A Non-invasive Physiological Parameter Moni-Toring System Based On Photoplethysmography In Anesthesia

Hypotension and nociceptive monitoring in anesthesia is very important, which can help the anesthesiologist to keep abreast of changes in the patient’s physiological state. Anesthesia monitoring equipments on the market are mostly only able to provide some simple parameters and alarm functions, which did not establish the link between parameters and physiological states. So it is difficult to play the subjective initiative of anesthesia doctors. In recent decades, a large number of clinical studies about photoplethysmography (PPG) were done, PPG has been extensive used in anesthesia physiological parameters monitoring. Based on these studies, a non-invasive physiological parameters monitoring system is designed.The main research works are as follows:A. A non-invasive physiological parameters monitoring system during anesthesia based on photoplethysmography is designed, which can monitor heart rate, oxygen saturation, systolic pressure, diastolic pressure, mean pressure, pulse wave conduction time, decay time constant. PPG amplitude, area ratio of descending limb and other parameters in the same time. Especially, decay time constant and area ratio of descending limb are the unique physiological parameters in this system.B. A low power wireless transmission scheme based on nRF24L01module is designed. The scheme uses a wireless network protocol base on Enhanced ShockBurst. which is an on-chip Agreement of nRF series, to achieve low-power data transmission. The scheme greatly reduceed the current of the data sent and received. The total power consumption is about1/3of the carrier sense multiple access protocol (CSMA). The same time, because there is no leak current through wireless, so the scheme saved the hardware costs and reduced the design complexity.C. A algorithm about monitoring pulse transmit time variability (PTTV) during anesthesia is proposed, which is applied to non-invasive physiological parameters monitoring system during anesthesia at the first time. Meanwhile, a new PPG signal feature detection algorithm is also proposed. This algorithm is the combination of the local search method in main window and first order derivative with logical judgment. When the acceptance interval is24.0ms. the detection rate of this algorithm is higher than95%. Pulse transmit time(PTT) can be calculated by the P wave position of PPG signal and the R wave position of electrocardiogram (ECG) signal, which is the original input of PTTV analysis algorithm. Finally, an auto regressive model is used in this algorithm. The algorithm has a reliable performance after the experiments.D. The PTTV analysis method is the first time used in hypotension research during anesthesia.24cases of clinical trials have been done in Women’s Hospital School of Medicine Zhejiang University. The results showed that the P value of the ratio of very low frequency power and low frequency power (VLF/LF) and the ratio of low-frequency power and total power (LF ALL) were:PVLF/LF=0.028. PLF/ALL=0.031. which indicates that these parameters have feasibility of anesthesia hypotension prediction.The system was used in clinical research about hypotension and nociceptive during anesthesia, which realized the effective assessment of hypotension and nociceptive preliminarily. The system is strictly in accordance with the relevant national standards, and it also has high reliability and good prospects for clinical application.