Acinar flow irreversibility caused by perturbations in reversible alveolar wall motion.
Mixing associated with "stretch-and-fold" convective flow patterns has recently been demonstrated to play a potentially important role in aerosol transport and deposition deep in the lung (J. P. Butler and A. Tsuda. J. Appl. Physiol. 83: 800-809, 1997), but the origin of this potent mechanism is not well characterized. In this study we hypothesized that even a small degree of asynchrony in otherwise reversible alveolar wall motion is sufficient to cause flow irreversibility and stretch-and-fold convective mixing. We tested this hypothesis using a large-scale acinar model consisting of a T-shaped junction of three short, straight, square ducts. The model was filled with silicone oil, and alveolar wall motion was simulated by pistons in two of the ducts. The pistons were driven to generate a low-Reynolds-number cyclic flow with a small amount of asynchrony in boundary motion adjusted to match the degree of geometric (as distinguished from pressure-volume) hysteresis found in rabbit lungs (H. Miki, J. P. Butler, R. A. Rogers, and J. Lehr. J. Appl. Physiol. 75: 1630-1636, 1993). Tracer dye was introduced into the system, and its motion was monitored. The results showed that even a slight asynchrony in boundary motion leads to flow irreversibility with complicated swirling tracer patterns. Importantly, the kinematic irreversibility resulted in stretching of the tracer with narrowing of the separation between adjacent tracer lines, and when the cycle-by-cycle narrowing of lateral distance reached the slowly growing diffusion distance of the tracer, mixing abruptly took place. This coupling of evolving convective flow patterns with diffusion is the essence of the stretch-and-fold mechanism. We conclude that even a small degree of boundary asynchrony can give rise to stretch-and-fold convective mixing, thereby leading to transport and deposition of fine and ultrafine aerosol particles deep in the lung. (+info)
Effect of diode laser trans-scleral cyclophotocoagulation in the management of glaucoma after intravitreal silicone oil injection for complicated retinal detachments.
AIMS: To evaluate the effect of trans scleral cyclophotocoagulation (TSCPC) on intraocular pressure (IOP) in the eyes retaining intravitreal silicone oil with medically uncontrolled secondary glaucoma following intravitreal silicone oil injection. METHODS: Medical records of 11 eyes of 11 patients who underwent TSCPC for medically uncontrolled glaucoma without pupillary block following intravitreal silicone oil injection for complicated retinal detachment were reviewed retrospectively. In all cases, intravitreal silicone oil was not removed for fear of retinal redetachment. Diode laser contact TSCPC was performed at a power of 1.5-2.5 W, for a duration of 2 seconds, and with 20-27 applications. IOP, number of glaucoma medications, and success rate were evaluated. RESULTS: After a mean follow up period of 52.5 (SD 8.2) (range 42-68) weeks, the mean pretreatment level of IOP, 43.0 (14.4) (26-67) mmHg, had fallen to 14.5 (4.3) (7-20) mm Hg (p=0.003). The number of glaucoma medications was reduced from 2.6 (0.8) to 0.6 (1.0) (p= 0.005). Qualified success was achieved in nine eyes (81.8%) and complete success in six (54.5%). After TSCPC, patients' retinal status had not changed. CONCLUSION: Patients with medically uncontrolled glaucoma secondary to intravitreal silicone oil injection can be treated with TSCPC in spite of the retained intravitreal silicone oil. (+info)
Changes in refraction and axial length according to the viscosity of intraocular silicone oil.
We performed this study to evaluate the changes in refraction and axial length induced by intraocular silicone oil, and to compare with various clinical parameters between 1,000 and 5,000 cSt silicone oil. The refraction length was measured with an autorefractometer, and the axial length was measured with A-scan ultrasonography. These measurements were performed before and after removal of the silicone oil, using a clear cornea technique in which the silicone oil was injected in combination with pars plana vitrectomy. The mean age of the 25 patients was 38.73 years. On average the intraocular retention after the removal of the silicone oil lasted 5.13 months, and the follow-up time following silicone oil removal was 4.37 months. The changes in refraction and axial length were 6.32 diopters and 12.02 mm, respectively. Eyes injected with 5,000 cSt (11 eyes) tended to have higher changes in the refraction (5.84 vs 6.86 diopters) and axial length (11.70 vs 12.34 mm) than did eyes injected with 1,000 cSt silicone oil (14 eyes). Statistically significant differences were shown for the changes in refraction (p = 0.010) and intraocular pressure (0.63 vs 2.00 mmHg; p = 0.006), whereas but not for the changes in axial length (p = 0.306) and visual acuity (14/100 vs 15/100; p = 0.125). Intraocular silicone oil induced changes in refraction and axial length, and these changes seemed to vary with different viscosities. (+info)
Induction of hypergammaglobulinemia and macrophage activation by silicone gels and oils in female A.SW mice.
Although most published epidemiological studies have found little evidence of systemic autoimmune disease associated with silicone breast implants, there still remains a question of whether silicones can cause local and/or systemic immune dysfunction. This study further investigates the effects of silicones on autoantibody and immunoglobulin production and macrophage activation in female A.SW mice. Sixty mice were divided among four treatment groups receiving a 0.5-ml intraperitoneal injection of either phosphate-buffered saline (PBS), pristane, silicone gel, or silicone oil. Test bleeds were taken periodically for 6 months. In contrast to pristane, neither silicone gel nor silicone oil induced lupus-associated antinuclear autoantibodies (immunoglobulin G [IgG] anti-nRNP/Sm, Su, and ribosomal P) or lupus nephritis. However, serum IgM became elevated persistently within 1 month of silicone gel or silicone oil administration. Also, the level of IgG3 was clearly elevated in silicone oil-treated mice. In contrast, IgG1, IgG2a, and IgG2b levels were not affected greatly by either silicone gel or oil. Furthermore, peritoneal macrophages from silicone- and pristane-treated mice produced higher levels of interleukin-1beta (IL-1beta) and IL-6 than those from PBS-treated mice after lipopolysaccharide stimulation. These results suggest that silicone gels and oils are capable of inducing hypergammaglobulinemia and activating macrophages in female A.SW mice. (+info)
Subconjunctival cysts following silicone oil injection: a clinicopathological study of five cases.
PURPOSE: To study the occurrence, risk factors and management of subconjunctival cysts formed following the use of intraocular silicone oil as a tamponade. METHODS: We analyzed 5 cases of single and multioculated subconjunctival oil cysts between 1986 and 1996. RESULTS: Cysts were observed 15 days to 4 months following silicone oil injection. Clinically they showed minimal inflammatory signs but histopathology of removed cysts showed emulsified silicone oil globules with chronic inflammatory cellular infiltration. CONCLUSION: Though silicone oil is considered to be nontoxic, it can cause chronic inflammation when spilled into the subconjunctival space. (+info)
Massive suprachoroidal hemorrhage with retinal and vitreous incarceration; a vitreoretinal surgical approach.
Suprachoroidal hemorrhage(SH) may cause the expulsion of the intraocular contents. Vitreous incarceration in the wound and retinal detachment with SH are extremely poor prognostic signs. Treatment modalities depend on the severity of eye damage. This particular patient had "kissing" hemorrhagic choroidal detachment which completely filled the vitreous cavity after cataract surgery. It seemed to be inoperable. Secondary surgery was delayed 3 days to lower IOP to normal levels. The eye underwent anterior drainage sclerotomy under constantly-maintained limbal or pars plana infusion fluid line pressure. The authors performed a pars plana vitrectomy, followed by perfluorocarbon liquid injection and a silicone oil tamponade. After this surgical approach, the patient attained an attached retina and a visual acuity of 5/200 at the 3 month follow-up. (+info)
Management of inferior retinal breaks during pars plana vitrectomy for retinal detachment.
AIMS: To determine whether it is necessary to support inferior retinal breaks with a scleral explant during pars plana vitrectomy (PPV) for rhegmatogenous retinal detachment (RD). METHODS: A prospective study was carried out on nine eyes of nine consecutive patients undergoing PPV for primary RD with associated inferior retinal breaks and no significant proliferative vitreoretinopathy. RESULTS: Eight eyes were successfully reattached with a single operation. No cases presented with redetachment because of failed closure of the original inferior breaks. CONCLUSIONS: It is not necessary to support inferior retinal breaks with a scleral explant during PPV for primary RD repair in selected cases. (+info)
Silicone oil-intraocular lens interaction: which lens to use?
AIM: To determine a suitable intraocular lens for implantation in patients at high risk of lens exposure to silicone oil in their lifetime. METHODS: PMMA, AcrySof, AR40, AQUA-Sense, and Raysoft lenses were examined. Each lens was immersed for 5 minute intervals in balanced salt solution (BSS), in stained silicone oil, and again in BSS before being photographed in air and in BSS. Percentage silicone oil coverage of the lens optic was determined. RESULTS: The mean percentage coating (MPC) for the lens biomaterials ranged from 5.2% to 21.5%. The Raysoft lens had significantly less oil coverage when statistically compared with the other lens types (p < 0.001). CONCLUSION: A Raysoft (Rayner) lens is a suitable lens for implantation in patients who are at risk of severe vitreoretinal disease. (+info)