Transcript more complicated than arterial physiology

Deep and Superficial
Venous Physiology
Stephen F. Daugherty, MD, FACS, FACPh, RVT, RPhS
Clarksville, Tennessee
Disclosures
No relevant conflicts of interest
No off label discussion
This presentation was originally developed by:
Neil Khilnani, MD
Associate Professor of Clinical Radiology
Division of Interventional Radiology
Weill Cornell Medical College
New York, USA
Venous Physiology
• More complicated than the arterial
physiology
• Arterial flow
- Ventricular contractions propel blood
- Minimally compliant conduit
- Pathology: insufficient perfusion
• Obstruction
- conduit
Venous Physiology
• More complicated than the arterial physiology
• Venous flow
- Muscle pumps
- Compliant conduit
- Pathology: Too much downstream pressure
• Obstruction
- conduit
- Reversal of flow
- External compression
• Solid structure
• Compartment pressure
Function of the Venous System
more than just a conduit to return blood
• Return blood back to the heart
and
• Large capacitance to store blood
– Great distensibility makes their capacitance
adjustable
• Smooth muscles in wall can alter distensibility
– In times of need, the veins can be squeezed to move
blood where needed
• Pressure does not increase with more blood
– until vein distensibility is exhausted
• Removing blood makes them flatter without changing
their pressure
– Hemodynamic buffer
Venous Physiology
more complicated than arterial physiology
• Venous conduits have
– Different capacitance properties
• 30x more compliant than arteries
– Valves that control the direction of
flow
Venous Physiology
more complicated than arterial physiology
• Susceptible to external
pressures
– Blood passes through
compartments
• exerting varied external pressures
–  impact on low pressure vein
– Propells or impede venous flow
Venous Physiology
Supine more simple
• Supine conditions
• gradient from feet to right atrium is small
• Normal Right Atrial Pressure - 0 mm Hg (1 ATM)
• Inspiration and early diastolic RA pressures suck blood “upward”
• (-) 2-3 mm Hg
• “vis a fronte” (force from in front)
• Foot pressure – (+) 3-4 mm Hg
• Arterial pressure
• “vis a tergo” (force from behind)
• Compression of veins by
• Normal anatomical pinch points
• Crossing arteries
• Intra-abdominal pressure (1-3mmHg)
Guyton and Hall, Textbook of Medical Physiology
Venous Physiology
Gravity adds to the pressure gradient
• Standing
• Foot pressure ≈ 90mmHg higher than that in the RA
• Pressure caused by weight of fluid column
•
1 mmHg for every 13.6 mm depth
• Getting blood back the heart at low pressure
requires
• Unidirectional valves
• Pumps
Venous Physiology
Gravity adds to the pressure gradient
• Standing
• Foot pressure ≈ 90mmHg higher than that in the RA
• Pressure caused by weight of fluid column
• 1 mmHg for every 13.6 mm depth
• Getting blood back the heart requires
• Unidirectional valves
• Pumps
Muscle pumps
required to move blood against gravity
“Deep vein physiology”
• Calf
– Most important (65% EF)
• Largest capacitance
• Generate the largest pressures
• Foot
– Plantar veins (15-20% EF)
• 20-30 ml pushed up per step
– Prime the tibial veins
• Thigh
– 15% of the EF
Calf Muscle pump
Parsi K, 2007 PDF
Intramuscular Venous Sinusoids
Gastrocnemius and Soleal
• Thin, large volume intramuscular veins
• In the muscle compartment
– Calf systole
• + 200-300 MmHg generated
– Calf diastole
• 100 mmHg gradient
– Superficial to deep vein flow
Intramuscular Venous Sinusoids
Gastrocnemius and Soleal
• Thin, large volume intramuscular veins
• In the muscle compartment
– Calf systole
• + 200-300 MmHg generated
Intramuscular Venous Sinusoids
Gastrocnemius and Soleal
• Thin, large volume intramuscular veins
• In the muscle compartment
– Calf systole
• + 200-300 MmHg
Musculo-venous “Calf” Pump
Analogous to a “peripheral heart”
• Pump
- Calf muscles
• Provide the force
- Intramuscular veins
• Pumping chambers
• Valves
- Maintain one-way flow
• Foot to heart
• Superficial to deep
Intramuscular Venous Sinusoids
Gastrocnemius and Soleal
• Thin, large volume intramuscular
veins
• In the muscle compartment
– Calf systole
• + 150 mmHg generated
– Calf diastole
• 100 mmHg gradient
– Superficial to deep
vein flow
Intramuscular Venous Sinusoids
Gastrocnemius and Soleal
–Calf diastole
•(-) 100 mmHg
–in muscle veins
–Superficial to deep vein flow
Parsi Anatomy for Phlebologists
Calf Pump Physiology
• After 10 steps
• ankle pressure
• 90  30 mm Hg
Other influences on blood movement
• Intra-abdominal pressure
– Veins are collapsible structures in abdominal compartment
• Affected by external pressures
• Diaphragm movement functions like a hydraulic pump
– Exhaling decreases intra abdominal pressure
Allows rapid inflow of blood to IVC from legs/viscera
• Obesity increases baseline abdominal pressure
– Hinders normal flow
Other influences on blood movement
• Intra-abdominal pressure
• Diaphragm movement functions like a hydraulic pump
• Veins are collapsible structures in abdominal compartment
• Obesity increases baseline abdominal pressure
• hinders flow
• Intra-thoracic and RA pressure
• ‘vis a fronte” (force from in front)
• Draws blood from the abdomen
• inspiration
• end diastolic RA pressure
• Ventricular contractions
• “vis a tergo” (force from behind)
• 10mm small veins
• 5 mm Hg in large veins
Superficial Vein Physiology
passively collect blood
• Extrafascial tributary veins:
• “collecting veins”
• Saphenous veins
• Gather blood from tributaries
• Supine:
• Slow flow toward the deep vein junctions
• Standing:
• Segments between valves with little upward flow
• each collects blood from tributary veins
• drains inward through perforating veins
• Feeds blood to to deep system
Medscape Varicose veins
Superficial Vein Physiology
passively collect blood
• Extrafascial tributary veins:
• “collecting veins”
• Saphenous veins
• Gather blood from tributaries
• Supine:
• Slow flow toward the deep vein junctions
• Standing:
• Segments between valves with little upward flow
• each collects blood from tributary veins
• drains inward through perforating veins
• Feeds blood to to deep system
Medscape Varicose veins
Physiological Testing
• No simple inexpensive test like an ABI to characterize venous
physiology
• Duplex Ultrasound
• Primarily anatomical
• Flow
• Direction
• Velocity
Physiological Testing
Air plethysmography
• Measures changes in volume
• Standing
• Leg elevation
• Muscle contraction
• Variety of performance indices
• Rate of refilling
• Rate of emptying
• Ejection fraction
Emptying Assessment
assesses deep venous patency
normal: fast drainage after tourniquet removal
tourniquet
Nicolaides Circulation. 2000;102:e126-e163
Emptying Assessment
assesses deep venous patency
normal: fast drainage after tourniquet removal
tourniquet
Nicolaides Circulation. 2000;102:e126-e163
Venous Physiology
• More complicated than arterial physiology
Summary
• Venous system
• Multiple components
• Valve, pumps and conduits
• Compliant conduits
• Susceptible to external pressures
• Gravitational effect more marked
• Goal
• To return blood
• Store blood
• Minimize lower limb venous pressure
• avoid hypertensive complications