Vascular Control I and II Flashcards
1
Q
Cardiac Output and Control
A
- the heart can be considered as a dynamic system that acts upon an input in order to produce an output
- input: Blood (volume/min). Venous Return
- output: Blood (volume/min). Cardiac Output
- it can react and dynamically change its functional characteristics in response to changes in venous return and if the body requires more O2
2
Q
Preload
A
- the amount of blood (volume) in the ventricle at the end of the inflow phase ie EDV
- preload technically refers not to EDV but to the pressure associated with myocyte stretch at the end of the inflow
- its the fuel guage= volume status
3
Q
Afterload
A
-the pressure needed to be generated by the ventricle to begin the ejection phase
4
Q
Overview of the operation of the vascular
A
- closed hydraulic circuit that includes heart,arteries, arterioles and veins
- assume that the pulmonary circuit doesn’t matter
- Starling’s law of the heart implies the end-diastolic volume of the right ventricle causes equal changes in end-diastolic volume of the left ventricle
- each segment has a distinct role to play because of differences in anatomical volume, resistance to flow and compliance
- two conceptually different compartments: large/diverse peripheral section and a smaller intrathroacic section includes vena cavae and right ventricle
5
Q
Properties of Components of Systemic Circuit
A
=the arterioles have high Resistance comparitively (13), so they represent the afterload of a system
- the peripheral venous compartment has a volume of 2500 and also highest compliance 110- blood will pool there without heart beat
- the central venous compartment represents the preload
6
Q
Cardiac Output and Venous Return
A
- the central venous compartment corresponds roughly to the volume enclosed by the right atrium and the great veins in the thorax
- blood leaves the central venous compartment by entering the right ventricle at a rate that is equal to the cardiac output
- venous return in contrast is by definition the rate at which blood returns to the thorax from the peripheral vascular beds and thus is the rate at which blood enters the central venous compartment
- the important distinction between venous return TO the central venous compartment and cardiac output FROM the central venous compartment
- venous return must equal cardiac output or blood would gradually accumulate in either the central venous compartment or peripheral resistance, there are sometimes temp differences
- central venous pressure has important effects on stroke volume and therefore cardiac output
7
Q
Venous Function Curve
A
- from the capillaries the PPv is 7 mm Hg from the peripheral venous compartment
- venous return is toward the central venous compartment because the intrathoracic pressure is 0 mmHg
- the venous function curves starts as a straight line until central venous pressure is 0, then decreases and when central venous pressure gets to 7 then there is no more flow in venous return
8
Q
Effect of Changes in Blood Volume and Venous Tone on Venous Function Curves
A
- control function curve
- increased blood volume or venous tone causes a shift where central venous pressure goes to 10 mmHg and venous return 10
- decreased blood volume or venous tone is 4 central venous pressure and 4 venous return
9
Q
Interaction of Cardiac Output and Venous Return through Central Venous pressure
A
- Central venous pressure 2 mmHg cardiac output/ venous return is 5 mmHg where they overlap
- cardiac function curve increases up
- venous function curve decreases
10
Q
Cardiac function and venous function curve
A
- intersection points indicate equilibrium values for cardiac output, venous return, and central venous pressure under various conditions
- normal cardiac function curve and then increased cardiac sympathetic nerve activity shifts the curve upward
- venous constriction after hemorrhage shifts the venous function curve down
- hemorrhage shifts the curve way down
11
Q
Vascular Function Curve
A
- in steady state, CO= VR
- increased flow shifts blood from venous to arterial side, thereby decreasing venous pressure and RAP
- partial venous collapse at negative RAPs produces plateau in vascular function curve
- MSFP occurs at zero flow and reflects blood volume
12
Q
Increasing Blood Volume Increases MSFP
A
- mean systemic filling pressure (MSFP) is the blood pressure at zero flow, with the heart not beating
- MSFP is thus the static equilibrium pressure that would be everywhere the same throughout the entire cardiovascular system when no blood is flowing
- MSFP increases with greater blood volume (transfusion) and decreases with lower blood volume (hemorrhage)
- a greater blood volume also expands the radius of the veins, thus decreasing their resistance to flow, contribuing to increased VR at any given RAP, thereby contributing to an upward shift of the vascular function curve
13
Q
Arteriolar Tone affects vascular function curves
A
- arterior vasoconstriction decreases central venous pressure, CVP, resulting in decreased venous return at any given RAP;
- arteriolar vasodilation increases CVP, resulting in increased venous return at any given RAP
- there is not a change in MSFP, mean systemic filling pressure because there is not much blood contained in the arterioles
14
Q
Venous Return curve and cardiac function curve
A
- the cardiac function curve essentially represents Starling’s law (right atrial pressure is proportional to right ventricular EDP)
- at steady state, CO=VR
- CO, RAP (central venous pressure), and venous return are independent
- mismatches between CO and VR are quickly resolved: you either have to change cardiac function curve or the vascular function curve
15
Q
Cardiovascular Response to Exercise
A
- contracting muscles- there is a muscle pump- increased venous return -> increased central venous pressure -> increased end diastolic pressure -> increased end diastolic volume -> increased stroke volume -> increased cardiac output
- chemical metabolites (low PO2, high CO2, low pH) -> local vasodilation of active muscle -> decrease arterial pressure (and also increase venous return) -> arterial baroceptor -> increases heart rate -> increase cardiac output
- baroreceptor also vasoconstriction of inactive muscle, splanchnic, cutaneous, renal circulations
