Skeletal Muscle Pump

Home ] Up ] Exercise Intolerance- the Exercise Pressor Reflex in POTS ] [ Skeletal Muscle Pump ] Normal Leg Venous Capacitance ] Postural Neurocognitive ] 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 ] Nitric Oxide is Decreased in Angiotensin-II dependent Low flow POTS but increased along with Splanchnic pooling Neuropathic POTS ] Local Vascular Responses in POTS ] Microvascular Filtration in High Flow POTS ] POTS as Thoracic Hypovolemia ]

Standing translocates thoracic blood volume into the dependent body. The skeletal muscle pump participates in preventing orthostatic intolerance by enhancing venous return. We investigated the hypothesis that skeletal muscle pump function is impaired in postural tachycardia (POTS) associated with low calf blood flow (“low flow POTS”) and depends in general on muscle blood flow. Twelve low flow POTS subjects were compared with 10 controls, and with 7 POTS patients with normal calf blood flow using strain gauge plethysmography to measure peripheral blood flow, venous capacitance, and calf muscle pump function. Blood volume was estimated by dye dilution. We found that calf circumference was reduced in low flow POTS (32±1 vs 39±3, 43±3 cm) and, compared to control and POTS patients with normal blood flow, is related to reduced fraction of calf venous capacity emptied during voluntary muscle contraction (ejection fraction, 0.52±.07 vs 0.76±.07, 0.80±.06). We found that blood flow was linearly correlated (rp=0.69) with calf circumference (used as a surrogate for muscle mass). Blood volume was 2.2±0.3 in low flow POTS vs 2.6±0.5 in controls (p=0.17) and 2.4±0.7 in normal flow POTS patients. Decreased calf blood flow may reduce calf size in POTS, impairing the upright ejectile ability of the skeletal muscle pump and further contributing to overall reduced blood flow and orthostatic intolerance in these patients.
Diagrammatic representation of typical recording of plethysmographically measured changes in calf volume during a sequence of leg lift, standing , and tiptoe exercise. The patient is first supine position with the leg elevated, then standing with weight on nonexamined leg, then performs several single tiptoe movements followed by 2 ten tiptoe movement sequences returning to quiet standing position in between. The complete venous volume is designated VV, the ejection volume of a tiptoe is designated EV, and the residual volume is RV. RV was defined from an average of the residual volume during multiple tiptoes. Ejection fraction is defined as the ratio EV/VV.
The relation between supine blood flow and calf size is shown. Low flow POTS patients are shown as crosses, control subjects are shown as triangles, normal flow POTS patients are shown as squares. Calf size increases (rp=0.74) with blood flow suggesting that the mass of the calf increases with blood flow to the calf.
The relation between calf ejection fraction = ejection volume (EV)/ venous volume (VV) and supine calf blood flow measured by venous occlusion strain gauge plethysmography. Low flow POTS patients are shown as crosses, control subjects are shown as triangles, normal flow POTS are shown as squares. Ejection fraction increases (rp=0.69) with blood flow suggesting that muscle pump efficacy increases with calf muscle perfusion.

 


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Exercise Intolerance- the Exercise Pressor Reflex in POTS
Skeletal Muscle Pump
Normal Leg Venous Capacitance
Postural Neurocognitive
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
Nitric Oxide is Decreased in Angiotensin-II dependent Low flow POTS but increased along with Splanchnic pooling Neuropathic POTS
Local Vascular Responses in POTS
Microvascular Filtration in High Flow POTS
POTS as Thoracic Hypovolemia