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

Claim 19:
20. A method of producing an implantable medical device comprising a volume measurement system, 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;
installing a volume measurement system in the implantable medical device, the volume measurement system comprising a temperature sensor configured to measure a temperature of a propellant gas within the propellant chamber and a pressure sensor configured to measure a pressure of the propellant gas within the propellant chamber;
charging the propellant chamber with a positive gauge pressure of the propellant gas; and
calibrating the volume measurement system so that the volume measurement system is configured to measure the pressure and the temperature of the propellant gas to provide current volume information of the therapeutic fluid in the drug reservoir;
wherein the volume measurement system is configured to measure the current volume of the therapeutic fluid based on the current volume of the propellant gas using the temperature and the pressure measured by the temperature sensor and the pressure sensor, wherein the current volume of the propellant gas is determined based on an ideal gas law;
wherein the volume measurement system is configured to measure the 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; and
wherein the volume measurement system is also configured to empirically determine at least A for calibrating the volume measurement system.