Method of measuring cardiac related parameters non-invasively via the lung during spontaneous and controlled ventilation
A method of identifying alveolar ventilation (V A ) in a subject, the method comprising: (1) using a breathing circuit which, at exhalation, keeps exhaled gas separate from inhaled gas and at inhalation, when a first gas set (FGS) flow is less than the subject's minute ventilation (V E ), results in a subject inhaling FGS first and then a second gas set (SGS), for the balance of inhalation; (2) setting the FGS flow at a rate greater that V E ; (3) measuring an end tidal CO 2 concentration at a steady state; (4) progressively lowering the FGS flow until a time equal to a recirculation time of CO 2 in the subject; and (5) deriving V A as the rate of FGS flow at the intersection between an average PETCO 2 in a steady state and a line fit to the PETCO 2 values after the rise in PETCO 2 values begins until the recirculation time.
1. A method of identifying alveolar ventilation (V A ) in a subject, the method comprising:
(1) using a breathing circuit configured to:
i. on exhalation by the subject, keep exhaled gas substantially separate from inhalation gas, and
ii. on inhalation by the subject, when a first gas set (FGS) flow is less than a minute ventilation (V E ) of the subject, first provide FGS flow to the subject, and then provide a balance of the V E of the subject that is substantially a second gas set (SGS);
(2) setting the FGS flow into the breathing circuit at a rate greater than the V E of the subject;
(3) measuring an end tidal CO 2 concentration (PETCO 2 ) in a steady state;
(4) progressively lowering the FGS flow into the circuit, either breath by breath or continuously, until after a time equal to a recirculation time of CO 2 within the subject after a rise in PETCO 2 values above a threshold value is observed; and
(5) deriving V A as the rate of FGS flow at a point of the intersection between two lines comprising:
(a) an average PETCO 2 in steady state; and
(b) a straight line fit to the PETCO 2 values after the rise in PETCO 2 values begins until the recirculation time.