Effects of intracranial hypertension on steady and pulsatile haemodynamics in dogs.

1. Intracranial hypertension (ICH) tends to elicit various cardiovascular changes. Previous studies on the haemodynamic responses to ICH have been confined mainly to measurements of arterial pressure (AP), cardiac output (CO) and total peripheral resistance (TPR). In the present study, we used the technique of arterial impedance analysis for a complete assessment of steady and pulsatile haemodynamics in ICH. 2. In anaesthetized dogs, aortic pressure and flow waves were obtained with high-fidelity Millar sensors. The pressure and flow waves were subjected to Fourier transformation (frequency analysis) for an analysis of impedance spectra. Intracranial pressure (ICP) was elevated by inflation of an epidural balloon. At an ICP of 50 mmHg, the changes in steady and pulsatile haemodynamics were slight. 3. Haemodynamic changes became evident at an ICP of 100 mmHg. The mean AP was elevated by 31 mmHg (+32%) and heart rate (HR) was reduced by 25 b.p.m. (-18%). There was also a significant decrease in CO by 27% and large increase in TPR by 82%. With respect to pulsatile haemodynamics, an elevation of ICP to 100 mmHg caused significant increases in characteristic impedance by 45% and wave reflection by 53%. Arterial compliance was reduced by 50%. The ventricular oscillatory work was increased without a significant change in steady work. 4. The results indicate that ICH causes constriction of resistance vessels to affect AP and TPR. Because the pulsatile haemodynamics reflect mainly the Windkessel functions, ICH also induces stiffness of the large vessels to affect arterial impedance, pulse wave reflection and ventricular oscillatory work.