Overview
This lecture covers the mechanical properties and physiological roles of arteries, including vascular distensibility, compliance, elastance, pulse pressure, and how these factors change with age, exercise, and disease.
Vascular Distensibility and Arterial Function
- All blood vessels are distensible (stretchable), enabling arteries to buffer blood pressure fluctuations.
- During systole (contraction), arteries expand and store energy; during diastole (relaxation), recoil maintains blood flow.
- Non-distensible (stiff) arteries cause pulsatile flow, risking damage to organs needing constant blood flow.
Compliance and Elastance
- Compliance measures how much volume changes per unit pressure change (ΔV/ΔP).
- Veins are more compliant and can store more blood than arteries.
- Elastance is the inverse of compliance (ΔP/ΔV); arteries have higher elastance than veins.
- High compliance in veins allows large volumes to be added with little pressure increase.
- Small volume increases in arteries cause significant pressure increases due to low compliance.
Delayed Compliance (Stress Relaxation)
- Vessels adjust to volume changes over time, causing pressure to slowly decrease after a rapid increase, and vice versa.
Pulse Pressure and Arterial Stiffness
- Pulse pressure = systolic pressure – diastolic pressure.
- Pulse pressure increases with stroke volume and decreases with arterial compliance.
- Normal compliant arteries buffer pressure changes; stiff arteries increase systolic pressure and reduce diastolic flow, causing wider pulse pressures.
- Arterial stiffness increases with age, leading to higher systolic and lower diastolic pressures.
Effects of Exercise on Arterial Properties
- Endurance (aerobic) exercise reduces arterial stiffness and increases compliance, especially in older adults.
- Resistance training may increase arterial stiffness, but evidence is mixed.
- Lower pulse wave velocity indicates healthier, more compliant arteries.
Pathologies Affecting Pulse Pressure
- Arteriosclerosis (stiff arteries) increases pulse pressure due to poor compliance.
- Aortic stenosis (narrow valve) lowers pulse pressure by reducing stroke volume.
- Patent ductus arteriosus causes rapid diastolic pressure drops due to backflow.
- Aortic regurgitation (leaky valve) widens pulse pressure by allowing blood to re-enter the ventricle.
Pulse Pressure Damping in Vasculature
- Pulse pressure dampens as it moves from aorta to capillaries due to increasing resistance and decreasing compliance.
- Most damping occurs at arterioles, where resistance is highest.
Blood Pressure Measurement and Determinants
- Systolic blood pressure is noted at the first Korotkoff sound; diastolic at the disappearance of sound.
- Arterial pressure is determined by cardiac output and total peripheral resistance: Pressure = Cardiac Output × Total Peripheral Resistance.
- Pulse pressure is mainly affected by arterial compliance and volume.
Key Terms & Definitions
- Distensibility — The ability of blood vessels to expand and stretch.
- Compliance — Measure of vessel's ability to change volume with pressure (ΔV/ΔP).
- Elastance — Vessel tendency to return to original shape (ΔP/ΔV); inverse of compliance.
- Pulse pressure — Difference between systolic and diastolic blood pressure.
- Delayed compliance (stress relaxation) — Slow adjustment of vessel pressure after a volume change.
Action Items / Next Steps
- Memorize the equation: Arterial Pressure = Cardiac Output × Total Peripheral Resistance.
- Review blood pressure measurement technique and Korotkoff sounds.
- Understand the clinical significance of compliance, elastance, and pulse pressure in vascular health.