Week 1 - HRV Review

Inspiration

            

What is HRV?

HRV or Heart rate variability is the measurement of the balance of the different systems within your body that speed up (stress hormones/sympathetic) or slow down (relaxation/parasympathetic) your heart rate.

These two systems are called the sympathetic and parasympathetic nervous systems respectively.

Sympathetic & Parasympathetic systems


There has been a research paper done by the Australian Journal of Applied and Basic Sciences that shows that there is a direct relationship between ones breathing and their heart rate, this phenomenon is called 'respiratory sinus arrhythmia'.

Respiratory sinus arrhythmia is the natural variation in heart rate that occurs in sync with the phases of breathing.

This is primarily influenced by the activity of the vagus nerve, a part of the parasympathetic nervous system. When you breathe in, the vagus nerve activity decreases slightly, allowing the heart rate to increase. Conversely, when you exhale, vagus nerve activity increases, leading to a decrease in heart rate. This synchronization between breathing and heart rate is a normal part of the body's regulatory mechanisms.

Vagus Nerve

        Ref: https://www.caringmedical.com/prolotherapy-news/vagus-nerve-compression-cervical-spine/


There has also been further research done that shows bad posture can put strain on the vagus nerve, this could lead to a damaged vagus nerve along with making it harder for one to breath properly.

However this should come as no surprise because it gives the breather optimal lung capacity in order for the lungs to fully expand and contract, It is also common for a doctor to ask you to sit up straight while he may be listening to your heart rate.

Vagus Nerve tension due to bad posture

        Ref: https://www.caringmedical.com/prolotherapy-news/vagus-nerve-compression-cervical-spine/

Whats on the market?

In today's modern landscape there is many different fitness wearable's and medical devices that can measure a users heart rate and other biological variables.

However currently the only smart watch on the market that is considered to be a Class II medical device is the Apple Watch series 4 which received approval as a medical device back in 2018 because of its ability to measure ECG and arrhythmia's. 

Apple watch series 4

        Ref: https://cardiologynownews.org/apple-watch-series-4-receivess-fda-approval-as-a-class-ii-medical-device/


Technologies to measure HRV:

Currently there are plenty of off the shelf components that can be used to measure heart rate, ECG and HRV. 

Examples of these technologies include the Sparkfun AD8232 heart monitor sensor for Arduino:
https://littlebirdelectronics.com.au/guides/173/heart-rate-sensor-with-arduino


                                                                            Sparkfun Heart monitor module

Serial plot of HRV
        


Feedback

Once a reading can be taken accurately it is then time to implement a type of feedback for the end user.

This can be done in a few different ways using anything from an LED matrix to glow for every heartbeat or to a vibration motor that beats along with the user.

Once an artifact design is decided on the data that is produced can then be sent via radio comms to a microbit MQTT board this will allow the team to view variables like BPM,ECG and HRV through a beebotte dash board.


A common design pattern used in the Applied Robotics lab is to use the BBC Microbits along with an MQTT expantion board which allows the Microbit to send data to an MQTT broker like Beebotte.

DFRobot IoT Cloud board

Coupled with the Microbits radio communication this gives users the option to use two Microbits, One as a receiver and the other as a transmitter.

This would make the device less intrusive because the user would not have to carry around this expansion board and could just have the transmitter Microbit on their person.


This also makes for a pleasant coding experience because of the Microbits drag and drop makecode blocks.

                                                                        Microbit MQTT Interface




Project Ideas.

Construct a 3-D LED matrix that lights the inner LED's when a heartbeat is reached and the farther out LED's light up if the more positive the HRV score.

A servo or stepper motor could be mapped to the heartbeat of the user also, this would be a nice way to simulate an active heart.


LED matrix




Implementation

As far as implementation goes there is currently three options for what embedded system can be used to process the heartbeat data.


1: Micro bit

Pros: 

- Easily programmable

- Built in A2D conversion

- Open source hardware/software

Cons: 

- Wifi comms can only be done with the use of Expansion board


2: Raspberry Pi 3/4

Pros: 

- Built in Wifi

- Higher computational power

- Open source hardware/software

Cons: 

- No Analog to digital conversion built in

- More expensive than the micro-bit

- No beginner friendly programming interface


3. Arduino

Pros:

- Built in A2D conversion

- Cheap

- Open source hardware/software

Cons:

- No built in wifi

- No beginner friendly programming interface

.


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