Instrumentation & Measurement Magazine 24-2 - 35

Table 3 - Algorithm Features
Actigraphy Features

Amount

Acceleration in X,Y,Z direction, 30 second zero crossing acceleration count, weighted sums actigraphy
accelerations

5

BCG Features
HRV, HR, RR, B2B, SV, SDNN, SDNN detrended, RMSSD, RMSSDLN, RMSSDLN detrended, RMSSD
detrended, LF & HF absolute units, LF & HF normalized units, LF & HF relative values, LF/HF ratio

18

Environment Features
30 sec average of light (lux), ambient temp (Celsius), probe temp (Celsius), ambient humidity (%relative
humidity), probe humidity (%relative humidity), sound (dB)
Total

6
29

Table 4 - Accuracy of classified sleep stages
Sensitivity

Specificity

Accuracy

Recall

Precision

F1 score

Kappa

Light and deep

0.45

0.72

0.49

0.45

0.41

0.50

0.20

Sleep and wake

0.48

0.83

0.70

0.48

0.62

0.54

0.32

came from wrist worn IMU. The BCG features obtained from
the bed sensor data were chosen based on Radha et al. [22]
with the most impactful features coming directly from the
bed sensor device. Environment features were obtained from
each device output.
Fig. 4a and Fig. 4b show the sleep stages for the sleep/
wake and wake/light sleep/deep sleep classifications, respectively. Table 4 shows the accuracy obtained was about
70% for identified instances of sleep and wake but around
50% for identifying the sleep stages. The model can distinguish between instances of sleep and wake but cannot
classify each sleep stage as accurately. Movement or elevated
cardiac parameters exist during the wake stage so it is easier

to identify the difference between each stage, as seen by the
higher precision, and be consistent with sleep and wake
identification. In addition, the specificity (correct sleeps identified) is higher in both cases as there are more sleep instances
since a participant was sleeping and inactive during a nightly
sleep cycle. Finally, the Cohen Kappa showed slight and fair
agreement for the light/deep sleep and sleep/wake models,
respectively.

Limitations of Work and Implications for Future
Research
As the above demonstration example was a pilot study, limitations must be considered with the implications for future work

Fig. 4. (a) The sleep and wake stages between predicted and PSG. (b) The wake, light, and deep sleep stages between predicted and PSG
April 2021	

IEEE Instrumentation & Measurement Magazine	35



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