Respiratory conditions are on the rise worldwide, and especially in developing countries like India which accounts for an estimated 18% of the world population. Findings from the Global Burden Disease Survey 1990-2016 make it clear that both acute and chronic respiratory diseases are highly prevalent in the country. Air pollution, tobacco, biomass fuels, and occupational exposures continue to overburden the Indian healthcare system with a variety of respiratory ailments, of which ‘cough’ remains the most common initial presenting symptom.1,2
Qualitative and Quantitative Cough Assessments Are Crucial To Optimize Disease Outcomes
Not only is cough an important indicator of underlying lung pathology, but cough pattern is known to be a key biomarker for the assessment and monitoring of acute or chronic pulmonary conditions. A detailed cough assessment can be helpful in objectively evaluating treatment responses to pharmacological/non-pharmacological antitussives, play important roles in predicting transmission of communicable respiratory conditions, and evaluate airway responsiveness in patients with neuromuscular conditions.
With such wide implications, it becomes important for a clinician to assess and document the cough using clinically validated tools.3,4
Several tools for subjective and objective measurement of cough exist, and their usage has been instrumental in advancing clinical and preclinical research and the advent of promising new treatments. These include methods for measuring cough-specific quality of life, subjective severity, cough frequency, intensity, and sensitivity of the underlying cough reflex.5
Subjective assessments help a clinician understand a patients’ personal experiences of cough,thereby assessing associated psychosocial elements that may otherwise be under-recognized.
Subjective assessments focus on the symptom of cough itself, such as cough severity, and the effects of the cough on a patient's general health status, such as cough-related quality of life.
● The Cough Severity Visual Analogue Scale is a standardized VAS 0- to 100-mm linear scale on which higher scores indicate higher severity.
● The Cough Severity Diary is a 7-item outcome measure with an 11-point Likert scale for each item in which higher scores indicate higher severity.
● The Leicester Cough Questionnaire consists of 19 items addressing physical, social, and psychological domains, with a 7- point Likert scale in which higher scores indicate better health status.
● The Cough Quality of Life Questionnaire comprises 28 items in 6 domains that include physical complaints, extreme physical complaints, psychosocial issues, emotional well-being, personal safety fears, and functional abilities.
Each item is rated with a 4-point Likert scale in which lower scores indicate better QOL.
There are tools available to assess and quantify cough frequency, intensity, and cough reflex sensitivity which help a clinician standardize and objectively document their evaluation.
● Ambulatory cough frequency monitors such as Leicester Cough Monitor comprises a portable battery-operated digital sound recorder and a lapel microphone that captures and records all sounds for 24 hours or longer. The recorded data is run through a custom-built detection algorithm to analyze and identify cough frequency.
● The force or intensity of coughing is an important parameter for assessing cough efficacy. Measurements of Cough Expiratory Flow Rates, Electromyogram activity of respiratory muscles, and Cough Sound Amplitudes are helpful markers of cough intensity assessment.
A controlled inhalation of pro-tussive compounds such as capsaicin is utilized to evoke a cough reflex and their minimum concentrations required to elicit the same is recorded. These Tussive Challenge Tests find wide implications in early phase evaluation of antitussive medications and to investigate the risk of respiratory complications in patients with neuromuscular diseases.
Current Research and Ongoing Developments in Cough Assessment
There is much interest in utilizing digital offerings to develop novel cough assessment tools. Considerable work is currently underway to test and analyze these technologies. Some recently published and notable work includes -
Lung congestion, which results in a wet cough or sputum production, is a strong indicator of numerous pulmonary conditions ranging from respiratory infection to more serious diseases such as pneumonia and cancer. Nemati E et al,  objectively evaluated the presence or absence of lung congestion through a smartphone recording and a multi-layer labeling platform with a system architecture comprising of Sensing, Annotation, Pre-processing, Feature Engineering and Classification.
Hand held cough testing was a novel setupused by Curtis et al.  which consisted of a facemask coupled to a handheld nebulizer and an analog peak flow meter. The HCT identified differences in cough airflow and sensation during reflex and voluntary cough tasks with high sensitivity and can be a portable, affordable, and a clinically feasible tool valid for cough assessment, dysphagia screening, and potentially identifying people at risk of aspiration pneumonia.
1. Singh V, Sharma BB. Respiratory disease burden in India: Indian chest society SWORD survey. Lung India. 2018 Nov-Dec;35(6):459-460.
2. India State-Level Disease Burden Initiative CRD Collaborators. The burden of chronic respiratory diseases and their heterogeneity across the states of India: the Global Burden of Disease Study 1990-2016. Lancet Glob Health. 2018 Dec;6(12):e1363-e1374.
3. Singh V, Sharma BB. Respiratory disease burden in India: Indian chest society SWORD survey. Lung India. 2018 Nov-Dec;35(6):459-460.
4. M. R. Pratter, “Overview of common causes of chronic cough: Accp evidence-based clinical practice guidelines,” Chest, pp.59S–62S, 2006.
5. Cho PSP, Birring SS, Fletcher HV, Turner RD. Methods of Cough Assessment. J Allergy Clin Immunol Pract. 2019 Jul-Aug;7(6):1715-1723.
6. Nemati E, Rahman MM, Nathan V, Vatanparvar K, Kuang J. A Comprehensive Approach for Classification of the Cough Type. Annu Int Conf IEEE Eng Med Biol Soc. 2020 Jul;2020:208-212.