Monoexponential Equation Research Articles

Agreement and Sensitivity of the Acceleration–Velocity Profile Derived via Local Positioning System

Sprint performance is commonly assessed via discrete sprint tests and analyzed through kinematic estimates modeled using a mono-exponential equation, including estimated maximal sprinting speed (MSS), relative acceleration (TAU), maximum acceleration (MAC), and relative propulsive maximal power (PMAX). The acceleration–velocity profile (AVP) provides a simple summary of short sprint performance using two parameters: MSS and MAC, which are useful for simplifying descriptions of sprint performance, comparison between athletes and groups of athletes, and estimating changes in performance over time or due to training intervention. However, discrete testing poses logistical challenges and defines an athlete’s AVP exclusively from the performance achieved in an isolated testing environment. Recently, an in situ AVP (velocity–acceleration method) was proposed to estimate kinematic parameters from velocity and acceleration data obtained via global or local positioning systems (GPS/LPS) over multiple training sessions, plausibly improving the time efficiency of sprint monitoring and increasing the sample size that defines the athlete’s AVP. However, the validity and sensitivity of estimates derived from the velocity–acceleration method in relation to changes in criterion scores remain elusive. To assess the concurrent validity and sensitivity of kinematic measures from the velocity–acceleration method, 31 elite youth basketball athletes (23 males and 8 females) completed two maximal effort 30 m sprint trials. Performance was simultaneously measured by a laser gun and an LPS (Kinexon), with kinematic parameters estimated using the time–velocity and velocity–acceleration methods. Agreement (%Bias) between laser gun and LPS-derived estimates was within the practically significant magnitude (±5%), while confidence intervals for the percentage mean absolute difference (%MAD) overlapped practical significance for TAU, MAC, and PMAX using the velocity–acceleration method. Only the MSS parameter showed a sensitivity (%MDC95) within practical significance (<5%), with all other parameters showing unsatisfactory sensitivity (>10%) for both the time–velocity and velocity–acceleration methods. Thus, sports practitioners may be confident in the concurrent validity and sensitivity of MSS estimates derived in situ using the velocity–acceleration method, while caution should be applied when using this method to infer an athlete’s maximal acceleration capabilities.

Effects of the Flying Start on Estimated Short Sprint Profiles Using Timing Gates.

Short sprints are predominantly assessed using timing gates and analyzed through parameters of the mono-exponential equation, including estimated maximal sprinting speed (MSS) and relative acceleration (TAU), derived maximum acceleration (MAC), and relative propulsive maximal power (PMAX), further referred to as the No Correction model. However, the frequently recommended flying start technique introduces a bias during parameter estimation. To correct this, two additional models (Estimated TC and Estimated FD) were proposed. To estimate model precision and sensitivity to detect the change, 31 basketball players executed multiple 30 m sprints. Athlete performance was simultaneously measured by a laser gun and timing gates positioned at 5, 10, 20, and 30 m. Short sprint parameters were estimated using a laser gun, representing the criterion measure, and five different timing gate models, representing the practical measures. Only the MSS parameter demonstrated a high agreement between the laser gun and timing gate models, using the percent mean absolute difference (%MAD) estimator (%MAD < 10%). The MSS parameter also showed the highest sensitivity, using the minimum detectable change estimator (%MDC95), with an estimated %MDC95 < 17%. Interestingly, sensitivity was the highest for the No Correction model (%MDC95 < 7%). All other parameters and models demonstrated an unsatisfying level of sensitivity. Thus, sports practitioners should be cautious when using timing gates to estimate maximum acceleration indices and changes in their respective levels.

Histopathological graded liver lesions: what role does the IVIM analysis method have?

This study aims to investigate three different image processing methods on quantitative parameters of IVIM sequence, as well as apparent diffusion coefficients and simple perfusion fractions, for benign and malignant liver tumors. IVIM images with 8 b-values (0-1000s/mm2) and 1.5T MRI scanner in 16 patients and 3 healthy people were obtained. Next, the regions of interest were selected for malignant, benign, and healthy liver regions (50, 56, and 12, respectively). Then, the bi-exponential equation of the IVIM technique was fitted with two segmented fitting methods as well as one full fitting method (three methods in total). Using the segmented fitting method, diffusion coefficient (D) is fixed with a mono-exponential equation with b-values that are greater than 200s/mm2. The perfusion fraction (f) can then be calculated by extrapolating, as the first method, or fitting simultaneously with the pseudo-diffusion coefficient (D*) as the second method. In the full fitting method, as the third method, all IVIM parameters were obtained simultaneously. The mean values of parameters from different methods were compared in different grades of lesions. Our results indicate that the image processing method can change statistical comparisons between different groups for each parameter. The D value is the only quantity in this technique that does not depend on the fitting process and can be used as an indicator of comparison between studies (P < 0.05). The most effective method to distinguish liver lesions is the extrapolated f method (first method). This method created a significant difference (P < 0.05) between the perfusion parameters between benign and malignant lesions. Using extrapolated f is the most effective method of distinguishing liver lesions using IVIM parameters. The comparison between groups does not depend on the fitting method only for parameter D.

A Novel Approach to the Determination of Time- and Fatigue-Dependent Efficiency during Maximal Cycling Sprints.

During maximal cycling sprints, efficiency (η) is determined by the fiber composition of the muscles activated and cadence-dependent power output. To date, due to methodological limitations, it has only been possible to calculate gross efficiency (i.e., the ratio of total mechanical to total metabolic work) in vivo without assessing the impact of cadence and changes during exercise. Eliminating the impact of cadence provides optimal efficiency (ηopt), which can be modeled as a function of time. Here, we explain this concept, demonstrate its calculation, and compare the values obtained to actual data. Furthermore, we hypothesize that the time course of maximal power output (Pmax) reflects time-dependent changes in ηopt. Twelve elite track cyclists performed four maximal sprints (3, 8, 12, 60 s) and a maximal-pedaling test on a cycle ergometer. Crank force and cadence were monitored continuously to determine fatigue-free force-velocity profiles (F/v) and fatigue-induced changes in Pmax. Respiratory gases were measured during and for 30 min post-exercise. Prior to and following each sprint, lactate in capillary blood was determined to calculate net blood lactate accumulation (ΔBLC). Lactic and alactic energy production were estimated from ΔBLC and the fast component of excess post-exercise oxygen consumption. Aerobic energy production was determined from oxygen uptake during exercise. Metabolic power (MP) was derived from total metabolic energy (WTOT). ηopt was calculated as Pmax divided by MP. Temporal changes in Pmax, WTOT, and ηopt were analyzed by non-linear regression. All models showed excellent quality (R2 > 0.982) and allowed accurate recalculation of time-specific power output and gross efficiency (R2 > 0.986). The time-constant for Pmax(t) (τP) was closely correlated with that of ηopt (τη; r = 0.998, p < 0.001). Estimating efficiency using τP for τη led to a 0.88 ± 0.35% error. Although efficiency depends on pedal force and cadence, the latter influence can be eliminated by ηopt(t) using a mono-exponential equation whose time constant can be estimated from Pmax(t).

{shorts}: An R Package for Modeling Short Sprints

Short sprint performance is one of the most distinguishable and admired physical traits in sports. Short sprints have been modeled using the mono-exponential equation that involves two parameters: (1) maximum sprinting speed (MSS) and (2) relative acceleration (TAU). The most common methods to assess short sprint performance are with a radar gun or timing gates. In this paper, we: 1) provide the shorts package that can model sprint timing data from these two sources; 2) discuss potential issues with assessing sprint time (synchronization and flying start, respectively); and 3) provide model definitions within the shorts package to help alleviate errors within the subsequent parameter outcomes.

Modeling Optimal Cadence as a Function of Time during Maximal Sprint Exercises Can Improve Performance by Elite Track Cyclists

In track cycling sprint events, optimal cadence PRopt is a dynamic aspect of fatigue. It is currently unclear what cadence is optimal for an athlete’s performance in sprint races and how it can be calculated. We examined fatigue-induced changes in optimal cadence during a maximal sprint using a mathematical approach. Nine elite track cyclists completed a 6-s high-frequency pedaling test and a 60-s isokinetic all-out sprint on a bicycle ergometer with continuous monitoring of crank force and cadence. Fatigue-free force-velocity (F/v) and power-velocity (P/v) profiles were derived from both tests. The development of fatigue during the 60-s sprint was assessed by fixing the slope of the fatigue-free F/v profile. Fatigue-induced alterations in PRopt were determined by non-linear regression analysis using a mono-exponential equation at constant slope. The study revealed that PRopt at any instant during a 60-s maximal sprint can be estimated accurately using a mono-exponential equation. In an isokinetic mode, a mean PRopt can be identified that enables the athlete to generate the highest mean power output over the course of the effort. Adding the time domain to the fatigue-free F/v and P/v profiles allows time-dependent cycling power to be modelled independent of cadence.

A Novel Approach of Modelling and Predicting Track Cycling Sprint Performance

In cycling, performance models are used to investigate factors that determine performance and to optimise competition results. We present an innovative and easily applicable mathematical model describing time-resolved approaches for both the physical aspects of tractional resistance and the physiological side of propelling force generated by muscular activity and test its validity to reproduce and forecast time trials in track cycling. Six elite track cyclists completed a special preparation and two sprint time trials in an official velodrome under continuous measurement of crank force and cadence. Fatigue-free force-velocity profiles were calculated, and their fatigue-induced changes were determined by non-linear regression analysis using a monoexponential equation at a constant slope. Model parameters were calibrated based on pre-exercise performance testing and the first of the two time-trials and then used to predict the performance of the second sprint. Measured values for power output and cycling velocity were compared to the modelled data. The modelled results were highly correlated to the measured values (R2&gt;0.99) without any difference between runs (p&gt;0.05; d&lt;0.1). Our mathematical model can accurately describe sprint track cycling time trial performance. It is simple enough to be used in practice yet sufficiently accurate to predict highly dynamic maximal sprint performances. It can be employed for the evaluation of completed runs, to forecast expected results with different setups, and to study various contributing factors and quantify their effect on sprint cycling performance.

Diffusion processes modeling in magnetic resonance imaging

BackgroundThe paper covers modern approaches to the evaluation of neoplastic processes with diffusion-weighted imaging (DWI) and proposes a physical model for monitoring the primary quantitative parameters of DWI and quality assurance. Models of hindered and restricted diffusion are studied.Material and methodTo simulate hindered diffusion, we used aqueous solutions of polyvinylpyrrolidone with concentrations of 0 to 70%. We created siloxane-based water-in-oil emulsions that simulate restricted diffusion in the intracellular space. To obtain a high signal on DWI in the broadest range of b values, we used silicon oil with high T2: cyclomethicone and caprylyl methicone. For quantitative assessment of our phantom, we performed DWI on 1.5T magnetic resonance scanner with various fat suppression techniques. We assessed water-in-oil emulsion as an extracorporeal source signal by simultaneously scanning a patient in whole-body DWI sequence.ResultsWe developed phantom with control substances for apparent diffusion coefficient (ADC) measurements ranging from normal tissue to benign and malignant lesions: from 2.29 to 0.28 mm2/s. The ADC values of polymer solutions are well relevant to the mono-exponential equation with the mean relative difference of 0.91%.ConclusionThe phantom can be used to assess the accuracy of the ADC measurements, as well as the effectiveness of fat suppression. The control substances (emulsions) can be used as a body marker for quality assurance in whole-body DWI with a wide range of b values.

A hybrid (iron-fat-water) phantom for liver iron overload quantification in the presence of contaminating fat using magnetic resonance imaging.

Assessment of iron content in the liver is crucial for diagnosis/treatment of iron-overload diseases. Nonetheless, T2*-based methods become challenging when fat and iron are simultaneously present. This study proposes a phantom design concomitantly containing various concentrations of iron and fat suitable for devising accurate simultaneous T2* and fat quantification technique. A 46-vial iron-fat-water phantom with various iron concentrations covering clinically relevant T2* relaxation time values, from healthy to severely overloaded liver and wide fat percentages ranges from 0 to 100% was prepared. The phantom was constructed using insoluble iron (II, III) oxide powder containing microscale particles. T2*-weighted imaging using multi-gradient-echo (mGRE) sequence, and chemical shift imaging spin-echo (CSI-SE) Magnetic Resonance Spectroscopy (MRS) data were considered for the analysis. T2* relaxation times and fat fractions were extracted from the MR signals to explore the effects of fat and iron overload. Size distribution of iron oxide particles for Magnetite fits with a lognormal function with a mean size of about 1.17µm. Comparison of FF color maps, estimated from bi- and mono-exponential model indicated that single-T2* fitting model resulted in lower NRMSD. Therefore, T2* values from the mono-exponential signal equation were used and expressed the relationship between relaxation time value across all iron (Fe) and fat concentration as [Formula: see text], with R-squared = 0.89. The proposed phantom design with microsphere iron particles closely simulated the single-T2* behavior of fatty iron-overloaded liver in vivo.

The National Football League Combine 40-yd Dash: How Important is Maximum Velocity?

Clark, KP, Rieger, RH, Bruno, RF, and Stearne, DJ. The NFL combine 40-yard dash: how important is maximum velocity? J Strength Cond Res 33(6): 1542-1550, 2019-This investigation analyzed the sprint velocity profiles for athletes who completed the 40-yard (36.6 m) dash at the 2016 National Football League (NFL) Combine. The purpose was to evaluate the relationship between maximum velocity and sprint performance, and to compare acceleration patterns for fast and slow athletes. Using freely available online sources, data were collected for body mass and sprint performance (36.6 m time with split intervals at 9.1 and 18.3 m). For each athlete, split times were used to generate modeled curves of distance vs. time, velocity vs. time, and velocity vs. distance using a monoexponential equation. Model parameters were used to quantify acceleration patterns as the ratio of maximum velocity to maximum acceleration (vmax/amax, or τ). Linear regression was used to evaluate the relationship between maximum velocity and sprint performance for the entire sample. In addition, athletes were categorized into fast and slow groups based on maximum velocity, with independent t-tests and effect size statistics used to evaluate between-group differences in sprint performance and acceleration patterns. Results indicated that maximum velocity was strongly correlated with sprint performance across 9.1, 18.3, and 36.6 m (r of 0.72, 0.83, and 0.94, respectively). However, both fast and slow groups accelerated in a similar pattern relative to maximum velocity (τ = 0.768 ± 0.068 seconds for the fast group and τ = 0.773 ± 0.070 seconds for the slow group). We conclude that maximum velocity is of critical importance to 36.6 m time, and inclusion of more maximum velocity training may be warranted for athletes preparing for the NFL Combine.

Quadriceps weakness associates with greater T1ρ relaxation time in the medial femoral articular cartilage 6months following anterior cruciate ligament reconstruction.

Quadriceps weakness following anterior cruciate ligament reconstruction (ACLR) is linked to decreased patient-reported function, altered lower extremity biomechanics and tibiofemoral joint space narrowing. It remains unknown if quadriceps weakness is associated with early deleterious changes to femoral cartilage composition that are suggestive of posttraumatic osteoarthritis development. The purpose of the cross-sectional study was to determine if quadriceps strength was associated with T1ρ relaxation times, a marker of proteoglycan density, of the articular cartilage in the medial and lateral femoral condyles 6months following ACLR. It is hypothesized that individuals with weaker quadriceps would demonstrate lesser proteoglycan density. Twenty-seven individuals (15 females, 12 males) with a patellar tendon autograft ACLR underwent isometric quadriceps strength assessments in 90°of knee flexion during a 6-month follow-up exam. Magnetic resonance images (MRI) were collected bilaterally and voxel by voxel T1ρ relaxation times were calculated using a five-image sequence and a monoexponential equation. Following image registration, the articular cartilage for the weight-bearing surfaces of the medial and lateral femoral condyles (MFC and LFC) were manually segmented and further sub-sectioned into posterior, central and anterior regions of interest (ROI) based on the corresponding meniscal anatomy viewed in the sagittal plane. Univariate linear regression models were used to determine the association between quadriceps strength and T1ρ relaxation times in the entire weight-bearing MFC and LFC, as well as the ROI in each respective limb. Lesser quadriceps strength was significantly associated with greater T1ρ relaxation times in the entire weight-bearing MFC (R2 = 0.14, P = 0.05) and the anterior-MFC ROI (R2 = 0.22, P = 0.02) of the ACLR limb. A post hoc analysis found lesser strength and greater T1ρ relaxation times were significantly associated in a subsection of participants (n = 18) without a concomitant medial tibiofemoral compartment meniscal or chondral injury in the entire weight-bearing MFC, as well as anterior-MFC and central-MFC ROI of the ACLR and uninjured limb. The association between weaker quadriceps and greater T1ρ relaxation times in the MFC suggests deficits in lower extremity muscle strength may be related to cartilage composition as early as 6months following ACLR. Maximizing quadriceps strength in the first 6months following ACLR may be critical for promoting cartilage health early following ACLR. Prognostic level 1.

Effects of Prior Heavy Exercise in Heart Failure with Preserved Ejection Fraction on V̇O2 Kinetics

Exercise intolerance and muscle dysfunction characterize heart failure with preserved ejection fraction (HFpEF). Prior heavy exercise (“priming”) speeds pulmonary oxygen uptake (V̇O2p) kinetics in older adults. The mechanism behind speeding of V̇O2p kinetics following priming is either through increased oxygen delivery to the exercising muscles or increased intracellular metabolic activity; the former remains dominant in older and diseased populations.PURPOSEWe tested the hypothesis that priming would not speed V̇O2p on‐kinetics in patients with HFpEF due to muscle dysfunction commonly found in patients with HFpEF.METHODSEight HFpEF patients, 4 high‐fit (CTL‐HF), and 5 low‐fit age‐matched controls (CTL‐LF) performed 3 repetitions of 2 exercise transitions: MOD1, rest to 4‐min moderate‐intensity cycling; and MOD2, MOD1 preceded by 2‐min heavy‐intensity cycling and 5‐min rest. V̇O2p (oxidative metabolism; pulmonary gas exchange), heart rate (HR, cardiac function; ECG), total peripheral resistance (TPR, vascular function; ModelFlow), and tissue oxygenation of the vastus lateralis (TOI, muscle oxygen delivery; near‐infrared spectroscopy) on‐kinetics were measured, linearly interpolated, time‐aligned, and averaged. V̇ O2p and HR were curve‐fitted using a monoexponential equation to yield a time constant (tau). ΔTPR and ΔTOI were calculated from baseline at 15s, 30s, and end‐exercise. Significance was P&lt;0.05.RESULTSHFpEF V̇O2p on‐kinetics (tau 45 ± 15 s) were slower than CTL‐HF (25 ± 6 s) but not CTL‐LF (50 ± 19 s; P=0.008). MOD2 V̇O2p on‐kinetics (tau 37 ± 14 s) were faster than MOD1 (47 ± 19 s), pooled across groups (P=0.039). Although not statistically significant, the priming effect was notably smaller in HFpEF compared to control groups (9% in HFpEF, 33% in low‐fit controls, and 30% faster in high‐fit controls). HR on‐kinetics were slower following priming in all groups (MOD1 tau 34 ± 21 vs. MOD2 44 ± 27 s; P=0.001), suggesting cardiac output as an unlikely assistant to the observed speeding in V̇O2p on‐kinetics across groups. TPR was lower in CTL‐HF throughout exercise compared to HFpEF (all P&lt;0.038) and at 30s and end‐exercise compared to CTL‐LF (all P&lt;0.032), pooled across conditions with no effect of priming. TOI in CTL‐HF increased at 15–30s (all P≤0.024) while HFpEF patients and CTL‐LF had decreased TOI at 15–30s in MOD1 (all P≤0.024). The latter suggests lower oxygen delivery at early exercise onset compared to CTL‐HF. Priming reduced TOI in HFpEF at 30s (P=0.033) and CTL‐HF throughout exercise (all P&lt;0.05), suggesting either lower muscle oxygen delivery or greater mitochondrial activity following priming.CONCLUSIONSlow HFpEF V̇O2p on‐kinetics may not be speeded by priming exercise. Heart rate and vascular responses to priming may not account for speeding of V̇O2p on‐kinetics in older adults. Intracellular mechanisms may limit HFpEF exercise tolerance.Support or Funding InformationCanadian Institutes of Health ResearchThis abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Fatigability, oxygen uptake kinetics and muscle deoxygenation in incomplete spinal cord injury during treadmill walking.

The purpose of the present study was to characterize hypothesized relationships among fatigability and cardiorespiratory fitness in individuals with chronic motor-incomplete SCI (iSCI) during treadmill walking. The theoretical framework was that exacerbated fatigability would occur concomitantly with diminished cardiorespiratory fitness in people with iSCI. Subjects with iSCI (n=8) and an able-bodied reference group (REF) (n=8) completed a 6-min walking bout followed by a walking bout of 30-min or until volitional exhaustion, both at a self-selected walking speed. Fatigability was assessed using both perceived fatigability and performance fatigability measures. Pulmonary oxygen uptake kinetics (VO2 on-kinetics) was measured breath-by-breath and changes in deoxygenated hemoglobin/myoglobin concentration (∆[HHb]) of the lateral gastrocnemius was measured by near-infrared spectroscopy. Adjustment of VO2 and ∆[HHb] on-kinetics were modeled using a mono-exponential equation. Perceived fatigability and performance fatigability were 52% and 44% greater in the iSCI group compared to the REF group (p=0.003 and p=0.004). Phase II time constant (τp) of VO2 on-kinetics and ∆[HHb] ½ time during resting arterial occlusion were 55.4% and 16.3% slower in iSCI vs REF (p<0.01 and p=0.047, respectively). The results of the present study may suggest that compromised O2 delivery and/or utilization may have contributed to the severity of fatigability in these individuals with iSCI. The understanding of the extent to which fatigability and VO2 and Δ[HHb] on-kinetics impacts locomotion after iSCI will assist in the future development of targeted interventions to enhance function.

SU‐F‐T‐477: Investigation of DEFGEL Dosimetry Using MRI

Purpose:The DEFGEL dosimeter/phantom allows for the measurement of 3D dose distributions while maintaining tissue equivalence and deformability. Although DEFGEL is traditionally read out with optical CT, the use of MRI would permit the measurement of 3D dose distributions in optically interfering configurations, like while embedded in a phantom. To the knowledge of the authors, this work is the first investigation that uses MRI to measure dose distributions in DEFGEL dosimeters.Methods:The DEFGEL (6%T) formula was used to create 1 cm thick, 4.5 cm diameter cylindrical dosimeters. The dosimeters were irradiated using a Varian Clinac 21EX linac. The MRI based transverse relaxation rate (R2) of the gel was measured in a central slice of the dosimeter with a Spin‐Echo (SE) pulse sequence on a 3T GE SIGNA PET/MR scanner. The R2 values were fit to a monoexponential dose response equation using in‐house software (MATLAB).Results:The data was well fit using a monoexponential fit for R2 as a function of absorbed dose (R2 = 0.9997). The fitting parameters of the monoexponential fit resulted in a 0.1229 Gy−1s−1 slope. The data also resulted in an average standard deviation of 1.8% for the R2 values within the evaluated ROI.Conclusion:The close fit for the dose response curve shows that a DEFGEL based dosimeter can be paired with a SE MRI acquisition. The Type A uncertainty of the MRI method shows adequate precision, while the slope of the fit curve is large enough that R2 differences between different gel doses are distinguishable. These results suggest that the gel could potentially be used in configurations where an optical readout is not viable, such as measurements with the gel dosimeter positioned inside larger or optically opaque phantoms.This work is partially funded by NIH grant R01CA190298.

A modified isotope dilution equation predicts vitamin A total body stores in individuals

Isotope dilution is used to successfully predict vitamin A (VA) total body stores (TBS) in populations but does not typically work for individuals. Using plasma kinetic data from 33 healthy young adults dosed with [13C10]retinyl acetate, we determined TBS using model‐based compartmental analysis (Simulation, Analysis and Modelling software [SAAM]) vs the equation TBS = F x S x (1/SA), where F= fraction of the orally administered stable isotope dose in stores, S= ratio of specific activity of retinol in plasma to that in stores, and SA = VA specific activity in plasma at 3 d post dosing. A high correlation (R=0.92) was found for the population. We found that the fractional catabolic rate (FCR) was a proxy for F and developed a mono‐exponential equation using 7 and 14 d data to predict F in individual subjects (R=0.999). Since S is ~1 at 3 d (when VA SA in stores crosses over plasma), the equation for d 3 simplifies to TBS = F x (1/SA). That is, by collecting blood samples at 3, 7 and 14 d and then calculating FCR based on 7 and 14 d data, we can accurately estimate an individual's TBS as individual F x (1/SA) at 3 d (R=0.94).This study was supported by BBSRC.

Investigation of Apparent Diffusion Coefficient from Ultra-high b-Values in Parkinson's Disease.

To assess brain damage in Parkinson's disease (PD) based on apparent diffusion coefficient (ADC) data obtained from ultra-high b-values. Eighteen PD patients and 18 controls received diffusion-weighted imaging (DWI) with standard b-values (0, 1,000 s/mm(2)) and 15 b-values (0-5,000 s/mm(2)). Standard ADC (ADCst) maps were calculated from standard b-values, while maps of pure diffusion coefficients (D), pseudo-diffusion coefficients (D(*)), and ultra-high ADCs (ADCuh) were calculated from the 15 b-values using a tri-component model. In this model, D and D(*) values were quantified with a bi-exponential equation using b-values less than 2,000 s/mm(2), while ADCuh was quantified by fitting the signals at ultra-high b-values (2,000-5,000 s/mm(2)) to the mono-exponential equation. ADCst, ADCuh, D, and D(*) of the globus pallidus (GP), putamen (P), and substantia nigra (SN) were compared between PD patients and normal control subjects. ADCuh of the GP, P, and SN was significantly lower in PD patients than those in control subjects (P < 0.001), while ADCst, D, and D(*) of the GP, P and SN were not different between the two groups (P > 0.05). ADCuh may be a useful measurement for evaluating brain damage in PD patients. • DWI with ultra-high b-values may provide new insight into Parkinson's disease pathology • ADC calculated using ultra-high b-values is different between PD and controls • ADC uh may be associated with water transportation by aquaporins.

Myocardial blood flow assessment in cardiac amyloidosis using myocardial contrast echocardiography

Cardiac amyloidosis (CA) patients may present with angina and coronary syndromes. Cardiac biomarkers are chronically elevated in some cases. Many proceed with coronary investigation which often reveals angiographically patent vessels. An explanation for their presentation is thought to be due to microvascular amyloid deposition resulting in microvascular dysfunction. We performed vasodilator myocardial contrast echocardiography (MCE) on a patient with CA to assess myocardial blood flow reserve (MBFR). She previously had patent epicardial coronary arteries on coronary angiography and a normal dobutamine stress echocardiogram. Real-time MCE was performed according to an established protocol using a commercial ultrasound machine and contrast agent. Images were recorded in the 3 apical views with low-power settings at a mechanical index of 0.1. Flash-impulse imaging at a high mechanical index (1.0) was performed to achieve complete myocardial bubble destruction, after which 10 end-systolic frames were recorded digitally in each view. Imaging was repeated after dipyridamole infusion. Background-subtracted plots of peak myocardial contrast intensity (representingmyocardial blood volume A) versus pulsing intervals (representing time) were constructed by QLab software to fit the monoexponential function conventional equation: y=A (1−e− t). From these plots, the slope of the replenishment curve was determined (representing myocardial blood velocity ). Per segment, the product of A and yielded rest MBF and post-dipyridamole MBFs (stress MBF), respectively. MBFR was calculated as the ratio of peak MBF to resting MBF. The results show a marked reduction in MBFR. This supports the hypothesis of microvascular dysfunction and adds to our pathophysiological understanding of this challenging condition.

Combined effect of polymeric nanocapsules and chitosan hydrogel on the increase of capsaicinoids adhesion to the skin surface.

This work explored the effect of the encapsulation in polymeric nanocapsules, as well as of the incorporation of such nanoparticles in a chitosan hydrogel, on the skin adhesion and skin penetration/permeation of capsaicinoids (capsaicin and dihydrocapsaicin), which are used as topical analgesic to treat chronic pain. The skin experiments were performed using a modified (drug adhesion and drug diffusion) and a normal Franz diffusion cell (drug diffusion) with porcine skin as membrane. The AUC0-h of the washability profile (% washed away vs. time) determined for the formulation combining both factors studied (chitosan hydrogel containing drug-loaded nanocapsules) was 198.88 +/- 10.05/153.53 +/- 5.99, for capsaicin and dihydrocapsaicin respectively, significantly lower than the values observed for the chitosan hydrogel containing free drug (291.57 +/- 3.83/278.18 +/- 5.28) and for the hydroxyethyl cellulose containing drug-loaded nanocapsules (245.47 +/- 13.18/197.69 +/- 15.78). By adequate fitting to the monoexponential first order equation, the washing rate values indicated that the nanocapsules were more efficient in increasing the drugs skin adhesion than the chitosan gel. Regarding the skin penetration/permeation study, after washing the skin, the formulation which presented the lowest washing rate (chitosan gel containing nanocapsules) was the one which led to a higher amount of capsaicinoids in the skin layers (epidermis and dermis). Without washing the skin, the nanoencapsules caused retention of the drugs in the outer skin layer (epidermis). In conclusion, the skin adhesion of the nanocapsules and their capability of controlling the drug diffusion were shown. Combining chitosan gel to nanocapsules led to a formulation of great skin bioadhesion.

Poly (vinyl alcohol)/SiO2 composite microsphere based on Pickering emulsion and its application in controlled drug release

In this paper, with W/O Pickering emulsion stabilized by modified SiO2 nanoparticles as template, PVA/SiO2 composite microspheres with PVA hydrogel cores and shells of SiO2 nanoparticles are successfully fabricated through freezing/thawing method. The final structure and constituents of the products are investigated through SEM, FTIR, and TGA. The PVA/SiO2 composite microspheres obtained are applied as a drug carrier to study their controlled release behaviors and methylene blue is used as a model drug. The effect of PVA concentration, SiO2 nanoparticle concentration, and freezing/thawing cycles on the morphology of products and release behaviors is studied. All release curves are, respectively, fitted by Monoexponential equation, Higuchi equation, Weibull equation, and Hixson-Crowell equation. Weibull equation is found to give the best fit to the release process. The fitted results prove that the drug release from the PVA/SiO2 composite microspheres follows Fick diffusion.

Can a first‐order exponential decay model fit heart rate recovery after resistance exercise?

The time-constant of postexercise heart rate recovery (HRRτ ) obtained by fitting heart rate decay curve by a first-order exponential fitting has being used to assess cardiac autonomic recovery after endurance exercise. The feasibility of this model was not tested after resistance exercise (RE). The aim of this study was to test the goodness of fit of the first-order exponential decay model to fit heart rate recovery (HRR) after RE. Ten healthy subjects participated in the study. The experimental sessions occurred in two separated days and consisted of performance of 1 set of 10 repetitions at 50% or 80% of the load achieved on the one-repetition maximum test [low-intensity (LI) and high-intensity (HI) sessions, respectively]. Heart rate (HR) was continuously registered before and during exercise and also for 10 min of recovery. A monoexponential equation was used to fit the HRR curve during the postexercise period using different time windows (i.e. 30, 60, 90, … 600 s). For each time window, (i) HRRτ was calculated and (ii) variation of HR explained by the model (R(2) goodness of fit index) was assessed. The HRRτ showed stabilization from 360 and 420 s on LI and HI, respectively. Acceptable R(2) values were observed from the 360 s on LI (R(2) > 0.65) and at all tested time windows on HI (R(2) > 0.75). In conclusion, this study showed that using a minimum length of monitoring (~420 s) HRR after RE can be adequately modelled by a first-order exponential fitting.