Further exploration of the Penh parameter

Area of Science:

• Respiratory Physiology
• Pulmonary Function Testing
• Animal Models of Respiratory Disease

Background:

• Unrestrained plethysmography (UP) is a common non-invasive method for assessing airway reactivity in mice, often using the Penh parameter.
• Previous studies have shown correlations between Penh and measures of airway constriction, but recent arguments question its validity for resistance measurements.
• Concerns exist that the UP waveform and Penh are primarily influenced by respiratory conditioning rather than airway resistance.

Purpose of the Study:

• To mathematically analyze unrestrained plethysmography (UP) waveforms from two types of whole body plethysmographs (WBPs): sealed (pressure, PWBP) and flow (FWBP).
• To evaluate the influence of respiratory conditioning versus airway resistance on UP measurements at room temperature.
• To determine if the Penh parameter accurately reflects changes in airway resistance during challenges like methacholine administration.

Main Methods:

• Mathematical analysis of UP waveforms generated by pressure-based WBPs (PWBP) and flow-based WBPs (FWBP).
• Comparison of waveform characteristics under different conditions, focusing on the impact of resistance and conditioning.
• Evaluation of the Penh parameter derived from FWBP signals in response to methacholine challenge.

Main Results:

• The PWBP waveform is predominantly influenced by respiratory conditioning, showing minimal changes due to airway resistance at room temperature.
• In contrast, the FWBP waveform clearly reflects changes in airway resistance (sRaw) even at room temperature.
• Changes in the FWBP waveform during methacholine challenge are attributable to airway resistance, not solely conditioning or respiratory timing alterations.

Conclusions:

• The validity of UP and Penh for measuring airway resistance depends critically on the type of whole body plethysmograph used.
• Pressure-based WBPs (PWBP) are not suitable for assessing airway resistance due to dominance by conditioning effects.
• Flow-based WBPs (FWBP) provide a waveform that accurately reflects airway resistance, and the Penh parameter derived from it can quantify these changes effectively.