Rebreather system with optimal PO2 determination

• US 6,302,106 B1
• Filed: 12/29/1998
• Issued: 10/16/2001
• Est. Priority Date: 07/18/1997
• Status: Expired due to Fees

• Current Assignee: John E. Lewis
• Original Assignee: John E. Lewis
• Inventors: Lewis, John E.
• Primary Examiner(s): Dawson, Glenn K.
• Application Number:
  US09/222,046
• Time in Patent Office: 1,022 Days
• Field of Search: 128/201.27, 128/205.28, 128/204.26, 128/204.29, 128/205.11, 128/914, 128/204.22
• US Class Current: 128/204.22
• CPC Class Codes: B63C 11/24 in closed circulation

Abstract

A method and apparatus for a self contained underwater breathing apparatus in which a breathing gas is supplied to a flow loop from two separate gas sources each having a different oxygen fraction, and each controlled by separate mass flow controllers having variable flow rate. The mass controller flow rates are adaptively adjustable to deliver gas at variable flow rates which depend solely on a function of depth. An algorithm determines these specific flow rates from each of the tanks at particular depths, such that the gas flow from an oxygen rich gas source decreases as a function of depth, while the gas flow from a diluent gas source increases as a function of depth, so as to maintain the oxygen partial pressure in the flow loop within a specific pre-determined range. The algorithm allows calculation of an optimum oxygen partial pressure, for a particular dive, which allows construction of a dive profile which maximizes bottom time while taking into account no-decompression time at depth, tank capacity limited time, and single-dive and daily pulmonary oxygen toxicity limits.

Claims

1. A rebreather system of the closed circuit-type comprising a flow loop including a counterlung, the rebreather system comprising:

a breathing gas supply source;

a pressure regulator, coupled between the breathing gas supply source and the flow loop;

a mass flow controller for controlling the flow rate of the breathing gas to the flow loop, coupled between the pressure regulator and the flow loop, the mass flow controller having a variable flow rate;

a pressure transducer for indicating depth as a function of ambient pressure;

a breathing gas source capacity indicator;

an oxygen sensor; and

a digital signal processing circuit, configured to receive data from the pressure transducer, the gas source capacity indicator and the oxygen sensor, the digital signal processing circuit being firmware programmed to perform calculations on said data and further programmed to perform calculations on data input by a user including whole body oxygen toxicity time limits, and no-decompression time limits, so as to define an oxygen partial pressure within the rebreather'"'"'s counterlung which maximizes bottom time and no-decompression time, while minimizing accumulated whole body oxygen toxicity time.

2. The rebreather according to claim 1, wherein the signal processing circuit calculates a first oxygen partial pressure for the case where breathing gas source capacity limited time is equal to a determined no-decompression time, the signal processing circuit further calculating a second oxygen partial pressure for the case where breathing gas source capacity limited time is equal to a remaining whole body oxygen toxicity limited time.

3. The rebreather according to claim 2, wherein the signal processing circuit is further adapted to determine a minimum of the calculated first and second oxygen partial pressures, the signal processing circuit further adjusting the mass flow controller so as to condition the breathing gas source to supply breathing gas at an oxygen partial pressure equal to said minimum.

4. The rebreather according to claim 3, wherein the signal processing circuit calculates the first and second oxygen partial pressures at periodic intervals throughout the course of a dive, the signal processing circuit defining the minimum of the periodically calculated first and second oxygen partial pressures so as to dynamically adjust the oxygen partial pressure within the rebreather'"'"'s counterlung in order to maximize bottom time.

5. The rebreather according to claim 3, wherein the breathing gas source further comprises:

a first, oxygen rich gas source having a first oxygen fraction, FO₂;

a second diluent gas source having a second oxygen fraction, F_AIR; and

wherein the mass flow controller comprises first and second mass flow controllers;

coupled respectively to the first oxygen rich gas source and the second diluent gas source, the first and second mass flow controllers individually adjustable for controlling gas flow from their respective sources to the counterlung.

6. The rebreather according to claim 5, wherein, the first and second mass flow controllers comprise electronically controlled valves, configured to receive control signals from the signal processing circuit and operative in response thereto, the first and second mass flow controllers adaptively adjustable so as to vary oxygen partial pressures in the counterlung in accordance with commands received from the signal processing circuit.

7. A method for adaptively configuring oxygen partial pressures in a rebreather system of the closed circuit-type, comprising a breathing gas source configured to provide a breathing gas mixture at variable oxygen partial pressures to a flow loop including a counterlung, to maximize dive time while minimizing decompression time and whole body oxygen toxicity acquired time, the method comprising;

defining a first time limit depending on a capacity of a breathing gas source tank;

calculating a second time limit depending on a no-decompression time at depth as a function of oxygen partial pressure;

calculating a third time limit depending on a whole body oxygen toxicity rate accumulation as a function of oxygen partial pressure;

determining a first oxygen partial pressure for the case in which the first capacity limited time is equal to the second no-decompression time;

determining a second oxygen partial pressure for the case where the first capacity limited time is equal to the third whole body oxygen toxicity limited time; and

defining an optimum value of oxygen partial pressure so as to maximize dive time while minimizing decompression time and whole body oxygen toxicity accumulation.

8. The method according to claim 7, wherein the optimum oxygen partial pressure is equal to the lessor of the first and second determined oxygen partial pressures.

9. The method according to claim 8, further comprising:

providing an oxygen sensor; and

providing a signal processing circuit configured to perform calculations, the signal processing circuit coupled to a mass flow controller and providing control signals to said mass flow controller, the signal processing circuit adaptively adjusting said mass flow controller so as to maintain oxygen partial pressure in the rebreather system at the optimum value.

10. The method according to claim 9, wherein the signal processing circuit determines the first and second oxygen partial pressures at periodic intervals throughout the course of the dive, the signal processing circuit defining an optimum value of oxygen partial pressure for each determination and adaptively adjusting the mass flow controller so as to dynamically maintain oxygen partial pressure in the rebreather at an instantaneous optimum value.

11. The method according to claim 10 further comprising:

defining a first, minimum, oxygen consumption value, O₂^MIN;

defining a second, maximum oxygen consumption value, O₂^MAX, to thereby define a parametric boundary space; and

adaptively adjusting the mass flow controller so as to vary the breathing gas flow rate in a manner solely dependent on ambient pressure expressed as a function of diving depth.

12. The method according to claim 11 further comprising:

calculating and recording an oxygen consumption rate, as measured by the oxygen sensor, the signal processing circuit defining a maximum and minimum oxygen consumption rate for a diver under actual conditions; and

adaptively adjusting the mass flow controller so as to deliver breathing gas to the rebreather at the optimal oxygen partial pressure in a manner dependent upon depth and the minimum and maximum calculated oxygen consumption rates.

13. A rebreather system comprising:

a breathing gas supply source;

a flow controller configured to control a flow rate of breathing gas from the breathing gas supply source;

a pressure transducer for measuring ambient pressure;

an oxygen sensor; and

a signal processing circuit configured to receive an input from the pressure transducer and an input from the oxygen sensor, the signal processing circuit being programmed to use the input from the pressure transducer and the input from the oxygen sensor to define an oxygen partial pressure which enhances bottom time.