Table 2.

Techniques for respiratory rate estimation.

Abbr.	Technique
	Frequency-based, ${\displaystyle E_{\mathrm{F}1,\dots ,5}}$
EF1	Fast Fourier transform spectral analysis (Karlen et al 2013).
EF2	Auto-regressive spectral analysis (Thayer et al 2002) using model order 8 (Orphanidou et al 2013).
EF3	Auto-regressive spectral analysis using the median spectrum for model orders 2–20 (Shah et al 2015).
EF4	Auto-regressive all-pole modelling (order 8), with the highest magnitude pole selected as the respiratory pole (Fleming et al 2008).
EF5	Auto-regressive all-pole modelling (order 8), with the lowest frequency pole selected as the respiratory pole (Fleming and Tarassenko 2006).
EF6	Find periodicity using the autocorrelation function (Schäfer and Kratky 2008).
EF7	Spectral analysis using the Welch periodogram (Lázaro Plaza 2015).
	Time-domain breath detection, ${\displaystyle E_{\mathrm{T}1,\dots ,5}}$
ET1	Breath detection by peak detection (Shah 2012).
ET2	Breath detection by positive gradient zero-crossing detection (Johansson 2003).
ET3	Breath detection by combined peak and trough detection (Fleming 2010): elimination of peaks less than the mean, and troughs greater than the mean; elimination of peaks (and troughs) within 0.5s of the previous peak (or trough); elimination of peaks (and troughs) which are immediately followed by a peak (or trough).
ET4	Breath detection using ‘Count-orig’ (Schäfer and Kratky 2008): detrend; detect peaks and troughs; define a threshold as 0.2 times the 75th percentile of peak values; ignore peaks with an amplitude below this threshold; identify valid breaths as consecutive peaks separated by only one trough with an amplitude less than zero.
ET5	Breath detection using ‘Count-adv’ (Schäfer and Kratky 2008): detrend; detect peaks and troughs; define a threshold as 0.3 times the 75th percentile of amplitude differences between consecutive extrema; eliminate the pair of extrema with the smallest amplitude difference if this is below the threshold; repeat until no more pairs can be eliminated; remaining peaks represent breaths.