Baroreflex sensitivity is becoming an important clinical measurement. Nevertheless there is no recommend standard measurement protocol. This study assessed the ability of eight protocols to induce regular changes in cardiac beat-to-beat interval and systolic pressure (SP), and the effect each protocol had on baroreflex sensitivity (BRS).
Twelve subjects had changes in cardiac beat-to-beat intervals and SP levels induced at 8 times a minute by following 8 different protocols, each for 3 min. These comprised breathing in a supine and standing posture, breathing through a resistance, breathing into a closed orifice (the breathing protocols), and performing handgrip exercises, being rocked, having legs raised and lowered, and being presented with mental arithmetic questions (the non-breathing protocols). Induction success of each protocol was determined by the percentage of cardiac beat-to-beat interval and SP level signals with a peak at 8 times per minute in their frequency spectra. The consistency of the induced changes was measured by a signal-to-noise ratio (SNR). BRS was calculated from the frequency spectra.
The induction success was 85% for breathing and 31% for non-breathing protocols. The consistency of cardiac beat-to-beat interval changes was highest with supine breathing (SNR = 1.6 ± 0.3) and resistance breathing (SNR = 1.5 ± 0.5) protocols. The consistency of SP level changes was highest with resistance breathing (SNR = 1.0 ± 0.3) and breathing into a closed orifice (SNR = 1.0 ± 0.5) protocols. BRS values in the supine breathing protocol (24 ± 10 ms mmHg(-1)) and the handgrip protocol (32 ± 3 ms mmHg(-1)) were significantly greater (p < 0.05) than for standing breathing (11 ± 5 ms mmHg(-1)), resistance breathing (17 ± 8 ms mmHg(-1)) or breathing into a closed orifice (12 ± 5 ms mmHg(-1)) protocols.
Different protocols have different induction successes and degrees of effectiveness in inducing cardiac beat-to-beat and SP level changes. BRS is affected by the induction protocol used, highlighting the need for a standard measurement protocol.
Bowers EJ, Murray A. Effects on baroreflex sensitivity measurements when different protocols are used to induce regular changes in beat-to-beat intervals and systolic pressure. Physiol Meas 2004; 25: 523-38.
Ms Emma Bowers, Freeman Unit, Newcastle upon Tyne. Tel: +44 (0)191-223-6161.
Regional Medical Physics Department, Freeman Hospital, Newcastle upon Tyne, NE7 7DN, UK.
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