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MCA V_mean and the arterial lactate-to-pyruvate ratio correlate during rhythmic handgrip

¹Department of Anesthesia, Copenhagen Muscle Research Center; ²Department of Infectious Diseases, Center of Inflammation and Metabolism, Rigshospitalet; ³Department of Medical Biochemistry and Genetics, University of Copenhagen, Copenhagen, Denmark; and ⁴Cardiovascular Research Institute Amsterdam, Department of Internal Medicine, Academic Medical Center, Amsterdam, the Netherlands

Submitted 11 April 2006 ; accepted in final form 16 June 2006

Regulation of cerebral blood flow during physiological activation including exercise remains unknown but may be related to the arterial lactate-to-pyruvate (L/P) ratio. We evaluated whether an exercise-induced increase in middle cerebral artery mean velocity (MCA V_mean) relates to the arterial L/P ratio at two plasma lactate levels. MCA V_mean was determined by ultrasound Doppler sonography at rest, during 10 min of rhythmic handgrip exercise at 65% of maximal voluntary contraction force, and during 20 min of recovery in seven healthy male volunteers during control and a 15 mmol/l hyperglycemic clamp. Cerebral arteriovenous differences for metabolites were obtained by brachial artery and retrograde jugular venous catheterization. Control resting arterial lactate was 0.78 ± 0.09 mmol/l (mean ± SE) and pyruvate 55.7 ± 12.0 µmol/l (L/P ratio 16.4 ± 1.0) with a corresponding MCA V_mean of 46.7 ± 4.5 cm/s. During rhythmic handgrip the increase in MCA V_mean to 51.2 ± 4.6 cm/s was related to the increased L/P ratio (23.8 ± 2.5; r² = 0.79; P < 0.01). Hyperglycemia increased arterial lactate and pyruvate to 1.9 ± 0.2 mmol/l and 115 ± 4 µmol/l, respectively, but it did not significantly influence the L/P ratio or MCA V_mean at rest or during exercise. Conversely, MCA V_mean did not correlate significantly, neither to the arterial lactate nor to the pyruvate concentrations. These results support that the arterial plasma L/P ratio modulates cerebral blood flow during cerebral activation independently from the plasma glucose concentration.

cerebral blood flow; cerebral activation; exercise; hyperglycemia; transcranial ultrasound Doppler

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