Excessive Hypocapnic Cerebral Vasoconstriction in Hypermobile Ehlers–Danlos Syndrome Assessed With Real‐Time Magnetic Resonance Imaging During Lower‐Body Negative Pressure

Background Orthostatic intolerance is common in hypermobile Ehlers–Danlos syndrome (hEDS) with one third of patients fulfilling postural orthostatic tachycardia syndrome criteria. Our aim was to assess cerebral blood flow in patients with hEDS and postural orthostatic tachycardia syndrome during orthostasis, which may be responsible for orthostatic intolerance. Methods In 18 individuals with hEDS and postural orthostatic tachycardia syndrome and 20 healthy controls, we conducted real‐time phase contrast magnetic resonance imaging of the middle cerebral artery with and without an orthostatic challenge through 30 mm Hg lower‐body negative pressure. Results During lower‐body negative pressure, heart rate increased more in hEDS than in controls (15.0±8.3 bpm versus 7.8±7.7 bpm, P =0.009); blood pressure remained unchanged; middle cerebral artery flow per heartbeat decreased more in hEDS (−28%±16% versus −15%±13% in controls, P =0.013) with decreased mean volumetric flow in hEDS (−12%±17%, P <0.001 versus −6%±8% in controls, P =0.102); average middle cerebral artery peak blood flow velocity decreased in both groups (hEDS: 44.6±8.1 cm/s to 37.6±8.4 cm/s, P <0.001; controls: 40.3±10.9 cm/s to 36.9±11.1 cm/s, P =0.018); respiration rate increased in hEDS (14.3±5.1/min to 17.4±5.3/min, P =0.002) leading to a decrease in end‐tidal CO 2 (39.2±4.2 mm Hg to 35.6±6.4 mm Hg, P =0.025), and cerebrovascular resistance increased more in hEDS (50.8%±48.4%, P <0.001) versus (20.3%±20.6%, P =0.005) in controls. Conclusions Individuals with hEDS and postural orthostatic tachycardia syndrome maintain cerebral perfusion primarily through tachycardic compensation during orthostatic stress despite hypocapnic vasoconstriction. Registration URL: https://drks.de/search/en ; Unique Identifier: DRKS00028279.