6 Venous Hemodynamics, Pressure and Flow

venous return is

phasic

what is the difference in pressure between arterial and venous system?

20mmHg

how do calf muscles affect venous blood?

contraction and relaxation of calf muscles cause venous blood to be propelled towards heart; capable of completely emptying the lower extremity veins

during inspiration what happens to

• diaphragm

• intrabdominal pressure

• blood from lower extremities

diaphragm descends

intrabdominal pressure increases

blood from lower extremeties decrease

during expiration what happens to

• diaphragm

• intrabdominal pressure

• blood from lower extremities

diaphragm ascends

intrabdominal pressure decreases

blood from lower extremeties increase

how does inspiration and expiration affect IVC

during inspiration IVC collapses

during expiration IVC is not collapsed

how does blood from from lower extremeties affect upper extremities

less blood flow from LE → increased blood flow from upper body

more blood flow from LE → decreased blood flow from upper body

what is hydrostatic pressure caused by?

weight of fluid as measured compared to reference point (RA)

where is HP highest?

in feet when patient is erect

what affects venous blood return?

muscle pump

presence of valves

respiratory pump

vena cava compression

gravity

pumping of heart

where are valves more numerous

below the knee

what can affect venous flow?

CHF or tricuspid insufficiency (doesn’t close properly)

shallow breathers/chest breathers (does not fully distend diaphragm)