Potential errors in measuring the phase difference between chest flow and mouth flow.
We have previously reported that the phase difference between chest and mouth flows was a useful indicator of obstructive lung disease. In this paper, we calculated the effects of (i) airway reactance, (ii) extrathoracic airway shunt impedance, (iii) heating and humidification of the inspired air, (iv) abdominal gas volume, and (v) respiratory quotient on the measurement of the phase difference between chest flow (Vc) and mouth flow (Vm) using computer simulations. When the airway impedance was approximated as simple airway resistance, the phase difference (theta r) was calculated to be 0.8% less than the phase difference (theta s) calculated from the airway impedance (Za), including airway inertance and shunt compliance, in the normal lung. theta s became larger than theta r when the peripheral resistance increased, but did not exceed 5%. The extrathoracic airway shunt impedance effect did not exceed 0.1%, regardless of the respiratory frequency, airway impedance or thoracic gas volume. The influence of heating and humidification of the inspired air on the phase difference was calculated to be within 5%. The effect of abdominal gas was highly dependent on the abdominal gas volume and the respiratory pattern, but was calculated to be within 5%. The influence of the respiratory quotient was calculated to be negligible. As a result, it was concluded that none of the factors discussed above are an obstacle to the clinical application of this method for the evaluation of pathological changes in obstructive airway disorders.
Mishima
M
M
Department of Clinical Physiology, Kyoto University, Japan.
Kawakami
K
K
Sugiura
N
N
Fukunaga
T
T
Sakai
N
N
Hirai
T
T
Kuno
K
K
D000403:Airway Resistance / Q000502:physiology; D003198:Computer Simulation; D005740:Gases; D006801:Humans; D007422:Intestines; D008954:Models, Biological; D009055:Mouth; D012123:Pulmonary Ventilation / Q000502:physiology*; D012016:Reference Values; D013909:Thorax
D005740:Gases