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T J Callahan

Publications and source records attributed to T J Callahan.

12 recordsLinked to original sources
PubMed1993

Risk assessment and management as related to evaluation of medical devices: a view from the FDA.

The regulatory management by the FDA of medical products should be thought of as a form of risk assessment and risk management. This is a new approach, a new way of thinking about product review and postmarket management processes. This paper outlines several aspects of risk assessment and management that have recently been incorporated into the FDA processes that will simplify reviews and lower the risks involved with the use of medical devices. These aspects include development of a new process for selecting the appropriate resources to dedicate to individual device applications, an increased emphasis on good experimental design for clinical studies, and continued development of a biomaterials database.

Equipment Failure↗
PubMed1979

The Na:K pump in red cells is electrogenic.

The membrane potential, E, of the red cell measured with a fluorescent dye, 3,3'-dipropylthiadicarbocyanine iodide, hyperpolarizes when the Na:K pump is activated by adding external K and depolarizes upon the subsequent addition of ouabain. The electrogenic pump is optimally observed in cells where internal Na+ has been raised, SO2-(4) has replaced Cl-, and SO2-(4) permeability has been inhibited by 4,4'-diisothiocyanostilbene-2,2'-disulfonate (DIDS)). The change in E associated with the electrogenic component is about 6 mV in human red cells, somewhat smaller in sheep, and larger in duck and Amphiuma red cells. The membrane resistance, Rm, can be estimated from the pump-dependent change in E and from the current flow assumed to be one-third the ouabain-sensitive Na efflux. In human red cells, Rm is about 1 X 10(6) ohm-cm2. Rm calculated from the residual DIDS-insensitive SO2-(4) flux is also about 1 X 10(6) ohm-cm2. The closeness of these two values of Rm is paralleled in the other three types of red cells (even though the absolute values of Rm vary among the four types by a factor of 10), indicating that the net current flow across the membrane can be accounted for by the net transport of Na by the pump.

Animals↗
PubMed1978

Anion inhibitor-sensitive unidirectional sodium movements in the human erythrocyte.

The increased unidirectional sodium influx found when human erythrocytes are suspended in isotonic salt solutions containing bicarbonate ions as a replacement for chloride ions was examined. The increased sodium movement appears to have the transport characteristics of anion movement. Inhibitors of anion transport such as furosemide, fluorodinitrobenzene (FDNB), and 4-acetamido-4'-isothiocyano-stilbene-2-2'-disulfonic acid (SITS) drastically inhibit these augmented sodium movements. An ion-pair mechanism appears to phenomenologically describe much of the data. A possible role for carbamino groups is considered. Such a model, however, required additional assumptions to explain the selectivity and the anion inhibitor effects.

Anions↗