Ding Xiao-Rong, Zhang Yuan-Ting
Annu Int Conf IEEE Eng Med Biol Soc. 2015;2015:398-401. doi: 10.1109/EMBC.2015.7318383.
The most commonly used method for cuffless blood pressure (BP) measurement is using pulse transit time (PTT), which is based on Moens-Korteweg (M-K) equation underlying the assumption that arterial geometries such as the arterial diameter keep unchanged. However, the arterial diameter is dynamic which varies over the cardiac cycle, and it is regulated through the contraction or relaxation of the vascular smooth muscle innervated primarily by the sympathetic nervous system. This may be one of the main reasons that impair the BP estimation accuracy. In this paper, we propose a novel indicator, the photoplethysmogram (PPG) intensity ratio (PIR), to evaluate the arterial diameter change. The deep breathing (DB) maneuver and Valsalva maneuver (VM) were performed on five healthy subjects for assessing parasympathetic and sympathetic nervous activities, respectively. Heart rate (HR), PTT, PIR and BP were measured from the simultaneously recorded electrocardiogram (ECG), PPG, and continuous BP. It was found that PIR increased significantly from inspiration to expiration during DB, whilst BP dipped correspondingly. Nevertheless, PIR changed positively with BP during VM. In addition, the spectral analysis revealed that the dominant frequency component of PIR, HR and SBP, shifted significantly from high frequency (HF) to low frequency (LF), but not obvious in that of PTT. These results demonstrated that PIR can be potentially used to evaluate the smooth muscle tone which modulates arterial BP in the LF range. The PTT-based BP measurement that take into account the PIR could therefore improve its estimation accuracy.
最常用的无袖血压测量方法是使用脉搏传输时间（PTT），它基于Moens-Korteweg（M-K）方程，该方程的前提假设是诸如动脉直径等动脉几何形状保持不变。然而，动脉直径是动态变化的，在心动周期中会发生改变，并且它是通过主要由交感神经系统支配的血管平滑肌的收缩或舒张来调节的。这可能是影响血压估计准确性的主要原因之一。在本文中，我们提出了一种新的指标，即光电容积脉搏波（PPG）强度比（PIR），以评估动脉直径的变化。分别对五名健康受试者进行深呼吸（DB）动作和瓦尔萨尔瓦动作（VM），以评估副交感神经和交感神经活动。从同步记录的心电图（ECG）、PPG和连续血压中测量心率（HR）、PTT、PIR和血压。结果发现，在DB过程中，从吸气到呼气，PIR显著增加，而血压相应下降。然而，在VM过程中，PIR与血压呈正相关变化。此外，频谱分析表明，PIR、HR和收缩压（SBP）的主导频率成分从高频（HF）显著转移到低频（LF），但在PTT中不明显。这些结果表明，PIR有可能用于评估在低频范围内调节动脉血压的平滑肌张力。因此，考虑到PIR的基于PTT的血压测量可以提高其估计准确性。
