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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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Previous investigations have demonstrated a subset of POTS patients characterized by normal peripheral resistance and blood volume while supine, but thoracic hypovolemia and splanchnic blood pooling while upright secondary to splanchnic hyperemia. Such “normal flow” POTS patients often demonstrate hypocapnia during orthostatic stress.

We studied 20 POTS patients aged 14-23 years and compared them to 10 comparably aged healthy volunteers. We measured changes in heart rate, blood pressure, heart rate and blood pressure variability, arm and leg strain gauge occlusion plethysmography (SPG), respiratory impedance plethysmography calibrated against pneumotachography, end tidal carbon dioxide (P_ETCO2), and 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 upright tilt to 70^o. Ten POTS patients demonstrated significant hyperventilation and hypocapnia (POTS_HC) while 10 were normocapnic (POTS_NC) with minimal increase in postural ventilation comparable to control. While relative splanchnic hypervolemia and hyperemia occurred in both POTS groups compared to controls, marked enhancement in peripheral vasoconstriction occurred only in POTS_HC and was related to thoracic blood flow. Variability indices suggested enhanced sympathetic activation in POTS_HC compared to other subjects.  The data suggest enhanced cardiac and peripheral sympathetic excitation in POTS_HC.

The figure depicts spontaneous (left panels) and voluntary (right panels) hypocapnia brought about in a POTS patient and by voluntary hyperventilation in a healthy control subject, respectively. Voluntary hyperventilation was achieved by having the subject take a breath every 6 seconds and to breath as deeply as possible. This was maintained this for  three and half minutes and stopped because of lightheadedness. For each set of panels, P_ETCO2, Respitrace volumes, and thoracic blood volumes are shown from top to bottom. Upright tilt was associated with an increase in thoracic blood volume. The onset of hypocapnic hyperventilation was not related to an increase in thoracic blood volume.

The figure demonstrates the construction of a time integrated tidal volume curve (bottom panel) from the record of time dependent relative Respitrace tidal volume (top panel). An intermediate step is to obtain the absolute value of the tidal volume curve as shown in the middle panel.

The figure shows P_ETCO2, (top panel) the Respitrace tidal volume record (middle panel) and the calculation of relative respiratory minute volume (bottom panel) as the slope of linear portions of the integrated tidal volume corresponding to times preceding and during upright tilt in a POTS_HC patient.

The figure depicts changes in heart rate (top panel) and mean arterial pressure (bottom panel) during upright tilt. Heart rate increased in all subjects and was most increased in POTS_NC, and next most in POTS_HC compared to control subjects.  Mean arterial pressure is increases similarly for all subjects. *=p<.05 compared to control. ^†= p<.05 compared to POTS_NC.

The figure shows changes in P_ETCO2 (top panel), and minute ventilation (bottom panel) during upright tilt. P_ETCO2 was decreased in all subjects but most markedly in POTS_HC patients. This was associated with enhanced minute ventilation (V_E) in these same subjects. *=p<.05 compared to control.

The figure shows percent change in minute volume compared to percent change in ETCO2 for all subjects. Individual data points are shown for each subject. ETCO₂ is decreased in most patients but is most markedly decreased in POTS_HC patients in association with a marked increase in minute ventilation.