Can we have more technical details, please?

Of course.

To the right is a snapshot of the monitor screen.  The green waveform and number is heart rate, measured via the adhesive pads affixed to their torsos.  (This particular screen shot is Anna's, but Evelyn's looks basically the same).  At this particular moment, it shows a heart rate of 149.  (Duh.)  The smaller green number further to the left says "PVC," which in this instance stands for "premature ventricular contraction," which for our purposes here is equivalent to a coronary hiccup.  The current count is zero, but I've seen some on Anna's monitor.  They're relatively benign, unless they're not.  We've not been told that the occasional PVC on Anna's monitor is any kind of indication of a problem, so we're not worried about it.  Note that there is a number for "Pulse" in blue.  That's because it's measured by another monitor entirely.  The green data comes from one probe, the blue from a second, and the white from a third.  So heart rate and PVCs are monitored by the green probe, but pulse (which a medically trained individual can tell you is merely a symptom of heart rate and is not the heart rate itself) is measured by the blue probe.

The blue pulse data, blue waveform and large blue number are the data from the oximeter.  The waveform shows the pulse as it goes through the right foot.  As you can see, the heart rate and pulse correspond in a general sense.  (The disparity between the measured heart rate of 149 and the pulse of 148 is probably a result of the fact that the heart rate is dynamic and at any given moment the number is changing, and then being multiplied to give a per minute figure.) The large blue number is the oxygen saturation.  At this particular moment, Anna is at 100% saturation, which is as good as it gets.  No one's worried if it occasionally drops below 90%.  If it's regularly low, or if it suddenly drops into the low 80s or 70s, there might be a problem to be solved.  At the moment this photo was taken, Anna was steady as a rock at 100%.  During the same timeframe, Evelyn was fluctuating around 97%.

The white waveform and number is the respiration rate, measured as respirations per minute.  I've happened to have caught Anna during a particularly steady period of breathing while she was asleep.  This waveform is the most variable of all; it could be all over the map if the baby is awake.  There are periods of a few seconds in which short, sharp, ineffective breaths are taken; the nurses call this "zipper breathing" (because of the shape of the waveform) and it's nothing to be particularly concerned about at this gestational age.  This is the waveform that would be flat during an apnea event.  An apnea of longer than 20 seconds is met with some kind of intervention, such as a pat on the back, a poke in the ribs, or tickling the feet.  Recurring apneas can be treated with medication -- in this case, caffeine.  I'm not kidding.  They administer caffeine because it is a benign central nervous system stimulant.  They haven't administered any caffeine to the girls yet, but it amuses me to think they would be hooked on a drug their father had to wait 'til college to discover.