Effects of continuously expanding intracranial lesions on vital physiological parameters. An experimental animal study.

The work described in this report confirms and extends the results described in a preliminary communication (Löfgren, J. and Zwetnow, N.N., Acta Neurol. Scand. (1970, 625) which examined the effects in cats of an expanding mass, in the form of an intracranial supratentorial balloon, on vital physiological parameters. In the present study, particular emphasis was placed on the possible significance of the rate of expansion of the mass in the range usually encountered in the clinical situation of intracranial haemorrhages. Results from the experiments on 37 cats and 8 dogs showed that changes in vital parameters appeared when the balloon had reached a volume of about 5% of the intracranial volume (the "reaction volume") while respiratory arrest occurred at an intracranial volume of about 10% (the "apnoea volume"). Both threshold volumes were independent of the rate of expansion within the range used. Alterations in EEG, heart rate, respiratory rate and systemic arterial pressure usually occurred simultaneously with the development of a transtentorial pressure gradient. When respiratory arrest occurred, the cerebral perfusion pressure was markedly reduced, usually to a value of about 30 mm Hg, suggesting that brain tissue ischaemia is an important component in the lethal mechanism underlying intracranial expanding lesions. It is proposed that the volume load tolerance of the organism towards an expanding intracranial lesion, as expressed by the reaction volume and the apnoea volume, may represent a biologically useful parameter potentially suitable for quantitative evaluation of adverse agents and therapeutic procedures.