Diagnosis
The diagnosis of autonomic failure may be confirmed by the following test results:
- cardiovascular reflexes:
- postural hypotension or more than 20 mmHg
- absence of sinus arrhythmia with deep breathing
- no bradycardia with carotid sinus massage
- no hypertension or tachycardia when stressed e.g. loud noise, immersion of hand in cold water, mental arithmetic
- no hypertension following Valsalva:
- patient forcibly exhales through a tube for 12 sec
- normally the blood pressure increases after, this is absent in autonomic failure
- plasma noradrenaline low and unchanged after 30 min standing or sitting
sweating:
þþ no sweating following 90 min at a body temperature 1 deg.C. above normal
- pupillary responses:
- pupil dilates after instillation of 1:1000 adrenaline
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