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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

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[ Valsalva Maneuver in Normal Flow POTS ]

Previous investigations have allowed for stratification of POTS patients based on peripheral blood flow. One such subset, comprising “normal flow POTS” patients is characterized by normal peripheral resistance and blood volume while supine but thoracic hypovolemia and splanchnic blood pooling when upright.

We studied 32 consecutive POTS patients aged 14-22 years comprising 13 with low flow POTS, 14 with normal flow POTS, and 5 with high flow POTS compared to 12 comparably aged healthy volunteers. We measured changes in impedance plethysmographic (IPG) indices of blood volume and blood flow within the thoracic, splanchnic, pelvic (upper leg), and lower leg regional circulations while supine and during incremental tilt to 20^o, 35^o, and 70^o. We validated IPG measures of thoracic and splanchnic blood flow against indocyanine green dye dilution measurements. We validated IPG leg blood flow against venous occlusion plethysmography. Control subjects developed progressive vasoconstriction with incremental tilt. In comparison splanchnic blood flow was increased supine in normal flow POTS despite marked peripheral vasoconstriction and did not change during incremental tilt producing progressive splanchnic hypervolemia. Absolute hypovolemia was present in low flow POTS; all supine flows and volumes were reduced; there was absence of vasoconstriction with tilt in all segments, and segmental volumes tended to increase uniformly throughout tilt. Lower body (pelvic and leg) flows were increased in high flow POTS at all angles with consequent lower body hypervolemia during tilt.

Our main finding is selective and maintained orthostatic splanchnic arterial vasodilation in normal flow POTS despite marked peripheral vasoconstriction in these same patients. Local splanchnic vasoregulatory factors may counteract vasoconstriction and venoconstriction in these patients. In addition there was abnormal lower body vasoconstriction in high flow POTS and unchanged vasoconstriction in low flow POTS which was sustained at initially elevated supine levels.

Of interest is that analogous findings were found in normal flow POTS patients during the Valsalva maneuver in which splanchnic pooling was related closely to blunting of the splanchnic vasoconstrictor response.

The figure depicts changes in mean arterial pressure (top panel) and heart rate (bottom panel) during incremental upright tilt. Mean arterial pressure was increased in low flow POTS at 20^o and 35^o upright tilt. Heart rate was significantly increased at 35^o and 70^o upright tilt.

The figure shows percent changes in thoracic, splanchnic, pelvic, and leg blood volumes during incremental upright tilt averaged over subject groups. Splanchnic changes dominate normal flow POTS. Low flow POTS patients have widespread blood collection. High flow POTS have blood pooling in the lower body.

The figure shows percent changes in segmental blood flow. From top down changes in thoracic, splanchnic, pelvic and leg (calf) are shown in order. Blood flow decreases for control in all segments. Blood flow does not change in the splanchnic segment for normal flow POTS while leg blood flow is markedly reduced. Blood flow does not change in the peripheral circulation (pelvic and leg) for high flow POTS. There is uniformly blunted blood flow changes in low flow POTS.