How PPG Measures Heart Rate and Pulse Changes
PPG uses light to follow the pulse at your finger. With each heartbeat, pressure and blood volume change through the arteries. An LED shines light into the tissue, and an optical sensor measures how much light returns. The repeating rise and fall in that reflected-light signal forms a pulse waveform. When the waveform is clear enough, algorithms can count the pulses to estimate heart rate and measure the timing between them. It is a useful optical method—but it is not the same as an ECG, and movement or poor contact can affect the result.
PPG begins with a simple idea
Photoplethysmography—usually shortened to PPG—is an optical way to detect changes in blood volume near the skin.
Think of the tissue in your finger as a changing filter. Some of the light sent into it is absorbed, and some returns to the sensor. When the pulse wave reaches your finger, local blood volume changes. Because blood absorbs light differently from the surrounding tissue, the amount of returning light also changes.
The sensor records this sequence many times. Instead of seeing a single number, the system sees a waveform with peaks, valleys, shape, timing, and noise.
PPG inside AIVELA RING PRO
AIVELA RING PRO uses a PixArt optical PPG sensor. The sensing system supports green, red, and infrared light for different optical measurements.
Green light is well suited to detecting pulse-related changes close to the skin and is commonly used for heart-rate sensing. Red and infrared light penetrate and interact with tissue differently; together, they can support blood oxygen estimation under suitable conditions. This article focuses on the pulse waveform used for heart rate and pulse timing.
The inside of the finger is a useful location because it can provide close contact and a strong blood supply. It is not automatically perfect. A reliable reading still depends on fit, contact, movement, circulation, and enough usable measurement time.
From a pulse waveform to heart rate
Heart rate is usually expressed in beats per minute (bpm). A PPG algorithm does not need to wait a full minute and count every beat. It can identify a sequence of suitable pulse cycles in a shorter analysis window, estimate the average time between pulses, and convert that timing into bpm.
For example, if clean pulses are about one second apart, the estimated heart rate is about 60 bpm. If they are about half a second apart, it is about 120 bpm. Real waveforms are less tidy: pulse shape changes, timing is not perfectly even, and motion can create peaks that are not heartbeats. The algorithm therefore needs several cycles and quality checks before reporting a result.
AIVELA uses different acquisition patterns for different contexts. During ordinary wear, heart-rate PPG is collected in scheduled windows. During sleep, recurring higher-frequency windows capture more detailed pulse information while the body is often relatively still. During workout-related use, continuous green-light PPG can follow faster changes in heart rate. The exact cadence is a device and firmware setting, while the user-facing result is based on the usable data within each relevant window.
Pulse timing can reveal more than pulse rate
Heart rate tells you how frequently pulses occur. The exact interval from one suitable pulse to the next also changes slightly from beat to beat.
After removing poor-quality and irregular sections according to the algorithm’s rules, those pulse intervals can support a pulse-derived estimate of heart rate variability (HRV). HRV is not “how much your heart rate changed during the day.” It describes variation in the timing between successive beats within a defined measurement period.
PPG detects the pulse wave after it travels from the heart to the finger. An electrocardiogram, or ECG, records the heart’s electrical activity. Their waveforms and timing markers are not identical. PPG can support useful pulse-rate and HRV estimates in suitable conditions, but it should not be described as an ECG or used to make ECG-based clinical conclusions.
AIVELA interprets HRV primarily in relation to your own reliable history because typical values and responses differ considerably between people. A dedicated HRV article explains that comparison in more detail.
Why the signal is sometimes difficult to read
PPG is sensitive because it is trying to detect small changes in light. That sensitivity also means other changes can appear in the waveform.
Movement
Finger motion can change the distance and pressure between the sensor and skin. It can also change blood flow and reflected light. These motion artifacts may resemble or obscure pulse peaks. Motion-sensor data and signal processing help identify affected periods, but not every disturbance can be removed.
Fit and contact
A ring that is too loose may rotate or allow light to enter inconsistently. A ring that is uncomfortably tight may affect wear and local tissue. The goal is stable, comfortable contact, with the sensors positioned as intended.
Cold hands and circulation
When blood flow near the skin is lower, the pulse-related optical change may be smaller. Cold conditions, individual circulation, and pressure on the finger can all make a reading more difficult.
Skin and environment
Ambient light, moisture, dirt, tissue characteristics, skin pigmentation, tattoos, and other individual or environmental factors can change how light travels and returns. The sensor and algorithm can adapt to some variation, but adaptation is not the same as guaranteeing an equally strong signal in every condition or every person.
Measurement time
A short, interrupted, or noisy window may not contain enough suitable pulse cycles. In that case, filtering the result or waiting for a better window can be more responsible than showing a precise-looking number built on weak evidence.
How to support a clearer PPG reading
- Wear the ring on a recommended finger with the sensors correctly oriented.
- Choose a size that stays in contact without being uncomfortable.
- Keep the sensor surface and skin clean and dry.
- Give the ring enough consistent wear time, especially during sleep.
- During an on-demand or workout reading, keep the hand as steady as the activity allows.
- If your hands are very cold, allow them to warm naturally before expecting a strong resting signal.
- Read isolated values alongside data quality, context, and longer trends.
More pressure is not the answer. If the ring causes discomfort, numbness, swelling, or skin irritation, remove it and follow the product’s wear guidance.
How AIVELA uses the result
Usable PPG supports several parts of the product. Heart rate and resting heart rate help describe cardiovascular patterns in the relevant time window. Pulse-derived HRV adds information about beat-to-beat timing. Optical information may also contribute to nighttime blood oxygen and respiratory-rate estimates.
These metrics can contribute to Calm and Balance, appear in signal views, and help build longer-term personal context. They do not all carry the same weight, and a change in one metric does not automatically explain a score or identify a cause.
What a PPG reading cannot tell you
PPG can estimate pulse-related metrics. By itself, it cannot tell you why heart rate or HRV changed. It cannot diagnose an arrhythmia, infection, sleep disorder, cardiovascular condition, or any other disease. It cannot replace an ECG, pulse oximeter used in clinical care, or assessment by a qualified professional.
AIVELA RING PRO is a consumer wellness product. If a reading is very different from what you expect, first check fit, stillness, and whether the result repeats. If you have symptoms, a persistent concern, or a medical question, seek appropriate professional advice regardless of what the ring displays.
PPG turns light into a pulse waveform. Good interpretation begins by respecting both the signal and its limits.