1. Unit Seven: Respiration
Chapter 38: Pulmonary Circulation, Pulmonary Edema, Pleural Fluid
Guyton and Hall, Textbook of Medical Physiology, 12 edition

2. Pulmonary Circulation
Two Circulatory Systems of the Lung
High pressure low flow circulation that supplies
systemic arterial blood supplied mostly by the
bronchial arteries
Low pressure high flow circulation that supplies
venous blood to the aveolar capillaries where
oxygen is added and carbon dioxide is removed.

3. 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

4. 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

5. Pressures in the Pulmonary System
Pressure Pulse Curve in the Right Ventricle
Fig Pressure pulse contours in the right ventricle, pulmonary artery, and aorta

6. Pressure s in the Pulmonary Artery Pulmonary Capillary Pressure
Pressures (cont.)
Pressure s in the Pulmonary Artery
Pulmonary Capillary Pressure
Left Atrial and Pulmonary Venous Pressures
Fig Pressures in the different vessels of the lungs

7. 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
Failure of the left side of the heart
Mitral stenosis or regurgitation

8. Blood Flow Through the Lungs
Decreased alveolar oxygen reduces local alveolar
blood flow and regulates pulmonary blood
flow distribution
When the concentration of oxygen in the air of the
alveoli decreases below normal, adjacent blood
vessels constrict and increases resistance 5-fold
This effect distributes blood flow to areas where
it is most effective

9. Effects of Hydrostatic Pressure on Pulmonary Blood Flow
Zones 1, 2, and 3 of Pulmonary Blood Flow
Zone 1: No blood flow during all portions of the
cardiac cycle
Zone 2: Intermittent blood flow only during the
peaks of pulmonary arterial pressure
Zone 3: Continuous blood flow because the
alveolar capillary pressure is greater than the
alveolar air pressure during the entire cardiac
cycle

10. Effects of Hydrostatic Pressure (cont.)
Fig Mechanics of blood flow in the three blood flow zones of the lung

11. 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

12. Effects of Hydrostatic Pressure (cont.)
During Heavy Exercise
Increased CO is normally accommodated by the
pulmonary circulation without large increases in
pulmonary artery pressure
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

13. Fig. 38.5 Effect on mean pulmonary arterial pressure caused by increasing CO during exercise

14. 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

15. Pulmonary Capillary Dynamics
Capillary Exchange of Fluid in the Lungs and
Pulmonary Interstitial Fluid Dynamics
Pulmonary capillary pressure is 7 mm compared
to 17 mm in the peripheral tissues
Interstitial fluid pressure in the lungs is slightly
more negative than in the peripheral s.c. tissue
Pulmonary capillaries are relatively leaky to protein
molecules, so colloid osmotic pressure is 14 mm
compared to 7 mm in the peripheral tissues
Alveolar walls are thin and weak; allows dumping
of fluid from the interstitial spaces into the alveoli

16. Pulmonary Capillary Dynamics
Interrelations Between Interstitial Fluid Pressure
and Other Pressures in the Lung
Fig. 38.6

17. 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 28
TOTAL INWARD FORCE
MEAN FILTRATION PRESSURE
29-28 = +1

18. Pulmonary Capillary Dynamics (cont.)
Negative Pulmonary Interstitial Pressure and
the Mechanism for Keeping the Alveoli “Dry”
Slightly negative pressure in the interstitial spaces simply sucks the fluid into the interstitium

19. Fluid in the Pleural Cavity
Fig Dynamics of fluid exchange in the intrapleural space

20. Fluid in the Pleural Cavity
Excess Fluid is Pumped Away by Lymphatic Vessels
Opening Directly from the Pleural Cavity into
The mediastinum
The superior surface of the diaphragm
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

21. Fluid in the Pleural Cavity
Pleural Effusion- collection of large amounts of
free fluid in the pleural space; caused by
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