Pulse transit time by R-wave-gated infrared photoplethysmography: review of the literature and personal experience

Practical Application of a New Cuffless Blood Pressure Measurement Method

It would be useful to develop a reliable method for the cuffless measurement of blood pressure (BP), as such a method could be made available anytime and anywhere for the effective screening and monitoring of arterial hypertension. The purpose of this study is to evaluate blood pressure measurements through a CardioQVARK device in clinical practice in different patient groups.

METHODS

This study involved 167 patients aged 31 to 88 years (mean 64.2 ± 7.8 years) with normal blood pressure, high blood pressure, and compensated high blood pressure. During each session, three routine blood pressure measurements with intervals of 30 s were taken using a sphygmomanometer with an appropriate cuff size, and the mean value was selected for comparison. The measurements were carried out by two observers trained at the same time with a reference sphygmomanometer using a Y-shaped connector. In the minute following the last cuff-based measurements, an electrocardiogram (ECG) with an I-lead and a photoplethysmocardiogram were recorded simultaneously for 3 min with the CardioQVARK device. We compared the systolic and diastolic BP obtained from a cuff-based mercury sphygmomanometer and smartphone-case-based BP device: the CardioQVARK monitor. A statistical analysis plan was developed using the IEEE Standard for Wearable Cuffless Blood Pressure Devices. Bland-Altman plots were used to estimate the precision of cuffless measurements.

RESULTS

The mean difference between the values defined by CardioQVARK and the cuff-based sphygmomanometer for systolic blood pressure (SBP) was 0.31 ± 3.61, while that for diastolic blood pressure (DBP) was 0.44 ± 3.76. The mean absolute difference (MAD) for SBP was 3.44 ± 2.5 mm Hg, and that for DBP was 3.21 ± 2.82 mm Hg. In the subgroups, the smallest error (less than 3 mm Hg) was observed in the prehypertension group, with a slightly larger error (up to 4 mm Hg) found among patients with a normal blood pressure and stage 1 hypertension. The largest error was found in the stage 2 hypertension group (4-5.5 mm Hg). The largest error was 4.2 mm Hg in the high blood pressure group. We, therefore, did not record an error in excess of 7 mmHg, the upper boundary considered acceptable in the IEEE recommendations. We also did not reach a mean error of 5 mmHg, the upper boundary considered acceptable according to the very recent ESH recommendations. At the same time, in all groups of patients, the systolic blood pressure was determined with an error of less than 5 mm Hg in more than 80% of patients. While this study shows that the CardioQVARK device meets the standards of IEEE, the Bland-Altman analysis indicates that the cuffless measurement of diastolic blood pressure has significant bias. The difference was very small and unlikely to be of clinical relevance for the individual patient, but it may well have epidemiological relevance on a population level. Therefore, the CardioQVARK device, while being worthwhile for monitoring patients over time, may not be suitable for screening purposes. Cuffless blood pressure measurement devices are emerging as a convenient and tolerable alternative to cuff-based devices. However, there are several limitations to cuffless blood pressure measurement devices that should be considered. For instance, this study showed a high proportion of measurements with a measurement error of <5 mmHg, while detecting a small, although statistically significant, bias in the measurement of diastolic blood pressure. This suggests that this device may not be suitable for screening purposes. However, its value for monitoring BP over time is confirmed. Furthermore, and most importantly, the easy measurement method and the device portability (integrated in a smartphone) may increase the self-awareness of hypertensive patients and, potentially, lead to an improved adherence to their treatment.

CONCLUSION

The cuffless blood pressure technology developed in this study was tested in accordance with the IEEE protocol and showed great precision in patient groups with different blood pressure ranges. This approach, therefore, has the potential to be applied in clinical practice.

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 (SBP_IBP, DBP_IBP, and MAP_IBP, respectively) and to detect SBP_IBP 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 SBP_IBP was determined by area under the curve (reported as AUC, sensitivity, specificity).

RESULTS

Significant correlations between 1/PTT and SBP_IBP were found for PES (r = 0.64) and PCS (r = 0.55) (p < 0.01), as well as MAP_IBP/DBP_IBP for PES (r = 0.6/0.55) and PCS (r = 0.5/0.45) (p < 0.05). A 7% decrease in 1/PTT_PES predicted a 30% SBP_IBP decrease (0.82, 0.76, 0.76), while a 5.6% increase predicted a 30% SBP_IBP increase (0.75, 0.7, 0.68). A 6.6% decrease in 1/PTT_PCS detected a 30% SBP_IBP decrease (0.81, 0.72, 0.8), while a 4.8% 1/PTT_PCS increase detected a 30% SBP_IBP 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 SBP_IBP. Thus, PES/PCS as a novel sensor technology may augment intraoperative hemodynamic monitoring during major surgery.

Cuff-less and continuous blood pressure measurement based on pulse transit time from carotid and toe photoplethysmograms

Blood pressure (BP) is a vital health parameter that varies throughout the day. As a single reading of high BP may not indicate hypertension, continuous monitoring of BP is usually recommended by medical doctors to confirm the diagnosis of hypertension. In the last few decades, researchers have investigated cuff-less and continuous BP measurements based on pulse transit time (PTT). The main purpose of this research is to develop an autoregressive (ARX) system identification (SI)-based PTT calculation model using two PPG signals acquired from carotid and toe. The signals were recorded from 65 subjects with an age range between 20 and 60 years. The results of the study have been validated in two stages. The first validation comprised the estimated BP from PTT using SI compared to the measured BP using the cuff-based method for all subjects. The results of the estimated BP using the proposed method compared to the measured BP obtained using the standard BP cuff measurement method are highly correlated to both systolic blood pressure (R² = 0.8132) and diastolic blood pressure (R² = 0.8357). The second validation consisted of comparing PTT values using system identification to the results of the PTT derived from the ECG-PPG method. The results showed that both methods are highly correlated (R² = 0.7808), and there is no significant difference between them (p < 0.05) with a slightly better PTT estimation related to DBP in the proposed method. Our results have proven that the PTT obtained from the carotid PPG and toe PPG using the system identification approach yielded SBP and DBP estimations that are consistent with the values of the conventional BP cuff method. The newly proposed method has the advantage of being cuff-less and able to provide continuous BP measurements.

Cuffless Blood Pressure Measurement Using a Smartphone-Case Based ECG Monitor with Photoplethysmography in Hypertensive Patients

The availability of simple, accurate, and affordable cuffless blood pressure (BP) devices has the potential to greatly increase the compliance with measurement recommendations and the utilization of BP measurements for BP telemonitoring. The aim of this study is to evaluate the correlation between findings from routine BP measurements using a conventional sphygmomanometer with the results from a portable ECG monitor combined with photoplethysmography (PPG) for pulse wave registration in patients with arterial hypertension.

METHODS

The study included 500 patients aged 32-88 years (mean 64 ± 7.9 years). Mean values from three routine BP measurements by a sphygmomanometer with cuff were selected for comparison; within one minute after the last measurement, an electrocardiogram (ECG) was recorded for 3 min in the standard lead I using a smartphone-case based single-channel ECG monitor (CardioQVARK^®-limited responsibility company "L-CARD", Moscow, Russia) simultaneously with a PPG pulse wave recording. Using a combination of the heart signal with the PPG, levels of systolic and diastolic BP were determined based on machine learning using a previously developed and validated algorithm and were compared with sphygmomanometer results.

RESULTS

According to the Bland-Altman analysis, SD for systolic BP was 3.63, and bias was 0.32 for systolic BP. SD was 2.95 and bias was 0.61 for diastolic BP. The correlation between the results from the sphygmomanometer and the cuffless method was 0.89 (p = 0.001) for systolic and 0.87 (p = 0.002) for diastolic BP.

CONCLUSION

Blood pressure measurements on a smartphone-case without a cuff are encouraging. However, further research is needed to improve the accuracy and reliability of clinical use in the majority of patients.

Hunting down the dominating subclone of cancer stem cells as a potential new therapeutic target in multiple myeloma: An artificial intelligence perspective

The development of single-cell subclones, which can rapidly switch from dormant to dominant subclones, occur in the natural pathophysiology of multiple myeloma (MM) but is often "pressed" by the standard treatment of MM. These emerging subclones present a challenge, providing reservoirs for chemoresistant mutations. Technological advancement is required to track MM subclonal changes, as understanding MM's mechanism of evolution at the cellular level can prompt the development of new targeted ways of treating this disease. Current methods to study the evolution of subclones in MM rely on technologies capable of phenotypically and genotypically characterizing plasma cells, which include immunohistochemistry, flow cytometry, or cytogenetics. Still, all of these technologies may be limited by the sensitivity for picking up rare events. In contrast, more incisive methods such as RNA sequencing, comparative genomic hybridization, or whole-genome sequencing are not yet commonly used in clinical practice. Here we introduce the epidemiological diagnosis and prognosis of MM and review current methods for evaluating MM subclone evolution, such as minimal residual disease/multiparametric flow cytometry/next-generation sequencing, and their respective advantages and disadvantages. In addition, we propose our new single-cell method of evaluation to understand MM's mechanism of evolution at the molecular and cellular level and to prompt the development of new targeted ways of treating this disease, which has a broad prospect.

Real-Time Monitoring of Blood Pressure Using Digitalized Pulse Arrival Time Calculation Technology for Prompt Detection of Sudden Hypertensive Episodes During Laryngeal Microsurgery: Retrospective Observational Study

Background

Laryngeal microsurgery (LMS) is often accompanied by a sudden increase in blood pressure (BP) during surgery because of stimulation around the larynx. This sudden change in the hemodynamic status is not immediately reflected in a casual cuff-type measurement that takes intermittent readings every 3 to 5 min.

Objective

This study aimed to investigate the potential of pulse arrival time (PAT) as a marker for a BP surge, which usually occurs in patients undergoing LMS.

Methods

Intermittent measurements of BP and electrocardiogram (ECG) and photoplethysmogram (PPG) signals were recorded during LMS. PAT was defined as the interval between the R-peak on the ECG and the maximum slope on the PPG. Mean PAT values before and after BP increase were compared. PPG-related parameters and the correlations between changes in these variables were calculated.

Results

BP surged because of laryngoscopic manipulation (mean systolic BP [SBP] from 115.3, SD 21.4 mmHg, to 159.9, SD 25.2 mmHg; P<.001), whereas PAT decreased significantly (from mean 460.6, SD 51.9 ms, to 405.8, SD 50.1 ms; P<.001) in most of the cases. The change in SBP showed a significant correlation with the inverse of the PAT (r=0.582; P<.001). Receiver-operating characteristic curve analysis indicated that an increase of 11.5% in the inverse of the PAT could detect a 40% increase in SBP, and the area under the curve was 0.814.

Conclusions

During LMS, where invasive arterial catheterization is not always possible, PAT shows good correlation with SBP and may, therefore, have the potential to identify abrupt BP surges during laryngoscopic manipulations in a noninvasive manner.

Measurement of normal retinal vascular pulse wave attenuation using modified photoplethysmography

Pulse wave attenuation characteristics reflect compliance and resistance properties of the vessel wall as well as initial pulse generation factors. Recently, it has become possible to measure and map the retinal vessel wall pulse wave amplitudes. Predictable pulse wave amplitude distribution may allow inferences to be made concerning vascular compliance and resistance. Twenty-eight eyes from sixteen subjects (8 male and 8 female) were examined using modified retinal photoplethysmography with simultaneous ophthalmodynamometry. This allowed the assessment of vessel wall pulsation amplitudes under a dynamic range of intraocular pressures. Pulse amplitudes were calculated using harmonic regression analysis. The pulse wave attenuation was measured under different ranges of ophthalmodynamometric force (ODF) as a function of distance along the vessel (V_Dist), which in turn was calculated in disc diameters (DD) from the center of the optic disc. A linear mixed-effects model with randomized slopes and intercepts was used to estimate the correlations between the logarithmically transformed harmonic regression wave amplitude (HRW_a) and the Fourier trigonometric coefficients with the predictors (V_Dist and ODF). The retinal venous harmonic regression wave attenuation (coefficient value±standard error) -0.40±0.065/DD, (p-value < 0.00001, 95% confidence interval (CI) -0.53 to -0.27), which was approximately twice that of the arterial -0.17±0.048/DD, (p-value < 0.0004, 95% CI = -0.27 to -0.08). There was a positive correlation between attenuation of the harmonic regression wave and ophthalmodynamometric force in both vascular systems. The attenuation of all but the sine coefficient of the second Fourier harmonic (b_n2) achieved statistical significance in the correlation with V_Dist. The cosine coefficient of the first Fourier harmonic a_n1 was the only coefficient to achieve statistical significance in the correlation with the predictors V_Dist and ODF in both vascular systems. The a_n1 coefficient value in the correlation with V_Dist was -3.79±0.78 and -1.269±0.37 (p < 0.0006), while this coefficient value in the correlation with ODF was 0.026±0.0099 and 0.009±0.04 (p < 0.01) in both the retinal veins and arteries respectively. The predictable attenuation characteristics in normal subjects suggest that this technique may allow the non-invasive quantification of retinal vascular compliance and other hemodynamic parameters.

Can arterial elasticity be estimated from heart rate variability response to paced 0.066 Hz sighing?

Arterial elasticity is an important indicator of risk for cardiovascular disease (CVD). It is influenced by both gradual vessel wall damage due to aging and disease and vascular tone that responds, at the moment, to system loading. Measuring changes in arterial elasticity are critical to early detection of CVD but can be time and resource intensive. This study proposes and tests a new method to approximate arterial elasticity from heart rate variability (HRV). ECG and pulse were simultaneously recording in 71 young healthy adults during three rhythmical sighing tasks paced at 0.02, 0.033, and 0.066 Hz. We evaluated arterial elasticity by measuring the reaction of pulse transit time (PTT) and RRI to each task specifically at the pacing frequency. The goal of the study was to describe our method, ground the methodology in current theory and mechanisms, and scientifically justify and validate this method by assessing differences in arterial elasticity in groups of healthy adults who differed in drinking behaviors. The amplitude PTT and HR oscillation responses at the pacing frequency were significantly correlated only when sighing was paced at 0.066 Hz. Both amplitudes also significantly correlated with power in the very low-frequency range of the baseline HRV spectrum. Abnormalities in these measures were observed among binge drinking healthy adults compared to non-drinkers and social drinkers. These preliminary results support using the HRV response to paced 0.066 Hz sighing as a correlate of arterial elasticity and warrant further study.

Breathing Signature as Vitality Score Index Created by Exercises of Qigong: Implications of Artificial Intelligence Tools Used in Traditional Chinese Medicine

Rising concerns about the short- and long-term detrimental consequences of administration of conventional pharmacopeia are fueling the search for alternative, complementary, personalized, and comprehensive approaches to human healthcare. Qigong, a form of Traditional Chinese Medicine, represents a viable alternative approach. Here, we started with the practical, philosophical, and psychological background of Ki (in Japanese) or Qi (in Chinese) and their relationship to Qigong theory and clinical application. Noting the drawbacks of the current state of Qigong clinic, herein we propose that to manage the unique aspects of the Eastern 'non-linearity' and 'holistic' approach, it needs to be integrated with the Western "linearity" "one-direction" approach. This is done through developing the concepts of "Qigong breathing signatures," which can define our life breathing patterns associated with diseases using machine learning technology. We predict that this can be achieved by establishing an artificial intelligence (AI)-Medicine training camp of databases, which will integrate Qigong-like breathing patterns with different pathologies unique to individuals. Such an integrated connection will allow the AI-Medicine algorithm to identify breathing patterns and guide medical intervention. This unique view of potentially connecting Eastern Medicine and Western Technology can further add a novel insight to our current understanding of both Western and Eastern medicine, thereby establishing a vitality score index (VSI) that can predict the outcomes of lifestyle behaviors and medical conditions.

Stressing the accuracy: Wrist-worn wearable sensor validation over different conditions

Wearable sensors are promising instruments for conducting both laboratory and ambulatory research in psychophysiology. However, scholars should be aware of their measurement error and the conditions in which accuracy is achieved. This study aimed to assess the accuracy of a wearable sensor designed for research purposes, the E4 wristband (Empatica, Milan, Italy), in measuring heart rate (HR), heart rate variability (HRV), and skin conductance (SC) over five laboratory conditions widely used in stress reactivity research (seated rest, paced breathing, orthostatic, Stroop, speech task) and two ecological conditions (slow walking, keyboard typing). Forty healthy participants concurrently wore the wristband and two gold standard measurement systems (i.e., electrocardiography and finger SC sensor). The wristband accuracy was determined by evaluating the signal quality and the correlations with and the Bland-Altman plots against gold standard-derived measurements. Moreover, exploratory analyses were performed to assess predictors of measurement error. Mean HR measures showed the best accuracy over all conditions. HRV measures showed satisfactory accuracy in seated rest, paced breathing, and recovery conditions but not in dynamic conditions, including speaking. Accuracy was diminished by wrist movements, cognitive and emotional stress, nonstationarity, and larger wrist circumferences. Wrist SC measures showed neither correlation nor visual resemblance with finger SC signal, suggesting that the two sites may reflect different phenomena. Future studies are needed to assess the responsivity of wrist SC to emotional and cognitive stress. Limitations and implications for laboratory and ambulatory research are discussed.

Comparison of short-term heart rate variability indexes evaluated through electrocardiographic and continuous blood pressure monitoring

Heart rate variability (HRV) analysis represents an important tool for the characterization of complex cardiovascular control. HRV indexes are usually calculated from electrocardiographic (ECG) recordings after measuring the time duration between consecutive R peaks, and this is considered the gold standard. An alternative method consists of assessing the pulse rate variability (PRV) from signals acquired through photoplethysmography, a technique also employed for the continuous noninvasive monitoring of blood pressure. In this work, we carry out a thorough analysis and comparison of short-term variability indexes computed from HRV time series obtained from the ECG and from PRV time series obtained from continuous blood pressure (CBP) signals, in order to evaluate the reliability of using CBP-based recordings in place of standard ECG tracks. The analysis has been carried out on short time series (300 beats) of HRV and PRV in 76 subjects studied in different conditions: resting in the supine position, postural stress during 45° head-up tilt, and mental stress during computation of arithmetic test. Nine different indexes have been taken into account, computed in the time domain (mean, variance, root mean square of the successive differences), frequency domain (low-to-high frequency power ratio LF/HF, HF spectral power, and central frequency), and information domain (entropy, conditional entropy, self entropy). Thorough validation has been performed using comparison of the HRV and PRV distributions, robust linear regression, and Bland-Altman plots. Results demonstrate the feasibility of extracting HRV indexes from CBP-based data, showing an overall relatively good agreement of time-, frequency-, and information-domain measures. The agreement decreased during postural and mental arithmetic stress, especially with regard to band-power ratio, conditional, and self-entropy. This finding suggests to use caution in adopting PRV as a surrogate of HRV during stress conditions.

Pulse transit time technique for cuffless unobtrusive blood pressure measurement: from theory to algorithm

Cuffless technique holds great promise to measure blood pressure (BP) in an unobtrusive way, improving diagnostics and monitoring of hypertension and its related cardiovascular diseases, and maximizing the independence and participation of individual. Pulse transit time (PTT) has been the most commonly employed techniques for cuffless BP estimation. Many studies have been conducted to explore its feasibility and validate its performance in the clinical settings. However, there is still issues and challenges ahead before its wide application. This review will investigate the understanding and development of the PTT technique in depth, with a focus on the physiological regulation of arterial BP, the relationship between PTT and BP, and the summaries of the PTT-based models for BP estimation.

Continuous non-invasive determination of nocturnal blood pressure variation using photoplethysmographic pulse wave signals: comparison of pulse propagation time, pulse transit time and RR-interval

OBJECTIVE

Cardiovascular diseases are the leading cause of death, whereas nocturnal ambulatory blood pressure (BP) is the most potent predictor for cardiovascular risk. The volume clamp and pulse transit time (PTT) are common methods for continuous non-invasive BP measurement, but have drawbacks during unsupervised ambulatory use and undisturbed sleep. The pulse propagation time (PPT), defined as the time between pulse wave systolic peak and diastolic peak, provides valid information about the pressure pulse waveform. However, the use of PPT for nocturnal BP variation determination and whether such variation is affected by BP or heart rate (i.e. RR-interval or RRI) has not been investigated.

APPROACH

To assess whether the PPT method is suitable for ubiquitous nocturnal BP monitoring, we compared systolic blood pressure (SBP) estimates derived from PPT, PTT, and RRI signals with parallel recorded BP measurements. The RRI-derived SBP signals were used as a baseline for testing a potential heart rate dependency. This work provides an overview of BP measurements, presents the developed real-time signal analysis, and describes the performance assessment. The signal analysis was validated with data records from 42 subjects acquired from an ergometry and sleep laboratory in equal parts.

MAIN RESULTS

The algorithms applied to the ergometry laboratory database achieved a correlation coefficient between reference SBP and estimated SBP_PPT of 0.89 (p  <  0.001) with bias 0.1 mmHg and limits of agreement (LoA)  -29.8 to 30.0 mmHg, SBP_PTT of 0.97 (p  <  0.001) with bias 0.0 mmHg and LoA  -15.2 to 15.3 mmHg, and SBP_RRI of 0.96 (p  <  0.001) with bias 0.0 mmHg and LoA  -19.5 to 19.5 mmHg. For the sleep laboratory database, the correlation coefficient was 0.95 (p  <  0.001) with bias 0.2 mmHg and LoA  -18.3 to 18.8 mmHg for SBP_PPT, 0.88 (p  <  0.001) with bias 0.0 mmHg and LoA  -25.0 to 24.9 mmHg for SBP_PTT, and 0.88 (p  <  0.001) with bias of 0.1 mmHg and LoA  -23.6 to 23.7 mmHg for SBP_RRI. A heart rate dependency of PPT or PTT could not be found. The analysis of variance shows no significant differences between the reference SBP values and the estimated values for either the ergometry (F(3, 627)  =  2.27, p  =  0.08) or the sleep laboratory (F(3, 327)  =  2.28, p  =  0.08).

SIGNIFICANCE

In conclusion, the PPT method seems to be an interesting alternative for continuous determination of SBP during simplified cardiovascular monitoring and sleep screening compared to more expensive devices based on volume clamp or PTT methods.

Wearable brain imaging with multimodal physiological monitoring

The brain is a central component of cognitive and physical human performance. Measures, including functional brain activation, cerebral perfusion, cerebral oxygenation, evoked electrical responses, and resting hemodynamic and electrical activity are all related to, or can predict, health status or performance decrements. However, measuring brain physiology typically requires large, stationary machines that are not suitable for mobile or self-monitoring. Moreover, when individuals are ambulatory, systemic physiological fluctuations—e.g., in heart rate, blood pressure, skin perfusion, and more—can interfere with noninvasive brain measurements. In efforts to address the physiological monitoring and performance assessment needs for astronauts during spaceflight, we have developed easy-to-use, wearable prototypes, such as NINscan, for near-infrared scanning, which can collect synchronized multimodal physiology data, including hemodynamic deep-tissue imaging (including brain and muscles), electroencephalography, electrocardiography, electromyography, electrooculography, accelerometry, gyroscopy, pressure, respiration, and temperature measurements. Given their self-contained and portable nature, these devices can be deployed in a much broader range of settings—including austere environments—thereby, enabling a wider range of novel medical and research physiology applications. We review these, including high-altitude assessments, self-deployable multimodal e.g., (polysomnographic) recordings in remote or low-resource environments, fluid shifts in variable-gravity, or spaceflight analog environments, intracranial brain motion during high-impact sports, and long-duration monitoring for clinical symptom-capture in various clinical conditions. In addition to further enhancing sensitivity and miniaturization, advanced computational algorithms could help support real-time feedback and alerts regarding performance and health.

Increased pulse wave transit time after percutaneous coronary intervention procedure in CAD patients

Pulse wave transit time (PWTT) has been widely used as an index in assessing arterial stiffness. Percutaneous coronary intervention (PCI) is usually applied to the treatment of coronary artery disease (CAD). Research on the changes in PWTT caused by PCI is helpful for understanding the impact of the PCI procedure. In addition, effects of stent sites and access sites on the changes in PWTT have not been explored. Consequently, this study aimed to provide this information. The results showed that PWTT significantly increased after PCI (p < 0.01) while the standard deviation (SD) of PWTT time series had no statistically significant changes (p = 0.60) between before and after PCI. Significantly increased PWTT was found in the radial access group (p < 0.01), while there were no significant changes in the femoral access group (p > 0.4). Additionally, PWTT in the left anterior descending (LAD) group significantly increased after PCI (p < 0.01), but the increase that was found in the right coronary artery (RCA) group was not significant (p > 0.1). Our study indicates that arterial elasticity and left ventricular functions can benefit from a successful PCI procedure, and the increase of peripheral PWTT after PCI can help to better understand the effectiveness of the procedure.

Rest, Reactivity, and Recovery: A Psychophysiological Assessment of Borderline Personality Disorder

Difficulty regulating emotion is a cardinal feature of borderline personality disorder (BPD), yet little is known about the automatic psychophysiological processes involved in this phenotype. Inconsistent findings have emerged from studies that employed limited assessments (e.g., heart rate variability, skin conductance) of autonomic nervous system response to emotional contexts, and compared groups based on the presence or absence of BPD as a categorical diagnosis. This exploratory study assessed a comprehensive set of autonomic nervous system processes in 44 individuals (22 with BPD) at rest, in response to emotionally evocative stimuli, and during a subsequent recovery period. BPD was characterized with a dimensional measure of BPD symptom severity, as a well by categorical diagnosis. At baseline and across experimental tasks, higher heart rate was observed in those diagnosed with BPD compared to controls, and in those expressing greater BPD symptom severity. These effects, however, were fully mediated by differences in physical exercise. In contrast, during recovery from emotional activation, greater symptom severity predicted consistently higher levels of multiple sympathetic and parasympathetic processes compared to lower symptom severity. Overall, these findings suggest that the heart rate elevations sometimes observed in those diagnosed with BPD may be associated with individual and group differences in levels of physical exercise. Results further indicate that adaptive psychophysiological recovery responses following emotional challenge may be disrupted in proportion to BPD symptom severity, independently of exercise. Results highlight the utility of considering lifestyle factors and symptom severity in studies of emotional activation and regulation processes in BPD.

Early signs of cardiovascular dysregulation in young adult binge drinkers

Binge drinking is widespread on American college campuses, but its effects on the cardiovascular system are poorly understood. This study sought evidence of preclinical cardiovascular changes in binge drinking young adults (n = 24) compared to nondrinking (n = 24) and social drinking (n = 23) peers during baseline, paced sighing (0.033 Hz), and paced breathing (0.1 Hz) tasks. Binge drinkers showed consistent but often statistically nonsignificant evidence of greater sympathetic activation and reduced baroreflex sensitivity. Interestingly, the structure of group-averaged baseline heart rate spectra was considerably different between groups in the low frequency range (0.05-0.15 Hz). In particular, the binge drinking group-averaged spectra showed several spectral peaks not evident in the other groups, possibly indicating two functionally distinct subranges (0.05-0.08 and 0.08-0.15 Hz) that reflect vascular tone baroreflex activity and heart rate baroreflex activity, respectively. Vascular tone baroreflex gain and power in two peaks in the 0.05-0.08 Hz range were associated with years of drinking in the binge drinking group. Vascular dysfunction may be an early indicator of drinking-related change in the cardiovascular system.

Feasibility study for the non-invasive blood pressure estimation based on ppg morphology: normotensive subject study

Background

Blood pressure is a critical bio-signal and its importance has been increased with the aged society and the growth of cardiovascular disease population. However, most of hypertensive patients have been suffered the inconvenience in monitoring blood pressure in daily life because the measurement of the blood pressure depends on the cuff-based technique. Nowadays there are many trials to measure blood pressure without cuff, especially, photoplethysmography (PPG) based research is carried out in various ways.

Methods

Our research is designed to hypothesis the relationship between vessel wall movement and pressure-flow relationship of PPG and to validate its appropriateness by experimental methods. PPG waveform is simplified by approximate model, and then it is analyzed as the velocity and the acceleration of blood flow using the derivatives of PPG. Finally, we develop pressure index (PI) as an estimation factor of blood pressure by combining of statistically significant segments of photoplethysmographic waveform.

Results

Twenty-five subjects were participated in the experiment. As a result of simulation, correlation coefficients between developed PI and blood pressure were represented with R = 0.818, R = 0.827 and R = 0.615 in systolic blood pressure, pulse pressure and mean arterial pressure, respectively, and both of result showed the meaningful statistically significance (P < 0.05).

Conclusions

Current study can estimate only the relative variation of blood pressure but could not find the absolute pressure value. Moreover, proposed index has the limitation of diastolic pressure tracing. However, the result shows that the proposed PI is statistically significantly correlated with blood pressures, and it suggests that the proposed PI as a promising additional parameter for the cuff less blood pressure monitoring.

Assessing the challenges of a pulse wave velocity based blood pressure measurement in surgical patients

Development of a continuous noninvasive blood pressure (cNIBP) monitor that is unobtrusive to patients is an attractive alternative to the cuff based measurements performed on medical-surgical floors in the hospital. Pulse wave velocity (PWV) provides a means to continuously monitor blood pressure in these patients. However, a PWV based cNIBP monitor faces a number of challenges in order to accurately measure blood pressure. In our study, we investigated some of the challenges faced by a body-worn cNIBP monitor (i.e. ViSi Mobile) on data collected on patients undergoing surgery. Results indicated that 1) pulse arrival time (PAT) values from ViSi Mobile were well correlated with PAT values obtained from an invasive reference; 2) the reciprocal of the PAT measurements were linearly correlated with blood pressure but the calibration curve was altered by administration of certain vasoactive substances; and 3) there are deterministic correlations between systolic pressure, diastolic pressure and the corresponding mean arterial pressure over a wide range of blood pressure values.

Effect of heat-induced pain stimuli on pulse transit time and pulse wave amplitude in healthy volunteers

Pain is commonly assessed subjectively by interpretations of patient behaviour and/or reports from patients. When this is impossible the availability of a quantitative objective pain assessment tool based on objective physiological parameters would greatly benefit clinical practice and research beside the standard self-report tests. Vasoconstriction is one of the physiological responses to pain. The aim of this study was to investigate whether pulse transit time (PTT) and pulse wave amplitude (PWA) decrease in response to this vasoconstriction when caused by heat-induced pain. The PTT and PWA were measured in healthy volunteers, on both index fingers using photoplethysmography and electrocardiography. Each subject received 3 heat-induced pain stimuli using a Temperature-Sensory Analyzer thermode block to apply a controlled, increasing temperature from 32.0 °C to 50.0 °C to the skin. After reaching 50.0 °C, the thermode was immediately cooled down to 32.0 °C. The study population was divided into 2 groups with a time-interval between the stimuli 20s or 60s. The results showed a significant (p  <  0.05) decrease of both PTT and PWA on the stimulated and contralateral side. Moreover, there was no significant difference between the stimulated and contralateral side. The time-interval of 20s was too short to allow PTT and PWA to return to baseline values and should exceed 40s in future studies. Heat-induced pain causes a decrease of PTT and PWA. Consequently, it is expected that, in the future, PTT and PWA may be applied as objective indicators of pain, either beside the standard self-report test, or when self-report testing is impossible.

The effect of local cold and warm exposure on index finger photoplethysmographic signal waveform

The study was carried out in order to analyse the changes in photoplethysmographic (PPG) signal waveform, which are caused by cold and warm stimulation. The study was carried out on 7 subjects. The right hand was immersed in cold and warm water up to the wrist during the experiment. The PPG signal was registered from right hand index finger. As a reference, the temperatures of index finger and pulse transit time (PTT) values were measured. A correlation of r = -0.70 was found between normalised slope of the PPG signal and the subject's age. The normalised slope increased noticeably due to the cold and decreased due to the warm water stimulation. It was opposite to the expected results with PTTs and the behaviour has to be investigated in future studies.

Pulse transit time measured by photoplethysmography improves the accuracy of heart rate as a surrogate measure of cardiac output, stroke volume and oxygen uptake in response to graded exercise

Heart rate (HR) is a valuable and widespread measure for physical training programs, although its description of conditioning is limited to the cardiac response to exercise. More comprehensive measures of exercise adaptation include cardiac output (Q̇), stroke volume (SV) and oxygen uptake (V̇O2), but these physiological parameters can be measured only with cumbersome equipment installed in clinical settings. In this work, we explore the ability of pulse transit time (PTT) to represent a valuable pairing with HR for indirectly estimating Q̇, SV and V̇O2 non-invasively. PTT was measured as the time interval between the peak of the electrocardiographic (ECG) R-wave and the onset of the photoplethysmography (PPG) waveform at the periphery (i.e. fingertip) with a portable sensor. Fifteen healthy young subjects underwent a graded incremental cycling protocol after which HR and PTT were correlated with Q̇, SV and V̇O2 using linear mixed models. The addition of PTT significantly improved the modeling of Q̇, SV and V̇O2 at the individual level ([Formula: see text] for SV, 0.548 for Q̇, and 0.771 for V̇O2) compared to predictive models based solely on HR ([Formula: see text] for SV, 0.503 for Q̇, and 0.745 for V̇O2). While challenges in sensitivity and artifact rejection exist, combining PTT with HR holds potential for development of novel wearable sensors that provide exercise assessment largely superior to HR monitors.

The effects of sighing on the cardiovascular system

Elicitation of high-amplitude oscillations in the cardiovascular system may serve to dampen psychophysiological reactivity to emotional and cognitive loading. Prior work has used paced breathing to impose clinically valuable high-amplitude ∼ 0.1 Hz oscillations. In this study, we investigated whether rhythmical sighing could likewise produce high-amplitude cardiovascular oscillations in the very low frequency range (0.003-0.05 Hz). ECG, respiration, skin conductance, and beat-to-beat blood pressure were collected in 24 healthy participants during baseline, 0.1 Hz paced breathing, and 0.02 Hz paced sighing (1 sigh every 50s, with normal breathing interspersed). Results showed that each sigh elicited a strong, well-defined reaction in the cardiovascular system. This reaction did not habituate when participants repeatedly sighed for 8.5 min. The result was a high-amplitude 0.02 Hz oscillation in multiple cardiovascular parameters. Thus, paced sighing is a reliable method for imposing very low frequency oscillations in the cardiovascular system, which has research and clinical implications that warrant further study.

Exploring the blood volume amplitude and pulse transit time during anger recall in patients with coronary artery disease

BACKGROUND AND PURPOSE

One psychopathological mechanism that links anger to coronary artery disease (CAD) is cardiac autonomic imbalance. Blood volume amplitude (BVA) and pulse transit time (PTT) are related to peripheral arterial elasticity and cardiac conduction, which are used as indirect markers for autonomic activation. The purposes of this study were to examine the relationships between BVA and PTT, and the reactivity of BVA and PTT during the anger recall task in patients with CAD.

METHODS AND SUBJECTS

A total of 112 patients with CAD and 93 healthy controls were recruited; BVA and PTT were collected during baseline, the neutral episode, the anger episode, and after recovery.

RESULTS

There were significant positive correlations between BVA and PTT in all participants. BVA reactivity during the anger episode was greater in patients with CAD than in healthy controls, and there were also lower BVA recovery values after the neutral and anger episodes. However, there was no significant difference in BVA reactivity between the two groups in the neutral episode. PTT recovered to baseline levels after the neutral and anger episodes in healthy controls, but not in the patients with CAD.

CONCLUSION

BVA and PTT were associated with peripheral vascular elasticity and cardiac conduction that were regulated by the cardiac autonomic system. Peripheral vasoconstriction and changes in travel time between left ventricular and peripheral vasculature during the anger episode, and impaired recovery to baseline levels may relate to the psychopathological mechanisms of CAD.

Can pulse transit time be useful for detecting hypertension in patients in a sleep unit?

INTRODUCTION

Pulse transit time (PTT) is the time that a pulse wave takes to travel between two different arterial points, and may be useful in estimating blood pressure. This noninvasive technique, which does not add any cost to the procedure, offers the advantage of avoiding 'arousals' during sleep measurement as occurs with ambulatory blood pressure monitoring (ABPM). We aim to confirm the usefulness of PTT for the detection of hypertension, and to study the correlation between both measurements.

METHODS

Prospective observational study in a multidisciplinary sleep unit. We recruited 30consecutive patients attending a sleep clinic and ran a baseline polysomnography followed by an ABPM the following day. Average systolic and diastolic blood pressure (SBP, DBP) by PTT were calculated and compared with ABMP results. In accordance with international guidelines, patients with mean nocturnal ABMP ≥ 120/70 mmHg were diagnosed as having arterial hypertension.

RESULTS

Mean age of 60years; 66% male, 80% suffered from sleep apnoea (OSAS). Taking the ABPM as the reference technique, we found that the diagnostic sensitivity of PTT is 85% with a specificity of 88% in the case of SBP, with a positive predictive value of 85% and negative predictive value of 88%. By studying the relationship between mean SBP measured by ABPM and PTT, we found a linear correlation coefficient (R) of 0.88, showing a distribution of all subjects with a difference of between ±15mmHg between tests. There is also a positive correlation between mean DBP measured for the two tests, with a weaker linear correlation.

CONCLUSIONS

Pulse transit time shows a strong correlation with blood pressure (measured by ABPM). PTT provides continuous, non-invasive, cuffless blood pressure monitoring free of additional cost and could be an alternative for screening hypertension.

A review of signals used in sleep analysis

This article presents a review of signals used for measuring physiology and activity during sleep and techniques for extracting information from these signals. We examine both clinical needs and biomedical signal processing approaches across a range of sensor types. Issues with recording and analysing the signals are discussed, together with their applicability to various clinical disorders. Both univariate and data fusion (exploiting the diverse characteristics of the primary recorded signals) approaches are discussed, together with a comparison of automated methods for analysing sleep.

Bivariate point process modeling and joint non-stationary analysis of pulse transit time and heart period

Pulse transit time (PTT) is strictly related to pulse wave velocity and may be used for non-invasive monitoring of arterial stiffness and pressure, whose assessment is fundamental to detect cardiovascular dysfunctions. We propose a new model to characterize instantaneous PTT dynamics, and the interactions between PTT and R-R interval (RRI). In this model, PTT is described as a point process whose probability function depends on previous PTT and RRI values. From the model coefficients, instantaneous powers, coherence and directed coherence of each spectral component are estimated. We used this framework to study the changes that tilt table test provoked in PTT and RRI dynamics in 17 healthy subjects. Time-varying spectral and coherence analysis revealed that, although PTT and RRI were locally correlated, direct contribution of RRI on PTT was low during the entire test in high frequency band, and just after postural changes in low frequency band. We conclude that PTT may add valuable information for a more accurate characterization of cardiovascular regulation.

Predicting haemorrhage in pre-hospital traumatic patients: evaluation of the novel heart-to-arm time index

BACKGROUND

Early recognition of hypovolaemia in trauma patients is very important. However, the most often used clinical signs, such as hypotension and tachycardia, lack specificity and sensitivity.

METHODS

We propose a non-invasive index of hypovolaemia, the heart to arm time (iHAT), based on a modified pulse transit time indexed to heart rate. Pulse transit time is the sum of pre-ejection period and vascular transit time. Following pre-load reductions due to hypovolaemia, ventricular diastolic filling time increases causing an increase in pre-ejection-period, pulse transit time, and hence iHAT. One hundred and four consecutive patients with suspected major trauma were enrolled. The primary aim was to evaluate the use of the iHAT for detecting haemorrhage in major trauma. The secondary end point was to compare the specificity and sensitivity of iHAT compared to commonly used indexes.

RESULTS

iHAT was calculated in 84 subjects, 11 of whom were haemorrhagic. iHAT discriminated haemorrhagic from non-haemorrhagic group (46.8% vs. 66.9%, P < 0.0001). The cut-off for iHAT with the best compromise between sensitivity (90.9%) and specificity (100%) was reached at the 58.78% level. Comparing haemorrhagic and non-haemorrhagic patients, the area under the ROC curve was 0.952 for iHAT, 0.835 for heart rate, and 0.911 for systolic blood pressure, showing no significant differences.

CONCLUSIONS

iHAT is a non-invasive index that can identify haemorrhage in trauma patients with high sensitivity and specificity. These data should be considered as an exploration, but any conclusion should be validated in a new set of consecutive patients.

Potential value of electrocardiogram and photoplethysmogram for non-invasive blood pressure estimation during exercise

Blood pressure (BP) monitoring is required to ensure safety of home-based exercise in seniors. Pulse transit time (PTT) defined as the time it takes a pulse wave to travel between two arterial sites is considered to be inversely proportional to BP. Different approaches have been described to calculate PTT using photoplethysmogram (PPG) and electrocardiogram (ECG) however it is not clear which approach produces better BP estimates. The purpose of this study was to compare potential value of different approaches for calculating PTT and other derivatives of PPG and ECG described in the literature for assessing BP during exercise. Three calibration points were collected from five study participants at different levels of exertion on three different days. A high precision automated BP monitor was used to obtain reference BP. A correlation matrix between PPG/ECG derivatives and the reference BP values was analyzed. Based on the bivariate correlation analysis, PPG/ECG derivatives that demonstrated the most prominent association with reference BP were identified. The results of the study confirmed the value of individualized calibration for BP estimation using PTT and identified optimal means to derive it from PPG and ECG.

Implantable acceleration plethysmography for blood pressure determination

This paper presents an implantable accelerometer which detects plethysmograms directly at an artery. The sensor provides a new method for continuous blood pressure monitoring. In vivo measurements indicate that the accelerometer is well suited for determining the Pulse Transit Time (PTT) and the Reflected Wave Transit Time (RWTT). Both parameters show a high correlation with the systolic blood pressure. By varying the blood pressure, it was seen that RWTT more closely agrees with theory than PTT. Through several blood pressure sweeps the RWTT, as detected by the accelerometer, coincided very well with the systolic blood pressure, with a correlation coefficient of 0.96 and mean deviation of 4.3% for 1800 pulses.

How accurate is pulse rate variability as an estimate of heart rate variability? A review on studies comparing photoplethysmographic technology with an electrocardiogram

BACKGROUND

The usefulness of heart rate variability (HRV) as a clinical research and diagnostic tool has been verified in numerous studies. The gold standard technique comprises analyzing time series of RR intervals from an electrocardiographic signal. However, some authors have used pulse cycle intervals instead of RR intervals, as they can be determined from a pulse wave (e.g. a photoplethysmographic) signal. This option is often called pulse rate variability (PRV), and utilizing it could expand the serviceability of pulse oximeters or simplify ambulatory monitoring of HRV.

METHODS

We review studies investigating the accuracy of PRV as an estimate of HRV, regardless of the underlying technology (photoplethysmography, continuous blood pressure monitoring or Finapresi, impedance plethysmography).

RESULTS/CONCLUSIONS

Results speak in favor of sufficient accuracy when subjects are at rest, although many studies suggest that short-term variability is somewhat overestimated by PRV, which reflects coupling effects between respiration and the cardiovascular system. Physical activity and some mental stressors seem to impair the agreement of PRV and HRV, often to an inacceptable extent. Findings regarding the position of the sensor or the detection algorithm are not conclusive. Generally, quantitative conclusions are impeded by the fact that results of different studies are mostly incommensurable due to diverse experimental settings and/or methods of analysis.

Effects of cold stimulation on the harmonic structure of the blood pressure and photoplethysmography waveforms

BACKGROUND

Cold stimulation (CS) accompanied by vasoconstriction can increase the stiffness of the arterial system. The vascular responses during CS have been studied using photoplethysmography (PPG), but most have focused on time-domain waveform indexes. Focusing on the radial arterial blood pressure (BPW) and the finger PPG waveforms, we aimed to determine if harmonic index could help to noninvasively characterize the changes in arterial pulse transmission following mild CS.

METHODS

Trials were measured on male healthy volunteers (n=29); mild CS was applied by placing a bag filled with 2000 cc of water at a temperature of 19-21°C around the right lower arm. For each experiment, we recorded a 3-min baseline-data sequence, applied local mild CS and recorded a 3-min effect sequence, and then recorded another 3-min effect sequence immediately after stopping CS. BPW and PPG spectra were used to calculate the amplitude proportion (C(n)) and phase angle (P(n)) for each harmonic (for n=1-10) from averages of all the pulses during the measurement period.

RESULTS

Several harmonic indexes were prominently increased following CS, including C(4)-C(10) and P(3)-P(10) for the BPW and C(5)-C(10) and P(3) and P(4) for PPG waveforms.

CONCLUSIONS

It was demonstrated that the application of mild CS significantly changes several harmonic-analysis indexes of the BPW and the PPG waveforms. By providing detailed information about the pulse transmission of each frequency component, harmonic analysis may improve the ability to detect arterial elastic properties induced by CS, other forms of external stimulation, or pathological factors. It may be pertinent to the development of medical devices for application in telemedicine.

Pulse arrival time is not an adequate surrogate for pulse transit time as a marker of blood pressure

Pulse transit time (PTT) is a proven, simple to measure, marker of blood pressure (BP) that could potentially permit continuous, noninvasive, and cuff-less BP monitoring (after an initial calibration). However, pulse arrival time (PAT), which is equal to the sum of PTT and the pre-ejection period, is gaining popularity for BP tracking, because it is even simpler to measure. The aim of this study was to evaluate the hypothesis that PAT is an adequate surrogate for PTT as a marker of BP. PAT and PTT were estimated through the aorta using high-fidelity invasive arterial waveforms obtained from six dogs during wide BP changes induced by multiple interventions. These time delays and their reciprocals were evaluated in terms of their ability to predict diastolic, mean, and systolic BP (DBP, MBP, and SBP) per animal. The root mean squared error (RMSE) between the BP parameter predicted via the time delay and the measured BP parameter was specifically used as the evaluation metric. Taking the reciprocals of the time delays tended to reduce the RMSE values. The DBP, MBP, and SBP RMSE values for 1/PAT were 9.8 ± 5.2, 10.4 ± 5.6, and 11.9 ± 6.1 mmHg, whereas the corresponding values for 1/PTT were 5.3 ± 1.2, 4.8 ± 1.0, and 7.5 ± 2.2 mmHg (P < 0.05). Thus tracking BP via PAT was not only markedly worse than via PTT but also unable to meet the FDA BP error limits. In contrast to previous studies, our results quantitatively indicate that PAT is not an adequate surrogate for PTT in terms of detecting challenging BP changes.

Assessment of bilateral photoplethysmography for lower limb peripheral vascular occlusive disease using color relation analysis classifier

This paper proposes the assessment of bilateral photoplethysmography (PPG) for lower limb peripheral vascular occlusive disease (PVOD) using a color relation analysis (CRA) classifier. PPG signals are non-invasively recorded from the right and left sides at the big toe sites. With the time-domain technique, the right-to-left side difference is studied by comparing the subject's PPG data. The absolute bilateral differences construct various diminishing and damping patterns. These difference patterns in amplitude and shape distortion relate to the grades of PVOD, including the normal condition, lower-grade disease, and higher-grade disease. A CRA classifier is used to recognize the various patterns for PVOD assessment. Its concept is derived from the HSV color model and uses the hue, saturation, and value to depict the disease grades using the natural primary colors of red, green, and blue. PPG signals are obtained from 21 subjects aged 24-65 years using an optical measurement technique. The proposed CRA classifier is tested using the physiological measurements, and the tests reveal its practicality for monitoring PPG signals.

Magnetic-stimulation-related physiological artifacts in hemodynamic near-infrared spectroscopy signals

Hemodynamic responses evoked by transcranial magnetic stimulation (TMS) can be measured with near-infrared spectroscopy (NIRS). This study demonstrates that cerebral neuronal activity is not their sole contributor. We compared bilateral NIRS responses following brain stimulation to those from the shoulders evoked by shoulder stimulation and contrasted them with changes in circulatory parameters. The left primary motor cortex of ten subjects was stimulated with 8-s repetitive TMS trains at 0.5, 1, and 2 Hz at an intensity of 75% of the resting motor threshold. Hemoglobin concentration changes were measured with NIRS on the stimulated and contralateral hemispheres. The photoplethysmograph (PPG) amplitude and heart rate were recorded as well. The left shoulder of ten other subjects was stimulated with the same protocol while the hemoglobin concentration changes in both shoulders were measured. In addition to PPG amplitude and heart rate, the pulse transit time was recorded. The brain stimulation reduced the total hemoglobin concentration (HbT) on the stimulated and contralateral hemispheres. The shoulder stimulation reduced HbT on the stimulated shoulder but increased it contralaterally. The waveforms of the HbT responses on the stimulated hemisphere and shoulder correlated strongly with each other (r = 0.65–0.87). All circulatory parameters were also affected. The results suggest that the TMS-evoked NIRS signal includes components that do not result directly from cerebral neuronal activity. These components arise from local effects of TMS on the vasculature. Also global circulatory effects due to arousal may affect the responses. Thus, studies involving TMS-evoked NIRS responses should be carefully controlled for physiological artifacts and effective artifact removal methods are needed to draw inferences about TMS-evoked brain activity.

Resonances in the cardiovascular system caused by rhythmical muscle tension

Paced 0.1 Hz breathing causes high-amplitude HR oscillation, triggering resonance in the cardiovascular system (CVS). This oscillation is considered to be a primary therapeutic factor in HRV biofeedback treatments. This study examined whether rhythmical skeletal muscle tension (RSMT) can also cause 0.1 Hz resonance in the CVS, and compared oscillatory reactivity in CVS functions caused by RSMT and paced breathing (PB). Sixteen young healthy participants completed five tasks: baseline, three RSMT tasks at frequencies of 0.05, 0.1, and 0.2 Hz, and a 0.1 Hz PB task. ECG, respiration, finger pulse, and skin conductance data were collected. Results showed that 0.1 Hz RSMT as well as 0.1 Hz PB triggered resonance in the CVS and caused equivalent oscillations in all measured CVS functions, although in women, RSMT compared to PB caused lower HR oscillation. Clinical application of 0.1 Hz RSMT is discussed.

Pulse transit time reveals drug kinetics on vascular changes affected by propofol

Pulse transit time (PTT) is the duration in which a pulse wave travels between two arterial sites within the same cardiac cycle. The aim of our study is to use PTT to examine propofol's effects on the vascular system. Methods. We collected data from 50 healthy women, between 28 and 51 years old, who underwent gynaecological surgery under general anaesthesia. The general anaesthesia was induced with propofol injection (2 mg/kg). PTT measurements were obtained from the R-wave of electrocardiogram and the pulse wave of photoplethysmograph. Two PTT values were obtained; one before (the control) and the other after propofol injection. The results were analysed by Student's t-test. Results. After propofol injection, the PTT was prolonged. The change in the PTT value from that of baseline was significant statistically (P < 0.05, by Student's t-test). The PTT change over time correlated with the degree of vasodilatation over time. Monitoring of PTT not only revealed the magnitude of vascular changes but also demonstrated the onset of vascular dilation, its peak and duration. We conclude that PTT is a useful guide in monitoring the drug kinetics of propofol.

PTT variability for discrimination of sleep apnea related decreases in the amplitude fluctuations of PPG signal in children

In this paper, an analysis of pulse transit time variability (PTTV) during decreases in the amplitude fluctuations of pulse photoplethysmography signal (PPG) (DAP) events for obstructive sleep apnea syndrome (OSAS) screening is presented. The temporal evolution of time-frequency PTTV parameters during DAP was analyzed. The results show an increase in the sympathetic activity index low-frequency component (LF) during DAP for PTTV (85%) significantly higher than for heart rate variability (HRV) (33%), (p < 10(-13)). However, decreases in parasympathetic activity produce lower decrements in high-frequency component (HF) indexes for PTTV (18%) than for HRV (22%). Thus, PTTV reflects sympathetic changes more clearly than HRV. A clinical study was carried out. DAP events were classified as apneic or nonapneic using a linear discriminant analysis from the PTTV indexes. The ratio of DAP events per hour r (DAP), the ratio after filtering based on HRV indexes r (HRV) (DAP), or on PTTV indexes r (PTTV) (DAP), were computed. The results show an accuracy of 75% for r (PTTV) (DAP) (14% increase with respect to r (DAP) and 5% increase with respect to r (HRV) (DAP)), a sensitivity of 81.8%, and a specificity of 73.9% when classifying 1-h polysomnographic excerpts as OSAS or normal. These results suggest that the combination of DAP and PTTV could be better alternative for sleep apnea screening using PPG with the added benefit of its low cost and simplicity.