Pulmonary Perfusion

Dr.Niranjan murthy H.L Asst. Professor Dept. of Physiology

• Oxygen inhaled into alveoli should be brought to peripheral cells of the body by means of blood in pulmonary circulation draining into left atrium • Carbon dioxide produced in the peripheral cells is to be expelled into alveoli by pulmonary circulation

Physiologic anatomy • Pulmonary vessels Pulmonary artery

Pulmonary capillaries

Pulmonary vein

Left atrium

2. Bronchial vessels• Arise from systemic circulation • 1 to 2% of total cardiac output • Supply supporting tissues of the lung (bronchi & pleura) • Drain into pulmonary veins and thus into left atrium • Left ventricular output is 1 to 2% higher

Lymphatics• Drain through hilum into right lymphatic duct • Removes particulate matter from alveoli and plasma proteins leaked into pulmonary interstitium

Pressures in pulmonary system Right ventricle• Systolic pressure of 25mm of Hg and diastolic pressure of 0 to 1mm of Hg Pulmonary artery• Systolic pressure of 25mm of Hg, diaspolic pressure of 8mm of Hg and mean pressure of 15 mm of Hg Pulmonary capillary• Mean pressure of 7mm of Hg

Left atrium and pulmonary veins• Mean pressure of 1 to 5mm of Hg Pulmonary capillary wedge pressure (PCWP)• Catheter from right side of heart into pulmonary arteries till it wedges tightly in small branch • 5mm of Hg • Left atrial pressure is 2 to 3 mm of Hg lower than PCWP • Used to study changes in left atrial pressure in CHF patients

Systemic Vs pulmonary circulatory pressures

PCWP

Blood volume of lungs • 1000ml • 100ml is present in pulmonary capillaries • Lungs act as reservoir of blood

Blood flow and distribution • Pulmonary blood flow is equal to cardiac output • Flow is directed to well ventilated parts of the lung • Pulmonary vessels act as passive, distensible conduits of blood

Effect of PAO2 • If PAO2 falls to <70% of normal, adjacent blood vessels constrict • Blood flow is redirected to better aerated parts of the lung

Effect of gravity • Highest point of lung has 15mm of Hg pressure lower than the pressure at the heart • Lowest point of lung has 8mm of Hg pressure greater than that at heart level

• Zones of pulmonary circulation• Zone 1: no blood flow throughout cardiac cycle • Zone 2: intermittent blood flow- only during systole • Zone 3: continuous blood flow • Zone 1 flow occurs only in abnormal conditions • Exercise converts whole lung into zone 3

Pulmonary capillary dynamics • Forces pushing fluid outwards (i) capillary hydrostatic pressure- 7mm Hg (ii) interstitial colloid osmotic pressure14mm Hg (iii) interstitial hydrostatic pressure- -8mm Hg • Forces causing absorption (i) plasma colloid osmotic pressure- 28mm Hg Mean filtration pressure: 29-28 = +1mm Hg

Pulmonary edema • Negative interstitial pressure keeps alveoli dry • Common causes of pulmonary edema(i) LVF/mitral valvular disease (ii) toxic gases like chlorine/sulfur dioxide or infections like pneumonia • Safety factor • Rapidity of death: 20-30min if capillary pressure rises 25-30mm Hg above safety factor

Pleural fluid • • • • •

Pleural membrane is porous Interstitial fluid carries tissue proteins Pleural fluid is mucoid Excess fluid is pumped away by lymphatics Causes of pleural effusion(i) blockage of lymphatic drainage (ii) cardiac failure (iii) reduced plasma proteins (iv) infection/neoplasm surfaces of pleural cavity

Functions of pulmonary circulatory system • To reoxygenate blood and to remove CO2