2. 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.
Thursday, February 4, 2016
3. REGULATION OF CARDIAC
OUTPUT.
Since CO = SV × HR
SO main factors
controlling are
Venous return
Myocardial
contractility
Peripheral resistance
Heart rate.
Thursday, February 4, 2016
5. 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.
Thursday, February 4, 2016
9. RESPIRATORY PUMP.
Intrapleural pressure
Diameter of IVC
increased – pressure
decreased
Increased blood flow
to right atrium during
inspiration.
Thursday, February 4, 2016
10. 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.
Thursday, February 4, 2016
11. MUSCLE PUMP.
Working of muscle
pumps.
During contraction
During relaxation.
With rhythmic
contraction – blood is
squeezed to the heart.
Applied – Varicose
Veins
Thursday, February 4, 2016
12. 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.
Thursday, February 4, 2016
13. BLOOD VOLUME.
MCFP – depends upon
level of blood volume.
Relationship of MCFP
& blood volume.
Thursday, February 4, 2016
14. 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.
Thursday, February 4, 2016
15. STANDING BODY POSITION.
Prolonged standing –
more venous pooling
– decrease venous
return.
Thursday, February 4, 2016
16. 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.
Thursday, February 4, 2016
17. EXTRINSIC MECHANISMS
AUTONOMIC NEURAL MECHANISM.
Increase in stroke
volume due to
increase in myocardial
contractility without
change in initial
muscle length.
Homometric
mechanism.
Sympathetic activity.
Parasympathetic
activity.
Thursday, February 4, 2016
18. 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%
Thursday, February 4, 2016
19. 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.
Thursday, February 4, 2016
20. PARASYMPATHETIC ACTIVITY.
Negative Inotropic
Effect.
Effect not much
pronounced as vagal
fibres supply mainly
atria not ventricles.
Thursday, February 4, 2016
21. 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.
Thursday, February 4, 2016
22. INTEGRATED CONTRL OF
CARDIAC OUTPUT.
Interaction of frank
starling mechanism &
myocardial contractility.
Shift to left – Increased
myocardial contractility
Shift to right - Decreased
myocardial contractility
Thursday, February 4, 2016
25. HEART LUNG PREPARATION.
To demonstrate effect
of various factors on
activities of Heart.
Thursday, February 4, 2016
26. 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.
Thursday, February 4, 2016
27. 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.
Thursday, February 4, 2016
30. VASCULAR FUNCTION CURVES.
Reflects relationship
between venous return
& venous pressure.
Normal
Effect of increased
blood volume.
Thursday, February 4, 2016