Dynamic cerebral autoregulation and baroreflex sensitivity during modest and severe step changes in arterial PCO2

Disassociation of static and dynamic cerebral autoregulatory performance in healthy volunteers after lipopolysaccharide infusion and in patients with sepsis

“…Thus, we did not find any significant correlations between the enhanced dynamic autoregulation and the decrease in Pa CO 2 , and although a previous study found that voluntary hyperventilation enhances dynamic performance as evaluated by step-induced changes in MAP by the thigh cuff deflation technique (1), this involved much more profound hypocapnia [Pa CO 2 ϳ22 Torr (2.93 kPa)] than encountered in the present study. Moreover, voluntary hyperventilation to similarly low Pa CO 2 values was not found to affect transfer gain or the MAP-to-MCAv phase difference in a later study (2). On the other hand, Brassard et al (7) recently reported a significant correlation between transfer function indices of dynamic autoregulation and the hyperventilatory response after administration of LPS.…”

Cerebral Autoregulation is Influenced by Carbon Dioxide Levels in Patients with Septic Shock

“…If, as in hypercarbia, the vascular tone was reduced, a further dilation in response to reduced MAP was either impaired or unnecessary. Moreover, elevations in PaCO 2 increase autonomic neural activity and this may alter the arterial baroreflex [19]. Mild hypercapnia can significantly impair cerebral autoregulation during general anesthesia [55].…”

“…With its potent vasodilating properties, PaCO 2 is an important regulator of the cerebral circulation [19] and hypercapnia can directly increase CBF [20]. Although the vascular response to PaCO 2 in the brain has been shown to be markedly attenuated by moderate hypotension in experimental studies [21], Thees et al recently reported normal reactivity to CO 2 in patients with sepsis [22].…”

Comparing cerebrovascular reactivity measured using BOLD and cerebral blood flow MRI: The effect of basal vascular tension on vasodilatory and vasoconstrictive reactivity

“…CO 2 is a potent vasodilator, triggering changes in vascular tension through the arterial baroreflex (Ainslie et al, 2008), and the vascular response to CO 2 is well established using transcranial Doppler ultrasound of arterial blood flow (BattistiCharbonney et al, 2011). Typically, CVR is measured as the ratio between changes in the BOLD fMRI signal and endtidal CO 2 (PETCO 2 ) change, a surrogate for arterial CO 2 (Robbins et al, 1990).…”