PulmonaryBloodFlowPreClass_Eiting2023.V1.pptx

Pulmonary Bloodflow Thomas P Eiting, PhD RESP I—Fall 2023 Image credit: Clouds Hill Imaging/Science Photo Libr Learning Objectives Guyton Ch. 39 Describe the major functions of the bronchial circulation. Contrast the systemic and pulmonary circulations with respect to pressures and resistance...

Pulmonary Bloodflow Thomas P Eiting, PhD RESP I—Fall 2023 Image credit: Clouds Hill Imaging/Science Photo Libr Learning Objectives Guyton Ch. 39 Describe the major functions of the bronchial circulation. Contrast the systemic and pulmonary circulations with respect to pressures and resistance to blood flow in response to hypoxia. Describe the regional differences in pulmonary blood flow in an upright person. Define zones one, two, and three in the lung, with respect to pulmonary vascular pressure and alveolar pressure. Describe how pulmonary vascular resistance changes with alterations in cardiac output or pulmonary arterial pressure. Explain in terms of distention and recruitment of pulmonary vessels. Identify the zones in which these two mechanisms apply. Describe how pulmonary vascular resistance changes with lung volume. Explain in terms of alterations in alveolar and extra alveolar blood vessels. Describe the consequence of hypoxic pulmonary vasoconstriction on the distribution of pulmonary blood flow. Describe the effects of inspired nitric oxide on pulmonary vascular resistance and hypoxic vasoconstriction. All images from Guyton text Explain the development of pulmonary edema A) increased hydrostatic pressure, B) unlessbynoted The Bronchial Circulation 1-2% of cardiac output flows to the lungs as oxygenated blood from the systemic circulation Once this blood has supplied tissues of the lungs, it returns back by way of pulmonary veins, thus entering the left atrium Berne and Levy, Fig. 20.7 The Pulmonary System is a HighCompliance System Pulmonary artery wall thickness is 1/3 that of the aorta Diameters are larger than counterpart systemic arteries Pulmonary arterial tree has a large compliance, about 7 ml/mm Hg Radiopaedia.or g • The Pulmonary System is a Low-Pressure System the cardiac cycle… Remember • Mean pulmonary capillary pressure is about 7 mm Hg Pressures Around the Pulmonary Vessels West, Fig. 4.2 West, Fig. 4.3 • Pulmonary capillaries are virtually surrounded by gas, and consequently are subject to alveolar pressures to a great degree • Larger vessels (e.g., pulmonary arteries and veins) are pulled open by radial traction of the surrounding lung parenchyma Lung Volumes and Pulmonary Vascular Resistance Alveolar vs Extra-alveolar vessels have opposing effects on PVR At end-inspiration, air-filled alveoli compress capillaries, whereas larger vessels are pulled open further by elastic recoil At end-exhalation, alveoli apply little to no pressure to the pulmonary capillaries, while the increase in pleural pressure compresses the extra-alveolar vasculature Effects of Resistance and Compliance Berne and Levy, Fig. Regulation of Blood Flow during Local Tissue Hypoxia Under normal conditions, blood flow is equal across alveoli When alveolar O2 decreases to ~70% of normal, adjacent vessels constrict (which is opposite to the effects in systemic vessels), increasing resistance by 5x in adjacent vessels • Why? • How? 23 mm Hg pressure difference Zones of Pulmonary Blood Flow Berne and Levy, Fig. 23.6 Pa, PA, Pv Blood Flow Gradients Cardiac output can increase 4-7 times, for example during exercise Relative distribution of blood flow during these periods is the same during resting, but magnitude everywhere is higher Accommodation to Increased Cardiac Output 1. Increase number of open capillaries (“Recruitment”) 2. Distend capillaries to increase rate of flow 3. Increase pulmonary arterial pressure (normally “last resort”) Inward and Outward Fluid Pressures Outward (from capillaries into interstitium): • Capillary pressure, 7 mm Hg • Interstitial fluid colloid osmotic pressure, 14 mm Hg • Negative interstitial fluid pressure, 8 mmofHg Inward (absorption fluid into capillaries): • Plasma colloid osmotic pressure, 28 mm Hg Thus, there is a slight negative pressure in the interstitium, which pulls excess flu Development of Pulmonary Edema the negative pressures tend to keep the alveoli dry under normal conditions As left atrial pressure rises, pulmonary capillary pressures rise by about 1-2 mm Hg more When pulmonary capillary pressure meets or exceeds plasma colloid osmotic pressure, fluid begins to accumulate in lungs