Pulse Transit Time Measurement Research Articles

Comparison of wavelet transformation and adaptive filtering in restoring artefact-induced time-related measurement

Photoplethysmography (PPG) can be used in time-related measurements such as heart rate (HR) and pulse transit time (PTT) estimations in the medical fields. The accuracy of these two parameters is heavily dependent on the minimal phase variability of the PPG signals. Moreover, motion artefact is a common phenomenon that can contaminate the PPG signals. This paper compares the capabilities of two signal processing techniques; digital adaptive filtering and discrete wavelet transformation, in restoring artefact-induced PPG signals during two regulated mild movements. HR comparison was evaluated against estimates attained from an electrocardiogram (ECG) while PTT evaluation was based on a reference PPG source free of artefacts. Comparison criteria was based on documented evidences that a HR difference of <10 beats per minute (bpm) and relative PTT changes of <15 ms can be considered as normal. The obtained results reveal that wavelet transformation is limited in restoring corrupted PPG signals for both HR and PTT measurements. It can also be observed its inherent algorithm can induce unwarranted phase variability that can compromise clinical interpretation of these two physiologic parameters. Promising signal processing algorithms may be attractive for its improved image and/or signal restoration however, its suitability in time-related measurements warrants further investigations.

Use of Pulse Transit Time To Distinguish Respiratory Events From Tidal Breathing in Sleeping Children

Currently, esophageal pressure monitoring is the "gold standard" measure for inspiratory efforts, but its invasive nature necessitates a better tolerated and noninvasive method to be used on children. Pulse transit time (PTT) has demonstrated its potential as a noninvasive surrogate marker for inspiratory efforts. The principle velocity determinant of PTT is the change in stiffness of the arterial wall and is inversely correlated to BP. Moreover, PTT has been shown to identify changes in inspiratory effort via the BP fluctuations induced by negative pleural pressure swings. In this study, the capability of PTT to classify respiratory events during sleep as either central or obstructive in nature was investigated. PTT measure was used in adjunct to routine overnight polysomnographic studies performed on 33 children (26 boys and 7 girls; mean +/- SD age, 6.7 +/- 3.9 years). The accuracy of PTT measurements was then evaluated against scored corresponding respiratory events in the polysomnography recordings. Three hundred thirty-four valid respiratory events occurred and were analyzed. One hundred twelve obstructive events (OEs) showed a decrease in mean PTT over a 10-sample window that had a probability of being correctly ranked below the baseline PTT during tidal breathing of 0.92 (p < 0.005); 222 central events (CEs) showed a decrease in the variance of PTT over a 10-sample window that had a probability of being ranked below the baseline PTT of 0.94 (p < 0.005). This indicates that, at a sensitivity of 0.90, OEs can be detected with a specificity of 0.82 and CEs can be detected with a specificity of 0.80. PTT is able to categorize CEs and OEs accordingly in the absence of motion artifacts, including hypopneas. Hence, PTT shows promise to differentiate respiratory events accordingly and can be an important diagnostic tool in pediatric respiratory sleep studies.

Pulse transit time as a derived noninvasive mean to monitor arterial distensibility changes in children

Changes in arterial distensibility have been widely used to identify the presence of cardiovascular abnormalities like hypertension. Pulse wave velocity (PWV) has shown to be related to arterial distensibility. However, the lack of suitable techniques to measure PWV nonintrusively has impeded its clinical usefulness. Pulse transit time (PTT) is a noninvasive technique derived from the principle of PWV. PTT has shown its capabilities in cardiovascular and cardiorespiratory studies in adults. However, no known study has been conducted to understand the suitability and utility of PTT to estimate PWV in children. Two computational methods to derive PWV from PTT values obtained from 23 normotensive Caucasian children (19 males, aged 5-12 years old) from their finger and toe were conducted. Furthermore, the effects of adopting different postures on the PWV derivations were investigated. Statistical analyses were performed in comparison with two previous PWV studies conducted on children. Results revealed that PWV derived from the upper limb correlated significantly (P<0.05) regardless of computing methods or postures adopted. The findings here suggest that PTT measurement can be used as a convenient and noninvasive surrogate measure of derived PWV in prolonged clinical studies, especially on younger or less cooperative children. Furthermore, the simple set-up and noninvasive nature of PTT can promote its usefulness in ambulatory monitoring.

Age-related factors that confound peripheral pulse timing characteristics in Caucasian children

Characteristics obtained from peripheral pulses can be used to assess the status of cardiovascular system of subjects. However, nonintrusive techniques are preferred when prolonged monitoring is required for their comfort. Pulse transit time (PTT) measurement has showed its potentials to monitor timing changes in peripheral pulse in cardiovascular and respiratory studies. In children, the common peripheries used for these studies are fingers or toes. Presently, there is no known study conducted on children to investigate the possible physiologic parameters that can confound PTT measure at these sites. In this study, PTT values from both peripheral sites were recorded from 55 healthy Caucasian children (39 male) with mean age of 8.4+/-2.3 years (range 5-12 years). Peripheries' path length, heart rate, systolic blood pressure, diastolic blood pressure (DBP) and mean arterial pressure (MAP) were measured to investigate their contributions to PTT measurement. The results reveal that PTT is significantly related to all parameters (P<0.05), except for DBP and MAP. Age is observed to be the dominant factor that affects PTT at both peripheries in a child. Regression equations for PTT were derived for measuring from a finger and toe, (6.09 age+189.2) ms and (6.70 age+243.0) ms, respectively.

Pulse Transit Time by R-Wave-Gated Infrared Photoplethysmography: Review of the Literature and Personal Experience

Pulse transit time (PTT) is the time it takes a pulse wave to travel between two arterial sites. A rela tively short PTT is observed with high blood pressure (BP), aging, arteriosclerosis and diabetes mellitus. Most methods used for measuring the PTT are cumbersome and expensive. In contrast, the interval between the peak of the R-wave on the electrocardiogram and the onset of the corresponding pulse in the finger pad measured by photoplethysmography can be easily measured. We review herein the literature and impart the experience at our institution on clinical applications of R-wave-gated photo-plethysmography (RWPP) as measurement of PTT. The MEDLINE data base on clinical applications of RWPP was reviewed. In addition, studies performed in the author's institution are presented. When used as a surrogate for beat-to-beat BP monitoring, RWPP did not meet the level of accuracy required for medical practice (two studies). RWPP produced accurate and reproducible signals when utilized as a surrogate for intra-thoracic pressure changes in obstructive sleep apnea, as well as BP arousals which accompany central sleep apnea (five studies). In estimation of arterial stiffness, RWPP was unsatisfactory (one study). In assessment of cardiovascular reactivity, abnormal values of RWPP were noted in autonomic failure (one study), while disease-specific reactivity patterns were identified utilizing a method involving RWPP (two studies). In clinical practice, sleep-apnea may be accurately monitored by RWPP. RWPP seems to reflect autonomic influences and may be particularly well-suited for the study of vascular reactivity. Thus, further descriptions of disease-specific cardiovascular reactivity patterns may be possible with techniques based on RWPP. Other clinical uses of RWPP are investigational.

Motion artefact reduction of the photoplethysmographic signal in pulse transit time measurement

Motion artefact is a common occurrence that contaminates photoplethysmographic (PPG) measurements. To extract timing information from signals during artefact is challenging. PPG signal is very sensitive to artefacts and can be used in applications like, pulse transit time (PTT) as part of the polysomnographic studies. A correlation cancellation or signal processing approach is implemented with the adaptive cancelling filter concept and a triaxial accelerometry. PPG signals obtained from a Masimo (Reference) pulse oximeter is used as reference to compare with the reconstructed PPG signals. Different hands are used for each PPG source, one stationary while the other involves typical movements during sleep. A second Masimo pulse oximeter is used to register intensity of timing errors on commercial PPG signals. 108 PTT measurements are recorded in three different movements with PTT estimates from unprocessed PPG signals showing 35.51+/-27.42%, Masimo 50.02+/-29.40% and reconstructed 4.32+/-3.59% difference against those from the Reference PPG. The triaxial accelerometry can be used to detect the presence of artefact on PPG signals. This is useful in PTT measurements when signal contaminated with artefacts are required for further analysis, especially after and during arousals in sleep. The suggested filtering model can then reconstruct these corrupted PPG signals.

광전용적맥파 센서를 이용한 맥파전달시간의 측정

In this study, we implemented the pulse transit time (PTT) system to examine usefulness of the monitoring method of distensibility and elasticity using photoplethysmography sensor in vivo. PTT is defined as the time interval between the peak of QRS complex in ECG signal and the maximum slope point of photoplethysmography. these two signals were converted to digital data by means of AID converter, then PTT was evaluated by heartbeat using PC. Results of analysis were displayed as a graph using spline interpolation method. The variance of PTT was measured repetitiously to verify efficiency of PTT system in resting state and hyperemic state. Repeated measurement of PTT was not same value but showed that coefficients of correlation were related with each other as 0.8302 (P

Arterial distensibility as determined by carotid-femoral pulse wave velocity in patients with Behçet's disease.

Behçet's disease (BD) is a chronic, multisystem disorder characterized by genital and oral aphthae, skin lesions, uveitis, and tendency to thrombosis. Pulse wave velocity (PWV) is an important factor in determining cardiovascular mortality and morbidity. It is an index of arterial wall stiffness and inversely related to the arterial distensibility. In this study we investigated the arterial distensibility in BD by PWV. We studied 14 patients with BD (18-44 years old, 10 men) and 28 healthy subjects (18-39 years old, 21 men) without known cardiovascular disease. Arterial distensibility was assessed by automatic carotid-femoral PWV measurement using the Complior Colson device. PWV is calculated from measurements of pulse transit time and the distance traveled by the pulse between two recording sites, according to the following formula: pulse wave velocity (m/s)=distance (m)/transit time(s). The mean ages, systolic blood pressure, diastolic blood pressure, pulse pressure, heart rate, and PWV of Behçet's disease and control subjects were 32.1+/-7.4 vs 27.9+/-6.1 years, 112.9+/-12.0 vs 108.7+/-10.0 mmHg, 72.1+/-10.7 vs 67.7+/-7.5 mmHg, 40.7+/-12.2 vs 41.0+/-10.7 mmHg, 74.1+/-10.2 vs 77.2+/-10.1 bpm, and 8.4+/-1.4 vs 8.5+/-1.1 m/s, respectively. Differences between all parameters studied were not found to be statistically significant (p>0.05). The carotid-femoral PWV, an index of arterial stiffness and a marker of atherosclerosis, is not increased in patients with BD compared with control subjects.

Ultrasound velocity measurement to determine lipid content in salmon muscle; the effects of myosepta

Currently, there are no reliable and inexpensive non-destructive techniques available to measure the composition of fish during processing. In this paper, ultrasound pulse transit time measurement techniques are applied to aquaculture to measure the intramuscular fat in salmon fillets. Measurements on samples of salmon white muscle are described and the results of velocity measurements on a group of samples of varying fat content are reported. Differences from theory are considered in the light of the muscle structure. Results suggest that it is possible to group the velocities into “high fat”, “medium fat” and “low fat” categories but not to predict fat content with great accuracy because of inhomogeneity in the structure of the muscle. Ray-tracing techniques were used to model the propagation velocity of a wavefront travelling through a single salmon sample. The model provided an insight into how variations in fat content, myoseptum thickness and myosepta configuration affect measured velocity.

Which aspects of breathing during sleep influence the overnight fall of blood pressure in a community population?

BACKGROUNDObstructive sleep apnoea (OSA) causes recurrent rises in blood pressure during sleep, and recent community surveys have suggested a link between mild OSA and diurnal hypertension. The fact that OSA...

MICROSCALE THERMAL RELAXATION DURING ACOUSTIC PROPAGATION IN AEROGEL AND OTHER POROUS MEDIA

The longitudinal acoustic velocity in silica aerogel is presented as a function of the interstitial gas type and pressure. This was measured using air-coupled ultrasonic transducers configured for differential pulse transit time measurements. The results are interpreted in terms of the thermal relaxation of the acoustic pulse. The microscale temperature oscillations of the gas and solid phases of the aerogel due to the acoustic pulse are not identical if the rate of heat transfer between the two phases is slow compared to the period of the acoustic oscillation. The energy transferred from the gas to the solid phase is lost to the acoustic propagation and, thus, reduces the amplitude and velocity of the acoustic wave. The gas type and pressure may provide independent variables for probing these effects in aerogel.

Health status in obstructive sleep apnea: relationship with sleep fragmentation and daytine sleepiness, and effects of continuous positive airway pressure treatment.

Patients with obstructive sleep apnea (OSA) have impaired health status that improves with nasal continuous positive airway pressure (nCPAP). The study reported here explored the relationships between health status, its improvement with nCPAP, sleep fragmentation, and daytime sleepiness. In the study, 51 patients (46 male, five female) ranging from nonsnorers to individuals with severe OSA (median apnea/hypopnea index [AHI] 25, 90% central range: 1 to 98) had polysomnography with microarousal scoring, respiratory arousal scoring, and measurement of pulse transit time. The Short Form-36 Health Survey (SF-36) questionnaire was administered before and after 4 wk of nCPAP treatment; daytime sleepiness was also measured before starting nCPAP. Relationships between pretreatment health status and sleep fragmentation were weak, but significant associations were found between all sleep fragmentation indices and health status improvement with nCPAP (e.g., arousals according to the criteria of the American Sleep Disorders Association versus change in the physical component summary, r = 0.44, p < 0.001). Compared with general population data, the dimensions of energy and vitality and physical role limitation were abnormal before nCPAP (p < 0.05) and normalized with treatment. Sleepiness and pretreatment SF-36 values correlated significantly (Epworth Sleepiness Scale versus energy and vitality, r = -0.47, p < 0.001; modified Maintenance of Wakefulness Test versus energy and vitality, r = 0.32, p < 0.05). We conclude that the health status of patients with OSA improves with nCPAP and this improvement correlates with sleep fragmentation severity. However, the correlation is not very close, which may reflect the improvement with nCPAP of other symptoms not directly related to disease severity.

脈波伝搬時間の簡便計測法

In this study an experiment was carried out to establish a convenient method of Pulse Transit Time(PTT) estimation. The time interval between ECG R-wave and PTG(τ EP) were measured under cooling stimulation and the induced autonomic response was analyzed. ECG R-Wave was used as a reference timing for PTT measurement. It was possible to use the time from EGG R-wave to PTG(τ EP) as an ergonomic measure.

Estimates of pulse wave velocity and measurement of pulse transit time in the human cerebral circulation

Knowledge of the velocity with which pressure and flow waves travel within the arterial tree has been fundamental to the understanding of important hemodynamic parameters, such as vessel wall elastance, impedance and reflection coefficients for the systemic circulation. To our knowledge, however, this pulse wave velocity (PWV) has not been previously measured for the human cerebral circulation. In this study, we estimate the PWV from 88 measurements during normocarbia and 95 measurements during hypocarbia in six healthy human volunteers. The measurements consisted of time delays between velocity waveforms obtained simultaneously from the cervical carotid artery and the ipsilateral middle cerebral artery. An estimation of the distance between these sites as 10 centimeters yielded a PWV of 12.8 m/s for both levels of pCO 2. Vessel elasticity could then be estimated between 17 and 34 dyne/cm 2 · 10 6. These values of PWV are among the highest of those found in the peripheral circulation, and may have implications for the interpretation of the shape of the cerebral pressure and flow waveforms.

Application of ultrasonic sensors to robotic seam tracking

An automatic seam tracking system that uses an ultrasonic-based sensor has been developed and interfaced to a P-50 Process Robot in an effort to achieve online seam tracking of joints, without the use of workpiece geometrical models or subsequent 'teaching' routines. The transducer is used to inspect the workpiece ahead of the torch and to measure joint orientation as well as lateral deviation caused by curvature or discontinuities in the joint path. Measurements of echo pulse amplitude and transit time are combined with a particular torch-sensor arrangement and transducer positioning strategy to eliminate ambiguities resulting from symmetry in the acoustic signal and from environmental factors such as joint geometry and roughness. Data pertaining to the joint orientation and lateral deviation are acquired periodically by sampling equispaced points along the joint as the torch advances. With each sample, data are transferred to the microcomputer, where a trajectory-generating algorithm calculates the (x, y, theta ) coordinates of the torch tip trajectory needed to meet the tracking requirements. The actual tracking task is accomplished online by executing a series of shifts in these coordinates.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Use of Ultrasonic Pulse Velocity for Fracture Testing of Cemented Materials

Abstract The paper describes the use of the ultrasonic pulse velocity technique to measure two important features of fracture in notched concrete beams: the extent of the zone of microcracking that develops ahead of the notch or crack, and the depth of the main (or stress-free) crack. Beams of 100 mm in width and ranging from 100 to 500 mm in depth were tested, and ultrasonic pulses were transmitted longitudinally through the beams at various elevations. Ultrasonic readings taken at elevations above or below the visible crack tip were found to be sensitive to the development of the microcracked zone or to main crack growth, respectively. Based on pulse transit time measurements, the average depth of the microcracked zone was about 44% of the residual beam depth, taking all the beam sizes together. Crack depths estimated from pulse transit times were found to agree with visible crack depths to less than 10% on average.

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.

Autonomic myocardial influences as a factor determining inter-task consistency of heart rate reactivity.

ABSTRACTThis study assessed the consistency of subjects’relative heart rate (HR) responsivity across four tasks and examined the role played by autonomic myocardial influences on this consistency. HR responses across tasks were predicted to covary to the extent that they reflected a similar autonomic mediation, assessed by measurement of pulse transit time (PTT).Forty‐eight male subjects performed two sensory intake (Tones and Lights RT) and two sensory rejection (Mental Arithmetic and Word Formation) tasks. Consistency of HR responsivity was revealed by significant positive correlations observed between HR changes during all task pairs. High HR reactors in rejection tasks displayed HR decreases during an intake task (Tones), whereas low reactors displayed the expected bradycardia. Significant correlations between HR and PTT changes suggested that SNS influences were evoked by mental arithmetic, whereas a dissociation of these indices in the Tones task implied a predominance of PNS influence in that task. Nevertheless, HR changes covaried reliably between these tasks, suggesting that HR responsivity is consistent across situations evoking different patterns of autonomic influence on the heart.

Vascular impedance in studies of arterial and cardiac function.

Vascular impedance in studies of arterial and cardiac function.