Monitoring, physiology and what to measure?

A question that I have received a number of times over past years is what to measure to ensure a healthy life? There are quite a few options out there but what of the sensors delivers and what is scientifically sound to do? The first thing to ask is really what is your life, age, how do you live, eat, sleep and stay active? What do you want to achieve and how much effort are you prepared to spend. Most of us are not data freaks and so we would like to have simple things that work. This small blog documents some things I learned over the years.

There are probably two to three things one should invest in that most people will benefit from. The first thing is a good scale and the second is a quality fitness watch. The third could be a quality heart rate sensor for monitoring ECG but more about that later as there are actually 2 different types of sensors now in the market and the other option is a sensor measuring the pulse wave. Most watches now have a pulse wave sensor (at the bottom you see green blinking lights) is complementary to ECG and contains a wealth of interesting information but more about that later.

Weight and Pulse Wave Velocity

Lets first dig into the scale topic: There is one scale that is significantly better and versatile than all other ones in the market. This is the Withings body cardio scale. The Withings scale measure a number of things that are all important:

Weight - Measuring a documenting weight changes to keep a normal weight is key to a long and healthy life. With this scale you can document weight changes over the years as it connects to the cloud over WIFI. Activity levels, sport, sleep and eating all affect weight so regular monitoring of weight is one of the foundations of a healthy life.

Body composition - Body composition using impedance tomography is a bit of a black art. The correlation is there but don′t count the decimals as absolute values coming from a simple scale. Rather this is indicative of general shifts in body composition over time. Body mass index (BMI) is something that you can disregard nowadays as research discredits this old measure. What is truly important is the amount of lean tissue you have as the muscle tissue basically determines your basic metabolic rate and how much to eat minimum. Sarcopenia or muscle loss/waste is something that we all experience over time, particularly over >50 years of age. Research shows it is particularly important to keep legs in good condition so that you are able to move e.g. at >70 but one needs to start maintaining muscles much earlier. Keep running and walking!

Pulse wave velocity (PWV) - Pulse wave velocity tells how fast the pressure pulse from the heart is moving throughout your body. The scale is using something fancy called ballistocardiography to measure PWV. A fast moving wave implies that arteries are stiff and indicates increased risk for diabetes, metabolic syndrome, diabetes, blood pressure and heart decease. A normal pulse wave velocity depend on age but generally is a number from e.g. 6 m/s to 9.5 m/s. There are many things that affect the stiffness of arteries but it is related to life style and ageing. Depending on your body-mind connection you may also see higher stress levels increasing the velocity. Some persons have greatly varying velocities while for other it stays more constant. Blood pressure medication, e.g. calcium blockers, directly lowers velocity and so do exercise and healthy diet, too. As said, pulse wave velocity is correlated with blood pressure but is much easier to measure and can be obtained just by waiting a few seconds and without cuff. If you do have blood pressure then you benefit from measuring both at the expense of a few extra seconds standing on the scale. The days when velocity is low then blood pressure will also tend to be low but don′t cite me on this. Summary: Pulse wave velocity is a simple measure to understand the condition of arterial walls, stress and increasing risk of cardiac decease with age. This is probably the easiest fitness test you can make! Here is a table of PWV as function of age.

What is important when measuring the human physiology is to always do the measurement in the same conditions: Same time, no eating, drinking or coffee. A good habit is make a detour to toilet first and then step on the scale.

Fitness Monitors and Their Systematic Use

Monitoring daily active and that sleep is of good quality is now easier than ever before. Modern monitors count steps, calories and displays activity. Some can also classify activities extremely well and tell what you did.

If you buy any of the high tech brands (Polar, Garmin, Fitbit, Suunto) you get a quality monitor (I left Apple out of the list as they don′t do sleep monitoring which I consider fundamental to healthy life). The last generations of fitness monitors monitors sleep with an accuracy that is coming or is at he same level as visiting a sleep laboratory. Sleep quality is gaining more importance as we have come to realise the restorative benefits of quality sleep on mind and body. Sleep is of healing nature and and good sleep is readiness for the next day of work. Sleep hygien is something to invest in.

Heart Rate / Pulse Rate Sensing

Today there are two common ways to monitor the function of the heart. This is by

1. measuring the electrical activity, the elctrocardiogram (ECG) or
2. detecting the pulse wave (PW) from the heart using photoplethysmography or PPG. Usually this is done on wrist, ear, finger or forehead. It works well at any place on the body that is highly capillarised.

It shows out that monitoring the electrical activity on the chest is easier, more accurate and reliable than monitoring PW. Monitoring ECG is the natural choice for e.g. athletes and other that do require high quality information. I recommend the Polar H10 as probably one of the best heart rate monitors you can buy. In particular it works everywhere with Bluetooth Low Energy (BLE) e.g. in the gym with fitness machines (legacy 5.4 kHz analog transmisssion).

Monitoring the pulse wave on the wrist is actually a very hard measurement that works for most but it is not as reliable and accurate. Cold conditions can lead to vascoconstricton and may further reduce accuracy. For the time being HR measurement using the pulse wave remains somewhat immature and doesn′t always work as expected. This is really normal. While you remain at rest pulse rate is accurate as the signal is good. The Apple watch actually implements both ways ECG and PPG. Apple is using ECG to detect arrhythmia probably due to the accuracy of the measurement and the fact that the conservative medical community do not accept PPG measurements which is actually good. PPG is not yet generally accepted but for pulse oximetry (the measurement of oxygen levels).

A healthy heart beats irregularly and this is called Heart Rate Variability, HRV or IBI, Interbeat Intervals. A regular heart beat can point to inflammation, cardiac decease, bad general condition, mental conditions, metabolic decease, low physical activity or stress etc. A low HRV alone implies that your life will be short. Thus, the primary goal with physical activity is to increase HRV. HRV changes over time but change is usually slow (give it months) because it requires underlying physical changes in your body. You can affect the variability through exercise and life style modifications. The fastest way is probably through high intensity training(HIIT) which is what you are likely to be prescribed if you go to a professional trainer today. Diet has been connected with changes in HRV which is not surprising either.

A good fitness monitor measures HR and HRV throughout the night and can report the average values (Polar Ignite for example). Episodes of high variability during night is indicative of restorative sleep. I believe Garmin also have all relevant features for HRV analysis.

The Vagus Nerve and HRV

The vagus nerve goes throughout the body and connects e.g. brain, heart, lungs, stomach and kidneys. Parasympathetic nervous system activity is associated with increased variability (HRV), lower heart rate&blood pressure, stomach function, less stress hormones, less inflamation. A calm mind. You can affect the vagal activity just by standing up and rising you arms towards the sun, hugging you partner or cat/dog, thinking positively, laughing, being grateful and humble, meditation, understanding and forgiving those you don′t like, exercising mindfulness or by breathing deeply and slowly.

You can also affect parasympathetic mediated activity through breathing. Deep breathing means breathing with the lower parts, stomach. Breathing in during 6 seconds and out for 4 seconds for 10 (total 10 sec. / breath) is a natural rythmen to relax body and mind. Typically after some minutes of breathing heart synchronize with lungs (cardiac coherence), blood pressure falls, the babbling inner voice that causes so much concern becomes more bearable, anxiety and stress disappears. The cardiac coherence can be measured using a heart rate sensor or PPG sensor.

Here is a small list of use cases where a PPG sensor can be used. Some of these are leading edge research:

• Pulseoxymetry
• Pulserate (or heartrate) for control of intensity in sports
• Pulse to pulse intervals (HRV)
• Blood pressure from the ear. A company called Valencell is becoming a world leader in the field of continous calibrationless blood pressure measurement using optical methods.
• Augmentation factor (vessel siffness)
• Atrial fibrillation (detection)
• Stress (ANS)
• Sleep quality
• Breathing rate
• Overtraining
• Detection of type 2 diabetes
• Thermoregulation
• Traditional Tibetan pulse reading can be done using PPG

Some of these are used in combination with biofeedback.

Other Useful Sensors

There are many highly sensors that can bring benefits. This is non-exhaustive list of interesting on or off body sensors to monitor physiology or environment around which is may be equally important.

• Air quality - typically CO2 sensor. What you learn is e.g. closing the door to bedroom during night will cause terrible air.
• Humidity, Temperature, Pressure
• GPS, magnetometer, gyro, inclinometer, accelrometer - position, speed, rotation, direction, rotation etc
• Step counter
• Cycling and running power sensors
• Cycling and running cadence sensors
• Breathing
• Gait
• Blood pressure
• Glucose - Diabetes
• Tonometer
• Pulseoxymetry, O2 sensor is useful for checking the function of lungs, mountain climbing and snoaring.

Conclusions

I hope this blog makes you curious enough that you go out and buy some of the devices measuring and understanding some of the interesting physiological variables. There are like 4 things I like you like to focus on

• Staying active
• Sleep
• Keeping a balanced life avoiding stressors
• Monitoring a few basic parameters to stay healthy

In the end what we all like to is to live a quality life and the technology is out there to help doing just that. It is no longer expensive either. Enjoy life and Corona is just an opportunity to stop, understand and go in new directions and learn more about our bodies.