Ventricular septal defect with bidirectional shunting: Mathematical considerations

Previously proposed formulae for the quantitative estimation of bidirectional shunts across ventricular septal defects require determination of the oxygen contents of mixed venous, pulmonary artery, pulmonary venous, and aortic blood. Because these formulae do not take into account the mixing of oxygenated with unoxygenated blood within the ventricles, their use must result in underestimation of shunt flows in each direction. A mathematical model for a ventricular defect is examined, in which it is assumed that mixing of blood occurs in each of six sites in the venae cavae or right atrium, right ventricle, pulmonary artery, left atrium, left ventricle, and aorta. A total of fourteen streams of blood can flow from one to another of these mixing sites. As long as complete mixing occurs in the six specified mixing sites, any degree of mixing or non-mixing of the various streams is permitted. From the equations characterizing the model, formulae are derived in which the shunt flow in each direction is expressed in terms of the oxygen contents in the six mixing sites and the fractions of blood which enter the shunt from either side without prior mixing in a ventricular mixing site. The previously reported formulae, which apply when no ventricular mixing is allowed to occur, lead to theoretical minimum values for the shunt flows in each direction. At the opposite extreme where all the shunting blood is required to mix in a ventricle before entering the shunt, formulae for maximum possible shunt flows are also obtained. The absolute values for the left-to-right and right-to-left shunt flows, which must lie somewhere between the theoretical maximum and minimum values, cannot be computed from blood gas data alone. This work was supported in part by grant HE-07563 from the National Heart Institute of the National Institutes of Health and grants-in-aid from the American and North Carolina Heart Associations and the Life Insurance Medical Research Fund. Work completed during tenure as U.S.P.H.S. post-doctoral fellow.     

Aerobic respiratory activity of the yeastlike phase of Sporotrichum schenckii as affected by high hydrogen ion concentrations

Summary Six strains ofSporotrichum schenckii were studied in regard to the effect of hydrogen ion concentration on certain aspects of the aerobic respiratory activity of the yeastlike phase.Optimal oxygen uptake of endogenous respiration occurred at pH 2.0, although no effects were observed on the oxygen-carbon dioxide exchange ratio (respiratory quotient) at this pH value when compared to the R.Q. obtained at pH 7.0. Endogenous respiratory activity at both pH 2 and 7 was markedly sensitive to the presence of certain respiratory inhibitors.Optimal respiratory activity using glucose as substrate occurred at pH 7.0 .On the other hand, oxidation of pyruvate as substrate proceeded at significant rates only at pH values below pH 4.0. With decreasing hydrogen ion concentration, accumulation of this organic acid occurred when glucose was employed as substrate. With the exception of acetate, none of the organic acid respiratory intermediates were found to stimulate respiration.The results reported herein suggest that the respiratory activity of the yeastlike phase ofS. schenckii differs in several respects from that observed for the yeastlike phases ofHistoplasma capsulatum andBlastomyces dermatitidis.From the Research Laboratory, Veterans Administration Hospital, Kansas City, Missouri, and The Department of Microbiology, Kansas University Medical Center, Kansas City, Kansas.Supported in part by USPHS Grant AI 03485.     

Identification of Fluorescent-Antibody Labeled Group A Streptococci by Fluorometry

A quantitative system, amenable to automation, for determining the presence of group A streptococci in broth culture is described. After separation from the broth, the cells' protein coats are removed by digestion with 0.1% trypsin, and they are then stained with anti-A fluorescent antibody (FA). Excess FA is removed, and bound FA is put into solution by dissociation with demineralized distilled water. The amount of FA bound to the cells is quantitated by fluorometry of the solution. The level of nonspecific staining is measured by staining the cells with fluorescein-conjugated normal rabbit globulin absorbed with group A cells, dissociating, and quantifying, as above. The two quantities are subtracted to measure specific binding of FA to group A cells. A clinical trial showed 92% agreement with microscopists.     

CYTOPLASMIC MICROTUBULE AND WALL MICROFIBRIL ORIENTATION IN ROOT HAIRS OF RADISH

The fine structure of young root hairs of radish was studied, with special attention to cytoplasm-wall relationships. Hairs up to 130 µ in length were examined after fixation of root tips in glutaraldehyde followed by osmium tetroxide. Microtubules occur axially aligned in the cytoplasm just beneath the plasmalemma, and extend from the base of the hair to within 2 to 3 µ of the tip. Poststaining with uranyl acetate and lead citrate clearly reveals in thin sections the presence of the two layers of cellulose microfibrils known from studies on shadowed wall preparations: an outer layer of randomly arranged microfibrils arising at the tip, and a layer of axially oriented microfibrils deposited on the inside of this layer along the sides. The youngest microfibrils of the inner, oriented layer first appear at a distance of about 25 µ from the tip. Although the microfibrils of the inner layer and the adjacent microtubules are similarly oriented, the oriented microtubules also extend through the 20- to 25-µ zone near the tip where the wall structure consists of random microfibrils. This suggests that the role of microtubules in wall deposition or orientation may be indirect.