Sensitivity of neural-hemodynamic coupling to alterations in cerebral blood flow during hypercapnia

Abstract

The relationship between measurements of cerebral blood oxygenation and neuronal activity is highly complex and depends on both neurovascular and neurometabolic biological coupling. While measurements of blood oxygenation changes via optical and MRI techniques have been developed to map functional brain activity, there is evidence that the specific characteristics of these signals are sensitive to the underlying vascular physiology and structure of the brain. Since baseline blood flow and oxygen saturation may vary between sessions and across subjects, functional blood oxygenation changes may be a less reliable indicator of brain activity in comparison to blood flow and metabolic changes. In this work, we use a biomechanical model to examine the relationships between neural, vascular, metabolic, and hemodynamic responses to parametric whisker stimulation under both NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author Manuscript normal and hypercapnic conditions in a rat model. We find that the relationship between neural activity and oxy-and deoxyhemoglobin changes is sensitive to hypercapnia-induced changes in baseline cerebral blood flow. In contrast, the underlying relationships between evoked neural activity, blood flow, and model-estimated oxygen metabolism changes are unchanged by the hypercapnic challenge. We conclude that evoked changes in blood flow and cerebral oxygen metabolism are more closely associated with underlying evoked neuronal responses.

Safety and Tolerability of Early Noninvasive Ventilatory Correction Using Bilevel Positive Airway Pressure in Acute Ischemic Stroke

“…Thus, hypoxia and hypercapnia alter cerebral autoregulation, and both states likely contribute to the pathogenesis of cardiovascular and cerebrovascular disease in patients with OSAS. 10 This is supported by recent observations that neural activity changes are sensitive to hypercapnia-induced alterations in baseline cerebral blood flow, 20,21 and that hypercapnia-induced perfusion changes are closely associated with impairments in learning and memory. 22 Notably, former studies indicate that impaired vasomotor reactivity can be reversed relatively rapidly when nightly exposure to intermittent hypoxia is eliminated with continuous positive airway pressure in patients with OSAS.…”

Biophysical model estimation of neurovascular parameters in a rat model of healthy aging

“…This is higher than values reported in the literature for capillaries saturation S cO2 of about 70% (Mesquita et al, 2009;Huppert et al, 2009). We tried fixing the value of S wO2 to literature values, but the constrained model would not fit our experimental data.…”

Simulation study of brain blood flow regulation by intra-cortical arterioles in an anatomically accurate large human vascular network. Part II: Flow variations induced by global or localized modifications of arteriolar diameters

“…Though it may be difficult to separate non-linear neuronal effects from vascular response nonlinearities, a recent study showed that hemodynamic nonlinearities do affect BOLD fMRI response timing and magnitude, and that, "if not properly taken into account such vascular nonlinearities confound the interpretation of underlying neuronal events" (de Zwart et al, 2009). Moreover, the fact that the absolute changes in blood flow, rather than the normalized (percent) changes, are most closely coupled to neural activity across normal and hypercapnic conditions (Huppert et al, 2009) might be at least partially interpreted through the biomechanical mechanisms pointed out in the present study.…”