Respiration, changes in RR-intervals and changes in systolic pressure (SP) levels are all linked. We considered the phase not only between SP levels and RR-intervals, but between respiration and RR-intervals and between respiration and SP levels. Twenty normal subjects breathed regularly at four and fourteen breaths a minute. Breathing was recorded and RR-intervals and SP levels extracted from the ECG and Finapres signal respectively. Cross spectral analysis was performed between respiration and RR-intervals, respiration and SP levels and SP levels and RR-intervals to calculate phase delays (Resp→RR, Resp→SP and SP→RR). Phase delay changed with breathing frequency. At four breaths per minute the phases were, Resp→RR ~-Π/2 rad, Resp→SP ~0 rad and SP→RR ~-Π/2 rad. At fourteen breaths per minute the phases Resp→RR and Resp→SP were both ~-3Π/4 rad resulting in SP→RR being ~0 rad (in phase). When calculating phase delays it is important that the same interactions are compared: this study highlighted a situation where 2Π had to be added to one set of results so that they were in keeping with those of the other subjects. This study showed that breathing frequency affects phase and that data should be carefully examined to establish if there is a requirement to add or subtract 2Π to the results.
Bowers EJ, Murray A. Phase representing the three interactions between respiration, changes in RR-intervals and changes in SP levels. European Study Group on Cardiovascular Oscillations ESGCO 2006. 2006;270-3.
Miss Emma Bowers, Freeman Unit, Newcastle upon Tyne. Tel: +44 (0)191-223-1370.
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