Intracranial pressure and pulsatility in different head and body positions

Intracranial pressure (ICP) is typically measured with the head in a neutral position whilst the body is in an upright or supine posture. The effect of body position on ICP is well studied, with ICP greater when supine than when upright. In daily life the head is frequently moved away from the neutral position but how this impacts ICP dynamics is unclear. Knowledge of ICP dynamics in different head-on-body positions may improve future treatments that restore normal ICP dynamics such as CSF drainage shunts. We recruited 57 relatively well, ambulatory patients undergoing clinical ICP monitoring for investigation of possible CSF dynamics disturbances to a single-centre, cross-sectional study. Forty-one patients were non-shunted, seven had a working shunt and nine had a malfunctioning shunt. We measured ICP and ICP pulsatility (pulse amplitude) over 10 or 20 s in different combinations of head and body positions. Positions included right and left head turn and forward tilt in upright (seated, standing) and supine body positions, and right and left lateral tilt and backward tilt in upright body positions. ICP increased by 3-9 mmHg, on average, when the head moved away from neutral to each head position in upright and supine body positions, except for head forward tilt when supine, where ICP did not change. The increase in ICP with head turn and forward tilt in upright body positions was larger in patients with a malfunctioning shunt than with no shunt or a functioning shunt. Pulsatility also increased by 0.5-2 mmHg on average when the head moved away from neutral to each head position in upright and supine body positions, except for head forward tilt in upright body positions where pulsatility slightly decreased by 0.7 mmHg on average. ICP and pulsatility generally increase when the head is moved away from the neutral position, but this depends on a combination of head and body position and shunt status. We propose our results can be explained by a combination of changes to neck vasculature and head orientation relative to gravity. Our findings provide potential reason for patient reports that ICP-related symptoms can be induced and/or exacerbated by head movement and could explain behaviours that avoid excess head movement, such as turning the body rather than the head when looking to the side. Our data describe the predicted change in ICP in different head and body positions and could underpin future smart shunt design.