Pulmonary Blood Flow

Comprehensive vocabulary flashcards covering the anatomy, hemodynamics, regulatory mechanisms, and fluid dynamics of pulmonary blood flow.

Bronchial Arteries

Systemic vessels originating from the aorta that supply oxygenated blood to the supporting tissues of the tracheobronchial tree.

Bronchial Venous Shunt

A normal anatomical shunt where deoxygenated bronchial systemic venous blood empties directly into the pulmonary veins, typically accounting for less than $2\%$ of total cardiac output.

Pulmonary Circulation

The low-pressure vascular circuit that begins at the pulmonic valve and pulmonary artery, flows through the alveolar capillaries for reoxygenation, and terminates where the four pulmonary veins connect to the left atrial wall.

Pulmonary Artery Pressure (PAP)

The systolic and diastolic pressure within the pulmonary arterial system, normally measuring $25\,\text{mmHg} / 8\,\text{mmHg}$.

Mean Pulmonary Artery Pressure (MPAP)

The average pressure sustained across the pulmonary artery throughout the cardiac cycle, normally between $10\,\text{mmHg}$ and $15\,\text{mmHg}$.

Swan-Ganz Catheter

A multi-lumen pulmonary artery catheter equipped with an inflatable balloon, thermistor, and injection ports used to invasively assess intracardiac and pulmonary vascular pressures.

Pulmonary Vascular Resistance (PVR)

The resistance against which the right ventricle must pump to move blood through the pulmonary vasculature; any factor that elevates this resistance increases right ventricular workload.

Right Ventricular Hypertrophy

Abnormal thickening and enlargement of the right ventricular muscular wall caused by chronically elevated afterload from increased pulmonary vascular resistance.

Alveolar Vessels

Pulmonary blood vessels directly adjacent to the alveoli and exposed to alveolar pressure, which become compressed as lung volume increases, thereby increasing pulmonary vascular resistance.

Extra-Alveolar Vessels

Pulmonary blood vessels located outside alveolar walls and exposed to intrapleural pressure, which dilate during lung inflation due to elastic tissue tethering and sub-atmospheric pressure, thereby decreasing pulmonary vascular resistance.

Capillary Recruitment

The opening of unperfused or collapsed pulmonary capillaries in response to elevated pulmonary artery pressure or blood volume, which expands total cross-sectional surface area and lowers pulmonary vascular resistance.

Nitric Oxide (NO)

A potent endogenous vasodilator synthesized by vascular endothelium that serves as the primary regulator of basal pulmonary vascular tone.

Hypoxic Pulmonary Vasoconstriction (HPV)

A local physiologic response to low alveolar oxygen tension ($PAO_2 < 60\text{--}70\,\text{mmHg}$) that constricts regional pulmonary arterioles to divert blood flow toward better-ventilated lung units.

Acidemia (in PVR regulation)

A systemic condition characterized by low blood $\text{pH}$ ($< 7.30$ when $PaO_2 < 50\,\text{mmHg}$, or $< 7.25$ at normal $PaO_2$) that augments hypoxic pulmonary vasoconstriction and elevates pulmonary vascular resistance.

Zone I Blood Flow

A condition in the lung where alveolar pressure exceeds both arterial and venous pressures ($P_A > P_a > P_v$), collapsing alveolar capillaries and creating ventilation without perfusion (alveolar dead space).

Zone II Blood Flow

A condition in the lung where arterial pressure exceeds alveolar pressure, but alveolar pressure exceeds venous pressure ($P_a > P_A > P_v$), resulting in intermittent capillary flow governed by arterial-alveolar pressure differences.

Zone III Blood Flow

A condition typically found at lung bases where gravity ensures arterial and venous pressures both exceed alveolar pressure ($P_a > P_v > P_A$), allowing continuous blood flow driven by the arteriovenous pressure gradient.

Pulmonary Shunt

Perfusion without ventilation, occurring when deoxygenated mixed venous blood travels through pulmonary capillaries of unventilated alveoli without picking up oxygen.

Alveolar Dead Space

Ventilation without perfusion, describing inspired gas that enters alveoli lacking pulmonary capillary blood flow.

Ventilation-Perfusion ($\dot{V}/\dot{Q}$) Ratio

The relationship between alveolar ventilation and pulmonary capillary blood flow, having a normal resting lung average of approximately $0.8$ (alveolar ventilation equals $80\%$ of blood flow).

Oncotic Pressure

The osmotic pressure produced by large plasma proteins within blood vessels that acts as an inward pulling force, drawing water into the capillary lumen.

Hydrostatic Pressure

The physical fluid pressure exerted against capillary walls that pushes fluid outward from the vascular lumen into the interstitial space.

Bronchial Arteries

Systemic arteries that supply oxygenated blood to the supporting tissues of the tracheobronchial tree.

Bronchial Venous Shunt

An anatomical shunt occurring when deoxygenated bronchial systemic venous blood empties directly into the pulmonary veins, typically comprising less than $2\%$ of total cardiac output.

Pulmonary Circulation

The low-pressure, low-resistance vascular circuit that begins at the pulmonic valve / pulmonary artery and terminates where the four pulmonary veins attach to the left atrial wall.

Pulmonary Artery Pressure ($\text{PAP}$)

The pulsatile pressure within the pulmonary arterial system, normally measuring $25\text{ mmHg} / 8\text{ mmHg}$ with a mean pulmonary artery pressure ($\text{MPAP}$) of $10\text{--}15\text{ mmHg}$.

Swan-Ganz Catheter

A balloon-tipped pulmonary artery catheter placed invasively to monitor and measure hemodynamic pressures within the pulmonary circulation.

Pulmonary Vascular Resistance ($\text{PVR}$)

The total resistance offered by the pulmonary vasculature against blood flow from the right ventricle; any elevation increases right ventricular workload.

Alveolar Vessels

Pulmonary capillaries that lie in direct contact with alveoli and are exposed to alveolar pressure; they become compressed as lung volume increases, which elevates $\text{PVR}$.

Extra-Alveolar Vessels

Pulmonary vessels outside the alveoli exposed to intrapleural pressure; they are pulled open and distended by the tethering action of the lung's elastic fibers during inspiration, decreasing $\text{PVR}$.

Capillary Recruitment

The opening of normally closed or collapsed pulmonary capillaries in response to elevated pulmonary arterial pressure or volume, expanding total cross-sectional surface area and reducing $\text{PVR}$.

Nitric Oxide ($\text{NO}$)

A potent endogenous vasodilator and the primary chemical mediator regulating pulmonary vascular tone, produced in response to substances such as acetylcholine, histamine, bradykinin, thrombin, and serotonin.

Alveolar Hypoxia

A reduction in alveolar oxygen tension ($\text{PAO}_2 < 60\text{--}70\text{ mmHg}$) that serves as the primary chemical stimulant triggering pulmonary vasoconstriction.

Hypoxic Pulmonary Vasoconstriction ($\text{HPV}$)

A homeostatic mechanism that constricts blood vessels in poorly ventilated, hypoxic lung units to divert blood toward well-ventilated regions, optimizing ventilation-perfusion matching.

Acidemia (in Pulmonary Vasculature)

A state of low blood $\text{pH}$ (such as $\text{pH} < 7.30$ when $\text{PaO}_2 < 50\text{ mmHg}$, or $\text{pH} < 7.25$ under normoxia) that potentiates hypoxic pulmonary vasoconstriction and elevates $\text{PVR}$.

Zone I Blood Flow

A lung region where alveolar pressure exceeds arterial and venous pressures ($P_{\text{Alv}} > P_{\text{art}} > P_{\text{venous}}$), completely compressing capillaries and halting blood flow to produce alveolar dead space.

Zone II Blood Flow

A lung region where arterial pressure exceeds alveolar pressure, but alveolar pressure exceeds venous pressure ($P_{\text{art}} > P_{\text{Alv}} > P_{\text{venous}}$), generating intermittent capillary flow.

Zone III Blood Flow

A gravity-dependent lung zone (typically the lung bases) where both arterial and venous pressures exceed alveolar pressure ($P_{\text{art}} > P_{\text{venous}} > P_{\text{Alv}}$), maintaining continuous blood flow.

Alveolar Dead Space

Alveoli that receive ventilation but lack capillary perfusion, a state characteristic of Zone I conditions and accentuated at the lung apices.

Pulmonary Shunt

Venous blood that flows past unventilated alveoli without becoming oxygenated (perfusion without ventilation), creating a shunt-like effect predominant at the lung bases.

Ventilation-Perfusion ($\text{V}/\text{Q}$) Ratio

The relationship between alveolar ventilation and pulmonary blood flow, averaging roughly $0.8$ across the normal resting lung (ventilation is about $80\%$ of perfusion).

Oncotic Pressure

The osmotic pressure produced by large plasma proteins that acts like a vacuum, drawing water molecules from regions of lower oncotic pressure into regions of higher oncotic pressure.

Hydrostatic Pressure

The physical fluid pressure within a vascular compartment that forces or pushes fluid outward across the semipermeable capillary endothelial membrane.

Bronchial Arteries

Systemic vessels that supply oxygenated blood to the supporting tissues of the tracheobronchial tree.

Bronchial Anatomical Shunt

The drainage of oxygen-poor bronchial systemic venous blood directly into the pulmonary veins, typically accounting for less than $2\%$ of cardiac output.

Pulmonary Circulation (Origin)

The starting point of the pulmonary circuit where the right ventricle pumps mixed venous blood through the pulmonic valve into the pulmonary artery.

Pulmonary Circulation (Termination)

The end of the pulmonary circuit where the four major pulmonary veins connect to the left atrial wall.

Systemic Circulation (Origin)

The vascular circuit beginning at the aortic valve, where the left ventricle ejects oxygenated blood into the aorta for systemic distribution.

Pulmonary Artery Pressure ($\text{PAP}$)

The blood pressure within the pulmonary arterial tree, normally measuring $25\text{ mmHg} / 8\text{ mmHg}$.

Mean Pulmonary Artery Pressure ($\text{MPAP}$)

The average pressure within the pulmonary artery across the cardiac cycle, normally between $10\text{--}15\text{ mmHg}$.

Swan-Ganz Catheter

A pulmonary artery catheter introduced invasively into the pulmonary circulation to monitor pulmonary vascular pressures and hemodynamics.

Pulmonary Vascular Resistance ($\text{PVR}$)

The opposition to blood flow posed by the pulmonary vessels against which the right ventricle must pump.

Alveolar Vessels

Pulmonary vessels in direct contact with alveoli and subject to alveolar pressure; lung inflation compresses these vessels, thereby increasing $\text{PVR}$.

Extra-Alveolar Vessels

Pulmonary vessels outside alveolar walls exposed to intrapleural pressure; lung elastic fiber tethering and sub-atmospheric pressure dilate them during inspiration, reducing $\text{PVR}$.

Capillary Recruitment

The opening of previously collapsed pulmonary capillaries caused by elevated pulmonary artery pressure or increased blood volume, expanding vascular cross-sectional area and lowering $\text{PVR}$.

Nitric Oxide ($\text{NO}$)

A potent endogenous vasodilator produced by vascular endothelium that serves as the primary regulator of pulmonary vascular tone.

Hypoxic Pulmonary Vasoconstriction ($\text{HPV}$)

A homeostatic response where alveolar hypoxia ($P_A\text{O}_2 < 60\text{--}70\text{ mmHg}$) constricts pulmonary vessels, redirecting blood flow to better-ventilated lung regions.

Acidemia (Effect on $\text{PVR}$)

A low arterial blood pH that potentiates hypoxic pulmonary vasoconstriction; an arterial pH $< 7.30$ at $Pa\text{O}_2 < 50\text{ mmHg}$ (or pH $< 7.25$ at normal $Pa\text{O}_2$) significantly elevates $\text{PVR}$.

Zone I Blood Flow

A condition in the lung where alveolar pressure exceeds arterial and venous pressures ($P_A > P_a > P_v$), completely compressing capillaries and halting perfusion.

Zone II Blood Flow

A region where arterial pressure exceeds alveolar pressure, but alveolar pressure exceeds venous pressure ($P_a > P_A > P_v$), resulting in intermittent capillary blood flow.

Zone III Blood Flow

A gravity-dependent region where both arterial and venous pressures exceed alveolar pressure ($P_a > P_v > P_A$), producing continuous blood flow driven by the arterio-venous pressure gradient.

Pulmonary Shunt

The flow of deoxygenated blood through the capillaries of unventilated alveoli, representing perfusion without ventilation.

Alveolar Dead Space

The ventilation of alveoli that lack capillary blood flow, representing ventilation without perfusion.

Ventilation-Perfusion ($\dot{V}/\dot{Q}$) Ratio

The relationship between alveolar ventilation and pulmonary capillary blood flow, which averages approximately $0.8$ in the normal resting lung.

Capillary Oncotic Pressure

The osmotic force exerted by large plasma proteins that pulls water molecules into the capillary lumen from the interstitial space.

Capillary Hydrostatic Pressure

The physical fluid pressure within a capillary that pushes fluid outward into the surrounding interstitial space.