Impact of propofol on mid-latency auditory-evoked potentials in children.

BACKGROUND: Propofol is increasingly used in paediatric anaesthesia, but can be challenging to titrate accurately in this group. Mid-latency auditory-evoked potentials (MLAEPs) can be used to help titrate propofol. However, the effects of propofol on MLAEP in children are unclear. Therefore, we investigated the relationship between propofol and MLAEP in children undergoing anaesthesia. METHODS: Fourteen healthy children aged 4-16 yr received anaesthesia for elective surgery. Before surgery, propofol was administered in three concentrations (3, 6, 9 µg ml(-1)) through a target-controlled infusion pump using Kataria and colleagues' model. MLAEPs were recorded 5 min after having reached each target propofol concentration at each respective concentration. Additionally, venous propofol blood concentrations were assayed at each measuring time point. RESULTS: Propofol increased all four MLAEP peak latencies (peaks Na, Pa, Nb, P1) in a dose-dependent manner. In addition, the differences in amplitudes were significantly smaller with increasing propofol target concentrations. The measured propofol plasma concentrations correlated positively with the latencies of the peaks Na, Pa, and Nb. CONCLUSIONS: Propofol affects MLAEP latencies and amplitudes in children in a dose-dependent manner. MLAEP measurement might therefore be a useful tool for monitoring depth of propofol anaesthesia in children.

Effects of increasing sevoflurane MAC levels on mid-latency auditory evoked potentials in infants, schoolchildren, and the elderly.

BACKGROUND: Detection of mid-latency auditory evoked potentials (MLAEPs) is a technology to monitor central nervous structures. As seen in adults and children, general anaesthesia influences the MLAEP latencies. MLAEP detection seems to be a promising tool to assess different levels of anaesthesia depth in adults and children. METHODS: MLAEPs were recorded in 10 infants (2 months-3 yr), 12 schoolchildren (6-14 yr), and 10 elderly (75-89 yr) under general anaesthesia with increasing concentrations of sevoflurane at steady state. In addition, MLAEPs were detected before and after the application of sufentanil. RESULTS: At all different ages, MLAEP latencies increased significantly with higher volume percentages of sevoflurane. These results were also detectable when MAC values of sevoflurane were compared with MLAEP peaks. An age-dependent effect could be displayed as elderly people need lower absolute sevoflurane concentrations to achieve the same MLAEP peak increase. Overall, the application of sufentanil under steady-state sevoflurane application at 1 MAC did not importantly affect the MLAEP latencies. CONCLUSIONS: MLAEP latencies increase at the influence of sevoflurane in a dose-dependent manner and in relation to age. These results imply that MLAEP detection is a reasonable tool for monitoring hypnotic effects at all ages. Further studies are required to standardize MLAEP alterations related to effects of medication used for general anaesthesia at all different ages.

Midlatency auditory evoked potentials in children: effect of age and general anaesthesia.

BACKGROUND: Midlatency auditory evoked potentials (MLAEP) are a promising tool for monitoring suppression of sensory processing during anaesthesia and might help to avoid awareness. MLAEP in children are different to those in adults and the exact changes during general anaesthesia are unknown. METHODS: In 49 children of age between 2 and 12 yr, MLAEP were recorded before anaesthesia, during tracheal intubation, at steady-state balanced anaesthesia, and after extubation. RESULTS: MLAEP were recordable in all children in the awake (premedicated) state with latencies but not amplitudes dependent on children's age. MLAEP latencies significantly increased during tracheal intubation and steady-state anaesthesia. Changes in amplitudes were inconsistent. All MLAEP variables returned to near baseline values after extubation. CONCLUSIONS: The results of this study imply that MLAEP can successfully be recorded during anaesthesia in children above the age of 2 yr. Further studies are necessary before MLAEP might be applicable for monitoring purposes in paediatric anaesthesia.

High-energy shock waves enhance hyperthermic response of tumors: effects on blood flow, energy metabolism, and tumor growth.

BACKGROUND: The ability to kill cancerous tissue by heating is often limited by heat lost to flowing blood. Recent studies demonstrate that high-energy shock waves (HESWs), when applied to solid tumors, destroy the tumor microvasculature and rapidly decrease blood flow. We hypothesized that impairment of tumor blood flow by HESWs might result in increased effectiveness of hyperthermia treatment. PURPOSE: The purpose of our work was to determine whether HESWs enhance the response of tumors to hyperthermia. METHODS: Seventy A-Mel-3 amelanotic hamster melanomas were exposed to either 700 HESWs (20 kV, 80 nanofarads), local hyperthermia (43.3 degrees C for 30 minutes), or a combination of both. Three, 12, or 24 hours later, tumor blood flow and adenosine triphosphate (ATP) concentrations were measured by [4-N-methyl-14C]iodoantipyrine autoradiography and quantitative ATP imaging bioluminescence, respectively. In separate experiments, the effects of the separate and combined treatments on tumor growth were studied in 52 animals. RESULTS: Combining HESWs and hyperthermia produced a significantly longer and more pronounced reduction of tumor and adjacent tissue perfusion than either HESWs or hyperthermia alone (P < .05). ATP concentrations were markedly reduced following HESW treatment alone and following the combined therapy compared with untreated controls (P < .05). Three hours after combined therapy, ATP concentrations were significantly below values measured after hyperthermia alone (P < .01). Tumor growth was delayed much more effectively by the combination of HESWs and hyperthermia than by either treatment alone (P < .001). Fifty-four percent of the animals receiving combined treatment showed complete local tumor cure over 52 days of observation, and 46% showed partial remission. CONCLUSION: The combination of HESWs and hyperthermia might be an effective new way of treating cancer, especially in patients who are not candidates for surgery. IMPLICATIONS: These results must be viewed cautiously, as the vasculature of human tumors seems to be less sensitive to hyperthermia than has been observed in experimental tumors.

Simultaneous high-resolution measurement of adenosine triphosphate levels and blood flow in the hamster amelanotic melanoma A-Mel-3.

BACKGROUND: Some studies suggest that nutritional blood flow and intratumor levels of high-energy phosphates such as adenosine triphosphate (ATP) affect tumor response to treatment. Reports of intratumor variabilities have shown that distribution of high-energy phosphates within experimental and human tumors is not uniform, and this variability may be related to differences in blood flow in different regions of the tumor. However, previous studies provide no insight into the intratumor relationship of these parameters. PURPOSE: To study the intratumor relationship between blood flow and ATP concentration, we have developed a method that allows simultaneous quantitation of the two variables almost at a cellular level at adjacent sites. In addition, this technique, which uses digital image processing and analysis, facilitates regional high-resolution measurements of blood flow and ATP concentrations in relation to histology. METHODS: We examined tissue samples cut in consecutive order from one representative hamster A-Mel-3 amelanotic melanoma. Specimens from the same tumor were analyzed for histological features, blood flow (measured autoradiographically by the use of [4-N-methyl-14C]iodoantipyrine), and ATP content (measured by a quantitative substrate-induced bioluminescence reaction, using single-photon imaging). The data on the three parameters were stored as digitized images, which were later transformed to reach geometric congruency. The relationship between blood flow and ATP was examined by nonlinear regression and correlation analyses. RESULTS: Regional distribution of blood flow was highly correlated with distribution of ATP within the A-Mel-3 tumor. For images of the tumor using measuring fields of approximately 20 tumor cells, the coefficient of correlation was .92 (P < .001). The relationship between the two parameters was described by a second-order function. At low blood flow values, small differences in blood flow were associated with large changes in levels of ATP, whereas at high blood flow values, differences in blood flow were associated with much smaller changes in ATP levels. CONCLUSION: This high-resolution technique may have applications in future studies investigating the relationship between tumor cell metabolism and regional blood flow and in studies aimed at identifying the locoregional target of various cancer therapies.

High-energy shock waves induce blood flow reduction in tumors.

We have studied the effect of extracorporeally applied high-energy shock waves (HESW) on blood flow in amelanotic melanomas (A-Mel-3). Two tumors were implanted in the dorsal skin of 21 Syrian golden hamsters. One of the tumors was treated with 200 HESW, and the other served as an intraindividual control. Mean blood flow in the whole tumor, or the tumor excluding necrotic areas, was quantitatively measured using autoradiography with iodo[14C]antipyrine at 30 min (n = 5), 1 h (n = 5), 3 h (n = 5), and 12 h (n = 6) after HESW treatment. As measured for the whole tumor, blood flow in the controls was 23.4 +/- 7.9 ml/100 g/min (median +/- SE) and thus in the range reported in the literature. Thirty min or 1 h after the application of HESW, tumor perfusion was reduced to 6 +/- 4% or 5 +/- 4% (median +/- SE) of the corresponding controls, respectively. Three h after treatment, perfusion increased slightly to 7 +/- 5% and after 12 h increased significantly to 55 +/- 25% of the corresponding controls. Values measured excluding the necrotic areas were higher in all groups. Temporary reduction of tumor perfusion after treatment with HESW was interpreted as a consequence of HESW-induced damage to tumor microcirculation. These effects should be taken into account for maximizing the therapeutic efficiency of HESW on tumors and for combining HESW treatment with other therapeutical modalities.

Noninvasive measurement of regional cerebral blood flow by near-infrared spectroscopy and indocyanine green.

Clinicians lack a practical method for measuring CBF rapidly, repeatedly, and noninvasively at the bedside. A new noninvasive technique for estimation of cerebral hemodynamics by use of near-infrared spectroscopy (NIRS) and an intravenously infused tracer dye is proposed. Kinetics of the infrared tracer indocyanine green were monitored on the intact skull in pigs. According to an algorithm derived from fluorescein flowmetry, a relative blood flow index (BFI) was calculated. Data obtained were compared with cerebral and galeal blood flow values assessed by radioactive microspheres under baseline conditions and during hemorrhagic shock and resuscitation. Blood flow index correlated significantly (rs = 0.814, P < 0.001) with cortical blood flow but not with galeal blood flow (rs = 0.258). However, limits of agreement between BFI and CBF are rather wide (+/- 38.2 +/- 6.4 mL 100 g-1 min-1) and require further studies. Data presented demonstrate that detection of tracer kinetics in the cerebrovasculature by NIRS may serve as valuable tool for the noninvasive estimation of regional CBF. Indocyanine green dilution curves monitored noninvasively on the intact skull by NIRS reflect dye passage through the cerebral, not extracerebral, circulation.

Microhemodynamics and leukocyte sequestration after pulmonary ischemia and reperfusion in rabbits.

OBJECTIVE: Investigation of leukocyte sequestration in alveolar capillaries and of microhemodynamic changes after pulmonary ischemia/reperfusion injury. METHODS: The kinetics of leukocyte passage and the hemodynamics in pulmonary microcirculation were investigated in 16 rabbits by intravital microscopy. Mean red blood cell velocity and the number of sticking leukocytes were measured in pulmonary arterioles, venules, and capillaries after 1 hour of tourniquet ischemia and 10 minutes and 1 hour after reperfusion. RESULTS: The decrease of red blood cell velocity after reperfusion was associated with a largely increased heterogeneity of blood flow. Immediately after the onset of blood flow, sequestered leukocytes were found in all microvascular segments. An increased number of leukocytes was present in arterioles, venules, and alveolar capillaries 10 minutes and 1 hour after reperfusion. Concomitantly, width of alveolar septa was increased while arterial oxygen tension was reduced, indicating the development of interstitial pulmonary edema. CONCLUSION: Leukocytes are sequestered after pulmonary ischemia and reperfusion not only in alveolar capillaries but also in arterioles and venules, and they may contribute to the development of reperfusion edema.

Measurement of microhemodynamics in the ventilated rabbit lung by intravital fluorescence microscopy.

Pulmonary microhemodynamic parameters were directly measured along with systemic pressures and cardiac output in the ventilated rabbit lung. Subpleural arterioles and venules ranging from 10 to 35 microns luminal diameter were investigated under zone 2 conditions, i.e., during inspiratory plateau at an airway pressure of 8 mmHg. Mean arteriolar and venular diameters (24.6 +/- 3.3 and 21.9 +/- 3.6 microns, respectively), mean red blood cell (RBC) fluxes (1,549 +/- 501 and 1,257 +/- 600 cells/s), and mean RBC velocities (0.79 +/- 0.21 and 0.82 +/- 0.21 mm/s) were measured using a fluorescence video-microscopic technique. Calculated microhematocrit (Hct mu) was below systemic values (Hctsys) (Hct mu/Hctsys: arterioles, 0.75 +/- 0.12; venules, 0.67 +/- 0.08). The mean capillary transit time of RBC was 0.47 +/- 0.16 s over a mean arteriovenous distance of 173 +/- 70 m. Significant correlations were demonstrated between microhemodynamic parameters. A correlation among cardiac output, pulmonary arterial pressure, and RBC velocity demonstrates the connection between macro- and microhemodynamics in the rabbit lung. In conclusion, the present model is the first one enabling the measurements of the principal circulatory determinants for gas exchange, i.e., microvascular blood flow, Hct mu, and capillary transit time of RBCs in the ventilated rabbit lung under simultaneous macrocirculatory control.

Leukocyte kinetics in pulmonary microcirculation: intravital fluorescence microscopic study.

To determine the site of sequestration of leukocytes in the lung, we investigated the kinetics of fluorescently labeled erythrocytes and leukocytes in pulmonary arterioles, venules, and alveolar capillaries in vivo by using fluorescence videomicroscopy. The subpleural pulmonary microcirculation of the ventilated rabbit lung was visualized via a transparent window implanted into the right thoracic wall. Fluorescein isothiocyanate-labeled erythrocytes were administered intravenously, whereas leukocytes were labeled in vivo by intravenous injection of rhodamine 6G. Rolling and adherence of leukocytes on the surface of the vessel walls were observed in arterioles as well as in venules. The median velocity of nonadherent leukocytes was significantly higher in arterioles than in venules (84 +/- 12 vs. 15 +/- 3% of erythrocyte velocity, respectively). In alveolar capillaries the majority of leukocytes were retained at distinct sites for periods of 0.1 to > 5 s (median 0.61 s). The relative velocity of leukocytes moving in capillaries was comparable to that determined in arterioles (80 +/- 9% of erythrocyte velocity). These measurements indicate that leukocyte sequestration in the lung is governed by the retention of leukocytes in capillaries and by the interaction of leukocytes with microvascular endothelium of arterioles and venules. We propose that the kinetics of these phenomena determine the equilibrium between circulating and sequestered leukocytes.

[Detection of intraoperative awareness via auditory evoked potentials in an infant]. / Detektion intraoperativer Wachheit bei einem Kleinkind mit akustisch evozierten Potenzialen.

Intraoperative wakefulness is not only limited to adults and can also be found at a similar percentage (0.8%) in paediatric anaesthesia. For prevention of awareness neurophysiologic methods like auditory evoked potentials might be helpful. We report a case of a 2-year-old boy receiving balanced anaesthesia with sevoflurane and alfentanil. Midlatency auditory evoked potentials (MLAEPs) were recorded continuously before, during and after the surgical procedure. During the surgical procedure sevoflurane was withdrawn unintentionally. After a short period of time the boy started coughing and moved his legs, which was interpreted as insufficient analgesia. Several boli of alfentanil did not lead to the expected clinical effect on the depth of anaesthesia. After a recheck of the anaesthetic ventilator the error was determined and delivery of the volatile anaesthetic restored. The postoperative evaluation of the MLAEPs revealed the inadequate suppression of auditory processing during this incident with latencies comparable to the awake state. After reapplication of sevoflurane the MLAEPs were almost completely suppressed demonstrating adequate anesthetic depth. Exemplarily this case suggests that MLAEPs could be used to detect intraoperative awareness also in paediatric anaesthesia. Investigations to prove the validity and reproducibility of MLAEPs in children will be necessary.

Leukocyte margination in alveolar capillaries: interrelationship with functional capillary geometry and microhemodynamics.

The pulmonary capillary microvasculature harbors a large pool of intravascularly marginated leukocytes. In this study, we investigated the interrelationship of leukocyte margination with characteristics of functional capillary geometry and microhemodynamics in alveolar capillary networks. In 22 anesthetized rabbits we assessed functional capillary density, average capillary length, red blood cell velocity and leukocyte kinetics in alveolar capillary networks in vivo by intravital fluorescence microscopy. In alveolar wall areas of 12,800 +/- 1,800 microm(2), we detected 3.6 +/- 0.5 sticking leukocytes and 21.0 +/- 1.9 functional capillary segments with an average capillary length of 35.7 +/- 2.1 microm. We calculated that approximately 15% of functional capillary segments are blocked by marginated leukocytes. Leukocyte margination was predominantly observed in capillary networks characterized by a high functional capillary density, short capillary segments and low red blood cell velocities. The multitude of interconnected capillary channels in these networks may allow alveolar blood flow to bypass marginated leukocytes. Hence, this interrelationship may be relevant for maintenance of adequate alveolar perfusion and low capillary network resistance despite excessive leukocyte margination in the pulmonary microvasculature. Local microhemodynamic factors may play a regulatory role in the spatial distribution of leukocyte margination.

Distribution of microvascular pressure in arteriolar vessel trees of ventilated rabbit lungs.

We have developed a new in vivo microscopic technique for comprehensive measurements of vessel diameter, segment length, and red blood cell velocity in discrete arteriolar vessel trees of the lung. In anesthetized and mechanically ventilated rabbits, a transparent window was implanted into the right thoracic wall. We injected fluorescently labeled red cells to visualize blood flow and to measure red blood cell velocity. The distribution of microvascular pressures was simulated in a computer model based on morphometric and microhemodynamic data. Of the total pulmonary vascular pressure drop from pulmonary artery to left atrium, on average 2.5% occurred in distal arteriolar vessel trees with main trunk diameters of 73-111 microns. Along the pathlength from main trunk to terminal arterioles (0.18-2.79 mm), the pressure drop ranged between 0.06 and 0.94 mmHg. The pressure drop along individual pathways correlated significantly with pathlength of terminal arterioles, whereas red blood cell velocity did not. The results indicate that in terminal arteriolar vessel trees of the ventilated rabbit lung the resistance to blood flow is low, and the heterogeneity of microvascular pressures in arterioles feeding capillary networks is high.

Quantitative analysis of network architecture, and microhemodynamics in arteriolar vessel trees of the ventilated rabbit lung.

An experimental model has been developed for morphometric and microhemodynamic analysis of discrete arteriolar networks in the ventilated lung. We implanted a transparent window into the right thoracic wall of anesthetized rabbits. Autologous red blood cells were labeled with FITC in vitro. Using a fluorescence video microscopic technique the vessels of superficial arteriolar networks were mapped and classified hierarchically. Networks were investigated under zone 2 conditions (alveolar > left atrial pressure) during continuous monitoring of macrohemodynamics. We comprehensively measured segment length, diameter (D) and branching pattern in the whole network. Microhemodynamic parameters (red blood cell flux (Frbc), red blood cell velocity (Vrbc) and microhematocrit (H mu) were determined in terminal branches. As a result of network analysis the branching rules were found to be similar to those found by cast techniques in human and cat lungs. In terminal arterioles D (21 +/- 4 microns), Frbc (1472 +/- 662 cells/s), Vrbc (863 +/- 250 microns/s) and H mu (0.28 +/- 0.067) were heterogeneously distributed. Geometric, as well as microhemodynamic parameters fitted best to a lognormal distribution. This study represents an example of in vivo analysis of discrete microvascular networks. The measurements in hierarchically equivalent segments of pulmonary arteriolar vessel trees have been shown to be appropriate for estimation of topological, geometrical and microhemodynamic heterogeneity in pulmonary arteriolar networks.

Effects of isoflurane on regional pulmonary blood flow during one-lung ventilation.

Isoflurane has been reported to inhibit hypoxic pulmonary vasoconstriction. However, the effects of one-lung ventilation and isoflurane on regional pulmonary blood flow (Qr) have not been investigated in detail. Therefore, using radionuclide labelled microspheres we measured Qr in rabbits (n = 8) in the left lateral decubitus position during two- and one-lung ventilation under i.v. baseline anaesthesia and during additional administration of 1.5% isoflurane. Macrohaemodynamic variables were recorded continuously. Isoflurane increased non-dependent lung blood flow during two-lung ventilation. One-lung ventilation caused a homogeneous decrease in Qr throughout the hypoxic lung, irrespective of isoflurane administration (P < 0.001). However, isoflurane significantly augmented Qr of the hypoxic lung during one-lung ventilation (P < 0.05). During all phases, Qr of the upper lobe was higher compared with that in the lower lobe in isogravitational slices of both lungs; a ventrodorsal perfusion gradient was found in the left upper lobe. We conclude that 1.5% isoflurane increased perfusion of the non-dependent lung, inhibited hypoxic pulmonary vasoconstriction-induced redistribution of pulmonary blood flow and did not influence isogravitational perfusion gradients.

[The effect of mechanical ventilation, thoracotomy, and one-lung respiration on intrapulmonary perfusion distribution. An animal experimental study]. / Einfluss von Beatmung, Thorakotomie und Ein-Lungen-ventilation auf die intrapulmonale Perfusionsverteilung. Eine tierexperimentelle Studie.

The physiological pattern of regional pulmonary blood flow is mainly determined by the relationship of pulmonary arterial, venous, and alveolar pressures. Changes in alveolar pressure and pulmonary geometry may therefore be expected to influence regional perfusion, which is a key determinant of pulmonary gas exchange. Unilateral thoracotomy is usually performed with the patient in the lateral decubitus position. The present study examined the influence of mechanical factors on regional pulmonary blood flow distribution in rabbits in the lateral decubitus position during normoxia and unilateral hypoxia. METHODS. Anaesthetised white New Zealand rabbits (n = 8) weighing 2200-3900 g (mean = 2860 g) received central venous injections of radioactive microspheres while in the left lateral decubitus position during spontaneous breathing (SB) and during mechanical ventilation (two-lung ventilation, 2LV), under closed (2LVC) and open chest (2LVT) conditions, as well as during unilateral hypoxia of the nondependent lung induced by nitrogen inflation (1LVN) or atelectasis (1LVA). The method used for one-lung ventilation (1LV) has been previously described in detail. Arterial, central venous, and pulmonary arterial pressures were recorded continuously. Lungs were excised, dried in the inflated state, and cut into 16 sagittal slices, which were further divided into lobar components, the lower lobes into center and periphery. The radioactivity of each specimen was measured in a gamma-counter; perfusion of the individual tissue specimens was quantified using the software program MIC III. The Friedman test followed by paired comparisons according to Conover was used for statistical analysis of differences between the experimental phases. Perfusion of central and peripheral parts of isogravitational slices was compared by use of the Wilcoxon matched pairs test. Values are given as means +/- SE; the level of significance was P < 0.05 unless otherwise indicated. RESULTS AND DISCUSSION. Haemodynamic parameters did not differ significantly between the experimental phases (Table 1). Compared to 2LV, a significant increase in venous admixture (P < 0.05) and a corresponding decrease in PaO2 (P < 0.01) were observed during 1LV. This effect was significantly more pronounced during 1LVA as compared to 1LVN (P < 0.01). Since inspiratory pressure was kept constant throughout the experiments, moderate respiratory acidosis developed during both phases of 1LV. Regional perfusion (Qr) of the nondependent lung was slightly reduced during 2LVC compared to SB and 2LVT. One-lung ventilation induced a significant decrease in perfusion of the hypoxic lung (P < 0.001 1LVN, 1LVA vs. SB,2LVC,2LVT). In accordance with the data obtained from blood gas analysis and oximetry, this effect was more pronounced during N2 insufflation than during atelectasis (P < 0.01 1LVN vs. 1LVA). Among the factors that may account for this effect, PaCO2 did not differ significantly between both phases of 1LV. During N2 insufflation PO2 at the hypoxia-sensitive site is lower than during atelectasis, where it equals mixed-versus PO2 (PvO2). The difference in local PO2 is unlikely, however, to have caused the changes in regional perfusion between 1LVN and 1LVA, since PvO2 was as low as 40 mmHg during 1LVA and the pulmonary vascular response to hypoxia has been found to reach its maximum in this PO2 range [2, 11]. Enhanced redistribution of regional perfusion during 1LVN as compared to 1LVA is therefore most likely attributed to differences in alveolar pressure and pulmonary geometry. Apart from a radial perfusion gradient in the right lower lobe during 2LVC and 2LVT, no isogravitational Qr gradients were observed. CONCLUSION. We conclude that controlled mechanical ventilation in the lateral decubitus position causes only minor changes in vertical blood flow distribution.

In vivo kinetics and spectra of 5-aminolaevulinic acid-induced fluorescence in an amelanotic melanoma of the hamster.

For successful photodynamic diagnosis (PDD) and effective photodynamic therapy (PDT) with the clinically used 'photosensitiser' 5-aminolaevulinic acid (ALA), knowledge of the maximal fluorescence intensity and of the maximal tumour-host tissue fluorescence ratio following systemic or local application is required. Therefore, time course and type of porphyrin accumulation were investigated in neoplastic and surrounding host tissue by measuring the kinetics and spectra of ALA-induced fluorescence in vivo. Experiments were performed in the amelanotic melanoma A-Mel-3 grown in the dorsal skinfold chamber preparation of Syrian golden hamsters. The kinetics of fluorescent porphyrins was quantified up to 24 h after i.v. injection of 100 mg kg-1, 500 mg kg-1 or 1,000 mg kg-1 body weight ALA by intravital fluorescence microscopy and digital image analysis (n = 18). In separate experiments fluorescence spectra were obtained for each dose by a simultaneous optical multichannel analysing device (n = 3). A three-compartment model was developed to simulate fluorescence kinetics in tumours. Maximal fluorescence intensity (per cent of reference standard; mean +/- s.e.) in the tumour arose 150 min post injection (p.i.) (1,000 mg kg-1, 109 +/- 34%; 500 mg kg-1, 148 +/- 36%) and 120 min p.i. (100 mg kg-1, 16 +/- 8%). The fluorescence in the surrounding host tissue was far less and reached its maximum at 240 min (100 mg kg-1, 6 +/- 3%) and 360 min p.i. (500 mg kg-1, 50 +/- 8%) and (1,000 mg kg-1, 6 +/- 19%). Maximal tumour-host tissue ratio (90:1) was encountered at 90 min after injection of 500 mg kg-1. The spectra of tissue fluorescence showed maxima at 637 nm and 704 nm respectively. After 300 min (host tissue) and 360 min (tumour tissue) additional emission bands at 618 nm and 678 nm were detected. These bands indicate the presence of protoporphyrin IX (PPIX) and of another porphyrin species in the tumour not identified yet. Tumour selectivity of ALA-induced PPIX accumulation occurs only during a distinct interval depending on the administered dose. Based on the presented data the optimal time for PDD and PDT in this model following intravenous administration of 500 mg kg-1 ALA would be around 90 min and 150 min respectively. The transient selectivity is probably caused by an earlier and higher uptake of ALA in the neoplastic tissue most likely as a result of increased vascular permeability of tumours as supported by the mathematical model.

Isoflurane inhibits hypoxic pulmonary vasoconstriction. An in vivo fluorescence microscopic study in rabbits.

BACKGROUND: Contradictory results have been reported in previous studies investigating the effect of isoflurane on hypoxic pulmonary vasoconstriction by indirect approaches. The current study measured the effects of one-lung ventilation (1LV) and isoflurane 1.5% by direct visual observation of the pulmonary microcirculation. METHODS: Ten New Zealand White rabbits were anesthetized with intravenous thiopental, alpha-chloralose, and piritramid. Arterial, central venous, pulmonary arterial, left atrial, and airway pressures and cardiac output were recorded continuously. 1LV was facilitated by a bronchial blocker in the right main bronchus. A transparent window was implanted into the right thoracic wall for videofluorescence microscopy of the subpleural pulmonary microcirculation. After intravenous injection of fluorescein isothiocyanate-labeled red blood cells, vessel diameters, red blood cell flux, red blood cell velocity, and dynamic microhematocrit were measured in pulmonary arterioles and venules during two-lung ventilation and 1LV during baseline anesthesia and with supplementary isoflurane 1.5%. RESULTS: During intravenous anesthesia, 1LV caused significant reduction of vessel diameters and red cell flux and velocity and an increase in microvascular hematocrit in pulmonary arterioles and venules. The decreases in arteriolar diameters and red blood cell flux and velocity induced by 1LV were significantly attenuated by isoflurane as compared with those measured during baseline anesthesia (P = 0.010, P = 0.029 and P = 0.047). Accordingly, 1LV-induced reduction of venular red cell flux (P = 0.023) and velocity (P = 0.036) were less pronounced during isoflurane. Isoflurane caused a significant decrease in arterial pressure. Venous admixture increased and arterial oxygen tension decreased significantly during 1LV; the changes were more pronounced during 1LV with isoflurane 1.5% than during 1LV with baseline anesthesia. CONCLUSIONS: 1LV leads to a marked reduction of microvascular diameters and blood flow in the hypoxic lung. Isoflurane 1.5% inhibits hypoxic pulmonary vasoconstriction in pulmonary arterioles and increases regional blood flow in the hypoxic lung.

Effect of blood flow on the leukocyte-endothelium interaction in pulmonary microvessels.

Circulating leukocytes are retained in the microcirculation of the lung. The site of leukocyte retention, however, is still a subject of controversy, and the effects of microvascular blood flow on the leukocyte-endothelium interaction in pulmonary microvessels are unknown. We used in vivo fluorescence microscopy to analyze microhemodynamics and the flow behavior of in vivo-labeled leukocytes in pulmonary arterioles, venules, and alveolar capillaries. Microvascular blood flow was altered by variation of cardiac output. Leukocytes were found to roll and to stick on arteriolar and more pronouncedly on venular endothelium. During their passage through alveolar capillaries, a fraction of passing leukocytes became static for 0.1 to > 5 s. Under control conditions, leukocytes were concentrated approximately 8-fold more in arterioles and 24-fold more in venules than in the blood passing through these vessels. The concentration in capillaries was 1.5 times greater than in venules. The velocity of rolling leukocytes in arterioles and venules correlated significantly with the shear rate in these vessels, whereas the density of sticking cells was negatively correlated with the shear rate. The differences between leukocyte rolling and sticking in arterioles and in venules cannot be explained by respective hemodynamic conditions. In alveolar capillaries, the percentage of temporarily static leukocytes and the time of their stasis were inversely correlated with red-blood-cell (RBC) velocity. We conclude that leukocytes are retained in pulmonary arterioles, venules, and alveolar capillaries according to microvascular blood flow and endothelial factors.

Effects of photodynamic therapy on leucocyte-endothelium interaction: differences between normal and tumour tissue.

An inflammatory reaction is regularly noticed in irradiated tissues following photodynamic therapy (PDT). This observation is potentially associated with leucocyte-mediated tissue damage, which might further contribute to the tumoricidal effect of this therapy. The objective of our study was to investigate the effects of PDT on leucocyte-endothelium interaction in the microvasculature of tumours and normal tissue. Experiments were performed in the dorsal skinfold chamber preparation of Syrian golden hamsters bearing amelanotic melanoma A-Mel-3. The photosensitiser. Photofrin (5 mg kg-1 i.v.) was injected 24 h before laser irradiation (630 nm, 100 mW cm-2, 10 J cm-2 or 100 J cm-2). Post-capillary confluent venules (diameter 15-40 microns) of subcutaneous (s.c.) tissue or the amelanotic melanoma A-Mel-3 were observed by intravital microscopy before, 5, 30, 60 and 180 min after laser irradiation and recorded for off-line analysis. Before treatment, the number of adherent leucocytes in tumour vessels was only 22% of the number observed in vessels of s.c. tissue (P < 0.01). The maximum increase in adhering leucocytes was observed in post-capillary venules of s.c. tissue 1 h after PDT (P < 0.01). In contrast, enhanced leucocyte-endothelium interaction was missing in tumour vessels and in control groups. These results indicate that the tumour destruction observed after PDT is not mediated by leucocyte-endothelium interaction in the tumour. Induction of leucocyte adhesion in the PDT-treated normal tissue suggests a contribution to the peritumoral inflammatory response. Different maturational status or biochemical properties of tumour microvascular endothelium may explain the lack of leucocyte adherence upon PDT.