Impact of Continuous Isotonic Saline Nebulisation Combined With Heated Humidification on the Rheology of Bronchial Secretions.

Aim- The objective of this study is to determine the effect of continuous isotonic saline nebulization combined with heated humidification on mucus rheology characteristics compared with heated humidification alone.

Design study- This experimental study will follow a cross-over design. As mucus rheology characteristics vary among individuals, this design will enable each subject to be his own control.

Population- 35 patients with excessive airway secretions will be included in this study (sample size calculated with a 95% confidence level and 80% power). Patients will undergo screening for eligibility upon admission to the pulmonology unit. Individuals with chronic pulmonary conditions leading to excessive airway secretions (> 20 mL of expectoration per day) and meeting the inclusion criteria will be invited to participate in the study. The study will take place on two days, after inclusion, randomization will determine the sequence of administration for the two treatments being compared.

Intervention- A continuous isotonic saline nebulization will be delivered combined with a heated humidification.

The continuous nebulization will be performed using the Aerogen continuous nebulization set to assure the continuous supply of isotonic saline solution into the aerogen solo mesh nebulizer.

The heated humidification will be delivered by Airvo 3 (Fisher & Paykel, Auckland, New Zeeland). Air flow will be set at 25L/min, temperature at 37°C and FiO2 will be set to obtain the SpO2 targeted by the physician.

The nebulizer will be installed on the airvo, thus saline particles will be delivered through the nasal prong.

Control- The heated humidification will be delivered by Airvo 3 (Fisher & Paykel, Auckland, New Zeeland). Air flow will be set at 25L/min, temperature at 37°C and FiO2 21%.

Experimental setting- The study will take place on two days. Subject will experience the intervention and the control treatment on a randomized order.

At the beginning of each experimental session manuals airway clearance maneuvers will be performed by a trained physiotherapist and mucus expectorated will be sampled. After secretion samples subject will undergo treatment, according to the randomization treatment order, for a 4-hour period. A new airway clearance session will be performed at the end pf the 4-hour period with secretion sampling. No Positive Expiratory Pressure or Oscillatory Positive Expiratory Pressure devices will be used to prevent from viscosity modification

Rheological measurements- Rheological measurement will be conducted using the rheometer MCR102 (Anton-Paar,Graz, Austria). Prior to analysis, the sputum will be incubated at 37°C for 30 min before analysis to allow relaxation of the sample. The rheometer comprises two parallels plates which will gently compress the secretion. The lower plate will perform oscillations with controlled angular displacement while the rheometer will measure the torque exerted on the opposite plate during these oscillations. Data will be captured using RheoCompassTM software (Anton-Paar) and various data will be extracted from this analysis.

During the linear phase of the analysis, the investigator will register the elastic modulus (G'), the viscous modulus (G''), the viscoelastic modulus (G*), the damping coefficient (tan δ ratio of G'' and G'). These data will provide insights into the secretion's propensity toward elasticity (solid-like) or viscosity (liquid-like).

During the non-linear phase of the analysis, the investigator will register the critical strain (γc) which represent the secretion's deformability capacity, the critical stress (τc) indicating the force required to initiate sputum flow, and the elastic force (G*p x τc) reflecting the elastic energy of the secretion that must be overcome to induce flow. These data will provide insights into the force required for patient airway clearance.

Outcomes- The primary outcomes will be the difference of the force required to evacuate the secretions between the two treatments (τc).

The secondary outcomes will include:

• Others rheological properties: elastic modulus, viscous modulus, viscoelastic modulus, damping coefficient, critical strain and elastic force.
• Comfort level evaluated using the Likert scale
• Dyspnea intensity assessed using the Modified Borg scale
• Airway clearance difficulty measured using a Visual Analogic Scale (VAS) before and after interventions. Airway clearance difficulty will also be monitored during the twelve hours after interventions.
• Sleep quality after interventions will be assessed using Likert

Inclusion criteria

• Age > 18 years old
• Hospitalized in pulmonology unit
• Excessive airways secretions disease: COPD, Bronchiectassies, Cystic Fibrosis, Primary Ciliary Diskynesia

Exclusion criteria

• Age < 18 years old
• Under invasive or non invasive ventilation
• >15L/min of oxygen
• Mucoactive treatment
• Artificial Upper Airway
• Respiratory Distress