Understanding Your Blood Pressure Readings
Blood pressure is one of the most asked-about features of the HLTH Band. Here's how your band measures blood pressure without a cuff, what the numbers mean, and how to get the most from your readings.
⚠️ If you feel unwell: If you have symptoms such as chest pain, shortness of breath, dizziness, fainting or a severe headache, contact a medical professional or emergency services straight away.
What Is Blood Pressure?
Blood pressure is the force of your blood against the walls of your arteries. It's shown as two numbers:
- Systolic (top number): the pressure when your heart beats and pumps blood out
- Diastolic (bottom number): the pressure when your heart relaxes between beats
For example, a reading of 118/76 mmHg means a systolic pressure of 118 and a diastolic pressure of 76.
How Does Your Band Measure Blood Pressure Without a Cuff?
Instead of squeezing your arm like a cuff, your band uses light. The optical sensors on the back of your band shine light into the skin on your wrist and measure how much is reflected back. This technique is called photoplethysmography (PPG).
Each time your heart beats, a pulse of blood moves through your wrist, slightly changing how much light is reflected back to the sensor. This creates a pulse wave showing the shape and timing of each heartbeat.
Your band uses this pulse wave to estimate Pulse Transit Time (PTT), which is how quickly the pulse travels through your arteries. When blood pressure is higher, the pulse generally travels faster. The band's algorithms use this to estimate your systolic and diastolic blood pressure.
How Often Does It Measure?
Your band takes blood pressure readings automatically throughout the day. The latest reading in the app may be up to 60 minutes old. For a reading right now, use One Key Measurement in the app.
Where to Find Your Blood Pressure Data
Open the QWatch Pro app and go to the Blood Pressure section. You'll see your latest reading and a graph of how your blood pressure has changed through the day.
No readings showing? Blood pressure may need to be switched on in the app before it starts recording.
Apple Health: Blood pressure readings stay in the QWatch Pro app. They don't currently sync to Apple Health and can't be exported.
Blood Pressure Reference Ranges
The QWatch Pro app uses these general reference ranges:
- Below typical: below 90 (top number) or below 60 (bottom number)
- Typical range: 90–140 (top number) and 60–90 (bottom number)
- Above typical: above 140 (top number) or above 90 (bottom number)
These are general reference ranges, not medical categories. Medical guidelines are stricter. For example, the American Heart Association defines normal blood pressure as below 120/80, and considers readings of 130/80 or higher to be high blood pressure. Only a healthcare professional can assess your blood pressure. If you have any concerns about your readings, speak to your doctor.
What Affects Your Blood Pressure?
Your blood pressure changes naturally throughout the day. Things that can affect it include:
- Time of day (it's usually lower while you sleep and rises in the morning)
- Physical activity (it rises during exercise and falls when you rest)
- Stress and anxiety
- Caffeine, alcohol and smoking
- Salt in your diet
- Sleep
- Temperature
- Your posture and arm position during a reading
Your Band vs a Blood Pressure Cuff
Some difference between your band and a cuff is expected:
- Differences of up to 10 mmHg can be normal
- Blood pressure changes from moment to moment, so even two cuff readings taken a few minutes apart won't match exactly
- Your band measures at your wrist using light, while a cuff measures at your upper arm using pressure, so the two naturally give slightly different results
If the difference is much bigger than this, see our Blood Pressure Troubleshooting Guide.
How to Get the Most Accurate Readings
- Wear your band correctly. Position it about one finger-width above your wrist bone, with the sensor flat against your skin and a snug but comfortable fit. This is the most important factor.
- Stay still. Sit with your arm resting at heart level, and don't talk or move during the reading.
- Use One Key Measurement to compare. When comparing with a cuff, use One Key Measurement rather than the hourly reading, and take both readings at the same time.
- Give it time. Allow a few weeks of consistent wear for your blood pressure trends to settle.
How to Use Your Blood Pressure Data
Blood pressure is most useful as a trend. A single reading tells you very little, but patterns over days and weeks can show how things like sleep, exercise, stress and diet affect your blood pressure.
Things you might notice:
- Patterns linked to certain times of day, activities or stressful situations
- How changes to your sleep, exercise or diet show up in your trends
Your trends can also be useful to bring to a conversation with your doctor.
Important
Your band's blood pressure readings are estimates designed for tracking trends over time. They aren't a replacement for a clinically validated blood pressure monitor, and shouldn't be used to diagnose any condition or make decisions about medication or treatment. If you have any concerns about your blood pressure, speak to a qualified healthcare professional.
Still have questions? Email us at info@hlthtrack.com.