Low Power Plethysmograph Sampling via Systolic Phase Detection

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Solution Overview

Problem

Conventional methods for reducing power consumption in pulse oximeters, which measure oxygen saturation and heart rate, require complex signal processing and are not efficient in sampling plethysmograph signals at low power, especially due to continuous operation of light sources.

Innovation Solution

A method and system that estimate and compute amplitudes and durations of plethysmograph waveforms for cardiac cycles, allowing for iterative sampling and reconstruction of plethysmograph data with reduced power consumption by powering light sources only during systolic rise periods.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If continuous operation of light sources (LEDs) is used to measure plethysmograph signals, then measurement precision is maintained, but power consumption increases

Engineering Contradiction:

Improvesampling accuracy of plethysmograph signalsVSAvoidpower consumption of light sources

Core Design Contradiction:

Measurement precisionVSUse of energy by moving object

Solution Approach 1:

The patent implements periodic sampling of plethysmograph signals at specific time instants within each cardiac cycle (during systolic rise periods) rather than continuous measurement. This allows LED activation to be periodic rather than continuous, reducing power consumption while capturing essential waveform characteristics for accurate SpO2 calculation.

Inventive Principle:

Principle #19Periodic action

Solution Approach 2:

The system performs preliminary detection of cardiac cycle phases and identifies optimal sampling time instants before actual measurement. By pre-determining when systolic rise periods occur based on detected waveform patterns, the system can activate LEDs only at these predetermined moments, avoiding continuous operation while maintaining measurement accuracy.

Inventive Principle:

Principle #10Preliminary action

2Use of energy by moving object

If sampling rates lower than the Nyquist rate are used to reduce LED power, then power consumption decreases, but signal processing complexity increases

Engineering Contradiction:

ImproveLED power consumptionVSAvoidsignal processing complexity

Core Design Contradiction:

Use of energy by moving objectVSDevice complexity

Solution Approach 1:

Instead of uniformly sampling the entire cardiac cycle at high rates, the patent applies non-uniform sampling that concentrates measurement resources on specific local segments of the waveform - specifically the systolic rise periods where critical information for SpO2 calculation is contained. This localised sampling approach reduces overall sampling rate requirements while maintaining signal fidelity where it matters most.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The system changes the sampling parameter from uniform time-based sampling to event-based sampling triggered by detected cardiac cycle phases. By transitioning from a fixed high sampling rate to adaptive sampling at detected systolic rise events, the system reduces average power consumption while the simplification of processing algorithms compensates for the lower sampling rate.

Inventive Principle:

Principle #35Parameter changes

3Use of energy by moving object

If amplitude and width of LED pulses are reduced to lower power consumption, then energy use decreases, but signal-to-noise ratio deteriorates

Engineering Contradiction:

ImproveLED energy consumptionVSAvoidsignal-to-noise ratio

Core Design Contradiction:

Use of energy by moving objectVSLoss of information

Solution Approach 1:

The patent maintains higher LED pulse amplitudes during active sampling periods by concentrating power delivery into brief, intense pulses during systolic rise periods rather than using continuous low-amplitude illumination. This periodic high-amplitude sampling preserves signal-to-noise ratio during measurement while the intermittent operation reduces overall energy consumption.

Inventive Principle:

Principle #19Periodic action

Solution Approach 2:

The system performs preliminary detection of cardiac cycle timing and pre-synchronizes LED pulse generation with detected systolic rise periods. By anticipating when optimal sampling moments occur and preparing high-amplitude pulses in advance, the system ensures sufficient signal strength is delivered at critical moments without requiring continuous high-power operation, thus maintaining SNR while reducing total energy use.

Inventive Principle:

Principle #10Preliminary action

Data Source

PatentUS9655533B2System and method for low power sampling of plethysmograph signals

Publication Date: 2017.05.23 GE PRECISION HEALTHCARE LLC

AI summary

A method for generating a sampled plethysmograph data, includes measuring a plethysmograph waveform indicative of a first cardiac cycle and a second cardiac cycle, each cycle including a systolic waveform and a diastolic waveform. The method further includes estimating a first start time and a first duration for the systolic waveform of the first cardiac cycle and computing a plurality of amplitudes at a plurality of time instants for the first duration. The method further includes determining a second start time and a second duration of the systolic waveform of the second cardiac cycle. The method also includes assigning the second cardiac cycle, the second start time, and the second duration to the first cardiac cycle, the first start time, and the first duration respectively. The method further includes iteratively performing the steps of measuring, estimating, computing, determining and assigning for the plurality of cardiac cycles acquired sequentially in time.