Abstract
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.
Highlights
Sickle cell disease (SCD) is caused by a single mutation in the β-globin gene, resulting in the production of sickle hemoglobin which polymerizes after deoxygenation (Rees et al, 2010)
The elevated blood pressure would stimulate the baroreceptors and produce compensatory changes in heart rate and cardiac contractility, as well as vascular resistance, which in turn lower blood pressure to a level consistent with the negative feedback. If this was the only factor involved, we would have expected a negative relationship between baroreflex sensitivity and the magnitude of vasoconstriction resulting from mental stress (MTS), since a higher BRSv would have triggered a compensatory vasodilation to minimize the increase in blood pressure
We examined the source of variability in the vasoconstriction responses of SCD and controls to MTS
Summary
Sickle cell disease (SCD) is caused by a single mutation in the β-globin gene, resulting in the production of sickle hemoglobin which polymerizes after deoxygenation (Rees et al, 2010). The polymerization changes liquid hemoglobin into a solid, transforming the flexible RBC into sickled-shaped RBC that tend to obstruct microvascular flow. The clinical manifestation of extensive obstruction of microvascular flow is episodic painful vaso-occlusive crisis (VOC), the hallmark symptom of SCD. Higher hemoglobin, or higher blood viscosity have been associated with higher frequent pain episodes (Nebor et al, 2011; Darbari et al, 2012, 2013). These factors do not account for immediate transition from steady state to VOC, and the mechanisms responsible for initiating VOC remain elusive
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
