BACKGROUND: Analysis of the transcranial Doppler blood flow velocity (FV) waveform is used clinically to detect changes in cerebral haemodynamic profile. Such changes may be initiated both by alterations in microvascular resistance and in the tone of the cerebral arteries. METHODS: The role of endothelial mechanisms was investigated using inhibition of NO synthesis by systemic administration of NG-nitro-L-arginine methyl ester (L-NAME, 6 mg/kg) followed by simultaneous monitoring of both basilar artery FV and cerebrocortical microcirculation (laser Doppler flowmetry, LDF) in anaesthetised, ventilated rabbits over 60 minutes. RESULTS: Arterial blood pressure (AP) increased significantly (p < 0.01) above baseline level in the second minute following L-NAME and remained elevated until the end of experiment. Time average mean and systolic FV decreased immediately following L-NAME injection, with the statistically significant (p < 0.01) decrease from the third minute. Diastolic FV did not show such radical changes. LDF exhibited a slow decrease with time becoming significantly lower than baseline (p < 0.01) at 50 min. CONCLUSION: A gradual decrease in cortical microcirculation preceded by a rapid reaction recorded in the TCD waveform implies that an increase in the tone of the great cerebral arteries is the predominant phenomenon seen during the acute phase of NO synthase inhibition.
BACKGROUND: Analysis of the transcranial Doppler blood flow velocity (FV) waveform is used clinically to detect changes in cerebral haemodynamic profile. Such changes may be initiated both by alterations in microvascular resistance and in the tone of the cerebral arteries. METHODS: The role of endothelial mechanisms was investigated using inhibition of NO synthesis by systemic administration of NG-nitro-L-arginine methyl ester (L-NAME, 6 mg/kg) followed by simultaneous monitoring of both basilar artery FV and cerebrocortical microcirculation (laser Doppler flowmetry, LDF) in anaesthetised, ventilated rabbits over 60 minutes. RESULTS: Arterial blood pressure (AP) increased significantly (p < 0.01) above baseline level in the second minute following L-NAME and remained elevated until the end of experiment. Time average mean and systolic FV decreased immediately following L-NAME injection, with the statistically significant (p < 0.01) decrease from the third minute. Diastolic FV did not show such radical changes. LDF exhibited a slow decrease with time becoming significantly lower than baseline (p < 0.01) at 50 min. CONCLUSION: A gradual decrease in cortical microcirculation preceded by a rapid reaction recorded in the TCD waveform implies that an increase in the tone of the great cerebral arteries is the predominant phenomenon seen during the acute phase of NO synthase inhibition.