Are changes in intracranial pressure detectable by measurement of the cerebrospinal fluid velocity wave speed in the spinal canal?
Craniospinal compliance has been thought to be an important indicator of craniospinal health. Some have postulated that, when properly functioning, the spinal subarachnoid space (SAS) compliance may act as a notch filter to dampen out cerebrospinal (CSF) flow pulsations (Madsen, Egnor et al. 2006; Luciano and Dombrowski 2007). However, a non-invasive technique for assessment of craniospinal compliance has not been validated. The proposed study aims to investigate the sensitivity of a novel non-invasive MR technique to changes in intracranial pressure (ICP), which is directly related with craniospinal compliance.
Communication between the intrathorasic and ICP due to postural changes (Dabrowski 2007; De Keulenaer, Cheatham et al. 2009), coughing (Sansur, Heiss et al. 2003), valsalva and Queckenstedt’s test, and abdominal pressure (Bloomfield, Ridings et al. 1997) has been well documented (Williams 1981; Williams 1981; Heiss, Patronas et al. 1999; Sansur, Heiss et al. 2003). These pressure changes are transmitted from the abdomen into the CSF system (ICP) through the dural venous sinuses and epidural venous plexus (Figure 1 and Figure 2). Thus, it is possible to vary ICP and compliance by a number of non-invasive tests. The changes in ICP are expected to be detectable by spinal CSF velocity wave speed, since the spinal canal forms a compliant tube-like system which transmits cranial CSF pulsations through the spinal SAS (~1 cc per cardiac cycle at C2 level (Loth, Yardimci et al. 2001; Martin, Kalata et al. 2005)).
Hypothesis and research objectives
We hypothesize that the spinal CSF velocity wave speed is indicative of ICP which can be modified non-invasively by a series of tests. The goal of this research is thus to validate the sensitivity of a novel MR protocol to changes in ICP.
Methods and study outline
- A. in vivo MR measurements.
Our approach is to obtain CSF velocity wave speed measurements using the technique described by Kalata et al. (Kalata, Martin et al. 2009) on healthy male 20-30 year old subjects under two conditions.
- Baseline MR CSF velocity wave speed measurements (Kalata, Martin et al. 2009) will be obtained on the subject at normal pressure in the supine position.
- A series of three tests will be performed on the subject while obtaining identical MR measurements as the baseline measurement. The three tests will include continuous positive airway pressure (CPAP) (Bowie, O'Connor et al. 2001), Queckenstedt’s test (Williams 1981; Williams 1981; Heiss, Patronas et al. 1999; Sansur, Heiss et al. 2003), and placement of a mass on the stomach. The CPAP and Queckenstedt’s test will be performed at moderately elevated pressures (i.e. ~15 cm H2O). A mass will be placed on the stomach (i.e. 10 Kg water bags). The subject’s heart rate, Oxygen saturation (SpO2), and transcutaneous carbon dioxide tension (PCO2) will be monitored. Subjects will be able to discontinue testing at any time. A medical doctor will be present throughout the duration of testing.
- The baseline measurement and all three tests will initially be conducted on three subjects to determine which are best suited to change CSF velocity wave speed in the spinal subarachnoid space. Subsequent tests will be performed using the most promising tests.
- B. Single-blind processing of MR data.
CSF velocity wave speed in the spinal canal for each subject will be obtained from the MR study data using the technique employed by Kalata et al. (Kalata, Martin et al. 2009) and Filden et al. (Fielden, Fornwalt et al. 2008). These calculations will be performed by an engineer blinded to the test case.
Expected results and potential impact
The proposed work will determine if the non-invasive MR test is sensitive to changes in ICP caused by a series of tests. If proven efficacious, it could be further explored to understand its sensitivity and accuracy, and could have the potential to provide a clinically useful tool for assessment of craniospinal compliance.
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