Related Experiment Video
Updated: Jun 19, 2026

MRI Mapping of Cerebrovascular Reactivity via Gas Inhalation Challenges
Published on: December 17, 2014
Effect of hyper- and hypocapnia on cerebral arterial compliance in normal subjects
Emmanuel Carrera1, Dong-Joo Kim, Gianluca Castellani
1Department of Clinical Neurosciences, Addenbrooke's Hospital, University of Cambridge, Cambridge, United Kingdom. emmanuel.carrera@chuv.ch
Background:
Changes in partial pressure of carbon dioxide (PaCO2) are associated with a decrease in cerebral blood flow (CBF) during hypocapnia and an increase in CBF during hypercapnia. However, the effects of changes in PaCO2 on cerebral arterial compliance (Ca) are unknown.
Methods:
We assessed the changes in Ca in 20 normal subjects using monitoring of arterial blood pressure (ABP) and cerebral blood flow velocity (CBFV). Cerebral arterial blood volume (CaBV) was extracted from CBFV. Ca was defined as the ratio between the pulse amplitudes of CaBV (AMPCaBV ) and ABP (AMPABP). All parameters were recorded during normo-, hyper-, and hypocapnia.
Results:
During hypocapnia, Ca was significantly lower than during normocapnia (.10±.04 vs. .17±.06; P<.001) secondary to a decrease in AMPCaBV (1.3±.4 vs. 1.9±.5; P<.001) and a concomitant increase in AMPABP (13.8±3.4 vs. 11.6±1.7 mmHg; P<.001). During hypercapnia, there was no change in Ca compared with normocapnia. Ca was inversely correlated with the cerebrovascular resistance during hypo- (R2=0.86; P<.001), and hypercapnia (R2=0.61; P<.001).
Conclusion:
Using a new mathematical model, we have described a reduction of Ca during hypocapnia. Further studies are needed to determine whether Ca may be an independent predictor of outcome in pathological conditions.
Related Concept Videos
Chemical Factors Affecting Respiration Centers
CO2 has a potent influence on respiration and is strictly regulated. Under...
Hyperpnea and Hyperventilation
Assessment of Diffusion and Perfusion
The Role of Diffusion in Respiration
Diffusion is the process by which molecules move from an area of higher concentration to an area of lower concentration. In the respiratory system, this principle...
Acute Respiratory Failure-III
Alterations in Respiration II
In Biot's breathing, the respiratory rate and depth are irregular, alternating between periods of deep gasping and apnea. Common causes include...
Diagnosing Acidosis and Alkalosis
First, the pH level is assessed to determine whether the blood pH is normal (7.35–7.45), low (acidosis), or high (alkalosis).
Next, the PCO2 and HCO3− values are examined to...

