Biosignal Variability Analysis and Its Application in the Evolution of Hypertension
|Keywords||biosignal variability pulse transit time pulse wave velocity power spectrum analysis cluster prehypertension autonomic nervous system cardiovascular risk estimation early diagnose|
Hypertension is one of the most popular cardiovascular diseases in the world. It not only leads to the lesion of heart, brain and kidney etc., but is the principle risk factor to atherosclerosis, thus it is the key point in cardiovascular disease prevention. At the stage of prehypertension (defined as systolic blood pressure between 120 and 139mmHg, or diastolic blood pressure between 80 and 89mmHg), the arterial wall and autonomic nervous function behaves abnormally, while no clinic symptom appears, thereby, to detect abnormality in vascular system or autonomic nervous function at prehypertension stage, and to estimate the evolution of hypertension will enable the early clinical intervention and lower the risk induced by hypertension and other cardiovascular diseases.Nowadays biosignal variability analysis attracts more and more attention from scientist. Heart rate variability (HRV) is widely accepted as the index of autonomic system activity, especially the regulation function of sympathetic-vagal system. HRV has applied to assessing the cardiovascular risks. Previous study showed that HRV parameters may indicate the abnormal autonomic nervous function in prehypertensive. However, it is insufficient to evaluate the evolution of hypertension only with HRV analysis.Pulse wave velocity (PWV) is considered as an independent index for atherosclerosis. The measurement of PWV is non-invasive and feasible. However, there is a large deviation during its computation, and PWV obtained by different tools or devices is not comparable. Thus, the clinical application of PWV is quite limited. However, variability analysis may provide a new approach for the application of pulse wave velocity or pulse wave transit time. Pulse wave transit time (PTT) can avoid the deviation in PWV, and beat to beat PTT variability is independent of measurement. Thereby, this study established a set of methods for biosignal variability analysis. The concept of PTTV (pulse transit time variability) was introduced. Animal (rat) experiment and clinical trial are carried out to investigate the possible relationbetween biosignal variability and cardiovascular diseases, in particular the evolution of hypertension. The physiological mechanism behind PTTV is discussed by comparing the properties of PTTV with those of HRV and blood pressure variability (BPV). The main tasks and results in this study are summarized as,> The schema for clinical trial was carefully proposed including the inquiry sheet design, noninvasive biosignal detection and parameter extraction. The platform for biosignal variability analysis was established, including PTTV, HRV and BPV analysis. Softwares for database management, parameters calculation and analysis were also designed.> The relationship between biosignal variability and the evolution of hypertension was analysed. It is concluded that combined with PWV and PTT, the spectral parameters of PTTV can discriminate the normotensive, prehypertensive and hypertensive from each other. The result is superior to using HRV parameters. 51.9% cases can be classified correctly using the PTTV analysis, but none cases can be classified using HRV analysis.> Clustering is applied to classify the spectrum of variability signals, including PTTV spectrum of man, and PTTV, HRV, SBPV and DBPV spectrum of rat. 5 specific frequency sectors are determined and characteristic parameters are achieved such as the power in each frequency sector, etc.> The physiological interpretation of PTTV was investigated. From animal experiment, the day-night rhythms of PTTV parameters were analysed. The sympathetic and vagal pathway is blocked with different drugs and the corresponding change in PTTV parameters is observed compared with HRV and BPV parameters. In clinical trial, biosignals under supine and sitting posture were detected to analyse the effect of posture to PTTV. According to the result from both animal experiment and clinical trail, the relationship between PTTV and the function of autonomic nervous system modulation was discussed. It shows that PTTV is related with blood pressure, the regulation activity of autonomic nervous system and respiration system.In conclusion, the method for biosignal variability analyzing established in thisstudy, especially the method for PTTV analyzing, can provide a new method to the early diagnosis of hypertension. Variability analysis method can also be applied into other cardiovascular diseases so as to investigate the nature of biosignal variability, and ultimately serve for the estimation of cardiovascular risk.