The influence of heart rate on the relationship between pulse transit time and systolic blood pressure.

OBJECTIVE: Pulse transit time (PTT) is a popular indicator of blood pressure (BP) changes. However, the relationship between PTT and BP is somehow individual dependent, resulting in the inaccuracy of PTT-based BP estimation. Confounding factors, e.g., heart rate (HR), of PTT and BP could be the primary cause. In this study we attempt to explore the impact of HR as a window to look at the influence of confounding factors on the relationship between PTT and BP. APPROACH: We investigated the relationship between PTT and systolic BP (SBP) at different HR levels by introducing the heterogeneous treatment effects (HTE) as a quantitative indicator. Compared to the average HR calculated using traditional indicators (e. g. regression coefficient, correlation coefficient), the HTE calculation method can compute the relationship between PTT and SBP at different HR levels, and reduce the influence of confounding factors. MAIN RESULTS: We analyzed the HTE of PTT and SBP of 47 subjects who are resting healthy young people with varying levels of HR. The results showed that the strength of the HTE of PTT and SBP varied with HR, indicating that the strength of the causal relationship between PTT and SBP is subject to HR levels. Whereas the correlation between SBP and PTT was individual dependent; either the strength or the direction of the correlation can vary with HR. We further investigated the group in which PTT and SBP exhibited a negative correlation, and found that about 50% of the subjects showed enhanced strength of HTE in with an increase in HR and the remaining showed the opposite. SIGNIFICANCE: This study means that HR needs to be considered when PTT is used as an indicator of SBP.

Simplified single neuron model for robust local pulse wave velocity sensing using a tetherless bioimpedance device.

Pulse arrival time (PAT), Pulse transit time (PTT), and Pulse Wave Velocity (PWV) have all been used as metrics for assessing a number of cardiovascular applications, including arterial stiffness and cuffless blood pressure monitoring. These have been measured using various sensing methods, including electrocardiogram (ECG) with photoplethysmogram (PPG), two PPG sensors, or two Bioimpedance (BioZ) sensors. Our study addresses the mathematical inaccuracies of previous bioimpedance approaches and incorporates PTT weights for the peak-peak (PTTpp), middle-middle (PTTmm), and foot-foot (PTTff) segments of the sensing signal into a single neuron model to determine a more accurate and stable PWV. In addition, we developed a tetherless bioimpedance device and compared our PTT estimation approaches, which yielded PWV across six subjects and two different arteries. Specifically, using our model, we found that the most reliable combination of weights corresponding to PTTpp, PTTmm, and PTTff was (0.260, 0.704, 0.036) for the brachial artery and (0.104, 0.858, 0.038) for radial artery. This model consistently yielded stable values across repetitions, with PWV values of 5.2 m/s, 5.3 m/s, and 5.9 m/s for the brachial artery and values of 5.8 m/s, 6.6 m/s, and 6.5 m/s for the radial artery. This system and model offer the possibility of obtaining higher reliability PTT and PWV values yielding better monitoring of cardiovascular health measures such as blood pressure and arterial stiffness.

Pulse signal may be a key bridge connecting cardiology and pulse diagnosis of TCM.

Objective: This study extracts atherosclerosis indices from six channels of C u n k o u and discusses the data distribution, aims to explore the connection between cardiology of modern medicine (MM) and traditional Chinese medicine (TCM) pulse diagnosis. Methods: We use a device capable of simultaneously collecting the pulse signals of the Cun, G u a n and Chi to test the population participating in routine physical examinations. Firstly, we collected pressure pulse waves from six channels of C u n k o u of 1045 healthy subjects (578 men and 467 women, average age=37.99±16.02 years). Secondly, we extracted the two most common arteriosclerosis indices pulse transit time (PTT) and Augmentation index (AIx) from six-channel pulse waves. Lastly, T-test and correlation test were taken to analyze the differences and relevance of the atherosclerosis indices extracted from six channels of C u n k o u . Results: When analyzing AIx and PTT at different wrist, it was found that AIx of left wrist is significantly higher than that of right wrist (P<0.001), while the PTT of left wrist is significantly lower than that of right wrist (P<0.001), a phenomenon that is common in both men and women. Furthermore, regardless of whether it is left or right wrist, the AIx at Chi channel is higher than that at Cun (P<0.05) and G u a n (P<0.05). At the same time, the PTT at G u a n is bigger than that at Cun in two wrists (P<0.05). However, when the specific channel is not considered, there is no significant difference in AIx and PTT between each channel and the corresponding wrist (P>0.05). In addition, regardless of gender, when the specific channel is not considered, AIx and PTT of each wrist are significantly correlated with age (P<0.001). Conclusions: The differences of the atherosclerosis indices AIx and PTT in six channels support that the method of six-channel pulse diagnosis is indispensable in TCM. Additionally, the pulse waves obtained from each channel can be utilized as a dependable foundation for diagnosing atherosclerotic conditions. This study is beneficial for promoting the integration of TCM and MM in diagnosing disease.

Evaluation of right ventricular function in patients with Behcet's disease by four-dimensional echocardiography.

AIM: Behcet's disease (BD) is a systemic disorder characterized by vasculitis, resulting in thickened vascular walls that reduce elasticity and impair function. BD can involve the cardiovascular system in three ways: cardiac, arterial, and venous. In this study, our objective was to evaluate the efficacy of pulmonary arterial stiffness (PAS) and pulmonary pulse transit time (PPTT) measures in demonstrating right ventricular functions in asymptomatic BD patients. We aimed to objectively evaluate right ventricular function in patients with BD using four-dimensional echocardiography (4DE). METHOD: This study included 40 patients diagnosed with BD and 40 healthy subjects. Demographic, clinical, laboratory, and echocardiographic parameters were compared. In addition to standard transthoracic echocardiographic evaluation, right ventricle quantification (RVQ) by using the 4DE and 2D-speckle tracking echocardiography were performed. RESULTS: The sPAP, 4D RVQ, and right ventricular strain values exhibited significant differences between the BD and control groups. Right ventricular end-diastolic diameter (RVDD), right ventricular end-systolic diameter (RVSD), right atrium (RA) area, right ventricular myocardial performance index (RVMPI), and PAS were increased in BD patients compared to the control group. Right ventricular ejection fraction (RVEF), right ventricular fractional area change (RVFAC), tricuspid annular plane systolic excursion (TAPSE), Tricuspid S', and PPTT were decreased in BD patients compared to control subjects. PPTT correlated with right ventricular free wall strain (RV-FWS) and PAS. In a multivariate linear regression analysis, PAS and RVFAC were found to be independent predictors of RVFWS. In addition, RVFAC and TAPSE are independent predictors for PPTT. CONCLUSION: Patients with BD may have elevated pulmonary arterial stiffness (PAS) in correlation with decreased PPTT. To ascertain the prognosis for these individuals, right ventricular (RV) functions must be evaluated. Measurements of RVFAC and RVEF via 4DE and deformation imaging techniques may be more useful in identifying subclinical impairment of RV. Individuals with BD, PAS, and PPTT may suggest a link between early pulmonary vascular remodeling and RV subclinical impairment.

Development of a Personalized Multiclass Classification Model to Detect Blood Pressure Variations Associated with Physical or Cognitive Workload.

Comprehending the regulatory mechanisms influencing blood pressure control is pivotal for continuous monitoring of this parameter. Implementing a personalized machine learning model, utilizing data-driven features, presents an opportunity to facilitate tracking blood pressure fluctuations in various conditions. In this work, data-driven photoplethysmograph features extracted from the brachial and digital arteries of 28 healthy subjects were used to feed a random forest classifier in an attempt to develop a system capable of tracking blood pressure. We evaluated the behavior of this latter classifier according to the different sizes of the training set and degrees of personalization used. Aggregated accuracy, precision, recall, and F1-score were equal to 95.1%, 95.2%, 95%, and 95.4% when 30% of a target subject's pulse waveforms were combined with five randomly selected source subjects available in the dataset. Experimental findings illustrated that incorporating a pre-training stage with data from different subjects made it viable to discern morphological distinctions in beat-to-beat pulse waveforms under conditions of cognitive or physical workload.

The use of pulse transit time in diagnostics of sleep-disordered breathing in children.

INTRODUCTION: Sleep is the physiological state of the body where proper morphology and duration are indispensable for human functions throughout both, physical and mental spheres. Disordered breathing during sleep impairs its morphology and results in major disorders in any age group. Adverse effects of Obstructive Sleep Apnea Syndrome in children and poor availability of centers offering children's polysomnography call for a reliable and easily accessible screening method. AIM: The aim of the study were to evaluate the usefulness of pulse transit time in the diagnostics of disordered sleep breathing in children and to attempt to employ the parameter in screening tests. Pulse transit time is a physiological parameter determining the time needed for the pulse wave to travel between two measurement points. MATERIAL AND METHODS: Enrolled in the retrospective study were 153 patients (100 boys and 53 girls) suspected of obstructive sleep apnea syndrome who underwent polysomnography at I. Moscicki ENT Hospital in Chorzów. RESULTS: Statistically significant relations between apnea/hypopnea index and pulse transit time were observed in both, individual age groups and all of the patients. Pulse transit time results proved a negative correlation with apnea/hypopnea index values commonly accepted as a parameter concluding the polysomnography procedures. CONCLUSIONS: The results of the study indicate that pulse transit time measurements may find application in screening tests of sleep-disordered breathing in children.

Determinants of hand pulse wave velocity and hand pulse transit time in healthy adults.

Arterial pulse wave velocity (PWV) is recognized as a convenient method to assess peripheral vascular stiffness. This study explored the clinical characteristics of hand PWV (hPWV) and hand pulse transit time (hPTT) in healthy adults (sixty males = 42.4 ± 13.9 yrs; sixty-four females = 42.8 ± 13.9 yrs) voluntarily participated in this study. The arterial pulse waveform and the anatomical distance from the radial styloid process to the tip of the middle finger of both hands were recorded in the sitting position. The hPWV was calculated as the traversed distance divided by hPTT between those two points. Male subjects showed significantly greater hPWV, systolic blood pressure, and pulse pressure than age-matched female subjects, while the hPTT was not significantly different between genders. Multiple linear regression analysis showed that gender is a common determinant of hPWV and hPTT, and that age and heart rate (HR) were negatively correlated with hPWV and hPTT, respectively. We conclude that male subjects have greater hPWV than female subjects. Ageing is associated with decreased hPWV, while increased HR is associated with a smaller hPTT. The hPWV and hPTT might be used as non-invasive indices to characterise the ageing and arterial stiffness of peripheral blood vessels.

Severe obstructive sleep apnea in children with syndromic craniosynostosis: analysis of pulse transit time.

STUDY OBJECTIVES: We examined the association between pulse transit time (PTT) and obstructive sleep apnea (OSA) in children with syndromic craniosynostosis (SCS), where OSA is a common problem and may cause cardiorespiratory disturbance. METHODS: A retrospective study of children (age < 18 years) with SCS and moderate-to-severe OSA (ie, obstructive apnea-hypopnea index ≥ 5) or no OSA (obstructive apnea-hypopnea index < 1) who underwent overnight polysomnography. Children without SCS and normal polysomnography were included as controls. Reference intervals for PTT were computed by nonparametric bootstrap analysis. Based on reference intervals of controls, the sensitivity and specificity of PTT to detect OSA were determined. In a linear mixed model, the explanatory variables assessed were sex, age, sleep stage, and time after obstructive events. RESULTS: In all 68 included children (19 with SCS with OSA, 30 with SCS without OSA, 19 controls), obstructive events occurred throughout all sleep stages, most prominently during rapid eye movement (REM) sleep and non-REM sleep stages N1 and N2, with evident PTT changes. The greatest reductions were observed 4-8 seconds after an event (P < .05). In SCS with OSA, PTT reference intervals were lower during all sleep stages compared with SCS without OSA. The highest sensitivity was observed during N1 (55.5%), and the highest specificity during REM sleep (76.5%). The lowest PTT values were identified during N1. CONCLUSIONS: Obstructive events occur throughout all sleep stages with transient reductions in PTT. However, PTT as a variable for OSA detection is limited by its sensitivity and specificity. CITATION: Yang S, van Twist E, van Heesch GGM, et al. Severe obstructive sleep apnea in children with syndromic craniosynostosis: analysis of pulse transit time. J Clin Sleep Med. 2024;20(8):1233-1240.

Analysis of influencing factors of sleep spindles / 临床神经病学杂志

Objective Sleep spindles play an important role in promoting cognition.This paper discusses the influencing factors of sleep spindles and provides objective evidence for clinical intervention and regulation of spindles to improve sleep and cognition.Methods Fifty patients with poor sleep quality were monitored overnight by sleep monitoring system,and physiological parameters of sleep structure,electroencephalography power spectrum,cardiovascular and respiratory function were obtained.The correlations between the parameters,age,sex and the spindle index and characteristics(frequency,duration and amplitude)of non rapid-eye-movement sleep(NREM)Ⅱphase were calculated.In Poincare diagram,SD1 represents the positive index of parasympathetic nerve activity,and SD2 represents the negative index of sympathetic nerve activity.Pulse transit time(PTT)decline index represents vascular sympathetic stability.Results SD1(β =-0.512,P＜0.05)and PTT decline index(β =-0.271,P＜0.05)were negatively correlated with spindle index respectively,while SD2 was positively correlated with spindle index(β =0.474,P＜0.05).The sleep change index,NREMⅠ phase proportion and cortical EEG microarousal index were negatively correlated with spindle index(r =-0.316,r =-0.359,r =-0.326;all P＜0.05).Age was negatively correlated with spindle index(β =-0.422,P＜0.05).δ power of deep sleep was negatively correlated with Spindle wave amplitude(β = 0.65,P＜0.001).No correlation was found between sex and sleep spindles.Conclusions The production of sleep spindles depends on good sleep and stable autonomic nerves.It is related to cognition and reflects the strength of synaptic connections,which provides evidence for clinical intervention and regulation of sleep spindles,and also provides a new physiological indicator for evaluating cognitive and brain function.

Effect of Cuff Inflation on Blood Pressure, Arousals, Sleep Efficiency, and Desaturations: Sub-Analysis of the VAST Pilot Study.

The influence of cuff inflations on night-time measurements during 24 h ambulatory blood pressure (BP) measurements is unknown. We investigated the potential effect of cuff inflations on sleep parameters using measurements taken simultaneously with a cuffless device using pulse-transit-time (PTT). On the first day of measurement, standard cuff-based 24 h BP and cuffless measurements were simultaneously performed on the right and left arms (CUFF/PTT-D). In this experiment, 1-2 days after the first measurement, the cuffless device was worn alone (PTT-D). Only data from the cuffless device were analyzed. The following mean sleep parameters were analyzed: mean systolic and diastolic BP, arousals, sleep efficiency, total arousals, arousal per hour, and desaturations. In total, 21 individuals were prospectively enrolled. The mean (SD) age was 47 (±15) years, and 57% were female. The mean systolic asleep BP during CUFF/PTT-D and during PTT-D were 131 (±21) and 131 (±26) mmHg, respectively. The mean diastolic asleep BP values during CUFF/PTT-D and during PTT-D were 80 (±14) and 84 (±14) mmHg, respectively (p = 0.860, p = 0.100, respectively). Systolic and diastolic asleep mean difference was 0.1 (±18.0) and -3.6 (±9.8) mmHg, respectively. There were significantly more total arousals during PTT-D (p = 0.042). There were no significant differences seen in sleep efficiency (p = 0.339) or desaturations (p = 0.896) between the two measurement periods. We could not show any significant impact from cuff inflations during sleep, as documented by PTT-D measurements.

Filtering-induced changes of pulse transmit time across different ages: a neglected concern in photoplethysmography-based cuffless blood pressure measurement.

Background: Pulse transit time (PTT) is a key parameter in cuffless blood pressure measurement based on photoplethysmography (PPG) signals. In wearable PPG sensors, raw PPG signals are filtered, which can change the timing of PPG waveform feature points, leading to inaccurate PTT estimation. There is a lack of comprehensive investigation of filtering-induced PTT changes in subjects with different ages. Objective: This study aimed to quantitatively investigate the effects of aging and PTT definition on the infinite impulse response (IIR) filtering-induced PTT changes. Methods: One hundred healthy subjects in five different ranges of age (i.e., 20-29, 30-39, 40-49, 50-59, and over 60 years old, 20 subjects in each) were recruited. Electrocardiogram (ECG) and PPG signals were recorded simultaneously for 120 s. PTT was calculated from the R wave of ECG and PPG waveform features. Eight PTT definitions were developed from different PPG waveform feature points. The raw PPG signals were preprocessed then further low-pass filtered. The difference between PTTs derived from preprocessed and filtered PPG signals, and the relative difference, were calculated and compared among five age groups and eight PTT definitions using the analysis of variance (ANOVA) or Scheirer-Ray-Hare test with post hoc analysis. Linear regression analysis was used to investigate the relationship between age and filtering-induced PTT changes. Results: Filtering-induced PTT difference and the relative difference were significantly influenced by age and PTT definition (p < 0.001 for both). Aging effect on filtering-induced PTT changes was consecutive with a monotonous trend under all PTT definitions. The age groups with maximum and minimum filtering-induced PTT changes depended on the definition. In all subjects, the PTT defined by maximum peak of PPG had the minimum filtering-induced PTT changes (mean: 16.16 ms and 5.65% for PTT difference and relative difference). The changes of PTT defined by maximum first PPG derivative had the strongest linear relationship with age (R-squared: 0.47 and 0.46 for PTT difference relative difference). Conclusion: The filtering-induced PTT changes are significantly influenced by age and PTT definition. These factors deserve further consideration to improve the accuracy of PPG-based cuffless blood pressure measurement using wearable sensors.

The importance of pulmonary pulse transit time in indicating right ventricular dysfunction and pulmonary arterial stiffness in rheumatoid arthritis.

SUBJECT: Rheumatoid arthritis patients are at risk of developing cardiovascular disease such as right heart failure and pulmonary hypertension (PH). Arterial stiffness can be used to assess pulmonary hemodynamics. Noninvasive approaches can also be used to assess pulmonary hemodynamics. Recently, there have been reports that pulmonary pulse transit time (PPTT) may also be a useful measure. This study aims to examine the effects of pulmonary hemodynamic alterations on PPTT in RA patients. METHODS: Forty RA patients and 40 healthy controls were included in the study. Sociodemographic characteristics, laboratory data, and echocardiographic examinations were performed in both groups. Conventional echocardiographic examination included left and right ventricular systolic and diastolic diameters, right ventricular myocardial performance index (RVMPI), right ventricular diastolic function, estimated pulmonary artery systolic pressure (sPAP), tricuspid annular plane systolic excursion (TAPSE), pulmonary artery stiffness (PAS), and PPTT. Right ventricular diastolic and systolic volumes, right ventricular ejection fraction (RVEF), and right ventricular fractional area change (RVFAC) were determined by four-dimensional echocardiography (4DE). RESULTS: There was no difference between the sPAP values of the patients. RVMPI and PAS were increased in RA patients compared with controls. The PPTT was shortened in RA patients and correlated with RVEF, RVFAC, RVMPI, TAPSE/sPAP, disease duration, and C-reactive protein (CRP). In univariate linear regression analysis, PPTT (p < .001) was thought to be an independent predictor of PAS. RVFAC, disease duration, and PAS were also independent predictors of PPTT. CONCLUSION: In RA patients, PPTT may be the first evidence of early abnormalities in pulmonary vascular hemodynamics. PPTT and PAS are the values that may predict each other in RA patients. Due to its more practical application, PPTT can be used instead of PAS to assess pulmonary hemodynamics.

Remote Estimation of Blood Pressure Using Millimeter-Wave Frequency-Modulated Continuous-Wave Radar.

This paper proposes to remotely estimate a human subject's blood pressure using a millimeter-wave radar system. High blood pressure is a critical health threat that can lead to diseases including heart attacks, strokes, kidney disease, and vision loss. The commonest method of measuring blood pressure is based on a cuff that is contact-based, non-continuous, and cumbersome to wear. Continuous remote monitoring of blood pressure can facilitate early detection and treatment of heart disease. This paper investigates the possibility of using millimeter-wave frequency-modulated continuous-wave radar to measure the heart blood pressure by means of pulse wave velocity (PWV). PWV is known to be highly correlated with blood pressure, which can be measured by pulse transit time. We measured PWV using a two-millimeter wave radar focused on the subject's chest and wrist. The measured time delay provided the PWV given the length from the chest to the wrist. In addition, we analyzed the measured radar signal from the wrist because the shape of the pulse wave purveyed information on blood pressure. We investigated the area under the curve (AUC) as a feature and found that AUC is strongly correlated with blood pressure. In the experiment, five human subjects were measured 50 times each after performing different activities intended to influence blood pressure. We used artificial neural networks to estimate systolic blood pressure (SBP) and diastolic blood pressure (SBP) with both PWV and AUC as inputs. The resulting root mean square errors of estimated blood pressure were 3.33 mmHg for SBP and 3.14 mmHg for DBP.

A Novel Equivalent Time Sampling-Based Method for Pulse Transit Time Estimation with Applications into the Cardiovascular Disease Diagnosis.

The increasing incidence of cardiovascular diseases (CVDs) is reflected in additional costs for healthcare systems all over the world. To date, pulse transit time (PTT) is considered a key index of cardiovascular health status and for diagnosis of CVDs. In this context, the present study focuses on a novel image analysis-based method for PTT estimation through the application of equivalent time sampling. The method, which post-processes color Doppler videos, was tested on two different setups: a Doppler flow phantom set in pulsatile mode and an in-house arterial simulator. In the former, the Doppler shift was due to the echogenic properties of the blood mimicking fluid only, since the phantom vessels are non-compliant. In the latter, the Doppler signal relied on the wall movement of compliant vessels in which a fluid with low echogenic properties was pumped. Therefore, the two setups allowed the measurement of the flow average velocity (FAV) and the pulse wave velocity (PWV), respectively. Data were collected through an ultrasound diagnostic system equipped with a phased array probe. Experimental outcomes confirm that the proposed method can represent an alternative tool for the local measurement of both FAV in non-compliant vessels and PWV in compliant vessels filled with low echogenic fluids.

Exploring the Potential of Pulse Transit Time as a Biomarker for Sleep Efficiency through a Comparison Analysis with Heart Rate and Heart Rate Variability.

The relationship between sleep dynamics and blood pressure (BP) changes is well established. Moreover, sleep efficiency and wakefulness during sleep (WASO) events have a significant impact on BP dipping. Despite this knowledge, there is limited research on the measurement of sleep dynamics and continuous blood pressure (CBP). This study aims to explore the relationship between sleep efficiency and cardiovascular function indicators such as pulse transit time (PTT), as a biomarker of CBP, and heart rate variability (HRV), measured using wearable sensors. The results of the study conducted on 20 participants at the UConn Health Sleep Disorders Center suggest a strong linear relationship between sleep efficiency and changes in PTT (r2 = 0.8515) and HRV during sleep (r2 = 5886). The findings of this study contribute to our understanding of the relationship between sleep dynamics, CBP, and cardiovascular health.

Towards continuous non-invasive blood pressure measurements-interpretation of the vasculature response to cuff inflation.

Blood pressure (BP) surrogates, such as pulse transit time (PTT) or pulse arrival time (PAT), have been intensively explored with the goal of achieving cuffless, continuous, and accurate BP inference. In order to estimate BP, a one-point calibration strategy between PAT and BP is typically used. Recent research focuses on advanced calibration procedures exploiting the cuff inflation process to improve calibration robustness by active and controlled modulation of peripheral PAT, as measured via plethysmograph (PPG) and electrocardiogram (ECG) combination. Such methods require a detailed understanding of the mechanisms behind the vasculature's response to cuff inflation; for this, a model has recently been developed to infer the PAT-BP calibration from measured cuff-induced vasculature changes. The model, while promising, is still preliminary and only partially validated; in-depth analysis and further developments are still needed. Therefore, this work aims to improve our understanding of the cuff-vasculature interaction in this model; we seek to define potential opportunities and to highlight which aspects may require further study. We compare model behaviors with clinical data samples based on a set of observable characteristics relevant for BP inference and calibration. It is found that the observed behaviors are qualitatively well represented with the current simulation model and complexity, with limitations regarding the prediction of the onset of the distal arm dynamics and behavior changes at high cuff pressures. Additionally, a sensitivity analysis of the model's parameter space is conducted to show the factors that influence the characteristics of its observable outputs. It was revealed that easily controllable experimental variables, such as lateral cuff length and inflation rate, have a significant impact on cuff-induced vasculature changes. An interesting dependency between systemic BP and cuff-induced distal PTT change is also found, revealing opportunities for improved methods for BP surrogate calibration. However, validation via patient data shows that this relation does not hold for all patients, indicating required model improvements to be validated in follow up studies. These results provide promising directions to improve the calibration process featuring cuff inflation towards accurate and robust non-invasive blood pressure estimation.

Causal inference based cuffless blood pressure estimation: A pilot study.

Enabled by wearable sensing, e.g., photoplethysmography (PPG) and electrocardiography (ECG), and machine learning techniques, study on cuffless blood pressure (BP) measurement with data-driven methods has become popular in recent years. However, causality has been overlooked in most of current studies. In this study, we aim to examine the feasibility of causal inference for cuffless BP estimation. We first attempt to detect wearable features that are causally related, rather than correlated, to BP changes by identifying causal graphs of interested variables with fast causal inference (FCI) algorithm. With identified causal features, we then employ time-lagged link to integrate the mechanism of causal inference into the BP estimated model. The proposed method was validated on 62 subjects with their continuous ECG, PPG and BP signals being collected. We found new causal features that can better track BP changes than pulse transit time (PTT). Further, the developed causal-based estimation model achieved an estimation error of mean absolute difference (MAD) being 5.10 mmHg and 2.85 mmHg for SBP and DBP, respectively, which outperformed traditional model without consideration of causality. To the best of our knowledge, this work is the first to study the causal inference for cuffless BP estimation, which can shed light on the mechanism, method and application of cuffless BP measurement.

Wearable Continuous Blood Pressure Monitoring Devices Based on Pulse Wave Transit Time and Pulse Arrival Time: A Review.

Continuous blood pressure (BP) monitoring is of great significance for the real-time monitoring and early prevention of cardiovascular diseases. Recently, wearable BP monitoring devices have made great progress in the development of daily BP monitoring because they adapt to long-term and high-comfort wear requirements. However, the research and development of wearable continuous BP monitoring devices still face great challenges such as obvious motion noise and slow dynamic response speeds. The pulse wave transit time method which is combined with photoplethysmography (PPG) waves and electrocardiogram (ECG) waves for continuous BP monitoring has received wide attention due to its advantages in terms of excellent dynamic response characteristics and high accuracy. Here, we review the recent state-of-art wearable continuous BP monitoring devices and related technology based on the pulse wave transit time; their measuring principles, design methods, preparation processes, and properties are analyzed in detail. In addition, the potential development directions and challenges of wearable continuous BP monitoring devices based on the pulse wave transit time method are discussed.

Intraoperative Beat-to-Beat Pulse Transit Time (PTT) Monitoring via Non-Invasive Piezoelectric/Piezocapacitive Peripheral Sensors Can Predict Changes in Invasively Acquired Blood Pressure in High-Risk Surgical Patients.

BACKGROUND: Non-invasive tracking of beat-to-beat pulse transit time (PTT) via piezoelectric/piezocapacitive sensors (PES/PCS) may expand perioperative hemodynamic monitoring. This study evaluated the ability for PTT via PES/PCS to correlate with systolic, diastolic, and mean invasive blood pressure (SBPIBP, DBPIBP, and MAPIBP, respectively) and to detect SBPIBP fluctuations. METHODS: PES/PCS and IBP measurements were performed in 20 patients undergoing abdominal, urological, and cardiac surgery. A Pearson's correlation analysis (r) between 1/PTT and IBP was performed. The predictive ability of 1/PTT with changes in SBPIBP was determined by area under the curve (reported as AUC, sensitivity, specificity). RESULTS: Significant correlations between 1/PTT and SBPIBP were found for PES (r = 0.64) and PCS (r = 0.55) (p < 0.01), as well as MAPIBP/DBPIBP for PES (r = 0.6/0.55) and PCS (r = 0.5/0.45) (p < 0.05). A 7% decrease in 1/PTTPES predicted a 30% SBPIBP decrease (0.82, 0.76, 0.76), while a 5.6% increase predicted a 30% SBPIBP increase (0.75, 0.7, 0.68). A 6.6% decrease in 1/PTTPCS detected a 30% SBPIBP decrease (0.81, 0.72, 0.8), while a 4.8% 1/PTTPCS increase detected a 30% SBPIBP increase (0.73, 0.64, 0.68). CONCLUSIONS: Non-invasive beat-to-beat PTT via PES/PCS demonstrated significant correlations with IBP and detected significant changes in SBPIBP. Thus, PES/PCS as a novel sensor technology may augment intraoperative hemodynamic monitoring during major surgery.

Variation of peripheral pulse transit time with internal vascular pressure changes induced by arm movement.

Pulse transit time (PTT) and blood pressure (BP) are widely used to quantify arterial characteristics. Arm position influences arterial BP and peripheral PTT. This study aims to quantify the relationship between PTT changes with internal vascular pressure variations induced by the arm moving. With left arm at horizontal position as reference and the right arm moving from 90 to 45, 0, -45, and -90° respectively, PTT difference was calculated by the difference of the pulse foot between right arm and left arm within the same heartbeat. The change in the BP was calculated from the gravitational effect with the measured arm length. Our results showed that the change in PTT with arm elevating is more obvious than that with arm lowering, indicating the different relationship between PTT changes due to the internal BP changes. This can help in understanding the inherent physiological/pathological mechanism of cardiovascular system.