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Title: The brain at altitude : the cerebral vasculature, hypoxia and headache
Author: Wilson, M. H.
ISNI:       0000 0004 5363 4410
Awarding Body: University College London (University of London)
Current Institution: University College London (University of London)
Date of Award: 2014
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This thesis studies the effect of hypoxia (at rest and during exercise) on the arterial and venous cerebral circulation, investigating the venous system role in high altitude headache. Methods: 1) Hypobaric hypoxic studies investigated 198 trekkers and 24 Investigators to 5300m, 14 to 6400m and 8 to 8848m. 2) Normobaric hypoxic studies used Magnetic Resonance Imaging (MRI)) at sea-level. Four domains were addressed: i. Arterial: Hypobaric hypoxia: (n=24) Transcranial Doppler (TCD) measured middle cerebral artery diameter (MCAD) and blood velocity (MCAv). Sea-Level normobaric hypoxia: (n=7) A hypoxicator (FiO2 = 11%) for 3 hours with a 3Tesla MRI scan measured MCAD and MCAv. ii. Brain Oxygenation: Near Infrared Spectroscopy (NIRS) monitored Regional Brain Oxygenation (rSO2). iii. Venous: Retinal imaging at altitude and MRI at sea-level assessed the venous system. iv. Headache: A daily diary recorded headache burden. Results: Arterial: Hypobaric and normobaric hypoxia induced MCA dilatation. Mean (±(SEM)) MCAD increased in hypoxia (from 5.23(±0.23)mm (at 5300m) to 9.34(±0.88)mm (at 7950m)(p<0.001) (TCD). At sea-level, (after 3 hours FiO2 = 11%) MCAD increased from 3.04(±0.13)mm to 3.27(±0.13)mm (MRI). Brain Oxygenation: rSO2 decreased more than peripheral arterial saturation (SaO2), especially during exercise. The relative percentage reduction in resting SaO2 and rSO2 from 75m to 5300m was -22.23 ±0.56% and -30.61 ±1.28% (p<0.001) respectively. Venous: Hypoxia induced retinal and cerebral venous distension. Twenty-three of 24 subjects exhibited retinal venous distension (range 5 to 44%). Degree of distension correlated with headache (r = 0.553, p=0.005). Possession of a narrow transverse sinus strongly related to retinal and cerebral venous distension and headache. Headache: Headache Severity Index (HSI) (headache score x duration) correlated inversely to both lateral and third ventricular volumes summed (r = -0.5, p = 0.005) and pericerebellar CSF volume (r = -0.56, p = 0.03). Conclusions: Large cerebral arteries dilate and veins distend with hypoxia. This suggests an important influence of cerebral venous anatomy and physiology on headache, with implications for pathophysiological states and their management.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available