This study assessed the interaction between cardiac beat-to-beat interval changes and systolic pressure (SP) changes. Twenty subjects breathed regularly following displayed breathing signals at 4, 6, 8, 10, 12 and 14 breaths per minute, each for 5 minutes. ECG, non-invasive blood pressure (Finapres) and respiration waveforms were recorded. Time offsets between the cyclic patterns of RR-interval and SP changes were calculated. Displayed breathing signals were well followed; the mean correlation between displayed and recorded breathing signals ranged from 0.72 to 0.86. The time offset between RR-interval peaks and subsequent SP troughs decreased with increasing respiration rate, 3.8 +/- 1.7 s, 3.5 +/- 0.7 s, 3.1 +/- 0.6 s, 2.6 +/- 0.4 s, 2.3 +/- 0.4 s and 2.0 +/- 0.4 s mean +/- SD at 4,6,8,10,12 and 14 breaths per minute respectively. The relationship between mean time offset and frequency was significant (p < 0.001), with a 95 % prediction interval of +/-0.24 s. Published data showed no relationship between time offset and frequency, with a 95% prediction interval of +/- 2.8 s. However, when the offset definition proposed in this research was applied to these data, a significant relationship (p < 0.01) was evident, with a 95% prediction interval of +/-1.5 s. In conclusion, apparently contradictory previous findings achieve good consensus when a standardized method for presenting results is applied. A delay exists between RR-interval and blood pressure changes, and this delay varies with breathing frequency.
