Sleep Health HRV

HRV (Heart Rate Variability) is a core non-invasive indicator that can be obtained by ordinary people at low cost and is clinically recognized. It is a core non-invasive indicator that takes into account sleep quality assessment and potential health risk warning. There is no need to myth its role, nor ignore the signal it sends to the body.

The first time I realized the usefulness of sleep HRV was when I was working on a quarterly project four years ago. I stayed up until 2 o'clock for ten days in a row. When I woke up in the morning, I always felt light-headed and like I was stuck in a slurry. The sports watch I was wearing at the time popped up a reminder saying that my average HRV at night had dropped to 28ms, which was 45% lower than my usual baseline. It was recommended to adjust my work and rest schedule. At that time, I didn’t take it seriously. It wasn’t until after two days of eight hours of sleep that the value jumped back to 47ms. When I woke up, my mind was so clear that I could directly calculate the budget for the second half of the year. I really believed that this thing was not an IQ tax created by watch manufacturers.

To put it bluntly, HRV is the change in the time difference between your two heartbeats. It is a bit like the "elasticity value" of the heart - when you have slept enough and your body is relaxed, the vagus nerve is dominant, and the heart is like a rubber band with sufficient elasticity. It can beat fast or slow, and the HRV value is high.； If you don't sleep well, watch stimulating short videos for two hours before going to bed, or if your body has undiscovered inflammation, the sympathetic nerves will be stretched all the time, and the heart will only freeze and beat at a constant speed, and the variability will naturally decrease.

The current attitude towards sleep HRV in the circle is actually quite polarized. Most friends who do sports science and digital medicine regard it as a treasure. After all, continuous nighttime HRV data can reflect the state of autonomic nervous regulation when you are asleep. Many studies have shown that HRV is more than 30% lower than the personal baseline for one consecutive week. Not only is the sleep repair efficiency reduced by half, but the probability of subsequent depression, reduced immunity, and even minor cardiovascular problems will be much higher. However, I have asked several doctors in the sleep department of tertiary hospitals, and most of them have reservations about HRV measured by consumer-grade equipment: after all, ordinary watches use photoplethysmography, and there is definitely a gap in accuracy with electrocardiogram. It can be used as a daily reference at most. If you really want to troubleshoot problems such as sleep apnea and insomnia disorders, you still have to do polysomnography. In fact, both sides are correct. One requires long-term continuous trend changes, and the other requires a single accurate diagnosis basis. The applicable scenarios are inherently different.

Don’t believe it. Last year, I helped a friend who works in operations check his sleep data. His nighttime HRV fluctuated around 22ms for half a month. He said he had nothing wrong with him except being unable to wake up. I advised him to take the time to check his blood routine. The results showed that the C-reactive protein was three times higher than the normal value. It was an acute attack of chronic pharyngitis and latent Helicobacter pylori infection. After half a month of treatment, the value returned to 38ms. He himself said that he fished less often during the day.

Many people always like to compare with the "standard value" on the Internet when they first get the monitoring data. They panic when they see that they are only 30. In fact, it is completely unnecessary. It is normal for a 20-year-old boy and a 60-year-old elder to have a difference of twice the basic value. To really compare, just compare it with your own average level in the past 1-2 months. Oh, by the way, there are still many people who think that the higher the HRV, the better. They stay up late and stare at the numerical value. In fact, it may be a problem if it exceeds your own baseline too much. For example, in the early stages of allergic attacks or hyperthyroidism, HRV may also increase abnormally. If it really deviates from the baseline for a long time, no matter how high or low it is, you must pay attention.

A little experience that I have used for almost three years is: if you stayed up late the day before but your HRV did not drop much the next day, it means that your body can still handle it, and you can go about your work that day without any worries.； If you obviously got enough sleep for 8 hours, but the value dropped by more than 20%, then don’t arrange high-intensity exercise or stay up late that day. Just soak in a cup of warm water and watch less stimulating content, which is better than anything else. After all, there are many influencing factors that you may not have paid attention to: drinking half a glass of red wine before going to bed may seem like you will fall asleep quickly, but in fact, HRV can drop by 20% at night. Alcohol directly inhibits the vagus nerve, making it difficult to sleep at all. ； One week before a woman's menstrual period, HRV generally drops by 15%-20%, which is a normal physiological fluctuation. Don't make it worse for yourself.

Anyway, the first thing I do when I wake up every day is not to touch my phone to check Moments, but to glance at the HRV value on my watch. If it is higher, I will give myself a glass of iced Americano. If it is lower, I will avoid two unnecessary needs. After all, when it comes to sleeping, your body will always be more honest than your words.