West Nile virus encephalitis in GATA2 deficiency.

We report a male with longstanding warts who presented with severe West Nile virus encephalitis (WNVE) and recovered after interferon alfa-2b and intravenous immunoglobulin. He was later found to have GATA2 deficiency and underwent successful hematopoietic stem cell transplant.

Allergic Diseases and Immune-Mediated Food Disorders in Pediatric Acute-Onset Neuropsychiatric Syndrome.

Background: The prevalence and impact of allergic and immune-mediated food disorders in pediatric acute-onset neuropsychiatric syndrome (PANS) are mostly unknown. Objective: We sought to explore the prevalence of atopic dermatitis (AD), asthma, allergic rhinitis (AR), IgE-mediated food allergies (FAs), and other immune-mediated food disorders requiring food avoidance in patients with PANS. In addition, to further understand the extent of food restriction in this population, we investigated the empiric use of dietary measures to improve PANS symptoms. Methods: Pediatric patients in a PANS Clinic and Research Program were given surveys regarding their caregiver burdens, allergic and food-related medical history, and whether food elimination resulted in perception of improvement of PANS symptoms. A review of health records was conducted to confirm that all responses in the survey were concordant with documentation of each patient's medical chart. Results: Sixty-nine (ages 4-20 years) of 80 subjects who fulfilled PANS criteria completed the surveys. Thirteen (18.8%) had AD, 11 (15.9%) asthma, 33 (47.8%) AR, 11 (15.9%) FA, 1 (1.4%) eosinophilic gastrointestinal disorders, 1 (1.4%) food protein-induced enterocolitis syndrome, 3 (4.3%) milk protein-induced proctocolitis syndrome, and 3 (4.3%) celiac disease. Thirty subjects (43.5%) avoided foods due to PANS; elimination of gluten and dairy was most common and was associated with perceived improvement of PANS symptoms (by parents). This perceived improvement was not confirmed with objective data. Conclusions: The prevalence of allergic and immune-mediated food disorders in PANS is similar to the general population as reported in the literature, with the exception of AR that appears to be more prevalent in our PANS cohort. More research will be required to establish whether diet or allergies influence PANS symptoms.

Development of a tool predicting severity of allergic reaction during peanut challenge.

BACKGROUND: Reliable prognostic markers for predicting severity of allergic reactions during oral food challenges (OFCs) have not been established. OBJECTIVE: To develop a predictive algorithm of a food challenge severity score (CSS) to identify those at higher risk for severe reactions to a standardized peanut OFC. METHODS: Medical history and allergy test results were obtained for 120 peanut allergic participants who underwent double-blind, placebo-controlled food challenges. Reactions were assigned a CSS between 1 and 6 based on cumulative tolerated dose and a severity clinical indicator. Demographic characteristics, clinical features, peanut component IgE values, and a basophil activation marker were considered in a multistep analysis to derive a flexible decision rule to understand risk during peanut of OFC. RESULTS: A total of 18.3% participants had a severe reaction (CSS >4). The decision rule identified the following 3 variables (in order of importance) as predictors of reaction severity: ratio of percentage of CD63hi stimulation with peanut to percentage of CD63hi anti-IgE (CD63 ratio), history of exercise-induced asthma, and ratio of forced expiratory volume in 1 second to forced vital capacity (FEV1/FVC) ratio. The CD63 ratio alone was a strong predictor of CSS (P < .001). CONCLUSION: The CSS is a novel tool that combines dose thresholds and allergic reactions to understand risks associated with peanut OFCs. Laboratory values (CD63 ratio), along with clinical variables (exercise-induced asthma and FEV1/FVC ratio) contribute to the predictive ability of the severity of reaction to peanut OFCs. Further testing of this decision rule is needed in a larger external data source before it can be considered outside research settings. TRIAL REGISTRATION: ClinicalTrials.gov identifier: NCT02103270.

A novel outpatient desensitization protocol for recombinant human erythropoietin allergy in a pediatric patient.

BACKGROUND: Recombinant human erythropoietin, such as epoetin alfa and darbepoetin alfa, is an important therapy for anemia due to chronic renal failure. Allergy to recombinant human erythropoietin and the need for desensitization are rare. CASE PRESENTATION: We report here a novel epoetin alfa outpatient desensitization protocol in a girl who developed delayed cutaneous hypersensitivity to subcutaneous epoetin alfa and intravenous darbepoetin alfa. An initial attempt at traditional epoetin alfa desensitization failed, so we created a slower 17-day outpatient desensitization that succeeded and allowed treatment continuation. CONCLUSIONS: This case highlights the notion that delayed-type hypersensitivity to recombinant human erythropoietin can occur as evident by reproducible reactions after repeated exposures and slow outpatient desensitization can be considered when a trial of more rapid induction of tolerance is unsuccessful.

Emergence of multiresistant methicillin-resistant Staphylococcus aureus in two patients with atopic dermatitis requiring linezolid treatment.

We report two patients with atopic dermatitis who developed methicillin-resistant Staphylococcus aureus (MRSA) skin infections resistant to clindamycin and trimethoprim-sulfamethoxazole requiring repeated linezolid treatment. For one patient and family members who received an aggressive regimen of staphylococcal decolonization, including intranasal mupirocin, dilute bleach baths, and bleach cleansing of household items and surfaces, subsequent culture results demonstrated methicillin-susceptible S. aureus colonization and infection. These findings underscore the challenges presented by multiresistant MRSA infections in children with atopic dermatitis.

Synergistic effect of obesity and lipid ingestion in suppressing the growth hormone response to exercise in children.

Diet plays an important role in modulating exercise responses, including activation of the growth hormone (GH)/insulin-like growth factor-I (IGF-1) axis. Obesity and fat ingestion were separately shown to reduce exercise GH responses, but their combined effect, especially important in children, has not been studied. We therefore measured the GH response to exercise [30-min intermittent cycling, ten 2-min bouts at ~80% maximal aerobic capacity (Vo(2max)), separated by 1-min rest], started 45 min after ingestion of a high-fat meal (HFM) in 16 healthy [controls; body mass index percentile (BMI%ile) 51 ± 7], and 19 obese (Ob, BMI%ile 97 ± 0.4) children. Samples were drawn at baseline (premeal), and at start, peak, and 30 min postexercise. In the Ob group, a marked ~75% suppression of the GH response (ng/ml) to exercise was observed (2.4 ± 0.6 vs. 10.6 ± 2.1, P < 0.001). This level of suppression was also significantly greater compared with age-, fitness-, and BMI-matched historical controls that had performed identical exercise in fasting conditions. Our data indicate that the reduction in the GH response to exercise, already present in obese children vs. healthy controls, is considerably amplified by ingestion of fat nutrients shortly before exercise, implying a potentially downstream negative impact on growth factor homeostasis and long-term modulation of physiological growth.

Inflammatory cytokine profiles during exercise in obese, diabetic, and healthy children.

OBJECTIVE: Modulation of inflammatory status is considered a key component of the overall health effects of exercise. This may be especially relevant in children with obesity (Ob) or type 1 diabetes (T1DM), in which an imbalance between pro- and anti-inflammatory mediators could accelerate onset and progression of cardiovascular complications. To date, exercise-induced alterations in immuno-modulatory mediators in Ob and T1DM children remain largely unknown. METHODS: In this study, we monitored the kinetic profiles of 8 pro-and anti-inflammatory cytokines (TNF-a, IL-6, IL-2, IL-8, IL-5, IL-13, IL-10, IL-4) during a standardized exercise challenge (ten 2-min cycling bouts at 80% VO2max, separated by 1-min intervals) in 23 Ob (12 females, 11 males), 23 T1DM (10 females and 13 males) patients and 20 healthy (CL, 10 females and 10 males) children. Blood glucose of T1DM patients was kept in the 4.4-6.1 mM range for at least 90 minute prior to and during exercise. Blood samples were drawn at rest and after every other exercise bout. RESULTS: In Ob, TNF-a and IL-2 were significantly greater (p<0.0167) as compared to T1DM and CL, both at baseline and throughout exercise. All other variables, while not significant, were quantitatively elevated in Ob vs. CL. In T1DM, IL-4 and IL-8 levels were similar to Ob, IL-2 and TNF-a similar to CL, and IL-6, IL-5, IL-13, IL-4 levels were intermediate between the Ob and CL groups. CONCLUSIONS: During exercise, therefore, both Ob and T1DM children displayed exaggerated pro-inflammatory responses, although with clearly different magnitude and involved mediators. Our data support the necessity to identify specific exercise formats through which each at-risk pediatric population can draw maximal beneficial health effects.

Altered inflammatory, oxidative, and metabolic responses to exercise in pediatric obesity and type 1 diabetes.

Obesity (Ob) and type 1 diabetes (T1DM) are associated with increased inflammation and oxidative stress, which are major pathogenetic pathways toward higher cardiovascular risks. Although long-term exercise protects against systemic inflammation and oxidation, acute exercise actually exerts pro-inflammatory and oxidative effects, prompting the necessity for better defining these molecular processes in at-risk patients; in particular, very little is known regarding obese and T1DM children. We therefore examined key inflammatory and oxidative stress variables during exercise in 138 peripubertal children (47 Ob, 12.7 ± 0.4 yr, 22 F, BMI% 97.6 ± 0.2; 49 T1DM, 13.9 ± 0.2 yr, 20 F, body mass index% [BMI] 63.0 ± 3.6; 42 healthy, CL, 13.5 ± 0.5 yr, 24 F, BMI% 57.0 ± 3.6), who performed 10 bouts of 2-min cycling ~80% VO(2max) , separated by 1-min rest intervals. Blood samples were drawn at baseline and peak exercise. Ob displayed elevated baseline interleukin-6 (IL-6, 2.1 ± 0.2 pg/mL, p < 0.005) vs. CL (1.5 ± 0.3), whereas T1DM displayed the greatest maximum exercise-induced change in IL-6 (1.2 ± 0.3) than in both Ob (0.7 ± 0.1, p < 0.001) and CL (0.6 ± 0.1, p < 0.0167). Myeloperoxidase (MPO) was elevated in T1DM (143 ± 30 ng/mL, p < 0.0167) vs. CL (89 ± 10) and Ob (76 ± 6), whereas increases in exercise only occurred in Ob and CL. Disparate baseline and exercise responses were also observed for 8-hydroxy-2'-deoxyguanosine, glutathione, and F(2) -isoprostane. This data show distinct patterns of dysregulation in baseline and adaptive immunologic and oxidative responses to exercise in Ob and T1DM. A full understanding of these alterations is required so that developing exercise regimens aimed at maximizing health benefits for specific dysmetabolic states can be achieved based on complete scientific characterization rather than empirical implementation.

Increased oxidative stress and altered substrate metabolism in obese children.

OBJECTIVE: Pediatric obesity, a major risk factor for cardiovascular diseases and diabetes, has steadily increased in the last decades. Although excessive inflammation and oxidation are possible biochemical links between obesity and cardiovascular events in adults, little information is available in children. Furthermore, effects of gender and fitness on the interaction between dyslipidemia and oxidative/inflammatory stress in children are mostly unknown. METHODS: Therefore, we measured systemic markers of oxidation (F(2)-isoprostanes [F(2)-IsoP] and antioxidants) and inflammation (interleukin-6 [IL-6] and leukocyte counts) and metabolic variables in 113 peripubertal children (55 obese [Ob] age and gender-adjusted BMI% ≥ 95(th), 25 Females [F]; 15 overweight [OW] BMI% 85(th)-95(th), 8 F; 43 normoweight [NW] 25 F). RESULTS: When compared with NW, Ob displayed elevated F(2)-IsoP (99 ± 7 vs. 75 ± 4 pg/mL, p<0.005), IL-6 (2.2 ± 0.2 vs. 1.5 ± 0.3 pg/mL, p<0.005), elevated total leukocytes and neutrophils, altered levels of total cholesterol , low- and high-density-lipoprotein cholesterol, triglycerides, free fatty acids, glucose, and insulin (all p<0.005). This pattern was present in both genders and over a broad range of fitness in Ob. CONCLUSIONS: Our data indicate that alterations in metabolic control and a concomitant increase in inflammation and oxidative stress occur early in life in obese children, likely exposing both genders to a similar degree of increased risk of future cardiovascular diseases.

Ex vivo TCR-induced leukocyte gene expression of inflammatory mediators is increased in type 1 diabetic patients but not in overweight children.

BACKGROUND: Abnormal systemic concentrations of proinflammatory cytokines/chemokines have been implicated in the development of long-term cardiovascular complications in type 1 diabetes (T1DM) and obesity. Whether leukocyte white blood cell (WBC) gene expression of these proinflammatory mediators contributes to their increased systemic levels, however, remains unclear, especially in the pediatric patient populations. This study examines mRNA changes of 9 cytokines and chemokines in WBCs following ex vivo immunostimulation from 9 T1DM (13.4 +/- 0.5 year, 4F/5 M), 23 overweight (OW, 12.3 +/- 0.5 year, 10F/13M, BMI% 97.1 +/- 0.5 and > 90.0), and 21 healthy (CL, 13.8 +/- 0.7 year, 9F/12 M, BMI% 59.6 +/- 4.6 and < 85.0) children. METHODS: All subjects had been maintained in euglycemic conditions for at least 90 min before blood draws. Whole blood was then sampled and incubated with anti-T-cell receptor (TCR) antibody or heat-aggregated IgG (HAG) to stimulate T-cell and Fc receptors (FcR), respectively. After lysis of leukocytes, mRNA levels of six tumor necrosis factor superfamily cytokines (TNFSF2, 5, 6, 7, 9, 14) and three chemokines (CCL8, 20, and CXCL10) were measured using RT-PCR. RESULTS: Following TCR stimulation, T1DM displayed significantly greater mRNA responses than CL for TNFSF5, 7, 9, and CCL8, and CXCL10; TNFSF9, CCL8, and CXCL10 were also significantly higher in T1DM than OW; no difference was observed between OW and CL. FcR stimulation induced similar responses across groups. CONCLUSIONS: Leukocytes of T1DM children displayed exaggerated gene expression in response to ex vivo TCR induction of five key proinflammatory cytokines/chemokines. This elevated leukocyte gene expression may be one of the pathophysiological contributors to the development of vascular complications in T1DM.

Dose-dependent relationship between severity of pediatric obesity and blunting of the growth hormone response to exercise.

In children, exercise modulates systemic anabolism, muscle growth, and overall physiological development through the growth hormone (GH)-insulin-like growth factor I (IGF-I) axis. GH secretion, at rest and during exercise, changes with age and maturational status and can be blunted by hyperlipidemia and obesity, with possible negative effects on physiological growth. However, little is known about the effect of progressively more severe pediatric obesity on the GH response to exercise and its relationship to pubertal status. We therefore studied 48 early- or late-pubertal obese children [body mass index (BMI) >95th percentile, separated in tertiles with progressively greater BMI] and 42 matched controls (BMI <85th percentile), who performed ten 2-min cycling bouts at approximately 80% of maximal O2 consumption, separated by 1-min rest intervals. Plasma GH and IGF-I were measured at baseline and end exercise. GH responses were systematically blunted in obese children, with more pronounced blunting paralleling increasing BMI. Although overall the GH response to exercise was greater in late-pubertal than in younger children, this blunting pattern was observed in early- and late-pubertal children. Our results reveal insight into the interaction between pediatric obesity and key modulators of physiological growth and development and underscore the necessity of optimizing physical activity strategies for specific pediatric dysmetabolic conditions.

Resting and exercise-induced IL-6 levels in children with Type 1 diabetes reflect hyperglycemic profiles during the previous 3 days.

Poor glycemic control in Type 1 diabetes (T1DM) causes long-term cardiovascular complications, at least in part via chronic, low-grade inflammation associated with recurrent hyperglycemia. While physical activity can reduce both inflammation and cardiovascular risks, the underlying molecular mechanisms remain unclear. This is particularly important for T1DM children, for whom the prevention of long-term cardiovascular complications must include optimization of exercise-related anti-inflammatory strategies. We therefore studied the effect of prior hyperglycemia on resting and exercise-induced inflammatory status (plasma IL-6) in T1DM children. Glycemia was continuously recorded with a continuous glucose monitoring system (CGMS) system for 63 h preceding a 30-min intermittent cycling exercise protocol at approximately 80% peak rate of oxygen uptake (VO2max). Euglycemia (4.4-6.1 mM) was maintained for 90 min before, during, and 30 min after exercise. IL-6 plasma concentration (pg/ml) was measured at baseline, at end exercise, and 30 min postexercise. Subjects were then divided into quartiles based on average glycemia during the CGMS recording. IL-6 levels (pg/ml) were lowest in the quartile with lowest average 3-day glycemia and increased proportionally to greater hyperglycemic exposure; this was observed at baseline (0.86 +/- 0.10, 1.06 +/- 0.16, 1.14 +/- 0.14, 1.20 +/- 0.16), absolute IL-6 change (Delta) at end exercise (0.20 +/- 0.16, 0.32 +/- 0.10, 0.48 +/- 0.09, 0.62 +/- 0.13), and Delta at 30 min postexercise (0.49 +/- 0.13, 0.71 +/- 0.16, 0.89 +/- 0.14, 1.38 +/- 0.33). Therefore, poorly controlled glycemic profile, even in the 63 h preceding an exercise challenge, can alter inflammatory adaptation in T1DM children. Our data underscore the necessity to fully understand all molecular aspects of physical activity to provide the scientific rationale for exercise regimens that will be able to maximize health benefits for T1DM children.

Exercise leukocyte profiles in healthy, type 1 diabetic, overweight, and asthmatic children.

Leukocytosis contributes to exercise-induced immune modulation, which is a mechanism of cardiovascular protection. However, this process is poorly defined in children. We therefore measured leukocytes in 45 healthy, 18 overweight, 16 type 1 diabetic, and 8 asthmatic children at pre, end-, and 30-min postexercise (30-min intermittent or 6-min continuous). In all groups, total leukocytes, neutrophils, lymphocytes, and monocytes increased at end-exercise, but returned to baseline by 30-min postexercise, including neutrophils, previously reported to remain elevated for at least some exercise formats. This highly preserved pattern indicates the importance of the adaptive response to physical stress across multiple health conditions.

Acute suppression of circulating sCD40L during hyperglycemia and euglycemic-hyperinsulinemia in healthy young males.

sCD40L is a proatherogenic cytokine, part of the tumor necrosis factor (TNF) superfamily and consistently associated with obesity, diabetes, and increased cardiovascular risk. Although the role of sCD40L in the onset/progression of cardiovascular complications of dysmetabolic diseases may be modulated by acute and/or chronic fluctuations of plasma insulin and glucose, very little has been done to clarify this interaction. The kinetic profile of sCD40L (and, in an exploratory manner, of several immunomodulatory factors), were measured during hyperglycemia and euglycemic-hyperinsulinemia in a group of 10 healthy young males (26.8 +/- 1.4 years). After an overnight fast, intravenous (iv) catheters were placed in antecubital veins of both arms for blood drawing and dextrose/insulin iv infusions. Procedures lasted 240 minutes including baseline (t = 0-60), hyperglycemia (t = 60-150; plasma glucose approximately 220 mg/dL via iv dextrose infusion), and euglycemic-hyperinsulinemia (t = 150-240; glucose infusion continued to clamp glycemic levels between 80 and 110 mg/dL; constant insulin infusion at 1.5 mU/kg/minute).Plasma for cytokine assays was sampled at 12 separate time-points. Plasma levels of sCD40L were significantly reduced (P < 0.01) during hyperglycemia and euglycemic-hyperinsulinemia, paralleling the kinetic profiles of free fatty acids and ketone bodies. This pattern was also observed in other immunomodulatory factors (notably cortisol and epidermal growth factor), while (interleukin [IL]-1alpha, IL-4, IL-6, IL-9, IL-10, TNF-alpha, Eotaxin) did not change significantly. Significant reductions of the proatherogenic cytokine sCD40L were observed during endogenous and exogenous hyperinsulinemia, independent of prevailing glucose concentration, in young healthy males. Our data suggest a mechanism by which correct insulin action may exert a beneficial protective role against inflammation, independent of its immediate glucose-lowering effect.

Altered kinetics of interleukin-6 and other inflammatory mediators during exercise in children with type 1 diabetes.

BACKGROUND: Leukocyte mobilization and secretions of cytokines, chemokines, and growth factors in children during exercise are necessary biochemical signals for physiological growth and long-term cardiovascular protection. Because of glycemic instability, altered exercise responses, particularly the proinflammatory cytokine interleukin (IL)-6, may occur in type 1 diabetes mellitus (T1DM) that could influence the onset/progression of diabetic vascular complications. Relatively little is known, however, on most molecular aspects of immunomodulatory adaptation to exercise in diabetic children. METHODS: We therefore studied 21 children (age, 13.4 +/- 0.3 years; 13 boys/8 girls) with T1DM and 21 age-matched healthy controls during 30 minutes of intense and intermittent cycling exercise. Euglycemia was maintained during and for greater than 90 minutes before exercise; blood samples for IL-6 and other cytokines/chemokines were drawn before, during (every 6 minutes), and after (every 15 minutes) exercise. RESULTS: In T1DM, exercise-induced IL-6 peak occurred earlier and with greater magnitude than that in controls; an exploratory analysis of additional inflammatory mediators displayed a similarly accelerated/exaggerated pattern in T1DM, including the kinetic profiles of tumor necrosis factor alpha, IL-4, IL-12p70, IL-17, granulocyte-monocyte colony-stimulating factor, monocyte chemoattractant protein-1, macrophage inflammatory protein-1alpha, and eotaxin (interferon-inducible protein-10 was the only measured variable essentially indistinguishable between groups). CONCLUSION: Therefore, during intense and intermittent exercise, significant alterations in the immunologic pattern of inflammatory regulation occurred in children with T1DM as compared with healthy controls. Our findings underscore how the understanding of all the underlying molecular mechanisms is a necessary prerequisite for achieving effective use of exercise and the full manifestation of its health benefits, particularly in understudied populations such as children with T1DM who are at increased risk for cardiovascular complications.

Sustained IL-1alpha, IL-4, and IL-6 elevations following correction of hyperglycemia in children with type 1 diabetes mellitus.

OBJECTIVE: An imbalance of pro-/anti-inflammatory cytokines may accelerate diabetic vascular complications and interfere with proper wound healing. Currently, limited available literature suggests that plasma concentrations of certain pro- and anti-inflammatory cytokines may be altered during hyperglycemia/diabetes mellitus. It is still unclear, however, whether these concepts also apply to children with diabetes, and whether alterations in circulating cytokine levels are a permanent feature of diabetes or an acute effect of fluctuating glucose concentrations. METHODS: Twenty-two children with type 1 diabetes mellitus (T1DM) were studied. In 13 children, postprandial morning plasma glucose was >11.1 mmol/L at least once (hyperglycemic group, or HyG group); in 9 subjects, plasma glucose never exceeded 10.6 mmol/L (non-hyperglycemic group, or non-HyG group). After admission, intensive euglycemia (5.0-6.1 mmol/L) was achieved in all participants via intravenous insulin and dextrose for at least 90 min. Blood samples were drawn every 30 min to determine plasma levels of 14 cytokines and chemokines. RESULTS: Interleukin IL-1alpha, IL-4, and IL-6 were elevated in HyG group compared with non-HyG not only when plasma glucose was elevated but also during the first 2 h following return to euglycemia. The levels of the other 11 cytokines were not significantly different. CONCLUSIONS: Specific cytokines (IL-1alpha, IL-4, and IL-6) are acutely elevated during hyperglycemia in children with T1DM, and these elevations persist for hours after hyperglycemia has been corrected. Therefore, aside from glycemic control, additional therapeutic measures against elevated proinflammatory signals may be necessary for preventing vascular complications in children with hyperglycemic diabetes.

Kinetic profiles of 18 systemic pro- and anti-inflammatory mediators during and following exercise in children.

While acute changes in systemic pro-/antiinflammatory cytokines occur with exercise, individual kinetics during and following exercise remain unclear; particularly, information is scarce regarding children. This study investigated the exercise-induced kinetic profiles of major pro-/anti-inflammatory mediators in 21 healthy children (13.9 +/- 0.8 yr, 7 M/14 F). Exercise was 30 min of intermittent cycling at approximately 80% VO2max. Multiple blood samples were drawn at baseline, during, and following exercise for cytokines assay. IL-1alpha, IL-6, IL-17, IL-8, IP-10, MIP-1alpha, and MIP-1beta initially decreased (nadir: 14-19 min into exercise) and subsequently exceeded baseline levels (peaks: 20-24 min into exercise). TNF-alpha, IL-12p70, IL-1RA, IL-4, EGF, TGF-alpha, GM-CSF, Eotaxin, and MCP-1 were moderately and persistently decreased throughout. VEGF was unchanged; sCD40L was elevated during exercise and recovery. Our results indicate that key immunomodulators display non-linear, biphasic kinetic profiles in response to exercise, suggesting that detection of exercise-induced changes over baseline may depend on exercise duration and sampling timing.