Continuous Cuffless Blood Pressure Estimation Using Pulse Transit Time and Photoplethysmogram Intensity Ratio

Abstract

Pulse transit time (PTT) has attracted much interest for cuffless blood pressure (BP) measurement. However, its limited accuracy is one of the main problems preventing its widespread acceptance. Arterial BP oscillates mainly at high frequency (HF) because of respiratory activity, and at low frequency (LF) because of vasomotor tone. Prior studies suggested that PTT can track BP variation in HF range, but was inadequate to follow the LF variation, which is probably the main reason for its unsatisfactory accuracy. This paper presents a new indicator, the photoplethysmogram intensity ratio (PIR), which can be affected by changes in the arterial diameter, and, thus, trace the LF variation of BP. Spectral analysis of BP, PTT, PIR, and respiratory signal confirmed that PTT was related to BP in HF at the respiratory frequency, while PIR was associated with BP in LF range. We, therefore, develop a novel BP estimation algorithm by using both PTT and PIR. The proposed algorithm was validated on 27 healthy subjects with continuous Finapres BP as reference. The results showed that the mean ± standard deviation (SD) for the estimated systolic, diastolic, and mean BP with the proposed method against reference were -0.37 ±5.21, -0.08 ±4.06, -0.18 ±4.13 mmHg, and mean absolute difference (MAD) were 4.09, 3.18, 3.18 mmHg, respectively. Furthermore, the proposed method outperformed the two most cited PTT algorithms for about 2 mmHg in SD and MAD. These results demonstrated that the proposed BP model using PIR and PTT can estimate continuous BP with improved accuracy.

Cuff-Less and Continuous Blood Pressure Monitoring: A Methodological Review

“…Another study [112] provided a comparison between algorithms by Chen et al and Poon et al and they found that Chen's algorithm gave results within the standards for only a 4 min calibration interval and was unreliable in tracking large changes in BP, whereas Poon's algorithm required shorter calibration intervals to maintain a favorable accuracy. A recent study claimed that the inaccuracy of existing algorithms using PAT in tracking Low-Frequency (LF) variations in BP was one of the main reasons for inaccurate results [90,113]. In order to improve the accuracy, they introduced a factor termed "photoplethysmogram intensity ratio" (PIR), which could be determined by the ratio of the peak (I p ) and the foot (I f ) PPG values (Figure 3c).…”

“…In order to improve the accuracy, they introduced a factor termed "photoplethysmogram intensity ratio" (PIR), which could be determined by the ratio of the peak (I p ) and the foot (I f ) PPG values (Figure 3c). PIR was found mainly dependent on the arterial diameter and correlated with DBP [90,113]. Recently, machine learning-based techniques have been investigated [114] and promising results have been reported.…”

“…Cold Pressure Placement of ice wrapped in wet cloth on subject's forehead for 2 min. Hand in 4 • C water for 1 min [102,103] Mental Arithmetic Counting backwards from 500 in intervals of 7, Continuous addition of 3 digit numbers for 2 min [104] Relaxation Slow breathing/Meditative music [105,106] Amyl Nitrate Inhalation of vasodilator [107] Anesthesia Dental anesthesia [84,108] Isometric Exercise Raising legs/arms against pressure [109] Sustained Handgrip Clenching one's fist forcefully [110,111] Technologies 2017, 5, 21 10 of 19 inaccuracy of existing algorithms using PAT in tracking Low-Frequency (LF) variations in BP was one of the main reasons for inaccurate results [90,113]. In order to improve the accuracy, they introduced a factor termed "photoplethysmogram intensity ratio" (PIR), which could be determined by the ratio of the peak (Ip) and the foot (If) PPG values (Figure 3c).…”

A Novel Method for Continuous, Noninvasive, Cuff-Less Measurement of Blood Pressure: Evaluation in Patients With Nonalcoholic Fatty Liver Disease

“…A relatively simple online algorithm has been used to derive PTT and correlate with BP. The work by Ding et al [10] indicates that combining other features from PPG signal traces in addition to PTT could potentially be a better way to estimate BP and adding features from the ICG trace could further increase the accuracy.…”

Preliminary study for hemodynamics monitoring using a wearable device network

“…Measurement of vascular parameters such as HR, electrocardiograph (ECG), arterial oxygen saturation (SpO 2 ) or photoplethysmograph (PPG) monitoring are commonly used [3], [4]. From these raw measurements, more complex information can be extracted such as BP [5], [6] or blood vessel elasticity [7]. Following MoensKorteweg equation, pulse wave velocity (PWV) depends on the blood vessel thickness, diameter and elasticity and PWV is inversely related to pulse transit time (PTT) which is itself related to BP [5].…”