Kardia reading and Fitbit reading

[Slattery]

My Kardia BPM reads 150, while my Fitbit reading reads 97. The Kardia tells me I am in possible AFIB. I had no idea that he Fitbit could give me such a wrong reading!! Anyone else experience this?

[Hidden]

Fitbit is only a tracker. It is not medically approved - nor does it advertised to be. It is not a medical device, it has not undergone the exhaustive testing that Kardia has! The readings with Fitbit are sensitive to how and where you wear it. Says all this in the box.

[Mercurius]

Cardia measures your heart rate, fitbit measures your peripheral pulse rate. Under pathological conditions the two data might be different. The difefrence is called "pulse deficit". This means, that if you have pulse defficit, then not every cardiac contraction was effective. Some contractions not pumped out blood to the perphery.

[momist]

The Fitbit measures your pulse by shining an LED light at your skin and measuring the amount of redness in the reflected light. This varies with your blood pressure, which varies rhythmically with your pulse. In order to measure in this way, the result has to be 'filtered' to eliminate variations due to movement of the device on your wrist, variations in BP due to exercise, temperature, etc. I have no doubt that the filtering includes limiting the range of possible pulse rates to within normal limits, 40 - 130 bpm?

Although useful to runners and fitness practitioners, this is not a medical indication of what is actually going on.

[Mercurius in reply to momist]

Exatly. The device is for sport and not for medical use. The problem when somebody is let say a runner with arrihthymias. During a cardio training she/he has target heart rate zone. Easily could happen that the heart rate is in the zone, but the fitbit pulse rate detector underestimates it. The athlet will try to increase the effort (based on the fitbit data) altough rather she/he should interrupt the workout.

An other problem of the fit bit is the inaccuracy at high heart rate. For details worth to search the internet for fitbit lawsuit case.

[Slattery]

Thanks you all for this information, very helpful

[akenclark]

I have read this with interest. I recently had an incident when I felt odd after climbing the stairs. My only device is a Choicemmed pulse oximeter which I pinched onto the end of my finger. As I sat quietly watching it the reading fluctuations bounced between 85 and 140. They rose and fell several times, gradually converging to 75. I wish I understood what I was seeing. Clearly it didn't count off 140 beats in a full minute. So it somehow projects a heartbeat rate from a smaller time sample...or maybe it measures the time elapsed for a certain number of beats???

[momist]

@akenclark: I have just been reading the Choicemmed web site about this, as I had not heard of that device. It looks very similar to the ones commonly in use at hospitals, for blood oxygen saturation. I assume that the pulse rate is measured in a similar way to the Fitbit, using the light that shines through your finger to measure the redness of the capillaries and how that is varying regularly with your heart beat. The problem with AF is that the heart is beating in a very irregular fashion, and that some of the beats are so close to the most recent one that the heart chambers have not filled correctly and therefore the beat has not resulted in pumping any blood. Those beats will be missed by any device counting this way. Also, the volume of blood flow is much reduced during AF and therefore potentially also lowering the blood oxygen levels (causing the weariness, breathlessness and dizziness) . Your pulse oxymeter might have revealed the lower oxygen level, if you were in AF. However, sitting quietly would raise that again due to lack of oxygen requirement?