The human brain and spinal cord are immersed in the

Chapter 9, Problem 9.75

(choose chapter or problem)

The human brain and spinal cord are immersed in the cerebrospinal uid. The uid is normally continuous between the cranial and spinal cavities and exerts a pressure of 100 to 200 mm of H2O above the prevailing atmospheric pressure. In medical work, pressures are often measured in units of mm of H2O because body uids, including the cerebrospinal uid, typically have nearly the same density as water. The pressure of the cerebrospinal uid can be measured by means of a spinal tap. A hollow tube is inserted into the spinal column, and the height to which the uid rises is observed, as shown in Figure P9.75. If the uid rises to a height of 160 mm, we write its gauge pressure as 160 mm H2O. (a) Express this pressure in pascals, in atmospheres, and in millimeters of mercury. (b) Sometimes it is necessary to determine whether an accident victim has suffered a crushed vertebra that is blocking the ow of cerebrospinal uid in the spinal column. In other cases, a physician may suspect that a tumor or other growth is blocking the spinal column and inhibiting the ow of cerebrospinal uid. Such conditions can be investigated by means of the Queckensted test. In this procedure, the veins in the patients neck are compressed, to make the blood pressure rise in the brain. The increase in pressure in the blood vessels is transmitted to the cerebrospinal uid. What should be the normal effect on the height of the uid in the spinal tap? (c) Suppose that compressing the veins had no effect on the level of the uid. What might account for this phenomenon?