Effect Of Nitroglycerin On The Cerebral Blood Flow Tested By Color Doppler Flow Imaging

Nitroglycerin (NTG) is a vasodilator that induces the vasodilatation of blood vessels and the relaxation of smooth muscle. NTG is commonly used to relieve angina pectoris and acute myocardial infarction and improve the symptoms of chronic heart failure in the clinic. However, adverse reactions often occur after taking NTG, with neurological symptoms being the most common reactions, including headache, syncope, dizziness and coma. Some Scholars had shown that these Symptoms triggered by NTG have a close relationship with changes in cerebral blood flow. The past studies were limited in the detection of intracrahial cerebral artery used Transcranial Doppler (TCD) and regional cerebral blood flow, especially the middle cerebral artery and perfusion area. The internal carotid artery (ICA) and vertebral artery (VA) are the major extracranial cerebral artery that supply blood of the brain, the change of ICA and VA blood flow can directly reflect the status of cerebral blood flow perfusion.The Color Doppler Flow Imaging (CDFI) with high frequency ultrasound probe can display structure of the cerebral artery accurately, and obtain hemodynamic parameters through doppler spectrum, such as blood flow velocity, resistance index of blood flow. According to the vascular diameter and blood flow velocity of blood flow, the blood flow volume can be calculated as well. The overall evaluation on the perfusion status of cerebral arterial is gradually accepted by clinic.In this study, CDFI was used to detect the blood flow of extracranial cerebral arteries before and after NTG administration, and to investigate the effect of NTG on the blood flow of the cerebral arteries, thus finding changes in the perfusion of cerebral blood arteries. To explore the potential risks caused by NTG in patients with cerebral circulation insufficiency.There are two parts in this study as follows:Part 1:To establish animal model, then high frequency CDFI was used to detect common carotid artery (CCA)of rabbit,and hemodynamic parameters were obtained before and after NTG administration, confirming whether extracranial cerebral arteries are affected by NTG; Find out the trend of of the NTG function, determine the time points of detection and as a reference for human experiments.Part 2:On the basis of the first part, CDFI was used to detect the effect of NTG on the blood flow in bilateral internal carotid arteries (ICA) and vertebral arteries (VA) of the human, and to obtain the hemodynamics parametres before and after NTG administration. The changes of blood flow in ICA and VA were analysed and to evaluate the condition of whole cerebral blood flow.Part 1:Cerebral Blood Flow Effected by Nitroglycerin Tested by Color Doppler Flow Imaging in RabbitsObjective To explore the effect of nitroglycerin (NTG) on cerebral blood flow.Methods In 15 anesthetized healthy adult rabbits, the diameter(D) and blood flow hemodynamic parameters of right common carotid artery(CCA) were measured by color doppler flow imaging (CDFI)before and after NTG administration. The measuring time points of post-administration were 5,10,15,20,25,30,35,40,45,50,55 and 60min. All data was compared and analyzed.Results Compared with the basal level in the absence of nitroglycerin, the D in every point were no changes (P> 0.05), peak systolic velocity (PSV), diastolic end velocity (EDV), Mean time-averaged velocity(TAMAX), pulsatility index (PI), resistance index (RI) 0.72± 0.07, the instantaneous blood flow volume (Q) were decreased sharply at first 5min, and then recovered to basic performance within rest 40 min gradually.Conclusion After NTG administration, the D of CCA is unchanged in rabbits, blood flow velocity, PI and RI of CCA are decreased at first and then recovery gradually, indicating that extracranial cerebral artery is affected by NTG as well,blood flow of CCA has the corresponding reduction.Part 2:Effect of Nitroglycerin on Cerebral Blood Flow Tested by Color Doppler Flow Imaging in HumanObjective To evaluate the effect of nitroglycerin (NTG) on extracranial cerebral artery blood in human by using color Doppler flow imaging (CDFI) and to evaluate the effect of NTG on wholy cerebral blood flow furtherly.Methods 1.CDFI was performed to detect the diameter and hemodynamic parameters of bilateral internal carotid arteries (ICA) and vertebral arteries (VA) before and after sublingual administration of 0.5 mg NTG in ten healthy adult volunteers. Diameter (D) and hemodynamic parameters of ICA and VA were used as the reference index.2. According to the results of animal experiment in rabbits, hemodynamic parameters decreased first and then recovery to the basic status. It was dropped to the lowest at the5 min points and and the recovery trend becomes slow gradually, so 5min,15min,30min and 60min four time points were selected and detection of ICA and VA were repeated in the same conditions.3. The diameter and hemodynamic parameters of ICA and VA were compared before and after taking NTG, and the changes of instantaneous total cerebral blood flow were calculated simply.Results Comparing to the basal level in the absence of NTG, the blood flow velocity and resistance index of the ICA and VA were decreased significantly at 5 min post-NTG administration and then gradually recovered to the basal state over the next 55 min. Significant differences in the ICA and VA were observed at each measurement time point post-NTG administration. However, the blood vessel diameters were not markedly altered before or after NTG administration.Conclusions The blood flow velocity and resistance index of the extracranial cerebral artery declined transiently after NTG administration, as did the cerebral blood flow. These results suggest that NTG administration may have an adverse effect on patients who have a potential disturbance of the cerebral circulation.