Wind in the Trees. Four AM.

Walking the Important Road on a warm night I heard the silent night change.

A heavy sound started in the trees back west beyond Maplewood, whooshing along the south side of the road, passing me, and merging in the trees on both sides of the road toward home.

Far to the north, an owl hooted high in the trees.

The steady sound surrounded me for a time before it faded in the east like a train gone by.

A cold drop of water touched my hand.

The owl kept hooting. I don’t know why.

Playing with the CMS50E Pulse Oximeter

All devices are toys. So, I played.

Here is a picture of the kind of waveform I would suppose you want to see from this device.

OK pulse

Fine, fine.

Now, let’s start with the first thing that made no sense.

Starting at, say, 96% SPo2 and doing a breath-out-hold, the SPo2 level goes up! Ditto, for the whole duration of a big-breath-in, breath-hold. The device’s 30 second lag confuses things. You stop holding your breath and start breathing – the SPo2 level goes down! Well, it’s just then reporting on the old, breath-hold blood.

Big-breath-in hold is peculiar. The SPo2 level never really goes down, but the pulse rate can go from 60 to 80+. It appears that my body, if not yours, compensates for no air by simply beating the heart faster.

Which brings up the really wild thing that this device showed about my body.

Here’s the deal:

After racing around Lake Sacajawea late one night with Strom a couple months before going in to the service, I had some ice cream and hit the sack. Soon, my chest felt very uncomfortable. It was plain that my heart had stopped beating. This can be disconcerting to an 18 year old. I felt my pulse. Nothing. It lasted several seconds at least. Who knows. Time passes slowly when you think your heart’s gone south. Two lessons learned:

  1. Don’t eat ice cream before bed.
  2. If your heart stops, sit up.

Of course, I wasn’t about to tell anyone about it. In fact, I pretty much forgot about it – but did remember the two lessons.

Years later, Scott’s just born. Imani is at the hospital. I’m home and going to sleep. Maybe I had ice cream. Dumb, sure, but hey, the lessons may have slipped my mind under the circumstances. Anyway, guess what. Yeah. I sat up to fix the problem. Bit of a scare.

Years later, I hooked up a heart monitor on the chance of seeing some indication of what was going on. Nothing. Still have a textbook-clean, ECG from Physio in a drawer somewhere.

Now, here’s the other half of the deal:

Some time recently when going to sleep, I noticed a half feeling like the heart-stop thing. Not dramatic, but not normal. This has been going on for some time, but it had never really bubbled up to daytime notice.

So, what does this CMS50E pulse oximeter display? A graph of heartbeat action. And it beeps when it senses a peak – at beat time – matching wrist-pulse and general senses perfectly.

The other day, I was up at Mark M’s and got him to try the device. Maybe the device was bad. The SPo2 level didn’t drop below 94%, after all. But, on Mark, the device worked just dandy – the SPo2 number went down as one would expect, though delayed a few seconds.

So, now what?

I put the device on me and turned on heart beat beeping. Mark’s like: “What’s with that?!” The beeping could have been a random number generator. Not all the time. But some times. No logic to it, though I suspect that things even out as soon as I do something other than sit still. Anyway, I’d already seen it for hours the night before. Several seconds, no beat. 5 steady beats, miss a beat, 5 steady beats, miss a beat. Couple weak beats. Etc. Random. Weird.

So … interesting. I’ll take the device for a walk as soon as it appears that the “kidney stone” can take shaking. (Postscript: Yes, erratic all the way around Maplewood.)

Here’s a waveform without much flatlining:

Rough Pulse

And, that’s not the only oddity.

How to get a solid 99% SPo2 instead of a wimpy 97% or 98%? Just sit there bouncing a leg on the toes.


Speaking of toes. The device works on toes as well as fingers. That’s nice, since you can’t type with the device on a finger. Coding involved a lot of un-clip/clipping.

So, what about the code?

Another post, is what.

Contec Medical Systems CMS50E Pulse Oximeter

For obscure, work reasons I ordered a Contec Medical Systems CMS50E Pulse Oximeter from Amazon.

front view

back view

This device clips on a finger, toe, or whatever and reads how much oxygen is in your blood.

Let’s get to the bottom line:

This is a neat little gizmo.

The out-of-box is nice, starting with – really – a metal box. That is so retro!

box view

The UI is all done with 1 button. I’m impressed! Very easy to figure out and use. The OLED screen is laid out simple and clean. The options are simple and clean. No instructions are needed, though they are written in understandable, native-Chinese English.

The device’s UI flow is impeccable.

The whole thing is tightly designed and built. Hats off to whoever put the user-package together.

The PC programs are unremarkable, but they do work and are also simple and clean. There should be only one program – a subject I’ll take up in a later, technical posting.

Apparently, the device is sold to the sleep apnea market. You can clip it on your finger and record a night of Oxi percentage and heart rate at per-second intervals (no untethered waveform recording). The device alarms when the two values go out of ranges you set. The alarm is loud. This could be quite handy for some people wanting to stay alive. Given my own experience with Oxi levels at anywhere near alarming values, it’s hard to imagine someone not waking up on their own if the Oxi value is too low. Pulse monitoring might be nice. Sit up to get the heart ticking again. Anyway, what little I looked at in this whole area worked fine.

OK. What about the device?

I wanted it to measure a quick dip in oxygen level under certain, odd circumstances. Apparently, no … can … do. So, for work/research purposes, this device looks like a disappointment. We’ll see. Jury’s still out.


Here’s the deal: Maybe 20 years ago, the kids and I were prowling high up in Bel Square where a local hospital had a show-and-tell for the day. They had a finger clip thing that was supposed to read the oxygen in your blood – presumably an early pulse oximeter. I thought: “Cool. Let’s see what happens.” And held my breath for a couple minutes – until the nurse looked more than a little concerned. The number, if I recall, dropped to around 70%.

So that’s what I expected from this device, tempered by body age.

I tried to get the Oxi number down. I tried some more. I tried taking a deep breath and going 100 seconds. I tried breathing everything out and going 30+ seconds.

The results did not match memory.

It took a day of struggle to get the Oxi level below 94%. Turns out, there’s a 30 second lag from when the level is lowest in the mind, so to speak, to when it goes low on the device. And getting the level below 94 requires a breath-out hold for 40+ seconds rather than take-a-big-breath hold for a minute or two.

But that’s just me. Mark M. had no problem getting the Oxi level to drop.

That said, it’s become an interesting toy – raising all sorts of questions.

Let’s do another blog post about my “user” experience.