Cardiovascular system blood pressure control

In MSA, the baroreceptor reflex pathways which control blood pressure on a beat-by-beat basis are impaired. This often results in orthostatic (postural) hypotension, a cardinal feature, leading to recognition of autonomic failure and consideration of MSA. Orthostatic hypotension is defined as a fall in systolic blood pressure of 20 mmHg or more, or in di-astolic blood pressure of 10mmHg or more, on either standing or head-up tilt to 60° for 3 minutes. Reduced perfusion of organs results in a variety of symptoms (Mathias et al., 1999). Hypoperfusion of the brain can cause dizziness, visual disturbances, loss of consciousness and transient impairment of cognition. Pain in the neck muscles ('coathanger' ache), and lower back result from muscle hypoperfusion. A low level of blood pressure reduces renal blood flow, causing oliguria during the day, and nocturia at night when the blood pressure is restored while supine. Non-specific symptoms such as weakness, lethargy, fatigue and falls (the last, especially in the elderly), may occur. Symptoms occur when upright, as blood pressure usually is promptly restored on returning to the horizontal (Fig. 1), with relief of symptoms.

In addition to postural head-up change, a variety of factors may lower blood pressure further while supine; these often unmask or worsen orthostatic hypotension. These include the speed of positional change, time of day, a warm environment, raising intrathoracic pressure during straining while micturating and defaecating, food ingestion, alcohol consumption and even mild physical exertion. In autonomic failure, drugs with usually mild vasodilatory effects may cause hypotension; these include certain anti-parkinsonian agents, and drugs used to treat autonomic deficits, such as sildenafil (Hussain et al., 2001).

The treatment of orthostatic hypotension is based on a combined approach, utilising

Multiple system atrophy and autonomic failure

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