## 3 Results and Discussion
Since silicone is produced by silicon and oxygen, this may suggest a relationship between high siloxane in the exhaled breath and the high normalized response sensitivity of the gas sensors used with the PD group. Figure 3: Normalized responses of the sensitivity characteristics for different types of gas sensors (System D). Response sensitivity of exhaled breath samples from patient and control groups to gas sensors. The data are represented as mean \(\pm\) standard deviation. The \(p\)-value was calculated using one-way analysis of variance (ANOVA). Differences were considered significant when the calculated \(\mathbf{{}^{\star\star}}\)\(p\leq\) 0.01, \(\mathbf{{}^{\star\star}}\)\(p\leq\) 0.001, and \(\mathbf{{}^{\star\star\star}}\)\(p\leq\) 0.0001. Figure 2: Normalized responses of the sensitivity characteristics for different types of gas sensors (System A). Response sensitivity of exhaled breath samples from the patients with Alzheimer’s disease (AD), Parkinson’s disease (PD), and from healthy individuals as a control group to gas sensors. The data are represented as mean \(\pm\) standard deviation. The \(p\)-value was calculated using one-way analysis of variance (ANOVA). Differences were considered significant when the calculated \(\mathbf{{}^{\star\star}}\)\(p\leq\) 0.01, \(\mathbf{{}^{\star\star}}\)\(p\leq\) 0.001, and \(\mathbf{{}^{\star\star\star}}\)\(p\leq\) 0.0001. Further clustering analysis of the exhaled samples showed that the AD, PD, and control groups were patterned into three clusters in system A (Figure 4) and system D (Figure 5). Our results demonstrated that the control group could be distinguished from the AD and PD patient groups based on the PCA and Sammon's mapping methods with a confidence limit of 95%. The PCA method showed a percentage of variance of 96.64% and 98.16% in system A and D, respectively. The [PERSON]'s mapping method had error rates of 9.441 \(\times\) 10\({}^{-4}\) and 9.820 \(\times\) 10\({}^{-4}\) in system A and D, respectively. The combination of both methods had error rates of 7.747 \(\times\) 10\({}^{-4}\) and 9.377 \(\times\) 10\({}^{-4}\) in system A and D, respectively. Using more types of sensors, the exhaled breath sensor system A showed better distribution patterns in the AD, PD, and control groups. The distinctive composition variations in the exhaled breath samples of the patient and control groups are most likely attributable to the discrete clusters. Some of the healthy individuals clustered with the patient groups were those who had or previously had smoking habits. In addition, personal eating habits and environmental factors may also cause a healthy individual to be clustered with those from the patient groups. Despite the variances in the chemical compositions observed from the exhaled breath samples, the source and origin of most of the chemical compounds in the exhaled breath remains unknown. Moreover, the specific pathways and biochemical reactions contributing to the differences in chemical composition are also undetermined. Perhaps, the development of neurodegenerative diseases contributes to increased levels of these chemical compounds in exhaled breath via the alteration of chemical reactions in the body. Moreover, effects of medication and life style could also vary the composition of exhaled breath, especially for patients with AD and PD, since long-term drug therapy might change the chemical compositions of exhaled breath. Figure 4: Distribution clusters for exhaled breath samples of Alzheimer’s disease (AD), Parkinson’s disease (PD), and control groups using exhaled breath system A. (**A**) Principal component analysis (PCA) clustering method for AD, PD, and control groups; (**B**) Sammon’s mapping for AD, PD, and control groups; (**C**) Combination of PCA and Sammon’s mapping for patient and control groups.