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

Claim 11:
12. An implantable medical device comprising:

a housing defining a propellant chamber therein;
a drug reservoir located within the propellant chamber of the housing configured to receive a therapeutic fluid therein;
a propellant gas within the propellant chamber; and

a volume measurement system comprising:
a temperature sensor configured to measure a temperature of the propellant gas within the propellant chamber;
a pressure sensor configured to measure a pressure of the propellant gas within the propellant chamber, wherein 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, and 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.