Analog Phase Detection for Differential Pulse Transit Time
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Solution Overview
Problem
Existing continuous non-invasive blood pressure monitoring systems face challenges in accurately measuring blood pressure using multiple pulse oximetry sensors due to differences in sensor placement distances from the heart, leading to errors in differential pulse transit time calculations.
Innovation Solution
The use of a monitoring device that receives analog physiological signals from multiple sensors, employs a processor and phase detector to generate phase information, and calculates differential pulse transit time (DPTT) to determine physiological information, including blood pressure, through analog and digital signal processing operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If digital signal processing is used to calculate phase difference, then measurement flexibility is improved, but quantization errors increase and measurement speed decreases
Solution Approach 1:
The patent separates the phase detection process into two distinct stages: analog phase detection using a phase detector circuit to generate phase difference information, followed by digital processing to calculate DPTT from the analog output. This segmentation allows the precision-critical phase detection to occur in the analog domain while maintaining flexibility in the digital calculation stage.
Solution Approach 2:
The patent introduces an analog phase detector as an intermediary component between the sensor signals and the digital processor. The phase detector converts the phase relationship between two PPG signals into an analog voltage signal that preserves continuous information, avoiding quantization errors that would occur if digital sampling were used directly for phase measurement.
2Adaptability or versatility
If digital signal processing is used to calculate phase difference, then processing flexibility is improved, but measurement speed decreases
Solution Approach 1:
The patent divides the signal processing workflow into analog phase detection (fast, continuous) and digital DPTT calculation (flexible, discrete). The analog phase detector operates continuously at high speed to generate real-time phase difference information, while the digital processor performs calculations at its own pace, eliminating the speed bottleneck of digital phase computation.
Solution Approach 2:
The patent replaces the mechanical/computational process of digital phase calculation with an analog electronic phase detection mechanism. The phase detector uses electronic circuits to directly measure phase relationships, providing instantaneous results without requiring digital sampling, filtering, and computational algorithms that limit processing speed.
3Adaptability or versatility
If sensors are placed at different distances from the heart, then blood pressure monitoring capability is improved, but measurement accuracy deteriorates due to path differences
Solution Approach 1:
The patent changes the measurement parameter from direct time-of-flight measurement to phase difference measurement. By measuring the phase relationship between two PPG signals at different body sites and converting it to DPTT, the system compensates for path length differences and provides accurate blood pressure monitoring regardless of sensor placement locations.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach reduces quantization errors and provides faster blood pressure measurements by performing phase measurements in the analog domain, enhancing the accuracy and efficiency of blood pressure monitoring.
Implementation Method 1
employs a processor and phase detector to generate phase information
Data Source
AI summary
Systems and methods are provided for patient monitors which apply phase detection operations to analog signals to identify differential pulse transit time (DPTT). Photoplethysmograph (PPG) signals measured at two sensor sites may be processed by a phase detection system to identify phase information that allows the calculation of a DPTT. The phase detection system may process analog PPG signals in the analog domain to determine phase information. In some embodiments, the phase detection system may process optical oximetry sensor signals to determine phase information using, for example, interferometric methods.