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      Influence of hypercapnic vasodilation on cerebrovascular autoregulation and pial arteriolar bed resistance in piglets.

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          Abstract

          Changes in both pial arteriolar resistance (PAR) and simulated arterial-arteriolar bed resistance (SimR) of a physiologically based biomechanical model of cerebrovascular pressure transmission, the dynamic relationship between arterial blood pressure and intracranial pressure, are used to test the hypothesis that hypercapnia disrupts autoregulatory reactivity. To evaluate pressure reactivity, vasopressin-induced acute hypertension was administered to normocapnic and hypercapnic (N = 12) piglets equipped with closed cranial windows. Pial arteriolar diameters were used to compute arteriolar resistance. Percent change of PAR (%DeltaPAR) and percent change of SimR (%DeltaSimR) in response to vasopressin-induced acute hypertension were computed and compared. Hypercapnia decreased cerebrovascular resistance. Indicative of active autoregulatory reactivity, vasopressin-induced hypertensive challenge resulted in an increase of both %DeltaPAR and %DeltaSimR for all normocapnic piglets. The hypercapnic piglets formed two statistically distinct populations. One-half of the hypercapnic piglets demonstrated a measured decrease of both %DeltaPAR and %DeltaSimR to pressure challenge, indicative of being pressure passive, whereas the other one-half demonstrated an increase in these percentages, indicative of active autoregulation. No other differences in measured variables were detectable between regulating and pressure-passive piglets. Changes in resistance calculated from using the model mirrored those calculated from arteriolar diameter measurements. In conclusion, vasodilation induced by hypercapnia has the potential to disrupt autoregulatory reactivity. Our physiologically based biomechanical model of cerebrovascular pressure transmission accurately estimates the changes in arteriolar resistance during conditions of active and passive cerebrovascular reactivity.

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          Author and article information

          Journal
          J. Appl. Physiol.
          Journal of applied physiology (Bethesda, Md. : 1985)
          American Physiological Society
          8750-7587
          0161-7567
          Jul 2008
          : 105
          : 1
          Affiliations
          [1 ] Department of Electrical and Computer Engineering, The University of Memphis, Engineering Science Bldg., Rm. 208B, Memphis, TN 38152-3180, USA.
          Article
          00988.2007
          10.1152/japplphysiol.00988.2007
          2494839
          18436696
          303dd3da-7214-4f1e-95b6-f512266b4a16
          History

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