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[ Home ] [ Up ] [ Exercise Intolerance- the Exercise Pressor Reflex in POTS ] [ Abnormal Skeletal Muscle Pump ] [ Normal Leg Venous Capacitance ] [ Splanchnic Pooling in Normal Flow POTS ] [ Nitric Oxide Dysfunction in Low Flow POTS ] [ Angiotensin-II in POTS ] [ Decreased Upright Cerebral Blood Flow and Cerebral Autoregulation in POTS ] [ Postural Hyperpnea ] [ Neuronal Nitric Oxide is Specifically Decreased in Low Flow POTS ] [ Local Vascular Responses in POTS ] [ Microvascular Filtration in High Flow POTS ] [ POTS as Thoracic Hypovolemia ] |
| Variants of postural tachycardia syndrome (POTS) are
associated with increased (“high flow” POTS, HFP), decreased (“low
flow POTS”, LFP) and normal
(“normal flow POTS”, NFP) blood flow measured in the lower extremities
while supine. We propose that postural tachycardia is related to thoracic
hypovolemia during orthostasis but that the patterns of peripheral blood
flow relate to different mechanisms for thoracic hypovolemia. We
studied 37 POTS patients aged 14-21 years: 14 LFP, 15 NFP and 8 HFP
patients and 12 healthy control subjects. Peripheral blood flow was
measured supine by venous occlusion strain gauge plethysmography of the
forearm and calf in order to subgroup patients. Using indocyanine green
techniques we showed decreased cardiac index (CI) and increased total
peripheral resistance (TPR) in LFP, increased CI and decreased TPR in HFP,
and unchanged CI and TPR in NFP while supine compared to control subjects.
Blood volume tended to be decreased in LFP compared to control subjects.
We used impedance plethysmography to assess regional blood volume
redistribution during upright tilt. Thoracic
blood volume decreased while splanchnic, pelvic and leg blood volumes
increased for all subjects during orthostasis, but were markedly lower
than control for all POTS groups. Splanchnic
volume was increased in NFP and LFP. Pelvic blood volume was increased in
HFP only. Calf volume was
increased above control in HFP and LFP.
The results
support the hypothesis of [at least] three pathophysiologic variants of
POTS distinguished by peripheral blood flow related to characteristic
changes in regional circulations. The data demonstrate enhanced thoracic
hypovolemia during upright tilt and confirm that POTS is related to
inadequate cardiac venous return during orthostasis.
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| The
figure shows changes in thoracic, splanchnic, pelvic, and leg percent
volume changes during upright tilt averaged over subject groups. High flow
POTS is red, low flow POTS is green, normal flow POTS is blue and control
is black. Splanchnic changes dominate normal flow POTS. Low flow POTS
patients have widespread blood collection. High flow POTS have blood
pooling in the dependent body parts |
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POTS as Thoracic Hypovolemia