Pulmonary Circulation Dr. Walid Daoud MBBCh, MSc, MD, FCCP Director of Chest Department, Shifa Hospital, A. Professor of Chest Medicine

Types of circulation 1. Systemic (bronchial): High pressure, low flow circulation 2. Pulmonary: Low pressure, high flow circulation Low pressure, high flow circulation

Pulmonary circulatory system ______________________________________ 1. Pulmonary vessels: - Pulmonary artery is thin with large diameter, distensible and large compliance - Pulmonary artery is thin with large diameter, distensible and large compliance 2. Bronchial vessels: Forms 1-2% of total cardiac output. Forms 1-2% of total cardiac output. 3. Lymphatics.

Pressures in pulmonary circulation ______________________________________ 1. Pressure pulse curve in RV: Systolic P in RV = 25 mmHg Systolic P in RV = 25 mmHg Diastolic P in RV = 0-1 mmHg Diastolic P in RV = 0-1 mmHg 2. Pressures in pulmonary artery: Systolic P = 25 mmHg Systolic P = 25 mmHg Diastolic P = 8 mmHg Diastolic P = 8 mmHg Mean pulmonary arterial P = 15 mmHg Mean pulmonary arterial P = 15 mmHg 3. Pulmonary capillary pressure = 7 mmHg 4. Left atrial P =1-5 mmHg, PCWP = 5 mmHg 4. Left atrial P =1-5 mmHg, PCWP = 5 mmHg

Blood volume of the lungs ______________________________________ 1. Lung serve as a blood reservoir: Blood volume in lung is 450 ml or 90% of Blood volume in lung is 450 ml or 90% of total blood volume and 70 ml of this in total blood volume and 70 ml of this in pulmonary capillaries. Loss of blood causes pulmonary capillaries. Loss of blood causes shift of blood from pulmonary to systemic shift of blood from pulmonary to systemic circulation circulation 2. Left heart failure may shift blood from systemic to pulmonary circulation: systemic to pulmonary circulation:

Blood flow through lungs & its distribution Blood flow through lungs & its distribution ______________________________________ Blood flow is the cardiac output Dilatation of pulmonary vessels increases blood flow and constriction decreases blood flow Decreased alveolar O2 below 70% produces constriction of pulmonary vessels and increase vascular resistance and reduces local blood flow. This leads to shift of blood from poorly ventilated to better areated alveoli This is opposite effects observed in systemic circulation.

Effects of hydrostatic pressure gradients in the lungs on regional pulmonary blood flow Effects of hydrostatic pressure gradients in the lungs on regional pulmonary blood flow ______________________________________ Lung apex is more ventilated and less perfused Lung base is less ventilated and more perfused Zones of pulmonary blood flow: Zone 1: no blood flow during all cardiac cycle Alveolar P > Capillary P Zone 2: Intermittent blood flow at lung apex Zone 2: Intermittent blood flow at lung apex Capillary P > Alveolar P only during systole Capillary P > Alveolar P only during systole Zone 3: continuous blood flow at lung base Capillary P > Alveolar P during all cardiac cycle Capillary P > Alveolar P during all cardiac cycle

Effects of hydrostatic pressure gradients in the lungs on regional pulmonary blood flow Effects of hydrostatic pressure gradients in the lungs on regional pulmonary blood flow ______________________________________ Normally, lungs have only zone 2 and 3 In upright position, pulm P at apex is 15 mmHg less than P at level of heart (25 mmHg) so the apical systolic P is 10 mmHg greater than zero alveolar P. so blood flows through apical pulm cap. During cardiac diastole, diastolic P at level of heart is 8 mmHg is not enough to push blood up the 15 mmHg hydrostatic pressure gradient to cause diastolic blood flow so blood flow at apex is intermittent.

Effects of hydrostatic pressure gradients in the lungs on regional pulmonary blood flow Effects of hydrostatic pressure gradients in the lungs on regional pulmonary blood flow ______________________________________ In the lower region of lung from 10 cm above level of heart, pulm art P during both systole and diastole is greater than zero alveolar P so there is continuous flow through alveolar capillaries (zone 3). In lying position blood flow is zone 3 in whole lung including apex.

Zone 1 blood flow occurs abnormally Zone 1 blood flow occurs abnormally ______________________________________ Zone 1 means no blood flow and occurs when pulm systolic P is too low or alveolar P too high to allow flow, as in the following: 1.Breathing positive pressure in upright position when alveolar pressure at 10 mmHg. 2.Severe blood loss in upright position where pulm systolic P is low. pulm systolic P is low.

Effect of exercise on pulm blood flow Effect of exercise on pulm blood flow ______________________________________ Blood flow increases in all parts of the lung, the increase in flow % at top of the lung Increase in flow % at lung base The increase in pulm art P during exercise converts zone 2 into zone 3 pattern of flow. Severe increase in cardiac output is not associated with large increase in pulmonary artery pressure and increase in pulm flow due to increase no. of open capillaries, dilatation of capilllaries and increase pulm art P.

Effect of left sided heart failure on pulmonary circulation Effect of left sided heart failure on pulmonary circulation ______________________________________ Normally left atrial P 1-5 mmHg When the left heart fails, the left atrial pressure increases (up to mmHg) and this increases the pulmonary artery pressure and capillary pressure and pulmonary edema results.

Pulmonary capillary dynamics Pulmonary capillary dynamics ______________________________________ Pulmonary capillary pressure 7 mmHg Pulmonary capillary pressure 7 mmHg Mean pulmonary capillary pressure 15 mmHg Transit time 0.8 sec and when cardiac output increases as in exercise transit time is decreased to 0.3 sec. So in only a fraction of second blood pass through alveolar capillaries and becomes oxygenated with removal of carbon dioxide.

Capillary exchange of fluid in lungs and pulmonary interstitial fluid dynamics Capillary exchange of fluid in lungs and pulmonary interstitial fluid dynamics ______________________________________

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