An objective test for orthostatic intolerance?

Symptoms of autonomic nervous system dysfunction are present in around three-quarters of ME/CFS patients (see our comment). One of these symptoms is orthostatic intolerance, the inability to remain standing without ill effects. Many patients know from experience that standing can bring on dizziness, nausea, altered vision and fatigue. Yet, their reports are often discounted by doctors who attach more importance to “objective” findings.

For several years, Dr John Allen and colleagues in Newcastle have been developing photoplethysmography (PPG), a simple-touse, relatively low-cost method of shining light onto skin to detect changes in blood volume. In their latest scientific report, they describe the use of novel state-of-theart multi-site PPG technology that takes measurements from sites on the ears, fingers and toes simultaneously in real time – a tool that is perfectly suited to the measurement of cardiovascular responses to standing. In the experiment, multi-site PPG pulses were collected from tissue pads of the ears, fingers and toes of 14 people with ME/CFS and 14 age-matched sedentary control subjects during ten minutes of lying down followed by three minutes on a tilt table (head-up to 70°). Percentage change in pulse timing, and pulse amplitude at each site were calculated using beat-to-beat pulse wave analysis. The results showed that the change in composite score measured on tilting was significantly less in the ME/CFS patients than in controls (26 versus 37%, p=0.002). Using both timing and amplitude measures, they could achieve a diagnostic accuracy of 82%.

The researchers say that these demonstrable pulse wave abnormalities have the potential to become a bedside diagnostic marker. They find it interesting that the predominant abnormalities of pulse wave form found in ME/CFS patients were at the ear rather than the fingers or toes, suggesting that reduced cardiac output or abnormalities of regulation of cerebral blood flow might underlie some of the symptoms experienced on standing.

Reference: Chronic fatigue syndrome and impaired peripheral pulse characteristics on orthostasis – a new potential diagnostic biomarker. Allen J, et al. Physiol Meas 2012 Feb; 33(2): 231-41.

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