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Effects of hemorrhagic hypotension on the cerebral circulation. II. Electrocortical function
Insights
This study shows that severe blood loss (hemorrhagic hypotension) significantly impacts brain activity in cats. Below 40 mm Hg, electroencephalogram (EEG) slows, and evoked responses diminish.
Area of Science:
- Neuroscience
- Physiology
Background:
- Hemorrhagic hypotension can affect cerebral function.
- Understanding the threshold for electrocortical changes is crucial.
Purpose of the Study:
- To investigate the effects of graded hemorrhagic hypotension on electrocortical function in cats.
- To determine the specific pressure thresholds at which changes in EEG and evoked responses occur.
Main Methods:
- 12 anesthetized cats (alpha-chloralose) underwent graded hemorrhagic hypotension.
- Cerebral function was assessed via spontaneous electroencephalogram (EEG) and somatosensory evoked responses.
- Mean arterial pressure was systematically reduced.
Main Results:
- No significant EEG or evoked response changes were noted above 40 mm Hg.
- Below 40 mm Hg, EEG rhythms slowed, with isoelectric EEG observed between 10-30 mm Hg.
- Evoked response amplitude reduction began around 35-40 mm Hg, reaching zero by 15-25 mm Hg.
Conclusions:
- Electrocortical function is relatively preserved until severe hypotension (below 40 mm Hg).
- Significant alterations in EEG and evoked potentials indicate critical cerebral perfusion thresholds.
- These findings highlight the sensitivity of brain function to reduced blood pressure.
Abstract:
The effects of graded hemorrhagic hypotension on electrocortical function was investigated in 12 cats anesthetized with alpha-chloralose. Cerebral function was assessed both in terms of spontaneous activity (EEG) and the somatosensory evoked response. No significant changes in the EEG trace or in the amplitude of the positive/negative waves of the primary evoked response were observed at mean arterial pressures of between 120 mm Hg and 40 mm Hg. At levels of systemic arterial pressure of less than 40 mm Hg cortical rhythms became slower as pressure was decreased and an isoelectric EEG was recorded in the pressure range 10--30 mm Hg. The earliest sign of any change in the amplitude of the primary evoked responses was observed at arterial pressures of approximately 35--40 mm Hg. Below this value the amplitude decreased with decreasing systemic pressure and became zero in the pressure range 15--25 mm Hg.