Assessment of craniospinal pressure-volume indices

Abstract

Background and purpose: The PVI(CC) of the craniospinal compartment defines the shape of the pressure-volume curve and determines the damping of cyclic arterial pulsations. Despite no reports of direct measurements of the PVI(CC) among healthy elderly, it is believed that a change away from adequate accommodation of cardiac-related pulsations may be a pathophysiologic mechanism seen in neurodegenerative disorders such as Alzheimer disease and idiopathic normal pressure hydrocephalus. In this study, blood and CSF flow measurements are combined with lumbar CSF infusion measurements to assess the craniospinal PVI(CC) and its distribution of cranial and spinal compartments in healthy elderly.

Materials and methods: Thirty-seven healthy elderly were included (60-82 years of age). The cyclic arterial volume change and the resulting shift of CSF to the spinal compartment were quantified by PC-MR imaging. In addition, each subject underwent a lumbar CSF infusion test in which the magnitude of cardiac-related pulsations in intracranial pressure was quantified. Finally, the PVI was calculated by using a mathematic model.

Results: After excluding 2 extreme values, the craniospinal PVI(CC) was calculated to a mean of 9.8 ± 2.7 mL and the estimated average 95% confidence interval of individual measurements was ± 9%. The average intracranial and spinal contributions to the overall compliance were 65% and 35% respectively (n = 35).

Conclusions: Combining lumbar CSF infusion and PC-MR imaging proved feasible and robust for assessment of the craniospinal PVI(CC). This study produced normative values and showed that the major compensatory contribution was located intracranially.

Fig 1.

A subject recording of ΔICP and ICP from a constant pressure lumbar CSF infusion test. The RPPC is the slope of the linear regression line between ΔICP and ICP. P₀ is calculated as the pressure at which this line intersects with ΔICP = 0.

Fig 2.

An overview of how the infusion and MR imaging modalities are combined to estimate compliance indices.

Fig 3.

A, Total cerebral arterial blood flow (summated flow of the internal carotid and vertebral arteries). B, Cumulative integration of the curve in A with the average flow subtracted yields the arterial volume change during a cardiac cycle. ΔV_ART was defined as the largest volume difference during a cardiac cycle.

Fig 4.

An ICP recording from a lumbar CSF infusion test. A, Baseline ICP recording. B, Infusion to predetermined ICP levels. C, Relaxation phase allowing ICP to normalize. D, A bolus test (rapid infusion of a 5.6-mL artificial CSF).

Fig 5.

The craniospinal PVI calculated from combined MR imaging and infusion (y-xis) and from the bolus test (x-axis). The difference was not statistically different from zero, P = .83 from a paired t test. There was no significant correlation after excluding 2 extreme values (dashed contours) (P = .8778).