ECG Compression - ECG Acquisition and Automated Remote Processing - page 109

Fig. 5.7 Data plot before compression and after decompression using mit-db record

DDF parameter estimation for ptb-db (In 10 -3 ) Table 5.4

RR i QRS dur QT int P dur

Mean SD Mean SD Mean SD Mean SD

12.3 15.59 32 41.11 22.12 32.1 11.21 47

P amp S amp T amp R amp

Mean SD Mean SD Mean SD Mean SD

28.21 25.83 41.38 12.14 5.87 5.21 10.40 9.30

5.3.4 Compression Performance Enhancement by Adaptive
Down-Sampling of ECG Array

In the next stage, the effort was to enhance the CR by a down-sampling process of
the raw dataset. However, it is also to ensure that the clinical signatures are not
affected. To achieve this, the down-sampling is continued and after the first stage
(i.e., pre-processing), the extrema (maximum and minimum) of the down-sampled
array are checked with the corresponding ones of the original array. Since ECG
signal with 1-kHz frequency was used for the validation, 2-3 stages of down-
sampling could be achieved using the criteria. For proper reconstruction, the
down-sampling factor is to be known to the decoding device, since the recon-
structed data need to be generated at 1 kHz. To minimize the quantization error
during the normalization procedure, the length of the each packet was (initially, it
was 1000, with 1 original sample and 999 first difference elements) also adjusted.
Hence, the down-sampling is 'adaptive' in nature.