Time constant of the cerebral arterial bed in normal subjects.
The time constant of cerebral arterial bed (in brief time constant) is a product of brain arterial compliance (C(a)) and resistance (CVR). We tested the hypothesis that in normal subjects, changes in end-tidal CO(2) (EtCO(2)) affect the value of the time constant. C(a) and CVR were estimated using mathematical transformations of arterial pressure (ABP) and transcranial Doppler (TCD) cerebral blood flow velocity waveforms. Responses of the time constant to controlled changes in EtCO(2) were compared in 34 young volunteers. Hypercapnia shortened the time constant (0.22 s [0.17, 0.26] vs. 0.16 s [0.13, 0.20]; p = 0.000001), while hypocapnia lengthened the time constant (0.22 s [0.17, 0.26] vs. 0.23 s [0.19, 0.32]; p < 0.0032). The time constant was negatively correlated with changes in EtCO(2) (R(partial) = -0.68, p < 0.000001). This was associated with a decrease in CVR when EtCO(2) increased (R(partial) = -0.80, p < 0.000001) and C(a) remained independent of changes in EtCO(2). C(a) was negatively correlated with mean ABP (R(partial) = -0.68, p < 0.000001). In summary, the time constant shortens with increasing EtCO(2). Its potential role in cerebrovascular investigations needs further studies.
Academic Neurosurgical Unit, Addenbrooke's Hospital, Cambridge, United Kingdom. magdalena.kasprowicz@pwr.wroc.pl
Magdalena
M
Kasprowicz
Jennifer
J
Diedler
Matthias
M
Reinhard
Emmanuel
E
Carrera
Luzius A
LA
Steiner
Peter
P
Smielewski
Karol P
KP
Budohoski
Christina
C
Haubrich
John D
JD
Pickard
Marek
M
Czosnyka
D000328:Adult; D001783:Blood Flow Velocity / Q000502:physiology; D001794:Blood Pressure / Q000502:physiology; D001810:Blood Volume / Q000502:physiology; D002245:Carbon Dioxide / Q000378:metabolism*; D002560:Cerebrovascular Circulation / Q000502:physiology*; D055119:Elastic Modulus / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D011659:Pulmonary Gas Exchange / Q000502:physiology*; D012016:Reference Values; D014655:Vascular Resistance / Q000502:physiology
D002245:Carbon Dioxide