Association between phonation and the vowel quadrilateral in patients with stroke: A retrospective observational study

Articulation disorder is associated with impaired control of respiration and speech organ movement. There are many cases of dysarthria and dysphonia in stroke patients. Dysphonia adversely affects communication and social activities, and it can interfere with everyday life. The purpose of this study is to assess the association between phonation abilities and the vowel quadrilateral in stroke patients. The subjects were stroke patients with pronunciation and phonation disorders. The resonance frequency was measured for the 4 corner vowels to measure the vowel space area (VSA) and formant centralization ratio (FCR). Phonation ability was evaluated by the Dysphonia Severity Index (DSI) and maximal phonation time (MPT) through acoustic evaluation for each vowel. Pearsons correlation analysis was performed to confirm the association, and multiple linear regression analysis was performed between variables. The correlation coefficients of VSA and MPT/u/ were 0.420, VSA and MPT/i/ were 0.536, VSA and DSI/u/ were 0.392, VSA and DSI /i/ were 0.364, and FCR and DSI /i/ were −0.448. Multiple linear regression analysis showed that VSA was a factor significantly influencing MPT/u/ (β = 0.420, P = .021, R(2) = 0.147), MPT/i/ (β = 0.536, P = .002, R(2) = 0.262), DSI/u/ (β = 0.564, P = .045, R(2) = 0.256), and DSI/i/ (β = 0.600, P = .03, R(2) = 0.302). The vowel quadrilateral can be a useful tool for evaluating the phonation function of stroke patients.