Influence of respiratory rate on the variability of blood volume pulse characteristics.

Photoplethysmogram (PPG) measures have been proven useful for the quantification of sympathetic reactivity and continuous monitoring of vascular reactivity. This study was designed to delineate the influence of respiratory rate on the variability of various PPG characteristics in time and frequency domains. PPG, electrocardiogram (ECG) and respiration were simultaneously recorded for 2 min from eight healthy volunteers during paced respiration of 6, 12 and 18 cycles min(-1). The PPG characteristics such as peak-to-peak interval (PPI), systolic peak amplitude, slope, T(crest), T(decay) and pulse transit time (PTT) were computed for every pulse. In time domain, the mean of amplitude, slope and T(crest) were not significantly different amongst three different respiratory rates. However, the mean of T(decay), PPI and PTT were significantly increased (p < 0.05, p < 0.05 and p < 0.01, respectively) during respiration of 6 cycles min(-1) compared to 12 cycles min(-1). The maximal spectral powers of the variability of all PPG measures were centred on the respiratory frequency in frequency domain. In conclusion, the results that the amplitude and slope in time domain are not altered by the respiratory frequency suggest their application in faithful assessment of cardiovascular reactivity. As the variability of PPI, T(decay) and PTT are altered by the slow respiration, the influence of respiration on these time derivatives should not be ignored during interpretation of vascular reactivity.