A 42-year-old man on ICU has a severe traumatic brain injury. His ICP is 15 mmHg, MAP 85 mmHg, CPP 70 mmHg. He is adequately sedated with propofol and alfentanil. The ICP waveform shows a Lundberg B wave pattern (regular oscillations of ICP between 10 and 20 mmHg at a frequency of 0.5-2 per minute). What do Lundberg B waves indicate?