However there can be periods ranging from months to decades where the average pressure differences between the two systems are either high (positive phase) or low (negative phase). (oceanmotion.org)
This created a very small pressure difference between the outside of the plates and the inside. (religion.blogs.cnn.com)
Many local doctors were concerned that the procedure could force the brain out of the hole at the base of the skull because of the potential pressure difference it could cause. (sciencedaily.com)