Home

Research Studies:

• Local Vasoconstriction and Sympathoexcitation in POTS
   

• Vascular Dysfunction in CFS
   

• Postural Hyperpnea in POTS
   

• Irritable Bowel Syndrome and Autonomic Dysfunction
   

• Microvascular Dysfunction in Obese Adolescents
  

Circulatory Measurements

• HR, BP

• Muscle Pump

• SPG

• IPG

• LDF

  • Microdialysis

• TCD

• Dye Dilution CO and BV

• Findings in POTS

Orthostatic Stress  Testing & instrumentation

Circulatory Autonomic Testing

Lay Review with glossary

Orthostatic Intolerance (OI)

• Physiology 

• Patterns of  OI

  • Normal

  • Vasovagal syncope

  • POTS

  • Dysautonomic

• Acute OI and  syncope

  • Splanchnic pooling

• Chronic OI

  • POTS and Chronic OI

  • Chronic Fatigue Syndrome

  • Circulatory Findings in POTS

Circulatory Findings in POTS

Orthostatic Hypotension

Links

Comments

Search

Transcranial Doppler ultrasound has been used to estimate cerebral blood flow velocity (CBFv) under a variety of conditions including orthostasis, Valsalva maneuver, etc. It has been used in functional form to interrogate the various branches of the Circle of Willis to localize and lateralize stroke and has been used to demonstrate that chronic orthostatic intolerance and POTS involve marked changes in cerebral blood flow velocity which appear to coincide with the onset of hyperpnea and often dyspnea.  We use a pulse range-gated 2 MHz probe focused by a plastic lens (Multigon TCD System 500M) via the anterior transtemporal approach to insonate the left and right middle cerebral artery (MCA). Data are synchronized with SGP, IPG, HR, and BP data through the DATAQ A/D interface. If the diameter of the MCA is relatively unchanged throughout an experiment, and if changes in maximum flow velocity can be substituted for changes in average velocity (the usual assumption which can be demonstrated for pulsatile laminar flow regimes) then changes in flow velocity reflect relative changes in flow. Changes in the MCA are often taken to be reasonably representative of overall cerebral blood flow changes if changes are global. The quantity [(Mean arterial pressure at heart level) – (.776* height of the MCA above the right atrium)] estimates the mean arterial pressure at the MCA. Autoregressive modeling of mean BP and CBFv  following the same principles used in obtaining any transfer function can be used to estimate cerebral autoregulation capability.