Table 3.

All analysed heartbeats were classified by cycle length in 4 similar sized groups. Second and third quartile group show best accordance in mean absolute difference between BCG and ECG and the resulting QI. The group with low or high heart rate show a poorer agreement. By filtering heartbeats with lower signal quality, the accordance could be improved especially in the quartiles with low and high cycle length compared to the two middle quartiles with normal cycle length.

Quartiles by cycle length
Cycle length [ms]	1005–2000	895–1000	800–890	330–795
Heartbeats [n]	92204	91859	89480	88497
ECG [ms]	1191 ± 238	945 ± 31	846 ± 27	699 ± 75
BCG [ms]	1115 ± 215	933 ± 105	835 ± 97	739 ± 140
Difference ECG – BCG [ms]	76 ± 236	11 ± 100	11 ± 94	−40 ± 148
Quality Index [au]	0.56 ± 0.32	0.63 ± 0.34	0.67 ± 0.35	0.57 ± 0.35
Quality Index≥0.4
Heartbeats [n]	54730	63728	66041	50868
Percentage [%]	59	69	74	58
ECG [ms]	1172 ± 220	945 ± 31	846 ± 27	714 ± 69
BCG [ms]	1155 ± 218	940 ± 55	842 ± 50	723 ± 91
Difference ECG – BCG [ms]	16 ± 106	4 ± 45	4 ± 43	−9 ± 82
Quality Index [au]	0.74 ± 0.3	0.78 ± 0.32	0.8 ± 0.32	0.78 ± 0.34