Correlation of Diaphragm Shear-Wave Elastography With Transdiaphragmatic Pressure in Healthy Adults: a Feasibility Study

Rationale:

Changes in intrapleural pressure after lung volume reduction in COPD patients may contribute to pneumothorax. Non-invasive monitoring of pleural pressure could help identify patients at risk. Diaphragm shear-wave elastography (SWE) has shown potential to reflect transdiaphragmatic pressure (Pdi), but has not yet been validated across ultrasound systems. This study aims to validate diaphragm SWE against gold-standard Pdi and mouth pressures in healthy volunteers before applying the technique in COPD patients.

Objective:

To validate diaphragm SWE as a non-invasive measure of inspiratory effort by assessing its correlation with transdiaphragmatic pressure (Pdi) and mouth pressure (PImax and submaximal inspiratory pressures). Secondary objectives are to determine feasibility and inter-rater reliability of SWE measurements.

Study design:

Prospective, single-centre, observational validation study.

Study population:

Twelve healthy adults aged 18-60 years, BMI 18-30 kg/m², without respiratory, neuromuscular or cardiothoracic disease.

Main study parameters/endpoints:

Participants will undergo simultaneous measurements of diaphragm SWE, transdiaphragmatic pressure (Pdi = Pga-Pes), and inspiratory mouth pressures (Pmo) at rest and during inspiratory efforts at 20%, 40%, and 60% of PImax. SWE will be performed twice by different operators to assess inter-rater reliability. The primary analysis will determine within-individual and overall correlations between SWE and Pdi.

• Pearson correlation coefficient repeated-measures correlation coefficient between SWE and Pdi across inspiratory efforts.

Nature and extent of the burden and risks associated with participation, benefit and group relatedness:

The study involves a single measurement session (~1-2 hours). Procedures include nasal insertion of esophageal and gastric balloon catheters, mouth pressure measurements, and diaphragm ultrasound. These are routinely used physiological techniques with mild, transient, discomfort (e.g., mild throat or nasal irritation). No therapeutic intervention or follow-up is required. Risks are considered negligible and proportionate to the scientific value of the validation.

Inclusion criteria

• 18-60 years, BMI 18-30 kg/m²
• No known respiratory, neuromuscular, or cardiothoracic disease
• Able to perform inspiratory maneuvers and consent.

Exclusion criteria

• Pregnancy
• History of smoking (> 10 pack years)
• Impaired swallowing, as well as esophageal diseases, or disorders at the level of the gastroesophageal sphincter