Cell Viability and DNA Denaturation Measurements by Two-Photon Fluorescence Excitation in CW Al:GaAs Diode Laser Optical Traps

Cell viability and DNA denaturation are measured through two-photon fluorescence excitation using a single diode laser beam as the trapping and exciting source simultaneously. Two-photon fluorescence emission spectra are presented for CHO cells and T lymphocytes loaded with various fluorescent probes. This single beam method is demonstrated to be a safe tool to monitor the viability of optically trapped cells, even under intense 809 nm diode laser illumination (∼106 W/cm2). The dynamics of cellular necrosis is monitored by adding ethanol to the cell suspension during trapping. Thermal damage to heat-treated samples is assessed by recording shifts in the emission spectra from trapped cells loaded with the nucleic acid probe, acridine orange. © 1999 Society of Photo-Optical Instrumentation Engineers.

Reflectance measurements of layered media with diffuse photon-density waves: a potential tool for evaluating deep burns and subcutaneous lesions

The basic principles of a non-contact, near-infrared technique for the mapping of layered tissues are discussed theoretically and verified experimentally. The propagation properties of diffuse photon-density waves in tissues depend on the optical properties of the tissue. When a layered medium is irradiated by amplitude modulated light, the difference in optical properties between the layers is evident in the phase and amplitude of the diffuse reflection coefficient, which is a result of the interference of the partial waves propagating in the different layers. Thus, diffuse photon-density waves are applicable to the analysis of the structure of layered tissue. The probing depth is determined by the modulation frequency of the incident light. For modulation frequencies between several hundred megahertz and a few gigahertz, this allows us to analyse the properties of muscle tissue of up to 4-8 mm below the surface. Experimental results based on chicken breast muscle are given. As an example, the technique might be of use for evaluating the depth of necrosis and the blood volume fraction in deep burns.

Systemic application of photosensitizers in the chick chorioallantoic membrane (CAM) model: photodynamic response of CAM vessels and 5-aminolevulinic acid uptake kinetics by transplantable tumors

The aim of this study is to modify the chick chorioallantoic membrane (CAM) model into a whole-animal tumor model for photodynamic therapy (PDT). By using intraperitoneal (i.p.) photosensitizer injection of the chick embryo, use of the CAM for PDT has been extended to include systemic delivery as well as topical application of photosensitizers. The model has been tested for its capability to mimic an animal tumor model and to serve for PDT studies by measuring drug fluorescence and PDT-induced effects. Three second-generation photosensitizers have been tested for their ability to produce photodynamic response in the chick embryo/CAM system when delivered by i.p. injection: 5-aminolevulinic acid (ALA), benzoporphyrin derivative monoacid ring A (BPD-MA), and Lutetium-texaphyrin (Lu-Tex). Exposure of the CAM vasculature to the appropriate laser light results in light-dose-dependent vascular damage with all three compounds. Localization of ALA following i.p. injections in embryos, whose CAMs have been implanted with rat ovarian cancer cells to produce nodules, is determined in real time by fluorescence of the photoactive metabolite protoporphyrin IX (PpIX). Dose-dependent fluorescence in the normal CAM vasculature and the tumor implants confirms the uptake of ALA from the peritoneum, systemic circulation of the drug, and its conversion to PpIX.

Laser-micropipet combination for single-cell analysis

Due to its potential for exquisite mass detection limits and resolving power, capillary electrophoresis is used for biochemical measurements on single cells; however, accurate measurements of many physiological parameters require sampling strategies that are considerably faster than those presently available. We have developed a laser-based technique to lyse single, adherent, mammalian cells on millisecond time scales. The cellular contents are then introduced into a capillary where electrophoretic separation and detection are performed. Improved temporal resolution of biological measurements results from the extremely rapid lysis made possible by this method. Additionally, the cell is not perturbed by mechanical or electrical stresses prior to sampling. Such disturbances can alter cellular physiology, resulting in inaccurate measurements. The fast cell lysis, the absence of cellular stresses prior to lysis, and the application to adherent mammalian cells are significant refinements to CE-based measurements on single cells. With this laser-micropipet combination, it will be possible to measure the intracellular concentration of molecules that change on subsecond to second time scales, for example, substrates of many cellular enzymes.

Uptake of the photosensitizer benzoporphyrin derivative in human endometrium after topical application in vivo

STUDY OBJECTIVE

To determine both the time leading to maximum endometrial drug uptake and distribution of the photosensitizer benzoporphyrin derivative-monoacid ring A (BPD-MA) after intrauterine instillation (Canadian Task Force classification ).

DESIGN

Assessment of histology specimens (Canadian Task Force classification I).

SETTING

University-based facility.

PATIENTS

Twenty-two women scheduled for hysterectomy.

INTERVENTIONS

We instilled 1.5 ml of a 2 mg/ml of BPD-MA-Hyskon solution into the uterine cavity of 22 women before hysterectomy. The fluorescence induced was measured by fluorescence microscopy on frozen sections of uterine samples from 20 of 22 patients. Systemic uptake of BPD-MA was determined in plasma of six patients by spectrofluorometry.

MEASUREMENTS AND MAIN RESULTS

The BPD-MA-induced fluorescence was maximum 1 hour after instillation, with significantly higher uptake in endometrial glands than in underlying stroma. Hormonal endometrial stimulation correlated with fluorescence intensity: atrophy < secretory phase < proliferative phase. Strongest fluorescence was seen in endometrial cancer. Drug uptake by endometrial glands was found at a depth of 2 mm from the surface. Systemic uptake of BPD-MA was under the detection level of 2 ng/ml after application.

CONCLUSION

Fluorescence in human endometrial glands suggests that selective destruction of human endometrium with photodynamic therapy may be possible 1 hour after topical application of BPD-MA for benign and malignant lesions. No systemic drug uptake, side effects, or major technical difficulties were detected. Limited penetration of the drug and selective uptake by endometrial glands provided a high degree of safety for endometrial ablation.

Effect of lung volume reduction surgery in a rabbit model of bullous lung disease

Clinical use of staple lung volume reduction surgery (LVRS) has proliferated for treatment of emphysema despite limited data regarding efficacy or optimal techniques. Recent studies in animal models of obstructive lung disease describe the decrease in lung compliance and increase in airway support as mechanisms of an improvement in pulmonary functions analogous to human data. We describe contrasting results in an animal model of bullous lung disease with a mixed but predominantly restrictive pattern of lung disease. Mixed restrictive and bullous lung disease was induced in 17 New Zealand white rabbits with i.v. Sephadex beads and endotracheally instilled carrageenan. Unilateral stapled lung volume reduction surgery was performed at 5 weeks postinduction of emphysema on the right lower lobe by lateral thoracotomy using a pediatric stapler. Static trans-pleural pressures were measured at 60, 40, and 20 cm3 inflation at preinduction (baseline), pre- and postoperatively, and 1 week postoperatively in anesthetized animals. Lungs were then harvested en bloc and examined histopathologically. The effects of volume reduction surgery on static lung compliance, lung conductance, and forced expiratory flows (FEF) were assessed. Five weeks after induction of lung disease, the animals had no significant change in static compliance and forced expiratory volume in 0.5 s (FEV0.5) or lung conductance compared to baseline. Immediately following LVRS, the animals showed a significant decrease in static compliance, FEV0.5, and conductance. One week postoperatively, compliance increased to approximately baseline levels along with a slight increase in FEFs and conductance toward preoperative levels. Histology examination revealed restrictive and bullous lung disease. Thus, we have demonstrated the feasibility of using an animal model for evaluation of volume reduction therapy for restrictive-obstructive lung disease. Physiologically, this model showed decrease conductance and decreased forced expiratory flows following lung volume reduction despite increased recoil. This is in contrast to increased conductance and flows seen in humans with severe emphysema following surgery and suggests that current criteria excluding patients with a significant restrictive component to their lung disease from LVRS surgery may be justified.

Multiphoton fluorescence excitation in continuous-wave infrared optical traps

The multiphoton fluorescence excitation observed in acontinuous-wave (cw) single-beam gradient force optical trap(optical tweezers) is reported for latex beads labeled with ayellow-green fluorescent dye (BODIPY). The fluorescenceemission spectra of the yellow-green beads trapped and excited by thesame 1064-nm laser light are identical to the spectra excited by the365-nm UV light. The influence of the numerical aperture of theobjective on the slope of the log-log power-dependence has beendemonstrated for BODIPY-Oil solution under cw and pulsed-laserconditions. The possibility that three-photon excitation processoccurs is discussed within the context of a dog-bone saturationmodel. Other possibilities for the observed fluorescence excitationhave been discussed.

In vivo detection of metastatic ovarian cancer by means of 5-aminolevulinic acid-induced fluorescence in a rat model

STUDY OBJECTIVES

To determine the feasibility of macroscopic visualization of small ovarian cancer metastases in vivo by fluorescence after intravenous administration of 5-aminolevulinic acid (ALA); to assess the time after drug injection when fluorescence of small metastases is maximum; and to correlate macroscopic in vivo fluorescence with both microscopic ex vivo fluorescence and histologic findings.

DESIGN

Controlled animal study (Canadian Task Force classification I).

SETTING

University-based facility.

SUBJECTS

Twenty-four healthy, female Fischer rats.

INTERVENTION

Diffuse peritoneal metastatic cancer was induced in Fischer 344 rats by intraperitoneal injection of 1 million syngeneic ovarian cancer cells (NuTu-19). Four weeks after induction ALA100 mg/kg was injected intravenously, and diagnostic laparotomy was performed 1, 3, 6, or 9 hours thereafter.

MEASUREMENTS AND MAIN RESULTS

The peritoneal cavity was illuminated with the Wood's lamp (ultraviolet light). Fluorescence was determined by direct visualization and compared with a calibrated fluorescent disk. Tissues were collected, sectioned, and examined by fluorescence and conventional light microscopy. Within 1 to 3 hours after intravenous injection of ALA, in vivo fluorescence of tumor nodules (diameter 0.4-5.0 mm) was macroscopically visible. Tumor-free peritoneum did not show fluorescence and was significantly distinguishable from cancer nodules. Fluorescence from intestinal tissues was comparable with tumor nodules. Microscopic fluorescence analysis showed similar values for tumor nodules and peritoneum. Stained histologic specimens of peritoneal surface revealed a superficial layer of cancer cells responsible for fluorescence. The time course of the fluorescence curve in the intestine peaked twice, at 1 and 6 hours after ALA injection. Macroscopically fluorescing nodules were histology confirmed as malignant.

CONCLUSIONS

Fluorescence detection of small cancer nodules after intravenous injection of ALA is feasible for nodules smaller than 0.5 mm on the peritoneum. One to 3 hours after drug injection is optimal for diagnosis of metastases.

An animal model for lung volume reduction therapy of pulmonary emphysema

Stapled lung volume reduction surgery (LVRS) has recently been described for treatment of emphysema. Many questions arise regarding physiologic mechanisms of response from surgical treatment of emphysema. The objective of this study was to develop an animal model for the study of lung volume reduction surgery in diffuse heterogeneous emphysema. We hypothesized that elastic recoil would increase, static respiratory system compliance would decrease, and expiratory flows would increase after lung volume reduction surgery in animals with emphysema. In the study, emphysema was induced in 31 New Zealand White rabbits (3-5 kg) with endotracheally aerosalized porcine elastase (10,000-12,000 U). Lateral thoracotomies were performed 4-6 weeks postinduction under general anesthesia and mechanical ventilatory support. Stapled volume reduction was performed on the right lower lobe using a standard multirow pediatric stapler (U.S. Surgical). Pulmonary function tests were performed at baseline (preinduction), before stapling LVRS (postemphysema induction), immediately post stapling LVRS, and 1 week poststapling. Static respiratory system compliance, flow, conductance and forced expiratory flows, and peak flows at 20 and 40 cm3 of exhaled volume were analyzed. Animals were sacrificed 1 week poststapling, and bilateral lungs were harvested for histopathology. Diffuse but heterogeneous pulmonary emphysema was seen in these animals treated with high-dose aerosolized elastase. Static compliance increased, while expiratory flows and conductance decreased after induction of emphysema. Immediately post stapled volume reduction therapy, animals had decreased static compliance. By 1 week following surgery, animals showed increased forced expiratory flows and decreased expiratory resistance, although compliance was similar to preoperative levels. In conclusion, we describe initial results in an animal model of obstructive emphysema suitable for the study of lung volume reduction surgery. Changes in pulmonary function indicate that unilateral lower lobe LVRS increases airway conductance in the rabbits. Findings from LVRS studies in animal models such as this may help explain clinical improvement following LVRS in humans.

Thermal imaging of the temporal bone in CO2 laser surgery: an experimental model

The unique properties of lasers create an enormous potential for specific treatment of chronic ear disease. Despite the widespread acceptance and use of the laser, however, a complete understanding of the time- and space-dependent temperature distribution in otic capsule bone immediately after pulsed laser exposure has not been elucidated. Using a liquid nitrogen-cooled mercury-cadmium telluride infrared detector, the temperature distribution in human cadaveric otic capsule bone was determined immediately after pulsed (100 msec) carbon dioxide laser exposure (0.3 to 4.0 W; 200 microm spot diameter). The time- and space-dependent temperature increases and thermal diffusion were determined as a function of the laser power density and were found to vary linearly.

Thermal Imaging of the Temporal Bone in CO2 Laser Surgery: An Experimental Model

The unique properties of lasers create an enormous potential for specific treatment of chronic ear disease. Despite the widespread acceptance and use of the laser, however, a complete understanding of the time- and space-dependent temperature distribution in otic capsule bone immediately after pulsed laser exposure has not been elucidated. Using a liquid nitrogen-cooled mercury-cadmium telluride infrared detector, the temperature distribution in human cadaveric otic capsule bone was determined immediately after pulsed (100 msec) carbon dioxide laser exposure (0.3 to 4.0 W; 200 urn spot diameter). The time- and space-dependent temperature increases and thermal diffusion were determined as a function of the laser power density and were found to vary linearly.

Laser scissors and tweezers

In summary, we described the use of laser scissors and tweezers from three perspectives: (a) the historical background from which these two techniques evolved, (b) an understanding and lack of understanding of the mechanisms of interaction with the biological systems, and (c) the applications of the scissors and tweezers alone and in combination. As the technology improves and we gain a better understanding of how these two tools operate they will become even more useful in probing cell structure and function, as well as practically manipulating cells in genetics, oncology, and developmental biology.

Photodynamic therapy of the ciliary body with tin ethyl etiopurpurin and tin octaethyl benzochlorin in pigmented rabbits

BACKGROUND AND OBJECTIVES

The authors used a pigmented rabbit model to investigate two photosensitizers, tin ethyl etiopurpurin (SnET2) and tin octaethyl benzochlorin (BNZ 203), to determine their potential for creating ciliary body injuries during photodynamic therapy (PDT).

MATERIALS AND METHODS

The biodistribution of SnET2 (n = 10) and BNZ 203 (n = 9) was studied by fluorescence microscopy using a low light detection system, based on charged-coupled device photography, with digital image processing at 1 and 24 hours after injection. PDT with SnET2 (n = 8; 664 +/- 7-nm light; 75 mW/cm2; 50 or 100 J/cm2; 1-mm spot size) and BNZ 203 (n = 6; 689 nm; 75 mW/cm2; 50 or 100 J/cm2; 1-mm spot size) was performed at 24 hours post-injection. The control subjects for SnET2 (n = 5) and BNZ 203 (n = 3) were given a maximal light dose (100 J/cm2).

RESULTS

Both photosensitizers demonstrated an intravascular distribution at 1 hour that shifted to a ciliary body distribution at 24 hours (SnET2 much greater than BNZ 203). In addition, the SnET2 demonstrated suborgan localization to the nonpigmented ciliary body epithelium. Both photosensitizing agents were able to produce selective injury to the rabbit ciliary body (SnET2 much greater than BNZ 203), with evidence of a small component of thermal damage (SnET2 greater than BNZ 203).

CONCLUSIONS

PDT with SnET2 or BNZ 203 can produce selective injury to the pigmented rabbit ciliary body. The nonpigmented ciliary body epithelium exhibits selective retention of SnET2. This finding warrants further investigation.

Photodynamic therapy for antifibrosis in a rabbit model of filtration surgery

BACKGROUND AND OBJECTIVE

The purpose of this pilot study was to investigate the use of photodynamic therapy (PDT) using tin ethyl etiopurpurin (SnET2) as an adjunctive antifibrotic therapy for filtering surgery in a rabbit model.

MATERIALS AND METHODS

The pharmacokinetics of SnET2 were established by intravenous (1 mg/kg) and subconjunctival (25, 50, or 75 micrograms) injections and compared with controls. Intravenous and subconjunctival SnET2 injections were given prior to posterior lip sclerectomies followed by postoperative laser irradiation (664 +/- 7 nm; 100 mW/cm2; 30 J/cm2). Antifibrotic efficacy was established by clinical response and histologic examination.

RESULTS

After subconjunctival injections, large areas of avascular conjunctiva were produced and filtering bleb survival was prolonged. No effect was found for intravenously administered photosensitizer followed by light irradiation.

CONCLUSIONS

PDT may be an alternative antifibrotic therapy for filtration surgery that does not use chemotherapeutic agents or ionizing radiation. Multiple parameters (light, drug dose, irradiation area) may be manipulated to improve predictability of the antifibrotic effect.

In vivo fluorescence detection of ovarian cancer in the NuTu-19 epithelial ovarian cancer animal model using 5-aminolevulinic acid (ALA)

The purpose of this study was to determine whether in vivo fluorescence detection of protoporphyrin IX (PpIX) could be used to identify intraperitoneal micrometastases of epithelial ovarian carcinoma after application of 5-aminolevulinic acid (ALA). ALA was applied intraperitoneal at different concentrations (25, 50, and 100 mg/kg) and iv (100 mg/kg) to immunocompetent Fischer 344 rats bearing a syngeneic epithelial ovarian carcinoma. At different time intervals after ALA administration (1.5, 3, and 6 hr) the peritoneal cavity was illuminated with ultraviolet (uv) light. In vivo fluorescence of PpIX initially was determined by direct visualization. Subsequently ex vivo measurements were made with a slow-scan, thermoelectrically cooled CCD camera. Red in vivo fluorescence was observed in ovarian micrometastases smaller than 0.5 mm in 100% of the ALA-administered animals independent of time interval, drug concentration, or route of administration. The intensity of the fluorescence was concentration dependent as strong fluorescence was consistently found only above 25 mg/kg ALA. Ex vivo tumor to peritoneum fluorescence yield peaked 3 hr after administration of a 100 mg/kg intraperitoneal dose. Direct visualization of in vivo fluorescence after ALA application may improve the detection of intraperitoneal ovarian cancer micrometastases.

Objective predictors of response for staple versus laser emphysematous lung reduction

Recently described surgical approaches to the treatment of emphysema, including buttressed stapled volume reduction and laser coagulation, are associated with variable clinical outcomes. We examined objective preoperative factors as predictors of response to treatment in patients enrolled in a randomized trial of staple versus laser volume-reduction surgery in order to help define patient selection criteria for these procedures. Seventy-two patients with severe symptomatic emphysema without bullae were entered into the protocol (39 staple, 33 laser). Preoperative objective variables (pulmonary function tests, smoking history, demographics, and graded chest computed tomographic [CT] scans) were evaluated as predictors of response to treatment (defined as a change in FEV1) at 3- to 6-mo follow-up, using linear and multivariate regression analysis. Follow-up pulmonary function was obtained on 90% of the 68 patients surviving at 6 mo. Overall improvement was significant only for staple-treated patients, and improved outcome correlated with greater smoking history and younger age for staple-treated patients. When physiologic variables were analyzed, greater smoking history, lower DL(CO), and younger age predicted improved outcome for laser-treated patients. Preoperative FEV1 and gas-exchange variables did not predict outcome in staple-treated patients. When CT scan grading was included in multivariate regression analysis, hyperinflation (increased thoracic gas volume) was the primary predictor of response for laser-treated patients. These findings suggest that younger patients with evidence of advanced emphysematous lung disease and hyperinflation are optimal candidates for lung-volume-reduction surgery, particularly by staple-reduction techniques. Additional studies with long-term follow-up, bilateral procedures, and assessment of other outcome measures must be performed to further define operative criteria for lung-volume-reduction surgery for emphysema.

Time-resolved and steady-state fluorescence measurements of beta-nicotinamide adenine dinucleotide-alcohol dehydrogenase complex during UVA exposure

beta-nicotinamide adenine dinucleotide (NADH)-alcohol dehydrogenase complex was compared to either UVA irradiation (364 nm; 50 mW cm-2; 0-60 min) or heat in order to investigate complex stability. Prior to irradiation, frequency-domain fluorescence lifetime measurements indicated the presence of two principal components having short (subnanosecond) and long (nanosecond) fluorescence lifetimes reflecting free and bound NADH respectively. UVA exposure resulted in decreased NADH fluorescence intensity concomitant with decreased absorption at 337 nm. However, UVA irradiation did not reduce the fractional contribution of the long-lived bound NADH. The photoinduced fluorescence decrease appeared to be caused by the formation of oxidized NAD+ and not on UVA-induced dissociation of the NADH-protein complex. Such dissociation, detected by a red-shifted fluorescence maximum and decreased fractional contribution of the nanosecond component, was observed when NADH-protein mixtures were heated.

Two-photon excitation of 4'-hydroxymethyl-4,5',8-trimethylpsoralen

Psoralens are a class of pharmaceutical agents commonly used to treat several cutaneous disorders. When irradiated with a mode-locked titanium: sapphire (Ti:sapphire) laser tuned to 730 nm, an aqueous solution of 4'-hydroxymethyl-4,5',8-trimethylpsoralen (HMT) emits blue light. The emission spectrum is centered at 452 nm and is identical to that obtained by one-photon excitation with UVA excitation, and its magnitude depends quadratically on the intensity of laser excitation. These results suggest that two-photon excitation occurs to a potentially photochemically active state. To estimate the two-photon absorption cross section, it was first necessary to measure the emission quantum yield of HMT using 365 nm excitation at room temperature that resulted in a value of 0.045 +/- 0.007. The two-photon absorption cross section of HMT at 730 nm is therefore estimated to be 20 x 10(-50) cm4 s (20 Göppert-Mayer). The excited-state photophysics and photochemistry of psoralens suggest potential applications to cutaneous phototherapy in diseases such as psoriasis and dystrophic epidermolysis bullosa.

Photodynamic therapy using topically applied dihematoporphyrin ether in the treatment of cervical intraepithelial neoplasia

OBJECTIVE

To perform a phase I study of topically applied dihematoporphyrin ether (DHE) in the photodynamic treatment (PDT) of cervical intraepithelial neoplasia (CIN) using fixed DHE doses and application schedules, and a variable dose of 630 nm red light delivered by an argon-pumped dye laser.

METHODS

Between February 1993 and April 1994, 24 nonpregnant women with a histologic diagnosis of CIN were enrolled. All patients had lesions involving at least 25% of the cervix that were colposcopically visible. Using a cervical cap, 2 ml of a 1% solution of DHE (Photofrin) in a 4% Azone and isopropyl alcohol vehicle were applied to the cervix 24 hr prior to PDT. An argon-pumped dye laser providing light at 630 nm was then used to perform PDT. Light was coupled into a 400-microm silica fiber optic terminating in a microlens which focused the laser radiation onto a circular field of uniform light intensity perpendicular to the tissue. The entire ectocervix was treated in a single field including a margin of 3-5 mm of normal cervix. Using a constant power density (150 mW/cm2) to avoid thermal injury, the PDT energy was increased every 4 patients in a phase I fashion (40, 60, 80, 100, 120, and 140 J/cm2).

RESULTS

Thirteen patients with CIN I, 7 patients with CIN II, and 4 patients with CIN III were treated. The maximal energy density was well tolerated. Toxicity was minimal with no patients experiencing local necrosis, sloughing, or scarring; however, a mild vaginal discharge was noted in several patients. Systemic effects were absent. After 12 months of follow-up at 3-month intervals, 22 patients are evaluable of whom 15 (68%) are disease free. One patient was lost to follow-up and in another the cervical cap was dislodged. Four of the 7 failures or recurrences occurred at energy densities of 80 J/cm2 or less, while 8 of 11 (73%) patients were treated successfully with PDT at an energy density of 100 to 140 J/cm2.

CONCLUSIONS

PDT with DHE and an argon-pumped dye laser at 630-nm wavelength delivering an energy density of 140 J/cm2 is safe and effective in treating CIN. Phase II studies using PDT at the prescribed application schedule and dose are indicated.

Doppler grid surface scanning applications for pulmonary subsurface parenchymal perfusion assessment

Subsurface perfusion to lung parenchyma underlying the pleura is difficult to assess in live ventilated animals. The purpose of this study was to assess applicability of a newly developed laser Doppler grid scanning imaging technology that measures perfusion of pleural subsurface lung regions in intact normal and abnormal animal lungs. Eighty-six Doppler grid perfusion measurements were performed in five New Zealand White Rabbits (3-5 kg); four with unilateral bullous lung disease, one normal control. Left upper lobe lung surface was exposed to 10 1-sec spot Nd:YAG exposures (70 W/cm2). One week following laser exposure, all rabbits underwent sequential bilateral open thoracotomy. Unaffected left lower lobes in these animals and all four lobes of a previously untreated rabbit were used as controls. Pleural subsurface perfusion measurements were recorded over a contiguous 900-pixel square surface grid using quantitative noncontact laser Doppler imaging during open thoracotomy procedures. Scans were obtained in a normal volume ventilation mode, at 30 cm of inspiratory hold airway pressure, and postinflation. A perfusion-pressure response curve was obtained in normal lung at 10-, 20-, and 30-cm static airway pressure. Post mortem measurements were used as 0 flow controls. Normal lung tissue was found to have relatively high pleural subsurface perfusion (1362 +/- 328 corrected units on a scale of 0-4095). Areas of atelectasis had decreased perfusion (659 +/- 512 U., 48.4 +/- 12.5% compared to normal lung, p < 0.02), but returned to normal levels after inflation of the lung (1253 +/- 363 U., p = 0.21 compared to normal). Pleural subsurface perfusion decreased uniformly and progressively as lung inflation pressure increased (p < 0.0001). Perfusion increased immediately to supranormal values following release of high inspiratory inflation pressure holds (1603 +/- 626 U., 117 +/- 18% compared to normal lung, p = 0.03). Bullae had markedly decreased perfusion (541 +/- 68 U.) that was not further reduced by increased inflation pressures. Noncontact laser Doppler grid perfusion imaging appears to provide a new tool for measuring pleural subsurface perfusion over a large area of lung surface in clinical experimental settings. Results are rapid, reproducible, and consistent. Sampling errors inherent in current point sampling Doppler flow techniques are reduced by the multiple contiguous measurements. We have used this technique to demonstrate inspiratory pressure-related reduction in pleural subsurface perfusion in normal lung, reversible decreased perfusion in atelectatic regions, and reduced perfusion in bullous and laser-treated lung regions.

Identification of photoacoustic transients during pulsed laser ablation of the human temporal bone: an experimental model

Laser ablation of hard tissues during neurotologic operations has been accomplished with continuous-wave (CW) lasers in the visible and midinfrared spectrum. The mechanism of ablation at these wavelengths is secondary to photothermal-induced tissue destruction. As a result, significant thermal damage to surrounding tissue may occur. Pulsed ultraviolet (UV) lasers have been suggested as an alternative to the argon, KTP-532, and CO2 lasers currently used in clinical practice. The pulse length of Excimer lasers are considerably shorter than the thermal diffusion time of bone tissue, and as a consequence thermal injury is minimal. This makes pulsed lasers an attractive tool for tissue ablation in the ear: in essence a "cold knife." However, the short pulse width of Excimer lasers (typically 10-150 ns) can create large thermoelastic stresses in the ablation specimen. This study identifies the presence of these photoacoustic waves during the Excimer laser treatment of the cadaveric human temporal bone. A XeCl (lambda = 308 nm, tau p = 12 ns) excimer laser was used to ablate hard tissue surrounding the oval window and facial ridge with energies of 75, 45, 25, and 12 mJ/pulse. Spot size was estimated to be 0.5 mm2. Custom high-frequency polyvinyldifluoride (PVDF) piezoelectric film transducers were fabricated and attached to the promontory, round window niche, and facial ridges. The signals were amplified using a low-noise preamplifier and recorded on a digitizing oscilloscope. Photoacoustic waves were clearly identified. Notably, large acoustic waves were measured on the promontory and on both sides of the facial ridge. The implications and clinical relevance of these findings is discussed and compared to findings obtained from a model system.