Dear all,
I want to detect stressful situations from a PPG (photoplethysmograph) signal in real time.
Could you please suggest me any method for doing this?
I've read that heart beat variability (HRV) should be measured, and it decreases for stressful situations. However, I haven't found any formula that states stress as a function of HRV.
Thank you very much in advance.
Best regards from Brazil,
Fernando
Hi Fernando,
there should be many articles which relate HRV to stress. A recent review is for example Article Stress and Heart Rate Variability: A Meta-Analysis and Revie...
In fact the interdependency is complex. Many factors affect HRV (first of all there are high interindividual differences) and "different" stress might result in different reactions. Very generally speaking, stress is assumed to lower parasympathetic activity. HRV parameters related to the high frequency content of tachograms (power in the high frequency range) are measures for the parasympathetic activity, so they might be an indicator (an probably this is most often exploited indicator). But even a lowered complexity in RR intervals might result from stress.
If you want to use the PPG you should have in mind that you are evaluating the pulse rate variability. There are many articles which compare pulse rate variability to heart rate variability. Obviously they are similar. However, particularly regarding the high frequency component there might be differences.
Independently from HRV or pulse rate variability, the amplitudes of PPG might carry useful information (at least within a person), because this amplitude depends on the vascular state which is modulated by stress (primarily sympathetic) as well.
Greetings, Sebastian
Hi Sebastian Zaunseder
Thank you for your valuable information. I will take a look at it and then I will get back to this discussion.
Have you been working with HRV and stress detection? Which algorithms have you used? I am using open-source hardware and software for PPG signal visualization and HR detection in real-time, see this video:
https://youtu.be/0nX9fknGoQw?t=63
Thank you again, regards.
Fernando
Hi Sebastian Zaunseder
I've read the paper you kindly suggested.
- It states that the HRV indicates the heart’s ability to respond to multiple physiologica environmental events (e.g. breathing, physical exercise, mental stress, hemodynamic and metabolic changes, and sleep and orthostatism).
- HRV can be used to measure the sympathetic and parasympathetic function of the ANS (autonomic nervous system).
- The HRV is evaluated in the time and frequency domains. The PSD (Power Spectral Density) provides information on the spectral power distribution of the HRV and is preferred for short-term measurements (5 min). It allows to compute the HF, the LF and the VLF, which are the intensities of the high frequency, low frequency and very low frequency bands, respectively.
- HF is a measure of PNS (parasympathetic nervous system), and it reflects the activity of the vagus nerve, whereas LF is a measure of the activity of the SNS (sympathetic nervous system).
- Regarding psychological stressors, the following was found:
1- Increases in stress were associated with decreases in the RR interval.
2- Psychological stress was significantly associated with an increase in the LF/HF ratio, suggesting increased SNS activity during stressful periods of the day.
One simple experiment is to compute the HRV from PPG signals, and then estimate the LF/HR ratio. It should be performed before, during and after stressful situations.
Do you have any other suggestion for detecting stressful situations from PPG signals?
Thanks,
Fernando
Are there other stress estimators from PPG signals?
Thanks!
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