Time- and frequency domain analysis of cerebrovascular control

Cerebral autoregulation (CA) as a control mechanism of perfusion pressure takes
care of the maintaining of perfusion pressure within the cerebrovascular system
and the reflective vasoconstriction of brain vessels for increasing cerebral
perfusion pressure (CPP) and vasodilatation when CPP decreases. This change in
vessel diameter, to great extent, influences cerebrovascular resistance (CVR).
The amount of blood flow towards the brain, the cerebral blood flow (CBF), is
inversely related to the CVR. When CA is impaired or absent, CBF will become
directly proportionally linked to changes in CPP as was shown by our studies as
well as by other authors for diseases as Diabetes Mellitus, the ischemic stroke
in large arteries as well as the lacunar brain infarction and sickle cell
disease. Diagnostically these diseases do not show differences in performance
of CA between individual patients, which complicates the possibility to make a
general statement for an entire category. At the moment CA can only be
investigated by looking at the response to changes in cardiovascular variables
such as blood pressure - usually expressed as mean arterial pressure (MAP) - on
CBF.



Cerebral Autoregulation (CA) is the occurrence of vasoconstriction as cerebral
perfusion pressure (CPP) increases and the occurrence of vasodilatation as CPP
decreases. This change in vessel diameter, in turn, results in an in- and
decrease in Cerebrovascular Resistance (CVR), inversely affecting Cerebral
Blood Flow (CBF). When CA is impaired or absent CBF is linearly dependent of
CPP. This has proven to be the case in several patient populations, such as:
Diabetes Mellitus, Stroke and Sickle Cell disease. Within these populations
impairment of CA exists in different gradations complicating retrieving the
clinical state the patient resides in. As of now it is impossible to assess CA
other than within an experimental laboratory (of physiology). This study
hypotheses that more simple methods can be equally useful in the assessment of
CA, providing a future outlook for more clinical application of CA assessment.

To measure CA, or more specifically dynamic cerebral autoregulation (dCA) -
describing the CVR adaptation over time - , perturbation have to be made to the
blood pressure. Eventually this change will be reflected in CBF, which in turn
initiates CA: altering CVR. The rate at which CVR changes is a parameter
describing dCA.

As subjects' vessel diameter is affected by arterial blood gas concentrations
(specifically PaCO2) the perturbations will be executed for three different
levels of Partial Pressure of carbon dioxide (PaCO2).

At the moment CA can only be assessed in laboratories that have been set-up to
perform the specific measurements. This study tries to use a diversity of
methods for measuring and analyzing CA and reach a method that is a simplified
version of current time- and frequency domain analysis. It is hypothesized that
other techniques to assess CA quantification can become available for more
clinical patient care and monitoring.

The experiments consists of resting in supine position followed by position
changes (standing up from supine position and from squat position), the
execution of thigh cuff maneuvers and the assessment of cerebrovascular reserve
capacity with the aid of hypo- and hypercapny.

There exist no risks to be expected by taking part to this study. The burden of
the subjects is small, because all measurements will be performed
non-invasively. In general the physical burden caused by the routine tests in
this study are endured well. Within our laboratory it is common practice to
continuously monitor patient both through measurement devices and (non-) verbal
communication.