Download pulmonary circulation

By
Dr. Mudassar Ali Roomi (MBBS, M.Phil.)
Assist. Prof. Physiology
Physiological anatomy of pulmonary
circulatory system
 The pulmonary vessels
 the pulmonary arterial tree has
a large compliance
 Bronchial blood vessels
 1 to 2 % of the total cardiac
output.
 the left ventricular output
is about 1 to 2 % greater
than the right ventricular
output.
 Lymphatic from the lungs
enter into right thoracic
lymph duct
Blood volume of the lungs
 500 milliliters
 9 % of the total blood
volume of the entire
circulatory system.
 Approximately 70 ml in the
pulmonary capillaries
 Lungs as a Blood Reservoir
(100-250 ml)
Automatic Control of Pulmonary Blood
Flow Distribution
 Hypoxia
vasoconstriction
 When concentration of oxygen in the air of the alveoli
decreases below 70 % of normal ,the adjacent blood vessels
constrict.
 This is opposite to effect observed in systemic vessels
 Undiscovered vasoconstrictor substance to be released from
the lung tissue
 Important function: to distribute blood flow to most
oxygenated alveoli.
Pressure Pulse Curve in the Right Ventricle.
 Systolic: 25 mm Hg
 Diastolic: about 0 to 1
mm Hg
Pressures in the Pulmonary Artery.
 Systolic: 25 mm Hg
 Diastolic: 8 mm Hg.
 Pulse pressure: 17 mm
Hg.
 Pulmonary Capillary
Pressure: 7 mmHg
 Left Atrial and Pulmonary
Venous Pressures:
 The mean pressure in the left
atrium and the major
pulmonary veins averages
about 2 mm Hg
 estimated with moderate
accuracy by measuring the
pulmonary wedge pressure (5
mm Hg). It is 2 to 3 mm Hg
greater than the left atrial
pressure
Comparison of pressures in systemic
and pulmonary circulations.
 Length of Time Blood
Stays in the Pulmonary
Capillaries (0.3-0.8
sec).
Effect of Increased Cardiac Output on Pulmonary Blood Flow and
Pulmonary Arterial Pressure During Heavy Exercise
 During heavy exercise, blood flow through the lungs
increases fourfold to sevenfold.
 This extra flow is accommodated in the lungs in three
ways:
(1) by increasing the number of open capillaries,
(2) by distending all the capillaries
(3) by increasing the pulmonary arterial pressure.
Shift of Blood Between the Pulmonary and Systemic Circulatory Systems
as a Result of Cardiac Pathology (left heart failure).
 affects the pulmonary
system greatly but
usually has only mild
systemic circulatory
effects.
Effect of Hydrostatic Pressure Gradients in the Lungs on
Regional Pulmonary Blood Flow
 Hydrostatic pressure is affected
by gravity
 Pulmonary arterial pressure at
the apex of lung of a standing
person is about 15 mm Hg less
than the pulmonary arterial
pressure at the level of the heart
 The pressure in the base of the
lungs is about 8 mm Hg greater
than the pulmonary arterial
pressure at the level of the
heart.
Zones of Pulmonary Blood Flow
Zone 1 blood flow
 No blood flow during all
portions of the cardiac
cycle
 Zone 1 Blood Flow Occurs
Only Under Abnormal
Conditions.
 occurs when either the
pulmonary systolic arterial
pressure is too low or the
alveolar pressure is too high
to allow flow
1. Too high alveolar pressure
e.g. Breathing against a
positive air pressure
2. After severe blood loss.
Zones of Pulmonary
Blood Flow
 Zone 2 (intermittent fblood
low) in the apices.
 In normal lungs, this zone is
about 10 centimeters above the
midlevel of the heart and
extends from there to the top of
the lungs
 Blood flows during systole but
not during diastole.
 Zone 3 (continuous blood flow
throughout the cardiac cycle) in
all the lower areas.
 from
about 10 centimeters
above the level of the heart all
the way to the bottom of the
lungs,
 In lying posture, all lung has got zone 3 .
Effect of exercise on pulmonary blood flow
Capillary Exchange of Fluid in the Lungs, and
Pulmonary Interstitial Fluid Dynamics
STARLING FORCES:
Capillary Exchange of Fluid in the Lungs, and
Pulmonary Interstitial Fluid Dynamics
 Negative Pulmonary
Interstitial Pressure
and the Mechanism
for Keeping the Alveoli
“Dry.”
Pulmonary Edema
CAUSES
 Left-sided heart failure
 mitral valve disease
 Damage to the pulmonary
blood capillary
membranes
1.
2.
Infections (pneumonia)
Breathing noxious
substances such as
chlorine gas or sulfur
dioxide gas
Pulmonary Edema Safety
Factor
 pulmonary capillary
pressure must rise from
the normal level of 7 mm
Hg to more than 28 mm
Hg
 Safety factor against
pulmonary edema of 21
mm Hg.
Safety Factor in Chronic Conditions (>2 weeks) e.g.
Chronic mitral stenosis
 No lethal edema in chronic lung conditions. This is
because Lymph vessels expand greatly and increase the
drainage of fluid (upto 10 fold).
 Pulmonary capillary pressures may rise upto 40 to 45 mm
Hg even without development of pulmonary edema.
Rapidity of Death in Acute Pulmonary Edema
 A medical emergency
 Cause: Acute left-sided heart failure
 Pulmonary capillary pressure may rise more than 50
mmHg
 Death frequently ensues in less than 30 minutes in severe
cases
Pleural Cavity
 the pleural space—the space
between the parietal and
visceral pleurae
 It is a potential space only
 It contains only a few ml
fluid.
 a thin layer of mucoid fluid
lies between the parietal and
visceral pleurae for easy
slippage of moving lungs.
The pleural membrane
 serous membrane through
which small amounts of
interstitial fluid transude
continually into the pleural
space.
 Pumping of fluid from the
space by the lymphatics
provides negative pressure
in pleural cavity (–7 mm
Hg).
Pleural Effusion
 Definition: Pleural effusion
means the collection of large
amounts of free fluid in the
pleural space.
 The effusion is analogous to
edema fluid in the tissues
and can be called “edema of
the pleural cavity.”
Causes:
1. Blockage of lymphatic
2. Cardiac failure
3. Greatly reduced plasma
colloid osmotic pressure
4. Infection or any other cause
of inflammation