Regularity of Respiratory Waveform Depends on Ventilation Parameters

Entropy is a nonlinear method for quantifying the regularity and order of a system. Entropy was originally born from thermodynamics and is now used in various fields, such as statistical mechanics and information ethics. Approximate Entropy (ApEn) is an index that has been developed to quantify the complexity of data over time. This study aimed to use ApEn measurement to clarify the relationship between the regularity of the respiratory waveform and ventilation parameters for humans in a resting state. The 5 minutes resting respiratory metabolism of thirteen healthy participants was measured, including respiratory rate (RR), tidal volume (VT), minute ventilation ("V" ̇E), end-tidal oxygen concentration (ETO2), end-tidal carbon dioxide concentration (ETCO2), end-tidal carbon dioxide tension (PETCO2), inspiration time (TI), expiration time (TE), and respiration time (TTOT), and the ventilatory response to end-tidal carbon dioxide tension ("V" ̇E /PETCO2) was calculated. ApEn values and ventilation parameters were examined using Pearson\u27s product-moment correlation coefficient. The ApEn value of the respiratory waveforms of participants was 0.291 ±0.050 (mean ±SD); these values were positively correlated with TI, TE, TTOT, ETO2, and PETCO2, and negatively correlated with RR, ETCO2, and "V" ̇E/PETCO2. There were no correlations with VT or "V" ̇E. The results revealed a correlation between ApEn values and RR, TI, TE, and TTOT. The respiratory waveform of a person with fast respiration and a high respiration rate was regular. The correlation between the regularity of the respiratory waveform and PETCO2 and "V" ̇E/PETCO2 showed that those with regular respiratory waveforms had increased sensitivity to CO2 and were in a respiratory state close to hyperventilation. Those with regular respiratory waveforms at rest may have unconsciously felt breathless due to anxiety. The fact that no correlation was observed between VT and "V" ̇E supports the notion that the regularity of the respiratory waveform is not determined by ventilation volume but by respiration rate