Intracranial Pressure Amplitude Research Articles

Detection of impaired cerebral autoregulation using spectral analysis of intracranial pressure waves.

Successful resuscitation following severe traumatic brain injury (TBI) requires rapid evaluation of intracranial pressure (ICP), cerebrovascular reactivity (autoregulation), and cerebral metabolism. During impaired autoregulation, inadequate cerebral blood flow (CBF) can lead to ischemia while excessive CBF can result in elevated ICP. Without information regarding the state of autoregulation, treatment of either situation may ameliorate one problem but exacerbate the other. It has been hypothesized that fast Fourier transform (FFT) analysis of arterial blood pressure (BP) and ICP waves can differentiate states of intact and impaired autoregulation. BP and ICP waves were recorded in canines before and after ischemic injury during arterial normotension, hypertension, and hypotension induced with dopamine or nitroprusside infusion. Transfer functions (TFn) were calculated from FFT spectra as ratios of ICP and BP harmonic peak amplitudes to distinguish states of vasoreactivity. During normotension and hypertension, autoregulation was intact and TF1 averaged 0.05. During hypotension, TF1 averaged 0.22 (8 x baseline, p < 0.010). During impaired autoregulation following ischemic injury, TF1 averaged 0.50 (18 x baseline, p < 0.010; 2 x nitroprusside levels, p < 0.01). This large difference in TF relative to baseline extended over a large range of BP (60 < BP < 180 mm Hg). Based on these data and previous results, it was estimated that TF can differentiate impaired autoregulation from effects solely related to elevated ICP or active vasodilation for ICP < 30-40 mm Hg. This suggests that for specific, but widely applicable physiologic conditions, spectral analysis can identify states of impaired autoregulation and, as an adjunct to traditional monitoring techniques, aid in acute resuscitation and prevention of secondary injury in TBI.

Fluctuation of intracranial pressure associated with the cardiac cycle

Within the intensive care setting, a portable microcomputer system was used to extract three parameters from the intracranial pressure fluctuation associated with the cardiac cycle. One parameter, the mean of sampled intracranial pressure, was defined as the average value of pressure for a 1.08-second interval following the R wave of the electrocardiogram. Another parameter, the amplitude of intracranial pressure, was defined as the difference between the mean and the peak value of the sampled intracranial pressure for the interval considered. The third parameter, a latent interval, was defined as the time period between the occurrence of the R wave and the occurrence of the peak value of the subsequent intracranial pressure fluctuation. Six adults and one pediatric patient were monitored. Both the amplitude and the mean of sampled pressure tended to vary inversely with the latent interval. For the adult patients, the latent interval varied between 503 and 804 ms; the mean pressure ranged between 2.4 and 19.0 mm Hg and the amplitude pressure ranged between 0.6 and 7.2 mm Hg. The latent interval for the child was much shorter (ranging between 269 and 325 ms), and both the mean and the amplitude pressures were much higher (ranging between 38.4 and 57.3 mm Hg and 14.2 and 16.5 mm Hg. respectively). Statistical correlation between hourly pulse rates and the latent interval among the adult cases revealed little association (r = -0.20). For all patients considered, the correlation between the amplitude and the mean of sampled intracranial pressure was quite high, with an r value of +0.91. These reported observations support a conceptual model in which blood volume changes associated with the cardiac cycle occurring within the semirigid craniospinal sac are assumed to underlie the fluctuation of intracranial pressure. (Neurosurgery 11:617-621, 1982)

Fluctuation of intracranial pressure associated with the cardiac cycle.

Within the intensive care setting, a portable microcomputer system was used to extract three parameters from the intracranial pressure fluctuation associated with the cardiac cycle. One parameter, the mean of sampled intracranial pressure, was defined as the average value of pressure for a 1.08-second interval following the R wave of the electrocardiogram. Another parameter, the amplitude of intracranial pressure, was defined as the difference between the mean and the peak value of the sampled intracranial pressure for the interval considered. The third parameter, a latent interval, was defined as the time period between the occurrence of the R wave and the occurrence of the peak value of the subsequent intracranial pressure fluctuation. Six adults and one pediatric patient were monitored. Both the amplitude and the mean of sampled pressure tended to vary inversely with the latent interval. For the adult patients, the latent interval varied between 503 and 804 ms; the mean pressure ranged between 2.4 and 19.0 mm Hg and the amplitude pressure ranged between 0.6 and 7.2 mm Hg. The latent interval for the child was much shorter (ranging between 269 and 325 ms), and both the mean and the amplitude pressures were much higher (ranging between 38.4 and 57.3 mm Hg and 14.2 and 16.5 mm Hg, respectively). Statistical correlation between hourly pulse rates and the latent interval among the adult cases revealed little association (r = -0.20). For all patients considered, the correlation between the amplitude and the mean of sampled intracranial pressure was quite high, with an r value of +0.91. These reported observations support a conceptual model in which blood volume changes associated with the cardiac cycle occurring within the semirigid craniospinal sac are assumed to underlie the fluctuation of intracranial pressure.