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Assoc. Prof. Chris O'Callaghan


Associate Professor of Medicine


The most common abnormality of blood pressure is 'hypertension' i.e. high blood pressure. It usually occurs in people who are overweight, >35 years old, and who have a near relative with the condition. It does not usually produce symptoms and it is relatively easily controlled with three or less medications. When these scenarios do not exist, it may be that special medications are required or the patient has one of the relatively rare 'secondary' causes of hypertension.


Low blood pressure (hypotension) is less common, more difficult to identify, and therefore less commonly diagnosed. Paradoxically, low blood pressure frequently co-exists with hypertension. In general, low blood pressure produces symptoms because of inadequate supply of blood to the brain, over-production of a hormone called adrenaline (which can increase the blood pressure) and alteration of the normal cycle between night and day:

Inadequate brain blood flow

  • Fainting/faintness
  • Fatigue
  • Blindness when upright
  • Exercise intolerance (especially for exercises performed when upright and after exercise)

Over-production of adrenaline

  • Anxiety - especially during prolonged standing such as in shopping centres or when in social situations
  • Sweating
  • Palpitations

Altered day-night cycle

  • Reduced production of urine in the day
  • Over-production of urine at night
  • Elevated night blood pressures

Causes of low blood pressure

Low blood pressure can occur when the nerves that control the blood vessels are damaged. This typically occurs in diabetes, Parkinson's disease, multiple system atrophy and spinal cord damage or injury. It can also be associated with rheumatoid arthritis, fibromyalgia, connective tissue disorders. Low blood pressure can sometimes run in familie.

What is POTS

The Postural Orthostatic Tachycardia Syndrome is a syndrome that is almost identical to 'low blood pressure', except the blood pressure is not found to be low. Instead, the hallmark of POTS is a fast heart rate when the patient is upright.

What is dysautonomia?

To tell the truth, I don't really know. I think it is probably just another name for POTS, which is probably also another name for low blood pressure.


Patients need to be referred by their treating practitioner. In general, I would prefer if you could mail/fax/email your referral so that I can allocate a suitable time to your consultation, and so that I can organise for your family members to attend if required. Patients from interstate must contact me beforehand so that I can organise appropriate tests before or when I see them.

Address 104 Mount Street
Heidelberg VIC 3079
Tel 03 9459 9998