Video Imaging Pulse Transit Time Measurement
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Solution Overview
Problem
Current methods for determining arterial pulse transit time require direct contact with the patient's skin, which is impractical for neonatal intensive care units, especially for premature babies with sensitive skin, and there is a need for non-contact means to capture physiological signals.
Innovation Solution
A system and method using video imaging to capture time-varying source signals from proximal and distal regions of the body, processing these signals to extract phase angle versus frequency curves, and calculating the arterial pulse transit time by computing the difference in slopes within a selected cardiac frequency range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If electrodes of an ECG device are attached directly to the patient's skin to obtain pulse transit time measurements, then measurement precision is improved, but ease of operation deteriorates due to the impracticality of direct skin contact
Solution Approach 1:
The patent replaces the mechanical contact-based ECG electrode system with an optical video imaging system. The video camera captures time-varying source signals from the patient's skin surface non-contactly, and signal processing algorithms extract pulse transit time information from the video data, eliminating the need for physical skin contact while maintaining measurement capability
Solution Approach 2:
The patent introduces video imaging as an intermediary between the measurement system and the patient. Instead of direct electrode-skin contact, the system uses video cameras to capture optical reflections from the skin, which then serve as the basis for extracting physiological signals through computational processing
2Ease of operation
If video imaging is used to capture time-varying source signals non-contactly, then ease of operation is improved, but measurement precision may deteriorate due to the indirect nature of the measurement
Solution Approach 1:
The patent performs preliminary signal processing operations on the video data, including computing phase angles with respect to frequency to produce phase versus frequency curves, extracting slopes within selected cardiac frequency ranges, and calculating time delays. These preliminary computational steps prepare the raw video signals for accurate pulse transit time determination
Solution Approach 2:
The system uses feedback through computational processing to enhance the weak optical signals. By analyzing phase relationships and frequency characteristics of the video-captured signals, the system iteratively refines the extraction of pulse transit time information, compensating for the indirect measurement approach
Data Source
AI summary
What is disclosed is a system and method for determining a subject of interest's arterial pulse transit time from time-varying source signals generated from video images. In one embodiment, a video imaging system is used to capture a time-varying source signal of a proximal and distal region of a subject of interest. The image frames are processed to isolate localized areas of a proximal and distal region of exposed skin of the subject. A time-series signal for each of the proximal and distal regions is extracted from the source video images. A phase angle is computed with respect to frequency for each of the time-series signals to produce respective phase v/s frequency curves for each region. Slopes within a selected cardiac frequency range are extracted from each of the phase curves and a difference is computed between the two slopes to obtain an arterial pulse transit time for the subject.