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

Despite its prevalence-affecting up to 10% of adults worldwide-objective measurement of the cough-one of the most common yet least quantifiable respiratory symptoms-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 Cough monitoring system, provide reproducible measures of cough frequency, now accepted as regulatory trial endpoints. In contrast, cough intensity remains difficult to capture objectively. While physiologic tools that include peak cough flow, esophageal manometry, and electromyography provide mechanistic insights, they are invasive, and impractical for real-world use. Acoustic amplitude serves as a promising noninvasive surrogate, but suffers from ambient noise interference and lack of cross-device calibration. Functional magnetic resonance imaging and experimental brain positron emission tomography have further revealed cortical and subcortical dysregulation underlying cough hypersensitivity, reframing the 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 physio-Cough as the Fifth Vital Sign in Pulmonary Diseases Past Present Future Subjective, low reproducibility Automated acoustic monitoring Multimodal cough-related physiologic signals brain-lung axis Respiratory muscle TJ An https://doi.org/10.4046/trd.2025.0164 https://e-trd.org/ logic, acoustic, and neuroimaging signals through AI-based analytics. Such approaches could transform the 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.