# 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
In one study [21], patients with septal deviation exhibited a significant postoperative decrease in VTI (\(p<0.05\)), with values approximating those of healthy controls (\(p<0.05\)). Soft phonation index (SPI): SPI measures the ratio of low- to high-frequency harmonic energy, acting as a marker for vocal fold addduction during phonation [43]. One study [21] indicates a significant postoperative reduction in SPI (\(p<0.05\)) and normalization relative to healthy adults (\(p<0.05\)). Degree of voiceless (DUV): DUV quantifies the proportion of nonharmonic segments within the voice sample, indicating the capacity for sustained voicing [44]. In one study [21], DUV exhibited a significant reduction postoperatively (\(p<0.05\)), with values approximating those of normophonic individuals (\(p<0.05\)). Degree of voice breaks (DVB): DVB indicates the proportion of voiced interruptions to overall phonation duration [44]. In patients with septal deviation, one study [21] observed a substantial postoperative decrease in DVB (\(p<0.05\)), with values markedly approaching those of healthy controls (\(p<0.05\)). Peak amplitude variation (vAm): vAm indicates long-term amplitude variations in the vocal signal [44]. In patients with septal deviation, one study [21] documented a significant decrease in vAm post-surgery (\(p<0.05\)), with values significantly aligning with the normative range found in healthy adults (\(p<0.05\)). Long-term average spectrum (LTAS): LTAS denotes a composite spectral signal obtained from a fast Fourier transform of speech, containing both glottal source and vocal tract resonance attributes [45]. In one work [18], LTAS analysis of typically speaking individuals was employed to simulate and compare normal, hyponasal, hypernasal, and mixed resonance conditions. The hyponasal condition showed unique spectral features, including a significantly higher amplitude at 2450 Hz compared to other conditions, alongside a consistent spectral peak at 450 Hz common with the normal condition. Z-score analysis indicated that hyponasal speech exhibited the lowest peak values overall, significantly lower than those of hypernasal and mixed conditions. At 450 Hz, the mixed condition exhibited significantly lower oral stimulus values compared to hyponasal and normal conditions, while at 650 Hz, hyponasal resonance yielded considerably higher z scores than the other two conditions. At 550 Hz, both normal and hyponasal conditions surpassed the hypernasal and mixed conditions in response to oral stimuli. In terms of function centroid values, the hyponasal condition demonstrated low Function 1 centroids, similar to the normal condition, whereas the hypernasal and mixed conditions displayed heightened values. Function 2 centroid analysis correlated low values with hypernasality, whereas the hyponasal condition exhibited a centroid of 0.20, in proximity to the normal condition's 0.40. The nasal stimulus at 250 Hz demonstrated diminished nasal formant energy in the simulated hyponasal condition relative to the normal pattern. Voice onset time (VOT): VOT quantifies the duration from the release of a stop consonant to the initiation of voicing [46]. In one work [24], individuals with nasal obstruction demonstrated elevated VOT values for /t/ and /k/, while showing reduced values for /p/ in comparison to controls; however, these differences lacked statistical significance.