[ < ] [ > ]   [ << ] [ Up ] [ >> ]         [Top] [Contents] [Index] [ ? ]

Answers to Selected Exercises

3.

280 adu = (280 adu - (-300 adu)) / 10 adu/mmHg = 58 mmHg.

4.

120 mmHg = 120 mmHg * 10 adu/mmHg + (- 300 adu) = 900 adu.

5.

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.

6.

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.

7.

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.

8.

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

[ < ] [ > ]   [ << ] [ Up ] [ >> ]

George B. Moody (george@mit.edu)