Have you heard the phrase: “one’s heart works like clockwork?” It refers to someone healthy and is used to mean that their heart works with perfect regularity and precision. Well, that’s not entirely accurate. In 1733 the English physiologist Stephen Hales discovered the phenomenon of variation in the time interval between heartbeats.
If a person’s heart rate is 60 heart beats per minute, that doesn’t at all mean that the intervals between the beats are one second long as might be assumed. It will vary with every beat and look something like this: 0.83 sec., 1.31 sec., 0.73 sec., and so on. This phenomenon is called Heart Rate Variability (HRV).
Sample of a cardiogram showing intervals between heart beats in milliseconds:
A few centuries later scientists observed something really interesting: changes in the fetal heart rate pattern precede severe heart diseases in the fetus. This was the first step on the way to the amazing discovery — the heart knows what’s happening with the body now and even what is going to happen in the future. Heart rate directly depends on the body’s needs at a particular time.
A little bit of physiology
Managing the heart, all internal organs and blood vessels is too important to give us direct control over it. That is why it is all regulated by the autonomic nervous system. It’s called like that because it functions autonomously. It is like an on-board computer which tracks the activity of all the systems in the body. We don’t think about the process of breathing, digesting or vasoconstriction. All this happens by itself.
The autonomic nervous system has two divisions: the sympathetic nervous system (SNS) and the parasympathetic nervous system (PNS). Each system dominates at a particular time which affects the body accordingly.
For example, when you are doing a run you may experience the effects of the SNS: the blood is pumped to the muscles and your breathing accelerates. You feel sleepy after a hearty meal? The secret is in the parasympathetic nervous system. It is responsible for digestion and we feel relaxed and at rest.
The two branches of the autonomic nervous system and the way they affect different systems and organs:
Obviously, these two branches affect the heart as well.
If the sympathetic branch is active it only means one thing — you need to provide the body with everything that is necessary for survival under stressful conditions. That is to pull all the resources, pump more blood to the muscles, make the heart beat faster. It’s no longer about variability, velocity — that’s what’s important now. That’s why stress decreases the general heart rate variability: the intervals between heart beats get shorter and the pulse becomes faster.
On the other hand, the prevalence of the parasympathetic nervous system slows the heart rate down and makes it more variable. You breath deeper and relax while the body recovers.
The diagram above is a rhythmogram where every point shows the time interval between two heart beats in milliseconds. The measurements were taken from a woman, 26 years old, at rest (average pulse 50-60 heart beats per minute, average interval between heart beats 1000-1300 ms) and during physical exercise (average pulse 100-120 heart beats per second, average interval between the heart beats 400-500 ms).
This ability of the autonomic nervous system to adapt to external and internal factors and keep the right balance in different situations is one of the essential functions of the human body which ensures its survival. Its dysfunction leads to diseases, illnesses and even fatal outcome.
The method’s history: from space to the gym
Scientists took notice of the heart rate variability method only in the middle of the 20th century. While researchers outside Russia were working out methods for clinical application of HRV, scientists in our country took the risk of already putting it into practice.
In the 60’s, when Gagarin was preparing for the first manned spaceflight, Soviet scientists faced a tough challenge. To collect as much information about the way spaceflights affect the human body as possible and at the same time not to overload the spacecraft with too many devices and sensors.
That was when they decided to examine austranauts’ health by analyzing their heart performance.
To do that Roman Baevsky, M.D. devised a method of mathematical analysis of heart rate variability which recorded intervals between heart beats. Bayevsky also created the first analogue of the modern heart rate sensor. It consisted of a portable computer and a monitoring device. The sensor was small and it could be used to examine a person on site.
Roman Bayevsky is one of the founders of aerospace cardiology. Doctor of Medicine, Professor, Honoured Scholar of the Russian Federation, Member of the International Academy of Astronautics, Member of the International Informatization Academy, Chief Research Fellow at Institute For Biomedical Problems of the Russian Academy of Sciences.
Roman developed a revolutionary approach to health assessment which is called prenosological diagnostics. It is the assessment of a person’s state of health when they haven’t yet fallen ill, but are already not entirely well. The analysis of prenosological conditions helps identify the premonitory signs of illnesses and detect when they will manifest themselves and what caused them. This method makes it possible to detect ill-being in advance.
Roman Bayevsky, his colleagues and students worked on this method for more than 40 years at the Institute for Biomedical Problems which dealt with space medicine first in the USSR and later in Russia. Bayevsky collaborated with NASA in a number of research programs regarding long-durability space missions’ impact on austronauts’ heart and lung performance. He also helped study austronauts’ adaptation process after their return to Earth.
In the late ’80s scientists proved that the heart rate variability assessment method could accurately predict fatal outcomes among patients who suffered a heart attack. In the mid ’90s, cardiologists developed uniform standards for the clinical application and analysis of HRV.
Today, half a century after the first manned spaceflight heart rate variability measurement method continues to be used in medicine and is also applied in an increasing number of new areas. For example, one of the biggest and most popular ones is sport.
Chinese scientists proved that HRV analysis shows the level of stress that the body experiences during physical exercise. That is why this method helps create personal training programmes for sportspeople taking into account how quickly the body recovers. The Finnish Research Institute for Olympic Sports developed a system called Firstbeat which is based on HRV. It is a program that tracks stress level changes and analyses training efficiency and recovery period duration. NBA Chicago Bulls, NHL Buffalo Sabers and others use this system.
HRV as a way to analyse your lifestyle
The method helps not just professional athletes, it is useful for ordinary people as well. Many scientists study the body’s response to a person’s lifestyle. Their eating habits, how often they do sports, the quality of their sleep and how much they weigh — how do all of these factors affect their health? The HRV method helps analyse that information.
- Everyday wellbeing and health
Turkish scientists discovered that smokers’ sympathetic nervous system is hyperactive. The more you smoke the more active it gets. Yet another proof that smoking kills. It wears out your heart by making it work faster. A group of Czech, Brazilian and Italian scientists found a correlation between sleep and heart rate variability. This proves that activity during the day and the state of health heavily impacts the quality of sleep. And sleeping disorders in their turn affect the overall wellbeing.
- Cognition and productivity
Indian scientists carried out a number of visuospatial tests with volunteers and found that those who had better results also had higher heart rate variability than those who didn’t do that well. Danish scientists discovered that even though the standard deviation in heart rate variability and pulse are not directly linked to long-distance lorry drivers’ workload, the changes within the 0.1 Hz range indicate how tired they are. Another experiment with students after passing their exams showed that heart rate variability assessment reflects their stress level with 90% accuracy.
- Physique and fitness
Swedish scientists examined patients with obesity and found that excess weight causes a stress level rise. The subjects had low HRV but it increased after they lost weight which meant that the heart worked under less pressure.
- Happiness and psychological state
Heart rate biocontrol sessions improved the state of patients with depression in a research study conducted by German scientists. Also, HRV analysis helped discover how the heart reacts to intense emotions.
There are a lot more examples of how this method can be applied. If you want to know more about it, you can find the information here.
Assessing your heart performance will help you analyse how your behaviour, habits and lifestyle affect your wellbeing. Want to find out what happens to your body after a burger for lunch, an hour of Game of Thrones, a 10 minute meditation session or sex? Yep, you can assess the impacts of all of that on your body through HRV analysis!
Obviously, we won’t be able to tell you right away what is bad or good for you.
But we can find that out if you measure your heart rate variability and collect factual data about your lifestyle and behaviour everyday (keep a food diary, jot down the amount of time you spent meditating, the amount of steps during the day, etc.) 2-4 week statistics is enough. You can analyse what has a good or bad impact on you based on that information.
The scientific method which was previously used only in labs is now available to everyone. You can learn more about your wellbeing and health without additional help and without leaving your house.
Availability in your smartphone
At Welltory we study lots of different parameters which analyse your heart rate variability by using all available methods (statistical, geometrical, spectral and non-linear).
To spare you from grappling with what each of them means we worked out two main indicators.
- Stress. It shows the level of the physiological tension in your body.
- Battery. It shows the amount of energy you have and assesses overall variability.
At the moment we are working on another index which will show the amount of mental tension.
How do we measure HRV without an ECG device?
It’s very simple. There are small portable gadgets that can fit in the palm of your hand. You don’t need to have a medical device with electrodes for a full electrocardiogram to know what your heart rate variability is.
Here are some examples of heart rate monitors
HRV sensor with an ear clip. For example, Kyto hrm-2935
Wristband, such as Mio Fuse
Chest strap, for example Polar H7
Even a smartphone case
Here is the full list of the heart rate monitors that we support.
You can also measure your HRV with the camera in your iPhone by simply putting your finger on it. Camera and ear-clip measurements are based on the same method. An infrared sensor and a light detector record the changes in the blood flow. More blood means less light and vice versa.
The methods for measuring HRV vary in their precision (the least precise is camera with a 5-7% margin of error). But you can use any of them to assess the dynamics. We offer our customers HRV monitors with ear clips. They don’t run your smartphone’s battery down like camera does, and they are suitable in any situation unlike chest straps.
So, Welltory app is your personal portable laboratory. 🙂
The most important thing is to connect data sources to record the amount of steps and sleep you have as well as your eating habits and take the measurements every morning.
They will show you how your lifestyle affects your health and will help you understand what can be improved. Our medical experts will give you personal recommendations and your personal health analyst will help you make necessary changes to your lifestyle, assist you and make sure you make progress.
Want to find out why you have headaches, or get into shape, reduce stress and feel 30% more energized? Download our app and become a better version of yourself. 🙂