# Hospital Heart Rate Monitors **URL:** \ **Category:** Factual Questions\ **Created:** [March 20, 2016, 4:35am UTC](https://boards.straightdope.com/t/hospital-heart-rate-monitors/749623 "2016-03-20T04:35:51Z")\ **Posts on this page:** 10\ **Page:** 1
**Author:** ![Deflagration](https://avatars.discourse-cdn.com/v4/letter/d/3ab097/32.png) [@Deflagration](https://boards.straightdope.com/u/Deflagration)\ **Post date:** [March 20, 2016, 4:35am UTC](https://boards.straightdope.com/t/hospital-heart-rate-monitors/749623/1 "2016-03-20T04:35:51Z")
Clip on heart rate monitors appear to be conventionally attached to the index finger. Since the thumb has a feelable pulse (the reason you never check if someone is dead with your thumb on the carotid). Why is the thumb not a preferential digit for monitoring? ---
**Author:** ![gotpasswords](https://avatars.discourse-cdn.com/v4/letter/g/c57346/32.png) [@gotpasswords](https://boards.straightdope.com/u/gotpasswords)\ **Post date:** [March 20, 2016, 4:54am UTC](https://boards.straightdope.com/t/hospital-heart-rate-monitors/749623/2 "2016-03-20T04:54:44Z")
It’s probably too thick, or at the least, there’s no need. The “ET finger” pulse oximeter needs to see through the finger as its calculating the pulse and oxygen level optically with infrared light. ---
**Author:** ![Deflagration](https://avatars.discourse-cdn.com/v4/letter/d/3ab097/32.png) [@Deflagration](https://boards.straightdope.com/u/Deflagration)\ **Post date:** [March 20, 2016, 5:35am UTC](https://boards.straightdope.com/t/hospital-heart-rate-monitors/749623/3 "2016-03-20T05:35:10Z")
I was aware that it used Infra Red light as a sensor but not that it was measuring oxygen levels too. Thanks for fighting my ignorance. ---
**Author:** ![elbows](https://avatars.discourse-cdn.com/v4/letter/e/b3f665/32.png) [@elbows](https://boards.straightdope.com/u/elbows)\ **Post date:** [March 20, 2016, 12:28pm UTC](https://boards.straightdope.com/t/hospital-heart-rate-monitors/749623/4 "2016-03-20T12:28:41Z")
I always thought it was ONLY measuring the oxygen level! Not also the pulse, I thought that was a different thing altogether. Thanks for setting me straight! ---
**Author:** ![nearwildheaven](https://avatars.discourse-cdn.com/v4/letter/n/90db22/32.png) [@nearwildheaven](https://boards.straightdope.com/u/nearwildheaven)\ **Post date:** [March 20, 2016, 6:15pm UTC](https://boards.straightdope.com/t/hospital-heart-rate-monitors/749623/5 "2016-03-20T18:15:35Z")
It’s called a pulse-ox because it measures both things. I’m guessing that it’s placed on the index finger because that’s the most comfortable place and also the easiest to keep it on. ---
**Author:** ![audiobottle](https://avatars.discourse-cdn.com/v4/letter/a/bc8723/32.png) [@audiobottle](https://boards.straightdope.com/u/audiobottle)\ **Post date:** [March 21, 2016, 5:33am UTC](https://boards.straightdope.com/t/hospital-heart-rate-monitors/749623/6 "2016-03-21T05:33:26Z")
The pulse-ox monitors work by shining infrared light through the finger. The heart rate monitoring is more of an added bonus, but since it’s not always a very accurate measurement (varies based on fingernail polish, thickness of nail, placement, etc). If the heart rate, or more importantly the heart rhythm, is desired, you need electrodes on the chest. As an aside, there are sticker ones that are more useful for longer term, or continuous monitoring. ---
**Author:** ![outlierrn](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/outlierrn/32/3005_2.png) [@outlierrn](https://boards.straightdope.com/u/outlierrn)\ **Post date:** [March 21, 2016, 7:15am UTC](https://boards.straightdope.com/t/hospital-heart-rate-monitors/749623/7 "2016-03-21T07:15:00Z")
You can use them any place that’s the right thickness, toes, earlobes, I’ll go sideways on a smaller finger if the patient has elaborate nails. ---
**Author:** ![SeaDragonTattoo](https://avatars.discourse-cdn.com/v4/letter/s/df705f/32.png) [@SeaDragonTattoo](https://boards.straightdope.com/u/SeaDragonTattoo)\ **Post date:** [March 21, 2016, 8:03am UTC](https://boards.straightdope.com/t/hospital-heart-rate-monitors/749623/8 "2016-03-21T08:03:26Z")
It would work just fine on the thumb, but patients need their thumb to do stuff. Any other finger can be held away from what you’re doing (like picking up a cup) but you kinda need your thumb. ---
**Author:** ![Squink](https://avatars.discourse-cdn.com/v4/letter/s/b5e925/32.png) [@Squink](https://boards.straightdope.com/u/Squink)\ **Post date:** [March 21, 2016, 3:52pm UTC](https://boards.straightdope.com/t/hospital-heart-rate-monitors/749623/9 "2016-03-21T15:52:35Z")
[Pulse oximeters](https://en.wikipedia.org/wiki/Pulse_oximetry#Function) use two LEDs of different wavelengths to measure oxygen saturation/pulse. The signal is light that passes through the tissue. To make it work on thicker tissue, you need more powerful LEDs. You can buy these things now for home use for about $12US. They’re handy when riding stationary bikes, and also nice to check out the efficacy of your breathing exercises. ---
**Author:** ![Tim\_T-Bonham.net](https://avatars.discourse-cdn.com/v4/letter/t/46a35a/32.png) [@Tim\_T-Bonham.net](https://boards.straightdope.com/u/Tim_T-Bonham.net)\ **Post date:** [March 21, 2016, 10:16pm UTC](https://boards.straightdope.com/t/hospital-heart-rate-monitors/749623/10 "2016-03-21T22:16:42Z")
SeaDragonTattoo identified the main reason – opposable thumbs are needed. A secondary reason is that thumbs tend to vary in size somewhat more than fingers, so it’s harder to get the sensor to fit accurately.