Continuous recording of cerebral blood flow by means of a thermal diffusion method using a Peltier stack

Development of noninvasive measurement of peripheral circulation and its medical application

Surveys were carried out on tissue blood flow measurement based on the thermal diffusion method and on the assessment of peripheral circulatory function using photosensors.Regarding the thermal diffusion method, first noninvasive measurement using a Peltier stack was carried out. Then, measurements using a thermal clearance curve at various temperatures were performed.For noninvasive measurement of the mechanical properties of peripheral arteries using photosensors, the author determined the vascular volume ratio and/or the relative vascular volume.For clinical application in field studies, it is necessary to develop an apparatus with which absolute evaluation of the intravascular volume can be carried out using the blood volume around the unit volume as an indicator. Therefore, an apparatus that removes a signal constituent from tissue other than the blood using two-wavelength photosensors is required.If a noninvasive method to accurately measure the intravascular volume is established, changes in the mechanical properties of the peripheral arteries that correspond to functional and organic changes in the normal response can be observed more directly. Moreover, quantitative assessment of peripheral circulatory function will become possible, and diagnosis of the severity of peripheral circulatory disorders will be facilitated.

Trans-cranial Doppler in severe head injury: Evaluation of pattern of changes in cerebral blood flow velocity and its impact on outcome

BACKGROUND

Trans-cranial Doppler (TCD) studies after head injury have been done in the first 24 hours after injury and do not specify the exact interval between injury and time of recordings. We have studied cerebral blood flow changes in patients with severe head injury using serial TCD starting within 6 hours after trauma, and present our findings and its correlation with clinical outcome.

METHODS

Thirty-two patients with closed severe brain injuries formed the study group. Six-hourly serial TCD studies were done starting within 6 hours after trauma until 48 hours after trauma or death of the patient, whichever was earlier. Flow velocities of the extracranial internal carotid (V(EC-ICA)) and middle cerebral artery (V(MCA)) were recorded to identify vasospasm, hyperemia, or oligemia. Serial changes in flow velocities were correlated with the clinical outcome of the patients at 12 months' follow-up after injury.

RESULT

Oligemia (n = 30) and vasospasm (n = 2) were the earliest changes observed within 6 hours of trauma. In the oligemia group, persistent oligemia (n = 14), hyperemia (n = 6), normal flow velocity (n = 5), and vasospasm developing within 24 hours (n = 5) were observed. Eight patients developed vasospasm after 24 hours. All patients with persistent oligemia and vasospasm developing within 24 hours had poor outcome.

CONCLUSION

Oligemia is the most common change within 6 hours of head injury. Persistence of oligemia beyond 24 hours is associated with poor outcome. Early (within 24 hours posttrauma) onset of vasospasm is associated with poor outcome; however, delayed (>24 hours after trauma) vasospasm is not associated with poor outcome.

Individual value of brain tissue oxygen pressure, microvascular oxygen saturation, cytochrome redox level, and energy metabolites in detecting critically reduced cerebral energy state during acute changes in global cerebral perfusion

The authors assessed the diagnostic value of brain tissue oxygen tension (PbrO2), microvascular oxygen saturation (SmvO2), cytochrome oxidase redox level (Cyt a+a3 oxidation), and cerebral energy metabolite concentrations in detecting acute critical impairment of cerebral energy homeostasis. Each single parameter as well as derived multimodal indices (arteriovenous difference in oxygen content [AVDO2], cerebral metabolic rate for oxygen [CMRO2], fractional microvascular oxygen extraction [OEF]) were investigated during controlled variation of global cerebral perfusion using a cisternal infusion technique in 16 rabbits. The objective of this study was to determine whether acute changes between normal, moderately, and critically reduced cerebral perfusion as well as frank ischemia defined by local cortical blood flow (lcoBF), brain electrical activity (BEA), and brain stem vasomotor control can be reliably identified by SmvO2, PbrO2, Cyt a+a3 oxidation, or energy metabolites (glutamate, lactate/pyruvate ratio). PbrO2, SmvO2, and Cyt a+a3 oxidation, but not cerebral perfusion pressure, were closely linked to lcoBF and BEA and allowed discrimination between normal, moderately reduced, and critically reduced cerebral perfusion (P < 0.01). Glutamate concentrations and the lactate/pyruvate ratio varied significantly only between moderately reduced cerebral perfusion and frank ischemia (complete loss of BEA and brain stem vasomotor control). Therefore, PbrO2, SmvO2, and Cyt a+a3 oxidation, but not glutamate and the lactate/pyruvate ratio, reliably predict the transition from moderately to critically reduced cerebral perfusion with impending energy failure.

Instant myocardial blood flow monitor: its calibration and assessment of flow capacity of the intracoronary shunt tube

BACKGROUND

We developed a new instant regional myocardial blood flow (RMBF) monitor utilizing the thermal diffusion method in which the RMBF value is presented as the value inversely proportional to the thermocouple voltage output (1/V). The purposes of this study were (1) to validate the accuracy of RMBF measurement by the instant RMBF monitor in comparison with the colored microsphere method for calibration; (2) to investigate influences of it on the RMBF; and (3) to assess changes in RMBF caused by the shunt tube insertion.

METHODS

Twenty pigs were used for this study: 4 for comparison between the instant RMBF meter and the colored microsphere method, 4 for validation of reproducibility, and 6 for measurement of RMBF during shunt tube.

RESULTS

The relation between RMBF values obtained by the colored microsphere method and 1/V values by instant RMBF monitor was colored microsphere = 140,992 (1/V)--231 in epicardial layer (R2 = 0.819) and colored microsphere = 111,381 (1/V)--165 in endocardial layer (R2 = 0.693). The correlation coefficient and R2 values between RMBF values measured by both methods were 0.985 and 0.839 in epicardial layer, and 0.963 and 0.679 in endocardial layer, respectively. The RMBF at each layer did not change after the attachment of the monitor. Fifteen minutes after shunt tube insertion, RMBF measured by the colored microsphere method decreased to 31.1% (p = 0.0001) and 33.7% (p = 0.0001) in epicardium and endocardium, respectively, and no difference was observed from the value measured by the instant RMBF monitor.

CONCLUSIONS

This instant RMBF monitor can provide instantaneous and continuous information of RMBF without requiring tissue examination.

Effects of olprinone on systemic and cerebral circulation in patients with subarachnoid hemorrhage

Olprinone is a promising new drug used for treating cerebral vasospasm. To clarify the effects of olprinone on systemic and cerebral circulation in patients with subarachnoid hemorrhage, hemodynamic and oxygenation parameters were evaluated as 12 such patients underwent surgery. After aneurysm clipping and confirmation of hemostasis, olprinone was administrated at a dose of 10 microg/kg over 5 minutes followed by 0.2 microg/kg/min for 25 minutes. Variables before and after administration were compared by paired t tests. Heart rate and cardiac index increased while no significant changes occurred in oxygen saturation of mixed venous blood, or oxygen extraction ratio. Cortical blood flow increased and cerebral vascular resistance decreased significantly, but oxygen saturation in the jugular bulb, arterio-jugular difference of oxygen content, and lactate oxygen index did not change significantly. In conclusion, olprinone increased cardiac output and cortical blood flow in patients with subarachnoid hemorrhage, but the balance between oxygen supply and consumption systemically and in the brain did not change. This observation suggests the possibility that olprinone increases cerebral metabolism.

Evaluation of hemodynamic responses in head injury patients with transcranial Doppler monitoring

Transcranial Doppler (TCD) can monitor middle cerebral artery (MCA) velocity which can be recorded simultaneously with other physiologic parameters such as end tidal (Et) CO2, arterial blood pressure and intracranial pressure (ICP), in head injured patients. Relative changes in MCA velocity can be used to reflect relative MCA blood flow changes during ICP waves, and also to evaluate cerebral autoregulation, CO2 reactivity and hemodynamic responses to mannitol and barbiturates. The utility and practicality of short intervals of TCD monitoring to evaluate hemodynamic responses, was evaluated in a group of 22 head injured patients (average Glasgow coma score 6). During ICP A waves, MCA velocity always decreased during the peak of the wave, and during ICP B waves, fluctuated synchronously with the ICP. Dynamic cerebral autoregulation, and reactivity to CO2, were reduced within 48 hours of admission. Impaired cerebral autoregulation within 48 hours of admission did not correlate with outcome at 1 month. Mannitol infusion caused an increase in MCA velocity (15.4 +/- 7.9%) which was significantly correlated to the impairment of dynamic autoregulation (r = 0.54, p < 0.0001). The MCA velocity response to a test dose of barbiturates was significantly correlated to the ICP (r = 0.61, p < 0.01) response as well as to the CO2 reactivity (r = 0.37, p < 0.05). Continuous MCA velocity monitoring using TCD may be useful in evaluating a variety of hemodynamic responses in head injury patients and may replace more cumbersome cerebral blood flow techniques which have been used in the past for these purposes.

Temporary vessel occlusion in spontaneously hypertensive and normotensive rats. Effect of single and multiple episodes on tissue metabolism and volume of infarction

Temporary occlusion of an intracranial artery is frequently necessary in the surgical management of intracranial aneurysms, arteriovenous malformations, and tumors. While the risks of vessel damage associated with clip application have been lessened by improved design, the threat of ischemic damage remains. It is unclear whether multiple, brief periods of clip application are more or less safe than a single period of occlusion, and whether the underlying cerebrovascular status influences the outcome from either method. The effect of each of these paradigms (single: 1-hour occlusion; multiple: three 20-minute episodes separated by 10 minutes of reperfusion) on histopathological outcome was assessed in a middle cerebral artery (MCA) occlusion model using both normotensive and spontaneously hypertensive rats. The mean volume of infarction (+/- standard error of the mean) was not different between the single-ischemic (49.4 +/- 17.3 cu mm) and the multiple-ischemic (42.9 +/- 12.9 cu mm) episode groups of normotensive rats, whereas in the spontaneously hypertensive rats a significant difference existed between the volume of infarction for the single-occlusion group (126.7 +/- 18.7 cu mm) and the multiple-occlusion group (162.4 +/- 15.5 cu mm) (p < 0.05). The metabolic data obtained from spontaneously hypertensive animals did not provide an explanation for the larger infarction in that there were no significant differences between the single- and multiple-occlusion groups with respect to tissue glucose, adenosine triphosphate, or lactate levels. The results suggest that intermittent reperfusion may have different effects depending not only on the degree and duration of ischemia and reperfusion, but also on the underlying cerebrovascular status.

Cortical blood flow recorded during early or delayed surgery for ruptured intracranial aneurysms

Forty-three patients were operated on for ruptured intracranial aneurysms during a 12-month-period. Intraoperative evaluation of cortical blood flow by means of a thermal diffusion probe was performed in 23 out of the 41 patients who were operated on for aneurysms of the anterior circulation. The autoregulation index was determined at the time of raising the systemic blood pressure after clipping of the aneurysm(s). No statistically significant difference was found between the averages of the autoregulation indexes calculated in the subgroups of patients submitted respectively to early or delayed surgery. There was no correlation of both cortical blood flow and autoregulation with either age of the patients, or preoperative neurological grade. On the contrary, the autoregulation index showed a statistically significant correlation with outcome.

Variations in regional cerebral blood flow investigated by single photon emission computed tomography with technetium-99m-d, l-hexamethylpropyleneamineoxime = l-h during temporary clipping in intracranial aneurysm surgery: preliminary results

Single photon emission computed tomography with technetium-99m-d, l-hexamethylpropyleneamineoxime was used to assess variations in regional cerebral blood flow during temporary clipping in the course of intracranial aneurysm surgery and during the postoperative period in 20 patients, 14 of whom underwent temporary clipping. Of these 14 patients (Group A), 9 had aneurysms of the anterior communicating artery, 2 had aneurysms of the middle cerebral artery, and 3 had aneurysms of the carotid siphon. Temporary clips were applied, according to the site of the lesion, on A1, on the trunk of the middle cerebral artery, or on the trunk of the internal carotid artery. The occlusion time ranged from 2 to 31 minutes. The six patients who did not undergo temporary clipping served as controls (Group B), as follows: three had aneurysms of the posterior communicating artery, one of the anterior communicating artery, one of the middle cerebral artery, and one of the internal carotid artery. All patients were investigated with cerebral single photon emission computed tomography preoperatively, perioperatively, and postoperatively. In all the patients of Group A, the preliminary results of the study show a sharp fall in the perfusion of the territories of the temporarily clipped parent vessel and practically a complete recovery within 2 to 7 days of surgery, with no significant neurological symptoms. No similar disturbance of perfusion was found in the patients of Group B.

Double-level cauda equina compression: an experimental study with continuous monitoring of intraneural blood flow in the porcine cauda equina

Compression of the spinal nerve roots may occur clinically at multiple levels at the same time; however, the basic pathophysiology of multi-level compression is largely unknown. In this study, the intraneural blood flow was analyzed continuously in the uncompressed segment between two compression balloons, with a pig used as an experimental model and a thermal diffusion method. At 10 mm Hg compression, there was a 64% reduction of total blood flow in the uncompressed segment compared with pre-compression values. Total ischemia occurred at pressures 10-20 mm Hg below the mean arterial blood pressure. After two-level compression at 200 mm Hg for 10 min, there was a gradual recovery of the intraneural blood flow towards the baseline. Recovery was less rapid and less complete after 2 h of compression. Double-level compression of the cauda equina can thus induce impairment of blood flow, not only at the compression sites, but also in the intermediate nerve segments located between two compression sites, even at very low pressures. These findings may have clinical importance in the understanding of the pathophysiology of multiple-level cauda equina compression.

Cerebral blood flow and intracranial pressure during experimental subarachnoid haemorrhage

The relationships of intracranial pressure (ICP), systemic blood pressure (SBP) and cerebral blood flow (CBF) during experimental subarachnoid haemorrhage were investigated in cats. Continuous monitoring of regional cerebral blood flow (rCBF) was done by a thermal diffusion method using a Peltier stack. During haemorrhage ICP rose within 5.4 +/- 0.97 minutes from 10.5 +/- 4.9 to 176.1 +/- 27.8 mmHg. This strong increase of ICP resulted in a temporary arrest of cerebral circulation. The Cushing response during the haemorrhage could not improve the cerebral circulation, but in contrast caused a further increase of ICP. After the haemorrhage the cerebral blood flow normalised within minutes. It is concluded, that the Cushing response during a subarachnoid haemorrhage should be regarded as a deleterious rather than a beneficial mechanism.

Cerebral blood flow and the thermal properties of the brain: a preliminary analysis

Safe and effective use of hyperthermia for the treatment of brain tumors requires precise control of the distribution of temperatures (that is, the thermal field) within the tumor and within the adjacent brain. Major influences upon the distribution of temperatures include the passive thermal properties of the brain, such as its specific heat (Cb), and the contribution of cerebral blood flow (CBF). Recently, an electrical-mechanical analog model of heat flow within the brain has been developed from which an expression for CBF has been derived: CBF = Cb/(tau rho c) where tau is the thermal decay constant, rho is the density of blood, and c is its specific heat. To test this model a series of experiments was carried out in adult dogs in which stereotaxically implanted microwave antennas operating at 2450 MHz, fluoro-optical thermometry probes, and platinum electrodes were used to simultaneously measure CBF by thermal washout and hydrogen clearance techniques. The correlation coefficient for estimates of CBF derived by the two methods in 52 paired observations was 0.89. Measurements of CBF were more reliable at increased distances from the microwave antenna, since CBF is sensitive to the degree of temperature elevation (delta T). The ratio of post-heating CBF to pre-heating CBF varies linearly with delta T and has a correlation coefficient of 0.86. When values of CBF determined by the hydrogen clearance method were employed in the above equation, it was possible to derive Cb as 0.70 +/- 0.08 cal/gm-degrees C. Use of this value for Cb in this equation produces estimates of CBF by thermal clearance that are within 10% of the values for CBF as measured by the hydrogen clearance method. It is concluded that this model of thermal flow within the brain may have heuristic value for treatment planning and that microwave antennas and fluoro-optical probes may represent a new methodology for the clinical estimation of CBF. These methods have recently been employed in patients undergoing combined hyperthermia and chemotherapy.