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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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 Heart rate (HR; top), mean arterial pressure (MAP; middle), and thoracic impedance (bottom) of a representative fainting patient during head-up tilt (HUT) to 70°. All patients were characterized by similar physiological events that occur at discrete times denoted "fiducial points". The fiducial points shown are “baseline,” “1 min” HUT, “early” onset of the gradual decrease in BP, “mid” decrease in BP, “late” decrease in BP, and “faint” are indicated. After a gradual decrease in BP, marked hypotension and bradycardia occurred.

Thoracic impedance gives an inverse measure of thoracic or central blood volume since, as blood within the heart and lungs decreases by upright positioning, the impedance (electrical resistance) increases substantially. 

Heart rate, HR (top), mean arterial pressure, MAP (middle), and cardiac index (CI; bottom) in fainters and healthy control subjects during 10 min of upright tilt at 70° are shown. Fainters had significant tachycardia and decreased CI until fainting supervened. MAP decreased throughout tilt, only reaching significance at faint. #P < 0.05 compared with baseline. *P < 0.05, between-group comparison.

Thus, peripheral resistance is higher in young fainters than in comparable healthy volunteers as is heart rate while the cardiac output is reduced. The extent of tachycardia in these syncopal youngsters may fulfill the "excessive tachycardia" criteria of POTS and the presyncopal symptoms are common to all forms of orthostatic intolerance. However, distinguishing these patients who faint from POTS patients is the episodic nature fainting separated by long periods of orthostatic well-being in the former (fainters) and the general absence of fainting in real life of POTS patients who generally have day-to-day symptoms of OI. 

Segmental volume changes (%change) in fainters and healthy control subjects during upright tilt. Thoracic blood volume is shown top left, splanchnic blood volume at top right, pelvic blood volume at bottom left, and leg blood volume at bottom right. Tilt results in thoracic emptying and splanchnic filling that are markedly enhanced in fainting subjects. Pelvic and leg filling are similar in fainters and control subjects. #P < 0.05 compared with baseline. *P <0.05, between-group comparison.

Arterial resistance in fainters and healthy control subjects during upright tilt. Total peripheral resistance (TPR) is shown at top left, splanchnic resistance at top right, pelvic resistance at bottom left, and leg resistance at bottom right. Fainters demonstrated biphasic change in TPR, pelvic, and leg resistances in which an initial increase in TPR was followed by a decrease in resistance until faint occurred. This was not observed in healthy control subjects. Splanchnic resistance never increased in fainters. #P < 0.05 compared with baseline. $P < 0.05 compared with 1 min. *P < 0.05, between group comparison.

In this panel we assessed blood pressure (top panel) and blood pressure variability using a wavelet analysis to separate systolic, diastolic and mean arterial pressure during HUT in fainters and controls. Bottom from top down: systolic, mean, and diastolic pressure low-frequency (low freq.) power. ■, Fainters;
, healthy controls. Systolic pressure initially increases above control and then gradually decreases until syncope when it abruptly falls. Diastolic pressure changes are less marked. With the exception of 1 min posttilt, LF systolic, mean, and diastolic power are significantly lower in fainters than in controls (P 0.05). The difference in power widens as HUT progresses. Bsl, baseline; ERec, early recovery; LRec, late recovery. Pgroup, probability of group differences; Ptime, probability of time differences.

Differences are particularly noted during late tilt as fainting approaches. The blood pressure variability at 0.1 Hz corresponds to the intrinsic frequency of the sympathetic baroreflex and suggests that sympathetic baroreflex failure may account for loss of TPR and vascular compensation during late tilt. 

Changes in respiratory parameters during HUT70 in fainters and healthy control subjects. Respiratory rate (Resp) is shown at top left, relative tidal volume (TV) at top right, relative minute volume ventilation (MVV) at bottom left, and end-tidal partial pressure of carbon dioxide (PETCO2, or ETCO2) at bottom right. Respiratory rate decreased while TV increased, reaching a maximum just before faint. MVV increased and ETCO2 decreased monotonically in fainters.#P < 0.05 compared with baseline. *P <  0.05, between group comparison.