In Vivo Measurement of Tidal Volume During Non-invasive Respiratory Support by Continuous-Flow Helmet CPAP

Area of Science:

• Respiratory Physiology
• Biomedical Engineering
• Critical Care Medicine

Background:

• Helmet interfaces for non-invasive respiratory support (NIRS) gained prominence during the COVID-19 pandemic.
• Helmet CPAP (H-CPAP) lacks tidal volume (V_T) measurement, a critical parameter for effective ventilation.
• Opto-electronic plethysmography (OEP) offers a non-invasive solution, unaffected by gas compression within the helmet.

Purpose of the Study:

• To evaluate the feasibility of using OEP to measure V_T during H-CPAP.
• To investigate the impact of posture, flow rate, and positive end-expiratory pressure (PEEP) on ventilatory patterns.
• To assess thoracic-abdominal mechanics and operational volumes under H-CPAP conditions.

Main Methods:

• OEP was employed on 28 healthy volunteers under baseline and H-CPAP conditions.
• Ventilatory parameters were recorded in semi-recumbent and prone positions.
• The effects of varying flow rates (50 vs. 60 L/min) and PEEP levels (0, 5, 10 cmH₂O) were analyzed.

Main Results:

• Prone positioning restricted vital capacity, abdominal expansion, and chest wall recruitment.
• A flow rate of 60 L/min reduced ventilatory effort and induced a slight recruitment (100 mL) in semi-recumbent posture.
• Increasing PEEP levels progressively enhanced recruitment, though this effect was diminished in the prone position.

Conclusions:

• OEP can accurately measure tidal volume during H-CPAP, addressing a key limitation of this interface.
• Understanding the influence of posture and ventilatory settings is crucial for optimizing NIRS.
• This study demonstrates the potential of OEP for precise V_T monitoring in diverse clinical scenarios involving H-CPAP.