Control of Circulation and Arterial Pressure Marijn Rolf Chapter 6

Introduction Physiology~Model Heart~Power source Organs~Resistors (mostly parallel)

Outline Heart –Autoregulation (Frank-Starling principle) –Central Nerve System Organs –Autoregulation –Central Nerve System Complete Model Description

Heart – Autoregulation Frank-Starling in short: ↑ venous return  cardiac output ↑

Heart – Autoregulation ↑ venous return  RV output ↑ Frank-Starling principle 1: With constant afterload the RV end-systolic volume is independent of the end-diastolic volume.

Heart – Autoregulation Frank-Starling principle 2: The afterload of the RV is independent of the LA preload. The lungs compensate by using more capillaries. So: ↑ RV output  LV filling ↑

Heart – Autoregulation Side effect of Frank-Starling: A higher pressure in the RA influences the depolarisation rate of the SA-node, resulting in an increased heartrate. So: ↑ venous pressure  heart rate ↑

Heart – Central Nerve System Sympathetic nerves ventricles increases heart rate and muscle contractility Parasympathic nerves (vagi) SA- and AV-node, atria decreases heart rate

Heart – Central Nerve System Control loop is closed by baroreceptors on large arteries. Rising arterial pressure excites the baroreceptors, followed by a decrease in sympathetic activity.

Heart Model description: CO = HR * SV = HR * K c * P v

Organs - Autoregulation Depends on the organs’ metabolic needs. Arteriolar vasodilation is caused by: Decreased O 2 concentration Increased CO 2 Adenosine release (waste product of ATP)

Organs – Central Nerve System Sympathetic activity (except in the brain) causes arteriolar vasoconstriction regulating mean arterial blood pressure

Organs

Model

Organs Model description CO = (P a -P v )/R per ΔP v = -C a /C v * ΔP a ↓ ΔP a = C v /(C v +C a )*R per *ΔCO ΔP v = C a /(C v +C a )*R per *ΔCO

Complete Model Heart: Organs: CO = HR * SV = HR * K c * P v ΔP v = C a /(C v +C a )*R per *ΔCO P v = P m + Δ P v CO = P m *HR*K c 1+HR*K c *R per *C a /(C a +C v )

Reference Cardiovascular Physiology Concepts Richard E. Klabunde, Ph.D.