Reference Equations Research Articles

Normative reference values, determinants and regression equations for the incremental shuttle walk test (ISWT) in healthy Asian population aged 21 to 80 years.

The validated Incremental Shuttle Walk Test (ISWT) is widely used for evaluating maximal exercise capacity, with the distance-walked (IWSD) as the primary outcome. However, there are no normative reference values (NRV) and reference equations to predict ISWD for the Singaporean population. This study aims to establish the NRV and reference equations for ISWD in healthy Singaporeans aged 21 to 80 and investigate the determining variables during ISWT. This cross-sectional study recruited community-dwelling healthy subjects aged 21-80 from the community via convenience sampling. Each subject completed two trials of the ISWT according to the standard protocol. Variables measured during the trials included ISWD, pre-and post-test heart rate (HR), oxygen saturation, blood pressure (BP), modified Borg's dyspnoea score and Borg's rate of perceived exertion (RPE). 199 healthy Singaporean (females = 114, males = 85) participated in the study. The overall median ISWD was 660.0 metres (m) [interquartile range (IQR):440.0-850.0]. The age-stratified mean ISWD ranged from 430.0 m (IQR:350.0-450.0) (aged 60-80) to 480.0 m (IQR:438.0-650.0) (aged 40-59) to 780.0 m (IQR:670.0-960.0) (aged 21-39). Gender, age, weight, height and HR change (highest post-test HR minus pre-test HR) were the most significant variables (p < 0.001). IWSD (m) = 651.4(Height, m) +89.7(Gender, male = 1; female = 0) -6.31(Age, years) -3.61(Weight, kilograms) +2.54(HR change, beats per minute); R2 = 0.741. Previously published ISWT reference equations cannot accurately predict the ISWD in the Singaporean population. This study investigated the ISWD NRV and established reference equations for healthy Singaporeans aged 21-80. The information would be beneficial in setting performance benchmarks to guide physical assessment, intervention and rehabilitation.

Are the Reference Equations for Maximal Respiratory Pressure in Children Adequately Predicting Their Value?

Are the Reference Equations for Maximal Respiratory Pressure in Children Adequately Predicting Their Value?

Functional capacity and dyspnea during follow-up after acute pulmonary embolism

BackgroundDissecting the determinants of functional capacity during long-term follow-up after acute pulmonary embolism (PE) can help to better characterize a patient population with persisting limitation. MethodsIn a prospective cohort study, consecutive unselected survivors of acute PE underwent 3- and 12-month follow-up, including six-minute walking distance (6MWD) and dyspnea assessment with the modified Medical Research Council (mMRC) scale. We used reference equations adjusting for age, sex, and anthropometric measurements to define abnormal 6MWD. ResultsOverall, 323 of 363 (89.0%) patients had at least one recorded 6MWD value at one year. At 3 months, the prevalence of abnormal 6MWD was 21.9% and at 12 months it was 18.3%. At 3 and 12 months, 58.8% and 52.1% with abnormal 6MWD did not report dyspnea, respectively. On average and during follow-up, 6MWD significantly improved with time, while the mMRC dyspnea scale did not. Abnormal 6MWD was associated with younger age (odds ratio per decade, 0.91; 95% CI, 0.88-0.94), higher body mass index (1.10; 1.03-1.17), smoking (3.53; 1.34-9.31), intermediate- or high-risk PE (3.21; 1.21-8.56), and higher mMRC grading (2.28; 1.59-3.27). Abnormal 6MWD at 3 months was associated with the prospectively defined endpoint of post-PE impairment (3.72; 1.50-9.28) and with poor disease-specific and generic health-related quality of life. ConclusionThree months after PE, 37% of patients reported dyspnea and 22% had abnormal 6MWD. After a year, 20% still had abnormal 6MWD. Dyspnea correlated with abnormal 6MWD, but over 50% of patients with abnormal 6MWD did not report dyspnea. Abnormal 6MWD predicted subsequent post-pulmonary embolism impairment and worse long-term quality of life. Clinical Trial RegistrationGerman Clinical Trials Register Identifier DRKS00005939.

Performance on the iSTEP and 10m-ISWT in boys with haemophilia.

Boys with haemophilia (BwH) have improved health outcomes. Measures of physical function in haemophilia are not challenging or sensitive enough to reflect physical limitations or guide rehabilitation. To identify meaningful tests, we aimed to: evaluate the performance of BwH on two physical performance measures: iSTEP and 10m-ISWT; identify factors which predict performance and compare BwH to their unaffected peers. BwH completed both iSTEP and 10m-ISWT. Disease severity, age, BMI, HJHS, lower limb muscle torque, time spent in moderate to vigorous physical activity, sedentary time, were included as factors to predict performance. Results were compared to unaffected peers. 43 boys median age 10 (10 mild/moderate, 26 severe, 7 inhibitors) were recruited. BwH were less likely to complete the iSTEP and performed less well on the 10m-ISWT than age matched peers. Ceiling effects were apparent for iSTEP, but not the 10m-ISWT test. Age was the only significant predictor for performance in the iSTEP, with older boys being more likely to achieve a higher level or complete the test. Greater age, lower BMI, milder disease severity and more time spent in MVPA all predicted better performance on the 10m-ISWT, with BMI and habitual physical activity a potential rehabilitation focus for underperforming individuals. HJHS and muscle strength did not predict performance on either test. Despite the space need to conduct the 10m-ISWT, it appears to be a superior performance measure than the iSTEP in BwH and provides clinically meaningful information, which can be interpreted using age-specific normative reference equations.

The modified Borg/6-min walk distance ratio: a method to assess exertional breathlessness and leg discomfort using the 6-min walk test.

The 6-min walk test (6MWT) is widely used to assess exercise capacity across chronic health conditions, but is currently not useful to assess symptoms, as the scores do not account for the 6-min walk distance (6MWD). We aimed to 1) develop normative reference equations for breathlessness and leg discomfort intensity expressed as modified Borg (mBorg)/6MWD ratios; and 2) validate the equations in people with COPD. Analysis of people aged ≥40 years who performed two 6MWTs (on a 20-m course) in the Canadian Cohort Obstructive Lung Disease (CanCOLD) study: a healthy cohort (n=291; mean±sd age 67.5±9.4 years; 54% male) with normal 6MWD and lung function, and a COPD cohort (n=156; age 66.2±9.0 years; 56% male; forced expiratory volume in 1 s (FEV1)/forced vital capacity 56.6±8.2%; FEV1 74.4±18.6% pred). The mBorg score was calculated as the Borg 0-10 category ratio intensity rating of breathlessness or leg discomfort recorded at the end of the 6MWT +1 (range 1-11), to avoid zeros and yield ratios proportional to the symptom score and 6MWD-1. Using data from the healthy cohort, sex-specific normative reference equations for breathlessness and leg discomfort mBorg/6MWD ratios were developed using multivariable linear regression, accounting for age, and body mass or body mass index. In the COPD cohort, abnormal breathlessness and leg discomfort (mBorg/6MWD>upper limit of normal) showed strong concurrent validity with worse airflow limitation, Medical Research Council breathlessness and COPD Assessment Test scores. Normative references for the mBorg/6MWD ratio are presented to assess breathlessness and leg discomfort responses to the 6MWT in COPD.

Race-Specific Spirometry Equations Do Not Improve Models of Dyspnea and Quantitative Chest CT Phenotypes

Race-specific spirometry reference equations are used globally to interpret lung function for clinical, research, and occupational purposes, but inclusion of race is under scrutiny. Does including self-identified race in spirometry reference equation formation improve the ability of predicted FEV1 values to explain quantitative chest CT abnormalities, dyspnea, or Global Initiative for Chronic Obstructive Lung Disease (GOLD) classification? Using data from healthy adults who have never smoked in both the National Health and Nutrition Survey (2007-2012) and COPDGene study cohorts, race-neutral, race-free, and race-specific prediction equations were generated for FEV1. Using sensitivity/specificity, multivariable logistic regression, and random forest models, these equations were applied in a cross-sectional analysis to populations of individuals who currently smoke and individuals who formerly smoked to determine how they affected GOLD classification and the fit of models predicting quantitative chest CT phenotypes or dyspnea. Race-specific equations showed no advantage relative to race-neutral or race-free equations in models of quantitative chest CT phenotypes or dyspnea. Race-neutral reference equations reclassified up to 19%of Black participants into more severe GOLD classes, while race-neutral/race-free equations may improve model fit for dyspnea symptoms relative to race-specific equations. Race-specific equations offered no advantage over race-neutral/race-free equations in three distinct explanatory models of dyspnea and chest CT scan abnormalities. Race-neutral/race-free reference equations may improve pulmonary disease diagnoses and treatment in populations highly vulnerable to lung disease.

A Simple Equation to Estimate Maximal Oxygen Uptake in Older Adults Using the 6 min Walk Test, Sex, Age and Body Mass Index.

The 6 min walk test (6MWT) is used in clinical and epidemiological practice as a simple tool to evaluate the maximal aerobic exercise capacity (VO2max). To date, little evidence has been provided regarding regression equation models to predict VO2max in older adults. Therefore, the main purpose of the study was to develop a reference equation to estimate objectively measured VO2max, based on the 6MWT, sex, age and body mass index (BMI). In this observational prospective study, we collected the data from 233 asymptomatic participants aged 60-80 years (52.4% women). VO2max and the 6MWT were measured using standardized protocols. BMI was calculated as weight (kg) divided by height squared (m2). To be able to develop the predictive equation for VO2max, we used linear generalized estimating equations (GEE). Older men performed better in VO2max (30.9 ± 8.8 vs. 26.3 ± 6.3 mL/kg/min, p < 0.001) and the 6MWT (673.9 ± 58.7 vs. 642.3 ± 48.0 m, p < 0.001), compared to women. VO2max was correlated with the 6MWT (r = 0.71, p < 0.001), sex (r = -0.29, p < 0.001), age (r = -0.62, p < 0.001) and BMI (r = -0.38, p < 0.001). The model to predict VO2max included: VO2max (mL/kg/min) = 59.44 - 3.83 *, sex (1-men; 2-women) - 0.56 *, age (years) - 0.48 *, BMI (kg/m2) + 0.04 *, and the 6MWT (m) (R = 0.85; R2 = 72.3%, SEE = 3.99 mL/kg/min, p < 0.001). The newly developed regression equation can be a guideline in clinical and epidemiological practice to predict the VO2max in apparently healthy older adults.

Measuring Evapotranspiration Suppression from the Wind Drift and Spray Water Losses for LESA and MESA Sprinklers in a Center Pivot Irrigation System

Wind drift and evaporation loss (WDEL) of mid-elevation spray application (MESA) and low-elevation spray application (LESA) sprinklers on a center pivot and linear-move irrigation machines are measured and reported to be about 20% and 3%, respectively. It is important to estimate the fraction of WDEL that cools and humidifies the microclimate causing evapotranspiration (ET) suppression, mitigating the measured irrigation system losses. An experiment was conducted in 2018 and 2019 in a commercial spearmint field near Toppenish, Washington. The field was irrigated with an 8-span center pivot equipped with MESA but had three spans that were converted to LESA. All-in-one weather sensors (ATMOS-41) were installed just above the crop canopy in the middle of each MESA and LESA span and nearby but outside of the pivot field (control) to record meteorological parameters on 1 min intervals. The ASCE Penman–Monteith (ASCE-PM) standardized reference equations were used to calculate grass reference evapotranspiration (ETo) from this data on a one-minute basis. A comparison was made for the three phases of before, during, and after the irrigation system passed the in-field ATMOS-41 sensors. In addition, a small unmanned aerial system (UAS) was used to capture 5-band multispectral (ground sampling distance [GSD]: 7 cm/pixel) and thermal infrared images (GSD: 13 cm/pixel) while the center pivot irrigation system was irrigating the field. This imagery data was used to estimate crop evapotranspiration (ETc) using a UAS-METRIC energy balance model. The UAS-METRIC model showed that the estimated ETc under MESA was suppressed by 0.16 mm/day compared to the LESA. Calculating the ETo by the ASCE-PM method showed that the instantaneous ETo rate under the MESA was suppressed between 8% and 18% compared to the LESA. However, as the time of the ET suppression was short, the total amount of the estimated suppressed ET of the MESA was less than 0.5% of the total applied water. Overall, the total reduction in the ET due to the microclimate modifications from wind drift and evaporation losses were small compared to the reported 17% average differences in the irrigation application efficiency between the MESA and the LESA. Therefore, the irrigation application efficiency differences between these two technologies were very large even if the ET suppression by wind drift and evaporation losses was accounted for.

Reference equations for quadriceps strength, endurance and power: a multicentre study.

The lack of reference values of lower-limb muscle function hinders the clinical recommendations of its measurement in patients with COPD. Therefore, this study aimed to develop reference equations to predict reference values for quadriceps strength, endurance and power and evaluate their construct validity in patients with COPD. Quadriceps strength, endurance and power were assessed in 158 healthy individuals and 87 patients with COPD. In addition, patients with COPD performed a 6-min walk test (6MWT) and a 1-min sit-to-stand test (1STS). Multiple linear regressions were performed to develop reference equations. The proportion of patients with COPD with reduced quadriceps function was determined, and correlations between quadriceps strength, endurance and power expressed in percentage of predicted values and 6MWT and 1STS performance were used to document the construct validity of the reference equation. Except for quadriceps isometric endurance, the proposed reference equations explained 50-70% of the variance of the quadriceps properties in healthy individuals. All quadriceps properties were systematically reduced in a large proportion of patients with COPD compared to healthy individuals. Correlation coefficients between quadriceps properties expressed in percentage of predicted values and 6MWT and 1STS performance ranged between 0.28 and 0.49 (all p<0.05). In healthy individuals, age, sex, height and body mass index explained 50-70% of the variance of quadriceps strength, endurance and power. When expressed in percentage of predicted values, these quadriceps properties correlated with 6MWT and 1STS performance, suggesting construct validity of the reference values in patients with COPD.

Implementation of instantaneous comparison methods in temperature gradient evaluation of stirred liquid temperature baths

Temperature gradient is an important performance indicator of a stirred liquid bath. Its evaluation requires measuring the temperature differences between different bath positions. A common way to do that is to place two SPRTs at two positions and measure their resistances against a standard resistor (R SPRT1/R S and R SPRT2/R S) sequentially (the sequential method). A drawback of this method is the existence of a time gap between the two measurements rendering the results susceptible to temporal temperature variation. The instantaneous comparisons method offers a better solution by measuring the resistance ratio of two SPRTs directly (R SPRT1/R SPRT2) and deriving their temperature difference at the same moment eliminating the time gap. To implement this method at the Standards and Calibration Laboratory (SCL) of Hong Kong, the resistance ratio of SPRT1 to a standard resistor (R SPRT1/R s) is firstly measured to determine the initial bath temperature. After that, the resistance ratios of SPRT1 to SPRT2 (R SPRT1/R SPRT2) are measured with the two SPRTs placed at different positions and immersion depths in the bath. This paper describes the derivation of the temperature difference from the SPRT resistance ratio using the ITS-90 reference equations and the estimation of the measurement uncertainties. The potential of reducing the uncertainties of measured temperature gradient by leveraging the correlation of the two SPRTs calibrated at the same set of temperature fixed points is discussed. The paper also compares the calibration results obtained by the instantaneous comparisons method and the sequential method.

Use of new paediatric VO2max reference equations to evaluate aerobic fitness in overweight or obese children with congenital heart disease.

Overweight and obesity in children with congenital heart disease (CHD) represent an alarming cardiovascular risk. Promotion of physical activity and cardiac rehabilitation in this population requires assessing the level of aerobic fitness (VO2max) by a cardiopulmonary exercise test (CPET). Nevertheless, the interpretation of CPET in overweight/obese children with CHD remains challenging as VO2max is affected by both the cardiac condition and the body mass index (BMI). The new paediatric VO2max Z-score reference equations, based on a logarithmic function of VO2max, height and BMI, were applied to overweight/obese children with a CHD and compared with overweight/obese children without any other chronic condition. In this cross-sectional controlled study, 344 children with a BMI > 85th percentile underwent a CPET (54% boys; mean age 11.5 ± 3.1 years; 100 CHD; 244 controls). Using the VO2max Z-score equations, aerobic fitness was significantly lower in obese/overweight CHD children than that in matched obese/overweight control children (-0.43 ± 1.27 vs. -0.01 ± 1.09; P = 0.02, respectively), and the proportion of children with impaired aerobic fitness was significantly more important in obese/overweight CHD children than in matched controls (17% vs.6%, P = 0.02, respectively). The paediatric VO2max Z-score reference equations also identified specific complex CHD at risk of aerobic fitness impairment (univentricular heart and right outflow tract anomalies). Using Cooper's weight- and height-based linear equations, similar matched-comparisons analyses found no significant group differences. As opposed to the existing linear models, the new paediatric VO2max Z-score equations can discriminate the aerobic fitness of obese/overweight children with CHD from that of obese/overweight children without any chronic disease. ClinicalTrials.gov NCT04815577.

Race-Specific Interpretation of Spirometry: Impact on the Lung Allocation Score.

Rationale: Interpretation of spirometry using race-specific reference equations may contribute to health disparities via underestimation of the degree of lung function impairment in Black patients. The use of race-specific equations may differentially affect patients with severe respiratory disease via the use of percentage predicted forced vital capacity (FVCpp) when included in the lung allocation score (LAS), the primary determinant of priority for lung transplantation. Objectives: To determine the impact of a race-specific versus a race-neutral approach to spirometry interpretation on the LAS among adults listed for lung transplantation in the United States. Methods: We developed a cohort from the United Network for Organ Sharing database including all White and Black adults listed for lung transplantation between January 7, 2009, and February 18, 2015. The LAS at listing was calculated for each patient under race-specific and race-neutral approaches, using the FVCpp generated from the Global Lung Function Initiative equation corresponding to each patient's race (race-specific) or from the Global Lung Function Initiative "other" (race-neutral) equation. Differences in LAS between approaches were compared by race, with positive values indicating a higher LAS under the race-neutral approach. Results: In this cohort of 8,982 patients, 90.3% were White and 9.7% were Black. The mean FVCpp was 4.4% higher versus 3.8% lower among White versus Black patients (P < 0.001) under a race-neutral compared with a race-specific approach. Compared with White patients, Black patients had a higher mean LAS under both a race-specific (41.9 vs. 43.9; P < 0.001) and a race-neutral (41.3 vs. 44.3; P < 0.001) approach. However, the mean difference in LAS under a race-neutral approach was -0.6 versus +0.6 for White versus Black patients (P < 0.001). Differences in LAS under a race-neutral approach were most pronounced for those in group B (pulmonary vascular disease) (-0.71 vs. +0.70; P < 0.001) and group D (restrictive lung disease) (-0.78 vs. +0.68; P < 0.001). Conclusions: A race-specific approach to spirometry interpretation has potential to adversely affect the care of Black patients with advanced respiratory disease. Compared with a race-neutral approach, a race-specific approach resulted in lower LASs for Black patients and higher LASs for White patients, which may have contributed to racially biased allocation of lung transplantation. The future use of race-specific equations must be carefully considered.

Race-neutral equations for assessment of lung function in children with thalassemia.

The aim of this study was to assess pulmonary dysfunction in children with transfusion-dependent thalassemia (TDT) using the Global Lung Function Initiative (GLI) 2022 race-neutral spirometric reference equations and to determine the main predicting factors. The spirometric results of 68 children with TDT were compared to the results of 68 healthy control subjects using both GLI-2012 reference equations for Caucasians and GLI-2022 global equations. Associations between the spirometric data and various anthropometric, clinical, and laboratory parameters were analyzed to detect predictors of pulmonary dysfunction in this group of patients. Children with TDT showed significantly lower values of FVC and FEV1 with a predominance of the restrictive pattern (23.53%). Thalassemic children with the restrictive pattern were significantly older, had a longer duration of regular blood transfusion, lower height, weight, and BMI z-scores, higher average serum ferritin, and higher frequency of having a serum ferritin level >2500 ng/mL. The strongest predictor for having a restrictive spirometric pattern was high serum ferritin. Our analysis shows that the transition from GLI-2012 spirometric reference equations for Caucasians to the GLI-2022 global equations has led to a reduction in the prevalence rate of restrictive pulmonary dysfunction in children with TDT, which should not affect the patient outcome in the long term. Asymptomatic children with TDT exhibited a restrictive spirometric pattern in a significant proportion. The most important predictor was high serum ferritin. We encourage the inclusion of pulmonary function testing in the routine monitoring of patients with TDT, especially in older patients and those with iron overload.

Global, Race-Neutral Reference Equations and Pulmonary Function Test Interpretation

Race and ethnicity are routinely used to inform pulmonary function test (PFT) interpretation. However, there is no biological justification for such use, and it may reinforce health disparities. To compare the PFT interpretations produced with race-neutral and race-specific equations. In this cross-sectional study, race-neutral reference equations recently developed by the Global Lung Function Initiative (GLI) were used to interpret PFTs performed at an academic medical center between January 2010 and December 2020. The interpretations produced with these race-neutral reference equations were compared with those produced using the race and ethnicity-specific reference equations produced by GLI in 2012. The analysis was conducted from April to October 2022. The primary outcomes were differences in the percentage of obstructive, restrictive, mixed, and nonspecific lung function impairments identified using the 2 sets of reference equations. Secondary outcomes were differences in severity of these impairments. PFTs were interpreted from 2722 Black (686 men [25.4%]; mean [SD] age, 51.8 [13.9] years) and 5709 White (2654 men [46.5%]; mean [SD] age, 56.4 [14.3] years) individuals. Among Black individuals, replacing the race-specific reference equations with the race-neutral reference equations was associated with an increase in the prevalence of restriction from 26.8% (95% CI, 25.2%-28.5%) to 37.5% (95% CI, 35.7%-39.3%) and of a nonspecific pattern of impairment from 3.2% (95% CI, 2.5%- 3.8%) to 6.5% (95% CI, 5.6%-7.4%) and no significant change in the prevalence of obstruction (19.9% [95% CI, 18.4%-21.4%] vs 19.5% [95% CI, 18.0%-21.0%]). Among White individuals, replacing the race-specific reference equations with the race-neutral reference equations was associated with a decrease in the prevalence of restriction from 22.6% (95% CI, 21.5%-23.6%) to 18.0% (95% CI, 17.0%-19.0%), a decrease in the prevalence of a nonspecific pattern of impairment from 8.7% (95% CI, 7.9%-9.4%) to 4.0% (95% CI, 3.5%-4.5%), and no significant change in the percentage with obstruction from 23.9% (95% CI, 22.8%-25.1%) to 25.1% (95% CI, 23.9%- 26.2%). The race-neutral reference equations were associated with an increase in severity in 22.8% (95% CI, 21.2%-24.4%) of Black individuals and a decrease in severity in 19.3% (95% CI, 18.2%-20.3%) of White individuals vs the race-specific reference equations. In this cross-sectional study, the use of race-neutral reference equations to interpret PFTs resulted in a significant increase in the number of Black individuals with respiratory impairments along with a significant increase in the severity of the identified impairments. More work is needed to quantify the effect these reference equations would have on diagnosis, referral, and treatment patterns.

Exercise systolic blood pressure indexed to work rate predicts future risk of incident stroke

Abstract Funding Acknowledgements Type of funding sources: Public Institution(s). Main funding source(s): 1) The CircM network, Linköping University 2) The Swedish Stroke Association. Background Hypertension is a major risk factor for stroke. Exaggerated peak systolic blood pressure (SBP) during exercise is associated with increased risk of hypertension in normotensive subjects, whereas low, rather than high, peak exercise SBP predicts cardiovascular and all-cause mortality. Purpose We aimed to study the risk of incident fatal and non-fatal stroke in relation to absolute and work rate indexed exercise SBP, in patients referred for exercise testing. Methods We cross-linked clinical data from 14,428 bicycle ergometer exercise tests with data from the National Patient Registry and the Registry of Prescribed Medications up until December 2019. Subjects with a history of cerebrovascular disease were excluded, as well as subjects with submaximal tests, a drop in SBP during exercise, or with missing SBP data at the end of exercise. Baseline comorbidity was defined as diagnosis of, or treatment for, hypertension, diabetes, hyperlipidemia, and coronary artery disease (CAD). Work rate indexed SBP response (SBP/Watt-slope) was calculated as the increase in SBP during exercise divided by the increase in work rate. We applied Cox regression to calculate hazard ratios (HR) with 95% confidence intervals (95% CI) for the risk of incident stroke in association to peak SBP and the SBP/Watt-slope. We used absolute values as well the upper limit of normal (≥2 Z scores) of a recently published reference population, with reference equation including age, sex, SBP at rest, Wmax (for SBP peak only) and height (for SBP/W-slope only). Analyses were adjusted for age, sex, and baseline comorbidity. Results In total, 7,946 subjects (54% male, age 55±13 years) were included, with baseline comorbidity of hypertension (28%), diabetes (7%), hyperlipidemia (16%), and CAD (13%). During a median follow-up of 8.4 years (inter quartile range 5.8-11.5), 3.1% developed ischemic (2.2%) or hemorrhagic (1.0%) stroke. There were positive associations to future stroke with absolute peak exercise SBP (HR: 1.08 [1.03 – 1.13] per 10 mmHg increase) and with SBP/Watt-slope (HR: 1.09 [1.05 – 1.14] per 1 mmHg/10 Watt increase), but not after adjustment for sex, age and baseline comorbidity. However, having a SBP/Watt-slope ≥2 Z scores was associated with an increased risk for stroke (HR: 1.56 [1.08 – 2.25)] after adjustment for baseline comorbidity, whereas an adjusted SBP peak ≥2 Z scores was not (HR: 0.62 [0.32 – 1.21]). Conclusion A workload-indexed SBP response (SBP/Watt-slope) above the upper limit of normal may help to identify subjects with no history of cerebrovascular disease at risk of future stroke. In contrast, the absolute exercise SBP response to exercise does not add substantial information to the risk estimation above age, sex, and baseline comorbidity.

A Computationally Efficient Dynamic Grid Motion Approach for Arbitrary Lagrange–Euler Simulations

The present article addresses the topic of grid motion computation in Arbitrary Lagrange–Euler (ALE) simulations, where a fluid mesh must be updated to follow the displacements of Lagrangian boundaries. A widespread practice is to deduce the motion for the internal mesh nodes from a parabolic equation, such as the harmonic equation, introducing an extra computational cost to the fluid solver. An alternative strategy is proposed to minimize that cost by changing from the parabolic equation to a hyperbolic equation, implementing an additional time derivative term allowing an explicit solution of the grid motion problem. A fictitious dynamic problem is thus obtained for the grid, with dedicated material parameters to be carefully chosen to enhance the computational efficiency and preserve the mesh quality and the accuracy of the physical problem solution. After reminding the basics of the ALE expression of the Navier–Stokes equations and describing the proposed hyperbolic equation for the grid motion problem, the paper provides the necessary characterization of the influence of the fictitious grid parameters and the analysis of the robustness of the new approach compared to the harmonic reference equation on a significant 2D test case. A 3D test case is finally extensively studied in terms of computational performance to highlight and discuss the benefits of the hyperbolic equation for ALE grid motion.

An intermolecular potential for hydrogen: Classical molecular simulation of pressure-density-temperature behavior, vapor-liquid equilibria, and critical and triple point properties.

An intermolecular potential is reported for molecular hydrogen that combines two-body interactions from abinitio data with three-body interactions. The accuracy of the two-body potential is validated by comparison with experimental second virial coefficient data. Experimental pressure-density-temperature data are used to validate the addition of three-body interactions, often yielding very accurate predictions. Classical Monte Carlo simulations that neglect quantum effects are reported for the vapor-liquid equilibria (VLE), critical properties, and the triple point. A comparison with experimental data indicates that the effect of quantum interactions is to narrow the VLE phase envelope and to lower the critical temperature. The three-body interactions have a considerable influence on the phase behavior, resulting in good agreement with the experimental density. The critical properties of the two-body + three-body potential for hydrogen provide an alternative set of input parameters to improve the accuracy of theoretical predictions at temperatures above 100K. In the vicinity of the critical point, the coexistence densities do not obey the law of rectilinear diameters, which is a feature that has largely been overlooked in both experimental data and reference equations of state.

Cardiorespiratory Fitness in Individuals Post-stroke: Reference Values and Determinants

ObjectiveTo provide reference values of cardiorespiratory fitness for individuals post-stroke in clinical rehabilitation and to gain insight in characteristics related to cardiorespiratory fitness post stroke. DesignA retrospective cohort study. Reference equations of cardiopulmonary fitness corrected for age and sex for the fifth, 25th, 50th, 75th, and 95th percentile were constructed with quantile regression analysis. The relation between patient characteristics and cardiorespiratory fitness was determined by linear regression analyses adjusted for sex and age. Multivariate regression models of cardiorespiratory fitness were constructed. SettingClinical rehabilitation center. ParticipantsIndividuals post-stroke who performed a cardiopulmonary exercise test as part of clinical rehabilitation between July 2015 and May 2021 (N=405). Main Outcome MeasuresCardiorespiratory fitness in terms of peak oxygen uptake (V˙O2peak) and oxygen uptake at ventilatory threshold (V˙O2-VT). ResultsReferences equations for cardiorespiratory fitness stratified by sex and age were provided based on 405 individuals post-stroke. Median V˙O2peak was 17.8[range 8.4-39.6] mL/kg/min and median V˙O2-VT was 9.7[range 5.9-26.6] mL/kg/min. Cardiorespiratory fitness was lower in individuals who were older, women, using beta-blocker medication, and in individuals with a higher body mass index and lower motor ability. ConclusionsPopulation specific reference values of cardiorespiratory fitness for individuals post-stroke corrected for age and sex were presented. These can give individuals post-stroke and health care providers insight in their cardiorespiratory fitness compared with their peers. Furthermore, they can be used to determine the potential necessity for cardiorespiratory fitness training as part of the rehabilitation program for an individual post-stroke to enhance their fitness, functioning and health. Especially, individuals post-stroke with more mobility limitations and beta-blocker use are at a higher risk of low cardiorespiratory fitness.

Managing Water Stress in Olive (Olea europaea L.) Orchards Using Reference Equations for Midday Stem Water Potential

The irrigation surface of olive orchards has increased over recent decades. In zones affected, deficit irrigation scheduling is a must. The aim of this work was to study water stress management based on reference equations for midday stem water potential. An experiment was conducted over three seasons in Seville (Spain) from 2020 to 2022. A young hedgerow olive orchard (cv Manzanilla de Sevilla) was irrigated using three different treatments: Control (full irrigated), RDI, and Rainfed, in a completely randomized design (six replications). The midday stem water potential and leaf conductance were measured throughout the three seasons. Stem water potential was more sensitive to water stress than leaf conductance and showed a clearer impact and rehydration. Individual data of stem water potential were grouped according to leaf conductance reduction. The relationship of these stem water potentials and temperature or vapor pressure deficit was significant, linear, and aligned to published baselines. Scattering in these equations increased when the leaf conductance reduction was greater. These reference equations would be useful to define moderate water stress conditions in the most sensitive processes, such as vegetative or fruit growth. Definition of severe water stress conditions would be better established with constant values.

Speed of Sound Measurements in Helium at Pressures from 15 to 100 MPa and Temperatures from 273 to 373 K.

The speed of sound in helium was measured along five isotherms in a temperature range from 273 to 373 K at pressures from 15 to 100 MPa with a relative expanded uncertainty (k = 2) from 0.02 to 0.04%. A dual-path pulse-echo system was utilized to conduct these measurements. The data were compared with the reference equation of state developed by Ortiz Vega et al. At pressures up to 50 MPa, relative deviations were within the uncertainty of our measurements, while, at higher pressures, increasing negative deviations were observed up to -0.26%. We also compared the results with predictions based on the virial equation of state correct to the seventh virial coefficient, using the ab initio virial coefficients reported recently by Gokul et al., finding agreement to within the experimental uncertainty at all investigated states.