Non-invasive MR imaging techniques for measuring femoral arterial flow in a pediatric and adolescent cohort.

Magnetic Resonance Imaging (MRI) is well-suited for imaging peripheral blood flow due to its non-invasive nature and excellent spatial resolution. Although MRI is routinely used in adults to assess physiological changes in chronic diseases, there are currently no MRI-based data quantifying arterial flow in pediatric or adolescent populations during exercise. Therefore the current research sought to document femoral arterial blood flow at rest and following exercise in a pediatric-adolescent population using phase contrast MRI, and to present test-retest reliability data for this method. Ten healthy children and adolescents (4 male; mean age 14.8 ± 2.4 years) completed bloodwork and resting and exercise MRI. Baseline images consisted of PC-MRI of the femoral artery at rest and following a 5 × 30 s of in-magnet exercise. To evaluate test-retest reliability, five participants returned for repeat testing. All participants successfully completed exercise testing in the MRI. Baseline flow demonstrated excellent reliability (ICC = 0.93, p = 0.006), and peak exercise and delta rest-peak flow demonstrated good reliability (peak exercise ICC = 0.89, p = 0.002, delta rest-peak ICC = 0.87, p = 0.003) between-visits. All three flow measurements demonstrated excellent reliability when assessed with coefficients of variance (CV's) (rest: CV = 6.2%; peak exercise: CV = 7.3%; delta rest-peak: CV = 7.1%). The mean bias was small for femoral arterial flow. There was no significant mean bias between femoral artery flow visits 1 and 2 at peak exercise. There were no correlations between age or height and any of the flow measurements. There were no significant differences between male and female participants for any of the flow measurements. The current study determined that peripheral arterial blood flow in children and adolescents can be evaluated using non-invasive phase contrast MRI. The MRI-based techniques that were used in the current study for measuring arterial flow in pediatric and adolescent patients demonstrated acceptable test-retest reliability both at rest and immediately post-exercise.

Sleep-disordered breathing, respiratory patterns during wakefulness and functional capacity in pediatric patients with rapid-onset obesity with hypothalamic dysfunction, hypoventilation and autonomic dysregulation syndrome.

OBJECTIVE: To characterize the clinical presentation of sleep-disordered breathing and respiratory patterns at rest and during a 6-min walk test (6MWT) in children with rapid-onset obesity, hypothalamic dysfunction, hypoventilation, and autonomic dysregulation (ROHHAD) syndrome. METHODS: Retrospective study of children with ROHHAD who had a diagnostic baseline polysomnography, daytime cardiorespiratory monitoring at rest and a 6MWT. Polysomnography data were also compared with body mass index-, age-, and sex-matched controls. RESULTS: Of the eight children with ROHHAD, all eight (100%) had obstructive sleep apnea (OSA) and 2/8 (25%) had nocturnal hypoventilation (NH) on their baseline polysomnography. Comparing the ROHHAD group to the control group, there were no significant differences in the median (interquartile range [IQR]) obstructive apnea-hypopnea index (11.1 [4.3-58.4] vs. 14.4 [10.3-23.3] events/h, respectively; p = .78). However, children with ROHHAD showed a significantly higher desaturation index compared to the control group (37.9 [13.7-59.8] vs. 14.7 [4.3-27.6] events/h; p = .05). While awake at rest, some children with ROHHAD experienced significant desaturations associated with central pauses. During the 6MWT, no significant desaturations were observed, but two children showed moderate functional limitation. CONCLUSIONS: Among children with ROHHAD, respiratory instability may be demonstrated by a significant number and severity of oxygen desaturations during sleep in the presence of OSA, with or without NH, and oxygen desaturations with central pauses at rest during wakefulness. Interestingly, during daily activities that require submaximal effort, children may not experience oxygen desaturations. Early recognition of respiratory abnormalities and targeted therapeutic interventions are important to limit associated morbidity and mortality in ROHHAD.

Dynamic Myocardial Response to Exercise in Childhood Cancer Survivors Treated with Anthracyclines.

BACKGROUND: Anthracycline cardiotoxicity can cause significant long-term morbidity in childhood cancer survivors (CCS), but many CCS do not manifest clinical symptoms until adulthood. The aims of this study were to characterize the dynamic myocardial response to exercise of CCS at long-term follow-up by combining semisupine bicycle exercise stress echocardiography with myocardial imaging techniques and to establish whether semisupine bicycle exercise stress echocardiography could identify CCS with abnormal exercise response. METHODS: This was a single-center prospective cross-sectional study. One hundred CCS and 51 control subjects underwent semisupine bicycle exercise stress echocardiography. Color Doppler tissue imaging peak systolic (s') and diastolic (e') velocities, myocardial acceleration during isovolumic contraction, and longitudinal strain were measured at rest and at incremental heart rates in the left ventricular (LV) lateral wall, basal septum, and right ventricle. The relationship with increasing heart rate was evaluated for each parameter by plotting the values against heart rate at each stage of exercise. Kernel density estimate was used to establish the normality of the individual CCS exercise responses. RESULTS: At rest, no significant differences were found for LV lateral wall, right ventricular (RV), and basal septal systolic and diastolic velocities between CCS and control subjects. Only septal e' was lower in CCS. LV longitudinal strain was similar between groups, while RV longitudinal strain was lower in CCS. At peak exercise, LV lateral wall, RV, and septal s' were not different between groups, while e' were significantly lower in CCS. LV lateral wall and septal isovolumic acceleration were also reduced in CCS. LV longitudinal strain was different between groups, while RV longitudinal strain was similar. The dynamic response of Doppler tissue imaging velocities, isovolumic acceleration, and strain was similar between CCS and control subjects. Kernel density estimate analysis confirmed that most CCS responses were within the normal range. CONCLUSIONS: At 10-year follow-up, anthracycline-treated CCS with normal baseline ejection fractions have LV and RV systolic and diastolic myocardial exercise response comparable with that of control subjects. Minor differences were observed between CCS and control subjects at rest and at peak exercise, but the dynamic response is within the normal range.

Skeletal Muscle Metabolic Dysfunction in Patients With Malignant Hyperthermia Susceptibility.

BACKGROUND: Malignant hyperthermia (MH), a pharmacogenetic disorder of skeletal muscle, presents with a potentially lethal hypermetabolic reaction to certain anesthetics. However, some MH-susceptible patients experience muscle weakness, fatigue, and exercise intolerance in the absence of anesthetic triggers. The objective of this exploratory study was to elucidate the pathophysiology of exercise intolerance in patients tested positive for MH with the caffeine-halothane contracture test. To this end, we used phosphorus magnetic resonance spectroscopy, blood oxygen level-dependent functional magnetic resonance imaging (MRI), and traditional exercise testing to compare skeletal muscle metabolism in MH-positive patients and healthy controls. METHODS: Skeletal muscle metabolism was assessed using phosphorus magnetic resonance spectroscopy and blood oxygen level-dependent functional MRI in 29 MH-positive patients and 20 healthy controls. Traditional measures of physical capacity were employed to measure aerobic capacity, anaerobic capacity, and muscle strength. RESULTS: During 30- and 60-second exercise, MH-positive patients had significantly lower ATP production via the oxidative pathway compared to healthy controls. MH-positive patients also had a longer recovery time with blood oxygen level-dependent functional MRI compared to healthy controls. Exercise testing revealed lower aerobic and anaerobic capacity in MH-positive patients compared to healthy controls. CONCLUSIONS: Results of this exploratory study suggest that MH-positive patients have impaired aerobic metabolism compared to healthy individuals. This could explain the exercise intolerance exhibited in MH-susceptible patient population.