A system configured to determine a breathing parameter of a subject receiving therapy, the system comprising: one or more sensors configured to generate output signals conveying information related to one or more gas parameters of the gas at or near the airway of the subject; and one or more processors configured to execute modules, the modules comprising: a therapy parameter module configured to determine one or more parameters of the therapy being provided to the subject; a breathing parameter module (34, 36) configured to determine a breathing parameter of the respiration of the subject, the breathing parameter module comprising: a first breathing parameter sub-module (44, 50) configured to make a first preliminary determination of the breathing parameter based on the output signals in accordance with a first algorithm; and a second breathing parameter sub-module (46, 52) configured to make a second preliminary determination of the breathing parameter based on the output signals in accordance with a second algorithm, wherein an impact of the one or more therapy parameters on the accuracy and/or precision of the first algorithm is different than an impact of the one or more therapy parameters on the accuracy and/or precision of the second algorithm; and a selection module configured to select the first preliminary determination of the breathing parameter or the second preliminary determination of the breathing parameter as a final determination of the breathing parameter; characterized in that the selection module is configured to base said selection on an analysis of the first and second preliminary determinations to identify artifacts indicative of inaccuracy and/or imprecision in determination of the breathing parameter by the first and second algorithms of respective first and second preliminary determinations, wherein the artifacts comprise artifacts commonly present under conditions described by the one or more parameters of the therapy being provided to the subject. one or more sensors configured to generate output signals conveying information related to one or more gas parameters of the gas at or near the airway of the subject; and one or more processors configured to execute modules, the modules comprising: a therapy parameter module configured to determine one or more parameters of the therapy being provided to the subject; a breathing parameter module (34, 36) configured to determine a breathing parameter of the respiration of the subject, the breathing parameter module comprising: a first breathing parameter sub-module (44, 50) configured to make a first preliminary determination of the breathing parameter based on the output signals in accordance with a first algorithm; and a second breathing parameter sub-module (46, 52) configured to make a second preliminary determination of the breathing parameter based on the output signals in accordance with a second algorithm, wherein an impact of the one or more therapy parameters on the accuracy and/or precision of the first algorithm is different than an impact of the one or more therapy parameters on the accuracy and/or precision of the second algorithm; and a selection module configured to select the first preliminary determination of the breathing parameter or the second preliminary determination of the breathing parameter as a final determination of the breathing parameter; a therapy parameter module configured to determine one or more parameters of the therapy being provided to the subject; a breathing parameter module (34, 36) configured to determine a breathing parameter of the respiration of the subject, the breathing parameter module comprising: a first breathing parameter sub-module (44, 50) configured to make a first preliminary determination of the breathing parameter based on the output signals in accordance with a first algorithm; and a second breathing parameter sub-module (46, 52) configured to make a second preliminary determination of the breathing parameter based on the output signals in accordance with a second algorithm, wherein an impact of the one or more therapy parameters on the accuracy and/or precision of the first algorithm is different than an impact of the one or more therapy parameters on the accuracy and/or precision of the second algorithm; and a first breathing parameter sub-module (44, 50) configured to make a first preliminary determination of the breathing parameter based on the output signals in accordance with a first algorithm; and a second breathing parameter sub-module (46, 52) configured to make a second preliminary determination of the breathing parameter based on the output signals in accordance with a second algorithm, wherein an impact of the one or more therapy parameters on the accuracy and/or precision of the first algorithm is different than an impact of the one or more therapy parameters on the accuracy and/or precision of the second algorithm; and a selection module configured to select the first preliminary determination of the breathing parameter or the second preliminary determination of the breathing parameter as a final determination of the breathing parameter;