Biomedical subjects

P Tong

Publications and source records attributed to P Tong.

57 records · Page 4Linked to original sources

PubMed1968

Theory of the sphering of red blood cells.

A rigorous mathematical solution of the sphering of a red blood cell is obtained under the assumptions that the red cells is a fluid-filled shell and that it can swell into a perfect sphere in an appropriate hypotonic medium. The solution is valid for finite strain of the cell membrane provided that the membrane is isotropic, elastic and incompressible. The most general nonlinear elastic stress-strain law for the membrane in a state of generalized plane stress is used. A necessary condition for a red cell to be able to sphere is that its extensional stiffness follow a specific distribution over the membrane. This distribution is strongly influenced by the surface tension in the cell membrane. A unique relation exists between the extensional stiffness, pressure differential, surface tension, and the ratio of the radius of the sphere to that of the undeformed red cell. The functional dependence of this stiffness distribution on various physical parameters is presented. A critique of some current literature on red cell mechanics is presented.

Biophysical Phenomena↗

PubMedDate not supplied

Branch retinal artery occlusion (BRAO) combined with branch retinal vein occlusion (BRVO) and optic disc neovascularization associated with HIV and CMV retinitis.

Two vaso-occlusive events, branch retinal artery occlusion (BRAO) and branch retinal vein occlusion (BRVO), were observed in the retina of an HIV-infected patient with cytomegalovirus (CMV) retinitis who developed neovascularization of the disc (NVD). Although BRVO and reversible NVD have been reported in association with CMV retinitis, we have seen no reports of concomitant BRAO. CMV damages endothelial cells and causes an occlusive vasculitis. In HIV-infected individuals, damaged endothelial cells and rheologic problems result in increased blood viscosity. HIV infection has also been associated systemically with elevated levels of cytokines, including tumor necrosis factor alpha (TNF-alpha). In vitro, TNF-alpha exerts effects that decrease fibrinolytic potential; this activity in the circulation of a patient with AIDS may lead to vascular occlusive events. In the patient reported here, the retinal changes were not reversed by induction therapy with ganciclovir and the NVD did not regress.

AIDS-Related Opportunistic Infections↗

PubMedDate not supplied

Laser in situ keratomileusis enhancement after radial keratotomy.

PURPOSE: To present results of laser in situ keratomileusis (LASIK) enhancement after radial keratotomy (RK). METHODS: Sixteen eyes of 10 patients were treated with LASIK for residual myopia and hyperopia after RK. Mean preoperative spherical equivalent refraction was -3.14+/-3.04 D (range, -6.675 to +6.00 D). Best spectacle-corrected visual acuity was 20/20 in 9 eyes, 20/25 in 6 eyes, and 20/30 in 1 eye. Uncorrected visual acuity was better than 20/40 in only 2 eyes. Patients were followed at 1 day, 1 week, 1, 3, and 6 months, and 1 year. Mean follow-up was 8.3 months (range, 1 to 17 mo). RESULTS: All eyes received one LASIK enhancement. Mean final spherical equivalent refraction was +0.16+/-0.68 D (range, -1.00 to +1.75 D). No eyes experienced any visual loss. Five eyes gained 1 line of best spectacle-corrected visual acuity. Uncorrected visual acuity was 20/20 in 9 eyes, 20/25 in 6 eyes, and 20/30 in 1 eye. Two eyes of one patient had the previous RK incisions open. CONCLUSION: LASIK was an effective treatment for correction of residual myopia and hyperopia after RK.

Adult↗