Study Of Hypotension Prediction With Pulse Transit Time Variability

Hypotension after spinal anesthesia for elective cesarean delivery is harmful, to predict its risk before anesthesia is meaningful to clinical area. Comparing with the research of heart rate variability, pulse wave signal, carrying abundant pathophysiological information of vascular characteristics, reflects regulation mechanism of blood pressure more directly. So the thesis conducts in-depth research on the prediction of hypotension after anesthesia by the analysis of pulse transit time variability (PTTV).The main contents include:Propose the analytical method of PTTV according to the correlationship of pulse transit time (PTT) and blood pressure. Discuss the feature detection method of electrocardiogram (ECG) and photoplethysmography (PPG) signal, and the frequency domain analytical method based on auto regressive (AR) model which is suitable for short-time series analysis.Define2new concepts of Relative Frequency of Heart Rate (RFHR) and Relative Cardiac Cycle (RCC), and propose a power spectrum analysis method based on RFHR. Setting as the basis for frequency division, the positions of valley points gather in the range of0.2559±0.0096,0.4213±0.01,0.6006±0.0116and0.7706±0.01817, with small discrete degree and high consistency. The spectral peaks in band0.1～0.26,0.26～0.42and0.42～0.6respectively correspond to five beats’ regulation, three beats’regulation and two beat’s regulation. The physical meaning is quite clear and this method solved the problem of peak clustering in spectrum.Statistically analysis69cases of clinical data with the power spectrum analysis method of RFHR. The PTTV analysis is performed on the day before surgery (DBS), the day of surgery before prehydration (DOS-BL), and the day of surgery after prehydration (DOS-AL). The results show that, when the threshold of RCC5/RCC3(The band energy ratio of five beats’ regulation and three beats’ regulation) was set to 0.7057, the prediction sensitivity reached80%and the specificity reached79.7%.It might be a potential index to predict severe hypotension on DOS-AL, which means some clinical significance on the prediction of hypotension after spinal anesthesia for elective cesarean delivery.