Cardiovascular System II - L07 - 10/06

How do you make a PV-Loop
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How do you make a PV-Loop
Image: How do you make a PV-Loop
Regulation of cardiac output
Image: Regulation of cardiac output
What is preload? What changes preload?

Describe the Length-tension relationship with CO
Initial passive stretch of the ventricle (related to the volume of blood in the ventricle at the end of diastole). Blood flow into ventricle inc. preload

more blood in ventricle > more stretch> Preload inc. to LVEDV/P > inc. in tension > inc. SV > inc. CO
Loading Conditions > Preload

What is the frank-starling law?
ventricular systolic contractile strength proportional to diastolic expansion. (i.e. more stretch = larger SV)
Image: Loading Conditions > Preload What is the frank-starling law?
Load conditions > preload >

Why does the frank-starling law work? Stretching of cardio myocytes
- Stretching of cardiomyocytes results in inc. troponin C Ca affinity.
- Increased Ca2+ release from SR
- Decreased spacing between thin/thick filaments

More cross bridges = more force
Image: Load conditions > preload > Why does the frank-starling law work? Stretching of cardio myocytes
How does a change in these factors affect preload?
- Atrial Contractility
- Ventricular Compliance
- Afterload
- Ventricular Inotropy
- Central venous pressure
- Venous Compliance
- Thoracic venous blood volume
Image: How does a change in these factors affect preload? - Atrial Contractility - Ventricular Compliance - Afterload - Ventricular Inotropy - Central venous pressure - Venous Compliance - Thoracic venous blood volume
Define Afterload
The required ventricular pressure to eject blood into the aorta during systole (aortic pressure) THINK LARGE DOOR
Image: Define Afterload
Factors affecting afterload
An increase in aortic pressure caused by an inc. in systemic vascular resistance or dec. in aortic compliance
Image: Factors affecting afterload
Define Inotropy & mechanism
Alteration of the force of muscle contractions WITHOUT change in sarcomere length (i.e. more cross bridges)
Image: Define Inotropy & mechanism
How do these factors affect inotropy?

PNS activity
SNS
Circulating
- Dec. in PNS (ACh) = Inc. Inotropy
- Inc. in SNS (NEpi) = Inc. Inotropy
- Inc. Circulating Catecholamines = Inc. Inotropy
Image: How do these factors affect inotropy? PNS activity SNS Circulating
TEST - All loading conditions - How do preload, afterload, & inotropy affect SV and LVEDP - Think back to the factors that affect each loading conditionLarge arteriesHigh elasticity due to hella smooth muscleDefine the following arteriolar structures: 1. Precapillary sphincters 2. Metarterioles 3. Throughfare channels1. Smooth muscle cells that regulate flow into capillary beds 2. Connect arterioles and capillaries (middle) 3. Connect metarterioles to venuleHow do sphincters change resistance in arterioles (resistance vessels)?Open sphincters increase resistanceCapillaries (Exchange Vessels)High metabolic areas = extensive capillary networks (muscles, liver, kidneys, nervous system) Low metabolic areas = lack capillaries (cornea and lens of eye, nails, hair follicles, cuticles, cartilage)Venules (Collection Vessels)- Collect blood from capillary bed - Low resistanceDescribe the characteristics of veins- Thin Walled (little smooth muscle) - Low Pressure (0-2 mmHg) - Valves - High compliance - Blood reservoir - Capable of radius changePressures in arterial vs venous circulationArterial circulation has greater pressure - Greatest in the aortaWhat part of the vasculature has the greatest cross-sectional area?CapillariesDefine compliance. How does it change with increasing P or V?How easily a chamber/ vessel lumen expands when it is filled with a volume of blood Decreases with increasing P or V (more full = less compliant)Changes in compliance 1. Factors 2. Loss of compliance causes... 3. Veins or Arterioles more compliant? 4. SNS stimulation?1 & 2 on pic 3. Veins 4. ↑ SNS > ↓ Compliance > ↑ venous returnArteries & Veins terminologyArteries - Resistance Veins - ComplianceBlood Flow Laminar vs Turbulent Venous return vs cardiac outputLaminar: Smooth Turbulent: disorderly found in branch points of large arteries or in diseased arteries/ valve Venous Return: Volume of blood returning from periphery to right atrium each minute Cardiac Output: Volume of blood ejected from heart each minuteFactors Affecting Venous Return 1. Venous Valves 2. Skeletal Muscle Pump 3. Respiratory Pump 4. Blood Volume - Total - Effective (compliance)1. Open/ close to keep from backflow 2. Muscle contraction > bottom valve closes & upper valve opens > blood pushed up > upper valve closes upon relaxation & lower valve opens to allow for blood flow 3. Diaphragm pulls down ↓ intrathoracic pressure > draws blood toward the heart 4. BV = Intrathoracic (Central Blood Volume) + Extrathoracic.How does central (intrathoracic) Blood Volume (CBV) affect venous return↑ CBV > ↑ CVP > ↑ Venous Return > ↑ Preload > ↑ SV > ↑ COCentral Venous Pressure (CVP)Pressure in thoracic vena cava near the right atrium (reflects right atrial pressure)Alterations of Central Blood Volume1. Changes in total blood volume 2. Shifts in blood to or from the extrathoracic blood volume - Hydrostatic pressure or venous compliance changesFactors affecting venous return - TESTHow is pressure transmitted in the blood?Wave fronts propagated by aortic recoil The further away from the heart the more faint it isDescribe how blood pressure is taken.Slow release of occlusion induces turbulent flow which is the sound we hear.How is Mean Arterial Pressure Calculated2/3 DBP + 1/3 SBP & MAP = CO * TPRHow does gravity affect blood pressure?Standing up blood pools in legs (less intrathoracic) therefore less central blood volume. Lying down distributes blood evenly increasing CBVFactors Affecting Vascular ResistanceViscosity: Directly proportional Length: Directly proportional Radius: Inverse exponentially proportional (To the 4th power)Parallel and Series Resistance Summation How does adding/ losing similarly-sized vessels in parallel and series affect resistanceSeries: Rt = R1 + R2 + R3 + Rn - More series = more resistance Parallel: 1/Rt = 1/R1 + 1/R2 + 1/Rn - More parallel = less resistanceRelationship of Flow, Pressure & ResistanceΔP = QR P = pressure Q = flow R = resistanceRelationship of Flow, Pressure & Resistance to MAPMAP = CO * TPR ΔP = Q * R MAP = Mean Arterial pressure CO = Cardiac Output TPR = Total Peripheral Resistance