Terahertz Breath Sensor for Asthma Inhaler Monitoring*

Inhaled medications can and are often used as short-term performance-enhancers for athletes, especially in endurance sports such as cycling. Notably, multiple Tour de France winners have been identified as taking asthma medication off-label, leading to public controversies about the controlled substance's source and legality. While urine tests can detect the use of the pharmacological agents within hours or days of the dose, there is a significant lag time due to human drug metabolism. Alternatively, detecting propellants, which carry the drug into the lungs, provides a more straightforward and immediate path for detecting broad pharmacological agents. In this work, we demonstrate the use of a terahertz (THz) sensor to detect the use of inhaled medications in human breaths. THz measurement of breath offers rapid, sensitive, and specific molecular identification of complex mixtures with near absolute specificity. The THz sensor interrogates volatiles using non-ionizing electromagnetic radiation to determine the molecules' vibrational modes and thus identify the content of compounds. We detect and quantitate the propellant (HFA 134a) in breath up to thirty minutes after using an asthma inhaler by obtaining the THz spectral fingerprint of HFA 134a. We then use this fingerprint to quantify HFA 134a in a human breath at three-time points (5 minutes, 15 minutes, and 30 minutes) post-use of an albuterol inhaler. The THz sensor detected HFA 134a in nearly all breath samples, and the concentration profile followed a predicted pharmacological decay curve with comparable results to GC-MS. The THz breath analysis outperforms urinalysis regarding detection thresholds and detecting during the therapeutic window. Furthermore, the presented THz method provides practical benefits in shortening the sample acquisition and processing times, minimizing sample treatment, and simplifying the test procedure. As a result, we provide evidence that a point-of-care THz sensor can detect when individuals have used pressure-mediated dose inhalers.