Different techniques have been used to induce regular changes in RR-intervals and SP levels, in order to try to understand influences on the interrelationship between these two variables. Unfortunately there has not be a comparison between these techniques.
This study aims to investigate firstly how successful different techniques were at inducing regular changes in RR-intervals and SP levels and secondly how consistent these changes were within the test procedures.
Two sets of four protocols designed to induce changes in RR-intervals and SP levels at 8 times per minute (0.133 Hz) were investigated. Set one, breathing induced variations, comprised of regularly breathing in a supine position, in a standing position, through a resistance, and blowing into a closed orifice. Set two, action induced variations comprised of regularly clenching a fist, performing mental arithmetic, being rocked and having legs regularly raised and lowered. All protocols lasted 3 minutes. Twelve subjects (30 ± 6 years) had their ECG and Finapres (continuous non-invasive blood pressure) recorded while partaking in both sets of protocols. Success of induction was determined by the presence of a peak in the frequency domain at 0.133 Hz for both the RR-interval signal and the SP level signal. Ability to perform the protocols and consistency of RR-interval or SP level changes were calculated by averaging signals over the 24 cycles for each method and establishing the normalised average 95% confidence range across the period.
Induction success was 65% for the breathing protocols and 35% for the action protocols. Assessment of performance showed that the 41% average 95% confidence range for the breathing protocols were not significantly difference from the 29% range for the action protocols. Consistency was best in the breathing methods, with a 95% confidence range of 142% (for RR-interval) and 218% (for SP level) compared with 440% and 748% respectively for the other protocols.
Breathing protocols are most successful at inducing regular changes in RR-intervals and SP levels. Even though the performance of the protocols was very repeatable, the changes of RR-interval and SP levels, even for short term changes, were much less repeatable. Indicating that other factors significantly influence these changes.
Bowers EJ, Murray A. Success of different techniques to induce regular changes in RR-intervals and systolic blood pressure levels. Computers in Cardiology 2003; 30: 37-40.
Ms Emma Bowers, Freeman Unit, Newcastle upon Tyne. Tel: +44 (0)191-223-1370.
Regional Medical Physics Department, Newcastle General Hospital, Newcastle upon Tyne, NE4 6BE, UK.
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