Dry weight predictor

Abstract

Methods and apparatus for predicting/estimating the dry weight of an individual, e.g., a patient undergoing dialysis treatment, are provided. The techniques employ a bioimpedance measurement (303) on the individual's calf (101) to obtain information regarding the extracellular fluid volume of the calf Using a measurement of the calfs circumference (309), a resistivity value is calculated, normalized by the individual's body mass index (BMI), and then offset by a reference value to obtain a new variable, ΔnRho, which is shown, by comparison with a “gold standard” (FIGS. 5-9), to be highly effective in predicting/estimating dry weight (FIGS. 10-13 and 15-16). The techniques are easy to use and provide accurate dry weight predictions/estimations without substantially adding to the complexity or cost of dialysis procedures. The techniques can also be used for individuals who are not renal patients, e.g., patients suffering from other diseases in which fluid overload can occur, athletes, fitness enthusiasts, and the like.

1 .- 62 . (canceled) 
     
     
         63 . A method of determining a target dry weight of an individual, comprising:
 obtaining a resistance value R of extracellular fluid volume of a calf of the individual;   obtaining a circumference C of the calf;   determining a normalized resistivity ρ N  based on the resistance value R, the circumference C, and a body mass index (BMI) value of the individual;   determining a difference value ΔnRho between the normalized resistivity ρ N  and a reference value K for the normalized resistivity ρ N , the reference value K being representative of a population of reference individuals; and   determining the target dry weight of the individual based on the difference value ΔnRho.   
     
     
         64 . The method of  claim 63 , comprising determining a dosage of a medicament based on the target dry weight to determine a dosage of a medicament. 
     
     
         65 . The method of  claim 64 , comprising administrating the dosage of the medicament to the user. 
     
     
         66 . The method of  claim 64 , the medicament comprising at least one of a diuretic or a calcium channel blocker. 
     
     
         67 . The method of  claim 63 , R measured using a bioimpedance measurement technique via recording electrodes separated by a distance L. 
     
     
         68 . The method of  claim 67 , comprising determining normalized resistivity ρ N  according to the following:
   ρ N   =R·C   2 /(4 πL ·BMI).
 
 
     
     
         69 . The method of  claim 68 , comprising determining the difference value ΔnRho according to the following:
   Δ n Rho=−(ρ N   −K ).
 
 
     
     
         70 . The method of  claim 69 , comprising determining the target dry weight according to the following:
   WT−( a·Δn Rho+β)−1.0≤TDW≤WT−(α·Δ n Rho+β)+1.0,
   
       where the equation is in kilograms, WT is a weight of the individual's when C and R are determined, and a and f3 are predetermined constants. 
     
     
         71 . The method of  claim 63 , wherein the reference value K is obtained by determining the resistance value R of extracellular fluid volume of the calf and measuring the circumference C of calves of at least one set of reference individuals. 
     
     
         72 . The method of  claim 71 , wherein the reference individuals are healthy subjects. 
     
     
         73 . An apparatus, comprising a computer system programmed to execute instructions to determine a target dry weight of an individual, the instructions, when executed by a computer of the computer system, to cause the computer to:
 receive a resistance value R of extracellular fluid volume of a calf of the individual;   receive a circumference C of the calf;   determine a normalized resistivity ρ N  based on the resistance value R, the circumference C, and a body mass index (B MI) value of the individual;   determine a difference value ΔnRho between the normalized resistivity ρ N  and a reference value K for the normalized resistivity ρ N , the reference value K being representative of a population of reference individuals; and   determine the target dry weight of the individual based on the difference value ΔnRho.   
     
     
         74 . The apparatus of  claim 73 , the instructions, when executed by the computer, to cause the computer to determine a dosage of a medicament based on the target dry weight to determine a dosage of a medicament. 
     
     
         75 . The apparatus of  claim 73 , the instructions, when executed by the computer, to cause the computer to determine an administration scheme of a medicament based on the target dry weight. 
     
     
         76 . The apparatus of  claim 75 , the medicament comprising at least one of a diuretic or a calcium channel blocker. 
     
     
         77 . The apparatus of  claim 73 , the instructions, when executed by the computer, to cause the computer to determine normalized resistivity ρ N  according to the following:
   ρ N   =R·C   2 /(4 πL ·BMI).
 
 
     
     
         78 . The apparatus of  claim 77 , the instructions, when executed by the computer, to cause the computer to determine the difference value ΔnRho according to the following:
   Δ n Rho=−(ρ N   −K ).
 
 
     
     
         79 . The apparatus of  claim 78 , the instructions, when executed by the computer, to cause the computer to determine the target dry weight according to the following:
   WT−(α·Δ n Rho+β)−1.0≤TDW≤WT−(α·Δ n Rho+β)+1.0,
   
       where the equation is in kilograms, WT is a weight of the individual's when C and R are determined, and α and β are predetermined constants. 
     
     
         80 . The apparatus of  claim 73 , wherein the reference value K is obtained by determining the resistance value R of extracellular fluid volume of the calf and measuring the circumference C of calves of at least one set of reference individuals. 
     
     
         81 . A method for administering a medicament to an individual based on a target dry weight for the individual, comprising:
 obtaining a measured resistance value R indicative of the extracellular fluid volume of a calf of the individual using a bioimpedance measurement technique via recording electrodes separated by a distance L;   obtaining a measured value indicative of the circumferential size C of the calf;   determining a normalized resistivity value ρ N  indicative of the extracellular fluid volume of the calf based on R and C, a BMI value of the individual, based on the following:
   ρ N   =R·C   2 /(4 πL ·BMI);
 
   determining a difference value ΔnRho between the normalized resistivity value ρ N  and a reference value K for the normalized resistivity value based on the following:
   Δ n Rho=−(ρ N   −K );
 
   determining the target dry weight TDW based on the following:
   WT−(α·Δ n Rho+β)−1.0≤TDW≤WT−(α·Δ n Rho+β)+1.0
 
   
       where the equation is in kilograms, WT is a weight of the individual when C and R are determined, and α and β are predetermined constants;
 determining a dosage of a medicament based on the target dry weight to determine a dosage of the medicament; and 
 administrating the dosage of the medicament to the user. 
 
     
     
         82 . The method of  claim 81 , the medicament comprising at least one of a diuretic or a calcium channel blocker.