## 4 Measurement Results of HR and HRV with Optical Homodyne and Heterodyne Technique
### Comparison of Results of Optical Homodyne and Heterodyne Technique  
The accuracy of heterodyne detection is found to be better than homodyne detection. The use of AOM in heterodyne detection limits the noise associated with the laser oscillator. However, both optical coherent detection techniques show much less deviation from the ECG recording. Table 6 shows a comparison of results obtained from homodyne detection and heterodyne detection and their deviation from the ECG results. The mean deviation between the electrical measurement and optical measurement methods for each subject is reported [48; 49; 50] and computed with the equation,  
\[Deviation=HR_{VCG}-HR_{ECG} \tag{26}\]  
A small value of deviation from the ECG proves that the VCG graph provides an accurate measurement of \(HR\) and \(HRV\). As shown in Table 6, the deviation values between the VCG and ECG approaches zero for a measurement of \(HR\) lower than 70 bpm. For a measurement of \(HR\) higher than 70 bpm, the deviation values are less than 0.5. The measurement of higher \(HR\) is associated with many factors, such as medical history and the psychological and emotional behavior of the subject under test. Table 6 clearly shows that \(HR\) values obtained from both techniques are very close to \(HR\) values obtained from the ECG recording. The obtained results are motivating because  
Figure 34: R-R and V-V variability from ECG and VCG for different values of \(HR\). \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Subject No.**} & **R-R Variability** & **V-V Variability** & **V-V Variability** & **HR in bpm** & **HR in bpm** & **HR in bpm** \\  & **ECG (ms)** & **Heterodyne (ms)** & **Homodyne (ms)** & **(ECG)** & **(Heterodyne)** & **(Homodyne)** \\ \hline \(1\) & \(555\pm 3\) & \(554.5\pm 3\) & \(554\pm 3\) & \(108.02\) & \(108.20\) & \(108.30\) \\ \(15\) & \(713\pm 5\) & \(711\pm 3\) & \(709\pm 5\) & \(84.13\) & \(84.38\) & \(84.60\) \\ \(12\) & \(745\pm 6\) & \(742\pm 3\) & \(741\pm 6\) & \(80.54\) & \(80.86\) & \(80.97\) \\ \(16\) & \(854\pm 8\) & \(852\pm 4\) & \(849\pm 5\) & \(70.26\) & \(70.42\) & \(70.67\) \\ \(5\) & \(1010\pm 6\) & \(1012\pm 4\) & \(1012\pm 4\) & \(59.37\) & \(59.29\) & \(59.25\) \\ \(7\) & \(1112\pm 6\) & \(1111\pm 6\) & \(1111\pm 6\) & \(53.96\) & \(54.00\) & \(54.00\) \\ \(19\) & \(1431\pm 10\) & \(1430\pm 8\) & \(1429\pm 8\) & \(41.92\) & \(41.96\) & \(42.00\) \\ \(10\) & \(1484\pm 17\) & \(1482\pm 8\) & \(1480\pm 15\) & \(40.41\) & \(40.54\) & \(40.68\) \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Analysis of variability from RR and VV interval (measurement on chest wall). optical detection is a completely non-contact type measurement technique. Table 7 shows the values of \(HR\) obtained from the coronary artery (chest wall position) and radial artery (wrist position) of two test subjects. The measurement of \(HR\) at the coronary artery and radial artery shows very little deviation, at less than 1 bpm. Figure 35a,b shows a comparison of homodyne and heterodyne techniques for the measurement of a \(HR\) of 54 bpm and 84 bpm, respectively. It is clear from Figure 35a that homodyne and heterodyne detection show identical results for measurement associated with the lower value of \(HR\). Figure 36b shows a deviation of 0.22 bpm when measuring the higher value of \(HR\). The measurement of deviation of the VCG values from ECG values are performed for both homodyne and heterodyne techniques. Figure 36a,b shows the mapping of the heterodyne and homodyne signal with the ECG signal for a \(HR\) of more than 70 bpm, respectively. Figure 36a shows that the R peak of the ECG precisely maps to the zero crossing between the \(V_{1}\) point and \(U_{2}\) point in the VCG associated with the heterodyne measurement system. Figure 36b shows that there is a small delay \(\Delta t\) between the R peak of the ECG and the zero crossing between the \(V_{1}\) point and \(U_{2}\) point in the VCG associated with the homodyne measurement system.