or narrowed vessels (mixing of layers).
• Factors that cause turbulent flow: increase in velocity, narrowing of vessels, decrease in blood viscosity.

Factors Affecting Cardiac Output

• Cardiac output is the total blood flow out of the heart per minute.
• Cardiac output = Heart Rate x Stroke Volume
• Factors affecting heart rate: atrial reflex, autonomic innervation, hormones.
• Factors affecting stroke volume: venous return, filling time, autonomic innervation, hormones, preload, contractility, afterload, end-diastolic volume.

Distribution of Blood to Organs

• Blood distribution to organs varies between rest and exercise.
• Cardiac output changes during exercise, significantly increasing blood flow to active muscles.

Blood Pressure

• Blood pressure is the force exerted by blood on the walls of blood vessels.
• Differences in blood pressure throughout the body drive blood flow.
• Pressure = force/area

Systolic and Diastolic Blood Pressure

• Systolic blood pressure (SBP) is the maximum pressure during systole (heart contraction).
• Diastolic blood pressure (DBP) is the minimum pressure during diastole (heart relaxation).
• Pulse pressure = SBP – DBP.
• Pulse pressure is directly proportional to stroke volume and inversely proportional to arterial compliance.

Korotkoff Sounds

• Korotkoff sounds are sounds heard during blood pressure measurement as the cuff deflates.
• Phases in Korotkoff sounds provide information during the blood pressure measurement.

Pressure Fluctuations in Blood Vessels

• Pressure fluctuations are largest in large arteries due to the speed of pressure waves, faster than blood flow.
• Mean pressure falls as it travels further in the body due to resistance in vessels.
• This fall in pressure maintains blood flow in a preferred direction.

Mean Arterial Pressure (MAP)

• MAP is the average arterial pressure during the cardiac cycle.
• MAP is important for maintaining the perfusion and health of tissues in the body.
• MAP = (2/3) DBP + (1/3) SBP or DBP + (1/3) Pulse Pressure

Interpretation of Blood Pressure

• Ranges for low blood pressure, normal, prehypertension, high blood pressure stage 1 and 2, high blood pressure crisis are provided.

Regulation of Blood Pressure

• Blood pressure is regulated by constricting or relaxing input arterioles to manage the flow through the organ.
• Vessels in the body must withstand the pressure that is generated by the blood within them.
• Vessels that are damaged from high pressure can rupture or leak.

Laplace's Law

• Laplace's law relates the pressure a blood vessel can withstand to its wall tension, radius, and thickness.
• A vessel's ability to withstand pressure and vessel wall tension are tightly linked.

Atherosclerosis

• Atherosclerotic plaques reduce vessel diameter, increasing resistance to flow.
• Halving vessel diameter increases resistance to flow by 16x.

Blood Viscosity

• Viscosity is the liquid's thickness or stickiness.
• Blood viscosity is largely dependent upon haematocrit.
• Higher haematocrit results in higher blood viscosity.

Haematocrit

• Haematocrit is the percentage of red blood cells in total blood volume.
• Haematocrit is a measure of red blood cell concentration in blood.

Conditions Increasing Viscosity

• Erythrocyte flexibility influences total peripheral resistance.
• Polycythemia increases blood's viscosity with too many red blood cells.
• Sickle cell disease leads to abnormal red blood cells that become inflexible.
• Macrocytosis results in larger red blood cells, increasing viscosity.

Blood Vessel Length

• Total blood vessel length is inversely proportional to flow, as longer vessels have higher resistance.
• Shorter vessels have lower resistance compared to longer vessels.

Compliance of Blood Vessels

• Compliance is the ability of the blood vessel wall to expand or contract passively in response to pressure changes.
• The stretchability of the vessels depends on their compliance.
• Large veins have high compliance to facilitate blood return to the heart and reduce afterload.
• Aortic compliance reduces afterload by allowing blood ejection from the left ventricle and recoil to prevent large pressure fluctuations during diastole.

Compliance During the Cardiac Cycle

• Aorta and large arteries' compliance increases flow to peripheral tissues during systole.
• During diastole, recoil of vessels allows bloodflow to continue efficiently.
• Overall, the ability of vessels to distend allows for larger volumes to be circulated.

Aging

• Blood vessels harden with age, leading to reduced compliance.
• This increased pressure necessitates higher pressure needed to maintain adequate blood flow.
• The consequence of this change in pressure is a higher aortic pulse pressure with age.

Putting It Together

• Diagram demonstrates connections between important factors: blood volume, preload, venous compliance, inotropy, heart rate, MAP, vascular resistance, renal function, neurohumoral factors, local factors.

Ohm's Law

• Fluid flow is directly proportional to pressure difference and inversely proportional to resistance.
• Ohm's law is applicable in the systemic circulation to understand blood flow.

Poiseuille's Law

• Poiseuille's Law describes how resistance to fluid flow is related to factors such as length of tube, blood thickness (viscosity), and vessel radius.
• Resistance in a blood vessel is inversely proportional to the fourth power of the vessel radius.
• Smaller vessel radii pose a greater resistance to blood flow

Vessel Diameter

• Flow is proportional to the fourth power of the vessel's radius.
• Small changes in radius produce large changes in blood flow.
• Changes in arteriolar radius are important for local control of blood flow. (vasoconstriction decreases diameter and increases resistance; conversely, vasodilation increases diameter and decreases resistance).

(Additional relevant points and related diagrams were also included in the notes. All details, data, and figures were extracted from the provided slides.)

This quiz explores the principles of haemodynamics, focusing on blood flow, cardiac output, and the physical laws governing circulation. Test your understanding of pulse pressure, mean arterial pressure, and the relationships outlined by Poiseuille's and Laplace's laws. Prepare to apply your knowledge of cardiovascular physiology in this engaging assessment.