## 4 SMRRPM Evaluation  
Several experiments were developed to test the main capabilities of the SMRRPM prototype. In the first level of the system, it is important to determine the response time for the acquisition of BT and HR signals. In the case of the BT response time, several measurements were performed using different values of \(\beta\). Temperature behavior is often represented as a first order system in which \(\tau\) is the time constant and k is the steady-state gain. The first order system is described by Equation (4). \[(\tau)(y(t))+y(t)=k\Delta x \tag{4}\]  
The plot in Figure 13 shows that the BT behaves as a first order system with an initial small delay. After several measurement trials, we found that the SMRRPM needs at least ten minutes to acquire an accurate value for the BT. This is not a disadvantage because it is generally recommended to wait three to five minutes to obtain an accurate BT value from commercial thermometers. Although the SMRRPM  
Figure 12: Example of VPF application: (**a**) VPF shows current BT value, and (**b**) VPF shows current HR value. exceeds the acquisition time of commercial thermometers, it is important to remember that the system was developed for continuous monitoring, which means that ten minutes have passed before the first measurement is performed after the setup of the system. The nurse can update the BT of a patient whenever necessary after approximately ten minutes, without any additional waiting time. Because the HR response time depends on the BPM, it is necessary to wait at least one minute to obtain the first sample. The measurement of the standard deviation of the averaged N-N intervals (SDANN) must be allowed sufficient time, preferably 24 h [37]. To determine the SDANN and the maximum change in the N-N intervals, the SMTRPM was tested in healthy patients with and without previous physical activity. The results obtained from the HR variability test are shown in Figure 14.  
The SMTRPM results show that after physical activity, the patients initially have a faster HR. However, after rest, the HR and the N-N intervals exhibit stable behavior, as shown in Figure 14, in  
Figure 14: Tests of HR measurements in patients following physical activity. Figure 13: BT measurement trials with different \(\beta\) values to determine the response time of the BT prototype. which the red dotted line shows the trend in two patients after previous physical activity. Figure 15 shows results from two patients who did not engage in previous physical activity. The HR and the N-N intervals are stable throughout the test period. The red dotted line shows the mean of the N-N intervals. The results show that the SMTRPM could be used to measure the HR variability parameters to alert heart attacks or other HR disorders. Additionally, it is important to determine the maximum distance over which a patient node can transmit the BT or HR information and the type of Internet network supported by the Android application. Data transmission from a patient node was tested over different lengths in the _ad hoc_ mode. Additionally, the last patient node was tested over a private network and a public Internet network. Table 5 shows the results obtained from both tests. As shown in Table 5, in the _ad hoc_ mode, the patient node is able to transmit data within a perimeter of twenty meters without an antenna. If any room is farther than that distance, it is necessary to include a wireless antenna to perform data transmission. In the case of the Internet mode, the SMTRPM was tested on a public Internet network, and any electronic devices such as computers, smartphones, and iPods could be on the network without authorization. Most of the time, the public network was congested, and for this reason it was difficult for the SMTRPM to establish communication. The SMTRPM was also tested on private networks that required a web key (WSK2 WAP) to access the Internet.