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

Tai Joon An

doi:10.4046/trd.2025.0164

Tuberc Respir Dis > Volume 89(2); 2026 > Article

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

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Tuberculosis and Respiratory Diseases 2026;89(2):193-201.

Published online: December 9, 2025

DOI: https://doi.org/10.4046/trd.2025.0164

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

Tai Joon An

Division of Pulmonary and Critical Care Medicine, Department of Internal Medicine, Yeouido St. Mary’s Hospital, College of Medicine, The Catholic University of Korea, Seoul, Republic of Korea

Address for correspondence Tai Joon An Division of Pulmonary and Critical Care Medicine, Department of Internal Medicine, Yeouido St. Mary’s Hospital, College of Medicine, The Catholic University of Korea, 10 63(yuksam)-ro, Yeongdeungpo-gu, Seoul 07345, Republic of Korea Phone 82-2-3779-1663 E-mail ds31316@gmail.com

Received October 8, 2025 Accepted December 6, 2025

It is identical to the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0/).

Abstract

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 physioclassilogic, 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.

Keywords: Cough; Chronic Cough; Monitoring, Physiologic; Cough Hypersensitivity Syndrome; Biomarkers

Key Figure

Introduction

The cough is among the most common respiratory symptoms encountered in clinical practice. A recent systematic review and meta-analysis reported a prevalence of 3.8% to 4.2% in Western countries, and 10.3% to 13.8% in other regions [1]. The chronic cough, typically defined as lasting more than 8 weeks, affects about 10% of the adult population worldwide (9.6%; 95% confidence interval, 7.6% to 11.7%) [2]. In South Korea, the prevalence of the chronic cough has been estimated at approximately 3% in earlier reports, with more recent analyses of the Korean National Health Insurance Service sample cohort suggesting rates as high as 9%, indicating that the burden may be greater than previously recognized [3,4].

Yet, paradoxically, the cough remains one of the hardest symptoms to measure precisely. Although clinicians routinely hear descriptors like ‘dry,’ ‘frequent,’ ‘persistent,’ or ‘severe,’ these expressions are very subjective, and suffer from recall bias, and poor reproducibility across time, patients, and settings [5,6]. These even hinder consistent communication among health care professionals [7,8]. To overcome these limitations, patient-reported outcome measures (PROMs) have been developed—capturing intensity (visual analog scale [VAS]), frequency (cough symptom score), quality of life (Leicester cough questionnaire or cough assessment tool [COAT]), and hypersensitivity (cough hypersensitivity questionnaire) [9-12]. While these are important for reflecting patient experience, they remain perception-based, rather than objective physiologic measures [13].

An important question in this field is how to define and establish an ‘objective’ measure of the cough. In essence, an objective COAT should quantify coughing in a measurable, reproducible, and observer-independent manner—ideally across observers, settings, and time points [6]. Over the past five decades, theoretical and methodological advances—from understanding of neuronal hypersensitivity in coughing to acoustic recording and digital health—have progressively transformed the cough from a subjective symptom into quantifiable methods. Yet despite these advances, many tools remain restricted to research settings, and face barriers in cost, usability, and integration into routine clinical workflows.

In this review, we trace the historical evolution of objective cough assessment and examine the taxonomy of current tools across domains such as frequency, intensity, acoustic features, and cough hypersensitivity. By exploring both present applications and future directions, we highlight the challenges that remain, and anticipate a next stage where the cough is established as a measurable ‘fifth vital sign,’ seamlessly embedded into respiratory care.

Historical Evolution of Objective Cough Assessment

Over the decades, the quest to quantify the cough has progressed in parallel with technological innovation and evolving conceptual views of the cough as reflex, symptom, and neurobehavioral phenomenon (Figure 1).

1. Early manual counts, recordings, and provocation era (1950s-1980s)

The first systematic efforts to measure coughing were pioneered by Bickerman and Barach [14] in the 1950s. Using citric acid aerosol inhalation to provoke coughing, they quantified responses by manual counting. This landmark study established the principle of cough challenge testing, while also exemplifying the earliest use of manual counts as an objective metric. Subsequent work extended these concepts with alternative chemical stimuli such as capsaicin, from which reproducible dose-response thresholds (e.g., C2, C5 concentrations) were derived to quantify cough reflex sensitivity [15-17]. During this period, researchers also explored mechanical provocation methods—such as tracheal probing and mechanical stimulation of the airway—as alternatives [18,19]. Hypertonic saline inhalation, generally classified as an osmotic challenge, was introduced later as another modality.

Manual counting was soon complemented by analog recording innovations. In the 1960s, a microphone was suspended above the patient’s bed and connected to a sound-triggered tape recorder that enabled prolonged cough monitoring, which was later analyzed manually by ear [20]. Similar room-based recording systems soon followed, though these approaches confined patients to fixed settings, while typically capturing only limited portions of the monitoring period [21]. Nevertheless, these developments laid the groundwork for quantitative challenge testing and continuous recording, ultimately setting the stage for automated and ambulatory cough monitoring in later decades.

2. Central and peripheral modulation paradigms of the cough (1990s-present)

Voluntary cough suppression and cortical control paradigms emerged in the early 1990s as researchers recognized that coughing is under cortical modulation, not merely a reflex [22-24]. In 1993, a pivotal study demonstrated that healthy individuals could voluntarily suppress capsaicin-induced coughing, challenging the long-held notion of the cough as a pure reflex [22]. Subsequent neuroimaging studies mapped key cortical and subcortical networks—including the anterior insula, anterior cingulate cortex, supplementary motor area, and right inferior frontal gyrus—thereby supporting a behavioral model in which coughing is under partial cortical control [24,25].

These methods allow objective analysis of central mechanisms of cough hypersensitivity, but are subject to individual variability and technical challenges, such as standardizing suppression tasks and interpreting outcomes. Nevertheless, these paradigms advanced the conceptual shift toward considering coughing as a cortically regulated behavior, rather than a simple brainstem reflex.

3. Beginning of automated acoustic monitoring (1990s-2010s)

The first steps toward automated cough monitoring were taken by Salmi et al. [26], who developed a system combining a static charge-sensitive bed with a directional microphone to detect coughing-linked sounds and movements with high accuracy in controlled settings. This proof-of-concept highlighted the need for mobile, real-life monitoring. The introduction of digital audio recording and signal processing fueled the evolution of scalable, objective cough monitors. The Leicester cough monitor (LCM) enabled 24-hour ambulatory cough analysis via automated algorithms, with high sensitivity and specificity for cough detection [27]. VitaloJAK (Vitalograph, Lenexa, KS, USA) offered a robust, validated solution for clinical trials, while systems such as the Hull Automatic Cough Counter, the Cayetano monitor, and LEOSound (Löwenstein Medical, Bad Ems, Germany) expanded methodological diversity and applications [28-31]. Together, these tools moved cough research from manual to continuous, objective, and validated acoustic quantification.

Current Domains of Objective Cough Assessment

Objective evaluation of coughing can be approached through distinct but complementary domains—frequency, intensity, acoustic features, and reflex sensitivity—each reflecting different physiological and clinical dimensions (Table 1).

1. Cough frequency

Coughing can occur as isolated events or in bouts (epochs) [32]. Validated cough monitors—such as the LCM and VitaloJAK—are currently the best-established tools for objective cough frequency measurement [33]. These systems record cough counts over fixed intervals (e.g., per hour or 24 hours), and are recognized official endpoints in regulatory antitussive trials [34-36]. The LCM, which uses an MP3 digital recorder with a free-field microphone, achieves approximately 91% sensitivity, 99% specificity, and a low false-positive rate (approximately 2.5 events/patient/hour), with repeatability sustained for at least 3 months [27]. The VitaloJAK, a custom dual-microphone system (free-field and contact), demonstrates 84%−88% sensitivity and >99% specificity [30]. However, current tools are bulky, sensor-intensive, and require manual validation, limiting their feasibility for real-world or long-term home monitoring.

In a recent systematic review encompassing 54 studies in adults with chronic respiratory diseases, the VitaloJAK and LCM were identified as the most extensively evaluated and validated platforms [33]. Other platforms—including LEOSound, PulmoTrack, Hull Automated Cough Counter, LifeShirt, and several smartphone- or wearable-based prototypes—were investigated in only a few small studies. Across these reports, concordance with manual cough counting was rarely tested, correlations with PROMs were generally low to moderate, and data on usability, cost, or real-world application were largely absent. Collectively, these findings underscore the need for standardized validation frameworks and longitudinal performance assessments before widespread clinical adoption.

2. Cough intensity

Frequency alone does not reflect how forceful or burdensome a cough feels. Cough intensity represents the mechanical effort and neural drive underlying the reflex, influencing both perception and clinical impact. Traditionally, intensity has been assessed subjectively using VAS, which measurements are simple, but limited by recall bias, interindividual variability, and poor reproducibility [12]. Objective measures include peak cough flow—the maximal expiratory airflow during a cough—commonly used in neuromuscular and pulmonary disorders but highly effort-dependent, and variable by age, sex, and technique [37,38]. Other physiologic tools, such as esophageal pressure manometry, high-resolution manometry, and electromyography of expiratory muscles, provide insights into cough biomechanics and neural activation, but remain invasive, equipment-heavy, and impractical for real-world use [39-43]. Acoustic amplitude has emerged as a noninvasive surrogate of cough intensity, showing correlation with subjective scales and airflow measures, yet remains susceptible to ambient noise, and lacks standardized calibration across devices [44,45].

Despite these advances, intensity assessment remains limited by the invasive nature of physiologic measurements, and the lack of well-validated, user-friendly alternatives. Though surface electromyography sensors and wearable acoustic systems have been explored, their validation across diverse clinical settings is incomplete, and signal processing for sound-based intensity remains technically demanding, hindering widespread clinical adoption.

3. Acoustic feature analysis

The cough is more than a countable event—its acoustic signature encodes physiologic, pathologic, and temporal information reflecting airway dynamics, neuromuscular control, and reflex drive. Traditional categories, such as ‘dry’ versus ‘wet,’ are crude approximations; in reality, waveform morphology, spectral harmonics, and temporal clustering together form a richer ‘acoustic phenotype.’ Commercial systems like LEOSound, which capture cough, wheeze, and crackles via multi-sensor bioacoustic arrays and automated spectrogram analysis, have demonstrated robust accuracy (e.g., >95% sensitivity and specificity for wheeze detection in pediatric data); but despite these promising metrics, they remain largely confined to research or selected populations, due to the need for further optimization and reduction of false-positives, prior to generalized clinical adoption [29].

4. Cough reflex sensitivity and neurophysiological pathophysiology

The concept of cough hypersensitivity has reframed the chronic cough as a disorder of neural hyperexcitability, often manifesting with laryngeal hypersensitivity. Patients describe throat irritation, tickling, or urge-to-cough in response to various stimuli. Early research emphasized C-fiber activation via transient receptor potential cation channel subfamily V member 1 (TRPV1), but more recent discoveries implicate multiple pathways, including transient receptor potential ankyrin 1 (TRPA1) and purinergic receptor P2X ligand-gated ion channel 3 (P2X3), underscoring a complex sensory landscape [46]. Traditional approaches to quantify this sensitivity have included chemical challenge tests (capsaicin, citric acid, mannitol) and mechanical provocation [47-50]. Though these tests yield consistent thresholds, they remain impractical for routine use, and offer limited diagnostic value.

Recent advances in neurophysiological imaging—particularly functional magnetic resonance imaging (fMRI) and experimental brain positron emission tomography (PET)—have provided new insights into the supramedullary control and cortical representation of the cough. fMRI studies reveal altered activation in the prefrontal, insular, and sensorimotor cortices during capsaicin-induced urge-to-cough, with chronic cough patients displaying enhanced connectivity and reduced gray matter volume in regulatory regions, compared to healthy controls [51-53]. In a complementary manner, PET imaging demonstrates discrete regional changes in the cerebellum, pons, and sensory cortex during both the voluntary and stimulus-evoked cough, supporting cortical and subcortical dysregulation in cough hypersensitivity [53,54]. Together, these neuroimaging modalities provide mechanism-oriented biomarkers that complement peripheral challenge tests, although their technical complexity, high cost, and limited accessibility restrict routine application.

The Arnold’s nerve reflex test—eliciting coughing by stimulating the auricular branch of the vagus—offers a simpler probe of vagal afferent excitability, but its diagnostic sensitivity remains variable among individuals [55]. Laryngeal sensory mapping, typically performed using flexible endoscopic evaluation of swallowing with sensory testing, provides a more localized assessment of laryngeal afferent integrity by delivering controlled airpulse stimuli to the mucosa and observing reflexive responses [56,57]. Although this approach has been used to characterize sensory thresholds relevant to cough initiation, its adoption within dedicated cough research remains limited, and further validation is needed to establish its role as an objective biomarker of cough hypersensitivity.

Current cough sensitivity tests show weak correlations with objective cough frequency, and substantial overlap between patients and healthy subjects [58-60]. Their responses are further influenced by pharmacologic interventions, repetition, and individual factors, such as age, sex, and smoking [47,61-64]. These limitations highlight the need for integrative, multimodal biomarkers that can capture both sensory and behavioral dimensions of the cough reflex.

Future of Objective Cough Assessment: From Detection to Digital Biomarkers

The future of objective cough assessment will move beyond isolated domains—frequency, intensity, acoustics, and sensitivity—toward an integrated, multimodal, and mechanistically grounded framework. Next-generation systems will be wearable, modular, and mobile, minimizing sensor burden, while maximizing analytical precision. AI-driven algorithms for automatic detection and classification will enable these tools to distinguish coughing from speech or environmental noise with minimal supervision, and extend monitoring from controlled research settings into everyday clinical practice.

Wearable and sensor-based systems are now emerging in various form factors—including watch-type, chest-adhered, necklace, and vest devices—to enable continuous, passive, and automated cough detection in real-world environments [31,65,66]. Building on earlier 24-hour recording systems, these technologies illustrate a broader transition from conventional sound-based counting toward AI-enhanced physiologic profiling that integrates acoustic, biomechanical, and neurophysiologic data. Beyond peripheral monitoring, emerging molecular, neurophysiologic, sensory-mapping biomarkers (e.g., TRPV1, P2X3, neuropeptide signaling, laryngeal sensory mapping) promise to delineate mechanistic subtypes and bridge molecular pathways with clinical phenotypes [67-69]. Collectively, these developments signal a shift from descriptive observation to an integrated, biologically anchored framework that may ultimately redefine coughing as a measurable digital biomarker within precision respiratory medicine.

Conclusion

From a national healthcare perspective, Korea faces structural challenges in its clinical adoption of emerging digital health technologies. Objective cough measurement remains absent from routine diagnostic pathways, and is not reimbursed under national insurance, revealing a persistent gap between technological capability and health-system readiness. Even validated PROMs for coughing—which are simple, inexpensive, and evidence-based—remain non-reimbursed, discouraging standardized symptom quantification in daily practice. This paradox stands out, given that coughing is among the most common symptoms across all age groups, and that the chronic cough itself represents a distinct disease entity with substantial impact on quality of life, healthcare utilization, and productivity.

Moving forward, governmental policies must actively facilitate the integration of validated digital and physiologic assessment tools into clinical workflows, supported by appropriate reimbursement structures, data governance, and clinician education. At the same time, clinicians must engage early in this process—understanding, validating, and contextualizing new technologies—to ensure that innovation serves universal applicability and genuine patient benefit. Only through collaboration among healthcare providers, policymakers, and industry can the promise of these tools be realized, and technological advances translated into equitable, evidence-based care.

Ultimately, physicians must bridge technology and empathy—translating digital signals into clinical meaning that improves patient lives: “Listen to the patient’s voice—the cough itself.”Ultimately, physicians must bridge technology and empathy—translating digital signals into clinical meaning that improves patient lives: “Listen to the patient’s voice—the cough itself.”

Notes

Conflicts of Interest

Tai Joon An is an early career editorial board member of the journal, but he was not involved in the peer reviewer selection, evaluation, or decision process of this article.

Funding

No funding to declare.

Fig. 1.

Timeline of objective cough assessment evolution versus subjective tools. NRS: numeric rating scale; VAS: visual analog scale; LCQ: Leicester Cough Questionnaire; COAT: cough assessment tool; CHQ: cough hypersensitivity questionnaire; HACC: Hull Automatic Cough Counter; LCM: Leicester cough monitor.

Table 1.

Summary of objective cough assessment tools by domain

Domain	Physiologic focus	Representative tools/Methods	Strengths	Limitations
Cough frequency	Quantifies the number of coughs (isolated or in bouts ≥2 coughs within 2 sec)	Leicester cough monitor; VitaloJAK; LEOSound; Hull Automated Cough Counter etc.	Gold-standard objective measurement; most validated tools; endpoints in antitussive trials; high sensitivity/specificity	Bulky, sensor-intensive, limited home feasibility; few data on usability, cost, or real-world performance; further large-scale validation and proof of generalizability needed before routine clinical adoption
Cough intensity	Reflects mechanical effort and neural drive underlying the reflex response	Peak cough flow; esophageal or high-resolution manometry; expiratory muscle EMG; acoustic amplitude analysis	Provides quantitative estimate of cough strength; links with symptom burden and functional capacity	Effort-dependent, individual factor; invasive or equipment-heavy methods; acoustic approaches need standardization and noise control
Acoustic feature	Evaluates the sound signature of cough events (waveform, spectral and temporal features)	LEOSound; automated spectrogram/AI classification	Captures physiologic and pathologic information; can differentiate wheeze, crackle, and cough types	Mostly research-use only; false-positive events; requires algorithm optimization and calibration across devices
Cough sensitivity & neurophysiology	Assesses afferent and central neural excitability of cough and laryngeal hypersensitivity	Chemical challenges (capsaicin, citric acid, mannitol); mechanical provocation (Arnold’s nerve reflex test); functional MRI; brain PET	Quantifies sensory thresholds; insight into neuro-sensory mechanisms (e.g., TRPV1, TRPA1, P2X3 pathways)	Weak correlation with objective frequency; poor discrimination between patients and controls; affected by age, sex, smoking, and repetition; limited clinical utility

EMG: electromyography; MRI: magnetic resonance image; PET: positron emission tomography; TRPV1: transient receptor potential vanilloid 1; TRPA1: transient receptor potential ankyrin 1; P2X3: purinergic receptor subtype X3.

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