# Acoustic Voice Analysis as a Tool for Assessing Nasal Obstruction: A Systematic Review
## 1 Introduction  
Nasal obstruction can be considered either a symptom (and therefore a subjective complaint of the patient) or an increase in nasal resistance to airflow (which can be an objective measurable parameter). As a symptom, nasal obstruction is a discomfort associated with a sensation of insufficient airflow through the nostrils. Objective and subjective nasal obstruction are therefore assessed with different strategies, but the causes are the same [1]. The most common ones include stenosis or collapse of the nasal valve, deviation of the nasal septum, hypertrophy of the inferior turbinates, rhinosiusitis with/without nasal polyps (CRSwNP, CRSsNP), choanal stenosis or atresia, and masses in the nasopharyngeal [2]. Nasal obstruction can be assessed through three distinct strategies: patient-reported outcomes, physician assessments, and objective measurements [3]. Patient-reported outcome measures (PROMs) include the Nasal Obstruction Symptom Evaluation (NOSE) scale [4] and visual analog scales (VAS) [5], which measure the severity of symptoms. Physicians frequently employ grading systems such as the modified Lund-Kennedy endoscopic score [6], the nasal polyp score (NPS), or semiquantitative clinical evaluations (e.g., mild, moderate, severe obstruction) obtained from rhinoscopy and nasal endoscopy. The objective measures consist of, among others, acoustic rhinometry, which evaluates the dimensions of the nasal cavity [7], rhinomanometry, which evaluates airflow resistance [8], and peak nasal inspiratory flow (PNIF) [9]. Imaging techniques, which include CT, can identify structural causes, such as septal deviation [10], and can also be scored (as in the Lund-Mackay scoring system). Although each method possesses limitations, their combined application enhances diagnostic accuracy. Nasal cavities are involved in resonance phenomena leading to the genesis of voice; therefore, obstruction may also result in perceptible alterations in voice quality. In fact, hyponasality, also known as rhinophia clausa, is a condition characterized by a decrease in the typical nasal resonance during speaking due to obstruction, that is, a hindered flow of air via the nasal channel [11]. Hyponasality may impact the articulation of nasal consonants, namely the sounds /m/,/n/, and /l/. Nasal consonants may sound like their oral phoneme cognates (b/m, d/n, and g/l) when nasal resonance is diminished. If hyponasality is extreme, it can also impact the quality of vowels [12]. The impact of nasal obstruction on voice output is evident, as it can be perceived not only by clinicians but also by lay listeners, who are usually able to detect nasal obstruction through hyponasality of speech. In the literature, various attempts can be found to objectify this perceptive detection of nasal obstruction through acoustic voice analysis, as acoustic analysis is increasingly used in clinical practice due to technological advances and lower equipment costs. A key study [13] indicated that nasometric measurements can accurately represent nasal patency, exhibiting moderate sensitivity and high specificity, and correlating hyponasality ratings with clinical airflow impairment. These findings confirm that analysis of voice can enhance conventional airflow and imaging evaluations, providing a practical clinical approach for diagnosing and monitoring nasal obstruction in conditions. The purpose of this systematic review is therefore to obtain a more comprehensive understanding of the present state of knowledge about voice analysis as a tool to assess and/or monitor nasal obstruction. It aims to consolidate limited but emerging evidence that shows how voice analysis can be utilized for screening for nasal obstruction. This review aims not only to summarize current knowledge but also to provide a conceptual framework for developing noninvasive, voice-based monitoring tools that could be useful in telemedicine and chronic care pathways.