Diffusion, convection and their coupling as gas transport mechanisms in the lungs: a model experiment

The roles of diffusion and convection in gas transport were studied by means of a lung model with a hollow bronchial cast of a dog. He, Ar and SF6 were chosen as indicators with different diffusivities. Axial dispersion of a heavier gas was much better, but the concentration gradient in a static gas phase was greater for a heavier gas, i.e., there was a larger stratified inhomogeneity for a less diffusible gas. Crossings of He and SF6 concentration curves were observed between diffusion distances of 6 and 8 cm, which could be assumed to be a critical point of conversion where either convective mixing or diffusion favored gas transport. The results observed also suggested that the effective diffusion coefficient and speed of respiration affected the efficiency of gas transport.

Simultaneous measurements of shifts of the center of gravity caused by ventilation and cardiac motions towards three body axes

A method is described for the simultaneous measurements of three dimensional shifts of the gravitational center of the body caused by ventilatory and cardiac motions. The measuring system consists fundamentally of three load cells which support an aluminum die-casting platform. Measurement of the shift towards the X axis (front-to-back) was achieved by double integration of the outputs of load cells in order to convert acceleration into a shift of gravity. The records of a volunteer subjects measured with ECG and ventilatory flow showed two cardinal oscillations; one coinciding with the heat rate and the other with the ventilatory frequency. This became clear when recorded through either a low-pass or high-pass filter. Animal who breathed a SF6-O2 mixture into one side of the lungs or those with partial occlusion of a bronchus showed distinct changes in the pattern of the Y axis (right-to-left). These preliminary experiments convinced us that the system can serve as a non-invasive monitoring system of cardiopulmonary functions.

Thiourea and cyanamide as inhibitors of thyroid peroxidase: the role of iodide

Thiourea, methylmercaptoimidazole, propylthiouracil, and thiouracil are all potent inhibitors of thyroid peroxidase (TPO)-catalyzed iodination. Unlike the cyclic thioureylenes, thiourea at 5 mM has no effect on guaiacol oxidation. If iodide is added to guaiacol assays containing thiourea, enzyme activity is lost. The latter observation may be explained as follows. In the presence of iodide, the iodinating species [TPO.Ioxid], oxidizes thiourea to formamidine disulfide. This product decomposes to cyanamide at neutral pH. We have shown cyanamide to be an inhibitor of the peroxidative and iodinating functions of TPO. Studies in rats demonstrate that doses of thiourea which completely inhibit in vivo protein-bound iodine formation have no irreversible effect on TPO, as measured by guaiacol peroxidation after removal of the thyroids. The major in vivo action of cyanamide is similar to that of thiourea. The data suggest that the primary in vivo and in vitro mode of action of thiourea is the reversible Ioxid-trapping mechanism. The anomalous inhibition of guaiacol peroxidation seen in the presence of thiourea plus iodide derives from the formation of formamide disulfide, followed by its nonenzymic decomposition to cyanamide.

Serum thyrotropin releasing hormone (TRH)-degrading activity: a sensitive and rapid radiochemical assay procedure

A rapid and sensitive method has been developed to assay thyrotropin releasing hormone (TRH)-degrading activity in serum. In this assay, the formation of proline, a major serum degradation product of TRH (pGlu-His-Pro-NH2), is measured. The procedure is based on the finding that proline can be readily separated from TRH with Dowex 50 by a batchwise procedure in a test tube.

The developmental pattern of thyrotropin-releasing hormone-degrading activity in the plasma of rats

The developmental pattern of TRH-degrading activity in rat plasma was determined by measuring the ability of plasma from rats of various ages to degrade TRH into degradation products. From a rate of 0.519 pmol TRH degraded/microliter-1.h-1 on day 8, plasma TRH-degrading activity increased to 18.1 pmol TRH by day 90 in female rats. The increase in rate of formation of proline, a major plasma degradation product, was in very good agreement with the increase in rate of TRH degradation. The major increase in TRH-degrading activity occurred between the third and seventh week of life. A similar pattern of development was observed in male rats; the only significant difference was that plasma from day 90 male rats was approximately 30% more active than that from female rats (P less than 0.002). Daily T3 administration to rats from days 8--26 resulted in a 2-fold increase in plasma TRH-degrading activity (P less than 0.05). The contribution of plasma degradation to the physiological control of TRH activity is not clear, but the magnitude of the increase in plasma TRH-degrading activity (approximately 30-fold) during the maturation of the rat is suggestive of a mechanism of biological significance.

A new anticoagulant medication in cardiac valve replacement

1. In the mitral valve replacement with Starr-Edwards prosthetic ball valve, the major thromboembolism occurred in 20% of the patients with the silastic ball valve series compared with 6% in those with a metal ball valve series. 2. The anticoagulant effect of Warfarin became stable and the occurrence of thromboembolism was reduced by the addition of Bucolome.

Lower levels of thyrotropin-releasing hormone-degrading activity in human cord and in maternal sera than in the serum of euthyroid, nonpregnant adults

Thyrotropin-releasing hormone (TRH)-degrading activity was investigated in human cord, maternal, and euthyroid adult sera by measuring (a) the rate of disappearance of TRH and (b) the rate of formation of degradation products. The rate of TRH degradation in cord and maternal sera was 25-33% of that in euthyroid adult serum. Concomitantly, in cord and maternal sera, the rate of formation of proline, a major TRH degradation product in serum, was one-quarter to one-third that in euthyroid adult sera. The differences were highly significant (P less than 0.001). The decreased levels of TRH-degrading activity in cord and maternal sera cannot be explained by (a) the presence of a dialyzable inhibitor, (b) the absence of an activator of TRH degradation, or (c) a reversal of the degradation process. There was no difference in the types of radioactive degradation products formed by cord, maternal, and euthyroid adult sera. The low level of TRH-degrading activity and its possible relationship to high thyrotropin-stimulating hormone levels in cord serum suggest that TRH-degrading activity may be a factor to consider in investigations of the perinatal pituitary-thyroid axis, but further studies are needed to determine the role of serum degradation of TRH in regulating physiological levels of TRH.

Clinical evaluation of a new anticoagulant therapy in prosthetic valve replacement

Thromboembolic complication was correlated with the methods of anticoagulant therapy used in the patients with Starr-Edwards non cloth-covered or cloth-covered ball valve. A new anticoagulant therapy combining Bucolome with Warfarin has been used for the patients who were unable to be maintained in a suitable range of thrombotest Owren with Warfarin alone. The results obtained in this new therapy showed that the incidence of thromboembolism was reduced to 0.02 per patient year or less in the patients with Starr-Edwards ball valve as well as Björk-Shiley tilting disc valve.