Exam 2 - Venous Hemodynamics

Venous Walls

Have elasticity - can distend several times original size

Not as muscular as arteries

Venous Valves are Made From

Connective tissue

The femoral vein contains how many valves?

1-6

The great saphenous vein contains how many valves?

10-12

The popliteal vein contains how many valves?

0-4

The anterior tibial vein contains how many valves?

8-11

The posterior tibial vein contains how many valves?

8-19

Venous Return

Returns blood back to heart

Requires pressure gradients to overcome gravity

Venous Capacitance

Veins act as a blood reservoir

Hold 2/3 of blood volume

Can distend 4x large than arteries

Hydrostatic Pressure Formula

= : ρ x g x h

(ρ is density of blood, g is gravity, h is height of column of blood)

Hydrostatic Pressure

Major force affecting venous system

Pressure within vessel that pushes blood

Negligible in a supine position

What happens if veins fall below tissue pressure (5 mmHg)?

Collapse

Transmural Pressure

Pressure difference between inside and outside of vein

Changes in vein shape are associated with...

Large volumes of flow

Once veins are distended, what is needed to change volume?

Large changes in pressure

Venous Dynamics During Inspiration

Pressure decreases in thorax

Increased intra-abdominal pressure

Blood pools into the pulmonary vascular bed

IVC collapses

Venous return from the legs is impeded

Venous Dynamics During Exhalation

Increased pressure in thorax

Decreased intra-abdominal pressure

Flow increases from legs into abdomen

Blood flow decreased to thorax

Valsava Maneuver

Increases intra-thoracic and intra-abdominal pressures

Eliminates pressure gradient

IVC has no flow

Edema

Fluid collection in tissues

Indicative of venous congestion

Calf Muscle Pump - When Muscles are Contracted

Proximal valves are open

Distal valves are closed

Calf Muscle Pump - When Muscles are Relaxed

Proximal valves are closed

Distal valves are open

Primary Varicose Veins

Develop in absence of DVT

Incompetent valves in common femoral or great saphenous veins - retrograde flow

Increased venous pressure

Secondary Varicose Veins

Associated with DVT

Incompetent valves in deep, superficial, and perforating veins

Increased venous pressure

Venous Stasis Ulcers

Open sores that develop on the lower legs due to poor blood circulation