Cerebral circulation in hypoxia and ischemia.

Area of Science:

• Neuroscience
• Physiology
• Pathophysiology

Background:

• The brain's autoregulation is robust, but prolonged hypovolemic conditions can still impair vital functions.
• Hemorrhagic shock leads to reduced cerebral blood flow (CBF), potentially causing ischemic brain damage.

Purpose of the Study:

• To investigate the impact of prolonged hypovolemia on brain function and cerebral blood flow.
• To explore the mechanisms underlying cerebral microcirculation impairment during hemorrhagic shock.

Main Methods:

• Regional cerebral blood flow (CBF) measurement using 133Xe clearance and 14C-antipyrine autoradiography.
• Assessment of sympathetic nervous system involvement and nociceptive input.
• Investigation of subcellular events, including high-energy phosphate depletion and calcium influx.

Main Results:

• Demonstrated progressive reduction in CBF with patchy, circumscribed ischemic areas during hemorrhagic shock, persisting post-reinfusion.
• Identified involvement of the sympathetic nervous system and local factors in cerebral microcirculation impairment.
• Observed that nociceptive afferent stimulation increased shock sensitivity, while denervation decreased it.

Conclusions:

• Prolonged hypovolemia impairs brain function, leading to focal brain damage and functional deficits.
• Sympathetic nervous system activation and local factors play significant roles in cerebral ischemia during shock.
• Depletion of high-energy phosphates and increased intracellular calcium are implicated in neuronal death during hemorrhagic shock.