June 10, 2006AJP Heart and Circulatory Physiology
Impaired cerebral CO₂ vasoreactivity: association with endothelial dysfunction
Why the study?
Does endothelial dysfunction impair CO2-dependent cerebral blood flow regulation and pressure-dependent autoregulation?
Population
16 patients with diabetes mellitus and/or hypertension and 12 age- and sex-matched healthy controls
Comparison
Physiological challenges before and after sodium… vs Healthy controls
Design
Case-control
Authors
Discussion
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Implication
Hypothesis-generating for selective NO mediation of CO2 vasoreactivity; requires confirmation before clinical autoregulation assessment.
Key Points
- To determine whether nitric oxide selectively mediates carbon dioxide-dependent chemoregulation rather than pressure-dependent autoregulation of cerebral blood flow in patients with endothelial dysfunction.
- Evaluated 16 patients with diabetes mellitus and/or hypertension alongside 12 age- and sex-matched healthy controls.
- Assessed pressure-dependent autoregulation using escalating doses of phenylephrine and calculated the CO2 vasoreactivity index during normocapnia, hyperventilation, and CO2 inhalation.
- Measured forearm blood flow and reactive hyperemia to quantify systemic endothelial function, repeating assessments after infusion of the nitric oxide donor sodium nitroprusside.
- Endothelial function was significantly reduced in patients compared to controls for maximal forearm blood flow (297 ± 31% vs. 488 ± 75%; P = 0.01) and area under the curve (127 ± 11 vs. 173 ± 17; P = 0.03).
- Cerebral CO2 vasoreactivity was significantly lower in patients than in controls (1.19 ± 0.1 vs. 1.54 ± 0.1 cm·s⁻¹·mmHg⁻¹; P = 0.04), whereas cerebrovascular resistance slopes during phenylephrine-induced blood pressure challenges were identical.
- Administration of sodium nitroprusside eliminated the disparity in CO2 vasoreactivity between patients and healthy controls.
Structured PICO
Does endothelial dysfunction impair CO2-dependent cerebral blood flow regulation and pressure-dependent autoregulation?
P
Population
16 patients with diabetes mellitus and/or hypertension (impaired endothelial function) and 12 age- and sex-matched healthy controls
I
Intervention
Physiological challenges (escalating doses of phenylephrine, CO2 inhalation, hyperventilation) before and after sodium nitroprusside infusion
C
Comparator
Healthy controls
O
Outcome
CO2 vasoreactivity index and pressure-dependent autoregulation (cerebrovascular resistance changes)surrogate
Patients with endothelial dysfunction have impaired CO2 vasoreactivity but preserved pressure-dependent autoregulation, suggesting nitric oxide is involved specifically in CO2-dependent cerebral blood flow regulation.
Cite This Study
Lavi et al. (2006) studied this question.