Monitoring Substitution Fluid Supply in Extracorporeal Blood Treatment
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Solution Overview
Problem
Current methods for monitoring predilution and postdilution in extracorporeal blood treatment devices lack reliability, particularly in distinguishing between the two based on pressure wave measurements, which can be interfered by other signals and require specialized pumps.
Innovation Solution
Measuring pressure changes after shutting off or starting the substitution fluid pump, recognizing predilution or postdilution through characteristic pressure increases or decreases, and using a low-pass filter to suppress interference, with optional Fourier analysis to differentiate between predilution and postdilution based on pressure signal harmonics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Difficulty of detecting and measuring
If pressure wave measurements are used to distinguish predilution and postdilution, then detection capability is provided, but reliability is reduced due to interference signals and requirement for specialized pumps
Solution Approach 1:
The patent extracts and eliminates the source of interference by not requiring specialized pumps that generate pressure waves. Instead, it uses a pressure sensor to measure pressure changes caused by the substitution fluid pump's operation cycles, separating the useful signal (pressure changes corresponding to pump on/off) from harmful interference signals.
Solution Approach 2:
The patent introduces an intermediary evaluation that analyzes the relationship between substitution fluid pump operation timing and pressure sensor signals. This intermediary evaluation distinguishes predilution from postdilution by detecting characteristic pressure increase/decrease patterns during pump on/off cycles, providing reliable detection without specialized equipment.
2Difficulty of detecting and measuring
If specialized pumps producing pressure waves are used for monitoring, then predilution and postdilution can be distinguished, but device complexity increases
Solution Approach 1:
The patent makes the existing substitution fluid pump serve a dual function: it continues to supply substitution fluid while simultaneously acting as the source of pressure changes for detection. The pump's regular on/off cycles create measurable pressure variations that the pressure sensor detects, eliminating the need for separate specialized pumps or complex monitoring equipment.
Solution Approach 2:
The pressure sensor in the fluid system serves multiple functions: it monitors pressure changes for predilution/postdilution detection, tracks substitution fluid supply status, and provides data for treatment parameter monitoring. This multi-functionality reduces device complexity by using existing components for multiple purposes.
3Measurement precision
If pressure measurements are taken continuously, then monitoring accuracy is improved, but interference from other signals increases
Solution Approach 1:
The patent utilizes the periodic on/off operation of the substitution fluid pump to create a periodic pressure signal pattern. By synchronizing the pressure measurement evaluation with the pump's operation cycles, the system identifies characteristic pressure increases during pump on and pressure decreases during pump off, distinguishing these periodic signals from random interference and achieving accurate monitoring.
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 method provides reliable detection of predilution and postdilution with minimal additional hardware requirements, improving dialysis dosage determination and reducing errors from interference signals, and is applicable for online clearance monitoring and other dialysis parameters.
Implementation Method 1
a pressure sensor (28) for measuring the pressure in the blood stream downstream of the dialyser (1)
Implementation Method 2
with optional Fourier analysis to differentiate between predilution and postdilution based on pressure signal harmonics
Data Source
AI summary
The invention relates to a process for monitoring the supply of substitution fluid upstream or downstream of a dialyser or filter arranged in an extracorporeal blood stream. One embodiment provides, for the detection of predilution or postdilution, for measuring the pressure in the blood stream downstream of the dialyser or filter, predilution or postdilution being recognized on the basis of the change in pressure following the shutting off and/or starting up of the substituate pump provided for conveying the substitution fluid. Another embodiment provides for recognizing predilution or postdilution on the basis of the comparison of the oscillating pressure signal attributable to the substituate pump to a characteristic reference signal. The characteristic reference signal to which the pressure signal of the substituate pump is compared is preferably the oscillating pressure signal of a blood pump arranged in the blood stream for conveying the blood upstream of the dialyser or filter. In addition, the invention relates to an extracorporeal blood treatment device with a facility for detecting predilution or postdilution, which device operates according to the processes detailed above.