Episodic slow pressure waves were detected in 10 of 120 severely head-injured (HI) children, continuously monitored with minute to minute recordings of ICP, MAP, CPP, Heart Rate (HR), O2Saturations etc.
The waveforms were detected in children of all ages (1.6-15years) in the ICP signal, which were in phase with similar fluctuations in the MAP, CPP, and HR signals. Their mean periodicity was 1 per 7 minutes (range 1 per 5 - 10minutes), with a mean ICP amplitude of 5.5 mmHg (range 4-7.5), and mean MAP amplitude of 11mmHg (range 5-15mmHg). The duration was variable (range approx 2 hours to 4.5days). They were detected in the preterminal phase after serious HI, as well as in those children who made an independent recovery (GOS 4/5). The waves were not related to the mean levels of ICP, CPP, MAP, or the state of cerebro-vascular autoregulation.
Figure 1, illustrates these waves from a 2 hour time period (in a 14 year old child who died following a RTA) showing fluctuations in both ICP and MAP, which were also reflected in the systolic and diastolic pressure, and in the pulse, but not in the O2 saturation recording.
We postulate that these slow frequency waveforms may reflect the very low frequency (VLF) and ultra low frequency (ULF) (?1 per 5 minutes) components of heart rate variability (HRV), assessed by frequency domain. HRV indicates disordered autonomic regulation of circulatory function, normally mediated via the negative feedback loop (baroreflex) through Nucleus Tractus Solitarius to coupled sympathetic and parasympathetic efferents from the vasomotor centre and vagal nucleus. Similar waveforms in the blood pressure and heart rate have been recognised in the neonate with and without asphyxial brain damage.
Minns RA, Jones PA and Chambers IR. Low frequency pressure waves of autonomic origin in severely head-injured children. International Symposium on Intracranial Pressure and Brain Monitoring, Mechanisms and Treatment. 23rd July 2007, San Francisco.
Dr. Iain R. Chambers, Cleveland Unit, Middlesbrough. Tel: +44 (0)1642-854-778.
Regional Medical Physics Department, Newcastle General Hospital, Newcastle upon Tyne, NE4 6BE, UK.
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