What is blood pressure?
Blood pressure is a way of measuring how much force is being exerted on the walls of your blood vessels (arteries) as blood flows through them. It's expressed as a fraction: systolic (pressure as your heart contracts to pump blood to the body) over diastolic (pressure between beats,when your heart relaxes).
The Samsung smartwatch is one of the first to introduce blood pressure measurements from the wrist, it only needs to be calibrated first.
Firstly, you must use a dedicated blood pressure cuff to take readings that will give accurate insights into current cardiovascular health. Once the watch is calibrated with this initial primer, then it's good to go.
How are blood pressure readings taken?
The Samsung smartwatch works through pulse wave analysis by utilising the sensors that are also used to track heart rate data. The device, with the calibration reading, analyses the relationship between the value taken from the reading and the blood pressure change to determine your overall blood pressure.
More specifically, the watch records the pulse transit time (PTT) which is the time between the contraction of the heart and when the pulse arrives at a particular body part, like the wrist. This pulse pressure waveform occurs when the blood is ejected from the left ventricle and moves with greater velocity than the forward movement of the blood itself. It's correlated with blood pressure as the faster the pulse transit time is, the more the vessels are tightening. Optical sensors on the watch also check to see if the vessels are tightening or widening based on how light is reflected back to the watch and, along with heart rate information, are used to estimate blood pressure. Therefore, PTT can be derived from calculations using electrocardiogram (ECG) and photoplethysmography (PPG) signals.
Limitations of the PTT approach
The limitation of this approach is that it only reliably measures relative blood pressure, hence the initial calibration with an accurate blood pressure device is needed. To overcome this, Samsung recommends that users recalibrate the blood pressure monitor on their smartwatches every four weeks.
Alternative method: oscillometric technology
Omron offers a wide range of blood pressure products including the series 10 designed for the upper arm and the series 7 taking readings from the wrist. Omron uses oscillometric technology to measure the vibration of your blood travelling through your arteries and converts the movement into digital readings. Oscillometric technology uses an encircling cuff which is inflated around a limb, the rising pressure in the cuff eventually stops arterial blood flowing into the underlying limb and pulsation ceases. Then the cuff deflates, and the sensor detects a small pressure wave which reflects the difference between the pressure in the cuff and that in the artery. The maximum volume change provides an indication of the acreage systolic and diastolic BP within the artery.
Why is it important to pay attention to our blood pressure?
High blood pressure is commonly linked to brain, kidney and heart diseases, and if left untreated, it can lead to stroke and coronary heart disease. Therefore, it is important to stay on top of it and ensure that it remains within healthy levels - for most adults this is defined as a systolic pressure of less than 120 and a diastolic pressure of less than 80.
Through the Terra API, we provide connections to a range of different devices so that your users can track their body temperature.
Below is a list of the wearables that track your blood pressure today:
- Samsung Galaxy Watch 4, Galaxy Watch 3
- Omron HeartGuide
