Around the world, stroke is a leading cause of death and disability. Environmental and biological factors are known to play a big part in increasing the risk and the severity of the outcomes of stroke.
A new study that focuses on the cerebral blood flow (CBF) regulation of individuals who have had a stroke, found that cerebral autoregulation (CA), one of the processes to maintain sufficient blood supply to the brain, displayed a daily rhythm in stroke patients.
This pattern showed to have more degraded regulation during nighttime and morning hours, compared to that in the afternoon hours.
The research team believe their results are relevant for health care planning during stroke recovery.
Senior author, Sun Hu, says: “The care and course of actions done after a stroke are essential for optimal rehabilitation. Our study suggests that the daily rhythm of CBF regulation in stroke patients may be highly relevant to managing an individual’s activity and stroke recovery.
“Exercise and surgery post-stroke could be more optimal when scheduled during afternoon hours, as this is when dynamic CA functions more effectively. These results may improve our understanding of a vulnerable time window for the cerebrovascular system and help guide daily activity and personal care during stroke recovery, which could improve health outcomes for patients who have had a stroke.”
For normal brain function, stable CBF is a necessary component, and drastic changes in CBF can cause increased cranial pressure and brain tissue damage. This means a process like CA which helps maintain relatively stable CBF through constriction and dilation of blood vessels in the brain, particularly during changes in an individual’s blood pressure (BP), is crucial.
Currently, there is a gap in knowledge concerning the daily variance of CA in stroke patients. Generally, the daily rhythms of physiological functions can be controlled by external behaviours like food intake, sleep and exercise, as well as the internal circadian clock.
This study is amongst the first to examine the potential variation of CA in the stroke population.
For this study, 28 participants being treated in a hospital in São Paulo, Brazil after experiencing a stroke. The patients received thrombolysis within 5 hours of the onset of their symptoms.
After undergoing this procedure, the participants’ CA was assessed over the course of 48 hours at various time points by examining the relationship between temporal changes in blood pressure and cerebral blood flow velocity of the middle cerebral artery.
Analysis of the results showed evidence of differing cerebral blood flow regulation during various times of the day, especially when cerebral blood flow and pressure fluctuated at large time scales or low frequencies < 0.05 Hz. In particular, amore degraded regulation motif was seen during the nighttime and morning hours when compared to the afternoon.
This dysregulation interval coincides with the increased prevalence of recurrent and first-ever stroke events during morning times.
While these results show potential, researchers have already identified future avenues to assist in creating a greater understanding of the regulation mechanism.
First author, Daniel Abadjiev, says: “Interestingly, the daily rhythm of CA was present in both stroke and non-stroke sides of the brain, suggesting the factor(s) driving the rhythm should affect CBF regulation globally.
“To better understand underlying mechanisms, future studies should consider more frequent assessments across the 24-hour cycle, an increase in patient sample size, inclusion of non-stroke controls, and monitoring of the daily activity rhythms like sleep and exercise as well as intrinsic circadian rhythm among the participants.”
Hu, says: “This study demonstrates that a daily rhythm does exist for stroke patients,” said Hu. “Rehab plans should look to identify the daily rhythm and design a strategy that makes use of optimal CA. The long-term goal is to see if we can further control the rhythm of CA by manipulating an individual’s daily behavioural cycles or endogenous circadian clock in order to deliver more personalised medicine and improve their recovery.”
