Changes In Transit Time Research Articles

Comparison of contrast-enhanced ultrasound imaging (CEUS) and super-resolution ultrasound (SRU) for the quantification of ischaemia flow redistribution: a theoretical study

The study of microcirculation can reveal important information related to pathology. Focusing on alterations that are represented by an obstruction of blood flow in microcirculatory regions may provide an insight into vascular biomarkers. The current in silico study assesses the capability of contrast enhanced ultrasound (CEUS) and super-resolution ultrasound imaging (SRU) flow-quantification to study occlusive actions in a microvascular bed, particularly the ability to characterise known and model induced flow behaviours. The aim is to investigate theoretical limits with the use of CEUS and SRU in order to propose realistic biomarker targets relevant for clinical diagnosis. Results from CEUS flow parameters display limitations congruent with prior investigations. Conventional resolution limits lead to signals dominated by large vessels, making discrimination of microvasculature specific signals difficult. Additionally, some occlusions lead to weakened parametric correlation against flow rate in the remainder of the network. Loss of correlation is dependent on the degree to which flow is redistributed, with comparatively minor redistribution correlating in accordance with ground truth measurements for change in mean transit time,dMTT(CEUS,R = 0.85; GT,R = 0.82) and change in peak intensity,dIp(CEUS,R = 0.87; GT,R = 0.96). Major redistributions, however, result in a loss of correlation, demonstrating that the effectiveness of time-intensity curve parameters is influenced by the site of occlusion. Conversely, results from SRU processing provides accurate depiction of the anatomy and dynamics present in the vascular bed, that extends to individual microvessels. Correspondence between model vessel structure displayed in SRU maps with the ground truth was>91%for cases of minor and major flow redistributions. In conclusion, SRU appears to be a highly promising technology in the quantification of subtle flow phenomena due ischaemia induced vascular flow redistribution.

Exercise-induced reductions in central command network cerebral blood flow assessed with arterial spin labeling MRI

Abstract Habitual aerobic exercise positively impacts brain health. However, less is known about the acute effects of exercise on regional cerebral blood flow (CBF). Most studies have used exercise methods that required a 10-minute or longer delay before acquiring CBF data or methods that assessed global, rather than regional, CBF. In the current feasibility study, an aerobic exercise stimulus was administered using an MRI-compatible cardio step module connected to the MRI table. This allowed participants (N = 12, mean age = 20 years) to exercise at light-to-moderate intensity while in the bore of the MRI scanner. Pseudo-continuous arterial spin labeling MRI with multiple delays was collected on a 3T Siemens MRI scanner immediately pre- and post-exercise. CBF and arterial transit time changes were examined within the central command network, which impacts motor and cardiovascular systems during exercise. Associations with perceived exertion and cardiorespiratory fitness were assessed. CBF in central command regions decreased following exercise, with greater decreases in regions associated with cardiovascular control. For example, CBF in the left insula decreased by -9.03 ± 8.69 mL/100g/min (-11.45%, p < 0.01); CBF in the left and right rostral anterior cingulate decreased by -4.91 ± 6.08 mL/100g/min (-6.17%, p = 0.02) and by -5.04 ± 6.34 mL/100g/min (-7.43%, p = 0.02); and CBF in the left lateral orbitofrontal cortex decreased by -7.30 ± 8.11 mL/100g/min (-9.50%, p = 0.01). Decreased CBF was also associated with greater ratings of perceived exertion in cardiovascular command regions including right insula (r = -0.67, p = 0.03), medial orbitofrontal cortex (r = -0.64, p = 0.04), and lateral orbitofrontal cortex (r = -0.75, p = 0.01). The current study further demonstrates the feasibility of assessing CBF immediately following exercise using an exercise stimulus in the bore of the MRI scanner. These results contribute to a small but growing body of literature describing cerebral hemodynamics immediately following exercise.

Proton-Pump Inhibitors and Fat Absorption in Cystic Fibrosis and Pancreatic Insufficiency: A Randomized Crossover Pilot Trial.

Dietary fat malabsorption contributes to poor nutritional status in patients with cystic fibrosis (CF) and exocrine pancreatic insufficiency (EPI). Prescribing gastric acid-reducing agents such as proton-pump inhibitors (PPI) as an adjunct to pancreatic enzyme replacement therapy (PERT) to improve dietary fat absorption has been accepted in clinical practice despite limited evidence. This was a pilot randomized, double-blind, placebo-controlled crossover trial of subjects aged 12 and older with CF and EPI assessed on placebo and omeprazole to determine if PPI improved the efficacy of PERT as indicated by measures of dietary fat absorption. Fat malabsorption via stool coefficient of fat absorption (CFA) and malabsorption blood test (MBT), gastrointestinal pH (wireless motility capsule [WMC]), and quality of life (QOL) were assessed after 14days on both placebo or PPI (omeprazole). Total 19 subjects enrolled, 13 were randomized, and 9 provided paired results on placebo and PPI. The 3 subject results for CFA were as follows: 1 increased, 1 decreased, and 1 was within the reference range in both tests for fat absorption. For 9 MBT subjects, 7 decreased and 2 increased fat absorption. For the 4 WMC studies, no change in transit times, nor in pH profiles were noted. No differences were seen in the domains of the two QOL questionnaires comparing placebo and PPI. These limited descriptive pilot study results in participants with CF and EPI on PERT evaluated by stool, blood, and QOL tests did not suggest improvement in fat absorption attributable to PPI.

Diet rich in soluble dietary fibres increases excretion of perfluorooctane sulfonic acid (PFOS) in male Sprague-Dawley rats

Perfluorooctane sulfonic acid (PFOS) belongs to a large group of anthropogenic compounds with high persistency named per- and polyfluorinated substances (PFAS). Widespread use from industry to household appliances and food-contact materials contributes to PFAS exposure with food as the primary source. Association studies suggest that vegetables and fibre rich diet may reduce PFOS levels in humans, but experimental data remain limited. Here, we investigated PFOS uptake and wash-out after seven days of PFOS (3 mg/kg/day) in two groups of rats (N = 12 per group) fed diets either high (HF) or low (LF) in soluble dietary fibres. Two control groups (N = 12/group) were fed the same diets without PFOS. Changes in pH and transit time were monitored alongside intestinal and faecal microbiota composition. We quantified systemic and excreted, linear and branched PFOS. Results revealed significantly lower pH and faster intestinal transit in the HF groups. Importantly, HF rats had lower serum PFOS concentrations and higher PFOS concentrations in caecal content and faeces, indicating a more efficient excretion on the fibre rich diet. In both dietary groups, PFOS affected the gut microbiota composition. Our results suggest that a diet rich in soluble dietary fibres accelerates excretion of PFOS and lowers PFOS concentration in serum.

The effect of fiber supplementation with agave fructans or psyllium plantago in symptoms of constipation and its relation with whole and regional transit time and pH.

Supplementation with the Agave tequilana Weber blue variety fructans is a feasible treatment option for functional constipation (FC). However, its effects on colonic function have not yet been studied. This study assessed whole gut transit time (WGTT) and regional transit time using a wireless motility capsule (WMC) before and after supplementation with different fiber treatments in patients with FC. A secondary analysis was performed on data collected from a randomized, double-blind clinical trial comparing agave fructans with psyllium plantago. WGTT, regional transit time, contractility, and pH were measured using WMC before and after fiber supplementation. Comparisons were performed using nonparametric tests. Twenty patients with FC were evaluated, with a median age of 39 (25-54 years), and 18 (90%) were women. Five patients were included in each intervention group. There were no changes in WGTT or regional transit times between the groups (p > 0.05). Similarly, there were no differences in the changes experienced by regional or general contractility among the groups (p > 0.05). The cecal pH profile did not differ between the groups before and after fiber supplementation (p > 0.05). The percentages of clinical responses and consistency of bowel movements between the groups were similar. FC presents a clinical response to a fiber challenge, regardless of the administered intervention. However, this response was not associated with improvement in contractility or regional transit time. We speculate that there are other mechanisms by which fiber consumption may improve FC.

Evaluation of cerebral microcirculation in a mouse model of systemic inflammation.

Perturbations in the microcirculatory system have been observed in neurological conditions, such as Alzheimer's disease or systemic inflammation. However, changes occurring at the level of the capillary are difficult to translate to biomarkers that could be measured macroscopically. We aim to evaluate whether transit time changes reflect capillary stalling and to what degree. We employ a combined spectral optical coherence tomography (OCT) and fluorescence optical imaging (FOI) system to investigate the relation between capillary stalling and transit time in a mouse model of systemic inflammation induced by intraperitoneal injection of lipopolysaccharide. Angiograms are obtained using OCT, and fluorescence signal images are acquired by the FOI system upon intravenous injection of fluorescein isothiocyanate via a catheter inserted into the tail vein. Our findings reveal that lipopolysaccharide (LPS) administration significantly increases both the percentage and duration of capillary stalling compared to mice receiving a 0.9% saline injection. Moreover, LPS-induced mice exhibit significantly prolonged arteriovenous transit time compared to control mice. These observations suggest that capillary stalling, induced by inflammation, modulates cerebral mean transit time, a measure that has translational potential.

Abstract TP151: Usefulness of 3D I-Flow Application in Predicting the Outcome of Flow Diverter Stenting for Large or Giant Carotid Aneurysms

Background and Purpose: The flow diverter (FD) has dramatically improved the treatment outcome of large / giant internal carotid artery (IC) aneurysms. However, it is difficult to predict the treatment outcome of FD just after the treatment. 3D iFlow is a novel application of 4D-digital subtraction angiography (4D-DSA) that can evaluate the arrival time of contrast media in 3D images, but its usefulness for neurointervention is unclear. Therefore, the aim of this study was to elucidate the utility of 3D iFlow in predicting the outcome of FD treatment for large / giant IC aneurysms. Methods: A total of 8 cases of large / giant aneurysms at IC cavernous portion treated with FD and were enrolled in this study. 3D iFlow images before and after placement of FD were acquired in all cases. Treatment outcome was evaluated by O’Kelly-Marotta(OKM) Grading Scale with DSA 6 months after treatment. The regions of interests (ROI) were set in IC bifurcation and petrous segment with 3D iFlow application, and the 3D iFlow transit time was measured by comparing the peak contrast intensities in 2 ROIs. We investigated the rate of changes in 3D iFlow transit time before and after the placement of FD. Results: FD was deployed successfully in all cases without coils. The number of OKM grade B, C and D with DSA 6 months after treatment were 2, 3 and 3 cases, respectively. The rate of changes in 3D iFlow transit time was significantly shorter in OKM grade D cases compared with grade B and C (52.5% vs 84.7%, p=0.03). Conclusion: 3D iFlow application may be effective to predict the treatment outcome of FD.

Analysis of Gut Characteristics and Microbiota Changes with Maternal Supplementation in a Neural Tube Defect Mouse Model

Adequate nutrient supply is crucial for the proper development of the embryo. Although nutrient supply is determined by maternal diet, the gut microbiota also influences nutrient availability. While currently there is no cure for neural tube defects (NTDs), their prevention is largely amenable to maternal folic acid and inositol supplementation. The gut microbiota also contributes to the production of these nutrients, which are absorbed by the host, but its role in this context remains largely unexplored. In this study, we performed a functional and morphological analysis of the intestinal tract of loop-tail mice (Vangl2 mutants), a mouse model of folate/inositol-resistant NTDs. In addition, we investigated the changes in gut microbiota using 16S rRNA gene sequencing regarding (1) the host genotype; (2) the sample source for metagenomics analysis; (3) the pregnancy status in the gestational window of neural tube closure; (4) folic acid and (5) D-chiro-inositol supplementation. We observed that Vangl2+/Lp mice showed no apparent changes in gastrointestinal transit time or fecal output, yet exhibited increased intestinal length and cecal weight and gut dysbiosis. Moreover, our results showed that the mice supplemented with folic acid and D-chiro-inositol had significant changes in their microbiota composition, which are changes that could have implications for nutrient absorption.

Ship-owner response to carbon taxes: Industry and environmental implications

We consider the effects of a maritime bunker levy on ship-owner profits, trade, and emissions. Standard and augmented gravity models are employed using data from 2016 to estimate the impact of a change in transit time and transit cost on grain and soybean trade flows and on vessel speed. Results for a bunker levy of 50 USD per tonne of fuel, or less, stress that it will not trigger a change in the optimal speed of the vessel which is contrary to most theoretical models that predict an increase in fuel costs will always lead to a reduction in speed and carbon emissions. Bunker levies exceeding 100 USD per tonne may be needed to reduce carbon emissions when trade flows are sensitive to trade costs and transport time, as may be the case for many agricultural commodities.

Ventilation Induces Changes in Pulse Wave Transit Time in the Pulmonary Artery.

Pulse wave transit time (PWTT) shortens as pulmonary artery pressure (PAP) increases and was therefore suggested as a surrogate parameter for PAP. The aim of this analysis was to reveal patterns and potential mechanisms of ventilation-induced periodic changes in PWTT under resting conditions. To measure both PWTT and PAP in five healthy pigs, two pulmonary artery Mikro-Tip™ catheters were inserted into the pulmonary vasculature: one with the tip placed in the pulmonary artery trunk, and a second one placed in a distal segment of the pulmonary artery. Animals received pressure-controlled mechanical ventilation. Ventilation-dependent changes were seen in both variables, PWTT and mean PAP; however, changes in PWTT were not synchronous with changes in PAP. Thus, plotting the value of PWTT for each heartbeat over the respective PAP revealed a characteristic hysteresis. At the beginning of inspiration, PAP rose while PWTT remained constant. During further inspiration, PWTT started to decrease rapidly as mPAP was about to reach its plateau. The same time course was observed during expiration: while mPAP approached its minimum, PWTT increased rapidly. During apnea this hysteresis disappeared. Thus, non-synchronous ventilation-induced changes in PWTT and PAP were found with inspiration causing a significant shortening of PWTT. Therefore, it is suggested that the respiratory cycle should be considered when using PWTT as a surrogate for PAP.

Biorelevant Dissolution Method Considerations for the Appropriate Evaluation of Amorphous Solid Dispersions: are Two Stages Necessary?

Biorelevant dissolution testing has been widely used to better understand a drug or formulation's behavior in the human gastrointestinal (GI) tract. The successful evaluation of biorelevant dissolution behavior requires recognizing the importance of utilizing suitable biorelevant media in conjunction with an appropriate dissolution method, especially for supersaturating drug delivery systems, such as amorphous solid dispersions (ASDs). However, most conventional biorelevant dissolution testing methods are not able to accurately reflect the dissolution, supersaturation, and precipitation tendencies of a drug or formulation, which could misinform ASD formulation screening and optimization. In this study, we developed a single compartment 2-stage pH-shift dissolution testing method to simulate the changes in pH, media composition, and transit time in the GI tract, and results were compared against the conventional single compartment 1-stage dissolution method. Nine model drugs were selected based on their ionization properties (i.e. acid, base or neutral) and precipitation tendency (i.e. moderate or slow crystallizer). The dissolution results confirmed that 2-stage pH-shift dissolution is the preferred biorelevant dissolution method to assess non-ionized weak base (nifedipine) and neutral (griseofulvin) compounds exhibiting a moderate precipitation rate from solution when formulated as ASDs. Finally, we designed a flowchart guidance for the appropriate biorelevant dissolution performance characterization of different categories of ASD formulations.

Transit Time of Lamb Wave-Based Ultrasonic Flow Meters and the Effect of Temperature.

Transit-time flow meters need to compensate for cross-sensitivity to temperature. We show that Lamb wave-based setups are less affected by temperature. An optimality criterion is derived that allows to tune the meter into a zero local sensitivity to temperature. For this end, the flow-induced change in ultrasonic transit time is revisited first. While wetted piston transducer meters are directly sensitive to the change in propagation speed, the change in time of flight of Lamb wave-based systems is due to the beam displacement. Second, the effect of temperature is incorporated analytically. It is found that the temperature-dependent radiation angle of Lamb waves is able to compensate for changes in the speed of sound, leading to an (almost) unaffected overall time of flight. This effect is achievable with any fluid and in a wide temperature range. As an example, we discuss a water meter in the range from 0°C to 100°C. The model is validated against temperature and flow rate-dependent measurements obtained on a prototype. The measured data fits well to the developed model and confirms the reduced cross-sensitivity to temperature. Although an in-line meter is considered here, the results extend to clamp-on devices.

Early-onset preeclampsia is characterised by an increased vascular tone in internal jugular veins.

PurposeThis study aimed to investigate Doppler characteristics of maternal internal jugular veins in uncomplicated pregnancies vs. those affected by hypertensive disorders.Materials and methodsVenous pulse transit time and venous impedance index were measured at three different locations (right proximal, right distal, left proximal) of internal jugular veins according to a standardised combined Doppler-Electrocardiogram protocol in five different groups of pregnant women: uncomplicated pregnancy, early-onset preeclampsia, late-onset preeclampsia, gestational hypertension, and normotensive pregnancies with a small for gestational age foetus. Values of both parameters of the latter four groups were plotted against the reference range of uncomplicated pregnancies at corresponding gestation. Linear mixed models with random intercept were used to investigate gestational changes in venous pulse transit time and venous impedance index at the three internal jugular vein locations within and between the different groups.ResultsA total of 127 women were included: 41 had uncomplicated pregnancies, 13 had early-onset preeclampsia, 25 had late-onset preeclampsia, 22 had gestational hypertension, and 26 had normotensive pregnancies with a small for gestational age foetus. Venous pulse transit time values were lower than uncomplicated pregnancy (p ≤ 0.001) at all three locations in the third trimester of early-onset preeclampsia.ConclusionContrary to late-onset preeclampsia and gestational hypertension, early-onset preeclampsia is characterised by a lower venous pulse transit time at internal jugular veins compared to uncomplicated pregnancy, suggesting increased venous vascular tone.

Effects of experimental hypovolemia and pain on pre-ejection period and pulse transit time in healthy volunteers.

Trauma patients may suffer significant blood loss, and noninvasive methods to diagnose hypovolemia in these patients are needed. Physiologic effects of hypovolemia, aiming to maintain blood pressure, are largely mediated by increased sympathetic nervous activity. Trauma patients may however experience pain, which also increases sympathetic nervous activity, potentially confounding measures of hypovolemia. Elucidating the common and separate effects of the two stimuli on diagnostic methods is therefore important. Lower body negative pressure (LBNP) and cold pressor test (CPT) are experimental models of central hypovolemia and pain, respectively. In the present analysis, we explored the effects of LBNP and CPT on pre‐ejection period and pulse transit time, aiming to further elucidate the potential use of these variables in diagnosing hypovolemia in trauma patients. We exposed healthy volunteers to four experimental sequences with hypovolemia (LBNP 60 mmHg) or normovolemia (LBNP 0 mmHg) and pain (CPT) or no pain (sham) in a 2 × 2 fashion. We calculated pre‐ejection period and pulse transit time from ECG and ascending aortic blood velocity (suprasternal Doppler) and continuous noninvasive arterial pressure waveform (volume‐clamp method). Fourteen subjects were available for the current analyses. This experimental study found that pre‐ejection period increased with hypovolemia and remained unaltered with pain. Pulse transit time was reduced by pain and increased with hypovolemia. Thus, the direction of change in pulse transit time has the potential to distinguish hypovolemia and pain.

Characteristics of the Maternal Jugular Venous Pulse Waveform by Combined Doppler-Electrocardiogram Assessment.

Standardized combined Doppler-electrocardiogram assessment was performed longitudinally at three different locations of internal jugular veins between 12 wk of gestation and 6 wk postnatally in 24 uncomplicated pregnancies. All images were classified as typical or non-typical based on the presence of the physiologic deflections A, X, H and C. Linear mixed models with random intercepts of typical images were used to investigate gestational changes in venous pulse transit time and venous impedance index. Unequivocal identification of venous pulse transit time and venous impedance index was possible in 2617 of 3798 (69%) and 2234 of 3798 (59%) images, respectively. The best identification rate (80%, 1018/1266) was at the right distal internal jugular vein. Venous pulse transit time increased with gestational age at all locations; venous impedance index decreased at the right sided internal jugular vein. Maternal jugular venous pulse waveform by combined Doppler-electrocardiogram allows unequivocal identification of A-deflection and calculation of venous pulse transit time and venous impedance index in around two-thirds of assessments, with the highest success rate at the right distal internal jugular vein. Gestational evolutions of venous pulse transit time and venous impedance index are similar to those reported at the level of renal interlobar and hepatic veins.

Diet and Gut Microbiome and the "Chicken or Egg" Problem.

Quantity and quality of the intestinal and fecal microbiome vary considerably between individuals and are dependent on a very large number of intrinsic and environmental factors. Currently, only around 15% of the variance in microbiome diversity can be explained by these factors. Although diet and individual food items have effects, other individual parameters such as gender, age, body mass index (BMI), but also plasma lipids and blood pressure reveal stronger associations with microbiome diversity. In addition, gastrointestinal functions that translate into changes in stool frequency, stool volume, and stool appearance rank very high as effectors of microbiome signatures. In particular, the intestinal/colonic transit time is a critical factor that alters the substrate load for bacterial growth and metabolism as it alters simultaneously stool volume, water content, bacterial mass, and diversity. Moreover, metabolic and neurological diseases are frequently associated with marked changes in intestinal transit time that may translate into the reported changes in gut microbiota. This review provides scientific arguments for a more comprehensive assessment of the individual's intestinal phenotype in microbiome studies to resolve the “chicken or egg” problem in these observational studies.

Effect of Portulaca Oleracea L. extract on functional constipation: A randomized, double-blind, placebo-controlled trial.

Background:This study aimed to investigate the efficacy of P. oleracea in the management of patients with functional constipation.Methods:A total of 60 patients with functional constipation as defined by the Rome IV criteria were enrolled in this randomized, double-blind, placebo-controlled study; 70% ethanol extracts of the aerial parts of P. oleracea were used for the intervention. Patients were randomly assigned to the P. oleracea or placebo groups. Treatment response, quality of life, and changes in colonic transit time (CTT) were evaluated.Results:Complete spontaneous bowel movement (CSBM) improved significantly in the P. oleracea group compared with that in the placebo group over 8 weeks of treatment (P = 0.003). Overall Patient Assessment of Constipation Quality of Life (PAC-QOL) and Patient Assessment of Constipation Symptoms (PAC-SYM) score improvements were observed in the P. oleracea group (P < 0.05). Moreover, CTT decreased from 44.5 ± 22.0 h to 33.7 ± 22.7 h in the P. oleracea group after 7 weeks of treatment (P = 0.04). There were no significant differences in the Bristol Stool Form Scale (BSFS) or adverse events between the groups.Conclusions:Compared to placebo, the use of P. oleracea in patients with functional constipation significantly improved CSBM, severity of symptoms, and quality of life. Further large studies are required to assess the benefits of P. oleracea in the treatment of functional constipation.

Specific Changes in the Mammalian Gut Microbiome as a Biomarker for Oxytocin-Induced Behavioral Changes

Prolonged exposure to psychiatric pharmacological agents is often associated with marked gastrointestinal phenomena, including changes in food intake, bowel motility, gastric emptying, and transit time. Those changes are reflected in the gut microbiota composition of the patient and can, therefore, be objectively measured. This is in contrast to the standard psychiatric evaluation of patients, which includes symptoms that are subjectively assessed (i.e., mood, anxiety level, perception, thought disorders, etc.). The association between a drug’s effect on the microbiota and psychiatric symptoms may allow for quantifiable surrogate markers of treatment effectiveness. Changes in the levels of specific drug-sensitive bacterial species can, thus, potentially serve as biomarkers for the intake and effectiveness of psychiatric drugs. Here, we show substantial microbiota changes that were associated with oxytocin administration and the decreased anxiety/depression-like behaviors it conferred in a rat model of corticosterone-induced stress. Compared with oxytocin, citalopram produced more minor effects on the rats’ microbiota. Alterations in the gut microbiota may, therefore, reflect the consumption and effectiveness of some psychiatric drugs.

Differential effects of the blood pressure state on pulse rate variability and heart rate variability in critically ill patients

Heart rate variability (HRV) utilizes the electrocardiogram (ECG) and has been widely studied as a non-invasive indicator of cardiac autonomic activity. Pulse rate variability (PRV) utilizes photoplethysmography (PPG) and recently has been used as a surrogate for HRV. Several studies have found that PRV is not entirely valid as an estimation of HRV and that several physiological factors, including the pulse transit time (PTT) and blood pressure (BP) changes, may affect PRV differently than HRV. This study aimed to assess the relationship between PRV and HRV under different BP states: hypotension, normotension, and hypertension. Using the MIMIC III database, 5 min segments of PPG and ECG signals were used to extract PRV and HRV, respectively. Several time-domain, frequency-domain, and nonlinear indices were obtained from these signals. Bland–Altman analysis, correlation analysis, and Friedman rank sum tests were used to compare HRV and PRV in each state, and PRV and HRV indices were compared among BP states using Kruskal–Wallis tests. The findings indicated that there were differences between PRV and HRV, especially in short-term and nonlinear indices, and although PRV and HRV were altered in a similar manner when there was a change in BP, PRV seemed to be more sensitive to these changes.

EVOLUTION OF TRANSIT TIME BETWEEN THE SYSTOLIC AND DIASTOLIC PRESSURE PEAKS OF THE RADIAL PULSE WAVEFORM AFTER KIDNEY TRANSPLANTATION

Objective: The transit time between peak systolic and peak diastolic digital volume pulse had been proposed as a measure of arterial stiffness. Indeed, the height of an individual divided by such transit time can be used to estimate a pulse wave velocity. In a cohort of patients with end-stage kidney disease, we aim to examine whether the reduction of aortic stiffness that occurs after kidney transplantation (KTx), translates into improvement of radial artery systolic-diastolic pulse transit time. Design and method: Before and three months after KTx, we recorded radial pressure waveforms using applanation tonometry in 62 patients. We used a two gaussian method to break down the radial pressure waveforms to extract transit time. Radial waveforms were recorded over a 10 seconds period and ensemble-averaged (using in house-MATLAB program) to obtain a single waveform and then modelled using two Gaussian functions. Transit time (dT) was determined as the difference between the first systolic peak (T1) and the early diastolic peak (T2). Generalized transfer function was used to estimate central blood pressures. Carotid-radial and carotid-femoral pulse wave velocities (cr-PWV, cf-PWV) were also measured. Results: 62 patients (66% male, mean age: 48 ± 14 years, mean eGFR: 66 ± 17 ml/min/1.73m2) were assessed. After KTx, there was a significant reduction in cr-PWV (9.49 ± 1.50 to 8.94 ± 1.34, p = 0.001) and cf-PWV (11.56 ± 2.65 to 10.19 ± 1.72, p &lt; 0.001), as well as in central and peripheral blood pressure (p &lt; 0.001). While T1 significantly declined (0.184 [0.172–0.199] to 0.179 [0.164–0.194]s, p = 0.008), there were no significant changes in transit time (0.139 [0.119–0.165] to 0.134 [0.118–0.178]s, p = 0.390) nor in T2 (0.325 [0.293–0.361] to 0.319 [0.283–0.357]s, p = 0.119). Conclusions: Contrary to our expectation, three months after KTx, we did not observe a significant change in transit time. Our results suggest that transit time between the systolic and diastolic pressure peaks of the radial pulse waveform may not be used as a marker of arterial stiffness. We propose that the radial artery pressure wave integrates information from both upstream and downstream vascular beds and so the transit time cannot be used as a reliable surrogate for arterial stiffness.