Pulse Transit Time Feedback and Bidirectional Blood Pressure Change

The current study examined the effects of pulse transit time feedback on systolic and diastolic blood pressure. Three subjects were given feedback designed to increase or decrease transit times. Eleven-twelve one-hour training sessions were provided over a two-week period. The results showed that during increase training, significant increases in systolic pressure and heart rate were observed, while pulse transit time showed a significant decrease. Diastolic blood pressure increases were moderate and only inconsistently observed. During decrease training, diastolic pressure and heart rate declined significantly below baseline. Pulse transit time increases were consistent but lower in magnitude than observed for the opposite training condition. Moderate systolic blood pressure decreases were inconsistently observed.     

Pulse Transit Time and Blood Pressure: An Intensive Analysis

Relationships between pulse transit time (PTT) and intra-arterial systolic (SBP), diastolic (DBP), and mean arterial blood pressure (MAP) were examined in 4 subjects under three conditions: rest, paced respiration, and mental arithmetic. PTT was measured from the EKG R-wave to two peripheral pulses (brachial and radial) and from one pulse to the other. Three points on each pulse wave were used (peak, foot, slope) in the measurements, yielding nine different measures of PTT. The nine PTT measures were not consistently intercorrelated. PTTs initiated by the R-wave were moderately correlated with SBP, but not with DBP or MAP. Brachial to radial PTTs were not correlated with any measures of BP. Relationships between PTT and BP also varied from subject to subject. The limited magnitude of the correlations and their inconsistency suggest caution in the simple substitution of PTT for beat-to-beat measures of BP.     

Pulse Wave Velocity as a Measure of Blood Pressure Change

The use of arterial pulse wave velocity (PWV) as a continuous measure of blood pressure changes is outlined. Theoretical considerations indicate that changes in PWV reflect changes in blood pressure, and an experiment was carried out to assess this relationship. PWV along an arm artery was monitored in 26 subjects at a time when the arterial distending pressure of the limb was altered over a wide range by means of externally applied positive and negative pressures. The results show that changes in PWV reliably follow changes in blood pressure. This method can be considered suitable for studies requiring changes rather than absolute values of blood pressure.     

Pulse Wave Velocity and Blood Pressure Change: Calibration and Applications

An adaptation of the technique for measuring pulse wave velocity is described in which the interval between the R wave of the ECG and the radial pressure pulse is monitored. The resulting transit time (TT) is suitable for use as an indirect measure of blood pressure change. The reliability of the measure was assessed in 5 subjects who volunteered for arterial cannulation on 2 occasions. Simultaneous recordings of intra-arterial pressure and TT were taken during a variety of maneouvres, including mental arithmetic, isometric exercise, and amyl nitrite inhalation. The dependence of changes in TT on arterial pressure was confirmed for all procedures except amyl nitrite inhalation. Linear correlations between TT and mean arterial pressure were high, varying between ?.913 and ?.98. The regression coefficients were reproducible and similar in all individuals. The reasons for the anomalous amyl nitrite response are discussed, together with the limits of application of the measure.     

Pulse Transit Time: Relationship to Blood Pressure and Myocardial Performance

The purpose of this research was to evaluate, in human subjects, the degree to which pulse transit time (PTT) covaries with systolic (SBP) and diastolic (DBP) blood pressure, and the degree to which PTT is sensitive to sympathetic influences on myocardial performance. Six studies were performed involving 118 young adult males. In all subjects, cardiovascular activity was assessed in both the resting state and during three stressors: the cold pressor, a pornographic movie and unsignaled shock avoidance reaction time task. The studies differed with respect to where on the arterial tree the pulse wave was transduced, whether blood pressure was measured invasively or noninvasively, and whether the myocardial sympathetic innervations were intact or not. It was observed that PTT covaried quite consistently with SBP but very inconsistently with DBP. The degree of covariation was influenced by the individual's reactivity and, with DBP, by the type of stress. PTT was appreciably influenced by myocardial sympathetic excitation and to a lesser degree by vascular processes. The use of PTT as an index of blood pressure and myocardial performance is discussed.     

Pulse Transit Time as an Indicator of Arterial Blood Pressure

The relationship between pulse-arrival times and diastolic blood pressure was measured in 10 anesthetized dogs. The pulse-arrival time was measured using the R-wave of the electrocardiogram (ECG) as a time reference. Pulse-transit time was also measured between the carotid and femoral pulses. Blood pressure was raised with epinephrine injected intravenously and lowered with vagal stimulation. In all cases, pulse arrival and transit times decreased with an increase in diastolic pressure for diastolic pressures ranging from 15 to 250 mmHg. The correlation between pulse-arrival time and pressure was poorest when the ECG was used as a timing reference. The best correlation was found with true pulse-transit time and diastolic pressure. When pulse-transit time was used to compute pulse-wave velocity, it was found to increase nearly linearly with blood pressure. From 90–100 mmHg, the pulse-wave velocity increased typically by slightly less than six percent.     

基于脉搏波传导时间的连续血压监测系统

为了实现无创连续血压测量,提出了一种基于脉搏波传导时间(pulse transit time,PTT)的连续血压测量方案。通过同步采集心电(electrocardiogram,ECG)信号与光电脉搏波(photoplethysmograph,PPG)信号,以ECG的R波峰值点作为PTT的开始点,PPG信号的最大值点作为PTT的结束点,得到PTT,与水银血压计测得舒张压(diastolic blood pressure,DBP)与收缩压(systolic blood pressure,SBP)进行回归分析,得到了DBP和SBP的数学模型。利用该方法对41名身体健康的青年人进行实验,利用本方案得到的SBP与水银血压计的相关系数为0.82,其差值的平均数与标准偏差为0.15±2.05 mm Hg;得到的DBP与水银血压计的相关系数为0.73,其差值的平均数与标准偏差为0.12±2.16 mm Hg。利用Bland-Altman差值法对本系统血压测量方法与水银血压计测血压方法进行一致性检验,结果显示两种血压测量方法具有很好的一致性。     

基于脉搏波传导时间的连续血压测量系统

针对现有连续无创血压测量系统采样频率和计算精度较低的问题,我们设计了一套基于STM32F103T4和DSP TMS320C5535芯片的双核血压测量系统。利用STM32和DSP芯片在信号高速采样及高精度运算上的优势,实现了对脉搏波信号的高速采样和计算,改善了连续无创血压测量方法的精度。实验测量30名随机受试者,其医用水银血压计和本系统测量结果的差值均符合美国医疗仪器促进协会(AAMI)标准要求,通过Bland-Altman差值法对两种方法进行一致性检验分析,结果表明两者具有很好的一致性。本研究设计的连续无创血压测量系统可初步在家庭和临床医疗方面进行人体血压的动态跟踪测量。     

The Regulation of Blood Pressure Reactions to Taxing Conditions using Pulse Transit Time Feedback and Relaxation

Two experiments are described in which 40 normotensive subjects were trained to reduce blood pressure (BP) both in undistracting conditions and while performing taxing tasks. Biofeedback was compared with relaxation in each case, and BP was continously monitored by the pulse wave velocity method. In Study 1, feedback and relaxation groups produced similar BP reductions when control was attempted in isolation. However, the relaxation group was significantly disturbed during performance of an auditory choice reaction time (RT) task. In contrast, feedback subjects showed identical BP modifications in the two conditions. In Study 2, the differences during the RT task proved to be short lived. However, the feedback group overcame pressor reactions to a mental arithmetic test more rapidly than could relaxation subjects, and the difference between groups persisted during no-feedback trials. In both studies, modifications were more specific in the feedback condition, since alterations in heart rate, respiration and general activity were less prominent. It is suggested that it may be fruitful to use feedback for training people to overcome BP reactions to taxing conditions, rather than trying to modify tonic level alone.     

利用脉搏波传播时间计算动脉血压的研究

本研究的目的是研究动脉血压和脉搏波传播时间的关系,探讨通过脉搏波传播时间计算动脉血压的可靠性。采用麻省理工学院MIMIC数据库,通过心电和光电容积脉搏波计算得到脉搏波传播时间,通过有创动脉血压获得平均动脉压,使用线性回归方法分段求得脉搏波传播时间和平均动脉压之间的线性方程,应用该方程结合脉搏波传播时间计算动脉血压,并与实际血压比较评价算法的效果。结果表明,脉搏波传播时间和动脉血压存在负相关关系,在一定时间范围内,可通过脉搏波传播时间计算平均动脉压,均方根误差小于5 mmHg。对临床采集数据的分析同样说明,通过脉搏波传播时间计算动脉血压是可行的。     

The Covariation of Blood Pressure and Pulse Transit Time in Hypertensive Patients

To examine the relationship between blood pressure (BP) and pulse transit time (PTT) as measured by the time between the ECG R-wave and an associated peripheral pulse, BP was recorded via a radial artery catheter in 3 hvpertensive subjects who underwent a variety of conditions to alter BP. Overall. 70% of the data was usable. Absolute levels of systolic blood pressure (SBP) but not diastolic blood pressure (DBP) were found to correlate appreciably with PTT. There were significant associations between PTT and both SBP and mean BP but not DBP for direction of BP change. With large SBP changes (> 4 mmHg) an increase in the strength of association occurred in 14 of the 21 conditions across subjects. Overall, PTT did not accurately predict actual BP. PTT and SBP covaried more appreciably in these hypertensives than has been reported for normotensives.     

The Relationship between Arterial Blood Pressure and Pulse Transit Time During Dynamic and Static Exercise

The relationships between arterial systolic and diastolic blood pressure (SBP and DBP), interbeat interval (IBI), and various pulse transit times were investigated in 5 young, healthy males during physical exercise and at rest. Transit times monitored were radial, brachial and dorsalis pedis RPIs (ECG R-wave to pulse intervals), and brachial-radial and radial-dorsalis pedis PPIs (pulse to pulse intervals). Experimental sessions consisted of three periods: two involving mild dynamic exercise plus rests, and one involving static exercise (handgrips) plus rests. Correlation and regression analyses within period and subject were performed on individual beat data. Radial RPI was highly correlated with SBP (during dynamic periods, range ?.57 to ?.89, median r?.81; during static periods, range ?.80 to ?.88, median r=?.87) and moderately correlated with DBP (during dynamic periods, range ?.10 to ?.63, median r?.52; during static periods, range ?.17 to ?.77, median r?.66). Median correlations of radial RPI with SBP and DBP during exercise and rest separately were ?.75 and ?.40 (dynamic), ?.79 and ?.57 (static), and ?.74 and ?.26 (rest). The IBI X radial RPI product was very highly correlated with the rate-pressure product (heart rate X SBP), an index of myocardial oxygen consumption (median r=?.96). The only PPI which reliably indexed SBP or DBP change was brachial-radial PPI during the static exercise period (median r=?.86 and ?.83).     

Relationships ol Pulse Transmission Times to Pre-ejection Period and Blood Pressure

This research addressed the question of whether pulse transmission time to the ear (E-PTT) serves as a satisfactory estimate of pre-ejcction period (PEP) and whether the intracardiac or arterial components of pulse transmission times are correlated with hlood pressure. A median correlation of .86 was found for within-suhject correlations between E-PTT and PEP, and a correlation of .97 was found on trial means across subjects. Pulse transmission times to the ear and finger (measured from the Q-wave) were substantially correlated with systolic but not diastolic blood pressure. PEP, the intracardiac component of pulse transmission time, was moderately correlated with systolic blood pressure, but the arterial components were not. It was concluded that E-PIT estimates PEP in within-subject comparisons, and that the association of the pulse transmission times with systolic blood pressure is by virtue of the fact that these intervals encompass PEP rather than the arterial components. It was further concluded that pulse transmission times more directly reflect sympathetic cardiac influences than they do blood pressure.     

Blood Pressure Control: A Comparison of Feedback and Instructions Using Pulse Wave Velocity Measurements

A comparison was made between blood pressure changes with exteroceptive feedback and simple instructions. Twenty subjects were instructed either to raise or lower pressure for four sessions, while a further 20 were allowed to view an analogue visual display of mean arterial pressure. Pressure changes were continuously monitored with the pulse wave velocity method. When changes were analyzed from the initial baseline, both groups showed divergence between Increase and Decrease over trials, but feedback enhanced control in Increase only. On assessment from the running baseline, feedback control was superior in both direction conditions. This difference may In due to interaction between running baseline changes and experimental conditions. Control by feedback groups deteriorated when feedback was withdrawn. Modifications were accompanied by alterations in heart rate, respiratory activity and movement, although the association was of a gross nature only, being more prominent in increase conditions.     

A System for Monitoring the Radial Pulse: Application to Pulse Transit Time Measurement

A transducer and circuit for continuous monitoring of the radial pulse are described. The wrist transducer is small, robust and easily constructed. The system responds mechanically to surface movement caused by the arterial pulse, and converts the motion photoelectrically to a signal suitable for AC amplification and input to a chart recorder. Output closely follows the shape of the intraarterial pressure pulse. A computer algorithm is described for beat-to-beat calculation of pulse transit time from an ECG R-wave reference.     

An Arterial to Peripheral Pulse Wave Velocity Measure

Optical pulse transducers (photoplethysmographs) provide convenient measures of pulse wave velocity (PWV). If measured between arterial and arteriolar sites, PWV should be a sensitive index of sympathetic nervous system influences on the vasculature. Evidence of such a sensitivity was found in a study of rats in which vasoactive drug reactions simulated changes in sympathetic activity. Application of arterial to arteriolar PWV in humans further required the definition of optimal points on the two waveforms to be used in velocity calculations. An examination of different PWV indices supported use of a foot-to-foot index. Overall, our results support the promise of optical PWV techniques, but do not yet establish its validity as an index of peripheral sympathetic influences.     

孕妇血压与其脉搏波的相关性研究与应用

通过实验研究发现：孕妇的血压与其脉搏波具有很好的相关性，在临床上，根据这一原理，实现对妊高征孕妇的血压进行连续监测，并同时获得心率、血管紧张素转换酶活性。结果表明：平均动脉压和血管紧张换酶活性的变化与临床上妊高征病情的变化一致。     

Voluntary Blood Pressure Reductions Measured With Pulse Transit Time: Training Conditions and Reactions to Mental Work

Blood pressure reductions aided by exteroceptive feedback were compared with those produced with simple instructions in two groups of 10 subjects. The degree of environmental stimulation during sessions was equated in the two conditions. Additionally, the effect of feedback on blood pressure reactions to an auditory choice reaction time task was studied. Pressure changes were monitored with the pulse wave velocity method. Feedback training led to greater modifications than instructions during pressure control trials. Associated adjustments in interbeat interval and respiration rate were also observed, but were of similar magnitude in the two groups. Some carryover of training effects to the reaction time task was found, but this comparison was confounded by larger initial reactions in the feedback group.     

基于舒张期时间的个体化血压建模方法研究

本研究提出了一种基于脉搏波舒张期时间(diastolic time,DT)的无袖带式血压估计方法,能够有效提升可穿戴式设备的血压测量精度。该方案首先从脉搏波(photoplethysmography,PPG)中提取DT,再利用线性回归方法建立个体化血压估计模型。本研究对采集的30个样本的实验数据,进行血压建模并加以验证,实验结果显示收缩压的平均误差为1.859 mmHg,标准差为5.640 mmHg;舒张压的平均误差为1.049mmHg,标准差为6.107 mmHg,证明了该方案的可行性。通过将该方案的估计结果与基于脉搏波传导时间(pulse transit time,PTT)的血压模型的估算结果进行对比研究,结果表明交感神经活动较强时,基于DT的血压模型能够有效提升血压估计精度。     

基于脉搏-心电的便携式血压仪的研制

设计一种体积小巧,测量过程无任何束缚的基于脉搏波传导时间(pulse wave transit time,PWTT)的血压仪。从反射式容积脉搏波(photoplethysmography,PPG)和心电波形(electrocardiogram,ECG)中提取脉搏波传导时间,再综合心率、每搏输出量和外周阻力对血压的影响,通过回归分析建立血压模型,最终实现血压测量。应用样机对20名志愿者进行血压测量,同时以传统水银血压计的测量结果作为标准,结果显示收缩压和舒张压的95%一致性界限分别为(-8.3,11.6),(-9.9,12.7),说明两种方法所测的血压值有较好的一致性。血压仪样机实体小巧,使用方便,使用过程没有任何束缚,同时在理论上对基于脉搏波传导时间的血压测量方法进行优化,实现了收缩压和舒张压的测量。