Breathing system with flow estimation

• US 9,295,796 B2
• Filed: 05/22/2010
• Issued: 03/29/2016
• Est. Priority Date: 05/22/2010
• Status: Active Grant

• Current Assignee: Maquet Critical Care AB (Getinge AB)
• Original Assignee: Maquet Critical Care AB (Getinge AB)
• Inventors: Eklund, Mathias, Hallbck, Magnus, Norrby, Fredrik
• Primary Examiner(s): Ho, Tan-Uyen (Jackie) T
• Assistant Examiner(s): Boecker, Joseph D
• Application Number:
  US13/699,072
• Publication Number:
  US 20130192600A1
• Time in Patent Office: 2,138 Days
• Field of Search: None
• US Class Current: 1/1
• CPC Class Codes: A61M 16/0057 Pumps therefor
• CPC Class Codes: A61M 16/026 specially adapted for predicting, e.g. for determining an information representative of a flow limitation during a ventilation cycle by using a root square technique or a regression analysis
• CPC Class Codes: A61M 16/04 Tracheal tubes catheters in general A61M25/00
• CPC Class Codes: A61M 16/06 Respiratory or anaesthetic masks
• CPC Class Codes: A61M 16/0816 Joints or connectors
• CPC Class Codes: A61M 16/0833 T- or Y-type connectors, e.g. Y-piece
• CPC Class Codes: A61M 16/0875 Connecting tubes
• CPC Class Codes: A61M 2016/0021 with a proportional output signal, e.g. from a thermistor
• CPC Class Codes: A61M 2016/0027 pressure meter
• CPC Class Codes: A61M 2016/0036 in the breathing tube and used in both inspiratory and expiratory phase
• CPC Class Codes: A61M 2205/3331 Pressure; Flow
• CPC Class Codes: A61M 2205/3334 Measuring or controlling the flow rate
• CPC Class Codes: A61M 2205/3344 Measuring or controlling pressure at the body treatment site
• CPC Class Codes: A61M 2230/46 Resistance or compliance of the lungs

Abstract

A breathing system for ventilating a patient has a gas channel enclosing a gas channel volume (V), and a compliance (C). The system has a flow calculation unit operative to determine a gas flow estimate (Fe) at a flow estimate location in the gas channel. The gas flow estimate (Fe) is based on a relationship between a monitored gas flow (Fm) in the gas channel and a compressible gas flow (Fc) which depends on the compliance (C) in the gas channel. The monitored gas flow (Fm) is a gas flow at a monitoring location in the gas channel and the compressible gas flow (Fc) is a flow of gas in the gas channel between the flow estimate location and the monitoring location, and the flow estimate location is remote from the monitoring location.

Claims

1. A breathing system for ventilating a patient, comprising:

a gas channel having a gas channel volume V and a compliance C;

a monitoring location in said gas channel;

a monitored gas flow Fm at said monitoring location which is either a measured flow at the monitoring location or a known flow from at least one gas source in communication with the gas channel;

a flow estimate location in said gas channel at which a gas flow estimate Fe is determined, said flow estimate location being remote from said monitoring location;

a plurality of pressure sensors measuring a respective plurality of pressures at different pressure measurement locations of said gas channel; and

a computer comprising a program and operative to determine said gas flow estimate Fe at said flow estimate location and wherein said gas flow estimate is based on a relationship between said monitored gas flow Fm and a compressible gas flow Fc dependent on said compliance C, said compressible gas flow Fc being a flow of gas in said gas channel between said flow estimate location and said monitoring location, said computer also being operative to determine an estimated pressure Pe based on said plurality of measured pressures from said respective pressure sensors, and wherein said estimated pressure Pe is a volume weighted pressure Pv with respect to said gas channel volume V, and said computer also being operative to determine said compressible gas flow Fc based on a relationship between said compliance C and a differential of said estimated pressure Pe for determining said gas flow estimate Fe.

2. The breathing system according to claim 1 further comprising:

said computer also being operative to determine said compliance C of said gas channel, and wherein said compliance C is a location specific compliance C′

at an arbitrary location in said gas channel between said flow estimate location and said monitoring location.

3. The breathing system according to claim 1 wherein said flow estimate location is remote from at least one of said pressure measurement locations.

4. The breathing system according to claim 1 wherein said computer is operative to determine said compressible gas flow Fc according to the relationship Fc =C*dPe/dt wherein said differential is dPe/dt which is time derivative of said estimated pressure Pe.

5. The breathing system according to claim 1 further comprising:

a breathing circuit; and

a patient tubing connected to said breathing circuit, wherein said gas flow estimate Fe is a patient gas flow Fp in said patient tubing, and wherein said patient gas flow is determined according to the relationship Fp=Fm−

C*dPe/dt wherein said differential is dPe/dt which is time derivative of said estimated pressure Pe.

6. The breathing system according to claim 5 wherein said gas channel volume V comprises a plurality of sub volumes Vk, and wherein said computer is operative to determine said volume weighted pressure Pv according to the relationship Pv=Σ

(Vk*Pk)/Σ

Vk, where Pk is a measured pressure in each of said plurality of sub volumes respectively.

7. The breathing system according to claim 6 wherein said plurality of sub volumes comprises a breathing circuit volume V_b of said breathing circuit and a patient tubing volume V_y of said patient tubing, wherein said pressure sensors comprise:

at least one breathing circuit pressure sensor adjacent to said breathing circuit volume V_b for providing a breathing circuit pressure P_b; and

at least one patient tubing pressure sensor for providing a patient tubing pressure P_p, wherein said computer is operative to determine said volume weighted pressure Pv according to the relationship P_v=(V_b*P_b+V_y*P_p)/(V_b+V_y).

8. The breathing system according to claim 7 wherein said patient tubing comprises:

y-piece tubing having an inspiratory tube and an expiratory tube; and

a y-piece connectable to said breathing circuit via said y-piece tubing, said y-piece having a patient connection port, wherein said y-piece has a patient interface connected to said patient connection port, wherein said flow estimate location is a patient interface location in said patient interface, and wherein said patient gas flow Fp is determined at said patient interface location.

9. The breathing system according to claim 8 wherein at least one of said pressure measurement locations is positioned away from said patient interface location by at least a distance corresponding to a length of said y-piece tubing.

10. The breathing system according to claim 9 wherein said y-piece tubing is connected to said breathing circuit at expiration and inspiration ports of said breathing system, and wherein said at least one patient tubing pressure sensor is adjacent to at least one of an expiration port and an inspiration port.

11. The breathing system according to claim 10 wherein said computer is operative to determine said compliance C based on a breathing circuit compliance Cb and a y-piece compliance Cy when said patient connection port is plugged, wherein said y-piece compliance is the compliance of said y-piece tubing and said y-piece.

12. The breathing system according to claim 11 wherein said patient interface comprises:

a proximal part disposed at said patient connection port and an opposite distal part, wherein said patient gas flow is determined at said distal part, wherein said computer is operative to determine said compliance C based on said breathing circuit compliance Cb and said y-piece compliance Cy when said patient interface is plugged, and wherein said y-piece compliance is the compliance of said y-piece tubing, said y-piece, and said patient interface.

13. The breathing system according to claim 10 wherein two of said gas sources are provided comprising a fresh gas source and a drive gas source, and further comprising:

two breathing circuit pressure sensors adjacent to each of said fresh gas source and said drive gas source; and

two patient tubing pressure sensors adjacent to each of said expiration and inspiration ports.

14. The breathing system according to claim 6 wherein said plurality of sub volumes comprises:

a total inspiratory volume Vyi of an inspiratory line in said breathing system; and

a total expiratory volume Vye of an expiratory line in said breathing system, wherein said computer is operative to determine said volume weighted pressure Pv according to a relationship between said total inspiratory volume and said total expiratory volume and at least one pressure measured by at least one of said pressure sensors.

15. The breathing system according to claim 14 wherein said pressure sensors comprise:

an expiratory pressure sensor adjacent to said total expiratory volume for providing an expiratory pressure Pexp; and

an inspiratory pressure sensor adjacent to said total expiratory volume for providing an inspiratory pressure Pinsp,

wherein said volume weighted pressure Pv is determined according to at least one of the following relationships,

during an inspiratory phase of said system

16. The breathing system according to claim 15 wherein said expiratory pressure sensor is adjacent to an expiration port, and wherein said inspiratory pressure sensor is adjacent to an inspiration port.

17. The breathing system according to claim 8 wherein

said breathing circuit volume comprises

a reflector volume Vrefl of a reflector,

an absorber volume Vabs of an absorber, and

a fresh gas volume Vfgas of a fresh gas channel,

a volume of said patient tubing comprises

an expiratory volume Vexp of said expiratory tube, and

an inspiratory volume Vinsp of said inspiratory tube,

said pressure sensors comprise,

a reflector pressure sensor adjacent to said reflector for providing a reflector pressure Prefl,

a fresh gas pressure sensor adjacent to a fresh gas channel for providing a fresh gas pressure Pfgas,

an expiratory pressure sensor adjacent to said expiration port for providing an expiratory pressure Pexp, and

an inspiratory pressure sensor adjacent to said inspiration port for providing an inspiratory pressure Pinsp.

18. The breathing system according to claim 1 wherein said volume weighted pressure Pv is determined according to at least one of the following relationships:

during an inspiratory phase of said system

19. The breathing system according to claim 2 wherein said computer determines said compliance C based on an isotherm compliance Ciso and an adiabatic compliance Cad wherein a time constant τ

describes a rate of transition from said adiabatic compliance to said isotherm compliance due to a temperature dependence in said system.

20. The breathing system according to claim 19 wherein said computer is operative to determine said gas flow estimate Fe according to the relationship Fe=Fm−

C*dPe/dt−

Ftherm(t), where Ftherm(t) is a thermal flow for correction of said temperature dependence at time t, wherein said thermal flow depends on said adiabatic compliance and said isotherm compliance, and wherein said differential is dPe/dt which is time derivative of said estimated pressure Pe.

21. The breathing system according to claim 1 comprising a low pass filter for filtering a signal comprising pressure values from at least one of said pressure sensors.

22. A method for ventilating a patient, comprising the steps of:

providing in a breathing system a gas channel having a gas channel volume V and a compliance C, a monitoring location in said gas channel, a monitored gas flow Fm at said monitoring location which is either a measured flow at the monitoring location or a known flow from at least one gas source in communication with the gas channel, a flow estimate location in said gas channel at which a gas flow estimate Fe is determined, said flow estimate location being remote from said monitoring location, a plurality of pressure sensors measuring a respective plurality of pressures at different pressure measurement locations of said gas channels, and a computer comprising a program; and

with said computer determining said gas flow estimate Fe at said flow estimate location and wherein said gas flow estimate is based on a relationship between said monitored gas flow Fm and a compressible gas flow Fc depended on said compliance C, said compressible gas flow Fc being a flow of gas in said gas channel between said flow estimate location and said monitoring location, determining an estimated pressure Pe based on said plurality of measured pressures from said respective pressure sensors, and wherein said estimated pressure Pe is a volume weighted pressure Pv with respect to said gas channel volume V, and with said computer also determining said compressible gas flow Fc based on a relationship between said compliance C and a differential of said estimated pressure Pe for determining said gas flow estimate Fe.

23. The method according to claim 22 wherein said breathing system includes a breathing circuit, and wherein said gas flow estimate Fe is a patient gas flow Fp in a patient interface connected to said breathing circuit, said patient gas flow being determined according to the relationship Fp=Fm−

C*dPe/dt wherein said differential is dPe/dt which is time derivative of said estimated pressure Pe.