PULMONARY CIRCULATION,
PULMONARY EDEMA,
PLEURAL FLUID.
Dr. Ayisha Qureshi
Assistant Professor,
MBBS, Mphil
OBJECTIVES
By the end of the lecture, you should be able to:
• Give the physiologic anatomy of the Pulmonary Circulatory
System.
• Name the 2 types of blood supplies of the lung.
• Differentiate between the Pulmonary and systemic
circulation.
• Give the different pressures in the Pulmonary Circulation.
• Name the different zones in the lungs on the basis of
regional pulmonary blood flow and the effect of gravity.
• Explain the pathogenesis of Pulmonary edema.
• Give the significance of Pleural fluid and explain the
pathogenesis of Pleural effusion.
Comparison of the Pulmonary &
Systemic Circulation
PULMONARY CIRCULATION
•
•
•
LOW PRESSURE
- because it only needs to pump
blood to the top of the lungs.
- if it is HI pressure, then following
Starling forces, the fluid would flood
the lungs.
LOW RESISTANCE
- only 1/10th of the resistance of
the systemic circ.
- arterioles have less smooth
muscle, veins are wider & shorter
& pulmonary vessel walls are
thinner.
HIGH COMPLIANCE
- accommodates 5 L of blood
(same as the systemic circulation)
- Accommodates shifts of blood more
quickly e.g. when a person shifts from
a standing to a lying position
SYSTEMIC CIRCULATION
• HIGH PRESSURE
- B/c it needs to send
blood to the brain even
when standing & to the
tip of en elevated
fingertip.
• HIGH RESISTANCE
- because of increased
smooth muscle in the
arterioles & the
metarterioles.
• LOW COMPLIANCE
- because of resistance
offered by the arterioles
and the metarterioles.
Advantages of Pulmonary Circulation
being a Low Resistance system:
1. Accommodates more blood as a person shifts
from the standing to the lying position.
2. High compliance allows the vessel to dilate in
response to modest increase in Pulmonary
arterial pressure.
3. Pulse pressure in the pulmonary circulation is
rather low.
PRESSURES IN THE PULMONARY SYSTEM
• Right Ventricle:
Systolic= 25 mmHg
Diastolic= 0-1 mmHg,
• Pulmonary artery:
Systolic= 25 mmHg
Diastolic= 8 mmHg
Mean Pulmonary arterial pressure= 15 mmHg.
• Pulmonary Vein:
Averages about 5 mmHg
• Pulmonary capillaries:
7 mm Hg
• Left atrium:
Averages 2 mmHg
BLOOD SUPPLY OF THE LUNGS:
LUNG RECEIVES 2 BLOOD SUPPLIES
From the Left
Ventricle
From the Right
ventricle
BRONCHIAL
ARTERIES
PULMONARY
ARTERIES
Carry oxygenated blood
Carry deoxygenated mixed venous blood
Blood supplied to the
conducting airways,
lung interstitium &
tissue.
Blood circulates the
alveoli to get
oxygenated.
Right
Ventricle
Pulmonary
artery
Capillaries
- this is
the point
where the
gaseous
exchange
takes
place
between
the alveoli
and the
blood
Pulmonary
Veins
Left
Atrium
Important Points
• The Pulmonary artery emerges from the Right Ventricle, follows the
bronchial tree, bifurcates with it and enters the lung. When it reaches the
alveoli, it forms a dense network of capillaries like a flowing sheet
surrounding the alveoli so that efficient oxygenation of the blood can
take place.
• The veins that arise carry the oxygenated blood and form the Pulmonary
Veins that take the blood to the Left Atrium.
• The Bronchial artery emerges from the aorta and supplies the lung
parenchyma and tissue. Deoxygenated blood is carried away by the
veins. A small amount of bronchial blood drains into the azygous and
hemiazygous veins.
• At the level of the respiratory bronchioles, capillaries derived from the
bronchial arteries anastomose with those derived from the pulmonary
arteries.
• Because veins of bronchial circulation drain into pulmonary veins, there
is some venous admixture of the oxygenated blood in pulmonary veins
and deoxygenated blood of the bronchial veins.
POINTS TO NOTE:
• The average RBC spends 0.75 sec in the Pulmonary
capillaries as it passes through at least 3 alveoli (can
decrease to 0.3 sec during exercise).
• 2 Lungs: 300 million alveoli
2 Lungs: 280 billion highly anastomosing capillaries
• Effect of diminished alveolar oxygen on local alveolar
blood flow:
Unlike the rest of the circulatory system where the decrease
in oxygen or metabolites leads to vasodilation of the vessels,
in the pulmonary circulation, a decrease in oxygen uptake by
the blood in the pulmonary vessels leads to pulmonary
vessel vasoconstriction with an increase in the resistance.
This effect of low oxygen on pulmonary vascular resistance
has an important function: to distribute blood flow where it
is most effective.
ZONES OF THE LUNGS
ZONES OF THE LUNGS
The alveoli are NOT created equal when it comes to PERFUSION(Q)
and VENTILATION(V).
The Perfusion (Q) varies because of 2 reasons:
• Posture
• Gravity
We can divide the upright Lung into 3 zones (some books say 4) based
on the relationship between the following pressures:
1. Pa= Alveolar Air Pressure
2. PPA= Pressure in Pulmonary arterioles
3. PPV= Pressure in Pulmonary Veins
Thus, standing on your head will reverse the flow-height relationship.
POINT TO NOTE:
Hydrostatic pressures in the Pulmonary vessels all continue to increase
by 1 cm H20 for each 1 cm decrease in height from the level of the left
atrium & continues to decrease by 1 cm for every 1 cm increase in
height above the left atrium.
The Zones of the Lung and the
Difference in Regional Blood Flow
ZONE 1:
No blood flow during
all portions of the
cardiac cycle
• Pulmonary
capillary pressure
never rises higher
than the alveolar
air pressure , so the
capillaries are
crushed and the
blood flow is
greatly reduced!
ZONE 2:
ZONE 3:
Intermittent blood flow
Continuous blood flow
• Intermittent blood
flow during the
systolic phase of the
cardiac cycle as then
only do the PPA and
PPV rise higher than
the Pa, so arterial end
dilated and open
during the systole.
• PPA & PPV are much
higher than Pa, so the
vessels dilated
throughout the
cardiac cycle and
blood flow at its
maximum.
ZONES OF THE LUNGS
Pathophysiology of the ZONES of the
Lungs
• Effect of Exercise:
The blood flow in all parts of the lungs may increase during
exercise. In the top of the lungs, the increase may be 700-800%
while in the lower parts may be 200-300%. This is because during
exercise pulmonary vascular pressures rise enough during the
exercise to convert the lung apices from zone 2 to zone 3 pattern
of flow.
• Zone 1 Blood flow occurs only during Abnormal conditions.
Usually this is not seen unless there are 2 condition:
- if an upright person is breathing against a positive air
pressure and the intra-alveolar air pressure is higher than normal.
- in an upright person, pulmonary circulatory pressure is
very low as seen after severe blood loss.
PULMONARY CAPILLARY DYNAMICS
PULMONARY CAPILLARY PRESSURES:
Forces tending to cause movement of fluid outward from the pulmonary capillaries and into
the pulmonary interstitium:
Capillary pressure
7
Interstitial fluid colloid osmotic pressure
14
Negative interstitial fluid pressure
8
29
TOTAL OUTWARD FORCE
Forces tending to cause absorption of fluid into the pulmonary capillaries:
Plasma colloid osmotic pressure
28
TOTAL INWARD FORCE
28
Total Outward Force
+ 29 mmHg
Total Inward Force
‒ 28 mmHg
MEAN ARTERIAL PRESSURE: +1 mmHg
The normal outward forces are slightly greater than the inward
forces, providing a mean filtration pressure at the pulmonary
capillary membrane.
This filtration pressure causes a slight continual flow of fluid from
the pulmonary capillaries into the interstitial spaces, and except
for a small amount that evaporates in the alveoli, this fluid is
pumped back to the circulation through the pulmonary lymphatic
system.
This keeps the alveoli “DRY”.
PULMONARY EDEMA
PULMONARY EDEMA
Definition:
It is a condition in which fluid accumulates in the lungs.
OR
It is the effusion of fluid into the alveoli and the
interstitial spaces of the lungs.
Underlying Cause:
Any factor that causes the Pulmonary Interstitial fluid
pressure to rise from the negative range into the positive
range will cause rapid filling of the pulmonary interstitial
spaces & alveoli with large amounts of free fluid.
• CAUSES OF PULMONARY EDEMA:
1. Left-sided heart failure or mitral valve disease (Most
common).
2. Damage to the pulmonary capillary membrane caused by
infections. e.g. pneumonia, inhalation of poisonous gases
as chlorine or sulfur dioxide. This causes the leakage of
the plasma proteins & fluids into the pulmonary
interstitial spaces & alveoli that raises the Pulmonary
Interstitial pressure.
Safety Factor in Pulmonary edema:
The plasma capillary pressure must rise from the normal value
of 7 mmHg to above 28 mmHg (plasma colloid osmotic
pressure) for edema to occur. So there is a safety factor of 21
mmHg.
Signs & Symptoms of Pulmonary edema:
• Difficulty breathing
• Coughing up blood (pink, frothy sputum)
• Anxiety
• Excessive sweating and pallor
• Inability to lie down due to breathlessness
• Signs of left ventricular failure like peripheral
edema & raised JVP.
• Respiratory failure
• Death
Treatment:
• Symptomatic treatment
• High-flow oxygen therapy.
• Diuretics to improve preload and afterload &
aid in improving the cardiac function.
PLEURAL CAVITY & FLUID IN THE
PLEURAL CAVITY
PLEURAL CAVITY
The pleural cavity is the
potential space between the
two pleura (visceral and
parietal) of the lungs. The
pleura is a serous membrane
which folds back onto itself to
form a two-layered, membrane
structure (like a balloon). It
normally contains a thin layer of
mucoid fluid. The outer pleura
(parietal pleura) is attached to
the chest wall. The inner pleura
(visceral pleura) covers the
lungs and adjoining structures,
as blood vessels, veins, bronchi.
The amount of fluid normally
present is only a few millilitres.
Thus, it is called a potential
space as it is too narrow to be
an obvious physical space.
Importance of Pleural Cavity
• The normal collapse tendency of the lungs is ‒
4 mmHg. Thus, the pleural fluid pressure must
always be at least as negative as the pressure
in the pleural cavity (‒ 4 mmHg) to keep the
lungs expanded.
• Actual measurement has shown it to be ‒ 7
mmHg. Thus, the negativity of the pleural fluid
keeps the normal lungs pulled against the
parietal pleura of the chest cavity.
PLEURAL EFFUSION
Definition:
Pleural effusion is accumulation of
large amounts of free fluid in the
pleural space. It is the same as
edema fluid in the tissues & can
be called “edema of the fluid”.
Causes:
1. Blockage of lymphatic
drainage from the pleural
cavity.
2. Cardiac failure
3. Greatly reduced plasma
colloid osmotic pressure.
4. Infection/ inflammation of
the pleural surfaces causing
leakage into the pleural
cavity.
Signs & Symptoms of Pleural Effusion:
1. Shortness of breath (as the fluid in the pleural cavity increases,
harder it becomes for the lungs to expand and more difficult for the
patient to breathe).
2. Chest pain occurs as the pleural lining is irritated. It is a sharp pain
that increases with a deep breath.
3. Sweating
4. Signs and symptoms of cardiac failure.
5. Weight loss.
Treatment:
• Symptomatic
• ABC (airways, breathing, circulation)
• Thoracocentesis
• Chest tube to remove excess pleural fluid