Poster W4 - Differential Pressure Spirometry: A Non-Invasive Method for Personalized Mechanical Ventilation Based on Patient Demographics

Introduction: Conventional spirometry remains the gold standard for evaluating lung function; however, it necessitates multiple forceful exhalations, which can potentially cause lung tissue damage. This research introduces an alternative method employing differential pressure spirometry via an orifice plate apparatus, enabling concurrent measurement of lung air pressure and flow rate. The primary objective is to standardise lung air pressure measurements based on age, gender, and smoking status through the development of a mathematical model aimed at optimising mechanical ventilation settings. This approach aspires to offer a non-invasive and comprehensive method for assessing lung functionality, with the potential to personalise mechanical ventilation strategies, thereby mitigating the risk of lung injury and enhancing respiratory outcomes. The findings from this study provide a robust preliminary foundation for subsequent research in developing mathematical models and clinical protocols for individualised ventilator management.

Materials and

Methods: A custom-designed orifice plate spirometer, incorporating a differential pressure sensor connected to an Arduino microcontroller, was utilised in this study. The spirometer was engineered to measure the pressure differential across the orifice plate, facilitating the simultaneous recording of lung air pressure and flow rate. A cohort of 20 subjects, aged 25-50, was recruited and categorized into four groups: male non-smokers, female non-smokers, male smokers, and female smokers. Each participant was instructed to breathe through the spirometer mouthpiece for 5-7 minutes, during which pressure, flow rate, and sensor voltage were recorded at a sampling rate of 200 milliseconds. Safety measures included monitoring oxygen saturation levels via a probe on the right index finger. The collected data were processed to calculate the positive end-expiratory pressure (PEEP) for each group. Preliminary statistical analyses were conducted to compare PEEP values among the different groups, and graphical representations were created to assess the expiratory/inspiratory pressure ratio throughout the breathing cycle.

Results, Conclusions, and Discussions: Results
The mean PEEP was observed to be significantly higher in non-smokers compared to smokers across both genders: non-smoking males exhibited a mean PEEP of 510.91 Pa, non-smoking females 492.66 Pa, smoking males 467.93 Pa, and smoking females 451.21 Pa. The expiratory/inspiratory pressure ratio increased from 0.98 to 1.19 during the breathing cycle, indicating a higher pressure requirement for exhalation compared to inhalation.

Discussion
Accurate measurement of lung air pressure is imperative to avert barotrauma associated with improper mechanical ventilator settings. Delivering standard tidal volumes at suboptimal pressures can result in lung injury. This method provides quasi-static pressure-volume data, which are instrumental in evaluating changes in lung elasticity due to factors such as surfactant levels, lung recoil, and alveolar recruitment/derecruitment. The pressure-volume curves derived from this technique facilitate a comprehensive evaluation of the respiratory system's elastic properties. Expanding this testing to a more diverse patient population could refine the mathematical models and clinical protocols for individualised mechanical ventilation settings. Additionally, standardising lung air pressure based on further demographic factors such as body mass index, ethnicity, and environmental exposures may enhance the precision of ventilator management.

Conclusion
Differential pressure spirometry, by concurrently measuring lung air pressure and flow rates, offers a non-invasive and all-encompassing approach to evaluating lung function. Standardising these measurements based on patient demographics enables the development of personalised mechanical ventilation strategies. This technique holds significant potential for optimising ventilator management, reducing the risk of lung injury, and improving respiratory care outcomes.

Acknowledgements (Optional):