Medical Devices: Using Technology at Home to Diagnose and Manage PoTS

In recent years wearable and easily portable devices have become very popular as a way of monitoring health such as heart rate and blood pressure outside of the medical setting. They can provide valuable information to physicians and consumers.

However, due to their widespread use and lack of guidance on how to use them and how accurate they are, caution needs to be taken to prevent misdiagnosis, over-treatment and anxiety.

There are devices useful in diagnosing and managing PoTS. Some are only available in a hospital setting, and some became available more recently for use in the community setting. Devices that are sometimes useful include:

• Home blood pressure and heart rate monitors
• Finger tip pulse oximeters (‘sats’ machines)
• Smart watches – heart rate monitors and ECGs
• Arm and chest bluetooth monitors
• Ear optical monitors

It is very important that you learn how to use the monitors correctly (either through reading manuals or training from your medical team). You need to know:

• how to take a recording
• when to record (eg at specific times of the day, with certain activities, or when you have symptoms)
• what is normal
• what is abnormal
• when to call for help.

Medical Device Regulation

The Medicines and Healthcare products Regulatory Agency (MHRA) is the UK equivalent of the FDA in the USA. The MHRA is responsible for regulating the UK medical devices market. Different rules apply in Northern Ireland.

The CE mark

Certain products such as electrical equipment, toys and medical devices

require CE marking in the European Economic Area. The CE mark indicates that a product has been assessed by the manufacturer and deemed to meet EU safety, health and environmental requirements. CE marking will still be recognised in the UK until June 2023 after which the UKCA mark must be used.

THE UKCA mark

UKCA marking came into effect in January 2021 and will replace CE marking for any applicable products in the GB market (not Northern Ireland). It will not be recognised in the EU market.

*Having a CE or UKCA mark does not mean that a device has been approved by the MHRA as a medical device.

Counterfeit devices

With the recent increase in demand for medical devices such as pulse oximeters (‘sats machines’), counterfeit devices have made their way onto the market, and even into hospitals. If buying a device, try to ensure you purchase it from a reputable retailer.

When are devices useful in PoTS?

For diagnosis

It has now been agreed by experts that an active stand test can be equally as useful; tilt tests are more useful for assessing other conditions, particularly other causes of blackouts.

To prepare for a medical appointment, some patients are asked to undertake a stand test at home. There is information here.

Some are also asked to keep a diary of heart rate and blood pressure when are lying/sitting/standing throughout the day. It can be helpful to relate recordings and symptoms i.e. record blood pressure, heart rate, posture and symptoms at the same time.

A doctor or nurse will not have time to read many pages of recordings, so it can be useful to keep recordings on an especially good and bad day only for your next appointment.

For monitoring PoTS

The most important issue when monitoring your PoTS for improvement or deterioration is how you feel. If your heart rate is high due to PoTS, but you feel fine, then it probably doesn’t matter. Conversely, your heart rate may reduce on a new medication but you may not feel any better. In these situations the recordings are not always helpful.

Some PoTS treatments can lower heart rate, and a monitor can help to identify if it becomes too low (especially if associated with symptoms of low blood pressure).

Some treatments for PoTS work by raising your blood pressure. However they can sometimes elevate it too much. If blood pressure rises excessively on lying down, this is called supine hypertension, and can be dangerous (it can cause stroke and heart problems). Supine hypertension is defined as a blood pressure above 140/90 after lying down for 5 minutes. Midodrine (if taken soon before lying flat), fludrocortisone (or even excessive salt) can cause supine hypertension. Your consultant may ask you to monitor your heart rate and especially your blood pressure if you start taking these medications.

Pitfalls

All monitors

• Most need to be checked regularly to ensure they are working properly. Some over the counter devices are not calibrated properly even before they are sold.
• It’s very easy to become obsessed with making recordings, and this can create health anxiety. Try to make recordings as frequently or infrequently as your healthcare professional recommends.
• When you are particularly unwell, recordings may change and temporarily may not reflect your usual readings.

Blood pressure monitors

Blood pressure (BP) is a measure of the pressure of the blood in your arteries- the vessels that carry blood from the heart to your brain and the rest of your body.

The highest number on the BP reading is called the systolic pressure, which indicates the pressure the blood exerts against the artery walls when the heart contracts/beats. The lower ‘diastolic’ number is the pressure on the arteries when the heart relaxes between contractions.

Electronic BP machines

Electronic BP machines simultaneously measure the heart rate alongside the BP.

It is recommended that machines with an upper-arm cuff are used, as the wrist-cuff machines have been found to be less accurate.

They are inexpensive, widely available, and easy to use.

Dr Gall, cardiology consultant, PoTS specialist and patron to PoTS UK has recommended that when looking to obtain a diagnosis of PoTS, an electronic arm-cuff BP machine is the best device to use to collect the information at home as described in the ‘for diagnosis’ section above. This is due to the fact that measuring the heart rate simultaneously with blood pressure allows for their comparison by medical professionals. Current guidelines for a PoTS diagnosis require there to be a sustained increase in the heart rate of at least 30 beats per minute from lying to standing (40 beats per minute in teenagers), in the absence of a blood pressure drop.

(A drop in BP along with symptoms similar to PoTS may indicate orthostatic hypotension).

Some people with PoTS may see an elevation of BP as well as the heart rate rise on standing, and it is important that this is monitored. Further information can be found here.

As previously mentioned in the ‘for monitoring PoTS’ section, some PoTS medication can cause an increase in BP.

In addition, when in medical settings, some people experience anxiety which can cause a rise in BP known as ‘white coat syndrome’. In this circumstance recordings made in your usual environment at home could be a more accurate representative of true values.

• A list of blood pressure monitors approved by the British and Irish Hypertension Society can be seen here: https://bihsoc.org/bp-monitors/for-home-use/. There is also a list of monitors you should not use.

• Home monitors should be calibrated (checked to see that they are working correctly) at least every 2 years-check the instructions.

You can see how to take a BP reading here.

Smartwatch for BP monitoring

Some smartwatches have introduced cuff-less technology to allow for convenient, comfortable and continuous blood pressure measurements.

More research needs to be carried out to determine their accuracy, although many studies have shown that compared to standard arm-cuff monitors, the results weren’t consistent enough to meet medical standards.

They are currently not recommended for systolic BPs of above 160mmHg or below 60mmHg, and are likely only to be useful in gaining awareness of BP, rather than accurate data for example to determine whether a medication is helping. They also need regular calibration as per the device instructions.

With improved accuracy continuous measurements may be useful in determining blood pressure variation throughout the day, including daily activity and physical/emotional stress.

Different and more accurate techniques for smartphones are currently being explored as potential for BP monitoring in the future. These include a phone camera application which measures facial blood flow changes.

Heart rate monitors

The heart rate is the number of times the heart contracts/beats per minute (bpm).

An electrocardiogram (ECG) is the precise gold standard technique for measuring heart rate (HR) via electrical signals generated by the heart. These readings are obtained by placing 12 electrodes on specific places on the body to gain an accurate heart rate and rhythm tracing, as well as other important cardiac details.

As the 12-lead ECG is not mobile enough for monitoring heart rate outside of a medical setting, another technique called Photoplethysmography (PPG) was found to be an inexpensive, simple and acceptable alternative way to calculate HR.

This PPG technology has been used to develop small, wearable, pulse rate sensors; ranging from finger pulse oximeters to smartwatches.

The PPG sensors work by measuring the changes in blood flow within the body tissue caused by pulses of blood from each cardiac contraction. These measurements are then used to estimate the heart rate. 

There are factors which affect the accuracy of the heart rates monitored by wearable devices which we will talk about below.

Pulse oximeters (‘Sats’ machines)

Finger pulse oximeters are small portable devices placed on the fingertip. They use PPG technologies to estimate heart rate, as well as the oxygen saturation level (SpO₂) in the arteries. They are very popular because they are cheap and easy to use. 

Those with PoTS sometime use the pulse oximeters to monitor their HR, although at times the result displayed is not accurate.

Care also needs to be taken when also observing the displayed oxygen saturation level.

This is because the monitors can measure inaccurate readings due to the fact that the oxygen levels are being measured in the fingers, as opposed to the actual oxygen levels within central blood. Normal levels are around 95%-100%. Low oxygen levels are not normally a feature of PoTS.

Many PoTS patients have cold fingers which would mean lower oxygen levels in that region and therefore measurements wouldn’t be accurate.

Sats machines can also give faulty recordings in the following situations:

– nail varnish, false nails

– dark coloured skin 

– anaemia

– irregular heart beat

– high-intensity lighting, typically fluorescent lights

– finger movement

– obesity

– smoking

– very low blood pressure

– reduced blood circulation to fingers 

Care also needs to be taken as monitors are often not accurately calibrated.

In many cases, the level of inaccuracy of the monitors may be small and not clinically meaningful; however, there is a risk that an inaccurate measurement may result in unrecognised low oxygen saturation levels.

Pulse oximeters intended for clinical use are regulated as medical devices and should display a valid CE, CE UKNI or UKCA mark.

Smartwatches – heart rate

Smartwatches are a convenient wrist-worn technology which can provide continuous real-time monitoring of the heart rate. They have become extremely popular in recent years and their technology is continually being upgraded.

At the time of writing we were unable to find any smartwatches that are MHRA approved (although some are approved by the US FDA) as wrist-worn wearable sensors were considered low risk and therefore not subject to active regulation. Despite this they are increasingly being used to inform clinical decision making.

They use PPG technology (described previously) to estimate the heart rate. Studies have found that at rest and in a normal rhythm they can have a high level of accuracy of within 5 bpm.  Most wrist-worn devices also adequately measure heart rate during activity and exercise.

Despite this, there are factors which can reduce their accuracy. The main cause is due to erratic wrist movement. Therefore, any actions which cause this including day to day activities or some high intensity exercises, will decrease the accuracy of the measured HR. Device companies are actively working on ways to reduce the effect that wrist movement has on an accurate HR measurement.

Other factors which slightly decrease the accuracy include; being male, obesity and darker skin tone – although these are still within an acceptable error range. Low blood circulation will also affect the reliability of measurements.

Smartwatch ECG

Many of the very latest models of smartwatches now have apps that can be used to produce an ECG recording. This is achieved by creating a circuit between the detector on the back of the watch and your finger which is placed on the side of the watch. This records a 30 second single-lead ECG tracing which shows the heart rhythm and an average HR, which can be saved as a PDF document. The recording needs to be taken with the arm completely still, therefore not during exercise.

Compared to the gold standard 12-lead ECG test carried out within medical settings, the single-lead smartwatch ECG tracings provide much less detailed information about heart activity, and therefore the apps can not be used as medical-grade equipment or to replace any medical advice.

Currently the main use of smartwatch ECG is to detect whether the heart is in a healthy normal regular rhythm or an irregular rhythm called atrial fibrillation (AF). This irregular rhythm is not part of a PoTS diagnosis.

Research on the Apple Watch ECG in particular, found that the PDF rhythm strips were correctly labelled 98% of the time, however 31% of these readings were labelled as ‘unreadable rhythms’. This is in contrast to Apple themselves stating ‘unreadable rhythms’ make up just 6%.  It was also found that although the PDF generated strip labelling was highly accurate, the additional rhythm notifications displayed by the watch were very inaccurate.

Apple themselves state their ECGs are not accurate with heart rates of below 50bpm or above 150bpm.

Another popular ECG device for monitoring heart rhythms is called the Alivecor KardiaMobile, which can provide a 6-lead ECG tracing for those who have heart rhythm problems. It has been shown to be highly accurate and very useful for capturing recordings outside of the medical setting. Although PoTS is not a heart rhythm disorder, ECGs can be useful to exclude other conditions with similar symptoms.

Smartphone apps

Smartphone apps are also available to measure heart rate via PPG by placing a finger over the phones camera.

It is important for the measurements to be taken without movement and with the appropriate amount of pressure applied- please see the app’s instructions.

A study which reviewed the research into these apps, found that they were consistently accurate if the heart rate was between 60- 100 beats per minute.

Chest straps

Chest straps continuously monitor heart rate and consist of an adjustable band that fastens tightly around the chest. The sensor contains two electrodes that enable an ECG-style heart rate recording by detecting the electrical activity of the heart.

Although they are not as comfortable as smartwatches, they are commonly worn for high intensity exercise, as research studies have found the ECG style-sensor to be close to perfect for heart rate accuracy at rest and during intensive exercise.

They are also more accurate at higher heart rates and less susceptible to error due to motion, as seen with wrist worn devices including sport/smart watches during exercise.

2 of the more popular and studied chest straps are the Polar and Garmin devices. They use wireless and Bluetooth technologies to link to other devices and transfer heart rate information from the strap to smartwatch apps.

Arm bluetooth monitors

Forearm and upper-arm strap monitors have also been produced with optical PPG sensors. They too have a high level of accuracy recording the heart rate at high intensity exercise, due to the fact the forearm has greater blood perfusion and less error due to motion compared to the wrist smartwatches.

Ear sensors

The ear is another area on the body that can be used to monitor heart rate.

The earlobe is a popular site for a pulse rate sensor clip as it has large blood supplies and is also less vulnerable to errors due to motion compared to the fingers. The clips are mainly used in hospital settings as, although they are effective, they can become uncomfortable and painful over time.

In more recent years in-ear earphone and earbud sensors are more commonly used commercially as they provide greater comfort.

Two devices that have been studied are Bragi Dash Prob and the Cosinuss One. Both were shown to be accurate when monitoring heart rate compared to a standard ECG. The highest accuracy was seen at rest which became slightly less accurate when at higher heart rates during exercise (but still within <5% error), again caused by motion.

Top tips for using devices in PoTS

• You need to know what is normal for you, what is abnormal and when you should worry – ask your healthcare professional when you next see them.
• It is normal for blood pressure and heart rate to fluctuate throughout the day in a healthy person.
• Don’t just rely on the numbers – the symptoms that you experience can be just as important.
• If you obtain an unexpected abnormal reading, check it again when rested (not exercising) and calm.