CARDIAC OUT PUT, CARDIAC OUT PUT, VENOUS RETURN, and VENOUS RETURN, and

THEIR REGULATIONTHEIR REGULATION

M. Rasjad IndraM. Rasjad Indra

IntroductionIntroduction

Cardiac output:Cardiac output:– The quantity of blood pumped into the aorta each The quantity of blood pumped into the aorta each

minute by heartminute by heart

Venous return:Venous return:– The quantity of blood flowing from the veins into the The quantity of blood flowing from the veins into the

right atrium each minuteright atrium each minute

The venous return & the cardiac output must be The venous return & the cardiac output must be equalequal– Except for a few heartbeats at a time when blood Except for a few heartbeats at a time when blood

might be temporarily being stored in or removed from might be temporarily being stored in or removed from the heart and lungthe heart and lung

The factors directly affect cardiac output:The factors directly affect cardiac output:– The level of body metabolismThe level of body metabolism– Physical exercisePhysical exercise– AgeAge– Body size Body size Cardiac index (3 L/minute/mCardiac index (3 L/minute/m22))

0 40 50 60 70 8010 20 30

Car

diac

Inde

x (L

/min

/m2

1

2

3

4

Age in years

Control of cardiac output by venous returnControl of cardiac output by venous return

Heart pump automatically whatever amount Heart pump automatically whatever amount of blood flows into the right atrium from the of blood flows into the right atrium from the veins (veins (Frank-Starling law of the heartFrank-Starling law of the heart).).

Stretching of the sinus Stretching of the sinus increase heart rate increase heart rate

Strechting atrium Strechting atrium increase heart rate & increase heart rate & cardiac contractility (Bainbridge reflex).cardiac contractility (Bainbridge reflex).

The cardiac output is controlled almost The cardiac output is controlled almost entirely by peripheral factors that determine entirely by peripheral factors that determine the venous returnthe venous return

CO~ The sum of blood flow regulation CO~ The sum of blood flow regulation in all the local tissues of the bodyin all the local tissues of the body

Factors that control local blood flow Factors that control local blood flow Sum Sum of blood flow regulation of blood flow regulation Venous return Venous return The heart pumps this returning blood The heart pumps this returning blood (cardiac output).(cardiac output).

The reciprocal relationship between The reciprocal relationship between total peripheral resistance & cardiac total peripheral resistance & cardiac output.output.

R

MAPCO

Cardiac Output CurveCardiac Output Curve

Factors can make the heart hyper-effective:Factors can make the heart hyper-effective:1.1. Nervous stimulationNervous stimulation

2.2. Hypertrophy of the heart muscleHypertrophy of the heart muscle

Factors that cause a hypo-effective heart:Factors that cause a hypo-effective heart: Any factors that decrease the heart ability:Any factors that decrease the heart ability:

1.1. Congenital heart diseaseCongenital heart disease

2.2. MyocarditisMyocarditis

3.3. Cardiac ischemia etc.Cardiac ischemia etc.

Venous Return CurveVenous Return Curve

Right Atrial PressureRight Atrial Pressure

Mean Systemic Filling PressureMean Systemic Filling Pressure– The pressure measured every where in the The pressure measured every where in the

systemic circulation when all flow of blood is systemic circulation when all flow of blood is stopped).stopped).

Resistance of blood flowResistance of blood flow

-4

5

10

+40 +8 +120

Psf=3.5 Psf=7Psf=14

Ven

ous

Ret

urn

(L/m

in)

Right Atrial Pressure (mm Hg)

Venous Return Curve

Mean Circulatory & Mean Systemic Mean Circulatory & Mean Systemic Filling PressureFilling Pressure

Blood volume ~ Mean Circulatory Blood volume ~ Mean Circulatory PressurePressureSympathetic stimulation ~ Mean Sympathetic stimulation ~ Mean Circulatory PressureCirculatory PressurePsf ~ Pcf because The pulmonary Psf ~ Pcf because The pulmonary circulation:circulation:– Capacitance = 1/8 x SystemicCapacitance = 1/8 x Systemic– Blood Volume = 1/10 x SystemicBlood Volume = 1/10 x Systemic

Psf normal = 7 mmHgPsf normal = 7 mmHg

Effect Psf. on Venous ReturnEffect Psf. on Venous Return

The greater the mean filling pressure The greater the mean filling pressure The The more the venous return curve shifts more the venous return curve shifts upwardupward and and to the rightto the right

The lower the mean systemic filling pressure The lower the mean systemic filling pressure The more the curve shifts The more the curve shifts downwarddownward and and to the to the leftleft

VR

RA

R

PPsfVR

VR = Venous ReturnPsf = Mean Systemic Filling PressurePRA = Right Atrial PressureRVR = Venous Return Resistance

Analysis of Cardiac Output & Right Atrial PressureAnalysis of Cardiac Output & Right Atrial Pressure

Using simultaneous Cardiac Output Curve & Venous Using simultaneous Cardiac Output Curve & Venous Return Curve.Return Curve.

-4

5

10

+40

15

+8 +120

Normal resistance2 x Resistance½ resistance1/3 resistance

Psf=2.3Psf=7

Psf=10

Ven

ous

Ret

urn

(L/m

in)

Right Atrial Pressure (mm Hg)

Method for Measuring Cardiac OutputMethod for Measuring Cardiac Output1.1. Oxygen Fick Method:Oxygen Fick Method:

Cardiac Out put (L/minute)=

O2 absorbed per minute by the lungs (ml/min) Aterio venous O2 difference (ml/L) of blood

2. Indicator Dilution Method: