Side-stream volumetric capnography
Techniques for determining a volume of exhaled CO 2 as a function of time using side-stream capnography, including obtaining flow dynamics measurements of a subject from a flow sensor; obtaining CO 2 concentration measurements of the subject from a side-stream CO 2 monitor; determining a duration of time (ΔT sl ) for a sample of gas to flow from a reference point to the side-stream CO 2 monitor; synchronizing in time the CO 2 concentration measurement with the flow dynamics measurement, based on the determined ΔT sl ; and determining a volume of CO 2 exhaled as a function of time, based on the flow dynamics measurement and the synchronized CO 2 concentration measurement.
1. A method for determining a volume of exhaled CO 2 as a function of time using side-stream capnography, the method comprising:
obtaining flow dynamics measurements of a subject from a flow sensor;
obtaining CO 2 concentration measurements of a subject from a side-stream CO 2 monitor;
determining a duration of time (ΔT sl ) for a sample of gas to flow from a reference point to the side-stream CO 2 monitor, wherein determining of the ΔT sl is performed based on an on-start of inhalation (T i ) a duration of time between T i until the capnograph depicts a deflection in the CO 2 concentration measurements (ΔT TOTAL ) and a time to wash away a gas volume encompassed between a Y-piece of a ventilator and the reference point RP (ΔT FLUSH ), wherein (ΔT FLUSH ) is calculated based on the inspiratory flow rate of the ventilator and the gas volume encompassed between the Y-piece of the ventilator and the RP
synchronizing in time the CO 2 concentration measurement with the flow dynamics measurement, based on the determined ΔT sl ; and
determining a volume of CO 2 exhaled as a function of time, based on the flow dynamics measurement and the synchronized CO 2 concentration measurement.
2. The method of claim 1 , wherein the T i is derived from the flow dynamics measurements.
3. The method of claim 1 , wherein the ΔT sl is calculated based on a difference in ΔT TOTAL obtained when supplying the volume of air at at least two different flow rates.
4. The method of claim 1 , wherein T i is determined based on the flow dynamics measurements.
5. A device for determining a volume of exhaled CO 2 as a function of time, the device comprising:
a side-stream CO 2 monitor configured to measure CO 2 concentration over time; and
a processor configured to:
obtain flow dynamics measurements;
obtain the CO 2 concentration measurements from the side-stream CO 2 monitor;
determine a duration of time (ΔT sl ) for a sample of gas to flow from a reference point to the side-stream CO 2 monitor, wherein the processor is configured to determine the ΔT sl based on an inspiratory time (ΔT in ) and a time to wash away a gas volume encompassed between a Y-piece of a ventilator and the RP (ΔT FLUSH ), wherein (ΔT FLUSH ) is calculated based on the inspiratory flow rate of the ventilator and the gas volume encompassed between the Y-piece of the ventilator and the RP;
synchronize in time the CO 2 concentration measurement with the flow dynamics measurement based on the determined ΔT sl ; and
determine a volume of CO 2 exhaled as a function of time based on the flow dynamics measurement and the synchronized CO 2 concentration measurement.
6. The device of claim 5 , comprising a flow sensor configured to provide flow dynamics measurements.
7. The device of claim 5 , wherein the processor is configured to calculate the ΔT in based on a volume of air supplied by the ventilator and an inspiratory flow rate of the ventilator.
8. The device of claim 5 , wherein the processor is configured to calculate the ΔT FLUSH based on a difference in ΔT in obtained when supplying the volume of air at at least two different flow rates.
9. The device of claim 5 , wherein T i is determined based on the flow dynamics measurements.