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Publication Number
US-12036007-B2
Publication Date
2024-07-16
Expiration Date
Abstract
Monitoring apparatus for monitoring the pulse transit time and/or estimating one or more blood pressure parameters of a subject and the method of use of the monitoring apparatus. The apparatus comprises an upper arm unit for attaching to a subject's upper arm in use and comprising at least one motion sensor, a photoplethysmograph comprising at least one light source and at least one light detector and at least one display.
Core Innovation
The disclosed invention provides a monitoring apparatus with an upper arm unit adapted to be worn on a subject’s upper arm. The upper arm unit comprises at least one motion sensor configured to monitor motion due to cardiac activity and output at least one motion signal while worn, and a photoplethysmograph (PPG) configured to monitor blood volume within the subject’s upper arm and output a PPG signal while worn. The apparatus includes at least one processor programmed to process both the motion signal and the PPG signal to calculate an estimate of a pulse transit time (PTT) parameter of the subject, or changes therein.
A central aspect of the processing is cross-calculating the motion signal with the PPG signal. Cross-calculating comprises time shifting the PPG signal and calculating an integral of a product of the motion signal and the time-shifted PPG signal across time shifts, to estimate the PTT parameter. Signal-processing techniques are used to derive PTT and refine estimation across windows, including quality/confidence criteria to reject unreliable time windows.
The processor can further estimate blood pressure (BP) parameters, such as SBP/DBP/MBP, based on relationships involving pulse wave velocity (PWV) and PTT derived from the motion and PPG signals. In example implementations, the apparatus uses a shared clock signal to synchronize acquisition of the motion signals and the PPG signal, and includes an upper-arm PPG with LEDs and photodiodes.
Claims Coverage
The partial content identifies two independent claims: one for a monitoring apparatus and one for a method. Both independent claims share the inventive concept of estimating a pulse transit time (PTT) parameter, or changes therein, from jointly processed upper-arm motion-sensor and PPG signals via cross-calculating that includes time shifting and integrating a product across time shifts.
Upper-arm monitoring of PTT using motion and PPG signals
A monitoring apparatus with an upper arm unit adapted to be worn on a subject’s upper arm, the upper arm unit comprising at least one motion sensor configured to monitor motion due to cardiac activity and output at least one motion signal, and a photoplethysmograph (PPG) configured to monitor blood volume within the subject’s upper arm and output a PPG signal, and at least one processor programmed to process both the at least one motion signal and the PPG signal to thereby calculate an estimate of the PTT parameter of the subject, or changes therein.
Cross-calculating via time shifting and integral product
Processing both the at least one motion signal and the PPG signal comprises cross-calculating the at least one motion signal with the PPG signal, wherein cross-calculating comprises time shifting the PPG signal and calculating an integral of a product of the at least one motion signal and the time-shifted PPG signal across time shifts.
Method for monitoring PTT using the same cross-calculation
A method of monitoring a pulse transit time (PTT) parameter of a subject, or changes therein, using a monitoring apparatus with an upper arm unit adapted to be worn on a subject’s upper arm comprising at least one motion sensor and a PPG, the method comprising processing both the at least one motion signal and the PPG signal to calculate an estimate of the PTT parameter and then outputting the calculated estimate.
Time shifting PPG and integrating product across time shifts in the method
The processing comprises cross-calculating the at least one motion signal with the PPG signal, wherein cross-calculating comprises time shifting the PPG signal and calculating an integral of a product of the at least one motion signal and the time-shifted PPG signal across time shifts.
Across both independent claims, the core claim coverage centers on using an upper-arm motion sensor together with an upper-arm PPG to estimate a PTT parameter, or changes therein, where the estimation is performed by cross-calculating through time shifting the PPG and integrating a product of the motion signal and the time-shifted PPG signal across time shifts.
Stated Advantages
quality/confidence criteria to reject unreliable time windows
estimate blood pressure (BP) parameters, such as SBP/DBP/MBP, based on relationships involving pulse wave velocity (PWV) and PTT derived from the motion and PPG signals.
Documented Applications
estimate blood pressure (BP) parameters, such as SBP/DBP/MBP
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