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2.3.3 MIMIC II waveform records

All MIMIC II waveforms are stored in WFDB format. Table 2.3 summarizes the types of files you will find for the MIMIC II waveform database.

The records vary in length; some are several weeks in duration. It is common for the signal sources to be interrupted or changed occasionally during recordings of such a long duration. In a typical waveform database, you will find a directory layout including several record names or ``cases''. All files associated with each record are gathered in a sub-directory named after the record. For example, the files associated with record a40001 are all located within the directory named a40001.

Table 2.4: WFDB file types
File type Extension Description
Header .hea Contain signal file names and attributes in plain text format.
Signal .dat Contain signals binary data.
Annotations -dependent, e.g. ``.al'' for alarms, ``.wqrs'' for ECG beat annotations Contain signal custom annotations in binary format
Calibration .cal Contain signal calibration specifications.

Table 2.4 presents some useful WFDB commands to navigate through the waveform records. In a typical WFDB database record, a header file specifies the names of the associated signal files and their attributes, briefly:

Figure 2.17, shows the output of the ``wfdbdesc'' command, which outputs a human-readable description of a waveform record.

Table 2.5: Useful WFDB commands
Command Description
wfdbdesc Reads specifications for the signals described in the header file for record.
rdsamp Reads signal files for the specified record and writes the samples as decimal numbers on the standard output. Each line of output contains the sample number and samples from each signal, beginning with channel 0, separated by tabs.
wave Can be used to view the specified WFDB record or records on any display controlled by an X11 server. It includes facilities for interactive annotation editing. The keyboard and mouse are used to control the display interactively

Figure 2.17: Sample output for wfdbdesc
\begin{verbatim}Starting time: [16:24:28.8... 0
Baseline: -100
Checksum: -4501\end{verbatim}

If you want to display the signal contents of a particular record, you can use the ``rdsamp'' command. Figure 2.18 shows the output of this program.

Figure 2.18: Sample output of rdsamp
\begin{verbatim}time II V ABP PAP
(sec) ...
0.176 -0.073 0.000 60.800 90.000\end{verbatim}

Another option is to use a visualization tool like WAVE, or ATM (, to display the contents of a particular waveform record. Figure 2.19 shows the display of a particular waveform record. Note that the signal processing algorithms can be run from this viewer.

Figure 2.19: Sample waveform record
Image waveform_record

next up previous contents
Next: 2.3.4 Alarms and Inops Up: 2.3 High resolution waveforms Previous: 2.3.2 The WFDB software   Contents
djscott 2011-09-07