Surgery – Diagnostic testing – Measuring or detecting nonradioactive constituent of body...
Patent
1998-10-28
2000-07-18
O'Connor, Cary
Surgery
Diagnostic testing
Measuring or detecting nonradioactive constituent of body...
600345, 600365, 600366, A61B 505, A61B 500
Patent
active
060919760
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
The invention relates to a method and apparatus to determine and monitor the concentration of tissue glucose as defined in the preambles of the independent claims 1 and 17.
Methods of this kind are applicable foremost in human medicine, in particular to monitor the blood sugar of diabetics. They are based on the insight that the glucose content of the interstitial tissue fluid is highly correlated, with little time delay, to the blood sugar level. It is known to recover glucose by dialysis and then to determine the glucose content by enzymatic-amperometric measurements in an flow-through test cell. For that purpose a continuous flow of perfusate is made to pass along the dialysis membrane of the dialysis probe. The yield so obtained depends essentially on the rate of perfusion and as a rule is less than 30%. The measurement is commensurately inaccurate because interfering factors such as tissue movement and changes in blood circulation strongly affect the yield and hence the test signal. Lowering the perfusion rate will not help because entailing a correspondingly higher dead time caused by the flow time between the microdialysis probe and the test site. On the other hand, high rates of flow velocity do indeed lower the dead time. However the dialysis yield relative to a unit volume of perfusion solution decreases to the same extent. Moreover a glucose gradient is formed in the tissue surrounding the microdialysis probe on account of continuously withdrawing glucose. However long-term treatment of diabetics mandates reliable glucose measurements to dose insulin administrations as needed and, where desirable, automatically.
Based on the above, the objective of the invention is to create a method and apparatus of the initially cited kinds which offer high reliability and accuracy as regards glucose determination.
The combinations of features stated in the patent claims 1 and 17 are proposed as solutions. Further advantageous implementations of the invention are stated in the dependent claims.
The conventional continuous enrichment of the perfusion solution is replaced in the invention by equalizing the liquid column, moved in segments with high yield through the microdialysis probe, and the tissue glucose content. Accordingly the invention proposes to reduce the time-averaged volumetric flow of the perfusion solution for the duration of dialysis intervals and that the volume of perfusion solution perfused during each dialysis interval through the microdialysis probe shall be moved on in an ensuing transport interval at a higher volumetric flow to the test cell. The equalization of concentration taking place during the dialysis intervals averts continuous impoverishment of the tissue. At the same time, high signal strength is achieved because of the higher yield. The enriched partial volumes can be moved at a higher conveyance flow and thus with a lesser dead time to the test cell.
In a preferred implementation of the invention, the perfusion solution is mixed with glucose before being made to pass through the microdialysis probe and a predetermined initial concentration is set, preferably within the physiological range. Using an initial solution mixed with glucose leads to diffusion enrichment or impoverishment at the dialysis membrane depending on the tissue glucose concentration. Accordingly a signal peak or a signal dip is observed in the time-sequence of the test signals at the test cell. On the other hand the subsequent perfusion solution passing at a higher flow during the transport intervals through the microdialysis probe essentially retains its initial glucose concentration. Accordingly a base line reflecting the initial glucose concentration is picked up during the subsequent flow through the cell.
Advantageously the volumetric flow of perfusion solution is so adjusted during the transport intervals that the glucose content of the perfusion solution changes less than 10%, preferably less than 5%, on account of the reduced duration of dialysis, when passing through the microdialysis pro
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Hoss Udo
Pfeiffer Margret
Natnithithadha Navin
O'Connor Cary
Roche Diagnostics GmbH
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