Portable Breathing Monitoring With Phase-Resolved Airflow Dynamics Enabled by a Dual-Response Flexible PZT Sensor

Respiratory monitoring in daily-life settings is important for health assessment, yet extracting physiologically interpretable information from breathing signals under natural conditions remains challenging, as breathing is inherently dynamic and strongly modulated by behavior. Here, a portable breathing monitoring device based on a flexible lead zirconate titanate sensor is developed to address this challenge. By exploiting polarity-opposed piezoelectric and pyroelectric responses through sensor orientation, the recorded breathing waveform exhibits a characteristic dual-component structure, consisting of a narrow transient spike followed by a broad quasi-steady peak within each breathing phase. This intrinsic waveform structure enables phase-resolved quantification of how breathing effort is distributed between transient and quasi-steady components during inhalation and exhalation. Pilot measurements and exploratory analyses in healthy subjects and patients with chronic obstructive pulmonary disease or asthma suggest a phase-specific redistribution of breathing dynamics in patients, mainly characterized by a coupled decrease in quasi-steady inhalation contribution and an increase in transient exhalation contribution. By transforming complex breathing dynamics into stable and physiologically meaningful signal components, this dual-response sensing approach enables more robust access to function-related changes during natural breathing in daily life.