Chapter 38: Pulmonary Circulation, Pulmonary
Edema, Pleural Fluid
Guyton and Hall, Textbook of Medical Physiology, 12 edition
Pulmonary Circulation
• Two Circulatory Systems of the Lung
a. High pressure low flow circulation that supplies
systemic arterial blood supplied mostly by the
bronchial arteries
b. Low pressure high flow circulation that supplies
venous blood to the aveolar capillaries where
oxygen is added and carbon dioxide is removed.
Physiologic Anatomy of the Pulmonary Circulation
• Pulmonary Vessels- pulmonary artery and its branches
are thin and distensible and exhibit large
compliance; this allows the pulmonary arteries
to accommodate the stroke volume output of
the right ventricle
• Bronchial Vessels- bronchial arterial blood is
oxygenated and supplies the supporting tissues
of the lungs; empties into the pulmonary veins
and enters into the left atrium
Physiologic Anatomy of the Pulmonary Circulation
• Lymphatic Vessels- present in the supporting tissues
of the lungs and enter the right thoracic duct.
Particulate matter entering the alveoli is removed
by way of the lymphatics and plasma protein is also
removed, helping to prevent pulmonary edema
Pressures in the Pulmonary System
• Pressure Pulse Curve in the Right Ventricle
Fig. 38.1 Pressure pulse contours in the right ventricle, pulmonary artery, and aorta
Pressures (cont.)
• Pressure s in the Pulmonary Artery
• Pulmonary Capillary Pressure
• Left Atrial and Pulmonary Venous Pressures
Fig. 38.2 Pressures in the different vessels of the lungs
Blood Volume of the Lungs
• Blood volume of the lungs is about 450 ml (about
9% of the total blood volume
• Lungs serve as a blood reservoir
• Cardiac pathology may shift blood from the systemic
circulation to the pulmonary circulation
a. Failure of the left side of the heart
b. Mitral stenosis or regurgitation
Blood Flow Through the Lungs
• Decreased alveolar oxygen reduces local alveolar
blood flow and regulates pulmonary blood
flow distribution
a. When the concentration of oxygen in the air of the
alveoli decreases below normal, adjacent blood
vessels constrict and increases resistance 5-fold
b. This effect distributes blood flow to areas where
it is most effective
Effects of Hydrostatic Pressure on Pulmonary Blood Flow
• Zones 1, 2, and 3 of Pulmonary Blood Flow
a. Zone 1: No blood flow during all portions of the
cardiac cycle
b. Zone 2: Intermittent blood flow only during the
peaks of pulmonary arterial pressure
c. Zone 3: Continuous blood flow because the
alveolar capillary pressure is greater than the
alveolar air pressure during the entire cardiac
cycle
Effects of Hydrostatic Pressure (cont.)
Fig. 38.4 Mechanics of blood flow in the three blood flow zones of the lung
Effects of Hydrostatic Pressure (cont.)
• Zone 1 Blood Flow Occurs Only Under Abnormal
Conditions- means no blood flow during any
part of the cardiac cycle; occurs when either
the pulmonary systolic pulmonary pressure is
too low or the alveolar pressure is too high to
allow flow
• Effect of Exercise on Blood Flow Through
Different Parts of the Lung- increases
in all parts
Effects of Hydrostatic Pressure (cont.)
• During Heavy Exercise
a. Increased CO is normally accommodated by the
pulmonary circulation without large increases in
pulmonary artery pressure
b. Extra flow is accommodated by
1. increasing the number of open capillaries
2. distending all capillaries and increasing
flow rate
3. increasing pulmonary arterial pressure
Fig. 38.5 Effect on mean pulmonary arterial pressure caused by increasing CO during exercise
Pulmonary Capillary Dynamics
• Pulmonary Capillary Pressure- about 7 mm Hg
(not measured directly)
• Length of Time Blood Stays in the Pulmonary
Capillaries- when cardiac output is normal,
it is about 0.8 sec
Pulmonary Capillary Dynamics
• Capillary Exchange of Fluid in the Lungs and
Pulmonary Interstitial Fluid Dynamics
a. Pulmonary capillary pressure is 7 mm compared
to 17 mm in the peripheral tissues
b. Interstitial fluid pressure in the lungs is slightly
more negative than in the peripheral s.c. tissue
c. Pulmonary capillaries are relatively leaky to protein
molecules, so colloid osmotic pressure is 14 mm
compared to 7 mm in the peripheral tissues
d. Alveolar walls are thin and weak; allows dumping
of fluid from the interstitial spaces into the alveoli
Pulmonary Capillary Dynamics
• Interrelations Between Interstitial Fluid Pressure
and Other Pressures in the Lung
Fig. 38.6
Pulmonary Capillary Dynamics (cont.)
Mm Hg
Forces tending to cause movement of fluid outward from the
capillaries and into the pulmonary interstitium
Capillary pressure
7
Interstitial fluid colloid osmotic pressure
14
Negative interstitial fluid pressure
8
TOTAL OUTWARD FORCE
29
Forces tending to cause absorption of fluid into the capillaries
Plasma colloid osmotic pressure
TOTAL INWARD FORCE
MEAN FILTRATION PRESSURE
28
28
29-28 = +1
Pulmonary Capillary Dynamics (cont.)
• Negative Pulmonary Interstitial Pressure and
the Mechanism for Keeping the Alveoli “Dry”
a. Slightly negative pressure in the interstitial
spaces simply sucks the fluid into the
interstitium
Fluid in the Pleural Cavity
Fig. 38.8 Dynamics of fluid exchange in the intrapleural space
Fluid in the Pleural Cavity
• Excess Fluid is Pumped Away by Lymphatic Vessels
Opening Directly from the Pleural Cavity into
a. The mediastinum
b. The superior surface of the diaphragm
c. The lateral surfaces of the parietal pleura
•
Negative Pressure in Pleural Fluid- negative
pressure is always required on the outside of the
lungs to keep the lungs expanded
Fluid in the Pleural Cavity
• Pleural Effusion- collection of large amounts of
free fluid in the pleural space; caused by
a.
b.
c.
d.
Blockage of lymphatic drainage from the pleural cavity
Cardiac failure
Greatly reduced plasma colloid osmotic pressure
Infection or any cause of inflammation on the surfaces
of the pleural cavity