A closer look at the signal within
Explore the science of PPG
Light meets physiology. Explore the signals, sensors, and science behind every pulse.
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PPG Guides
Signal, sensor, and physiology explainers
Explore
Plethscape
Interactive pulse-signal simulation
Compare
Wearables
Documented capabilities and limitations
Build Better PPG Intuition
Use clear educational guides and interactive signal exploration to understand what PPG can measure, where it struggles, and how wearable designs differ.
Evidence-Conscious Guides
Read practical explanations that distinguish documented device behavior, research findings, and open questions.
Focused PPG Library
Browse guides on optical sensing, waveform morphology, motion artifacts, algorithms, and wearable form factors.
Interactive Learning
Use Plethscape to see how wavelength, body location, movement, and physiology can change a simulated PPG waveform.
A future research workflow
1. Adaptive Filtering: Least Mean Squares (LMS) and Recursive Least Squares (RLS) filters using an accelerometer reference.
2. Signal Decomposition: Methods like Singular Value Decomposition (SVD) and Independent Component Analysis (ICA) may help separate motion-related components from the cardiac signal.
3. Learned Models: Performance depends on the training data, activity, sensor placement, and evaluation protocol, so results need source-specific review.
Direct answer
What is ChatPPG?
ChatPPG is a public education resource for photoplethysmography (PPG) and wearable biosignals. It offers explainers, device comparisons, and the interactive Plethscape simulator. A research-assistant product is a future area of interest, and visitors can register for launch updates.
What is PPG (Photoplethysmography)?
Photoplethysmography (PPG) is a simple and low-cost optical technique that can be used to detect blood volume changes in the microvascular bed of tissue. It is often used non-invasively to make measurements at the skin surface. The PPG waveform comprises a pulsatile ('AC') physiological waveform attributed to cardiac synchronous changes in the blood volume with each heart beat, and is superimposed on a slowly varying ('DC') baseline with various lower frequency components attributed to respiration, sympathetic nervous system activity and thermoregulation.
In recent years, the technology has become ubiquitous in wearable devices like smartwatches (e.g., Apple Watch, Fitbit, Garmin) and fitness trackers. It allows for the continuous monitoring of Heart Rate (HR), Heart Rate Variability (HRV), Oxygen Saturation (SpO2), and potentially even Blood Pressure (BP) via Pulse Transit Time (PTT) or Pulse Wave Analysis (PWA).
However, PPG signals are highly susceptible to motion artifacts, ambient light interference, sensor contact, and physiological variation. The guides and Plethscape simulator help readers explore these factors while recognizing that a simulation is not a medical measurement.
Is ChatPPG free?
The educational guides and Plethscape are free to explore. The research assistant is a future product concept; launch timing and pricing have not been announced.
Common PPG Research Questions
PPG Glossary
Dicrotic Notch
A small downward deflection in the arterial pulse or pressure contour immediately following the closure of the semilunar valves.
Perfusion Index (PI)
The ratio of the pulsatile blood flow to the non-pulsatile static blood flow in peripheral tissue.
Pulse Transit Time (PTT)
The time it takes for the arterial pulse pressure wave to travel from the aortic valve to a peripheral site.
AC Component
The pulsatile portion of the PPG signal, synchronous with the heartbeat.
DC Component
The slowly varying baseline of the PPG signal, related to respiration and thermoregulation.
Motion Artifact (MA)
Noise introduced into the signal caused by voluntary or involuntary movement of the subject.
Frequently Asked Questions
What is PPG?
Photoplethysmography is an optical technique for observing blood-volume changes in tissue. It is widely used in pulse oximeters and wearable heart-rate sensors.
Is ChatPPG free?
The public educational guides and Plethscape experience are available to explore. Pricing for any future research product has not been announced.
What can I use on ChatPPG today?
You can browse PPG educational guides, compare wearable sensing approaches, and use the Plethscape simulator. You can also register your interest in future research-product updates.
Does ChatPPG provide medical advice?
No. ChatPPG is a research tool for scientists and engineers. It is not a diagnostic tool and should not be used for medical decision-making.