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+<!--#set var="TITLE" value="Apnea-ECG Database Annotations"-->
+<!--#include virtual="/head.shtml"-->
+
+
+<p>
+Two sets of annotations are supplied with the data for the
+<a href="/challenge/2000/">Computers in Cardiology Challenge
+2000</a>.  These can be identified by the file name suffixes <tt>.apn</tt>
+and <tt>.qrs</tt>.
+
+<p>
+The <tt>.apn</tt> files contain apnea annotations.  These are currently
+available for the 35 records in the learning set only; those for the test set
+will be posted here after the conclusion of the Challenge in September.  (To
+view these annotations, use <a
+href="/physiotools/wag/rdann-1.htm"><tt>rdann</tt></a> to convert the binary
+annotation files into text.  If you have not used <tt>rdann</tt> previously,
+see the detailed instructions <a href="#rdann-notes">below.</a>) These
+annotations have been prepared on the basis of expert visual review of
+simultaneously recorded respiration and oxygen saturation signals.  These
+additional signals can be studied for 8 records (a01er - a04er, b01er, and
+c01er - c03er; these contain the same ECG data as a01 - a04, b01, and c01 -
+c03, respectively).
+
+<p>
+When these files were first posted here, the following (incorrect) description
+of the <tt>.apn</tt> annotation files was also posted:
+
+<blockquote>
+In these files, an "A" annotation indicates that apnea occurs during the
+<em>following</em> one-minute interval, and an "N" annotation indicates that
+there is no apnea during the following one-minute interval.
+</blockquote>
+
+<p>
+Following is a corrected description:
+
+<blockquote>
+In each of these files, the first annotation is placed at 0 seconds and is
+associated with the following one-minute interval (i.e., 0-59.99 seconds
+elapsed time from the beginning of the record), the second annotation is placed
+at 60 seconds and is associated with the next one-minute interval (60-119.99
+seconds), etc.  Each "A" annotation indicates that apnea was in progress <em>at
+the beginning of the associated minute</em>; each "N" annotation indicates that
+apnea was not in progress at the beginning of the associated minute.  The
+diagram below may help to clarify this:
+
+<pre>
+|       |       |       |       |       |       |       |       |
+        ****************              ********     ********
+N       A       A       N       N       A       N       A       N
+</pre>
+
+In this diagram, elapsed time is represented by distance from the left edge.
+The '*'s mark apneic periods, the '|'s mark the times of the <tt>.apn</tt>
+annotations (0, 60, 120, ... seconds), and the "N"s and "A"s are the "no apnea"
+and "apnea" annotations.
+</blockquote>
+
+<p>
+The <tt>.qrs</tt> files were created using <a
+href="/physiotools/wag/sqrs-1.htm"><tt>sqrs125</tt></a>, initially with its
+default threshold (250).  In these files, all detected beats (including any
+abnormal beats that were detected) are marked with "N" annotations, and
+QRS-like artifacts are marked with "|" annotations.  Based on visual review of
+the heart rate time series (using <a
+href="/physiotools/wag/hrfft-1.htm"><tt>hrplot</tt></a>), and review of
+selected portions of the original ECGs and annotations (using <a
+href="/physiotools/wag/wave-1.htm">WAVE</a>), <tt>sqrs125</tt> was run again
+using its <tt>-m</tt> option to select lower thresholds on some recordings (in
+some cases, more than once) to obtain better detection of low-amplitude QRS
+complexes.  In no case were the annotations hand-edited.  Only small numbers of
+annotations were inspected in each recording to determine if the threshold had
+been set appropriately.  If you wish to experiment further with
+<tt>sqrs125</tt> or with your own QRS detector, it may be helpful to know
+exactly how the <tt>.qrs</tt> files provided here were made, so here are the
+commands that are needed to do so:
+
+<pre>
+sqrs125 -r a01
+sqrs125 -r a02 -m 125
+sqrs125 -r a03
+sqrs125 -r a04
+sqrs125 -r a05
+sqrs125 -r a06 -m 125
+sqrs125 -r a07
+sqrs125 -r a08
+sqrs125 -r a09
+sqrs125 -r a10
+sqrs125 -r a11
+sqrs125 -r a12 -m 125
+sqrs125 -r a13
+sqrs125 -r a14
+sqrs125 -r a15
+sqrs125 -r a16
+sqrs125 -r a17 -m 100
+sqrs125 -r a18
+sqrs125 -r a19
+sqrs125 -r a20 -m 125
+sqrs125 -r b01
+sqrs125 -r b02 -m 125
+sqrs125 -r b03 -m 125
+sqrs125 -r b04 -m 75
+sqrs125 -r b05 -m 125
+sqrs125 -r b06
+sqrs125 -r b07
+sqrs125 -r b08
+sqrs125 -r b09
+sqrs125 -r b10
+sqrs125 -r c01 -m 125
+sqrs125 -r c02
+sqrs125 -r c03
+sqrs125 -r c04 -m 125
+sqrs125 -r c05 -m 125
+sqrs125 -r c06 -m 125
+sqrs125 -r c07 -m 100
+sqrs125 -r c08 -m 100
+sqrs125 -r c09
+sqrs125 -r c10
+sqrs125 -r x01
+sqrs125 -r x02
+sqrs125 -r x03
+sqrs125 -r x04
+sqrs125 -r x05
+sqrs125 -r x06
+sqrs125 -r x07
+sqrs125 -r x08
+sqrs125 -r x09
+sqrs125 -r x10
+sqrs125 -r x11
+sqrs125 -r x12
+sqrs125 -r x13
+sqrs125 -r x14 -m 125
+sqrs125 -r x15 -m 125
+sqrs125 -r x16
+sqrs125 -r x17 -m 50
+sqrs125 -r x18
+sqrs125 -r x19
+sqrs125 -r x20
+sqrs125 -r x21
+sqrs125 -r x22
+sqrs125 -r x23
+sqrs125 -r x24
+sqrs125 -r x25
+sqrs125 -r x26
+sqrs125 -r x27
+sqrs125 -r x28
+sqrs125 -r x29 -m 125
+sqrs125 -r x30
+sqrs125 -r x31
+sqrs125 -r x32
+sqrs125 -r x33 -m 125
+sqrs125 -r x34 -m 125
+sqrs125 -r x35
+</pre>
+
+<a name="rdann-notes"><h2>How to use <tt>rdann</tt></h2></a>
+
+<p>
+<strong>Install <tt>rdann</tt>:</strong>
+
+<p>
+If you haven't already downloaded and installed <tt>rdann</tt>, do so now.
+Search for <tt>rdann</tt> (type <tt>rdann</tt> into the text box above
+the <em>Search</em> button in the left margin of this page, then click
+on <em>Search</em>), and you will find the C-language source as well
+as a UNIX-style manual page that describes <tt>rdann</tt>'s options
+in more detail than below.  All versions of <tt>rdann</tt> are compiled from
+the same source, so you can create a version for your operating system,
+provided that you have a C compiler.  If you do this, you will also need to
+download and compile the sources for the
+<a href="/physiotools/wfdb.shtml">WFDB library</a> used by <tt>rdann</tt>.
+<a href="/physiotools/binaries">Binaries</a> (executable versions of the
+program) for several popular operating systems can also be downloaded.  Note
+that <tt>rdann</tt> is a text-mode application;  users of MS-Windows can run
+the MS-DOS version of <tt>rdann</tt> in a DOS window.
+
+<p>
+<strong>Locate the files you need:</strong>
+
+<p>
+Each of the data files has a <em>record name</em> (the first part of the
+file name, before the '.') and a suffix (the second part of the file name,
+following the '.').  For example, the file <tt>a19.apn</tt> has the record
+name <tt>a19</tt> and the suffix <tt>apn</tt>.
+
+<p>
+Files with <tt>qrs</tt> or <tt>apn</tt> suffixes are binary annotation files.
+For these files, the suffix is the <em>annotator name</em>.  Files with the
+suffix <tt>hea</tt> are (text) header files containing information about the
+format of the related files, and those with the suffix <tt>dat</tt> are binary
+signal files (containing digitized samples of the ECG and other signals).
+
+<p>
+In order to read an annotation file successfully, you will need to download
+both the annotation file itself and the associated header file.  For example,
+to read <tt>a19.apn</tt>, download <tt>a19.apn</tt> and <tt>a19.hea</tt>.
+(The Linux version of <tt>rdann</tt> can act as an HTTP client and can read the
+files directly from the PhysioNet server without the need to store them
+locally.  If you have compiled your own version of the WFDB library with
+<a href="/physiotools/wpg/wpg_43.htm">NETFILES</a> support, your version
+of <tt>rdann</tt> will also have this capability.)
+
+<p>
+<strong>Use <tt>rdann</tt> to convert binary annotations to text:</strong>
+
+<p>
+Once you know the <em>record name</em> and the <em>annotator name</em>, you can
+use <tt>rdann</tt> to read the file.  For example, to read <tt>a19.apn</tt>,
+use the command
+
+<pre>
+     rdann -r a19 -a apn -f 0
+</pre>
+
+<p>
+This command will produce output on the screen that begins:
+
+<pre>
+    0:00.000        0     N    0    0    0
+    1:00.000     6000     A    0    0    0
+    2:00.000    12000     A    0    0    0
+    3:00.000    18000     A    0    0    0
+    4:00.000    24000     A    0    0    0
+    5:00.000    30000     A    0    0    0
+    6:00.000    36000     A    0    0    0
+    7:00.000    42000     N    0    0    0
+    8:00.000    48000     N    0    0    0
+    9:00.000    54000     A    0    0    0
+   10:00.000    60000     A    0    0    0
+</pre>
+
+(The '-f 0' option was not required by the version of rdann that was
+available when this page was written.  If omitted, the first annotation,
+at 0:00.000, will not appear in the output.)
+
+<p>
+To capture the output of <tt>rdann</tt> in a file, redirect it using a command
+such as:
+
+<pre>
+     rdann -r a19 -a apn -f 0 &gt;<font color=blue><em>textfile</em></font>
+</pre>
+
+In this command, replace <font color=blue><tt><em>textfile</em></tt></font>
+with any desired file name.  This method works under MS-DOS/Windows
+as well as under all versions of UNIX.
+
+<p>
+Each line of <tt>rdann</tt>'s output corresponds to one annotation.  The first
+two columns indicate the elapsed time (i.e., the interval) from the beginning
+of the record to the sample marked by the annotation. (Column 1 gives this in
+hours, minutes, and seconds, and column 2 gives the same information in sample
+intervals.  In these records, one sample interval equals 10 milliseconds.)  The
+third column contains a mnemonic code for the annotation type.  As noted above,
+in the <tt>apn</tt> files, these codes are <tt>A</tt> for "apnea" and
+<tt>N</tt> for "no apnea".  In the <tt>qrs</tt> files, the codes are <tt>N</tt>
+for a QRS complex and <tt>|</tt> for a QRS-like artifact.  In these annotation
+files, the remaining columns can be ignored.
+
+<p>
+The sample output shown above can therefore be interpreted thus: during the
+first minute (beginning at 0:00.000, or sample number 0) there is no apnea
+(<tt>N</tt>); during each of the next several one-minute periods (beginning at
+1:00.000, 2:00.000, 3:00.000, ...), there is apnea (<tt>A</tt>).
+
+<!--#include virtual="/footer.shtml"-->
+</body>
+</html>