Abnormal autonomic cardiac response to transient hypoxia in sickle cell anemia

McDAPS: A multi-channel physiological signals display and analysis system for clinical researchers

We introduce McDAPS, an interactive software for assessing autonomic imbalance from non-invasive multi-channel physiological recordings. McDAPS provides a graphical user interface for data visualization, beat-to-beat processing and interactive analyses. The software extracts beat-to-beat RR interval systolic blood pressure, diastolic blood pressure, the pulse amplitude of photoplethysmogram and the pulse-to-pulse interval. The analysis modules include stationary and time-varying power spectral analyses, moving-correlation analysis and univariate analyses. Analyses can also be performed in batch mode if multiple datasets have to be processed in the same way. The program exports results in standard CSV format. McDAPS runs in MATLAB, and is supported on MS Windows and MAC OS systems. The MATLAB source code is available at https://github.com/thuptimd/McDAPS.git.

Autonomic and Vascular Responses during Reactive Hyperemia in Healthy Individuals and Patients with Sickle Cell Anemia

Background and Objectives: To compare autonomic and vascular responses during reactive hyperemia (RH) between healthy individuals and patients with sickle cell anemia (SCA). Materials and Methods: Eighteen healthy subjects and 24 SCA patients were subjected to arterial occlusion for 3 min at the lower right limb level. The pulse rate variability (PRV) and pulse wave amplitude were measured through photoplethysmography using the Angiodin^® PD 3000 device, which was placed on the first finger of the lower right limb 2 min before (Basal) and 2 min after the occlusion. Pulse peak intervals were analyzed using time-frequency (wavelet transform) methods for high-frequency (HF: 0.15-0.4) and low-frequency (LF: 0.04-0.15) bands, and the LF/HF ratio was calculated. Results: The pulse wave amplitude was higher in healthy subjects compared to SCA patients, at both baseline and post-occlusion (p < 0.05). Time-frequency analysis showed that the LF/HF peak in response to the post-occlusion RH test was reached earlier in healthy subjects compared to SCA patients. Conclusions: Vasodilatory function, as measured by PPG, was lower in SCA patients compared to healthy subjects. Moreover, a cardiovascular autonomic imbalance was present in SCA patients with high sympathetic and low parasympathetic activity in the basal state and a poor response of the sympathetic nervous system to RH. Early cardiovascular sympathetic activation (10 s) and vasodilatory function in response to RH were impaired in SCA patients.

The Cardiopulmonary Complications of Sickle Cell Disease

Sickle cell disease (SCD) is a genetic hemoglobinopathy associated with extensive morbidity and early mortality. While there have been recent improvements in available disease-modifying therapies for SCD, cardiopulmonary complications remain a major risk factor for death in this population. We provide an overview of current knowledge regarding several of the major acute and chronic cardiopulmonary complications in SCD, including: acute chest syndrome, airway disease, lung function abnormalities, nocturnal hypoxemia and sleep disordered breathing, pulmonary vascular disease, and sickle cell cardiomyopathy.

Heart Rate Variability in Adults with Sickle Cell Anemia During a Multitasking Field Test

Background: The integrity of the autonomic nervous system (ANS) is essential for keeping physiological processes stable, even under stress. Since there is growing interest in heart rate variability (HRV) analysis for the noninvasive assessment of the ANS in sickle cell anemia (SCA) patients, we studied the behavior of the ANS in the presence of a stressor that simulates daily-life multitasking, the Glittre ADL test (GA-T). Objectives: To evaluate the involvement of the ANS using HRV in adults with SCA during the GA-T and to quantify the strength of the correlation of HRV with lung and muscle functions. Methods: In this cross-sectional study, 16 adults with SCA and 12 healthy controls without sickle cell disease underwent HRV assessment during the GA-T, pulmonary function tests (spirometry, diffusing capacity for carbon monoxide (DLCO), and respiratory muscle testing). Peripheral muscle function [handgrip strength (HGS) and quadriceps strength (QS)] were also measured. Results: Compared to the healthy controls, adults with SCA showed lower HRV, with worse parasympathetic modulation due to reductions in the following indices: the root-mean-square difference of successive normal iRRs (iRR) (RMSSD); the percentage of pairs of consecutive iRRs whose difference is > 50 m (pNN50); the high-frequency component of heart rate variability (HF); and the standard deviation of instantaneous beat-to-beat variability (SD1) (P < 0.001 for all). Compared to healthy controls, individuals with SCA showed greater sympathovagal imbalance (higher ratio between low-frequency and HF components) and lower complexity of the ANS (lower approximate entropy). The GA-T time was correlated with parasympathetic activity indices: RMSSD (rs = -0.650, P < 0.01); pNN50 (rs = -0.932, P < 0.0001), HF (rs = -0.579, P < 0.01), and SD1 (rs = -0.814, P < 0.0001). Correlations between parasympathetic activity indices and DLCO, HGS, and QS measures were also significant. Conclusions: Adults with SCA have low HRV, with low parasympathetic activity, sympathovagal imbalance, and abnormal ANS complexity. In addition, lower HRV is associated with longer GA-T time, greater impairment of pulmonary diffusion, and greater muscle strength dysfunction.

Cardiovascular Sequelae of Sickle Cell Disease

Sickle cell disease (SCD) is one of the most common hereditary hemoglobinopathies worldwide. It is a multisystem disease that causes considerable patient morbidity. Despite advances in medical treatment, cardiopulmonary complications remain the most common cause of death in individuals with SCD. A growing body of evidence has shown that SCD results in a spectrum of cardiovascular complications through a variety of mechanisms, including chronic hemolysis, local tissue hypoxia, increased oxidative stress, and autonomic instability. Herein, we will examine the pathophysiology of sickle cell vasculopathy and discuss the spectrum of cardiovascular sequelae of the disease, while highlighting the impact of SCD on the cardiovascular health of the patients.

Cardiovascular Health in African Americans: A Scientific Statement From the American Heart Association

BACKGROUND AND PURPOSE

Population-wide reductions in cardiovascular disease incidence and mortality have not been shared equally by African Americans. The burden of cardiovascular disease in the African American community remains high and is a primary cause of disparities in life expectancy between African Americans and whites. The objectives of the present scientific statement are to describe cardiovascular health in African Americans and to highlight unique considerations for disease prevention and management.

METHOD

The primary sources of information were identified with PubMed/Medline and online sources from the Centers for Disease Control and Prevention.

RESULTS

The higher prevalence of traditional cardiovascular risk factors (eg, hypertension, diabetes mellitus, obesity, and atherosclerotic cardiovascular risk) underlies the relatively earlier age of onset of cardiovascular diseases among African Americans. Hypertension in particular is highly prevalent among African Americans and contributes directly to the notable disparities in stroke, heart failure, and peripheral artery disease among African Americans. Despite the availability of effective pharmacotherapies and indications for some tailored pharmacotherapies for African Americans (eg, heart failure medications), disease management is less effective among African Americans, yielding higher mortality. Explanations for these persistent disparities in cardiovascular disease are multifactorial and span from the individual level to the social environment.

CONCLUSIONS

The strategies needed to promote equity in the cardiovascular health of African Americans require input from a broad set of stakeholders, including clinicians and researchers from across multiple disciplines.

Anemia Is Associated With Blunted Response to β-Blocker Therapy Using Carvedilol - Insights From Japanese Chronic Heart Failure (J-CHF) Study

BACKGROUND

Anemia portends a poor clinical outcome in patients with chronic heart failure (CHF). However, its mechanism remains unknown. We sought to elucidate the effect of anemia on patients with HF with reduced ejection fraction (HFrEF) who receive carvedilol therapy.Methods and Results:J-CHF study was a prospective, randomized, multicenter trial that assigned 360 HFrEF patients to 2.5 mg/5 mg/20 mg carvedilol groups according to the target dose. At baseline 70 patients (19%) had anemia ([A]) defined as hemoglobin level (Hb) <13 g/dL (male) or <12 g/dL (female) and the remaining 290 did not ([N]). Allocated and achieved doses of carvedilol were similar. Left ventricular ejection fraction (LVEF) and plasma B-type natriuretic peptide (BNP) level significantly improved in both groups over 56 weeks, but they were smaller in [A] than in [N] (LVEF, P=0.046; BNP, P<0.0001 by ANOVA). Baseline Hb was an independent predictor of absolute change in LVEF (β=0.13, P=0.047) and BNP (β=-0.10, P=0.01). Presence of chronic kidney disease defined as estimated glomerular filtration rate (eGFR) <60 mL/min/1.73 m²at baseline was not associated with differential response to carvedilol therapy. During 3.8±1.4 years follow-up, group [A] had a higher incidence of the composite endpoint of death, hospitalization for cardiovascular causes including HF compared with [N] (P=0.006). Baseline Hb was an independent predictor of the composite endpoint (hazard ratio 0.86, P=0.04), whereas baseline eGFR was not.

CONCLUSIONS

Our data suggested that anemia was associated with a blunted response to carvedilol in HFrEF patients.

Physical activity level is not a determinant of autonomic nervous system activity and clinical severity in children/adolescents with sickle cell anemia: A pilot study

BACKGROUND

Autonomic nervous system (ANS) activity has been suggested to modulate the clinical severity of sickle cell anemia (SCA) by increasing the risk for vaso-occlusive events. Regular physical activity (PA) is known to improve ANS activity and health status in several cardiovascular and metabolic diseases. Whether regular PA improves the health status of SCA patients remains unknown.

PROCEDURE

Twenty-two patients with SCA and 15 healthy (AA) children/adolescents participated to the study. Heart rate variability was measured in supine position and after a tilt-test to quantify the ANS activity. PA energy expenditure (PAEE) was assessed with questionnaire.

RESULTS

1) PAEE was lower in SCA compared to AA (190 ± 152 vs. 432 ± 277 kcal · d(-1), respectively, P < 0.01), 2) overall ANS activity was lower in SCA compared to AA, 3) parasympathetic withdrawal was observed in SCA with aging, 4) ANS reactivity was slightly impaired in SCA compared to AA (reduction in HFnu: -38 ± 27 vs. -58 ± 14%, respectively, P < 0.05), 5) ANS indices, PAEE, and rates of clinical events were not correlated.

CONCLUSION

Both the level of PA and ANS activity are reduced in SCA compared to AA children/adolescents, particularly in those older than 15 years. Neither PAEE, nor ANS activity seem to influence the clinical severity of children/adolescents with SCA.

Autonomic responses to cold face stimulation in sickle cell disease: a time-varying model analysis

Sickle cell disease (SCD) is characterized by sudden onset of painful vaso-occlusive crises (VOC), which occur on top of the underlying chronic blood disorder. The mechanisms that trigger VOC remain elusive, but recent work suggests that autonomic dysfunction may be an important predisposing factor. Heart-rate variability has been employed in previous studies, but the derived indices have provided only limited univariate information about autonomic cardiovascular control in SCD. To circumvent this limitation, a time-varying modeling approach was applied to investigate the functional mechanisms relating blood pressure (BP) and respiration to heart rate and peripheral vascular resistance in healthy controls, untreated SCD subjects and SCD subjects undergoing chronic transfusion therapy. Measurements of respiration, heart rate, continuous noninvasive BP and peripheral vascular resistance were made before, during and after the application of cold face stimulation (CFS), which perturbs both the parasympathetic and sympathetic nervous systems. Cardiac baroreflex sensitivity estimated from the model was found to be impaired in nontransfused SCD subjects, but partially restored in SCD subjects undergoing transfusion therapy. Respiratory-cardiac coupling gain was decreased in SCD and remained unchanged by chronic transfusion. These results are consistent with autonomic dysfunction in the form of impaired parasympathetic control and sympathetic overactivity. As well, CFS led to a significant reduction in vascular resistance baroreflex sensitivity in the nontransfused SCD subjects but not in the other groups. This blunting of the baroreflex control of peripheral vascular resistance during elevated sympathetic drive could be a potential factor contributing to the triggering of VOC in SCD.

Cardiac Events Theoretically Cannot Be Produced By Non-Ischemic And/Or Iso-Ischemic Myocardium: Challenging Postulations And Vitality Of The Concept Of "Ischemia-Dependent Conflictogenic Arrhythmias"

Ischemia plays a key role in cardiac arrhythmogenesis, particularly in elderly patients. Healthy, non-ischemic and structurally normal myocardium is universally free from dysrhythmias. Thereby intact coronary blood flow prevents potential cardiac events. Hypothetically, ischemia-related electrophysiological differences are responsible for the supraventricular and/or ventricular rhythm irregularities. The goal of this review is to determine the role of systemic and coronary circulatory peculiarities and their association with heart rhythm abnormalities. The current analytical review extends and enriches previous knowledge about the influence of these peculiarities on the genesis of ischemia-dependent conflictogenic arrhythmias. Different intensity of coronary blood flow resulting from stenotic obstacles or vasospasm potentially leads to the non-uniform perfusion of myocites thus creating albeit subtle but vulnerable and powerful electrophysiologic substrate impending cardiac rhythm disturbances. Apparently, the behavior of both non-ischemic and iso-ischemic myocardium in respect to electric cardiac activity is very similar, at least theoretically. Some different clinical entities, e.g. arterial hypotension and/or anemia containing ischemic component, in most cases are free from arrhythmias. This postulation may be helpful in furthering arrhythmogenicity insights which have been generated previously. On the contrary, increased blood pressure often concurs with the supraventricular and/or ventricular arrhythmias; this pattern also favorably reflects our previous hypothetical assumptions associated with the mechanisms of arrhythmogenesis. Conclusively, both non-ischemic and iso-ischemic myocardium may be attributed to nonarrhythmogenic milieu. Nevertheless, the inventive analysis and more explorative data are required to support the suggested postulations.

Selective enhancement of contractions to α1-adrenergic receptor activation in the aorta of mice with sickle cell disease

Sickle cell disease (SCD), the most common inherited hematologic disorder in the United States and the most common single gene disorder in the world, causes substantial morbidity and mortality. The major pathobiologic processes that underlie SCD include vaso-occlusion, inflammation, procoagulant processes, hemolysis, and altered vascular reactivity. The present study examined the vasoactive response to a-adrenergic activation in a murine model of SCD. Isolated aortas from sickle mice as compared with wild-type mice exhibit heightened contractions to norepinephrine and phenylephrine; such responses were completely blocked by an a1-receptor antagonist, prazosin. Aortas from either group exhibited comparable contractile responses to potassium chloride and the thromboxane agonist U46619 and no contractile response to an a2-adrenergic receptor agonist, UK14304. We conclude that there is an exaggerated vasoconstrictive response to a1-receptor agonists in SCD. Because sickle crisis is induced by diverse forms of stress, the latter attended by increased adrenergic activity, our findings may be relevant to the occurrence of sickle crisis. We also suggest that such heightened reactivity may contribute to vaso-occlusive processes that underlie ischemic injury in SCD. Finally, our findings urge caution in the use of phenylephrine in patients with SCD.

Peripheral vasoconstriction and abnormal parasympathetic response to sighs and transient hypoxia in sickle cell disease

RATIONALE

Sickle cell disease is an inherited blood disorder characterized by vasoocclusive crises. Although hypoxia and pulmonary disease are known risk factors for these crises, the mechanisms that initiate vasoocclusive events are not well known.

OBJECTIVES

To study the relationship between transient hypoxia, respiration, and microvascular blood flow in patients with sickle cell.

METHODS

We established a protocol that mimics nighttime hypoxic episodes and measured microvascular blood flow to determine if transient hypoxia causes a decrease in microvascular blood flow. Significant desaturations were induced safely by five breaths of 100% nitrogen.

MEASUREMENTS AND MAIN RESULTS

Desaturation did not induce change in microvascular perfusion; however, it induced substantial transient parasympathetic activity withdrawal in patients with sickle cell disease, but not controls subjects. Marked periodic drops in peripheral microvascular perfusion, unrelated to hypoxia, were triggered by sighs in 11 of 11 patients with sickle cell and 8 of 11 control subjects. Although the sigh frequency was the same in both groups, the probability of a sigh inducing a perfusion drop was 78% in patients with sickle cell and 17% in control subjects (P < 0.001). Evidence for sigh-induced sympathetic nervous system dominance was seen in patients with sickle cell (P < 0.05), but was not significant in control subjects.

CONCLUSIONS

These data demonstrate significant disruption of autonomic nervous system balance, with marked parasympathetic withdrawal in response to transient hypoxia. They draw attention to an enhanced autonomic nervous system–mediated sigh–vasoconstrictor response in patients with sickle cell that could increase red cell retention in the microvasculature, promoting vasoocclusion.

Autonomic nervous system reactivity: children with and without sickle cell disease

BACKGROUND

Previous studies of healthy children have indicated a link between autonomic nervous system (ANS) reactivity and health outcomes, but there is limited research on whether ANS reactivity is similar for children with chronic conditions.

OBJECTIVE

The aim of this study was to determine if ANS reactivity differs for children with sickle cell disease (SCD) compared with a community sample of children without SCD.

METHOD

In two cross-sectional, descriptive studies, 32 public school children without chronic health problems were compared with 33 children with SCD. The children were 5-8 years old and they completed standardized protocols measuring ANS responses (respiratory sinus arrhythmia and preejection period) during rest and challenge conditions in social, cognitive, sensory, and emotion domains. Reactivity was calculated as the difference between challenge response minus rest for each domain and overall.

RESULTS

There were differences in the distributions of the samples in parent education and child age, so these variables were adjusted for in subsequent analyses. The community sample showed parasympathetic withdrawal (low respiratory sinus arrhythmia scores) and greater parasympathetic reactivity (low respiratory sinus arrhythmia difference scores and percentage of negative scores) compared with the children with SCD in the social (p < .05) and sensory (p < .05) domains. The children with SCD showed greater sympathetic reactivity (low preejection period difference scores) compared with the community children in the cognitive domain (p < .05), and a greater percentage of children with SCD versus the community children showed negative preejection period difference scores (sympathetic reactivity) in the social domain (p < .05). The community sample, but not the children with SCD, showed changes in respiratory sinus arrhythmia across domains (p < .05).

DISCUSSION

Children with SCD may display a different pattern of ANS responses to laboratory challenges compared with children without SCD from the same community.

Frequency of pain crises in sickle cell anemia and its relationship with the sympatho-vagal balance, blood viscosity and inflammation

BACKGROUND

Recent evidence suggests that autonomic nervous system activity could be involved in the pathophysiology of sickle cell disease, but it is unclear whether differences in autonomic nervous system activity are detectable during steady state in patients with mild and severe disease. The aim of the present study was to compare the autonomic nervous system activity, blood rheology, and inflammation in patients with sickle cell anemia according to the frequency of acute pain crisis.

DESIGN AND METHODS

Twenty-four healthy volunteers, 20 patients with sickle cell anemia with milder disease, and 15 patients with sickle cell anemia with more severe disease were recruited. Milder disease was defined as having no pain crisis within the previous year. More severe disease was defined as having had within the previous year three or more pain crises which were documented by a physician and required treatment with narcotics. The autonomic nervous system activity was determined by spectral analysis of nocturnal heart rate variability. Blood viscosity determination and measurements of several inflammatory markers (interleukin-6, soluble vascular cell adhesion molecule-1, soluble CD40 ligand and sL-selectin) were made on blood samples collected in steady-state conditions.

RESULTS

Results showed that: 1) patients who had suffered more frequent pain crises had lower parasympathetic activity and greater sympatho-vagal imbalance than both controls and patients with milder disease. However, when adjusted for age, no significant difference was detected between the two sickle cell anemia patient groups; 2) patients who had suffered more frequent pain crises had higher blood viscosity than patients with milder disease, and this was not dependent on age.

CONCLUSIONS

Results from the present study indicate that both the autonomic nervous system activity and blood viscosity are impaired in patients with sickle cell anemia exhibiting high frequency of pain crisis in comparison with those who did not experience a crisis within the previous year.

Time-varying analysis of autonomic control in response to spontaneous sighs in sickle cell anemia

Sickle cell anemia (SCA) is a genetic disease which is characterized by painful episodes of vascular occlusions. In the present study, we investigated a potential contribution of the autonomic nervous system (ANS) in initiating such episodes. We observed prominent decreases in microvascular perfusion in response to spontaneous sighs, which may increase the likelihood of red blood cell polymerization followed by vascular occlusions in SCA patients. Time-varying spectral analysis of heart rate variability (HRV), based on recursive least squares estimation, was employed to study the modulation of the ANS in response to sighs. To improve robustness of the spectral estimation while retaining its ability to track rapid changes, we propose a time-varying parameter estimate variability reduction (TV-PEVR) technique. Because respiration patterns can vary considerably across subjects, we employed a time-varying autoregressive with exogenous input (TV-ARX) model to adjust for the effect of respiration patterns on the HRV indices. Results from 8 SCA subjects and 9 normal controls suggested that the cardiac ANS responses to sighs are not different between the two groups, after adjusting for the effect of post-sigh respiration. However, the peripheral sympathetic response in SCA appeared to be enhanced in this group relative to normals, and sighs may play a role in initiation of vaso-occlusive events in this group of patients.

Reconstructing sickle cell disease: a data-based analysis of the "hyperhemolysis paradigm" for pulmonary hypertension from the perspective of evidence-based medicine

The "hyperhemolytic paradigm" (HHP) posits that hemolysis in sickle disease sequentially and causally establishes increased cell-free plasma Hb, consumption of NO, a state of NO biodeficiency, endothelial dysfunction, and a high prevalence of pulmonary hypertension. The basic science underpinning this concept has added an important facet to the complexity of vascular pathobiology in sickle disease, and clinical research has identified worrisome clinical issues. However, this critique identifies and explains a number of significant concerns about the various HHP component tenets. In addressing these issues, this report presents: a very brief history of the HHP, an integrated synthesis of mechanisms underlying sickle hemolysis, a review of the evidentiary value of hemolysis biomarkers, an examination of evidence bearing on existence of a hyperhemolytic subgroup, and a series of questions that should naturally be applied to the HHP if it is examined using critical thinking skills, the fundamental basis of evidence-based medicine. The veracity of different HHP tenets is found to vary from true, to weakly supported, to demonstrably false. The thesis is developed that the HHP has misidentified the mechanism and clinical significance of its findings. The extant research questions identified by these analyses are delineated, and a conservative, evidence-based approach is suggested for application in clinical medicine.

Sickle cell disease: selected aspects of pathophysiology

Sickle cell disease (SCD), a genetically-determined pathology due to an amino acid substitution (i.e., valine for glutamic acid) on the beta-chain of hemoglobin, is characterized by abnormal blood rheology and periods of painful vascular occlusive crises. Sickle cell trait (SCT) is a typically benign variant in which only one beta chain is affected by the mutation. Although both SCD and SCT have been the subject of numerous studies, information related to neurological function and transfusion therapy is still incomplete: an overview of these areas is presented. An initial section provides pertinent background information on the pathology and clinical significance of these diseases. The roles of three factors in the clinical manifestations of the diseases are then discussed: hypoxia, autonomic nervous system regulation and blood rheology. The possibility of a causal relationship between these three factors and sudden death is also examined. It is concluded that further studies in these specific areas are warranted. It is anticipated that the outcome of such research is likely to provide valuable insights into the pathophysiology of SCD and SCT and will lead to improved clinical management and enhanced quality of life.

Tonic chemoreflex activation contributes to increased sympathetic nerve activity in heart failure-related anemia

Sympathetic activation contributes to both the initiation and progression of heart failure. The role of anemia in determining sympathetic overactivity in chronic heart failure (CHF) patients is unknown. We tested the hypothesis that, in CHF patients, anemia could lead to increased sympathetic activity through tonic activation of excitatory chemoreceptor afferents. We conducted a double-blind, randomized, vehicle-controlled study to examine the effect of chemoreflex deactivation on muscle sympathetic nerve activity in CHF patients with and without anemia. We compared the effect of breathing 100% oxygen for 15 minutes in 18 stable CHF patients with anemia and 18 control CHF patients matched for age, sex, blood pressure, and body mass index. Baseline muscle sympathetic nerve activity was significantly elevated in CHF patients with anemia compared with patients with CHF alone (56.0+/-3.2 versus 45.5+/-3.1 bursts per minute; P<0.0237). Administration of 100% oxygen led to a significant decrease in muscle sympathetic nerve activity in CHF patients with anemia (from 56.0+/-3.4 to 50.9+/-3.2 bursts per minute; P<0.0019). In contrast, neither room air nor 100% oxygen changed muscle sympathetic nerve activity or hemodynamics in patients with CHF alone. We report for the first time direct evidence of increased sympathetic nerve traffic in patients with CHF-related anemia. Sympathetic hyperactivity in patients with CHF and anemia is partially chemoreflex mediated and could explain how anemia contributes to the progression of CHF and increases morbidity and mortality in these patients.

Stress reactivity as a moderator of family stress, physical and mental health, and functional impairment for children with sickle cell disease

OBJECTIVE

To evaluate whether autonomic nervous system (ANS) reactivity modifies the relation between family stress, and physical and mental health, and functional impairment for children with sickle cell disease.

METHODS

Thirty-eight 5-to 8-year old children with sickle cell disease completed a 20-minute ANS reactivity protocol measuring respiratory sinus arrhythmia and pre-ejection period during comparison and challenge tasks in social, cognitive, sensory, and emotion domains. Domain-specific reactivity was calculated as the difference between challenge and comparison tasks; overall reactivity was calculated across domains as the mean of the difference scores. ANS profile scores combined the overall respiratory sinus arrhythmia and pre-ejection period reactivity scores. Caregivers completed measures of family stress, child physical and mental health symptoms, and functional impairment.

RESULTS

Family stress was associated with child functional impairment whereas overall and cognitive ANS reactivity was associated with co-morbid internalizing and externalizing mental health symptoms. Interaction models showed that children with the classic ANS profile (parasympathetic inhibition and sympathetic activation) in the cognitive and emotion domains were most vulnerable to the effects of stress, with more functional impairment and injuries when family stress was high, controlling for age, sex, and parent education.

CONCLUSION

The costs to patients and families in diminished quality of life and to the health care system could be reduced by further exploration of strategies to identify children with sickle cell disease who are most vulnerable under conditions of high family stress and heightened psychobiologic reactivity.

Abnormal cardiac autonomic control in sickle cell disease following transient hypoxia

Abnormalities in autonomic control in sickle cell anemia (SCA) patients have been reported by multiple researchers. However their potential causal association with sickle cell crisis remains unknown. We employed hypoxia, a known trigger to sickle cell crisis, to perturb the autonomic systems of the subjects. Cardiac autonomic control was non-invasively assessed by tracking the changes in heart rate variability (HRV) that occur following brief exposure to a hypoxia stimulus. Time varying spectral analysis of HRV was applied to estimate the cardiac autonomic response to the transient episode of hypoxia. The results demonstrate that cardiovascular autonomic response to hypoxia is substantially more sensitive in SCA than in normal controls. We also developed a model to compensate for the confounding effects of respiration on the HRV spectral indices by using the corresponding respiration signal to compensate for the respiratory correlated part of the HRV. This technique improved the resolution with which the effect of hypoxia on changes in HRV could be measured.

Comment on 'Abnormal autonomic cardiac response to transient hypoxia in sickle cell anemia'

Our recent results support the suggestions made by Sangkatumvong et al regarding autonomic dysfunction in sickle cell anemia.