Wave Transit Time Research Articles

Effect of abdominal aortic endoprostheses on arterial pulse wave velocity in an in vitro abdominal aortic flow model

Objective: Aortic pulse-wave-velocity (aPWV) is a measure for arterial stiffness, which is associated with increased cardiovascular risk. Recent evidence suggests aPWV increases after endograft-placement for aortic aneurysms. The aim of this study was to investigate the influence of different aortic endoprostheses on aPWV and structural stiffness in vitro. Approach: Three different abdominal aortic endoprostheses (AFX, Endurant II, and Nellix) were implanted in identical silicone aneurysm models. One model was left untreated, and another model contained an aortic tube graft (Gelweave). The models were placed in an in vitro flow set-up that mimics physiological flow. aPWV was measured as the transit time of the pressure wave over the flow trajectory of the suprarenal to iliac segment. Structural stiffness corrected for lumen diameter was calculated for each model. Results: aPWV was significantly lower for the control compared to the AFX, Endurant, Nellix and tube graft models (13.00 ± 1.20, 13.40 ± 1.17, 18.18 ± 1.20, 16.19 ± 1.25 and 15.41 ± 0.87 m s−1, respectively (P < 0.05)). Structural stiffness of the AFX model was significant lower compared to the control model (4718 N m−1 versus 5115 N m−1 (P < 0.001), respectively), whereas all other models showed higher structural stiffness. Significance: Endograft placement resulted in a higher aPWV compared to a non-treated aortic flow model. All models showed increased structural stiffness over the flow trajectory compared to the control model, except for the AFX endoprosthesis. Future studies in patients treated with an endograft are needed to evaluate the current results in vivo.

A New Blood Pressure Estimation Method Based on Neural Network Algorithm Model

Measuring blood pressure is one of the main approach of assessing cardiovascular status and heart disease. The method of using PWTT to estimate blood pressure in clinical practice has matured. However, some uncontrollable subtle changes are likely to affect the measurement accuracy of pulse wave transit time. To solve the above problems, a new blood pressure estimation method based on neural network algorithm model is proposed based on the data of a hospital in Nanjing. The blood pressure is first calculated in advance by traditional PWTT algorithm through data analysis, and then modified with the algorithm of BP neural network algorithm. The method is divided into four steps: signal preprocessing and feature points extraction, PWTT computing BP value, neural network algorithm, 4 significant factors selection and blood pressure calculation, and finally combined with PWTT algorithm to estimate the final blood pressure. Compared with the real blood pressure data of 100 hypertensive patients, the error of our new method is less than 5 mmHg and the standard deviation is less than 9 mmHg. The results show that using this method to estimate blood pressure can meet the clinical needs and has good practical value.

Data driven model for sonic well log prediction

Near wellbore failure during the exploration of hydrocarbon reservoirs presents a serious concern to the oil and gas industry. To predict the probability of these undesirable phenomena, engineers study the mechanical rock properties of the formation such as Young's modulus, Bulk modulus, shear modulus and Poisson's ratio. Conventionally, these are measured indirectly using the established petro physical relationships from sonic wave velocities which can be obtained from sonic well logs. Unfortunately, reliable sonic well logs are not always available, due to poor borehole conditions (wash out), damaged tools and offset well data. Most offset well log data are not acquired with dipole sonic tools; they are acquired with a borehole compensated logging tool. This limits the application of acoustic measurements to estimate the mechanical rock properties.In this study, a three-layer feedforward multilayered perceptron artificial neural network model is presented. This model aims to estimate compressional wave transit time and shear wave transit time using real gamma ray and formation density logs. The validation of the model is confirmed by using an oil and gas offshore shaley sandstone reservoir located in West Africa. The results of the validation show that the model presented in this study can be used to determine the sanding potential of the formation without performing a compressive geoscientific analysis in the absence of sonic well logs. The developed model's effectiveness is tested by comparing the predicted results with results obtained from the measured well log. The paper provides a tool to give preliminary recommendations of the likelihood of the formation to produce sand. Implementation of the proposed model can serve as a cost-effective and reliable alternative for the oil and gas industry.

The effect of cuff occlusion on the pulse wave transit time from the heart to the cuff

Background: Pulse wave transit time (PWTT) is widely used to characterize the dynamic properties of the arteries. PWTT is most often calculated as the time interval from the R peak in the electrocardiogram (start of the pulse wave) to the rise in the finger photoplethysmogram (arrival of the pulse wave). This is the PWTTHF. The aim of this study was to analyse the effect of cuff occlusion on PWTT, and using this information to improve the reliability of cuff-based indirect blood pressure (BP) measurement.Methods: PWTT was measured with a home health monitoring device that inflates and deflates the cuff slowly (6 mmHg/s). The change in the arterial wall rigidity caused by cuff occlusion is different in the parts of the arterial section proximal and distal to the cuff. Accordingly, PWTT was divided into two parts: PWTT from the heart to the cuff (PWTTHC) and PWTT from the cuff to the fingertip (PWTTCF). Seven patients with various cardiovascular diseases (55–66 years old), seven healthy senior subjects (55–65 years old) and seven healthy young subjects (22–26 years old) were included in the research.Results: Changes in PWTT characterise appropriately the effect of cuff occlusion on BP measurement. Cuff occlusion affected PWTTHC and PWTTCF differently; it increased the former and decreased the latter. Increased PWTTHC reflects a less rigid arterial wall, resulting in an underestimation of BP. The changes in PWTT values are person-specific and not group-specific (patient, healthy senior, and healthy youth).Conclusion: Occlusion with the cuff is an excitation to the cardiovascular system, causing a temporary change in the dynamic properties of the arteries from the heart to the cuff. The change influences the result of indirect BP measurement. Arterial rigidity in the part proximal to the cuff can be characterized by PWTTHC, which provides different information about the arteries than the widely used PWTTHF.

Blast resistance of slurry infiltrated fibre concrete with hybrid fibre reinforcement

This paper investigates experimentally the blast resistance of slurry infiltrated fibre concrete (SIFCON) with hybrid fibre reinforcement realized by various combinations of polypropylene (PP), aramid, carbon, glass, wollastonite and steel fibers. The binary reinforcement systems were designed using the combinations of steel/PP, steel/aramid, steel/glass, steel/wollastonite and steel/carbon fibres with various fibre geometry. Six different batches (including one reference specimen) were examined with aim to determine the influence of the parameters of hybrid reinforcement on blast resistance of the concrete. Mechanical parameters at quasistatic load (flexural strength, compressive strength) were determined and load-deflection curves were captured. Real blast tests were performed on the slab specimens (500 × 500 × 40 mm) according to the modified methodology M-T0-VTU0 10/09. The change of the ultrasonic wave transit time before and after the blast load in certain measurement points, damage of the slab, the weight of fragments and their damage potential were evaluated and compared. The results indicate, that hybrid fibre reinforcement, when properly designed, can highly enhance overall blast resistance of SIFCON and can significantly reduce the spalling. Steel-aramid combination brought the best blast resistance.

Non-invasive continuous blood pressure measurement based on mean impact value method, BP neural network, and genetic algorithm

BACKGROUND: Non-invasive continuous blood pressure monitoring can provide an important reference and guidance for doctors wishing to analyze the physiological and pathological status of patients and to prevent and diagnose cardiovascular diseases in the clinical setting. Therefore, it is very important to explore a more accurate method of non-invasive continuous blood pressure measurement.OBJECTIVE: To address the shortcomings of existing blood pressure measurement models based on pulse wave transit time or pulse wave parameters, a new method of non-invasive continuous blood pressure measurement – the GA-MIV-BP neural network model – is presented.METHOD: The mean impact value (MIV) method is used to select the factors that greatly influence blood pressure from the extracted pulse wave transit time and pulse wave parameters. These factors are used as inputs, and the actual blood pressure values as outputs, to train the BP neural network model. The individual parameters are then optimized using a genetic algorithm (GA) to establish the GA-MIV-BP neural network model.RESULTS: Bland-Altman consistency analysis indicated that the measured and predicted blood pressure values were consistent and interchangeable.CONCLUSIONS: Therefore, this algorithm is of great significance to promote the clinical application of a non-invasive continuous blood pressure monitoring method.

Meta-analyses on measurement precision of non-invasive hemodynamic monitoring technologies in adults

An ideal non-invasive monitoring system should provide accurate and reproducible measurements of clinically relevant variables that enables clinicians to guide therapy accordingly. The monitor should be rapid, easy to use, readily available at the bedside, operator-independent, cost-effective and should have a minimal risk and side effect profile for patients. An example is the introduction of pulse oximetry, which has become established for non-invasive monitoring of oxygenation worldwide. A corresponding non-invasive monitoring of hemodynamics and perfusion could optimize the anesthesiological treatment to the needs in individual cases. In recent years several non-invasive technologies to monitor hemodynamics in the perioperative setting have been introduced: suprasternal Doppler ultrasound, modified windkessel function, pulse wave transit time, radial artery tonometry, thoracic bioimpedance, endotracheal bioimpedance, bioreactance, and partial CO2 rebreathing have been tested for monitoring cardiac output or stroke volume. The photoelectric finger blood volume clamp technique and respiratory variation of the plethysmography curve have been assessed for monitoring fluid responsiveness. In this manuscript meta-analyses of non-invasive monitoring technologies were performed when non-invasive monitoring technology and reference technology were comparable. The primary evaluation criterion for all studies screened was aBland-Altman analysis. Experimental and pediatric studies were excluded, as were all studies without anon-invasive monitoring technique or studies without evaluation of cardiac output/stroke volume or fluid responsiveness. Most studies found an acceptable bias with wide limits of agreement. Thus, most non-invasive hemodynamic monitoring technologies cannot be considered to be equivalent to the respective reference method. Studies testing the impact of non-invasive hemodynamic monitoring technologies as atrend evaluation on outcome, as well as studies evaluating alternatives to the finger for capturing the raw signals for hemodynamic assessment, and, finally, studies evaluating technologies based on aflow time measurement are current topics of clinical research.

EFFECTS OF SACUBITRIL/VALSARTAN ON THE ARTERIAL STIFFNESS AND LEFT VENTRICULAR-ARTERIAL COUPLING IN PATIENTS WITH HEART FAILURE WITH REDUCED EJECTION FRACTION

Aim. To study the effects of sacubitril/valsartan on left ventricular-arterial coupling (LVAC) and arterial stiffness in HFrEF patients. Material and methods. Arterial stiffness by applanation tonometry and LVAC – by two-dimensional echocardiography were evaluated in 18 patients with compensated HFrEF (age 69Ѓ}9 years, 89% male, arterial hypertension – 83%, diabetes – 39%, myocardial infarction – 89%, left ventricular ejection fraction 32Ѓ}4%) initially and after 6 and 12 months of therapy based on sacubitril/valsartan. LVAC was calculated as the Ea (arterial elastance)/ Ees (left ventricular elastance) ratio. Differences were considered statistically significant at p 10 m/s). The decrease in PWV (from 11.5Ѓ}2.9 to 10.2Ѓ}2.9 m/s, p<0.05), of the augmentation pressure (from 15.3Ѓ}8.9 to 10.5Ѓ}5.0 mm Hg, p=0.002), the increase in the reflected wave transit time (from 132Ѓ}9 to 143Ѓ}29 ms, p=0.02) and the subendocardial viability ratio (from 164Ѓ}25 to 177Ѓ}37%; p=0.009) were found after 12 months. Sacubitryl/valsartanbased therapy was associated with a decrease in central systolic blood pressure (from 116Ѓ}19 to 106Ѓ}10 mm Hg; p=0.001) and central pulse blood pressure (from 44Ѓ}15 to 38Ѓ}7 mm Hg; p<0.05). Decrease in Ea (from 2.20Ѓ}0.84 to 1.79Ѓ}0.63 mm Hg/ml/m2; p=0.005) and Ea/Ees ratio (from 2.26Ѓ}0.77 to 1.68Ѓ}0.32, p=0.05) was found after 12 months. Ees did not change statistically significantly (1.00Ѓ}0.34 vs 1.01Ѓ}0.44 mm Hg/ml/m2). The relationship between the decrease in PWV, Ea and the dynamics of blood pressure was not found. Conclusion. Sacubitryl/valsartan-based therapy in HFrEF patients results in a BP-independent improvement in LVAC due to a decrease in Ea, an improvement in the parameters of the central pulse wave.

Normal impact of a low-velocity projectile against a taut string-like membrane

For the impact system in which a moving projectile transversely impacts against a taut fabric band, 1-D linearized model applies because of low-velocity, sufficient pretension, and the sizes of the objects. This projectile-to-band impact model can serve as the physical prototype of applications in engineering such as cable-membrane architectures and seat belts. In this fundamental work, the response properties under central and non-central impacts are investigated analytically from the viewpoint of wave propagations, while comparisons and verifications are made with finite element (FE) analysis. For a central impact after the first separation, band can catch up with the projectile such that a contact-impact state is re-established when m is in the small interval neighbouring m = 1. For a non-central impact, the projectile would be subjected to a combination of translation and rotation due to asymmetric wave propagations. From every certain instant, the projectile is subjected to an additional rotational acceleration (principal moment) with an abrupt or zero initial value in the anti-clockwise or clockwise direction. The swing amplitude of a small-j or a flat projectile is susceptible to significant fluctuations, and vice versa. The band with a rather large off-centre ratio for the impacted zone and a rather short length of the shorter segment would facilitate a larger accumulation of swing amplitude in a single direction soon after the impact. The linearized impact models proposed can be used to well describe the small-deflection responses for the system, based on 1-D wave propagations or the dependence of quasi-static band deflection on time if the impact duration is much longer than the double wave transit time for the band.

Response to Comment on "Retinal pulse wave velocity measurement using spectral-domain optical coherence tomography".

Spahr et al. recently commented on our latest paper "Retinal pulse wave velocity measurement using spectral-domain optical coherence tomography" with a conclusion that the measured retinal pulse wave velocity (rPWV) in our paper was contradictory to theoretical predictions and previously published results. However, the theoretical predictions by Spahr et al. based on Moens-Korteweg equation are questionable, since the Moens-Korteweg equation should not be used for small arteries like retinal arteries. Previously, various measurements of rPWV using different technologies have been reported. The results on human and rats are not consistent. As the rPWV is an unknown value, we argue that the time delay derived between 2 arterial sites should be verified to see if the delay truly represents the pulse wave transit time. In the future, special emphasis should be placed on demonstration of the reproducibility of technologies and data analysis of large samples.

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.

Biomarker and cardiovascular profiles of healthy aging, putting multiple biomarkers in perspective

Although many studies have reported age-specific changes in selected cardiovascular (CV) markers, few have analyzed the simultaneous changes that occur in the cardiac, metabolic, immune and growth factor axis with healthy aging. To assess the relationship between CV parameters and circulating biomarkers with aging. We prospectively recruited 150 healthy volunteers, of whom 44 were excluded due to reported illness on a comprehensive health questionnaire or the presence of CV disease on screening. Echocardiography and vascular Doppler were performed in all participants as per international guidelines, with Pulse Wave Velocity (PWV) calculated as the path length traveled divided by transit time of the aortic pulse wave. All cardiac-specific biomarkers, including NT-proBNP and GDF-15 were undertaken in the Abbott Core Laboratory, cytokines and growth factors were assessed using a 48-plex Luminex bead kit and comprehensive lipid profile with a Vertical Auto Profile lipid test. There was a wide age range, from 20 to 95 years, 45% females with a mean body mass index of 24.1 ± 3.1 kg/m 2 and systolic blood pressure of 118 ± 13 mmHg. Among CV ultrasound parameters, average E’ showed the highest correlation with age ( r 2 = 0.55, P < 0.001) with the highest significant correlation on each diagnostic group, as shown in Table 1 . Partial correlation mapping was used to represent the complex relationships between variables most correlated with age ( Figure 1 ). PWV, a measure of arterial stiffness appeared to be well correlated to E/A, a parameter of ventricular relaxation and GDF-15, which has been associated with CV mortality. On multivariate regression when considering the other modulating factors, insulin ( r = 0.29, P = 0.001) in addition to age ( r = 0.75, P < 0.001) explained the majority of the variance in PWV. The study presents the interactions in CV and biomarker profiles with aging, with insulin emerging as a major modulator of PWV. PWV indicates Pulse wave Velocity; GDF-15, Growth-differentiation factor-15; NT-proBNP, N-terminal pro-B-type natriuretic peptide; Gal-3, Galectin-3; CysC, Cystatin C; BUN, Blood Urea Nitrogen; HDL, high-density lipoprotein; CXCL, Chemokine (C-X-C motif) ligand; CCL, Chemokine (C-C motif) ligand.

Retinal pulse wave velocity measurement using spectral-domain optical coherence tomography.

The human eyes provide a natural window for noninvasive measurement of the pulse wave velocity (PWV) of small arteries. By measuring the retinal PWV, the stiffness of small arteries can be assessed, which may better detect early vascular diseases. Therefore, retinal PWV measurement has attracted increasing attention. In this study, a jump-scanning method was proposed for noninvasive measurement of retinal PWV using spectral-domain optical coherence tomography (SD-OCT). The jump-scanning method uses the phase-resolved Doppler OCT to obtain the pulse shapes. To realize PWV measurement, the jump-scanning method extracts the transit time of the pulse wave from an original OCT scanning site to another through a transient jump. The measured retinal arterial PWV of a young human subject with normal blood pressure was in the order of 20 to 30 mm/s, which was consistent with previous studies. As a comparison, PWV of 50 mm/s was measured for a young human subject with prehypertension, which was in accordance with the finding of strong association between retinal PWV and blood pressure. In summary, it is believed the proposed jump-scanning method could benefit the research and diagnosis of vascular diseases through the window of human eyes.

Central pulse wave parameters are associated with valve calcification in patients with end-stage renal disease on maintenance hemodialysis

BackgroundArterial stiffness is known marker of poor cardiovascular prognosis. The aim if the study was to assess the incidence of valve calcification (VC) in patients with end- stage renal disease (ESRD) and its associations with clinical parameters of arterial stiffness.MethodsIn 68 adults with ESRD on maintenance hemodialysis for >3 months (45.6% males, median age 58.3 (interquartile range (IQR) 54.6; 61.6) years, dialysis duration 62.7 (47.8; 77) months, echocardiography and applanation tonometry was performed.ResultsCalcification of the aortic, mitral and both valves was revealed in 46 (67.6%), 34 (50%) and 33 (48.5%) of patients. 20 (29%) patients had no signs of VC. Patients with vs without AVC were older (65.1 ± 9.5 vs 41.4 ± 11,9 years, p< 0.001), had higher dialysis duration (51 (8; 252) vs 21 (10; 38) months, p<0.01), lower peripheral diastolic blood pressure (DBP) (76 ± 17 vs 84 ± 12mmHg, p<0.05), central DBP (75 ± 15 vs 82 ± 11 mmHg, p<0.05), reflected wave transit time (RWTT) (131 ± 17 vs 137 ± 15 ms, p<0.05). Patients with vs without MVC were older (67.8 ± 8.2 vs 47.9 ± 13,5 years, p < 0.001), had higher dialysis duration (51 (34; 111) vs 36 (14; 57) months, p<0.01), carotid-femoral pulse wave velocity (10.1 ± 2.7 vs 8.9 ± 3.5 m/s, p<0.05), lower peripheral DBP (73 ± 17vs 84 ± 14 mmHg, p< 0.01), central DBP (72 ± 13 vs 83 ± 13 mmHg, p< 0.001), higher central pulse pressure (52 ± 13 vs 45 ± 16mmHg, p<0.05), lower RWTT (133 (120; 130) vs 135 (132; 142) ms, p < 0.05).ConclusionHigh prevalence of VC (71%) was revealed in patients with ESRD on maintenance hemodialysis. Patients with vs without VC were older, had higher duration of dialysis and more pronounced arterial stiffness.

Non-Invasive Monitoring of Cardiac Output in Critical Care Medicine.

Critically ill patients require close hemodynamic monitoring to titrate treatment on a regular basis. It allows administering fluid with parsimony and adjusting inotropes and vasoactive drugs when necessary. Although invasive monitoring is considered as the reference method, non-invasive monitoring presents the obvious advantage of being associated with fewer complications, at the expanse of accuracy, precision, and step-response change. A great many methods and devices are now used over the world, and this article focuses on several of them, providing with a brief review of related underlying physical principles and validation articles analysis. Reviewed methods include electrical bioimpedance and bioreactance, respiratory-derived cardiac output (CO) monitoring technique, pulse wave transit time, ultrasound CO monitoring, multimodal algorithmic estimation, and inductance thoracocardiography. Quality criteria with which devices were reviewed included: accuracy (closeness of agreement between a measurement value and a true value of the measured), precision (closeness of agreement between replicate measurements on the same or similar objects under specified conditions), and step response change (delay between physiological change and its indication). Our conclusion is that the offer of non-invasive monitoring has improved in the past few years, even though further developments are needed to provide clinicians with sufficiently accurate devices for routine use, as alternative to invasive monitoring devices.

PP.24.31] ONE YEAR SACUBITRIL/VALSARTAN THERAPY IS ASSOCIATED WITH DECREASE OF ARTERIAL STIFFNESS IN PATIENTS WITH STABLE HEART FAILURE WITH REDUCED EJECTION FRACTION

Objective: Angiotensin receptor-neprilysin inhibitor (ARNI) is recommended to further reduce the morbidity and mortality for patients with chronic symptomatic heart failure with reduced ejection fraction (HFrEF). Increased arterial stiffness (AS) has been shown to correlate with adverse cardiovascular events. The aim of the study was to assess long-term sacubitril/valsartan effects on parameters of AS in patients with HFrEF. Design and method: In the open-label follow-up to PARADIGM HF study 16 patients with stable HFrEF (14 male, 69 ± 9 years (M ± SD), arterial hypertension 88%, previous myocardial infarction 88%, diabetes 43%, LVEF 32 ± 6%, eGFR 55 ± 13 ml/min/1.73 m2, potassium 4.43 ± 0.38 mmol/l) were enrolled. Patients received a stable background treatment for at least a month (ACEI 94%, beta-blockers 100%, aldosterone receptor antagonists 81%, loop diuretics 75%). ACEI treatment was interrupted for 36 h and replaced with sacubitril/valsartan 50, 100 or 200 mg BID according to baseline BP (mean dose 185.7 ± 36.3 mg BID). AS was assessed by applanation tonometry baseline and after 6 and 12 months sacubitril/valsartan therapy. Wilcoxon and Spearman test was considered significant if p < 0.05. Results: After 6 months of sacubitril/valsartan therapy carotid-femoral pulse wave velocity (PWV) significantly decreased (11.5 ± 2.9 vs 10.2 ± 2.9 m/s, p < 0.05) while other parameters of AS did not change (p > 0.05). After 12 months sacubitril/valsartan therapy was associated with significant decrease of aortic augmentation pressure (AP) (15.3 ± 8.9 vs 10.5 ± 5.0 mmHg, p = 0.002), increase of reflected wave transit time (RWTT) (132 ± 9 vs 143 ± 29 ms, p = 0.02), subendocardial viability ratio (SEVR) (164 ± 25 vs 177 ± 37%, p = 0.009). Changes of PWV between 6 and 12 months were nonsignificant (10.2 ± 2.9 vs 10.8 ± 2.0 m/s; p > 0.05). Changes of augmentation pressure correlated with changes of SEVR (R = −0.56), augmentation index (AIx) (R = 0.52), stroke volume (R = 0.52), p < 0.05 for all. There was significant correlation between changes of SEVR and stroke volume (R = −0.85), changes of RWTT and AIx (R = −0.68), p < 0.05. Conclusions: In stable patients with HFrEF 12-month sacubitril/valsartan therapy is associated with significant improvement of central pulse wave parameters: decrease of aortic AP, increase of RWTT. Sacubitril/valsartan therapy was associated with beneficial increase of SEVR, index that reflects the subendocardial oxygen supply-demand ratio.

Accuracy and Precision of Non-invasive Cardiac Output Monitoring Devices in Perioperative Medicine

Abstract Cardiac output (CO) measurement is crucial for the guidance of therapeutic decisions in critically ill and high-risk surgical patients. Newly developed completely non-invasive CO technologies are commercially available; however, their accuracy and precision have not recently been evaluated in a meta-analysis. We conducted a systematic search using PubMed, Cochrane Library of Clinical Trials, Scopus, and Web of Science to review published data comparing CO measured by bolus thermodilution with commercially available non-invasive technologies including pulse wave transit time, non-invasive pulse contour analysis, thoracic electrical bioimpedance/bioreactance, and CO2 rebreathing. The non-invasive CO technology was considered acceptable if the pooled estimate of percentage error was

Experiments on acoustic measurement of fractured rocks and application of acoustic logging data to evaluation of fractures

Fractures in oil and gas reservoirs have been the topic of many studies and have attracted reservoir research all over the world. Because of the complexities of the fractures, it is difficult to use fractured reservoir core samples to investigate true underground conditions. Due to the diversity of the fracture parameters, the simulation and evaluation of fractured rock in the laboratory setting is also difficult. Previous researchers have typically used a single material, such as resin, to simulate fractures. There has been a great deal of simplifying of the materials and conditions, which has led to disappointing results in application. In the present study, sandstone core samples were selected and sectioned to simulate fractures, and the changes of the compressional and shear waves were measured with the gradual increasing of the fracture width. The effects of the simulated fracture width on the acoustic wave velocity and amplitude were analyzed. Two variables were defined: H represents the amplitude attenuation ratio of the compressional and shear wave, and x represents the transit time difference value of the shear wave and compressional wave divided by the transit time of the compressional wave. The effect of fracture width on these two physical quantities was then analyzed. Finally, the methods of quantitative evaluation for fracture width with H and x were obtained. The experimental results showed that the rock fractures linearly reduced the velocity of the shear and compressional waves. The effect of twin fractures on the compressional velocity was almost equal to that of a single fracture which had the same fracture width as the sum of the twin fractures. At the same time, the existence of fractures led to acoustic wave amplitude attenuations, and the compressional wave attenuation was two times greater than that of the shear wave. In this paper, a method was proposed to calculate the fracture width with x and H, then this was applied to the array acoustic imaging logging data. The application examples showed that the calculated fracture width could be compared with fractures on the electric imaging logs. These rules were applied in the well logs to effectively evaluate the fractures, under the case of no image logs, which had significance to prospecting and development of oil and gas in fractured reservoirs.

Defects in Vascular Mechanics Due to Aging in Rats: Studies on Arterial Wave Properties from a Single Aortic Pressure Pulse.

Changes in vascular mechanics due to aging include elevated vascular impedance, diminished aorta distensibility, and an accelerated return of pulse wave reflection, which may increase the systolic workload on the heart. Classically, the accurate measurement of vascular mechanics requires the simultaneous recording of aortic pressure and flow signals. In practice, it is feasible to estimate arterial wave properties in terms of wave transit time (τw) and wave reflection index (RI) by using aortic pressure signal alone. In this study, we determined the τw and magnitudes of the forward (∣Pf∣) and backward (∣Pb∣) pressure waves in Long–Evans male rats aged 4 (n = 14), 6 (n = 17), 12 (n = 17), and 18 (n = 24) months, based on the measured aortic pressure and an assumed triangular flow (Qtri). The pulsatile pressure wave was the only signal recorded in the ascending aorta by using a high-fidelity pressure sensor. The base of the unknown Qtri was constructed using a duration, which equals to the ejection time. The timing at the peak of the triangle was derived using the fourth-order derivative of the aortic pressure waveform. In the 18-month-old rats, the ratio of τw to left ventricular ejection time (LVET) decreased, indicating a decline in the distensibility of the aorta. The increased ∣Pb∣ associated with unaltered ∣Pf∣ enhanced the RI in the older rats. The augmentation index (AI) also increased significantly with age. A significant negative correlation between the AI and τw/LVET was observed: AI = −0.7424 − 0.9026 × (τw/LVET) (r = 0.4901; P < 0.0001). By contrast, RI was positively linearly correlated with the AI as follows: AI = −0.4844 + 2.3634 × RI (r = 0.8423; P < 0.0001). Both the decreased τw/LVET and increased RI suggested that the aging process may increase the AI, thereby increasing the systolic hydraulic load on the heart. The novelty of the study is that Qtri is constructed using the measured aortic pressure wave to approximate its corresponding flow signal, and that calibration of Qtri is not essential in the analysis.

A novel Blood Pressure estimation method combing Pulse Wave Transit Time model and neural network model.

Blood Pressure (BP) measurement can assist doctors to assess patients' cardiovascular status and diagnose heart diseases. Pulse Wave Transit Time (PWTT) model is one frequently used BP estimation method to monitor BP continuously in clinics. However, individual variations may influence the measurement accuracy of PWTT model. Focusing on above promble, this paper proposes a novel BP estimation method combining a classical PWTT model and a neural network model. The novel method is composed of five steps: signal pre-processing, feature extraction, initial PWTT model selection, model correction by neural network model, and final PWTT model identification. A validation experiment based on 10 patients from Multiparameter Intelligent Monitoring in Intensive Care (MIMIC) database showed that the BP estimation results by our method had a minimum mean of error readout value 5 mmHg with a standard deviation of error readout value ±8mmHg. As a result, both the diastolic blood pressure and systolic blood pressure estimation by our method can meet clinical requirements.