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280 adu = (280 adu - (-300 adu)) / 10 adu/mmHg = 58 mmHg.
120 mmHg = 120 mmHg * 10 adu/mmHg + (- 300 adu) = 900 adu.
The range of sample values is
-2047 to +2047 adu, or -174.7 to +234.7 mmHg. The special value -2048
adu, if found in the input, is replaced with WFDB_INVALID_SAMPLE
(-32768) to indicate missing or out-of-range samples.
We don't know how big `signal.dat' is, because we don't know how
many other signals are multiplexed with the BP
signal. If there
are no others, `signal.dat' is 1,500,000 bytes (nsamp
* 1.5
bytes/sample). One-third of the space occupied by `signal.dat' could be
saved if it were converted to format 8. The maximum slew rate
representable in format 8 is 127 adu/sample interval * 100 sample
intervals/sec / 10 adu/mmHg = 1270 mmHg/sec.
One way to save a little space is to resample the signal at 120 Hz, and then change to format 8 (maximum slew rate = 1524 mmHg/sec). This can be done using `xform'; it reduces the storage requirement by one-fifth.
If you have installed PhysioToolkit's plt
package, a simple
solution is to write the sample numbers and values on the standard
output in two-column ASCII format. The plotting is then performed by
the pipeline:
your-program | plt 0 1 |
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George B. Moody (george@mit.edu)