Estimation of Inspiratory Muscle Effort in Healthy Subjects

The airway pressure and flow data of human breathing provide opportunities to assess their respective respiratory system conditions. Clinically, non-critically ill patients normally undergo spirometry test, which only measures the expiratory flow and volume, but not the airway pressure. In addition, the spirometry test requires the patient to breathe differently than normal, and thus, there is a need to measure airway pressure and flow data of the human breathing normally. In this study, a modified pneumotachometer is developed to collect the airway pressure and flow profile of healthy human subjects. 20 healthy (13 normal-weight and 7 overweight) subjects underwent breathing tests with their airway pressure and flow profile measured using the modified pneumotachometer. The subjects were also required to breathe through a spirometry test for comparison. A single compartment lung model is used in the analysis of the inspiratory muscle effort (<tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$P_{mus}$</tex>) of the subject. This study found that normal-weight subjects' median peak <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$P_{musis}$</tex> -11.98 cmH-<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf>O [Interquartile range (IQR): -8.56 -15.59], and overweight subjects' is higher at a median of -13.82 cmH<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf>O [IQR: -9.23 -17.57], p<0.05. The slope and magnitude of the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$P_{mus}$</tex> are found to be dependent on the subject's respiratory system elastance and resistance. Higher respiratory elastance or resistance will result in higher peak <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$P_{mus}$</tex> : The modified pneumotachometer enables continuous monitoring of the respiratory muscle effort and can provide more insight into the lung condition.