Abstract
The aqueductal CSF and superior sagittal sinus (SSS) blood flow were quantified in 9 healthy volunteers using a Phase Contrast Cine MR technique with retrospective cardiac gating and velocity of encoding of 10 and 30 cm/s.
All subjects were examined in basal conditions, during hypocapnia determined by sustained hyperventilation and during hypercapnia (>5%) obtained with rebreathing in a plastic bag. In basal conditions, the aqueductal CSF flow area showed a mean increase of 24% synchronous with the cerebral systole, whereas variations of the SSS flow area during the cardiac cycle were negligible (>9%).
The mean flow velocity and volume in the SSS were 11.7 cm/s and 236 ml/min. Mean peak systolic and diastolic aqueductal CSF velocity were + 2 cm/s and −2 cm/s. Hypocapnia determined in all but one subjects a decrease of the SSS blood and aqueductal CSF velocities.
During hypocapnia a decrease of the aqueductal CSF flow area was also observed. Hypercapnia was associated with a decrease of the SSS flow velocity in 3 subjects and to minor changes in the remaining 6 subjects. Hypercapnia determined an increase (up to 30%) in the peak systolic and diastolic aqueductal CSF flow velocity in 3 subjects, negligible changes in 5 subjects and a decrease of the same parameters in one subject. The aqueductal CSF flow area was decreased in 8 subjects during hypercapnia.
Hypocapnia and hypercapnia are relatively simple tests which can be used to modify the intracranial hydrodynamic equilibrium in healthy subjects. Further investigations are however needed before their application to the study of intracranial hydrodynamics in patients with hydrocephalus.
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