Unit Seven: Respiration 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 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.

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

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

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

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

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 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

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 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

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

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

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 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

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