Patent ID: 7699788

Claim:
A method for substantially noninvasively estimating effective lung volume of a subject, the method comprising the acts of: effecting a change in effective ventilation of a subject; considering a change in the amount of carbon dioxide in gases residing within the alveoli of the subject's lungs from baseline breathing to breathing in which the change in effective ventilation is effected; considering a change in carbon dioxide elimination from baseline breathing to breathing in which the change in effective ventilation is effected; and compensating for changes in the amount of carbon dioxide in gases residing within the alveoli that occur during a breath for estimating the effective lung volume of the subject; wherein the acts of considering the change in the concentration of carbon dioxide, considering the change in carbon dioxide elimination, and compensating for changes in the amount of carbon dioxide comprise employing the following algorithm in processor: V ^ A * = 1 f ACO ⁢ ⁢ 2 ⁡ ( n ) - f ACO ⁢ ⁢ 2 ⁡ ( n - 1 ) · [ V M ⁢ CO 2 ⁢ PRE - V M ⁢ CO 2 ⁡ ( n ) - V M ⁢ CO 2 ⁢ PRE - V M ⁢ CO 2 ⁢ DUR p ACO ⁢ ⁢ 2 ⁢ DUR - p ACO ⁢ ⁢ 2 ⁢ PRE · ( p ACO ⁢ ⁢ 2 ⁡ ( n ) - p ACO ⁢ ⁢ 2 ⁢ PRE ) ] ⁢ where {circumflex over (V)} A * represents the effective lung volume, f ACO2 (n) and f ACO2 (n−1) represent the concentration of carbon dioxide during successive breaths, only one of which occurs when a change effective ventilation has been effected, V M CO 2 PRE represents the carbon dioxide elimination measured at or near the mouth of the subject during baseline breathing, V M CO 2 (n) represents the carbon dioxide elimination measured for breath (n), V M CO 2 DUR represents the carbon dioxide elimination measured at or near the mouth when the change in effective ventilation has been effected, p ACO2 PRE represents the partial pressure of carbon dioxide within the alveoli of the subject's lung during baseline breathing, and p ACO2 (n) represents the partial pressure of carbon dioxide within the alveoli during breath (n).