Optimal flow rate sampling designs for studies with extended exhaled nitric oxide analysis

Area of Science:

• Respiratory Medicine
• Pulmonary Physiology
• Biomarker Analysis

Background:

• Fractional concentration of exhaled nitric oxide (FeNO) is a key biomarker for airway inflammation.
• Extended NO analysis uses multiple exhalation flow rates to model proximal and distal nitric oxide (NO) sources.
• A standardized protocol for FeNO testing flow rates is currently lacking.

Purpose of the Study:

• To derive theoretically optimal exhalation flow rate sampling designs for extended NO analysis.
• To provide guidance for planning studies using FeNO measurements.
• To identify optimal designs balancing accuracy and feasibility.

Main Methods:

• Reviewed existing FeNO study designs.
• Utilized nonlinear regression and simulation studies within a two-compartment NO model.
• Identified optimal four-flow rate designs based on minimizing NO parameter standard errors (SEs).

Main Results:

• Most reviewed designs (77%) were unbiased.
• Optimal designs featured more target flows, replicates, and a wider flow range.
• High flows are crucial for alveolar NO, low flows for proximal NO; an optimal design (10, 50, 100, 400 ml/s) outperformed a common design.

Conclusions:

• A class of theoretically sound FeNO flow rate designs exists.
• Practical selection should balance design optimality with feasibility.
• Optimal designs can reduce required sample sizes for detecting associations.