Pulmonary Blood Flow Flashcards
What blood goes through pulmonary circulation? IN this process what must happen?
All of venous return (cardiac output) goes through the pulmonary circulation. In the process of doing so surface area for gas exchange must be maximized, and on a regional basis pulmonary blood flow should match ventilation.
Compare the pulmonary and systemic blood flow vascular pressures?
If mean pulmonary arterial pressure and left atrial pressures are 15 and 5 mm Hg, respectively, and total pulmonary blood flow is 6 liters/min, what is pulmonary vascular resistance? What are the units?
compare resistance, pressure and compliance between pulmonary and systemic circulation?
What are the two circulations in the lungs?
The lung has two circulations (the heart also has two circulations), the pulmonary circulation that perfuses alveoli, and the bronchial circulation that provides nutrients and gas exchange for the conducting airways.
Explain the bronchial circulation? Where do the arteries arise from? Where does the bronchial circulation drain?
The bronchial circulation is part of the systemic circulation and receives about 2% of the cardiac output from the left heart. Bronchial arteries arise from branches of the aorta, intercostal, subclavian, or internal mammary arteries. The bronchial arteries supply the tracheobronchial tree with both nutrients and O2. Vascular pressures in the bronchial circulation are similar to those in other systemic vascular beds. About a third of the venous drainage from the bronchial circulation is via the azygos, hemiazygos, and intercostal veins, which returns bronchial venous blood to the right atrium. However, about two-thirds of bronchial capillary blood is thought to drain into anastomoses or communicating vessels that empty into the pulmonary veins. This vascular connection between the bronchial and pulmonary circulation is called the bronchopulmonary circulation. This communicating circulation adds a small volume of poorly oxygenated bronchial venous blood to the freshly oxygenated blood in the pulmonary vein.
Function of the pulmonary circulation?
While the lung is superbly designed for gas exchange, it is also ideally suited to functions unrelated to gas exchange owing to the large blood volume that passes through the lung each minute and the immense capillary surface area available for metabolism. Functions of the lung not directly related to gas exchange are referred to as non-respiratory functions. Some non-respiratory functions of the lung vasculature include its role as a blood filter, blood reservoir, and a metabolizer of circulating substances
Pulmonary artery branches to? Gas exchange happens where? how?
The pulmonary artery branches rapidly to give rise to nearly 300 billion pulmonary capillaries. Gas exchange between the alveolar gases and blood occurs within the lung capillaries. Gas exchange between alveoli and pulmonary capillary blood is by simple diffusion. O2 diffuses from the alveolus to the pulmonary capillary blood, while CO2 diffuses in the reverse direction, as determined by their respective concentration gradients.
Explain how the pulmonary circulation serves as a filter?
Because pulmonary microvessels are so numerous, some can effectively serve as filters to trap foreign materials present in the blood. If such materials are not trapped by pulmonary vessels, they might occlude or impede flow in systemic vessels with a lower tolerance to blood flow interruption. For example, if fibrin blood clots, gas bubbles, fat cells or other emboli were to enter the arterial side of the systemic circulation, they could occlude vascular beds with little blood flow reserve. For example, emboli blocking vessels of the brain or heart, could have disastrous consequences, such as a stroke or heart attack. However, the pulmonary circulation contains more capillaries than are normally required for gas exchange at rest. Because of this large anatomical and functional reserve, some lung microvessels can be used to trap particles without seriously affecting gas exchange. Emboli trapped by pulmonary vessels can later be removed by enzymatic processes, macrophage ingestion, or absorption into the lymphatic system. Thereby, the blood filter function of lung microvessels prevents entry of potentially harmful particles into systemic vessels.
Explain the role of the lungs as a reservoir for blood for the LV?
The vessels of the pulmonary circulation are very compliant (easily distensible) and thus typically accommodate about 500 ml of blood in an adult male. This large lung blood volume can serve as a reservoir for the left ventricle, particularly during periods when left ventricular output momentarily exceeds venous return. Thus, cardiac output can be increased rapidly by drawing upon pulmonary blood volume without depending on an instantaneous increase in venous return. Because of this function, the lung is sometimes referred to as an “accessory” heart.
Explain the metabolic functions of the pulmonary circulation?
Cells comprising the lung vasculature, particularly endothelial cells that line the vessel lumen, are involved in the uptake or metabolic conversion of several vasoactive substances in the circulation. Lung vascular cells also release biologically active compounds into the circulation that act either locally or in other organs. Some of the substances metabolized by the lung from mixed venous blood are listed in the table. The lung may also synthesize and/or release substances such as histamine, prostaglandins, leukotrienes, platelet activating factor, serotonin and nitric oxide in response to certain conditions, such as pulmonary emboli or shock (anaphylaxis).
How does posture affect lung pressures?
The upright human lung measures about 30 centimeters from the apex to the base. The pulmonary artery enters the lung at the level of the hilum, located approximately midway between the apex and base of the lung. In order for the right heart to pump blood to the apex of the lung, it must pump against a column of blood about 15 cm high (11 mmHg) or against a pressure head of about 15 cm H2O resulting from gravity. Thus, mean intravascular pressure at the lung apex (about 4 cm H2O) is 11 cm H2O lower than arterial pressure at the hilum. In contrast, mean intravascular pressures at the base of the lung is about 11 cm H2O higher than pulmonary arterial pressure at the hilum. Hence, due to gravitational forces, both intravascular pressures and blood flow are considerably less at the apex than at the base of the lung. When a person assumes a supine position, the pressure differences between the apex and base are less. This results in a more uniform distribution of blood flow and smaller vascular pressure differences.
Explain the 4 zone model of pulmonary blood flow?
Four zone model of pulmonary circulation in which hydrostatic, arterial and venous pressures fall with increasing distances up the 30 cm height of the lung. (a = arterial, A = alveolar, V = venous).
Because the lung is about 30 cm from apex to base, gravity exerts a measurable role in determining blood flow along the lung’s height. The hydrostatic blood pressure is highest at the lung base and least at the apex. Under some conditions both arterial and venous pressures at the apex may both be less than the alveolar pressure and there will be no blood flow: ordinarily there is very little, if any, ZONE 1 of no blood flow. Further down the lung in ZONE 2 arterial pressure is above alveolar pressure but venous pressure is less than alveolar pressure: thus, instead of blood flow being determined by the usual (a-v) pressure difference, it is determined by the (arterial-alveolar) difference. Since arterial pressure increases down Zone 2 due to gravity, while alveolar pressure remains relatively constant, the (arterial-alveolar) difference increases down Zone 2 and thus blood flow increases from the top to the bottom of this zone. In ZONE 3 both the arterial and venous pressures exceed alveolar pressures and blood flow is determined as usual by the (arterial-venous) difference. Since both arterial and venous pressures are increasing down this zone due to gravity, the compliant pulmonary vessels passively distend, resulting in increased radii and thus reduced resistance: thus, blood flow rises from the top to the bottom of Zone 3.
Some pulmonary investigators speak of a ZONE 4 at the very base of the lung where there are very low ratios of ventilation/blood flow and thus alveolar hypoxia occurs, evoking compensatory vasoconstriction in that area with consequent fall in local blood flow.
Explain the blood flow characteristics in zone 1-3?
What are the bondaries dependent on? Zone one usually? Zone 2 or 3 can be converted to zone 1 by?
What are stimulators of Pulmonary Vascular resistance?
How does alveolar hypoxia affect lung pressure?
When the airway or alveolar PO2 is lower than normal, it can elicit constriction of the arterial vessels leading to them. This is called hypoxic pulmonary vasoconstriction (HPV). The precise factors responsible for HVP are not known with certainty. However, HPV is thought to redirect blood flow away from poorly oxygenated alveoli towards alveoli that have higher PO2 levels. HPV is a mechanism that normally operates to help optimize or improve gas exchange by decreasing blood flow to poorly oxygenated alveoli.
what is the effect on lung volume on pulmonary vascular resistance?
What is the function of pulmonary circulation? What are the active factors that affect (stimulate) PVR? The passive?
