Download Cardiac Out Put

CARDIAC OUT PUT
Dr.Sisara Bandara Gunaherath
MBBS
What is Cardiac Out Put ?
• The pumping ability of the heart
• Cardiac out put is equal to the volume of blood pumped
per minute by each ventricle
• Cardiac out put = Stroke volume * Cardiac
rate
( ml/min)
(ml/beat)
(beats/min)
Factors Regulate Cardiac Rate
Autonomic nervous system
• In the complete absence of neural influences the heart will
continue to beat according to the rhythm set by the SA
node
• With influence of the ANS cardiac rate changes
• The activity of autonomic innervation of the heart is
coordinated by the cardiac center in the medulla
oblongata
Factors Regulate the Stroke Volume
• End diastolic volume ( Volume of blood in the ventricles at
the end of diastole immediately before contraction )
• Peripheral resistance ( The resistance to blood flow in the
arteries)
• Contractility ( Strength of ventricular contraction )
• When the End diastolic volume is more the Stroke volume
also increases
• When the contractility is more the Stroke volume also
increases
• But when the peripheral resistance is more the Stroke
volume decreases
Factors affecting End Diastolic Volume
• Controlled by the factors that affect the Venous return (
Return of blood to the heart via veins)
• Mainly depends on the total blood volume and the venous
pressure
• Total blood volume depends on the balance between
water loss and the water gain
• Venous pressure highest in venules (10mmHg) and
lowest at the junction of superior vena cava with right
atrium (0mmHg)
In addition to the pressure difference, venous return to the
heart is aided by
• Sympathetic nerve activity , which stimulates the smooth
muscle contraction in the venous walls
• The skeletal muscle pump, which squeezes veins during
muscle contraction
• The pressure difference between the thoracic and
abdominal cavities, which promotes the flow of venous
blood back to the heart.
EXCHANGE OF FLUID
BETWEEN CAPILLARIES AND
TISSUES
What is Osmotic Pressure ?
• The ability to take the water in to a solution
by osmosis
• Greater the solute concentration greater the osmotic
pressure
What is Hydrostatic Pressure?
• The pressure created by the liquid atoms in side the
solution
• Filtration results due to the pressure differences within the
capillaries and the tissue fluid
• This hydrostatic pressure, which is exerted against the
inner capillary wall, is equal to 37mmHg at the arteriolar
end of systemic capillaries and drops to about 17mmHg at
the venular end of the capillaries
• The net filtration pressure is equal to the hydrostatic
pressure of the blood in the capillaries minus the
hydrostatic pressure of tissue fluid out side the capillaries
which opposes the filtration.
• Glucose, comparably sized organic molecules, inorganic
salts and ion are filtered along with water through the
capillary channels
• The concentration of these substances in tissue fluid are
thus the same as in plasma
• The protein concentration of tissue fluid , however is less
than the protein concentration of plasma
• This difference is due to the restricted filtration of proteins
through the capillary pores
• The osmotic pressure exerted by plasma proteins , called
the colloid osmotic pressure of the plasma is greater than
the colloid osmotic pressure of tissue fluid
• The difference between these two pressures is called the
oncotic pressure
• Usually the colloid osmotic pressure of tissue fluid is very
low ( can be neglect )and the colloid osmotic pressure of
the plasma is about 25mmHg
Venular
End
Arteriolar
End
HP = 37mmHg
OP = 25mmHg
OP
=25mm
Hg
HP =
17mmHg
Net Fluid Movement
Tissue Fluid
Osmotic
Pressure of
Tissue Fluid
Hydrostatic
Pressure of
Tissue Fluid
Osmotic Pressure of Blood Plasma
Hydrostatic Pressure of Blood Plasma
Blood Vessel
• Fluid Movement
( HPc + OPt) – ( HPt + OPc)
Fluid Out
Fluid In
HPc – Hydrostatic Pressure in the capillary
OPt – Osmotic Pressure in the tissue fluid
HPt - Hydrostatic Pressure in the tissue fluid
OPc - Osmotic Pressure in the capillary