Laser Doppler flowmetry of focal ischaemia and reperfusion in deep brain structures in rats

Summary Monitoring cerebral blood flow during focal ischaemia and reperfusion with established techniques such as hydrogen clearance and autoradiography is difficult. Laser Doppler flowmetry is a new technique, it allows one to continuously measure blood flow in small tissue samples. The objective of this study was to compare laser Doppler flowmetry with hydrogen clearance using a new single fiber probe to obtain measurements in deep brain structures and then to show the temporal profile of cerebral blood flow during focal ischaemia and after reperfusion.First, the single fiber laser Doppler method was compared with the hydrogen clearance method in ten Wistar rats.Second, focal cerebral ischaemia was induced in fifteen Wistar rats using a model of middle cerebral artery occlusion based on the intravascular insertion of a nylon suture; reperfusion occurred after withdrawal of the suture. The laser Doppler probe was placed in the lateral caudatoputamen, and local cerebral blood flow was measured continuously before and during occlusion as well as after reperfusion.The relative blood flow values obtained by the laser Doppler method and the hydrogen clearance method showed a good correlation (r=0.76) and a linear relationship. A rapid decrease in laser Doppler flowmetry to 42±16% of former baseline values was seen with occlusion of the middle cerebral artery; during occlusion cerebral blood flow remained at this level. Reperfusion resulted in a heterogeneous pattern of cerebral blood flow as laser Doppler flowmetry values ranged from 25% to 134% of baseline values.The effects of middle cerebral artery occlusion and reperfusion on cerebral blood flow can be monitored on-line with laser Doppler flowmetry. Our findings suggest that this method, with the high spatial and temporal resolution characteristics of its new single fiber probe, allows one to continuously measure microcirculatory blood flow in deep brain structures.Supported in part by the Deutsche Forschungsgemeinschaft (Ku 294/18-1) and by Schering AG, Berlin, Federal Republic of Germany.     

Transmyocardial laser – revascularization: experimental studies on prolonged acute regional ischemia

Objective: This experimental study in pigs was undertaken to answer the question whether TMLR after acute myocardial infarction may improve regional myocardial perfusion, left ventricular function and diminish myocardial necrosis in the area at risk. Methods: Thirty open-chest anesthetized pigs were observed for 6 h, six pigs served as controls. In 24 pigs, occlusion of the left anterior descending artery (LAD) beyond the first diagonal branch was performed: seven pigs had LAD occlusion only (ischemia group), and 17 pigs were treated by TMLR (using a CO₂-laser, energy: 40 J) prior to coronary occlusion; nine pigs received one laser channel (1 mm diameter) per cm² (laser group 1) and eight pigs two channels per cm² in the LAD territory (laser group 2). Regional myocardial blood flow by microspheres, function (franc starling curves), histochemical assessment (triphenyl tetrazolium chloride, TTC and histology), were performed. Results: The lased pigs were less prone to ventricular fibrillation (laser group 2, 38%; laser group 1, 56%; ischemic group, 100%; P<0.05), and showed a significant smaller area of necrosis (TTC) in the area at risk (laser group 1, 23%; laser group 2, 14%; vs. ischemia group, 31%; P<0.01). There was no significant difference between laser-treated and ischemia hearts regarding the amount of blood flow into the infarcted LAD region and the maximal left ventricular stroke work index after 6 h (P=n.s). Regional myocardial blood flow: ischemia group, 4±5 ml/100 g/min; laser group 1, 3±10 ml/100 g/min, and laser group 2, 2±10 ml/100 g/min; maximal left ventricular stroke work index: ischemia group, 1.8 mJ/g; laser group 1, 2.1 mJ/g and laser group 2, 2.1 mJ/g. Conclusions: This model of acute regional ischemia demonstrates that CO₂-laser revascularization diminish significantly the incidence of ventricular fibrillation and necrosis in the area at risk, and does not change regional myocardial perfusion and global left ventricular function. This experiment indicates that TMLR may be an alternative in treating advanced ischemic heart disease.     

Detecting changes of arterial and venous blood flow in flaps

Island skin flaps based on the latissimus dorsi muscle were raised in domestic pigs. Simultaneous recordings of laser Doppler flowmetric and laser photometric values were made on the skin in the middle of the flap. Occlusion of either the artery or the vein of the pedicle was accompanied by very low laser Doppler flow values. In laser photometry the total intensity of backscattered light remained unchanged or was sightly increased during arterial occlusion. In response to venous occlusion, however, it decreased markedly. As venous outflow pressure was increased step by step, both the laser Doppler flow value and the laser photometry value fell proportionally; thus, the greater the increase in pressure the lower were the steady state levels of both variables. Stepwise reductions of arterial inflow pressure were followed by proportional decreases in both mean blood volume flow, recorded using electromagnetic flowmetry, and in laser Doppler flowmetric values. However, laser photometric values varied only minimally. Laser Doppler flowmetry thus might be a useful clinical aid in detecting decreased blood flow in transferred flaps, and laser photometry may determine whether the decreased flow is due to arterial or venous causes.     

Effect of increased intra-abdominal pressure on hepatic arterial, portal venous, and hepatic microcirculatory blood flow.

The effects of increased intra-abdominal pressure (IAP) on hepatic perfusion were studied in five anesthetized pigs. Doppler flow probes were used to measure hepatic artery blood flow (HABF) and portal venous blood flow (PVBF), and laser Doppler flowmetry was used to assess changes in hepatic microvascular blood flow (HMVBF). Hepatic blood flow responses to 10, 20, 30 and 40 mm Hg increases in IAP were assessed while the mean arterial BP (MAP) was maintained at baseline levels with IV crystalloid infusions. Although cardiac output and MAP were normal, HABF and HMVBF fell significantly with 10 mm IAP, and at 20 mm Hg IAP, HABF was 45% of the control value, PVBF was 65% of the control value, and HMVBF was 71% of the control value (p less than 0.05). At 30 and 40 mm Hg, hepatic blood flow was reduced even more. Thus, modest increases in IAP can cause significant impairment of hepatic perfusion despite a normal BP and cardiac output.     

Continuous recording of middle cerebral artery blood velocity in clinical neurosurgery

Summary Intracranial pressure, arterial blood pressure, and middle cerebral artery blood velocity were monitored for periods from 1 to 10 days in 30 neurosurgical intensive care patients. The recordings revealed rapid changes in the cerebral perfusion and gave insight into individual cerebral haemodynamic states.Twenty patients consistently showed CO₂ reactivity within normal limits, between 2.5 and 5% per mm Hg (19–38% per kPa). Severely impaired CO₂ reactivity, considerably below 1% per mm Hg (7.5% per kPa) was observed in four patients. Three of these patients died, while the fourth patient survived in a persistent vegetative state.Seven patients demonstrated pressure-passive blood velocity changes throughout the observed CPP range. The four patients with severely impaired CO₂ reactivity all belonged to this group. The recordings from three of the remaining 23 patients showed signs of MCA blood velocity autoregulation with a lower regulatory limit of about 40–45 mm Hg. This observation is in keeping with findings from electromagnetic flowmetry on brain arteries in the neurosurgical operating field, and supports blood velocity measurements as a relevant index of brain perfusion in clinical neurosurgery and neuro-intensive care settings.     

Evaluation of a laser Doppler flowmetry implantable fiber system for determination of threshold thickness for flow detection in bone

Laser Doppler flowmetry (LDF) with the use of a standard metal shafted probe, has been successfully used to study bone blood flow in a wide variety of settings. The use of the standard probe is limited by the requirement that the probe be replaced onto the bone surface or driven into the bone with a trocar. In response to this, a system of implantable, detachable fibers was developed. This system allows repeated measurement over time without repeated surgical manipulation of the area of interest. This study was performed to evaluate the implantable fiber system by determining threshold thickness for flow detection in bone. A flow chamber with perpendicular and end-on flow was designed to collect results under controlled conditions for flow detection. Threshold thickness for bovine cortical and cancellous bone samples was determined after sequentially grinding the specimens and placing them in the flow chamber. A 2% solution of latex circulated in the chamber and each specimen was exposed to both flow directions and both types of probe. The laser Doppler probe was able to detect flow by resting on top of the sample, with the latex on the other side of the sample. The results showed a significantly greater threshold thickness for the standard probes than for the implantable probes, and a significantly greater threshold thickness for trabecular bone than for cortical bone. Despite the reduced threshold thickness with the implantable fiber, this new system was able to consistently detect depth of perfusion of 80–90% of the values for the standard probe. The minimum value for threshold thickness in cortical bone with the implantable fiber was 2.43 mm. This was well within a clinically relevant range for flow detection. Threshold thickness and the LDF output were not affected by the flow direction. The study provides baseline information on the utility of this technique and demonstrates the potential usefulness of the implantable fiber system.     

Effects of Heat Stress on Ocular Blood Flow During Exhaustive Exercise

The hypothesis that heat stress reduces the ocular blood flow response to exhaustive exercise was tested by measuring ocular blood flow, blood pressure, and end- tidal carbon dioxide partial pressure (P_ETCO₂) in 12 healthy males while they performed cycle ergometer exercise at 75% of the maximal heart rate at ambient temperatures of 20°C (control condition) and 35°C (heat condition), until exhaustion. The blood flows in the retinal and choroidal vasculature (RCV), the superior temporal retinal arteriole (STRA) and the superior nasal retinal arteriole (SNRA) were recorded at rest and at 6 and 16 min after the start of exercise period and at exhaustion [after 16 ± 2 min (mean ± SE) and 24 ± 3 min of exercise in the heat and control condition, respectively]. The mean arterial pressure at exhaustion was significantly lower in the heat condition than in the control condition at both 16 min and exhaustion. The degree of P_ETCO₂ reduction did not differ significantly between the two thermal conditions at either 16 min or exhaustion. The blood flow velocity in the RCV significantly increased from the resting baseline value at 6 min in both thermal conditions (32 ± 6% and 25 ± 5% at 20°C and 35°C, respectively). However, at 16 min the increase in RCV blood flow velocity had returned to the resting baseline level only in the heat condition. At exhaustion, the blood flows in the STRA and SNRA had decreased significantly from the resting baseline value in the heat condition (STRA: -19 ± 5% and SNRA: -30 ± 6%), and SNRA blood flow was lower than that in the control condition (-14 ± 6% vs -30 ± 6% at 20°C and 35°C, respectively), despite the finding that both thermal conditions induced the same reductions in P_ETCO₂ and vascular conductance. These findings suggested that the heat condition decreases or suppresses ocular blood flow via attenuation of pressor response during exhaustive exercise.

Key Points

• The ocular (retinal and choroidal) blood flow response to exhaustive exercise with heat stress is unknown.
• We hypothesized that the heat stress decreases ocular blood flow response to exhaustive exercise, since cerebral flow, which is regulated similarly to ocular flow, was reported to decrease during heat stress.
• To test this hypothesis, ocular blood flow was measured during exhaustive exercise at 20°C (control condition) and 35°C (heat condition).
• At exhaustion in the heat condition, the ocular flow response was suppressed or decreased with an attenuated pressor response.
• It is suggested that the heat condition decreases or suppresses the ocular blood flow to exhaustive exercise via attenuation of pressor response.

Key Words: Hyperthermia, exercise, healthy subjects, retinal circulation, choroidal circulation, laser-speckle flowgraphy     

Assessment of myocardial perfusion with laser Doppler flowmetry. An experimental study on porcine heart

Laser Doppler flowmetry was applied to the arrested heart of four pigs and to the fibrillating heart of three pigs during cardiopulmonary bypass. The coronary blood flow was maintained during cardiac arrest by infusion of hyperkalemic blood into the aortic root. A significant correlation (r = 0.88, n = 52, p less than 0.001) between laser Doppler signal and coronary blood flow was found during cardiac arrest. During ventricular fibrillation after release of the aortic cross-clamp there was significant correlation (0.84, n = 38, p less than 0.01) between laser Doppler signal and extracorporeal blood flow. A residual laser Doppler signal of about 60% of the maximal value was recorded even after the bypass flow was discontinued. Laser Doppler flowmetry is concluded to permit measurement of myocardial perfusion in the arrested porcine heart. Muscular activity of the heart contributes to the output signal during ventricular fibrillation.     

Measurement of femoral head microcirculation by laser Doppler flowmetry

Perfusion of the capital femoral epiphysis was measured by laser Doppler flowmetry (LDF) in a series of skeletally immature pigs. After induction of balanced general anesthesia, selective occlusion of the arterial blood supply to the hip was performed with continuous monitoring by a laser Doppler probe applied to the articular surface of the femoral head. The lateral femoral circumflex artery, a main branch of the superficial femoral artery in the pig, was largely responsible for femoral head perfusion in eight of nine pigs, according to LDF measurements. This finding was confirmed by postmortem silicone rubber injections and Spalteholz preparations of the femoral heads.     

Measuring cochlear blood flow by laser Doppler spectroscopy

Cochlear blood flow (CBF) was studied with a commercially available laser Doppler system in 20 guinea pigs. The cochlea was exposed to permit placement of the laser Doppler probe over the intact lateral wall of the basal turn. Ketamine and xylazine were used for anesthesia, and blood pressure was monitored from the femoral artery. In some cases, skin blood flow was monitored with a second laser Doppler system, and cardiac output was monitored with an ultrasonic Doppler system placed over the right brachiocephalic artery. We found that the laser Doppler signal is composed primarily of blood flow supplied by the internal auditory artery. Local pressure on the contents of the internal auditory canal after occipital craniotomy was found to reduce CBF to 15% of its original value in a reversible fashion. There was no change in CBF after bilateral occlusion of the common carotid arteries. There appears to be a mechanism governing CBF that stabilizes its value in the face of changes in blood pressure and cardiac output. This is similar to the vascular behavior of the central nervous system. Through the use of positive airway pressure and blood removal at different rates, cardiac output could be depressed to varying degrees. The magnitude of decrease in CBF was clearly related to the rate at which cardiac output and blood pressure dropped. This was confirmed when intravenous phenylephrine was given in sequential and increasing doses. CBF increased as blood viscosity decreased, as expected according to the vascular behavior of the central nervous system.(ABSTRACT TRUNCATED AT 250 WORDS)     

Laparoscopy without pneumoperitoneum

Laparoscopic surgery with CO₂ insufflation is associated with adverse effects on hemodynamics and gas exchange. The abdominal wall retractor (AWR) is an alternative for pneumoperitoneum. Hemodynamics and gas exchange during the use of an AWR were compared to those of CO₂ pneumoperitoneum.In eight pigs subjected to 1 h of CO₂ pneumoperitoneum or abdominal wall retraction, hemodynamics, gas exchange, and oxygen transport were studied in a randomized cross-over study design.The only change observed during abdominal wall retraction was mild respiratory alkalosis. In contrast, during CO₂ pneumoperitoneum mean arterial blood pressure increased 13%, central filling pressures doubled, and a small increase in cardiac output was observed. Peak airway pressures increased 50%, end-tidal CO₂ increased 20%, and respiratory acidosis was induced (arterial pH from 7.46±0.07 to 7.31±0.06 and pCO₂ from 33±3 mmHg to 53±4 mmHg). Arterial PO₂ decreased but mixed venous oxygen saturation and oxygen consumption were unaffected.In contrast with CO₂ pneumoperitoneum, laparoscopy using abdominal wall retraction was not associated with adverse effects on hemodynamics or gas exchange.     

Effects of carbon dioxide vs helium pneumoperitoneum on hepatic blood flow

Background: Elevated intraabdominal pressure due to gas insufflation for laparoscopic surgery may result in regional blood flow changes. Impairments of hepatic, splanchnic, and renal blood flow during peritoneal insufflation have been reported. Therefore we set out to investigate the effects of peritoneal insufflation with helium (He) and carbon dioxide (CO₂) on hepatic blood flow in a porcine model. Methods: Twelve pigs were anesthetized and mechanically ventilated with a fixed tidal volume after the stabilization period. Peritoneal cavity was insufflated with CO₂ (n= 6) or He (n= 6) to a maximum intraabdominal pressure of 15 mmHg. Hemodynamic parameters, gas exchange, and oxygen content were studied at baseline, 90 mm and 150 min after pneumoperitoneum, and 30 min after desufflation. Determination of hepatic blood flow with indocyanine green was made at all measured points by a one-compartment method using hepatic vein catheterization. Results: A similar decrease in cardiac output was observed during insufflation with both gases. Hepatic vein oxygen content decreased with respect to the baseline during He pneumoperitoneum (p < 0.05), but it did not change during CO₂ insufflation. Hepatic blood flow was significantly reduced in both the He and CO₂ pneumoperitoneums at 90 min following insufflation (63% and 24% decrease with respect to the baseline; p < 0.001 and p < 0.05, respectively) being this decrease marker in the He group (p= 0.02). Conclusions: These findings suggest that helium intraperitoneal insufflation results in a greater impairment on hepatic blood flow than CO₂ insufflation. Received: 27 March 1996/Accepted: 19 January 1997     

Renal hemodynamic response to ureteral obstruction during converting enzyme inhibition

Acute unilateral obstruction (UUO) of the pig kidney is associated with an increased secretion of intrarenally generated angiotensin II (ANG II). In order to clarify the importance of this intrarenal ANG II generation during acute UUO, ipsilateral and contralateral renal blood flow and renal secretion rate of ANG II were determined in pigs during continuous infusion of an angiotensin I converting enzyme (ACE) inhibitor. Pigs were operatively equipped with electromagnetic flow probes and catheters in the renal veins and aorta. Intravenous administration of the ACE inhibitor SQ 14 225 (captopril), 1 mg/kg per hour, resulted in a significant increase in renal blood flow in the contralateral kidney from 340±28 ml/min to 435±36 ml/min (P<0.01), whereas renal blood flow in the ipsilateral kidney was significantly reduced from 388±23 ml/min to 248±24 ml/min, similar to the reduction in controls. Captopril reduced mean aortic blood pressure, renal vascular resistance consistently on both sides, and plasma concentrations of ANG II and aldosterone from all sample sites. Renal secretion rate of ANG II showed a clear tendency to be reduced from the ipsilateral kidney. The results suggest that in UUO a compensatory increase in renal blood flow may be inhibited in part due to an enhanced secretion of ANG II in the ipsilateral kidney. However, a captopril-mediated inhibition of bradykinin breadown may also explain some of the observed changes.     

Contact fibre Nd: YAG laser for partial nephrectomy: experimental study in pigs

Summary Thirty-two partial nephrectomies were performed without renal cooling on 13 pigs with a contact fibre Nd: YAG laser (10 W) or a steel scalpel with or without a vascular pedicle clamp. Nine pigs had a 2-week follow-up with an abdominal ultrasound 1 week postoperatively. The time for haemostasis was 6.9±5.8 min (mean ±SD) with the laser and 9.1±5.8 min with the steel scalpel when the clamp was used (P=0.028). There was no significant difference in the total operating time (13.2±4.5 min with the laser vs 12.6±4.6 min with the steel scalpel, P=0.203). Intraoperative blood loss was similar in the two groups when the clamp was used. Clamping the renal pedicle decreased the blood loss by 61% in the laser group and 31% in the steel scalpel group. The number of ligatures used was significantly lower in the laser group (3.7±2.6) compared with the steel scalpel group (6.6±3.4) (P=0.013). Five urinomas developed on the laser side and four on the steel scalpel side. These results indicate that the contact fibre Nd:YAG laser method can be used in partial nephrectomy, but it offers no definitive advantage over the conventional technique.     

Regional blood flow in skeletal muscle after high-energy trauma. An experimental study in pigs, using a new laser Doppler technique and radioactive microspheres

The regional blood flow in skeletal muscle after high-energy trauma was studied. The thigh musculature of anesthetized pigs was wounded with a high-velocity missile. The blood flow was measured with a technique using radioactive microspheres and also with a new laser Doppler flowmeter. Both methods showed very little flow in the discolored, traumatized muscle tissue nearest the missile track, whereas normal flow was found in more distal, normally colored muscle. There was good correlation between the results with the two methods. The laser Doppler flowmeter was shown to be a noninvasive technique permitting flow recordings in small areas of tissue surface. The restriction of flow impairment to the discolored areas of the traumatized muscle implies that discoloration is a useful clinical guide during debridement of traumatized muscle.     

Sapphire probe laser ablation of human arteries with CO2 gas and saline perfusion: The effect of flow rate,lasing power and lasing time

To evaluate flow rate dependence of CO₂ gas and saline perfusion for sapphire probe ablation, all together 204 human arterial specimens of atheroma and normal vessel were irradiated with Nd-YAG laser, in an experimental circulation-occlusion model within 37°C flowing whole blood. During lasing procedures, various flow rates of CO₂ gas (0.2–2.01 min⁻¹) and saline (2.0–20.0 ml min⁻¹), and various lasing powers (7, 12 and 17 W) and lasing time (1–20 s) were used. Histological changes of all specimens irradiated were microscopically examined. The results showed that the laser ablation area enlarged with increasing CO₂ flow rates and decreasing saline flow rates. Relative ablation efficiency on atheromatous plaque, in comparison to those on normal vessel wall and surrounding tissue site, increased slightly with increasing lasing power and lasing time. In this experimental setting, the mode of action of the sapphire probe ablation on human arterial atheroma seems to be more satisfactory with CO₂ gas perfusion than with saline perfusion.     

Detecting arterial and venous obstruction in flaps

Island skin flaps based on the latissimus dorsi muscle were raised in domestic pigs. Flap circulation, maintained only by the vascular pedicle, was monitored by laser Doppler flowmetry, laser photometry, and transcutaneously measured carbon dioxide tension. Both arterial and venous occlusion were accompanied by very low laser Doppler flow values. In laser photometry, the backscattered intensity of light remained unchanged or was slightly increased during arterial occlusion. In response to venous occlusion, however, the light intensity decreased markedly. Transcutaneous carbon dioxide tension increased in both venous and arterial occlusion. When venous outflow pressure was raised incrementally, both the laser Doppler flow value and the total backscattered light intensity fell proportionately. Laser Doppler flowmetry might thus be useful clinically to detect decreased blood flow in transferred flaps, and laser photometry may determine if the decreased flow is related to the arterial or venous side.     

Validation of esophageal Doppler for noninvasive hemodynamic monitoring under pneumoperitoneum

Background Commonly used perioperative measurements of hemodynamics, such as Swan-Ganz catheter assessment, are invasive and may not be reliable under pneumoperitoneum. The purpose of this study was to validate the use of esophageal Doppler for noninvasive hemodynamic monitoring under pneumoperitoneum in an experimental pig model. Methods Eight female pigs were submitted to two 30-min study periods, one each for the baseline (no interventions) and pneumoperitoneum (12-mmHg carbon dioxide pneumoperitoneum) conditions. One pig was excluded because of tachycardia (>140 at baseline). A Swan-Ganz pulmonary artery catheter was used to measure cardiac output (CO-SG) and pulmonary capillary wedge pressure (PCWP). An esophageal Doppler probe was inserted to record cardiac output (CO-ED) and corrected flow time (FTc), an index of preload. Transthoracic echocardiography was used to measure left ventricular end-diastolic diameter (LVEDD) and cardiac output (CO-TTE). Pearson correlation was used to assess individual associations between the measured hemodynamic parameters. Results There was good correlation between CO-ED and CO-SG (r = 0.577; p < 0.001) and excellent correlation between CO-ED and CO-TTE (r = 0.815; p < 0.001). There was no correlation between FTc and LVEDD or PCWP. These relationships were consistent when analyzed separately at baseline and during pneumoperitoneum. Conclusion Esophageal Doppler monitoring is a valid noninvasive method of estimating cardiac output at baseline and during pneumoperitoneum in a porcine model. Corrected flow time did not correlate with other estimates of preload at baseline or during pneumoperitoneum. Presented at the annual meeting of the Society of American Gastrointestinal and Endoscopic Surgeons (SAGES), Dallas, TX, USA, April 2006     

Comparison of Near-Infrared Spectroscopy and Laser Doppler Flowmetry for Detecting Decreased Hepatic Inflow in the Porcine Liver

Hepatic artery and portal vein thrombosis are devastating complications of partial liver transplantation. Early detection of inflow complications is important, as re-reconstruction can salvage the graft. Near-infrared spectroscopy or laser Doppler flowmetry can be used to detect tissue oxygenation or microcirculation on the liver surface. The aim of this study was to examine which of these two methods better detects changes in hepatic inflow. Sangen-strain pigs (n = 5) were used. The tips of the near-infrared spectroscopy and laser Doppler flowmetry probes were placed separately on the surface of the right liver. Inflow to the liver was controlled during the following seven conditions: control (not clamped), half- and totally clamped portal vein, half- and totally clamped hepatic artery, and half- and totally clamped portal vein and artery. Tissue blood flow was calculated using laser Doppler flowmetry. Oxyhemoglobin, deoxyhemoglobin, and the tissue oxygenation index were measured and calculated using a near-infrared spectroscopy system. The tissue blood flow and oxygenation index could not be used to differentiate between the half-clamped portal vein, half-clamped hepatic artery, and totally clamped portal vein conditions. The oxyhemoglobin minus deoxyhemoglobin value was significantly decreased after half or total clamping of the portal vein or hepatic artery (p <. 001 for each condition). The findings of the present study indicate that near-infrared spectroscopy was more sensitive than Doppler flowmetry for detecting changes in hepatic tissue inflow from the liver surface.     

A hollow sapphire waveguide for stereotactic intraventricular CO2 laser neurosurgery: a rat model

A hollow sapphire waveguide was used for stereotactic delivery of CO₂ laser radiation through the cerebro-spinal fluid to the ventricular surface of rat brains. The tissue was irradiated with single pulses (spot size ≈0.5 mm) ranging from 0.125 to 0.5s in duration and from 1.68 to 5.2 W in power. The radius, depth and variation in histological appearance of the lesions were measured as a function of energy density, and the repair response was evaluated by observing changes in the laser-induced lesions from 1 to 28 days post-injury. A lack of charring and limited size of the lesions were noted, and the lesions were repaired in a normal manner over the course of observation. Our results demonstrate that hollow sapphire waveguides are both safe and effective for the transmission of CO₂ laser light for intraventricular neurosurgical applications.