A wearable arm device for night and sleeveless blood pressure measurement [translation]

A wearable arm device for night and sleeveless blood pressure measurement

Abstract

24 Hourly blood pressure (BP) It has important prognostic value for cardiovascular risk screening , But for now BP The equipment is mainly cuff type , Not suitable for long-term measurement BP, Especially at night . In this paper , We have developed a wearable armband with pulse transmission time (PTT) System , be used for 24 Hours without cuffs BP measurement , And evaluate it in the unattended environment outside the Laboratory .10 Healthy young subjects participated in this dynamic study , Use this wearable system every 30 One minute measurement PTT, Use standard oscillating ambulatory blood pressure monitor to measure reference blood pressure . in the light of BP and PTT Two kinds of BP Different measuring principles of equipment lead to the problem of non coincidence of recording time , A new estimation method is proposed : Remove from the original data according to the defined criteria PTT Transient in , Then evenly interpolate 、 Low pass filtering 、 Resampling , In record BP Synchronize when . It turns out that , The night PTT And the dynamic range is 21.8 14.2 mmHg Systolic blood pressure of (SBP) The correlation from 0.50 0.24 Up to 0.62 0.20 (p <0.1), The systolic pressure difference between the estimated value and the reference value ranges from 0.7 10.7 mmHg Up to 2.8 8.2 mmHg, The root mean square error ranges from 10.7 mmHg Down to 8.7 mmHg. Besides , This method is obtained at night SBP Elf component and PTT The correlation is 0.80 0.10, And in the dynamic BP Range 13.5 8.0 mmHg when , The difference between the two is 2.4 5.7 mmHg. therefore , It can be concluded from this study , The proposed wearable system has great potential for nocturnal systolic blood pressure monitoring , In particular, measure the long-term mean systolic blood pressure .

brief introduction

Cardiovascular disease (CVD) It is still the number one cause of death in the world [1].2008 year , Cardiovascular disease leads to . Global presence 1 700 Ten thousand deaths , It accounts for nearly one third of all deaths , Estimated to 2030 In, the figure will reach 2 330 ten thousand people . Blood pressure (BP) It is one of the most important risk factors for predicting cardiovascular events . However , Clinical blood pressure has been questioned , Because it is due to the white clothing effect [3] May not reflect normal BP level .24 Hourly ambulatory blood pressure monitoring is increasingly used in hypertension [4] Clinical diagnosis and treatment . Other relevant parameters , Such as night blood pressure and blood pressure variability , It has been proved to be able to predict CVD event [5]、[6] Provide independent clinical value .

Although the importance of ambulatory blood pressure monitoring has been recognized , But the current blood pressure measurement equipment is mainly cuff type , The expansion of cuff during measurement will cause discomfort , Not suitable for long-term monitoring , Especially at night . Pulse transmission time (Pulse transit time, PTT) It is defined as the time when the pulse is transmitted from the heart to the peripheral part , Has been proposed as BP[7][10] Potential alternative indicators . because PTT Wearable devices [11][13] From electrocardiogram (ECG) And light plethysmography (PPG) It's easy to get , It provides a very practical solution for ambulatory blood pressure monitoring . However , Most of the current research focuses on BP and PTT Short term correlation between , To verify PTT Opposite shooting room BP Estimated potential . for example , Two recent studies reported blood pressure and PTT, But we only studied the pulsatile blood pressure and PTT The correlation between , Not overnight Correlation . As far as the author knows , No research has been conducted in the daily living environment outside the Laboratory ,24 Blood pressure within hours or overnight and PTT The correlation between . therefore , The purpose of this study is to explore PTT Can it be replaced in an unattended environment 24hBP.

System and method

The system design

A wearable monitoring device based on armband is developed , For Holter and PPG The measurement of , Pictured 1 Shown . The electrocardiogram is measured by three electrodes . This wearable device is what we are [16] An improved version of the system reported in . In this system , In order to avoid long wires passing through the body , Sew two electronic textile electrodes in the arm belt wrapped on the left arm , The other uses bonding Ag Ag/Cl electrode , Place it on the right side of the subject's chest . An electrode on the arm belt and the right leg drive circuit are used as a common electrode , To actively eliminate common mode interference . In reflection mode , Near infrared LED Emitter and phototransistor measurement PPG. Collected ECG and PPG Use them separately 0.5 17 and 0.5 10 Hz Band pass filter for amplification and filtering . The filtered analog signal is controlled by a single chip microcomputer ATmega 8 The sampling rate is 500hz、 A resolution of 8 Bit analog signal for digital processing , Stored in flash memory module on armband . To save electricity , Design SCM every 30 Turn on the power every minute , Record 1 Cut off the power supply after minutes of data . The buzzer was used to remind the subjects to stay still during the signal recording , Avoid motion artifacts .

chart 1 Shown . Wearable armband 24 Hour ECG and PPG Measuring device .

(a) System diagram .(b) System circuit . Finally, it is packaged as a telescopic boom belt .

agreement

This study recruited 10 Healthy young subjects (27 name 3 year ). There was no serious physical activity during the monitoring . This study uses Oscar 2 Swing ambulatory blood pressure monitor (SunTech Medical) As 24 Standard equipment for hourly ambulatory blood pressure measurement , Measure reference blood pressure . According to clinical guidelines [3] Set every... Throughout the day 30 min Automatic measurement of systolic blood pressure (SBP) And diastolic pressure (DBP). Every time 30 min Record 1 min ECG and PPG.24 After hours of monitoring , The subjects returned to the Laboratory , Take out all sensors . Start 、 end 、 The time of sleeping and waking up was self-reported by each subject . All subjects signed informed consent , And approved by the university ethics committee .

The benchmark BP The measurement of

In previous laboratory research [14]、[15] in , Commonly used Finapres and Portapres As a benchmark BP Measuring device . Because these devices are huge , This study chose the standard 24 Hour ambulatory sphygmomanometer as a reference . Reference device every 30 Measure intermittent blood pressure in about minutes , Based on ptt The method of in 24 Performance in hours .

However , such 24 The measurement principle of hour ambulatory blood pressure monitor makes it difficult to obtain 24 Synchronized blood pressure and PTT Measured value . First , Although both devices set the same sampling rate ( Every time 30 Every minute ), But because of 24 Built in sampling mode of hour ambulatory blood pressure monitor , They tend to be out of sync a few hours after the start of the study . second , Use cuff inflation to trigger PTT Recording can better synchronize the two devices , However, due to other practical problems, this design is not adopted :1) If the two devices placed on the subjects' arms are connected by physical cables , It will bring great inconvenience to the subjects , Therefore, doctors do not recommend this design ;2) If Bluetooth and other wireless communication methods are adopted , The power consumption of wireless module is large , Not suitable for 24 Hour study . Third , Because the oscillation measurement principle of this ambulatory blood pressure monitor has intermittent nature , Therefore, it is essentially difficult to make PTT And BP Sync on exactly the same beat . say concretely , This blood pressure oscillation device measures blood pressure by detecting the maximum oscillation of the sphygmomanometer cuff caused by blood flow , It assumes that blood pressure is in the measurement cycle [17] Not much has changed in the past . This may be reasonable for a well control program in a laboratory environment that requires subjects to remain stationary throughout the process . However , about 24 Hourly dynamic research , In daily activities , Like walking 、 Eat or drink 、 Deep breathing and posture changes [18][20] when , Blood pressure may change briefly in a few seconds , Pictured 2 Shown . Because it is difficult to know during the inflation of the cuff , When does the blood pressure reading displayed on the device occur , Therefore, it is impossible to accurately synchronize blood pressure and PTT. therefore , Resampling is required to synchronize BP and PTT.

chart 2 Shown . Automatic oscillation measurement BP Principle .

In this study , A new processing algorithm is proposed to overcome the above synchronization problem . On this basis , Studied BP and PTT stay 24 h Correlation within , And the estimation accuracy of the wearable device .

Data analysis

• PTT: Collected ECG and PPG Carry out low-pass filtering respectively , The cut-off frequencies are 30 Hz and 16 Hz.ECG and PPG Every episode 1 min, PTT take ECG r Peak and PPG The time interval between the maximum points of the rising edge slope . For data segments with poor signal quality caused by motion artifacts , Before further analysis , Discard manually .

• Proposed PTT Analysis method : Put the subjects 24 The hourly data is divided into daytime and nighttime according to sleep and waking time , Study day and night BP and PTT The relationship between . because BP and PTT It is measured intermittently by two separate devices , And the oscillation measurement mentioned above BP The limitations of , Resample , To calibrate the measurement BP At the time of the PTT Record . Due to the low sampling rate of data acquisition , Can't capture PTT High frequency components of variability . therefore , Use a low-pass anti aliasing filter before resampling . Besides ,PTT May change temporarily due to daily activities ; Some interruptions may cause misunderstanding . Considering these problems , We propose two analysis methods for comparison , Pictured 3 Shown , As shown in the figure below

chart 3 Shown . Use this method to analyze SBP and PTT Example . Symbols and lines are shown below : Open circle primitive SBP and PTT; Cross symbol removal transients ; Method of use 1 Dashed lines smooth data ; Method 2 Solid line smoothing data ; Open triangle SBP Smoothing and resampling to BP Measured time ; Black triangle PTT By way 2 Smooth to BP Measured time .

In the method 1 in , At sampling rate 0.00056 Hz( namely 1/30/60 Hz) Uniformly resample the original SBP and PTT, Then use a cut-off frequency lower than Nyquist frequency ( namely 0.00028 Hz) Low pass filter for smoothing . The cut-off frequency used in the analysis is 0.00019 Hz (1/30/60/3 Hz) Low pass Butterworth digital filter . Measuring raw SBP Data time , For the smoothed SBP( chart 3 Open triangle in ) and PTT Do resampling . All data are resampled by linear interpolation .

Method 2 It includes the following processing steps .1) Through a defined standard from the original PTT Remove transients : When raw data points and smooth data (DPTT) When the deviation exceeds a defined threshold , This raw data point is considered transient , And will be removed from the original data set . A previous study showed that , A change in posture can lead to PTT[12] The change of is about 5%, So for all subjects , exclude PTT The threshold of the transient is determined as 9 ms.2) Repeat the method 1 Step in ( Low pass filtering and resampling ), Get a new smoothing PTT( chart 3 Solid triangle in ).3) Remove SBP and PTT The interpolation point in the transition period between day and night . The discard interval is greater than 3 h Interpolation between two adjacent original data points .

computing method 1 And methods 2 The systolic blood pressure and PTT The correlation between .

• BP Estimated nonlinear model : To evaluate PTT Whether there is substitution BP The potential of , This study adopts our previous work [10] First proposed in BP-PTT Model , The details are as follows : Compare blood pressure with PTT The basic concept of connection is based on Moens Korteweg equation , The equation uses the elastic modulus of the arterial wall when it expands laterally ($E_{in}$)、 Arterial wall thickness (h)、 End diastolic artery radius and blood density (ρ) Express PWV, namely .

Besides , Elasticity or compliance of the arterial wall is required as BP The mathematical representation of a function , To get an equation , Allow from PWV It is estimated that BP. A very common experimental discovery is based on Hughes wait forsomeone [21] Yes 12 In vivo and in vitro studies of anesthetized dogs . This study found that , Modulus of elasticity (Ein) With the dog descending aorta in vivo mean blood pressure (MBP) Exponential growth , That is, the elastic modulus of blood vessels (Ein) Mean blood pressure with descending aorta (MBP) Exponential growth .

$P_t$ by MBP. Human arteries [22] The effect of elastic modulus on BP Exponential dependence of , And in the picture 4 To reproduce . according to (2) Sum graph 4 In vivo experimental data ,(2) The coefficient of can be fitted as :$E_0$ = 1429 mmHg, γ = 0.031 mmHg${}^{-1}$.

take (2) Plug in (1), obtain MBP And PTT Logarithmic relation of , namely

On the other hand , according to Bramwell-Hill equation ,

For a given pulse , If ΔP It's pulse pressure (PP), namely SBP and DBP The difference between the , It is assumed that the change of arterial diameter can be ignored , be PP And $1/PT{T}^2$ In direct proportion to , namely :

among ,$P{P}_0$、$MB{P}_0$、$PT{T}_0$ It can be obtained by calibration .

because MBP It is often estimated as $1/3\cdot SBP+2/3\cdot DBP$, So (3) and (5) It can be estimated separately SBP and DBP

The advantage of this model is that only one calibration point is needed to determine a single parameter , This is of great significance to the practical application of this method . In this study , use BP and PTT The first measured value of , The rest of the data is used to verify the accuracy of the model . Compare the two methods ( Method 1 And methods 2) And different references ( Raw and smooth SBP) Based on PTT The difference between the estimation and the reference device .

result

24 Within hours , Correlation between day and night

In most subjects ,24 Hourly systolic blood pressure / Diastolic blood pressure and PTT The correlation between them is very weak . take 24 Hourly data is divided into day and night , After night smoothing, all subjects SBP And PTT It is negatively correlated with the median , See table I.

surface 1 The systolic blood pressure after smoothing and PTT The correlation coefficient of

On the other hand , Daytime systolic blood pressure and PTT There is no consistent correlation between , Some are positively correlated , Some are negatively correlated or irrelevant . Method 2 For most subjects, daytime systolic blood pressure and PTT There is no significant improvement in the correlation of .DBP And PTT There is very little correlation , This article does not find . There are two ways to deal with 24h SBP and PTT A typical example of data , And the smoothed day 、 Night and 24h SBP and PTT The correlation of is shown in the figure 5 Shown .

chart 5 Shown .(a) 24 h Reference resources SBP and PTT Typical example .(b) Method 1 And methods 2 Smoothing of three time periods SBP and PTT The relevance of .

BP The range of change 、PTT And SBP Correlation coefficient and reference BP With the method 1 And methods 2 be based on PTT Estimate of the BP See table 2. Method 2 Compare the original systolic blood pressure with PTT The correlation from $-0.50\pm 0.24$ Up to $-0.62\pm 0.21(p<0.1)$. Besides , Smooth systolic blood pressure and PTT The correlation between them is significantly stronger than that between original systolic blood pressure and PTT( Method 1 by $-0.61\pm 0.24vs-0.50\pm 0.24$, Method 2 by $0.80\pm 0.10vs0.62\pm 0.21,p<0.05$).

Table 2 Comparison of two analysis methods and different literatures

PTT-Based BP It is estimated that

Method 1 And methods 2 After removing the first point for separate calibration , There were 90 Right and 70 Yes, at night SBP and PTT Be included in the method 1 And methods 2 Estimation . Through estimation and reference SBP The mean value of the difference of 、 Standard deviation and root mean square error (RMSE) To evaluate the estimation performance . surface II Show , Usage method 2, The root mean square error between original systolic blood pressure and smooth systolic blood pressure ranges from 10.7 To 8.7 mmHg and 8.9 To 6.2 mmHg Reduce . Method 1 And methods 2 Of ptt The difference between estimated and original systolic blood pressure is 0.7 10.7 and 2.8 8.2 mmHg. For smooth reference systolic blood pressure , Method 1 And methods 2 The differences are 0.5 8.9 and 2.4 5.7 mmHg. The dynamic ranges of nocturnal systolic blood pressure in all subjects were 80 - 145mmhg and 91 - 141mmhg. chart 6 by ptt Estimate with different references Bland Altman chart .

chart 6 Shown .Bland Altman The figure shows all subjects at night PTT The difference between the estimated value and the reference systolic blood pressure .(a) original SBP As a reference .(b) smooth SBP As a reference .

Discuss

chart 6 Shown .Bland Altman The figure shows all subjects at night PTT The difference between the estimated value and the reference systolic blood pressure .(a) original SBP As a reference .(b) smooth SBP As a reference . The model describes the relationship between stroke by stroke blood pressure and PTT The physiological basis of negative correlation . However ,BP and PTT It is still unknown whether this relationship will be established for a longer time . This paper is carried out in an unattended environment outside the Laboratory 24 Hour outpatient study , To explore 24 Intermittent blood pressure and PTT The relationship between . Because based on cuff and based on ptt No cuff BP The measuring principle of the measuring method is different , It is impossible to accurately measure two at the same time BP. therefore , Resampling is required to calculate PTT and BP The correlation between . Because the sampling rate is very low , That is, the sampling interval is 30min, Can't capture BP and PTT in HF Fluctuation , This is the sampling theorem . therefore , Before interpolation BP and PTT Low pass filtering . We found that the systolic blood pressure after smoothing is related to PTT The correlation between original systolic blood pressure and PTT The correlation between , This indicates that systolic blood pressure is related to PTT The relationship between them is frequency dependent . This result is related to Liu Research [23] The conclusion is the same ,SBP Low frequency of (LF) And high frequency (HF) The ratio of , That's low frequency / High frequency ratio , Than PTT high 4 About times .

Two previous studies investigated nighttime in a laboratory environment BP-PTT The relationship between [14],[15]. stay Chua In the research of , The nighttime data is divided into 5 Minutes do not overlap epoch, these epoch Inside SBP and PTT The correlation of is reported to be about 0.2[14]. This result is very different from our research results , This may be caused by two factors :1)Chua The research focuses on the frequency band 0 0.15 Hz, The frequency band concerned in this study is 0 0.00019 Hz;2) stay Chua In the research of , Reference resources BP By Portapres Measured , It can provide continuous BP Relative changes in levels , Not the absolute BP level , This research is based on the principle of automatic oscillation measurement [24] Standard dynamics BP device .Vlahandonis Research to Finapres For reference ,SBP And PTT There is a good negative correlation (r = 0.57 0.65). However, this study only investigated the short-term Correlation , That is, in each sleep stage 500s, Instead of investigating nighttime correlations [15]. in addition , Both studies were not evaluated by criteria BP Estimated performance . In this regard , This study is the first to investigate night BP PTT Relationship , And shows PTT Used in unattended environment without cuff and at night BP Estimated potential .

eliminate PTT The basic principle of outliers

It is worth noting that , From method 2 Remove from the original data PTT The transients in are not because they are incorrect , But to propose a more reasonable measurement to compare the measurement results of two different devices . say concretely , Due to different measurement principles and other practical problems , Lead to two BP There is a deviation in the measurement time of the equipment . therefore , Before calculating the measurement difference , Resampling is required to synchronize BP and PTT. But because of PTT The sampling rate of is very low (1/30/60 Hz), according to Nyquist Sampling theorem , Only keep PTT Medium and very low frequency components (1/30/60 /2 Hz within ). therefore , Linear interpolation near transients is unreliable . therefore , We believe that the smooth line obtained after excluding the transient is more representative of the real PTT trend . For example, figure 5(a) Due to the existence of the second PTT outliers ( Open circle ) And move down to the blue dotted line . therefore , It is recommended to remove the transient signal before resampling .

• Ignore the basic principle of interpolation in the transition period : The basic principle of ignoring interpolation during the transition period between day and night is , Due to the very low sampling rate , In those instantaneous changes PTT The interpolation around the sample is not like those that change slowly PTT The interpolation around the sample is reliable . Healthy subjects [25] Of 24 Hours PTT During the transitional period between day and night, about 20% The dramatic changes in the world , Therefore, linear interpolation in these periods is not true . To evaluate PTT and BP The correlation between , It is reasonable to eliminate this non systematic error source . After removing these points , We found that SBP And PTT The correlation between them has improved significantly . Some subjects passed the method 2 There is no significant correlation improvement , Because according to the defined standard , The transient is not removed from the raw data at night .

• Blood pressure and PTT The correlation between : Night and day , Systolic and diastolic blood pressure : We found that , Systolic blood pressure and PTT It shows a better negative correlation at night than during the day . There are two factors that may affect daytime PTT BP The impact of relationships is greater than at night :1) Vascular tension . The effect of smooth muscle relaxation and contraction on PWV BP The impact of relationships , The results showed that vasoactive drugs [22]、[26] Can significantly change PWV BP Relationship . Daytime activities such as posture changes 、 Walking and working can adjust vascular tension , Change blood pressure and PTT The relationship between .2) electrocardiogram Rpeak To PPG The delay time of characteristic points includes pre ejection (PEP) And pulse wave conduction time from heart to periphery , That is, vascular conduction time .PEP It refers to the time delay between ventricular depolarization and aortic valve opening . In different physiological states , Such as pressure 、 mood 、 Physical strength, etc , It may flow back with the vein 、 Cardiac contractility 、 Arteries BP[27] And change [28]. There are studies that show that ,PEP In posture change and dynamic movement [29]、[30] Of PTT Great contribution to change . In some cases ,PEP It even changes in the opposite direction to the vascular transmission time [31]、[32]. The above reasons can be explained SBP and PTT The correlation is not significant during the day . On the other hand , It is determined by vasoconstriction and left ventricular contraction SBP Different ,DBP It has nothing to do with left ventricular contraction , Therefore, PEP irrelevant . That's why DBP and PTT The correlation between them is weak . Other studies have reported similar results , And suggest vascular transit time instead of PTT And DBP[32] It's more relevant [33

• Estimation error of original and smooth systolic blood pressure : be based on ptt The difference between the estimated and reference original systolic blood pressure is 2.8 8.2 mmHg Inside , Slightly higher than the advanced medical device Association (AAMI) Differences in standard recommendations , namely 5 8 mmHg. Results and Poon The study of (0.6 9.8 mmHg)[10] Use the same model as the other [34] A comparative study of (1.2 9.7 mmHg) Agreement . There are several sources of systematic errors in this model :1) Elasticity related parameters γ Is set to a constant for all accounts . Because the elastic properties of the arterial wall change with age and sex , The feasible scheme to reduce this error is to adopt different methods according to the gender and age of the subjects γ[9].2) PTT The changes are not only related to BP It's about , Also with PEP It is related to vascular tension . stay BP PTT Considering these confounding factors in the model can reduce the error . Besides , from SBP and DBP To approximate MBP Is another source of error . Besides , In this study, smooth PTT Estimate the original BP It may also cause errors . because BP and PTT The relationship is proved to be frequency dependent [23], Smooth PTT It may not be possible to estimate accurately BP Of HF composition . This explains why after smoothing BP It is estimated that it is better than the original BP The result of estimation is better . however , The result is very close AAMI Standard pair BP Evaluation requirements for measuring devices . therefore , The wearable device and the proposed estimation method are sleeveless at night BP Estimation provides an effective and practical solution , as everyone knows , And the day BP[5] comparison , The night BP It is estimated that CVD Events have more clinical value .

be based on ptt The difference between the estimated value of and the smooth reference systolic blood pressure 2.4 5.7 mmHg Much less than the difference of the original reference systolic blood pressure . Although there is no research to evaluate the smoothed BP The clinical value of , But it actually contains different physiological significance and important clinical significance . We know , In blood pressure HF wave (>0.15 Hz) Related to the mechanical effects of breathing , And low-frequency fluctuations (0.05 0.15 Hz) Vasodilation rate with sympathetic nerve [35] Related to the regulation of . Although low frequency low frequency (VLF) wave (<0.05 Hz) The mechanism is not clear , But we think that ,VLF It may depend on myogenic regulation or thermoregulation , This is related to HF and LF composition [36] Provides different information . Besides , Commonly used in clinical diagnosis of hypertension [37] The method is every 1 Minute measurement 2 ~ 3 Time BP Average of readings . Besides , Many clinical studies have confirmed 24 The average value of hourly ambulatory blood pressure is a prediction CVD Independent risk factors for death [3],[38]. These facts illustrate the clinical significance of blood pressure smoothing .

This study has some limitations :1)BP and PTT No alignment . However , It's important to note that , On the technical , It is difficult to make two kinds of noninvasive measurements with different principles BP The measurement results of the equipment are perfectly aligned .2) The number of data samples is small . The number of data points is mainly limited by the sampling frequency of the reference sphygmomanometer , The sampling frequency of the reference sphygmomanometer is set to every 30 Minutes at a time , Like most of the world 24 As outlined in the clinical guidelines for hourly ambulatory blood pressure measurement [4],[39],[40]. Although the sampling points are reduced after resampling , But it is more fair to judge the difference between the two methods .3) This method takes into account the transient changes during the day , It is difficult to estimate accurately BP value . The correlation at night is much better , It may be because there are few short-term events during this period . therefore , Lack of synchronization BP PTT Correlation has little effect . But during the day PTT and BP There is no transient change , Therefore, precise synchronization is needed . therefore , Continuous BP and PTT. However , Two main practical problems make it based on ptt The method is continuous and long-term in the mobile environment BP Estimation becomes difficult :1) Wearable devices for continuous and long-term PPG Measured high power consumption ;2) Availability of continuous blood pressure reference devices for outpatient use . As far as we know , Current continuous sphygmomanometers are either invasive , Or it is not portable . Based on these considerations , Despite the above limitations , But it is already using the most advanced technology , At the same time, the best research in line with clinical guidelines . Although the study was done during the day BP There are certain limitations in estimation , But it still has important clinical significance . The results of this study show that , Once the correction starts at night ,PTT It can provide an accurate estimate of nocturnal systolic blood pressure without cuff . Many clinical studies have confirmed , In predicting cardiovascular disease or events , Nocturnal systolic blood pressure is higher than daytime blood pressure [5]、[38] Better predict clinical outcomes .

Conclusion and future work

In this study, a method based on PTT Dharma armband wearable BP Long term measuring device . Conduct 24 Hours to go home to study , To evaluate the accuracy of the equipment . In order to overcome PTT It is difficult for wearable devices and oscillation reference devices to record data that do not coincide in time , A new PTT Analysis method . It turns out that : Nocturnal systolic blood pressure and PTT The correlation is significantly improved to $0.62\pm 0.21$,PTT The difference between the estimated value and the reference systolic blood pressure is $2.8\pm 8.2$ mmHg. After smoothing systolic blood pressure , The result is further improved to $0.80\pm 0.10$ and $2.4\pm 5.7$ mmHg. therefore , This study provides a complete and effective solution for nocturnal systolic blood pressure measurement , It has important clinical value for cardiovascular risk screening .

future , We will conduct a larger cohort study , Including more healthy subjects and patients with cardiovascular diseases , To further verify the effectiveness of this wearable device for nighttime blood pressure monitoring