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The size of the respiratory swings in blood pressure (pulsus paradoxus) correlate well with the degree of inspiratory effort measured with an oesophageal balloon. To take advantage of this phenomenon to estimate changes in inspiratory effort requires a measure of beat to beat blood pressure. In a respiratory sleep study to identify obstructive sleep apnoea (OSA) and its variants, such measurements are useful to indicate increased inspiratory effort following upper airway narrowing. Our unit has shown that two non-invasive devices, the photoplethysmographic volume clamp (Finapres, Ohmeda) and pulse transit time (RM50, Parametric Recorders) can provide this information. Pulse transit time (PTT) measures BP indirectly because the pulse wave propagation time (eg from heart to finger) is inversely related to arterial wall tension, which in turn depends on blood pressure. This report on snorers, taking part in another study on oral appliances, was done to verify that indirect measurements of PTT could detect the increases in inspiratory effort that usually accompany snoring. In 14 snorers (with no evidence of significant OSA on their diagnostic study) snoring (using a throat microphone), posture, oxygen saturation, thoracic excursions, and indirect blood pressure (PTT) were measured during overnight studies at home. Where available, paired ten minute periods each of continuous regular snoring, and of no snoring, were selected when there was no evidence of accompanying apnoeas, desaturations or hypopnoeas. These periods were during assumed sleep (no body movements on the thoracic excursion tracings) and selected blind of the PTT measurements. The mean size of the respiratory swings in PTT were then calculated for each of the 18 paired data sets available from 13 patients. All but three of the paired data sets showed a rise in respiratory swings during snoring periods, with the means swings being 13.5ms (SD10.5) and 18.6 (SD8.7) silence and snoring respectively. This study shows that swings in PTT can detect the increased inspiratory effort during snoring, even in the absence of any associated apnoeas and hypopnoeas.


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