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[Uhthoff ’s phenomenon or symptom is the worsening of visual acuity (‘amblyopia’ in Uhthoff’s 1890 description) with exercise in optic neuritis, reflecting the temperature sensitivity of demyelinated axons (i.e. reduced safety factor for faithful transmission of action potentials). The term has...
[The Valsalva manoeuvre is a simple test of autonomically mediated cardiovascular reflexes, comprising forced expiration against resistance (‘straining’), followed by release of the resistance and completion of expiration. The first phase produces impaired cardiac filling due to impaired venous...
[Weakness of the proximal leg and hip girdle muscles, most often of myopathic origin, impairs the stability of the pelvis on the trunk during walking, leading to exaggerated rotation with each step, an appearance likened to the waddling of a duck. In addition, the hips may be slightly flexed and...
[Xanthopsia is a visual disturbance characterized by excessive perception of yellow colours (literally ‘yellow vision’).]
[Yawning is an arousal reflex thought to be generated in the brainstem reticular formation to counteract brain hypoxia; it may precede vasovagal syncope. Excessive or pathological yawning (chasm) is compulsive, repetitive yawning not triggered by physiological stimuli such as fatigue or boredom.]
[The zeitraffer phenomenon has sometimes been described as part of the aura of migraine, in which the speed of moving objects appears to increase, even the vehicle in which the patient is driving.]
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