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Biomedical subjects

M H Friedman

Publications and source records attributed to M H Friedman.

At least 127 records · Page 7Linked to original sources
PubMed1972

A quantitative description of equilibrium and homeostatic thickness regulation in the in vivo cornea. I. Normal cornea.

By combining a description of the coupled solute and water flows through the in vivo cornea with a set of appropriate mechanical equilibrium conditions, it is possible to calculate directly the corneal thickness, given the corneal temperature, the state of the aqueous and tears, the swelling pressure-hydration relation of the corneal stroma, and the transport properties of the corneal membranes. Active transport of ions or water by the corneal epithelium or endothelium, or both, are explicitly included. When published parameters are inserted into the formulation, the normal corneal thickness is recovered, and the corneal potential, anteriorly directed water flux, and stromal salt content are in reasonable to quantitative agreement with experiment. The analysis yields a simple physical explanation of the stromal imbibition pressure and the opposing forces which cause the cornea to assume its normal thickness.

Animals↗
PubMed1972

A quantitative description of equilibrium and homeostatic thickness regulation in the in vivo cornea. II. Variations from the normal state.

The description of corneal mechanics and transport developed in part I and used there to describe normal corneal behavior is here applied to corneas whose properties or boundary conditions are abnormal. The predicted effects of changing intraocular pressure, aqueous concentration, and tear tonicity are examined, and these compare favorably with available experimental data. The periodic variation in tear tonicity which accompanies the sleep-wake cycle prevents the cornea from achieving a true steady state, but a time-average steady state, about which corneal behavior oscillates, can be defined. The in vivo effects of endothelial dystrophy and epithelial removal are explained, and it is suggested that the epithelial sodium pump may act homeostatically to maintain corneal thickness in the face of ambient temperature variations. Part II concludes with a discussion, from the standpoint of the present theory, of the role of metabolically coupled water transport in the maintenance of the normal corneal thickness.

Animals↗
PubMed1970

Mass transfer in the cornea. I. Interacting ion flows in an arbitrarily charged membrane.

The formalisms of irreversible thermodynamics are used to describe multi-ionic nonconvective flow through an arbitrarily charged membrane. Interactions between oppositely charged ions are included and are measured by a single phenomenological coefficient. The consequent generalized Nernst-Planck flux equations are integrated to yield a relation between the species fluxes and the composition of the solutions bounding the membrane. It is assumed in the derivation that activity coefficient gradients within the membrane and direct interactions between ions of like charge are negligible. Some special cases are examined. To illustrate the use of the final equations, a single membrane separating solutions of differing composition is modeled, and the effect of ion-ion interactions on the membrane potential and the ion fluxes is demonstrated for several values of diffusion current density and membrane charge density.

Bicarbonates↗
PubMed1970

Previously uncharacterized Mycoplasma isolates from an investigation of canine pneumonia.

Mycoplasmas recovered from the respiratory tract and genitourinary system of dogs, with and without respiratory infection, have been characterized by biological and immunological methods. Some of the isolates were indentified as being similar to the three species of canine mycoplasmas described earlier under the designation Mycoplasma spumans, M. canis, and M. maculosum. Other mycoplasmas placed in three groups (A, C, and D) were found to be clearly distinct from the three classified species. Group A strains fermented glucose but not mannose and were serologically distinct from other canine mycoplasmas recovered in this study. These strains were subsequently found to be biologically and serologically related to a previously reported, but unclassified, canine mycoplasma. Group D strains differed in some biological properties but were serologically related. These were found to be nonfermenting mycoplasmas representing isolations from the throat and bladder of dogs. They were serologically distinct from other canine mycoplasmas and were apparently unrelated to other known mycoplasma serotypes. Group C mycoplasmas were recovered only from the lungs of dogs. Within the group, they differ in some immunological properties but appear to be serologically distinct from other canine strains. They can also be separated from other dog strains in their ability to ferment glucose and mannose. Group B strains were found to have biological properties similar to M. canis strains but seemed to be only partially related to this serotype when examined in several serological techniques. It is suggested that these strains might represent antigenic variants of M. canis.

Journal Article↗