Tissue effects of a new laparoscopic carbon dioxide laser probe.

The effects of CO2 laser beam delivered through a new laparoscopic probe on rabbit uteri is presented. This device has an outer diameter of 4.9 mm and can be delivered through most of the standard operative laparoscopic accessories. Two probes with miniature zinc selenide lenses of 6.5 mm and 17 mm back focal length attached at the distal end were tested. Through each probe, constant 0.5-second pulses and power levels of 5, 10, and 15 W were applied in three different lens-to-target distances. Measurements of beam spot diameters and microscopic crater characteristics revealed significant differences as a result of minor shifting of lens-target distance. From 7 to 9 mm beyond the focal plane and at power levels of 5 to 10 W, negligible tissue effects could be detected. This was defined as an "optical back-stop" effect. A new application mode using an easily maneuverable probe for cutting and coagulating [focusing/defocusing] effects increases the options available for operative laparoscopy.

A non-steady compartmental flow model of the cerebrovascular system.

A lumped parameter compartmental model for the cerebrovascular fluid system is constructed and solved for the general linear problem of a nonsteady flow with constant resistances and compliances. The model predicts the intracranial pressure waves in the various compartments of the brain in response to pressure changes in the vascular system.

An outline of continuum modeling of brain tissue mechanics.

Modern, very sensitive, and noninvasive devices (strain-gauges, accelerometers, etc) detect deformations and motions in the order of a few microns. The observation that the rise in intracranial pressure produces measurable suture strain suggests that noninvasive determination of mechanical parameters in the intracranial cavity, such as density, velocity, pressure, energy, and their time rates, is clearly possible. Based on the above premise, and utilizing the concept of representative elementary volume (REV), this paper presents the conceptual part of a theory that defines the mechanical behavior of the brain and skull under various conditions. The systematic review of brain tissue mechanics leads to a continuum model of a mixed stress-displacement boundary value type, which defines the dynamics of the visco-elastic brain tissue in mathematical terms.

Resistances and compliances of a compartmental model of the cerebrovascular system.

A lumped parameter compartmental model for the nonsteady flow of the cerebrovascular fluid is constructed. The model assumes constant resistances that relate fluid flux to pressure gradients, and compliances between compartments that relate fluid accumulation to rate of pressure changes. Resistances are evaluated by using mean values of artery and cerebrospinal fluid (CSF) fluxes and mean compartmental pressures. Compliances are then evaluated from clinical data of simultaneous pulse wave recordings in the different compartments. Estimate of the average CSF compartmental deformation, based on the compliance between the CSF and brain tissue compartments, proves to be of the order of magnitude of actual experimental measurements.

Strain uterography in labour.

Multi-strain measurements of uterine contractions were made on 36 women at 36 to 42 weeks of pregnancy. The tracings obtained supported the existence of one dominant pacemaker area in the fundal region of the uterus and indicated that the contractile wave travelled in a downward direction with an average speed of 6 cm/second. The analysis of all normal labours showed that strains of the longitudinal muscle fibres changed from extension in the fundal region of the uterus to compression in its lower part, through a local zero strain in a narrow zone below the umbilicus. Intensity of the uterine contractions reached 6 per cent in extension and -2 per cent in compression. Information about the number of peak contractions, the frequenty of contractions and the tonus of the myometrium during relaxation are of importance in the evaluation of uterine dysfunction.

Use of the giant-pulse Nd:YAG laser for ab-externo sclerostomy in rabbits and humans.

The giant-pulse Neodymium:YAG laser, a recently developed laser source, delivers up to 200 W of peak power at pulse widths of 20 or 40 msec. The instrument can create a sclerostomy with minimal surrounding damage and, consequently, relatively little postsurgical inflammation and scarring. We tested its efficacy in performing ab-externo sclerostomy in 10 adult pigmented rabbits and in five patients with end-stage glaucoma. All of the animal eyes were hypotonus immediately after the procedure. However, the intraocular pressure increased gradually, and by the third day, returned to presurgical levels in all of the eyes. All five of the glaucoma patients treated had patent sclerostomies following the procedure. They all had early hypotony, but after 3 months, four of the five sclerostomies apparently failed. The giant-pulse Nd:YAG laser appears useful for performing sclerostomy, but modifications are needed to solve the problems of early hypotony and late closure of the fistulula.

Endometrial laser ablation in rabbits: a comparative study of three laser types.

Endometrial laser ablation is one of the alternatives to hysterectomy in cases of intractable uterine bleeding. It is currently performed using the Nd:YAG laser at 1.06 microns. The aim of this study was to compare the tissue effect of three types of laser irradiation (Nd:YAG laser at 1.06 and 1.32 microns and holmium laser at 2.12 microns) on the rabbit endometrium. Crater formation, coagulation necrosis, and muscle necrosis were evaluated at the time of ablation, as well as at 1 week and 4 weeks postablation. The results were assessed by determining the depth and width of the affected portion in the uterine wall (lumen to serosa). It was shown that Nd:YAG laser at 1.32 microns caused more generalized and extended effects as compared with the other laser types examined. Endometrial regeneration was faster after ablation by the Nd:YAG laser at 1.06 microns and the holmium laser than by the Nd:YAG laser at 1.32 microns. The widest range of "ablation energy" (defined as that causing ablation without muscle damage) was achieved by applying the holmium laser. Further evaluation of the holmium laser for this indication is recommended.