Objective Assessment of Cough: Listening to the Patient’s Voice: A Narrative Review

Cough is one of the most common yet least quantifiable respiratory symptoms. Despite its prevalence-affecting up to 10% of adults worldwide-objective measurement remains challenging. Conventional descriptors such as "frequent" or "severe" are inherently subjective and poorly reproducible, limiting clinical interpretation and standardization. Over the past five decades, technological advances have transformed cough assessment from manual counting and provocation testing to automated acoustic monitoring and neurophysiologic imaging. Modern validated systems such as the Leicester Cough Monitor and VitaloJAK™ provide reproducible measures of cough frequency, now accepted as regulatory trial endpoints. In contrast, cough intensity remains difficult to capture objectively. Physiologic tools including peak cough flow, esophageal manometry, and electromyography provide mechanistic insights but are invasive and impractical for real-world use. Acoustic amplitude serves as a promising noninvasive surrogate, yet suffers from ambient noise interference and lack of cross-device calibration. Functional MRI and experimental brain PET have further revealed cortical and subcortical dysregulation underlying cough hypersensitivity, reframing chronic cough as a disorder of aberrant sensory processing. However, these approaches remain research tools, constrained by cost, accessibility, and limited validation. The future of cough assessment lies in integrated, multimodal systems that combine physiologic, acoustic, and neuroimaging signals through AI-based analytics. Such approaches could transform cough into a measurable digital biomarker-an objective "fifth vital sign." Realizing this vision will require collaborative efforts among clinicians, engineers, and policymakers to ensure validation, standardization, and clinical applicability.