# Acoustic Voice Analysis as a Tool for Assessing Nasal Obstruction: A Systematic Review
## 3 Results
### Using Voice to Assess Nasal Obstruction
#### 3.2.1 Acoustic Analysis  
Several acoustic parameters have been assessed in relation to nasal obstruction in the included studies in correlation with nasal obstruction. Jitter: Jitter indicates short-term variations in the fundamental frequency, signifying inconsistencies in vocal fold vibration during phonation [39]. This metric was assessed in eight studies included in this review. No significant alterations in jitter were noted before and after surgery for nasal obstruction in most studies [19; 20; 22; 23; 25; 26; 27]. Only one study [21] reported a significant postoperative reduction in jitter (%) after surgery (\(p<0.05\)) in patients with septal deviation, with values nearing those of healthy controls. Shimmer: Shimmer indicates short-term amplitude fluctuations in the vocal signal, indicating instability in vocal intensity [39]. This review included eight studies that assessed shimmer. In some of them, shimmer did not significantly change after surgery for nasal obstruction [19; 20; 25; 26; 27]. The research by [23] indicated that in groups I and II (patients with minor and moderate nasal deviation, respectively), the differences in mean pre- and postoperative shimmer values were not statistically significant (\(p>0.05\)). However, in group III (patients with severe nasal deviation), the mean postoperative shimmer value was significantly lower than the preoperative value (\(p=0.003\)). Other studies [21; 22] noted a decrease in shimmer after surgery. Fundamental frequency (F0): F0 represents the frequency of vocal fold vibration, quantified in cycles per second (Hz) [39]. Eight studies included in this review assessed F0 in relation to nasal obstruction. Most studies found no effect of nasal obstruction surgery on F0 [19; 20; 22; 23; 26; 27]. Conversely, two of them describe the impact of surgery for nasal obstruction on F0 values [21; 25]. F1: F1 represents the first formant and is affected by tongue height during articulation [40]. This review included three papers that evaluated F1. None of them reported significant modifications after surgery for nasal obstruction [22; 23; 27]. F2: F2 represents the second resonance frequency of the vocal tract and is linked to tongue frontness [40]. Research [22; 23; 27] indicated no significant modifications in F2 values after surgery for nasal obstruction. F3: F3 represents the third formant, typically associated with lip rounding [40] and has been assessed in three studies included in the present review in relation to surgery for nasal obstruction. None of the studies reported significant changes in F3 between pre- and postoperative periods [22; 23; 27]. F4: F4 represents the fourth formant, influenced by the size of the pharyngeal cavity in relation to the laryngeal inlet [40; 41] and has been evaluated in three studies. None of them [22; 23; 27] detected significant variations between preoperative and postoperative F4 values. Noise to harmonic ratio (NHR)- Harmonic to noise ratio (HNR): NHR measures the ratio of aperiodic (noise) to periodic (harmonic) elements in the vocal signal; elevated values generally suggest dysphonia. Conversely, HNR assesses voice quality by measuring harmonic energy in relation to noise, with elevated values indicating a more normophonic voice [42]. NHR was evaluated in six studies, whereas HNR was assessed in one. Most of them failed to detect any statistically significant modifications in NHR and HNR post-surgery (FESS or septoplasty) at multiple time points or among patient groups with varying degrees of nasal obstruction [19; 20; 22; 23; 26; 27]. However, only one study [21] reported a significant reduction in NHR (\(p<0.05\)) in patients with septal deviation after surgery, with values approaching those of healthy controls. Voice turbulence index (VTI): VTI indicates the energy of high-frequency noise in the voice, frequently associated with turbulent airflow resulting from inadequate vocal fold addiction [43].