## Results
### Reliability of Human Pulse Wave Measurements at Standard Conditions  
In order to address our main goal of assessing the reliability of human pulse wave measurements in general, we evaluated the test-retest variability of pulse wave parameter analysis under standard conditions. For this purpose, resting measurements were repeated 10 times in 10 healthy individuals. After calculating the coefficient of variation for each individual, the CVs of the 10 subjects were averaged. The mean CVs for each parameter are presented in Table 2. These show that b/a, left ventricular ejection time index, mean interbeat interval, stiffness index, and mean heart rate are parameters that remain stable under standard measurement conditions (CVs lower than 10%). However, the aging index is slightly variable (CV: 13.6%), and d/a and c-d point detection ratio are highly variable even when measured under unchanged conditions.  
In order to visualize how the detected test-retest (intrapersonal) variability relates to interpersonal variability, Figure 4 displays the mean of measurements obtained from the 10 subjects for each sequential measurement time point, with confidence intervals (CIs), along with the individual graphs of the subjects. The graphs show that for each parameter, individual curves appear similar and show no trend, only random fluctuations. The mean curves show no trends or extremes and have homogeneous confidence intervals. The variability of the individual curves among measurements and the variability between the individual curves look comparable.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Pulse Contour Variables** & **CV \% [CI]** \\ \hline Aging index & 13.6 [4.78; 22.5] \\ b/a & 3.84 [2.13; 5.55] \\ c–d point detection ratio (\%) & 33.6 [17.1; 50.1] \\ d/a & 83.9 [9.5; 177] \\ Left ventricular ejection time (ms) & 1.30 [0.75; 1.84] \\ Heart rate (1/min) & 3.19 [1.99; 4.39] \\ Interbeat interval (ms) & 3.23 [2.11; 4.35] \\ Reflection index (\%) & 7.43 [2.79; 12.1] \\ Stiffness index (m/s) & 4.34 [2.20; 6.48] \\ \hline \hline \end{tabular}
\end{table}
Table 2: Results of test–retest variability measurements. Test–retest variability of pulse contour parameters measured by the SCN4 ALL telemedicine system. Measurements were performed on 10 healthy volunteers 10 times repeatedly under standardized conditions. Coefficient of variation (CV) for the results of the consecutive measurements was calculated for each individual. Afterwards individual CVs were averaged; they are presented in the table along with bracketed confidence intervals (CI).  
Figure 4: Graphs demonstrating the relationship between interpersonal variability and intrapersonal variations of the computed pulse contour parameters. Measurements were performed on 10 healthy volunteers 10 times repeatedly under standardized conditions. Means (\(\pm\)confidence intervals) are presented (red solid line) for each consecutive measurement along with individual measurement data (black lines). Individual lines are similar to each other and to the average line. The variability of the individual curves among measurements and the variability between the individual curves seem to fall in the same order of magnitude.