Pulse transit time technique for cuffl ess unobtrusive blood pressure measurement: from theory to algorithm

Cuffless technique holds great promise to measure blood pressure (BP) in an unobtrusive way, improving diagnostics and monitoring of hypertension and its related cardiovascular diseases, and maximizing the independence and participation of individual. Pulse transit time (PTT) has been the most commonly employed techniques for cuffl ess BP estimation. Many studies have been conducted to explore its feasibility and validate its performance in the clinical settings. However, there is still issues and challenges ahead before its wide application. This review will investigate the understanding and development of the PTT technique in depth, with a focus on the physiological regulation of arterial BP, the relationship between PTT and BP, and the summaries of the PTT-based models for BP estimation.

Dual-modality arterial pulse monitoring system for continuous blood pressure measurement.

Accurate and ambulatory measurement of blood pressure (BP) is essential for efficient diagnosis, management and prevention of cardiovascular diseases (CVDs). However, traditional cuff-based BP measurement methods provide only intermittent BP readings and can cause discomfort with the occlusive cuff. Although pulse transit time (PTT) method is promising for cuffless and continuous BP measurement, its pervasive use is restricted by its limited accuracy and requirement of placing sensors on multiple body sites. To tackle these issues, we propose a novel dual-modality arterial pulse monitoring system for continuous blood pressure measurement, which simultaneously records the pressure and photoplethysmography (PPG) signals of radial artery. The obtained signals can be used to generate a pressure-volume curve, from which the elasticity index (EI) and viscosity index (VI) can be extracted. Experiments were carried out among 7 healthy subjects with their PPG, ECG, arterial pressure wave and reference BP collected to examine the effectiveness of the proposed indexes. The results of this study demonstrate that a linear regression model combining EI and VI has significantly higher BP tracking correlation coefficient as compared to the PTT method. This suggests that the proposed system and method can potentially be used for convenient and continuous blood pressure estimation with higher accuracy.

A preliminary study on multi-wavelength PPG based pulse transit time detection for cuffless blood pressure measurement.

Pulse transit time (PTT) has been widely studied as an index of blood pressure (BP) changes. In recent years, some prototypes of PTT-based wearable BP measurement devices have been developed, which can relieve users from the discomfort caused by the inflating cuff used in auscultatory and oscillometric BP measurement techniques. However, in the common practice for PTT detection, multi-site sensor implementation on human body is required, making it difficult for the integration of wearable devices. Since multi-wavelength (MW) photoplethysmogram (PPG) signals carry blood pulsation information of different blood vessels embedded in different skin depths, the time difference between different wavelength PPG signals collected at the same body site can be treated as a special PTT on a short length of blood vessels beneath the skin. In this work, the time difference between MW PPG, denoted as PTT_MW, was explored to track BP changes as a substitute of infrared (IR) PTT_EP. (PTT_EP is the time interval between electrocardiogram (ECG) and IR PPG.) Ten healthy adult subjects participated in the experiment, and their continuous BP, ECG and fingertip MW PPG signals generated from blue, green, yellow and IR light were recorded after 2-minute static handgrip exercise at 33% maximal voluntary contraction. The results showed that the correlation between Systolic BP (SBP) and IR-Blue PTT_MW (|r|= 0.52) was comparable to the correlation between SBP and IR PTT_EP (|r|= 0.59). Moreover, we optimized the wavelength combination of PTT_MWs for each subject and found the average value of optimal correlation between SBP and PTT_MW reached 0.76, which was significantly (p<;0.01) higher than the correlation between IR PTT_EP and SBP. This study reveals that the time difference between MW PPG can be potentially used as PTT for cuffless BP measurement with its unique advantage in simple sensor implementation at only one body site.

Risk prediction for heart failure incidence within 1-year using clinical and laboratory factors.

Validated risk scores for heart failure incidence are still lacking, especially for short-term prediction. In this paper we aim at developing a 1-year risk prediction model for heart failure (HF) incidence using both clinical risk factors and laboratory variables. The public MIMIC II clinical database is studied. Two multivariable Cox models are built to assess the 1-year risk of HF, one with conventional clinical risk factors only, another combined with laboratory parameters, including serum creatinine (SCR), blood urea nitrogen (BUN), glucose, prothrombin time (PT), activated partial thromboplstin time (APTT) and total bilirubin (TBIL). The discrimination performances of the different models are internally validated at last with bootstrapping. In addition to known risk factors, more clinical and laboratory indices, including pulmonary circulation diseases, peripheral vascular disease, chronic pulmonary disease, hypothyroidism, electrolyte and fluid disorders, BUN and APTT are identified to be independent predictors of heart failure incidence. Moreover, we found that the long-term risk factor, hypertension, has opposite effect on short-term risk. The C-statistics of 0.712 with internal validation has demonstrated the effectiveness of the prediction model combined clinical and laboratory factors.

M-health: trends in wearable medical devices / 中国医疗器械杂志

This paper focuses on the trends in wearable medical devices for the applications in m-health. The state-of-art technologies for the continuous and noninvasive measurements of physiological parameters, implementation platforms of wearable medical devices - e-textile, and body sensor networks are reviewed here with examples of related recent research projects conducted in different countries. In addition, we introduce our recent research project on the e-textile-based health shirt (h-shirt), which can measure arterial blood pressure noninvasively, continuously and cufflessly.