# Speech-Based Support System to Supervise Chronic Obstructive Pulmonary Disease Patient Status
## 4 Discussion  
From the results in Tables 3 and 4, based on the experimental dataset, it can be inferred that, with regards to speech features, they all exhibit statistically significant differences between rest and physical/medication conditions, ranging from 4% to 38% (except for speaking rate) depending on the speech feature and the group of analysis, although no significant correlation is observed between the number of relevant modifications in speech features and COPD variables (FEV\({}_{1}\), mMRC and CAT). However, when validating the significant modification in f0 values after taking the medication by computing the correlation of such changes (i.e., f0 after medication--f0 before medication) with four different COPD indicators: the FEV\({}_{1}\) value without bronchodilator, the FEV\({}_{1}\) value with bronchodilator, the modified Medical Research Council (mMRC) scale, and the COPD assessment test (CAT), the obtained results showed that high FEV1 values and low mMRC and CAT indicators (which are related to healthier subjects), clearly showed a tendency to smaller f0 modifications. This means that f0 modifications after medication are larger in those subjects with higher severity COPD degrees. Regarding the effect of physical effort, in the study group, the less significant differences are observed in the prosodic features related to rhythm, and the most significant differences are in f0 and shimmer. Effort tends to be more relevant in the control group, with voice quality, f0, f0 range, and pause ratio being the most affected speech features. Regarding the effect of medication, the greatest effect is observed on the speaking rate. The difference of the physical effort effect on both the study and control groups is significant. While a larger effect would have been expected in the COPD group due to their pulmonary and respiratory impairments, the results show the opposite. This could be explained by the fact that COPD patients might not have the same capability of making a large effort as the healthy group, and the resulting physical effort is lighter, so is their effect; or perhaps their voice parameters are always impaired, so no differences are perceived before and after exercise. A detailed look at a feature basis reveals that physical effort in general causes higher f0 values, more pauses, longer syllables, a more flattened intonation (lower values of f0 range and slope), lower voice quality features (probably due to a lower \begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & \multicolumn{3}{c}{**preFEV\({}_{1}\)**} & \multicolumn{3}{c}{**postFEV\({}_{1}\)**} \\ \hline  & **Acc (\%)** & **Sens (\%)** & **Spec (\%)** & **Acc (\%)** & **Sens (\%)** & **Spec (\%)** \\ \hline baseline & & 50.0 & & 50.0 & \\ in-rest condition & 62.1 & 61.4 & 62.8 & 59.6 & 59.7 & 59.5 \\ all conditions (rest, effort, medication) & 56.5 & 58.1 & 55.6 & 56.1 & 55.9 & 56.2 \\ all conditions + additional information & 75.0 & 81.1 & 71.0 & 73.9 & 77.7 & 71.1 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Accuracy (Acc), sensitivity (Sens) and specificity (Spec) values for the automatic classification of FEV\({}_{1}\) given a reference threshold. air pressure), and lower speech rates. The results also suggest that, unlike the physical effort effect, medication produces a less flattened intonation (f0 range and slope), and faster rhythm characteristics: higher speech rates, fewer pauses, and lower segment durations. By contrasting the results with the smoking habits of the subjects (currently smoker (s), never smoked (ns), and ex-smoker (es)), it transpired that there is no direct correspondence between the number and the degree of changes in speech features neither in the physical effort nor in the medication conditions. Even for the two smokers of the control group, their behaviour is similar, and they do not differ with respect to the non-smoking subjects.