cardiac output 2
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CARDIAC OUTPUT-
IIDR NILESH KATEASSOCIATE PROF
DEPARTMENT OF PHYSIOLOGY.
Wednesday, May 3, 2023
OBJECTIVES. Regulation of cardiac output. Control mechanisms. Extrinsic & intrinsic. Role of heart rate in cardiac output Integrated control. Heart lung preparation. Cardiac & vascular function curves.
Wednesday, May 3, 2023
REGULATION OF CARDIAC OUTPUT.
Since CO = SV × HR SO main factors
controlling are Venous return Myocardial
contractility Peripheral resistance Heart rate.
Wednesday, May 3, 2023
CARDIAC OUTPUT CONTROL MECHANISMS.
Intrinsic. Respiratory pump. Cardiac pump. Muscle pump. Blood volume. Sympathetic discharge. Standing body position. Resistance to venous
return.
Extrinsic. Sympathetic activity. Parasympathetic
activity.
Wednesday, May 3, 2023
INTRINSIC MECHANISMS. Based on Frank Starling’s
mechanism/law –
“Within Physiological limits the force of contraction of cardiac muscle is directly proportional to initial length of muscle fibre.”
Initial length of muscle fibre decided by condition of muscle before contraction – affected by End-diastolic Volume.
Wednesday, May 3, 2023
Wednesday, May 3, 2023
FRANK-STARLING CURVES LENGTH – TENSION RELATIONSHIP.
Wednesday, May 3, 2023
FACTORS AFFECTING END-DIASTOLIC VOLUME.
Respiratory pump. Cardiac pump. Muscle pump. Blood volume. Sympathetic discharge. Standing body position. Resistance to venous
return.
Wednesday, May 3, 2023
RESPIRATORY PUMP. Intrapleural pressure Diameter of IVC
increased – pressure decreased
Increased blood flow to right atrium during inspiration.
Wednesday, May 3, 2023
CARDIAC PUMP. VIS – A- TERGO Forward push from
behind. Due to myocardial
contraction during systole & elastic recoil of arterial wall (windkessel effect)
VIS – A – FRONTE. Suction force acting
from front which pulls the blood from great veins into right atrium. Ventricular systolic
suction Ventricular diastolic
suction.
Wednesday, May 3, 2023
MUSCLE PUMP. Working of muscle
pumps. During contraction During relaxation. With rhythmic
contraction – blood is squeezed to the heart.
Applied – Varicose Veins
Wednesday, May 3, 2023
BLOOD VOLUME. Mean circulating filling
pressure (MCFP) Mean systemic filling
pressure.(MSFP) – equilibrated pressure everywhere in circulation at rest.
It influences venous return. VR
More MSFP – More VR.
Relationship of MSFP & Venous Return.
Wednesday, May 3, 2023
BLOOD VOLUME. MCFP – depends upon
level of blood volume.
Relationship of MCFP & blood volume.
Wednesday, May 3, 2023
SYMPATHETIC DISCHARGE. Sympathetic stimulation Increase venous tone Decrease venous system
capacity- MCFP increases – increase VR
At normal blood volume sympathetic stimulation raises MCFP from 7 to 17 mm Hg & Inhibition lowers MCFP 7 to 4 mmHg.
Wednesday, May 3, 2023
STANDING BODY POSITION. Prolonged standing –
more venous pooling – decrease venous return.
Wednesday, May 3, 2023
RESISTANCE TO VENOUS RETURN. 2/3rd by Veins & 1/3rd by Arteries. Decrease resistance to half increases venous
return twice & vice –versa. Relation of VR & resistance.
Wednesday, May 3, 2023
EXTRINSIC MECHANISMSAUTONOMIC NEURAL MECHANISM.
Increase in stroke volume due to increase in myocardial contractility without change in initial muscle length.
Homometric mechanism.
Sympathetic activity. Parasympathetic
activity.
Wednesday, May 3, 2023
SYMPATHETIC ACTIVITY. Stimulation of
sympathetic nerves. Positive inotropic effect –
i.e. increase in maximal velocity of shortening.
Inhibition of sympathetic. When sympathetic
inhibited pumping decreases by 30%
Wednesday, May 3, 2023
CHARACTERISTICS OF INCREASED MYOCARDIAL CONTRACTILITY.
Mechanism – activation of B1 adrenergic receptors– activation of Adenyl cyclase – increase intracellular Camp – rapid intake of Ca via protein kinase.
Ventricle contracts more forcefully
EDV – Decreased.
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PARASYMPATHETIC ACTIVITY. Negative Inotropic
Effect. Effect not much
pronounced as vagal fibres supply mainly atria not ventricles.
Wednesday, May 3, 2023
ROLE OF HEART RATE IN CARDIAC OUTPUT.
SINCE CO = HR × SV But if HR increased alones
CO not changes as increase HR decrease diastolic time & EDV
During exercise increase HR along with Chronotropic (Rate)effect increases CO.
Wednesday, May 3, 2023
INTEGRATED CONTRL OF CARDIAC OUTPUT.
Interaction of frank starling mechanism & myocardial contractility. Shift to left – Increased
myocardial contractility Shift to right - Decreased
myocardial contractility
Wednesday, May 3, 2023
INCREASED MYOCARDIAL CONTRACTILITY
Sympathetic stimulation – β adrenergic receptors.
Catecholamine. Xanthenes – caffeine,
Theophylline , inhibit breakdown of cAMP
Glucagon- increase cAMP Digitalis & related drugs –
Inhibitory effect on Na-K-ATPase.
Wednesday, May 3, 2023
DECREASED MYOCARDIAL CONTRACTILITY
Parasympathetic (vagal) stimulation.
Heart failure. Myocardial infarction. Hypercapnia, hypoxia &
acidosis decrease in cAMP Drugs – Quinidine,
Procainamide, Barbiturates
Wednesday, May 3, 2023
HEART LUNG PREPARATION. To demonstrate effect
of various factors on activities of Heart.
Wednesday, May 3, 2023
USES OF HEART LUNG PREPARATION
Effect of venous return on stroke volume ( Frank starling mechanism)
Effect of sympathetic stimulation on SV.
Combined effect of both. Effect of peripheral
resistance on CO. Cardiac Function Curves.
Wednesday, May 3, 2023
CARDIAC FUNCTION CURVES. It’s the graphical
analysis of CO, capacity of ventricles to pump & relationship between CO & CVP
Useful in patients with cardiac failure.
Normal cardiac function curve.
Wednesday, May 3, 2023
HYPER EFFECTIVE CARDIAC FUNCTION CURVE.
Sympathetic stimulation of heart.
Heart hypertrophy.
Wednesday, May 3, 2023
HYPO EFFECTIVE CARDIAC FUNCTION CURVE.
Reduced sympathetic discharge.
Decreased ventricular compliance, in MI, myocarditis.
Insufficient pumping ; valvular, septal defects
Reduced ventricular filling. Increased load
Wednesday, May 3, 2023
VASCULAR FUNCTION CURVES. Reflects relationship
between venous return & venous pressure.
Normal
Effect of increased blood volume.
Wednesday, May 3, 2023
CARDIOVASCULAR FUNCTION CURVES.
Normal During exercise In CCF.
Wednesday, May 3, 2023
Thank you.
Wednesday, May 3, 2023
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