Functional near-infrared spectroscopy-based prefrontal cortex oxygenation during working memory tasks in sickle cell disease.

Significance: Sickle cell disease (SCD), characterized by painful vaso-occlusive crises, is associated with cognitive decline. However, objective quantification of cognitive decline in SCD remains a challenge, and the associated hemodynamics are unknown. Aim: To address this, we utilized functional near-infrared spectroscopy (fNIRS) to measure prefrontal cortex (PFC) oxygenation responses to N-back working memory tasks in SCD patients and compared them with healthy controls. Approach: We quantified the PFC oxygenation rate as an index of cognitive activity in each group and compared them. In half of the participants, a Stroop test was administered before they started N-back to elevate their baseline stress level. Results: In SCD compared to healthy controls, we found that (1) under a high baseline stress level, there were significantly greater oxygenation responses during the 2-back task, further elevated with histories of stroke; (2) there was a marginally slower N-back response time, and it was even slower with a history of stroke; and (3) the task accuracy was not different. Conclusions: Additional requirements for processing time, PFC resources, and PFC oxygenation in SCD patients offer an important basis for understanding their cognitive decline and highlight the potential of fNIRS for evaluating cognitive functions.

Vasoconstriction Response to Mental Stress in Sickle Cell Disease: The Role of the Cardiac and Vascular Baroreflexes.

Recent studies have shown that individuals with sickle cell disease (SCD) exhibit greater vasoconstriction responses to physical autonomic stressors, such as heat pain and cold pain than normal individuals, but this is not the case for mental stress (MTS). We sought to determine whether this anomalous finding for MTS is related to inter-group differences in baseline cardiac and vascular autonomic function. Fifteen subjects with SCD and 15 healthy volunteers participated in three MTS tasks: N-back, Stroop, and pain anticipation (PA). R-R interval (RRI), arterial blood pressure and finger photoplethysmogram (PPG) were continuously monitored before and during these MTS tasks. The magnitude of vasoconstriction was quantified using change in PPG amplitude (PPGa) from the baseline period. To represent basal autonomic function, we assessed both cardiac and vascular arms of the baroreflex during the baseline period. Cardiac baroreflex sensitivity (BRSc) was estimated by applying both the "sequence" and "spectral" techniques to beat-to-beat measurements of systolic blood pressure and RRIs. The vascular baroreflex sensitivity (BRSv) was quantified using the same approaches, modified for application to beat-to-beat diastolic blood pressure and PPGa measurements. Baseline BRSc was not different between SCD and non-SCD subjects, was not correlated with BRSv, and was not associated with the vasoconstriction responses to MTS tasks. BRSv in both groups was correlated with mean PPGa, and since both baseline PPGa and BRSv were lower in SCD, these results suggested that the SCD subjects were in a basal state of higher sympathetically mediated vascular tone. In both groups, baseline BRSv was positively correlated with the vasoconstriction responses to N-back, Stroop, and PA. After adjusting for differences in BRSv within and between groups, we found no difference in the vasoconstriction responses to all three mental tasks between SCD and non-SCD subjects. The implications of these findings are significant in subjects with SCD since vasoconstriction reduces microvascular flow and prolongs capillary transit time, increasing the likelihood for vaso-occlusive crisis (VOC) to be triggered by exposure to stressful events.

Tricuspid regurgitant jet velocity and myocardial tissue Doppler parameters predict mortality in a cohort of patients with sickle cell disease spanning from pediatric to adult age groups - revisiting this controversial concept after 16 years of additional evidence.

Sickle cell disease (SCD) is a monogenic hemoglobinopathy associated with significant morbidity and mortality. Cardiopulmonary, vascular and sudden death are the reasons for the majority of young adult mortality in SCD. To better understand the clinical importance of multi-level vascular dysfunction, in 2009 we assessed cardiac function including tricuspid regurgitant jet velocity (TRV), tissue velocity in systole(S') and diastole (E'), inflammatory, rheologic and hemolytic biomarkers as predictors of mortality in patients with SCD. With up to 9 years of follow up, we determined survival in 95 children, adolescents and adults with SCD. Thirty-eight patients (40%) were less than 21 years old at initial evaluation. Survival and Cox proportional-hazards analysis were performed. There was 19% mortality in our cohort, with median age at death of 35 years. In the pediatric subset, there was 11% mortality during the follow up period. The causes of death included cardiovascular and pulmonary complications in addition to other end-organ failure. On Cox proportional-hazards analysis, our model predicts that a 0.1 m/s increase in TRV increases risk of mortality 3%, 1 cm/s increase in S' results in a 91% increase, and 1 cm/s decrease in E' results in a 43% increase in mortality. While excluding cardiac parameters, higher plasma free hemoglobin was significantly associated with risk of mortality (p=.049). In conclusion, elevated TRV and altered markers of cardiac systolic and diastolic function predict mortality in a cohort of adolescents and young adult patients with SCD. These predictors should be considered when counseling cardiovascular risk and therapeutic optimization at transition to adult providers.

Progressive vasoconstriction with sequential thermal stimulation indicates vascular dysautonomia in sickle cell disease.

Persons with sickle cell disease (SCD) exhibit subjective hypersensitivity to cold and heat perception in experimental settings, and triggers such as cold exposure are known to precipitate vaso-occlusive crises by still unclear mechanisms. Decreased microvascular blood flow (MBF) increases the likelihood of vaso-occlusion by increasing entrapment of sickled red blood cells in the microvasculature. Because those with SCD have dysautonomia, we anticipated that thermal exposure would induce autonomic hypersensitivity of their microvasculature with an increased propensity toward vasoconstriction. We exposed 17 patients with SCD and 16 control participants to a sequence of predetermined threshold temperatures for cold and heat detection and cold and heat pain via a thermode placed on the right hand. MBF was measured on the contralateral hand by photoplethysmography, and cardiac autonomic balance was assessed by determining heart rate variability. Thermal stimuli at both detection and pain thresholds caused a significant decrease in MBF in the contralateral hand within seconds of stimulus application, with patients with SCD showing significantly stronger vasoconstriction (P = .019). Furthermore, patients with SCD showed a greater progressive decrease in blood flow than did the controls, with poor recovery between episodes of thermal stimulation (P = .042). They had faster vasoconstriction than the controls (P = .033), especially with cold detection stimulus. Individuals with higher anxiety also experienced more rapid vasoconstriction (P = .007). Augmented vasoconstriction responses and progressive decreases in perfusion with repeated thermal stimulation in SCD are indicative of autonomic hypersensitivity in the microvasculature. These effects are likely to increase red cell entrapment in response to clinical triggers such as cold or stress, which have been associated with vaso-occlusive crises in SCD.

Mental stress causes vasoconstriction in subjects with sickle cell disease and in normal controls.

Vaso-occlusive crisis (VOC) is a hallmark of sickle cell disease (SCD) and occurs when deoxygenated sickled red blood cells occlude the microvasculature. Any stimulus, such as mental stress, which decreases microvascular blood flow will increase the likelihood of red cell entrapment resulting in local vaso-occlusion and progression to VOC. Neurally mediated vasoconstriction might be the physiological link between crisis triggers and vaso-occlusion. In this study, we determined the effect of mental stress on microvascular blood flow and autonomic nervous system reactivity. Sickle cell patients and controls performed mentally stressful tasks, including a memory task, conflict test and pain anticipation test. Blood flow was measured using photoplethysmography, autonomic reactivity was derived from electrocardiography and perceived stress was measured by the State-Trait Anxiety Inventory questionnaire. Stress tasks induced a significant decrease in microvascular blood flow, parasympathetic withdrawal and sympathetic activation in all subjects. Of the various tests, pain anticipation caused the highest degree of vasoconstriction. The magnitude of vasoconstriction, sympathetic activation and perceived stress was greater during the Stroop conflict test than during the N-back memory test, indicating the relationship between magnitude of experimental stress and degree of regional vasoconstriction. Baseline anxiety had a significant effect on the vasoconstrictive response in sickle cell subjects but not in controls. In conclusion, mental stress caused vasoconstriction and autonomic nervous system reactivity in all subjects. Although the pattern of responses was not significantly different between the two groups, the consequences of vasoconstriction can be quite significant in SCD because of the resultant entrapment of sickle cells in the microvasculature. This suggests that mental stress can precipitate a VOC in SCD by causing neural-mediated vasoconstriction.

A novel cross-correlation methodology for assessing biophysical responses associated with pain.

PURPOSE: The purpose of this work was to noninvasively detect and quantify microvascular blood flow changes in response to externally applied pain in humans. The responsiveness of the microvasculature to pain stimulation might serve as an objective biomarker in diseases associated with altered pain perception and dysregulated vascular functions. The availability of such a biomarker may be useful as a tool for predicting outcome and response to treatments, particularly in diseases like sickle cell anemia where clinical manifestations are directly linked to microvascular perfusion. We, therefore, developed a method to distinguish the blood flow response due to the test stimulus from the blood flow measurement that also includes concurrent flow changes from unknown origins. SUBJECTS AND METHODS: We measured the microvascular blood flow response in 24 healthy subjects in response to a train of randomly spaced and scaled heat pulses on the anterior forearm. The fingertip microvascular perfusion was measured using laser Doppler flowmetry. The cross-correlation between the heat pulses and the blood flow response was computed and tested for significance against the null distribution obtained from the baseline recording using bootstrapping method. RESULTS: We estimated correlation coefficients, response time, response significance, and the magnitude of vasoreactivity from microvascular blood flow responses. Based on these pain response indices, we identified strong responders and subjects who did not show significant responses. CONCLUSION: The cross-correlation of a random pattern of painful stimuli with directly measured microvascular flow can detect vasoconstriction responses in a noisy blood flow signal, determine the time between stimulus and response, and quantify the magnitude of this response. This approach provided an objective measurement of vascular response to pain that may be an inherent characteristic of individual human subjects, and may also be related to the severity of vascular disorders.

Individuals with sickle cell disease have a significantly greater vasoconstriction response to thermal pain than controls and have significant vasoconstriction in response to anticipation of pain.

The painful vaso-occlusive crises (VOC) that characterize sickle cell disease (SCD) progress over hours from the asymptomatic steady-state. SCD patients report that VOC can be triggered by stress, cold exposure, and, pain itself. We anticipated that pain could cause neural-mediated vasoconstriction, decreasing regional blood flow and promoting entrapment of sickle cells in the microvasculature. Therefore, we measured microvascular blood flow in the fingers of both hands using plethysmography and laser-Doppler flowmetry while applying a series of painful thermal stimuli on the right forearm in 23 SCD patients and 25 controls. Heat pain applied to one arm caused bilateral decrease in microvascular perfusion. The vasoconstriction response started before administration of the thermal pain stimulus in all subjects, suggesting that pain anticipation also causes significant vasoconstriction. The time delay between thermal pain application and global vasoconstriction ranged from 5 to 15.5 seconds and increased with age (P < .01). Although subjective measures, pain threshold and pain tolerance were not different between SCD subjects and controls, but the vaso-reactivity index characterizing the microvascular blood flow response to painful stimuli was significantly higher in SCD patients (P = .0028). This global vasoconstriction increases microvascular transit time, and may promote entrapment of sickle cells in the microvasculature, making vaso-occlusion more likely. The rapidity of the global vasoconstriction response indicates a neural origin that may play a part in the transition from steady-state to VOC, and may also contribute to the variability in VOC frequency observed in SCD patients.

Biophysical markers of the peripheral vasoconstriction response to pain in sickle cell disease.

Painful vaso-occlusive crisis (VOC), a complication of sickle cell disease (SCD), occurs when sickled red blood cells obstruct flow in the microvasculature. We postulated that exaggerated sympathetically mediated vasoconstriction, endothelial dysfunction and the synergistic interaction between these two factors act together to reduce microvascular flow, promoting regional vaso-occlusions, setting the stage for VOC. We previously found that SCD subjects had stronger vasoconstriction response to pulses of heat-induced pain compared to controls but the relative degrees to which autonomic dysregulation, peripheral vascular dysfunction and their interaction are present in SCD remain unknown. In the present study, we employed a mathematical model to decompose the total vasoconstriction response to pain into: 1) the neurogenic component, 2) the vascular response to blood pressure, 3) respiratory coupling and 4) neurogenic-vascular interaction. The model allowed us to quantify the contribution of each component to the total vasoconstriction response. The most salient features of the components were extracted to represent biophysical markers of autonomic and vascular impairment in SCD and controls. These markers provide a means of phenotyping severity of disease in sickle-cell anemia that is based more on underlying physiology than on genotype. The marker of the vascular component (BMv) showed stronger contribution to vasoconstriction in SCD than controls (p = 0.0409), suggesting a dominant myogenic response in the SCD subjects as a consequence of endothelial dysfunction. The marker of neurogenic-vascular interaction (BMn-v) revealed that the interaction reinforced vasoconstriction in SCD but produced vasodilatory response in controls (p = 0.0167). This marked difference in BMn-v suggests that it is the most sensitive marker for quantifying combined alterations in autonomic and vascular function in SCD in response to heat-induced pain.