The evolution of blood brain barrier permeability changes after stroke, and its implications on clinical outcome: a systematic review and meta-analysis

BACKGROUND

Blood-brain barrier permeability (BBBp) is key process involved in ischemic stroke pathophysiology. However, there is a lack of consensus on how BBBp evolves after the ischaemic injury, and its clinical relevance at different time points post stroke.

AIMS

To assess BBBp evolution through stroke phases, and its implications on patient outcomes.

METHODS

We screened PubMed/MEDLINE, EMBASE, Web of Science, Scopus and Cochrane Central Register of Controlled Trials up to December 31, 2021. We included research quantitatively using neuroimaging to assess BBBp in stroke patients. BBBp in the different phases was evaluated by a random effect model based on the standardized mean difference (SMD) between the ipsilateral and contralateral sides of the brain. We performed subgroup analysis on clinical outcome, reperfusion treatment, haemorrhagic transformation and imaging method.

RESULTS

We identified 3761 studies of which 22 (1592 patients, 1787 evaluations) were included in our study. Overall, 17 studies reported BBBp for the hyperacute phase, eight for the acute, five for the subacute and two for the chronic phase. All phases were associated with increased BBBp : 0.74 (0.48-0.99), 1.68 (0.94-2.42), 1.98 (0.96-3.00) and 1.00 (0.45-1.55) respectively. An increase in BBBp was associated with hemorrhagic transformation in the hyperacute phase, and with improved functional outcomes in the late subacute phase.

CONCLUSIONS

BBBp is persistently increased after stroke, peaking in the acute and subacute phases. The degree of BBBp influences patient outcomes depending on stroke phase. Our findings support the clinical relevance of BBBp dynamics in stroke care.

A pathway for information transmission to the ear

The use of implantable hearing aids and cochlear implants as an aid to neurosensory deafness is becoming an established procedure. The transmission of a processed speech signal is accomplished either transcutaneously via radiofrequency or percutaneously by connector coupling. Whereas the former is sensitive to electromagnetic interference, the latter increases the risk of infection. To overcome these disadvantages, an infrared (IR) system for transmission through the tympanic membrane was devised and tested. The transmitter/receiver consisted of an IR light emitting diode (LED; 920nm) and a photovoltaic cell. The LED was placed inside the auditory canal of four dogs and the photovoltaic cell in the tympanic cavity over the cochlear promontory. A sinusoidal signal modulation was applied to the LED. The emitted signal was detected undistorted after crossing the tympanic membrane, with an average absorbance of 20%. High-frequency cut-off was adequate for cochlear implant purposes and audio prosthetic devices in general. The authors conclude that the tympanic membrane may be used as a translucent sealed interface to transmit data in the audio range to the middle and inner ears, with small power loss, good frequency response, and immunity to interface.

A pathway for information transmission to the inner ear. Application to cochlear implants

The use of cochlear implants as an aid to neurosensory deafness is becoming an established procedure. The transmission of a processed speech signal is accomplished either transcutaneously via radiofrequency or percutaneously by connector coupling. Whereas the former is sensitive to electromagnetic interference, the latter increases the risk of infection. To overcome these disadvantages, an infrared (IR) system for transmission through the tympanic membrane was devised and tested. The transmitter/receiver consisted of an IR light emitting diode (LED; 920 nm) and a photovoltaic cell. The LED was placed inside the auditory canal of four dogs and the photovoltaic cell in the tympanic cavity over the cochlear promontory. A sinusoidal signal modulation was applied to the LED. The emitted signal was detected undistorted after crossing the tympanic membrane, with an average absorbance of 20%. High frequency cut-off was adequate for cochlear implant purposes and audio prosthetic devices in general. The authors conclude that the tympanic membrane may be used as a translucent sealed interface to transmit data in the audio range to the middle and inner ears, with small power loss, good frequency response, and immunity to interference.