CARDIAC OUTPUT AND CARDIAC OUTPUT AND VENOUS RETURNVENOUS RETURN

BYBY

DR. MUDASSAR ALI ROOMI DR. MUDASSAR ALI ROOMI ((MBBS, M. PHILMBBS, M. PHIL))

STROKE VOLUME (SV)STROKE VOLUME (SV)

S.V is the amount of blood pumped out by S.V is the amount of blood pumped out by each ventricle during each beat. When each ventricle during each beat. When heart rate is normal (72/min), it is 70ml heart rate is normal (72/min), it is 70ml (60-80ml).(60-80ml).It is the difference between EDV & ESV = It is the difference between EDV & ESV = 120 – 50 = 70ml.120 – 50 = 70ml.

CARDIAC OUTPUTCARDIAC OUTPUT

CARDIAC OUTPUT (CO): CARDIAC OUTPUT (CO): Quantity of Quantity of blood pumped into the aorta each minute blood pumped into the aorta each minute by the heart. In a resting supine man, it is by the heart. In a resting supine man, it is 5L/min5L/min C.O = C.O = ARTERIAL PRESSURE ARTERIAL PRESSURE (Ohm’s (Ohm’s

Law) TPRLaw) TPR

C.O = STROKE VOLUME (SV) X HEART RATE (HR)C.O = STROKE VOLUME (SV) X HEART RATE (HR)

C.O = 70ml x 72 beats/min = 5000ml = 5 L C.O = 70ml x 72 beats/min = 5000ml = 5 L (approx)(approx)

EJECTION FRACTIONEJECTION FRACTION: is the fraction of : is the fraction of

EDV that is ejected out by each ventricle EDV that is ejected out by each ventricle per beat. Normally it is 60-65%.per beat. Normally it is 60-65%.

CARDIAC INDEXCARDIAC INDEX: It is the correlation : It is the correlation between resting C.O & body surface area.between resting C.O & body surface area.

C.I = C.O / min / mC.I = C.O / min / m2 of body surface of body surface

70kg man has body surface area = 1.7 m70kg man has body surface area = 1.7 m2

So, C.I = 5L/min = 3L / min / mm2 (approx) 1.7mm2

CARDIAC RESERVECARDIAC RESERVE: is the maximum : is the maximum amount of blood that can be pumped out amount of blood that can be pumped out by the heart above normal value.by the heart above normal value.SIGNIFICANCESIGNIFICANCE: In normal persons, C.O : In normal persons, C.O increases during stress like exercise.increases during stress like exercise.C.R = 300-400% (in young adult)C.R = 300-400% (in young adult)C.R = 200-250% (in old age)C.R = 200-250% (in old age)C.R = 500-600% (in athletes)C.R = 500-600% (in athletes)C.R = 0% approx (in cardiac diseases)C.R = 0% approx (in cardiac diseases)

VENOUS RETURNVENOUS RETURN is the quantity of blood is the quantity of blood flowing from the veins into the right atrium each flowing from the veins into the right atrium each minute.minute.Normally V.R = C.O (Frank starling law)Normally V.R = C.O (Frank starling law)

FACTORS AFFECTING C.O:FACTORS AFFECTING C.O:

PHYSIOLOGICAL FACTORSPHYSIOLOGICAL FACTORS

PATHOLOGICAL FACTORSPATHOLOGICAL FACTORS

PHYSIOLOGICAL FACTORSPHYSIOLOGICAL FACTORS

1. AGE: 1. AGE: CHILDREN = less C.O (due to low B.Vol) & C.I of children >C.I CHILDREN = less C.O (due to low B.Vol) & C.I of children >C.I

of adults (due to less body surface area).of adults (due to less body surface area). OLD AGE = less C.O (due to low metabolic activity).OLD AGE = less C.O (due to low metabolic activity).

2. SEX: 2. SEX: In FEMALES: C.O = less,In FEMALES: C.O = less, C.I = more (due to less surface area)C.I = more (due to less surface area) In MALES: C.O = more,In MALES: C.O = more, C.I = less (due to more body surface area)C.I = less (due to more body surface area)

3. BODY BUILD: 3. BODY BUILD: C.O is more if body build is greaterC.O is more if body build is greater

PHYSIOLOGICAL FACTORS (cont…)PHYSIOLOGICAL FACTORS (cont…)

4. DIURNAL VARIATION:4. DIURNAL VARIATION: C.O = low in morning (due to low BMR)C.O = low in morning (due to low BMR) C.O = more in day time (due to high BMR)C.O = more in day time (due to high BMR)

5. TEMPERATURE:5. TEMPERATURE: C.O = increases if temp increases above 30C.O = increases if temp increases above 30°°C.C.

6. EMOTIONAL CONDITIONS:6. EMOTIONAL CONDITIONS: C.O = increases by 50-100% in Anxiety & excitement.C.O = increases by 50-100% in Anxiety & excitement. Mechanism: Release of CATS Mechanism: Release of CATS increased H.Rate & Force of increased H.Rate & Force of

contraction.contraction.

PHYSIOLOGICAL FACTORS (cont…)PHYSIOLOGICAL FACTORS (cont…)

7. AFTER MEALS:7. AFTER MEALS: C.O = increased during 1C.O = increased during 1stst hour after meal. hour after meal.

8. EXERCISE:8. EXERCISE: C.O = increased (depending on severity of exercise).C.O = increased (depending on severity of exercise). MECHANISM: Increase in H.Rate & Force of contraction.MECHANISM: Increase in H.Rate & Force of contraction.

9. HIGH ALTITUDE:9. HIGH ALTITUDE: C.O = increasedC.O = increased MECHANISM: Due to hypoxia MECHANISM: Due to hypoxia secretion of adrenaline. secretion of adrenaline.

PHYSIOLOGICAL FACTORS (cont…)PHYSIOLOGICAL FACTORS (cont…)

10. POSTURE: 10. POSTURE: C.O = decreases when recumbent C.O = decreases when recumbent upright position. upright position. MECHANISM: Pooling of blood MECHANISM: Pooling of blood in lower limbs, when we in lower limbs, when we

stand up from lying position.stand up from lying position.

11. PREGNANCY: 11. PREGNANCY: C.O = increased by 45-60% in later months of pregnancy.C.O = increased by 45-60% in later months of pregnancy.

12. SLEEP:12. SLEEP: C.O = reduced / unchanged during sleep.C.O = reduced / unchanged during sleep.

PATHOLOGICAL FACTORS:PATHOLOGICAL FACTORS:

1. PYREXIA / FEVER:1. PYREXIA / FEVER: C.O = increased (rapid metabolism)C.O = increased (rapid metabolism)

2. ANEMIA:2. ANEMIA: C.O = increased (due to hypoxia C.O = increased (due to hypoxia secretion of adrenaline). secretion of adrenaline).

3. ABNORMAL THYROID FUNCTION:3. ABNORMAL THYROID FUNCTION: HYPERTHYROIDISM: C.O increases (due to increased BMR).HYPERTHYROIDISM: C.O increases (due to increased BMR). HYPOTHYROIDISM: C.O decreases (due to decreased BMR).HYPOTHYROIDISM: C.O decreases (due to decreased BMR).

4. ABNORMAL HEART CONDITIONS:4. ABNORMAL HEART CONDITIONS: ATRIAL FIBRILLATIONATRIAL FIBRILLATION: C.O is decreased (due to incomplete : C.O is decreased (due to incomplete

filling).filling). INCOMPLETEINCOMPLETE HEART BLOCKHEART BLOCK with coronary sclerosis or myocardial with coronary sclerosis or myocardial degeneration:degeneration: C.O is decreased (due to defective pumping). C.O is decreased (due to defective pumping).

CCFCCF: C.O is less (due to weak contraction of heart).: C.O is less (due to weak contraction of heart).

5. ABNORMAL CIRCULATORY CONDITIONS:5. ABNORMAL CIRCULATORY CONDITIONS: SHOCKSHOCK: C.O = less (due to poor pumping & circulation).: C.O = less (due to poor pumping & circulation). HEMORRHAGEHEMORRHAGE: C.O = less (due to low blood volume).: C.O = less (due to low blood volume).

DISTRIBUTION OF Cardiac Output TO DISTRIBUTION OF Cardiac Output TO VARIOUS ORGANS:VARIOUS ORGANS:

BLOOD BLOOD LEFT VENT. LEFT VENT. SYSTEMIC SYSTEMIC CIRCULATION: CIRCULATION: LIVER = 1500ml = 30%LIVER = 1500ml = 30%KIDNEYS = 1300ml = 26%KIDNEYS = 1300ml = 26%SKELETAL MUSCLES = 900ml = 18%SKELETAL MUSCLES = 900ml = 18%BRAIN = 800ml = 16%BRAIN = 800ml = 16%SKIN+BONE+GIT = 300ml = 6%SKIN+BONE+GIT = 300ml = 6%HEART = 200ml = 4%HEART = 200ml = 4%TOTAL = 5000ml = 100%TOTAL = 5000ml = 100%

REGULATION OF C.O:REGULATION OF C.O:

C.O = STROKE VOL. X HEART RATEC.O = STROKE VOL. X HEART RATE

C.O REGULATING FACTORS INCLUDE:C.O REGULATING FACTORS INCLUDE: 1. 1. FACTORS REGULATING S.V (EDV-ESV)FACTORS REGULATING S.V (EDV-ESV) 2. 2. FACTORS REGULATING HEART RATEFACTORS REGULATING HEART RATE

FACTORS AFFECTING EDV :FACTORS AFFECTING EDV :

1. V.R (most important factor)1. V.R (most important factor)2. M.S.F.P2. M.S.F.P3. SYMPATHETIC STIMULATION3. SYMPATHETIC STIMULATION4. SKELETAL MUSCLE PUMP4. SKELETAL MUSCLE PUMP5. GRAVITY5. GRAVITY6. RESPIRATORY PUMP6. RESPIRATORY PUMP7. DURATION OF DIASTOLE7. DURATION OF DIASTOLE8. DISTENSIBILITY OF VENTRICLE8. DISTENSIBILITY OF VENTRICLE9. ATRIAL CONTRACTION9. ATRIAL CONTRACTION

FACTORS AFFECTING ESV :FACTORS AFFECTING ESV :

1. FORCE OF HEART CONTRACTION 1. FORCE OF HEART CONTRACTION (FRANK STARLING LAW)(FRANK STARLING LAW)

2. AFTER LOAD2. AFTER LOAD

3. SYMPATHETIC /VAGUS NERVES3. SYMPATHETIC /VAGUS NERVES

4. CONDITION OF MYOCARDIUM4. CONDITION OF MYOCARDIUM

5. HORMONES/DRUGS WHICH 5. HORMONES/DRUGS WHICH INCREASE CONTRACTILITY OF HEARTINCREASE CONTRACTILITY OF HEART

FACTORS AFFECTING EDV:FACTORS AFFECTING EDV:

1. VENOUS RETURN: 1. VENOUS RETURN:

Most important factor.Most important factor. Amount of blood which returns to heart/min.Amount of blood which returns to heart/min. Basic factors affecting V.R:Basic factors affecting V.R:

V.R = V.R = ARTERIAL B.PARTERIAL B.P TPRTPRV.R = V.R = MEAN SYSTEMIC FILLING Pr – Rt. At. PrMEAN SYSTEMIC FILLING Pr – Rt. At. Pr RESISTANCE TO V.RRESISTANCE TO V.RV.R = V.R = MSFP-RAPMSFP-RAP RVRRVR

2. MSFP:2. MSFP: Mean Systemic Filling Pressure is average pressure Mean Systemic Filling Pressure is average pressure

in systemic blood vessels which tends to push the in systemic blood vessels which tends to push the blood towards the heart, when there is no active blood towards the heart, when there is no active circulation. It indicates the degree of filling of blood circulation. It indicates the degree of filling of blood vessels.vessels.

MSFP depends on:MSFP depends on:A) how much vessel is filled with bloodA) how much vessel is filled with bloodB) compression from outsideB) compression from outside

Normal MSFP = 7mmHg (MCQ)Normal MSFP = 7mmHg (MCQ) MSFP is affected by blood volume, sympathetic MSFP is affected by blood volume, sympathetic

Stimulation & contraction of skeletal muscles. Stimulation & contraction of skeletal muscles. (Directly proportional)(Directly proportional)

More Blood VolumeMore Blood Volume more MSFP more MSFP more V.R (in blood more V.R (in blood loss loss low B.V low B.V low V.R) low V.R)Symp. StimULATION Symp. StimULATION VenoConstriction VenoConstriction more V.R more V.R Skeletal muscle contraction Skeletal muscle contraction more MSFP more MSFP more V.R more V.R

RIGHT ATRIAL PRESSURE = C.V.P = 0 RIGHT ATRIAL PRESSURE = C.V.P = 0 in most of Cardiac Cycle.in most of Cardiac Cycle.RVR (RESISTANCE TO V.R) is resistance RVR (RESISTANCE TO V.R) is resistance offered by veins against the return of blood offered by veins against the return of blood = 1.4mmHg/L= 1.4mmHg/LSo V.R =So V.R = MSFP-RAP MSFP-RAP RVRRVR V.R = V.R = 7-0 7-0 = 5L= 5L 1.4 1.4

Effect of hormones & drugs etc which increase Effect of hormones & drugs etc which increase C.O: (C.O: (byby increaseing contraction of heartincreaseing contraction of heart))1.1. CatsCats2.2. ThyroxineThyroxine3.3. GlucagonGlucagon4.4. Increased temperatureIncreased temperature5.5. CaffeineCaffeine6.6. TheophyllineTheophylline7.7. DigitalisDigitalis8.8. Calcium ionsCalcium ions

Factors which decrease C.O By Factors which decrease C.O By depressing the heart:depressing the heart:1.1. Heart failureHeart failure

2.2. HypoxiaHypoxia

3.3. AcidosisAcidosis

4.4. BarbituratesBarbiturates

5.5. Beta adrenergic blockersBeta adrenergic blockers

FLOW CHART OF C.O:FLOW CHART OF C.O:

C.OC.O

H.RATE STROKEVOLUME

EDV ESV

CARDIAC CONTRACTILITY

NERVOUS STIM.DRUGS & MET

CARDIAC NUTR

PRELOADSTARLING LAW

AFTER LOADART. Pr

TEMP

SYMP ST

P.SYM INHIB

IMPULSES FROM CVS RECEPTORS

& BRAIN CENTERS

FILLING TIME

ATRIAL CONTRDIST OF VENT

VR

ART BP & TPR MSFP

THOR. MOVE& I.Th.Press. B.VOL SYMP ST SK MUS CONTR

RELATION BETWEEN H.R & C.O:RELATION BETWEEN H.R & C.O: Generally when H.R increases Generally when H.R increases C.O C.O

increases. (but the limit is 150/min)increases. (but the limit is 150/min) Between 150-180 beats/min, there is no Between 150-180 beats/min, there is no

increase in C.O.increase in C.O. Beyond 180-190 beats/min, C.O decreases, Beyond 180-190 beats/min, C.O decreases,

with increasing heart rate. It is because of too with increasing heart rate. It is because of too short diastoleshort diastole

NERVOUS CONTROL OF HEART NERVOUS CONTROL OF HEART RATE:RATE:

Heart beat is autonomous but is modified Heart beat is autonomous but is modified by nervous mechanisms:by nervous mechanisms:

1) Autonomic nerves supplying the heart:1) Autonomic nerves supplying the heart: SympatheticSympathetic ParasympatheticParasympathetic

2) Vasomotor centre (effected by impulses 2) Vasomotor centre (effected by impulses

from different parts of the body).from different parts of the body).

EFFECTS OF SYMPATHETIC STIMULATIONEFFECTS OF SYMPATHETIC STIMULATION

1) +ve CHRONOTROPIC EFFECT:1) +ve CHRONOTROPIC EFFECT: Increase in heart rate.Increase in heart rate.

2) +ve INOTROPIC EFFECT:2) +ve INOTROPIC EFFECT: Increased force of contraction.Increased force of contraction.

3) +ve DROMOTROPIC EFFECT:3) +ve DROMOTROPIC EFFECT: INCREASED CONDUCTIVITY IN HEART.INCREASED CONDUCTIVITY IN HEART.

4) +ve BATHMOTROPIC EFFECT:4) +ve BATHMOTROPIC EFFECT: INCREASED EXCITABILITY OF HEART.INCREASED EXCITABILITY OF HEART.

EFFECTS OF VAGAL STIMULATIONEFFECTS OF VAGAL STIMULATION

1) –ve CHRONOTROPIC EFFECT:1) –ve CHRONOTROPIC EFFECT: SLOWING OF H.R.SLOWING OF H.R.

2) 2) SLIGHT –ve IONOTROPIC EFFECT:SLIGHT –ve IONOTROPIC EFFECT: Decrease force of contractionDecrease force of contraction Only slight effect because vagal fibers do not supply Only slight effect because vagal fibers do not supply

ventricular muscle.ventricular muscle.

3) –ve DROMOTROPIC EFFECT:3) –ve DROMOTROPIC EFFECT: Slowing of conduction in heart & AV nodal delay is Slowing of conduction in heart & AV nodal delay is

prolonged.prolonged.

4) –ve BATHMOTROPIC EFFECT:4) –ve BATHMOTROPIC EFFECT: Decreased excitability of heart.Decreased excitability of heart.

Factors affecting venous Factors affecting venous returnreturn

1.1. Vis a tergo (force from behind).Vis a tergo (force from behind).2.2. The pressure gradient The pressure gradient 3.3. Vis a Fronte (force from front) : Right Vis a Fronte (force from front) : Right

Ventricular Contraction. Sucking force is Ventricular Contraction. Sucking force is producedproduced

4.4. Muscle venous pump (peripheral heart)Muscle venous pump (peripheral heart)5.5. Thoracoabdominal pump or Respiratory Thoracoabdominal pump or Respiratory

PumpPump6.6. Venous reservoirsVenous reservoirs7.7. Effect of posture and gravity Effect of posture and gravity

Cardiac Output CurvesCardiac Output Curves

Factors That Can Cause Factors That Can Cause Hypereffective Heart:Hypereffective Heart:1.1. Sympathetic stimulationSympathetic stimulation

2.2. hypertrophy of the heart muscle.hypertrophy of the heart muscle.

Factors That Cause a Hypoeffective Factors That Cause a Hypoeffective Heart:Heart:1.1. Coronary artery blockage, causing Coronary artery blockage, causing

a “heart attack”a “heart attack”

2.2. Inhibition of sympathetic excitation Inhibition of sympathetic excitation of the heartof the heart

3.3. Pathological factors that cause Pathological factors that cause abnormal heart rhythm or rate of abnormal heart rhythm or rate of heartbeatheartbeat

4.4. Valvular heart diseaseValvular heart disease

5.5. Increased arterial pressure against Increased arterial pressure against which the heart must pump, such which the heart must pump, such as in hypertensionas in hypertension

6.6. Congenital heart diseaseCongenital heart disease

7.7. MyocarditisMyocarditis

8.8. Cardiac hypoxiaCardiac hypoxia

Cardiac output curves at different levels of Cardiac output curves at different levels of intrapleural pressure and at different intrapleural pressure and at different degrees of cardiac tamponadedegrees of cardiac tamponade

Venous ReturnVenous Return

DefinitionDefinition: it is the quantity of blood flowing from : it is the quantity of blood flowing from the veins into the right atrium each minute.the veins into the right atrium each minute.Normally V.R = C.O (Frank starling law)Normally V.R = C.O (Frank starling law)VENOUS RETURN = (MEAN SYSTEMIC FILLING PRESSURE – VENOUS RETURN = (MEAN SYSTEMIC FILLING PRESSURE – RIGHT ATRIAL PRESSURE)/ RESISTANCE TO VENOUS RIGHT ATRIAL PRESSURE)/ RESISTANCE TO VENOUS RETURNRETURN

VENOUS RETURN CURVEVENOUS RETURN CURVE

““Pressure Gradient for Pressure Gradient for Venous Return”—When Venous Return”—When This Is Zero, There Is This Is Zero, There Is No Venous Return.No Venous Return.

Increase in Blood Increase in Blood Volume increases Volume increases MSFPMSFP

Sympathetic Sympathetic Stimulation increases Stimulation increases MSFP.MSFP.

Increase in MSFP shifts the VR curve to Increase in MSFP shifts the VR curve to the right and vice versa.the right and vice versa.

EFFECT OF TPR ON VENOUS RETURNEFFECT OF TPR ON VENOUS RETURN

Decrease in TPR Decrease in TPR causes a clockwise causes a clockwise rotation of the VR rotation of the VR curve and vice versa.curve and vice versa.

Combinations of the major patterns of venous return curves,Combinations of the major patterns of venous return curves,showing the effects of simultaneous changes in mean systemicshowing the effects of simultaneous changes in mean systemic

filling pressure (Psf) and in “resistance to venous return.”filling pressure (Psf) and in “resistance to venous return.”

Cardiac Output and Cardiac Output and Venous Return Curves combinedVenous Return Curves combined

The point at which the The point at which the CO and VR curves CO and VR curves intersect each other is intersect each other is the the equilibrium or equilibrium or steady state point.steady state point.

At this point CO and At this point CO and VR are equal.VR are equal.

Cardiac Output and Cardiac Output and Venous Return Curves combinedVenous Return Curves combined

Cardiac output can be Cardiac output can be changed by altering changed by altering the CO curve or VR the CO curve or VR curve or both the curve or both the curves curves simultaneously.simultaneously.