Computer determination of thoracic gas volume using plethysmographic "thoracic flow"

Area of Science:

• Pulmonary Function Testing
• Respiratory Physiology
• Medical Instrumentation

Background:

• Conventional plethysmography for thoracic gas volume (TGV) calculation relies on plotting thoracic volume against mouth pressure.
• Signal drift is a significant challenge in volumetric plethysmography, affecting measurement reliability.
• Automated TGV calculation using minicomputers requires robust signal processing to overcome drift issues.

Purpose of the Study:

• To propose and validate a novel method for calculating TGV by using the time derivatives of thoracic volume (Vt) and mouth pressure (Pm) signals.
• To address the limitations of signal drift in conventional plethysmographic techniques.
• To enhance the reliability of computer-assisted TGV determination.

Main Methods:

• Replaced raw thoracic volume (Vt) and mouth pressure (Pm) signals with their time derivatives (Vt and Pm).
• Applied a regression-line technique to the derivative signals during panting maneuvers for TGV calculation.
• Analyzed 121 patient recordings comparing the conventional Vt-Pm method with the proposed Vt-Pm method.

Main Results:

• The time-derivative method (Vt-Pm) significantly improved the correlation coefficient (r=0.993) compared to the conventional method (r=0.954).
• The Vt-Pm method demonstrated a lower standard error of the estimate (SEE=0.14 L) in computer-derived TGV compared to the Vt-Pm method (SEE=0.34 L).
• The proposed method effectively eliminates signal drift, crucial for accurate computer analysis.

Conclusions:

• The time-derivative method (Vt-Pm) is superior to the conventional Vt-Pm method for TGV calculation, particularly for computer-based analysis.
• This technique is essential for reliable automated TGV determination, overcoming the limitations of signal drift.
• The proposed method offers improved accuracy and reliability in pulmonary function testing.