Patent ID: 11964130
Assignee: MEDTRONIC, INC.
Field: Medical technology (Instruments)
Classification: CPC A | IPC A

Claim 22:
23. A method of determining a reservoir volume information of an implantable medical device, the method comprising:
providing an implantable medical device comprising a housing that defines a propellant chamber, and a drug reservoir positioned within the propellant chamber, a propellant gas within the propellant chamber, a volume measurement system comprising a temperature sensor and a pressure sensor, and processing circuitry connected to the volume measurement system;
measuring, using the processing circuitry, a current temperature of the propellant gas in the propellant chamber with the temperature sensor;
measuring, using the processing circuitry, a current pressure of the propellant gas in the propellant chamber with the pressure sensor; and
determining, using the processing circuitry, current volume information of a therapeutic fluid in the drug reservoir based on the current temperature and the current pressure of the propellant gas in the propellant chamber;
wherein the volume measurement system is configured to measure a current volume of the therapeutic fluid based on Equation 4 below:, V
          Dr
        
        =
        
          
            V
            T
          
          -
          
            A
            ⁢
            
              T
              P
            
          
        
      
    
    
      
        Equation
        ⁢
        
          
        
        ⁢
        4
      
    
  

wherein VDr is the current volume of the therapeutic fluid having SI units of m3, T is the temperature of propellant gas measured by the temperature sensor having SI units of K, P is the pressure of propellant gas measured by the pressure sensor having SI units of J·m−3, VT is a volume constant of the propellant chamber having SI units of m3, and A is a gas constant of having SI units of J·K−1.