Cortical Blood Flow and Cerebral Perfusion Pressure in.docx

1、Cortical Blood Flow and Cerebral Perfusion Pressure inCortical Blood Flow and Cerebral Perfusion Pressure in a New Noncraniotomy Model of Subarachnoid Hemorrhage in the Rat Joshua B. Bederson, MD; Isabelle M. Germano, MD; Lorraine Guarino, BS From the Department of Neurosurgery, The Mount Sinai Scho

2、ol of Medicine, New York, NY. Correspondence to Joshua B. Bederson, MD, Department of Neurosurgery, Box 1136, The Mount Sinai School of Medicine, 1 Gustave L. Levy Pl, New York, NY 10029.Abstract Background and Purpose Acute cerebral ischemia after subarachnoid hemorrhage (SAH) is a major cause of m

3、orbidity whose precise etiology is unclear. The purpose of this study was to examine the relationships between cerebral perfusion pressure (CPP) and cortical blood flow during SAH using a new experimental model in the rat. Methods CPP (mean arterial pressure minus intracranial pressure), cortical la

4、ser-Doppler flowmetry (LDF), and electroencephalogram were continuously recorded during and after SAH in 16 ventilated rats. SAH was produced by advancing an intraluminal suture from the external carotid artery through the internal carotid artery to perforate the vessel near its intracranial bifurca

5、tion. Results Eight rats (50%) died within 24 hours of SAH. In all rats, blood was widely distributed throughout the basal, convexity, and interhemispheric subarachnoid spaces and throughout the ventricular system. CPP decreased after SAH at an initial rate of 1.10.2 mm Hg/s, reaching its nadir 599

6、seconds after the onset of SAH. During the same period, LDF fell at a rate of 1.40.3%/s (P=NS vs CPP). After reaching its nadir, CPP rose at a rate of 0.40.01 mm Hg/s, but LDF continued to fall at 0.20.03%/s (P.05 vs CPP) reaching a nadir of 21.72.5% significantly later than CPP (189.539 s after SAH

7、, P.05). No correlation was found between peak changes in CPP and LDF. Electroencephalogram activity followed the changes in LDF, reaching nadir values 28955 seconds after SAH. Conclusions These findings demonstrate that although reduced CPP causes the initial decrease in cortical blood flow after S

8、AH, secondary reductions occurring after CPP has reached its nadir are caused by other factors such as acute vasoconstriction. This noncraniotomy model of SAH in the rat has several advantages over existing models. Key Words: animal models cerebral blood flow hemodynamics subarachnoid hemorrhage rat

9、s Introduction Subarachnoid hemorrhage (SAH) causes brain injury both acutely and as the result of delayed vasospasm. Despite progress in understanding and treating delayed ischemia, acute brain damage is the primary cause of mortality after SAH,1 yet its etiology remains unclear. Acute cerebral isc

10、hemia is an important contributor to brain damage in this setting, as demonstrated in patients who die shortly after SAH, in whose brains extensive ischemic damage is seen.2 Acute ischemia from SAH has been attributed to decreased cerebral perfusion pressure (CPP),3 and this is supported by data fro

11、m repeat hemorrhages in humans with intracranial pressure (ICP) monitors.4 5 However, brain compliance is reduced by the initial bleed and may lead to greater rises in ICP during the second bleed. Experimental studies of first-time hemorrhages demonstrate that CPP does not drop to the point of perfu

12、sion arrest.6 7 8 Physiological data suggest that decreased CPP cannot fully account for acute ischemic brain damage after SAH.5 6 7 9 10 However, previous studies have used time-averaged or intermittent measurements of cerebral blood flow (CBF) that may not demonstrate acute changes after SAH. Such

13、 changes could be evaluated by use of an experimental model with continuous recordings of CBF. Currently available animal models of SAH6 8 9 10 11 12 13 14 15 16 17 are limited by the need for craniotomy and arachnoidal dissection or surgical placement of an infusion catheter, by the use of dorsal c

14、isterns rather than the basal subarachnoid space, and by catheter-induced dampening of arterial pulsations, small elevations of ICP, or limited distribution of blood. In this study we investigated a new rat model of SAH that avoids many problems of currently available models and allows continuous un

15、disturbed measurements of cortical blood flow and CPP during the hemorrhage. Based on preliminary results,18 our primary hypothesis was that acute SAH-induced reductions in CBF are, at least in part, independent of reductions in CPP. Materials and Methods Surgical PreparationAll procedures were appr

16、oved by our accredited animal care committee. Male Sprague-Dawley rats (n=22) weighing 250 to 300 g were housed under diurnal lighting conditions and given free access to food and water before and after the experiment. The rats were anesthetized with chloral hydrate (350 mg/kg IP) and intubated tran

17、sorally with a polyethylene catheter (OD 2.5 mm); anesthesia was maintained with inspired halothane (1% to 2% in O2-supplemented room air). The right femoral artery was cannulated for monitoring blood gases, and ventilation was adjusted to maintain arterial blood gases in the normal range (PCO2, 371

18、 mm Hg; PO2, 1403 mm Hg; pH 7.370.01 meanSEM). Body temperature was monitored with a rectal probe and maintained at 37C with a homeothermic blanket (Harvard Apparatus). Rats were placed in a stereotaxic frame (Stoelting) modified to allow longitudinal rotation and permit manipulations with the rat p

19、rone or supine. Four 1-mm-diameter burr holes were placed 4 mm lateral, 2 mm rostral, and 2 mm caudal to bregma. Epidural electroencephalogram (EEG) electrodes were hooked under the edge of each burr hole and secured to the stereotaxic frame. Nasion reference and femoral ground electrodes were conne

20、cted to a custom-built amplifier-computer (see below) to achieve a bilateral hemispheric bipolar EEG montage. For measurement of cortical blood flow, a 3-mm burr hole was made 5 mm to the left of midline at the coronal suture, and a laser-Doppler flowmetry (LDF) probe (0.8 mm diameter, model P-433,

21、Vasamedics Inc) was advanced under stereotaxic control to the cortical epidural surface away from large pial vessels. The side contralateral to the site of SAH was chosen to ensure that observed changes were attributable to SAH rather than to transient occlusion. A modification of the technique of B

22、arth et al19 was used to monitor ICP. A burr hole was made in the midline occipital bone to accept a stainless steel screw. A 25-gauge butterfly cannula primed with saline and attached to a pressure transducer centered at the ear bars was advanced through the atlanto-occipital membrane into the cist

23、erna magna until a good ICP waveform was obtained. The cannula was secured to the screw with methylmethacrylate cement. The rat was then rotated into the supine position with all recording devices in place and kept there for the remainder of the experiment. Induction of SAHThe cerebral ischemia mode

24、l of Zea-Longa et al20 was modified to produce SAH. In brief, the right carotid artery was identified along with all its extracranial branches, and the external carotid artery was dissected, transected distally, and reflected inferiorly. A 3-0 monofilament suture with one end sharpened was advanced

25、centripetally into the external carotid artery past the common carotid bifurcation and into the internal carotid artery (ICA). The suture was advanced distally into the intracranial ICA until resistance was felt (at 18 to 20 mm) and then was pushed 3 mm further, penetrating the ICA near its intracra

26、nial bifurcation (n=18). Preliminary studies in 4 rats showed that the suture penetrated the ICA, middle cerebral artery, or anterior cerebral artery within 1 mm of the intracranial bifurcation. The suture was then withdrawn into the external carotid artery, reperfusing the ICA and producing SAH (Fi

27、g 1).18 The duration of endovascular occlusion was 30 seconds to 4 minutes. Four sham-operated control rats underwent an identical procedure except that the suture was not advanced beyond the point of resistance; reperfusion occurred after 4 minutes of occlusion. After each experiment, the ICP cathe

28、ter was crimped and cut at its attachment to the occipital screw, which was left in situ. Rats were returned to single, warmed cages while still intubated for airway protection. Self-extubation occurred as the rats recovered from anesthesia, usually within 30 minutes. Rats underwent neurological exa

29、mination after recovery from anesthesia and 24 hours after SAH, as previously described,21 and were killed after the second examination. View larger version (21K):In this windowIn a new window Figure 1. Diagram shows endovascular suture technique for inducing subarachnoid hemorrhage. A 3-0 monofilam

30、ent suture sharpened at one end is introduced through the external carotid artery (eca) and advanced through the intracranial internal carotid artery (ica), penetrating near the bifurcation. Withdrawal of the suture results in subarachnoid hemorrhage. aca indicates anterior cerebral artery; mca, mid

31、dle cerebral artery; pta, pterygopalatine artery; and cca, common carotid artery. Data Acquisition and StorageBlood pressure, LDF, ICP, and EEG waveforms were processed and stored on a Macintosh Quadra 950 (Apple Computer Inc) by use of customized analog-to-digital signal conversion and processing h

32、ardware and software from National Instruments (SCSI, NB-MIO16XL, LABVIEW 3.0). The system was configured to acquire 16 bipolar signals at sampling rates of 1024 Hz. The EEG signal was processed on-line with a fast Fourier transform at 4-second intervals, and the resulting spectrum was divided into

33、power bands. LDF, ICP, mean arterial pressure (MAP), and the amplitude (V2) of the delta power band (1 to 4 Hz) were logged at 0.25 Hz. CPP, defined as MAP minus ICP, was computed for each pair of simultaneously logged data points. LDF data were normalized by comparing each 4-second epoch to the average of a