Clinical Cardiovascular Anatomy & Physiology Concepts, Definitions, & Principles Slides developed in...

Clinical Cardiovascular Anatomy & Physiology

Concepts, Definitions, & Principles

Slides developed in collaboration with Dr. John Green, 2003.

Intima

Adventitia

Media

The Normal Heart - Coronary Artery Anatomy

Left Main CA

Circumflex

Left Anterior Descending CA

Right CA

Marginal Branch

Layers of the Arterial Wall

The Heart as a Pump

Reference: Berne and Levy, “Physiology”

Cardiac Muscle Differences

• Fibers organized into functional syncytium– branching, interconnected fibers

• ends separated by intercalated disks fused to adjoining fibers by tight junctions; low resistance

• all-or-none law applies to entire myocardium

• Cannot be tetanized– due to phase 2 (plateau) of action potential

Left Ventricular Volumes - Definitions

End Diastolic Volume (EDV) Volume at the end of diastole (end of ventricular filling)

End Systolic Volume (ESV)Volume at the end of systole(end of ventricular contraction)

Stroke Volume (SV) = EDV - ESV

Ejection Fraction (EF) = SV EDV

Left ventricular norm: 62%

Ejection Fraction is the best indicator of heart performance and disease prognosis

• Cardiac Output (Q) = HR X SV

• Cardiac Index = Q / body surface area

• Preload: diastolic filling volume of the left ventricle (EDV reflects stretch of the cardiac muscle cells)

• Afterload: resistance to ventricular emptying during systole (the amount of pressure the left ventricle must generate to squeeze blood into the aorta

• Frank Starling Law of the Heart - the heart will contract with greater force when preload (EDV) is increased

• Myocardial Contractility - the squeezing contractile force that the heart can develop at a given preload

•regulated by:•sympathetic nerve activity (most influential)•catecholamines (epinephrine norepinephrine)•amount of contractile mass •drugs

Definitions

Starlings Law of the Heart and Contractility

SV

leftventricular

performance

preload (venous return)

↑ contractility

normal contractility

↓ contractility(heart failure)

0

120

dP/dt dP/dt

Using Ventricular Pressure Curves as Indices of Contractility & Cardiac Function

Normal

Heart Failure

dP/dt = change in pressure per unit of time

Note elevation in end diastolic pressure

Contractility• - a change in developed tension at a given

resting fiber length OR an increase in Vmax

– increase max dP/dt from LV pressure curve– Positive and negative inotropic effects– Ejection fraction (EF = SV/EDV) used in clinical

practice• increase contractility assumed with increase EF

with Ca, NE, digitalis, exercise; with [K]o, [Na]o

↑ Contractility related to : beta-sympathetic adrenergic nerves

catecholamines: epinephrine norepinephrine

drugs: digitalissympathomimetics

↓ Contractility related to:loss of contractile mass - myocardial Infarction

myocardial muscle disease - cardiomyopathy

drugs: anesthetics, barbiturates

Influences on Myocardial Contractility

• Arteriovenous Oxygen Difference (AVO2D) the difference in oxygen content between arterial and venous blood

• measured in ml% - ml O2 / 100 ml blood

• Oxygen Consumption (VO2) - the rate at which oxygen can be used in energy production and metabolism

• “absolute” measures: L / min , ml / min• “relative measures: ml / kg body wt. / min• Fick equation: VO2 = Q X AVO2D

• Maximum Oxygen Consumption (VO2max) maximum rate at which a person can take in and utilize oxygen to create usable energy

• defined as plateau of consumption rate increase• often estimated with VO2peak

• Myocardial Oxygen Consumption VO2 of the heart muscle (myocardium)• "estimated" by RPP: HR X SBP

• Functional Aerobic Impairment:predicted VO2max - attained VO2max

predicted VO2max

mild 27% - 40%moderate 41% - 54%marked 55% - 68%severe > 69%

Definitions

• Systolic Blood Pressure (SBP) pressure measured in brachial artery during systole (ventricular emptying and ventricular contraction period)

• Diastolic Blood Pressure (DBP) pressure measured in brachial artery during diastole (ventricular filling and ventricular

relaxation)

• Mean Arterial Pressure (MAP) "average" pressure throughout the cardiac cycle against the walls of the proximal systemic

arteries (aorta)• estimated as: .33(SBP - DBP) + DBP

• Total Peripheral Resistance (TPR) - the sum of all forces that oppose blood flow

• length of vasculature (L)

• blood viscosity (V)

• hydrostatic pressure (P)

• vessel radius (r)

Definitions

TPR = ( 8 ) ( V ) ( L )

() ( r 4 )

Cardiovascular Hemodynamic Basics

Flow (Q) Pressure (MAP) P aorta – P vena cava

= = Resistance (TPR) (8) (V) (L)

() (r 4)

Flow (Q) = () (Pa – Pv) (r 4)

(8) (V) (L)

V = viscosity of fluid (blood) flowing through the pipe L = length of pipe (blood vessel) r = radius of the pipe (blood vessel) Pa = aortic pressure Pv = venous pressure

Normally Resting Q is about 5 - 6 liters / minute

Lungs

Brain

Veins (Flexible Compliant “Pipes”)

Arteries (Stiff Inflexible “Pipes”)

Liver

Stomach

Pancreas

Intestines

Kidneys

Skin

Muscle

Arterioles

Precapillary Sphincters

The Systemic Circulation

Smooth Muscle Arteriole

Anastomosis (Shunt)

Precapillary Sphincter

True Capillary With Single

Layer of Endothelium

Metarteriole

Venule

Microcirculatory Anatomy

Left Ventricular Pressure

(mmHg)

Volume (ml)

120

6

40 140

Effects of an Increase in Preload on Left Ventricular Pressure Volume Loop

↑ EDV↑ EDP

↑ Ejection Pressure

↑ SV

Left Ventricular Pressure

(mmHg)

Volume (ml)

120

6

40 140

Effects of an Increase in Afterload on Left Ventricular Pressure Volume Loop

↑ ESV↑ ESP

↓ SV

Mechanism of Control of Cardiovascular and

Respiratory Systems

Sites of Cardiorespiratory

Control

Stroke Volume – regulated by Frank Starling mechanism

• ↑ venous return → ↑ EDV → ↑ stroke volume

Cardiac Output (Q) – main determinant: body O2 needs

• Autoregulated by intrinsic changes in preload, & SV

•↑ afterload → initial ↓ in Q → ↑ EDV → ↑ SV back to normal

•↑ venous return → ↑ preload → ↑ SV

• Autoregulated by extrinsic hormonal influences• Norepinephrine release → ↑ HR and SV

Cardiorespiratory Control

Cardiorespiratory ControlExercise Systemic Blood Flow: Autonomic influences

Sympathetic outflow & circulating catecholamines• activation → vasoconstriction in non - exercising tissue

• Approximate redistribution of blood flow during maximal exercise• NC in brain blood flow 500 ml/min ↑ to heart

• 11,300 ml/min ↑ to muscle 400 ml/min ↑ to skin

• 500 ml/min ↓ to kidneys 800 ml/min ↓ to viscera

• 200 ml/min ↓ to various other parts of the body

Rest Max Exercise

Acute Cardiorespiratory Responses to Endurance

Exercise

Acute Responses to Aerobic Exercise• Heart Rate

• ↑ up to 3 times resting value at peak exercise (↓ time spent in diastole)

• Oxygen Consumption (VO2)

• Expressed in both relative and absolute terms

• Relative: ml O2/kg/min Absolute: ml/min or L/min

• average VO2max for 40 year old male 37 ml/kg/min

• Resting metabolic equivalent = 1 MET = 3.5 ml/kg/min

• Oxygen consumption linked to caloric expenditure (1 liter of O2 consumed = 5 kcal)

180

160

140

100

HeartRate

1.0 2.0 3.0Oxygen Uptake (L / min)

50 150 250

Workloads (Watts)

HR – VO2

relationship is

linear until about

90% VO2max

• Cardiac Output (Q)• ↑ up to 4 times resting value at peak exercise (↑ is rapid at onset, then levels off)• ↑ Q → ↑ venous return

• Venous return mediated by and related to:• sympathetic venoconstriction• muscle pump• ↑ inspiration → ↓ thoracic pressure

• blood flows to an area of reduced pressure• ↑ inspiration → ↑ abdominal pressure

• contraction of abdominal muscles • squeezing of abdominal veins

• Stroke Volume• ↑ up to 1.5 resting value at peak exercise

• increase levels off at 40% - 50% VO2 max

• ↑ in venous return → ↑ EDV (Starling mechanism)• ↓ ESV eluding to an ↑ in myocardial contractility• ↑ ejection fraction: rest: 58% max exercise: 83%

StrokeVolume(ml/beat

120

110

70

25% 50% 75%

Percentage of VO2 max

Acute Responses to Aerobic Exercise

• Arteriovenous oxygen difference• Difference in [O2] between arterial and mixed venous blood

• Illustrated by the oxyhemoglobin desaturation curve• ↑ approximately 3 fold from rest to max exercise• at rest, about 25% of arterial O2 is extracted

• at peak exercise 85% of arterial O2 is extracted

• Blood Pressures and Resistance to Flow• SBP: ↑ - failure to ↑ signifies heart failure• DBP: slight ↑ or slight ↓ or NC• MAP: slight ↑ • TPR: ↓ - mainly due to vasodilation in exercising muscle

• Coronary (Myocardial) Blood Flow• 4.5% of Q goes to myocardium at rest and at peak exercise

• this increase is due to ↑ MAP and CA vasodilation

• Blood Flow to the Skin• ↑ as exercise duration ↑ to allow for heat dissipation• ↓ at max exercise to meet exercising muscle demands

• ↑ during exercise recovery, again for heat dissipation


• Minute Ventilation• resting average: 6 Liters/min• peak exercise average: 175 Liters/min• respiratory rate: resting 12-18 peak exercise: 45-60• tidal volume: resting .5 liters peak exercise: 2.25 Liters

• Plasma Volume• blood plasma ↑ in the interstitum of exercising muscle• fluid shift results in a 5% ↑ in the hemoconcentration• blood viscosity increases


Untrained or people with certain cardiorespiratory diseases will have larger DEBTS and DEFICITS

Oxygen DEBT & Oxygen DEFICIT

Oxygen Debt(EPEOC)

Oxygen Deficit“Steady State”VO2

VO2

Rest

Onset TerminationEXERCISE TIME

Oxygen Debt and Deficit

Oxygen Deficit due to:

• delay in time for aerobic ATP production to supply energy

Oxygen Debt due to:

• resynthesis of high energy phosphates (CP, ATP)

• replace oxygen stores

• lactate conversion to glucose (gluconeogenesis)

• ↑ HR, respiration, catecholamines, body temperature

V O 2

VCO 2VO 2

V E

HCO 3-

pH

m ax

P CO P COA 2 a 2&

P Oa 2

P OA 2

Increasing workload

OBLA Respiratory Compensation(hyperventilation)

No Change inVE

VCO2

Ventilatory and Metabolic Changes During

Exercise

Training Adaptations to Chronic Endurance

Exercise

RestingNC ↓ NC

VO2 = HR x SV x AVO2diff

due to: due to: ↑ time in diastole ↑ preload

↓ afterload↑ ventricle size↑ blood volume

Submax Workload (measured at same pre-training workload)

NC NC VO2 = HR x SV x AVO2diff

note: a ↓ in afterload (mentioned above) accompanied by a ↓ in HR response translates into

a ↓ myocardial VO2 at rest or at any workload

Max Workload (measured at peak exercise) NC

VO2 = HR x SV x AVO2diff

some studies show a slight decrease

Effects of Exercise Training on the Components of the Fick Relationship

↑↑

• Mean Arterial Pressure• NC at rest or during exercise

• Systolic and Diastolic Blood Pressure• usually NC at rest or during exercise• possible ↓ at submaximal workload• may ↓ at rest in borderline hypertensives

• some studies report a mean ↓ of about 9 mmHg

• Total Peripheral Resistance and Afterload• ↑ capillarization (more parallel circuits) → ↓ TPR• ↓ TPR → ↓ Afterload (slight – not of major significance)

• Respiratory Variables• Respiratory Rate

• Rest: NC• Submax exercise: d• Max exercise: slight ↑

• Tidal Volume• Rest: NC• Submax exercise: NC or slight ↑ • Max exercise: slight ↑

• Anaerobic Threshold• Occurs at a higher percentage of VO2 max• Pre-training: 50% VO2max Post-training: 80% VO2max

Training Adaptations

• Mitochondria• ↑ number, size and membrane surface area

• Aerobic Enzymes in Exercising Muscle• ↑ Krebs cycle enzymes (succinate dehydrogenase)• ↑ oxidation enzymes (carnitine acyltransferase)• ↑ electron transport enzymes (cytochrome oxidase)

• Fatty Acid & Glycogen Utilization• ↑ utilization of oxidative pathways to produce ATP• Called the “glycogen sparring” effect• ↓ RER for any given submaximal workload• ↑ muscle glycogen stores (with high carbohydrate diet)

• ↓ Platelet Aggregation

• ↑ Fibrinolytic Activity

• ↓ Circulating Catecholamines• ↑ vagal tone → ↓ risk of arrhythmia

• No Appreciable Change in Resting Metabolic Rate• Exception: training induced ↑ in lean muscle mass

• Resistance to Pathological Events• smaller infarct size and quicker recovery• Less of a ↓ →in ventricular function during ischemia

Training Adaptations

75

185

60

185

0

50

100

150

200

sedentary-rest sedentary-max trained-rest trained-max

"Average" Values for Sedentary and Trained Individuals

Heart Rate( beats / minute )

Stroke Volume( ml / beat )


60

120

80

160

0

50

100

150


Cardiac Output( liters / minute)


5

22

5

30

05

10152025303540


A-V O2 Difference( ml%)


6

14

6

16

0

5

10

15

20


Oxygen Consumption( liters / minute)


0.25

3

0.25

4.5

0

1

2

3

4

5

6



3.5

38

3.5

55

0

10

20

30

40

50

60


Oxygen Consumption( ml / kg / minute)


134

210

130

206

0

50

100

150

200


Systolic Blood Pressure( mm Hg)


8284

80

82

747678808284868890


Diastolic Blood Pressure( mm Hg)


6

120

6

150

0

20

40

60

80

100

120

140

160


Minute Ventilation( liters / minute)

Clinical Cardiovascular Anatomy & Physiology Concepts, Definitions, & Principles Slides developed in...

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