## 4 Discussion  
The most important aspect of the data was that salivary conductivity was significantly correlated with the CTR in chronic HD patients. Patients with a lower salivary conductivity were at high risk for cardiomegaly. Other than traditional cardiovascular risks, the fluid overload in the body increases the afterload of the heart, aggravates myocardial stress, and therefore, eventually leads to an increased CTR and heart failure [38; 39]. Previous results have confirmed CTR as an important and independent predictor of CVD in patients under HD. In an 18-year Q-cohort study, [PERSON] et al. [5] found that a higher CTR was related to higher mortality and CVD events in HD patients. The body fluid accumulation can lead to an increased CTR in the chest X-ray due to high fluid overload [40; 41]. [PERSON] et al. [9] reported that age, sex, and CTR correlated with CVD death when NT-proBNP, a diagnostic biomarker for cardiac dysfunction and heart failure, was not available. CTR could be a reliable tool for CVD risk stratification in chronic dialysis patients [10; 42]. The finding of a negative correlation between salivary conductivity and CTR has implicated lower salivary conductivity as a marker of volume overload and also a risk for cardiovascular events or deaths (Tables 1 and 2 and Figure 3). In our study, Table 1 showed patients with cardiomegaly also had a higher percentage of underlying atrial fibrillation. Patients on HD have been reported to have a higher incidence of atrial fibrillation [43]. Chronic atrial fibrillation may cause decompensated heart failure. Furthermore, atrial fibrillation could attribute to increased CTR which correlated with a longer duration of hospitalization [44]. In support of our finding, a recent cohort study in patients under maintenance HD showed atrial fibrillation was  
Figure 5: The 3D scatter plot graph of the correlation among age, blood osmolality, and salivary conductivity. \begin{table}
\begin{tabular}{c c c c} \hline \hline  & \multicolumn{3}{c}{**Salivary Conductivity**} \\ \hline \multicolumn{3}{c}{**Standardized Beta**} \\ \multicolumn{3}{c}{**Coefficient (Standard Error)**} \\ \hline Age, per year & 0.309 (0.000) & 3.694 & \textless{}0.001 * \\ Serum osmolality, & 0.192 (0.000) & 2.300 & 0.023 * \\ \(\text{R2}=0.35\) & & & \\ \hline \hline \end{tabular} Parameters included in the regression model: age, creatinine, serum osmolality, serum potassium level, and Thirst scale (VAS). Note: * \(p\leq 0.05\).  
\end{table} 
Table 3: The relationship between salivary conductivity and clinical parameters by multiple linear regression. associated with ventricular hypertrophy and cardiovascular death. A significantly negative correlation was also found between predialysis serum sodium and CTR (Tables 1 and 2). Excessive accumulation of extracellular volume is the main pathophysiological factor of hyponatremia in the dialysis population [45]. A recently large-scale cohort study reported that a low pre-dialysis serum sodium level was associated with a greater risk of mortality in HD patients. Since there is a close correlation between serum sodium and salivary conductivity [30], we removed salivary conductivity from the multiple linear regression analysis for the prediction of CTR. In addition to the relative pre-dialysis hyponatremia in HD patients showing cardiomegaly, we also demonstrated that serum sodium levels were independently associated with CTR. Both the thirst intensity scale and serum osmolality were used for assessing fluid status in this study. The thirst intensity scale VAS and CS measures subjective feelings about thirst. Our study revealed no difference in VAS and CS between normal and abnormal CTR patients (Table 1). The prevalence of thirst is strikingly high in HD patients, 94.1% of whom had never complained of thirst [46]. Xerostomia and blunted autoregulation of blood osmolality may partly explain that the thirst intensity scales are invalid in assessing fluid state among ESKD patients [47].