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FAQ | Emfit QS | Sleep Monitor with Heart Rate Variability (HRV)

Why should I monitor my sleep?

Generally we may say that cornerstones of our health and wellbeing are exercise, nutrition and sleep.

From these three, the importance of sleep is widely neglected, whereas almost everybody knows how important it is to eat well and get enough exercise. People are often willing to sacrifice sleep time for other activities, such as work, partying, studying, etc. Especially in long term, this may be very unwise.

It has been shown in research studies that a person cannot very accurately report their own sleep quantity or quality. When one starts to monitor their sleep patterns, it becomes transparent, and the person begins to see connections between lifestyle choices and sleep quality and quantity. For example, they may notice that light exercise improves sleep, whereas heavy exercise degrades it. Also, tracking sleep can prove that consuming couple of alcoholic drinks in the evening actually degrades sleep quality, even though a person may feel that they slept better.

How to install the sensor in bed?

For long lasting durability, the sensor should be installed under the mattress or the mattress topper, not directly under the sheet.

For the strongest signal pickup, middle part of the sensor should be located directly under the location of your heart when you are lying straight on your bed. Usually this measures around 50 cm (20 inches) down from top of the bed.

If you have double bed with your spouse, to avoid picking up your spouse after you have the bed, you need to set the sensor as close to the edge of the bed as possible, and cord towards the side. Do not make the cord go in middle of the bed as it also pick movements and spouse's activity may make presence continue after you left the bed.

Can I use the device in double bed with my partner?

Yes, you can use the device in double bed. In our tests, as well from customers feedback, signal crosstalk from partners side has not been a problem. However, sensor cord end should be installed as close the edge as possible. It is though possible that spouse movements in bed after you left the bed may cause longer presence recording.

What is HRV?

HRV is acronym for Heart Rate Variability. Even though we may think that the heart beats regularly, like a metronome, this is not the case. Instead, even if our heart rate is steady 60 beats per minute, individual intervals from beat-to-beat will vary considerably, and peaks in ballistocardiogram or electrocardiogram may be for example at intervals of 890 ms, 1020 ms, 980 ms, 1005 ms, etc., having an average of 1000 MS in some time window, corresponding to 60 BPM.

Maybe somewhat surprisingly, heart beats more irregularly - heart rate variability is higher - with more fit and healthy individuals, and reduction in heart rate variability may indicate many health or lifestyle related problems. Furthermore, certain HRV based parameters tell us about the state of the autonomic nervous system, giving us valuable view into what is happening inside our body.

In long term monitoring of HRV one can see whether his/her cardiovascular fitness is increasing, as baseline HRV increases along with it. In short term, HRV gives valuable information about stress and recovery, as both tend to decrease HRV from the baseline, which is when one should avoid heavy exercise sessions until HRV has returned to baseline values.

In Emfit QS heart rate variability is automatically measured every night during deep sleep phase. This guarantees maximal consistency in measurements by minimizing the amount of disturbing factors, which are present if HRV is recorded either awake or in REM or LIGHT sleep.

Results include heart rate variability indices RMSSD and LF/HF ratio, telling status of your nervous system, recovery status, and readiness for another exercise, whether it should be light or heavy.

With this data you can choose optimal training intensity at every day and avoid over-reaching condition.

What is HRV RMMSD?

RMSSD, "Root Mean Square of Successive Differences", is one of the most widely used time domain heart rate variability values. Mathematically, it is the square root of the mean of the squares of the successive differences between adjacent heart’s beat-to-beat intervals.

In the scientific literature RMSSD is widely accepted as a measure of parasympathetic nervous system (PNS) activity. According to Wikipedia, PNS is responsible for stimulation of "rest-and-digest" or "feed and breed" activities that occur when the body is at rest, and complementary to that of the sympathetic nervous system (SNS), which is responsible for stimulating activities associated with the fight-or-flight response.

For efficient recovery from training and stress, it is essential that parasympathetic nervous system is active, and our body gets sufficient rest and replenishment. With HRV RMSSD value one can monitor what his/her general baseline value is and see how heavy exercise, stress, etc. factors influence it, and see when the value gets back to baseline, indicating for example capability to take another bout of heavy exercise. RMSSD can be measured in different length time windows and in different positions, e.g. supine, sitting or standing. In our system, RMSSD is naturally measured at night in a 3-minute window during deep sleep, when both heart and respiration rates are even and slow, and number of movement artifacts is minimized.

RMSSD value is highly individual and depends on age, gender, fitness level, stress level, lifestyle choices, etc. For this reason, one should monitor values for a few weeks, and only after that make conclusions on what kind of implications different values have for him/her.

The optimal respiration rate?

The typical respiratory rate for a healthy adult at rest is 12–20 breaths per minute. Respiration rates may increase with medical conditions, such as fever or illness.

What does the Sleep Score mean?

Sleep Score in a mathematical form is as:

Sleep Score= (total_duration_of_sleep + (duration_of_REM_sleep) *0.5 + (duration_of_DEEP_sleep) *1.5) - ((duration awake/3600) *0.5 + number_of_wakenings/15) ) * 8.5

Simply said, this means that the more you sleep, the more you have REM sleep, and the more you have DEEP sleep, and the better your Sleep Score is.

On the other hand, the more you are awake and the more often you wake up during the night, the worse your Sleep Score is.

By this formulation Sleep Score can reach values over 100, but in this case the value is truncated to a maximum of 100, which should be indication of sufficiently good sleep.

What are the different stages of sleep?

At a higher level, there are two sleep stages: REM sleep (Rapid Eye Movement) and NREM sleep (Non-REM).

At a laboratory level somnography NREM-sleep is further divided into four stages (N1, N2, N3, N4), but in practice, 3-stage classification is often used and sufficient: REM sleep, LIGHT sleep (consisting of N1 and N2 stages) and DEEP sleep (consisting of N3 and N4 stages).

These stages have different physiological characteristics, and their meaning to your body is different.

— LIGHT sleep is transitionary state from awake state to DEEP sleep. Eyes are not moving, and muscle tone is decreased.

— In DEEP sleep physical movement and muscle tone is almost non-existent. Breath rate is slow and steady, heart rate is slow and blood pressure low. DEEP sleep is essential for physical recovery and most physiological systems in you are in a heightened anabolic state, showing increased production of proteins, the essential building blocks needed for cell growth and repair and rejuvenation of the immune, nervous, skeletal and muscular systems.

— REM sleep is dreaming phase, characterized by rapid eye movements, paralyzed muscles, and variable blood pressure and heart rate. REM sleep is needed for mental recovery; during this sleep stage synaptic connections can be re-organized, which enables learning, storage of memories, and forgetting unnecessary things.
For complete recovery of your body and mind you need to have sufficient amount sleep in general, but also enough both REM and DEEP sleep. REM sleep should constitute 20-25 % of your total sleep, and DEEP sleep 10-20 %. This leaves some 50-60 % for LIGHT sleep.

The benefits of good night sleep?

Although we naturally think of sleep as a time of rest and recovery from the stresses of everyday life, research is revealing that sleep is a dynamic activity, during which many processes vital to health and well-being take place. New evidence shows that sleep is essential with helping to maintain mood, memory, and both cognitive and physical performance. Sleep also plays a pivotal role in the normal function of the endocrine and immune systems. In fact, studies growingly show a link between sleep duration and a variety of serious health problems, including obesity, diabetes, hypertension, and depression.

Flashing red light in the device?

Generally red flashes are indication of network connection problems. Other devices may trigger those flashes, threre might be a problem is between your device and wifi router. If those gaps are only short in duration, they should not be worried about.

Do I have to unplug the device when I am not sleeping to save electricity?

The device uses negligible amount of power, so there is no need to unplug it in order to save electricity. Though, if you want to plug it off for some reason, do it only after few minutes after bed exit, so that device has ample time to send bed exit event to our servers. Otherwise excessively long presence periods may occur.

Can partner or pet have affect on data?

Usually there should be only one person over one sensor, and signal from your partner from other side of the bed is much lower in amplitude, so it can not cause problems to heart rate accuracy. Same is probably true for the pets.

On the other hand, if you both are over the same sensor, then it is impossible for the system to tell whose heart is beating, so results may be erratic.

One known problem is, that if you are using the system, and you leave the bed while your partner still stays in bed, the device may see this lower amplitude signal from other side of the bed, and still assume that you are in bed. We have made fix to this, and in the near future system will indicate these "noise sequences" and ask if you want them to be removed.

How to improve my sleep?

As for us it is impossible to know what is happening in each of our users daily life we cannot give direct recommendations. General principle behind our system is that "what you can measure, you can manage". This means that while you measure your sleep, recovery, and stress levels, you start to see correlations between certain measurements and certain lifestyle choices.

For example, many of our users have noticed that alcohol intake very easily wrecks sleep quality, whereas light exercise and good time with friends improves sleep quality and lowers stress level. With this kind of personal observations anyone can adjust their lifestyle choices accordingly.

Further, in our FAQ we give general recommendations to improve sleep quality, for example, it is useful to avoid caffeine intake in the evening, bedroom should be dark enough, quiet, and relatively cool, etc.

Difficulties understanding the HRV RMSSD and Recovery

For RMSSD we have Evening and Morning values, and whole night graph. Usually Morning value should be higher, indicating that recovery has occurred. We also compute Recovery Ratio, which is Morning value divided by Evening value, and numbers around 1.5 should be regarded as good recovery. If number is lower than 1, then there has been excessive stress or some problem with your physiological or mental system, preventing the recovery.

Evening value itself is kind of a measure how heavy the load of the day was, let it be mental or physical. Thus, athletes can decide if their training load was sufficient by checking that Evening RMSSD is low enough, and with the Morning RMSSD they can see how much they recovered during the night (Recovery value is difference between Morning and Evening values), and did they reach their normal baseline RMSSD value. If Morning RMSSD is back to baseline, an athlete is ready for another heavy exercise, otherwise it might be reasonable to train little bit lighter on that day.
If Morning RMSSD tends to remain under baseline, or there is no recovery, this may be indication of overtraining syndrome for an athlete. In this case training load should be lightened for some time.

In the near future we are adding visual tools to assess Morning and Evening RMSSD values intuitively with regard to historical distrubution of these values. This way it is easier to see the baseline and identify different physiological modalities, such as light and heavy training days (in Evening values), and complete and incomplete recovery (in Morning values).

What would be normal numbers for a healthy sleep?

I would say that something over 100 is quite normal, but we dont have any rigorous general recommendations for this. At some point we may add some reference group data in to our user interface, but currently we dont have any schedule for it.