Influence of zero flow pressure on fractional flow reserve

Fractional flow reserve (FFR) is a commonly used index to assess the functional severity of a coronary artery stenosis. It is conventionally calculated as the ratio of the pressure distal (P_d) and proximal (P_a) to the stenosis (FFR=P_d/P_a). We hypothesize that the presence of a zero flow pressure (P _zf), requires a modification of this equation. Using a dynamic hydraulic bench model of the coronary circulation, which allows one to incorporate an adjustable P _zf, we studied the relation between pressure-derived FFR=P_d/P_a, flow-derived true FFR_Q=Q_S/Q_N (=ratio of flow through a stenosed vessel to flow through a normal vessel), and the corrected pressure-derived FFR_C=(P_d–P_zf)/(P_a–P_zf) under physiological aortic pressures (70 mmHg, 90 mmHg, and 110 mmHg). Imposed P_zf values varied between 0 mmHg and 30 mmHg. FFR_C was in good agreement with FFR_Q, whereas FFR consistently overestimated FFR_Q. This overestimation increased when P_zf increased, or when P_a decreased, and could be as high as 56% (P_zf=30 mmHg and P_a=70 mmHg). According to our experimental study, calculating the corrected FFR_C instead of FFR, if P_zf is known, provides a physiologically more accurate evaluation of the functional severity of a coronary artery stenosis.     

Assessing the pressure at zero flow in canine epigastric skin flaps

The pressure at zero flow was examined using three independent techniques in island epigastric skin flaps in dogs under sodium pentobarbital anesthesia. (i) The flap was perfused from a reservoir which was varied in height to supply a range of pressures. The corresponding flows were measured by electromagnetic blood flowmetry and the pressure at zero flow was determined by extrapolation to zero flow. (ii) Arterial inflows as low as 2.2 microL/min were delivered by a Harvard pump and corresponding pressures were measured. The pressure at zero flow was determined by inspection. (iii) The artery supplying the flap was occluded with a microclip and the plateau following the decay of pressure was read as the pressure at zero flow. The pressure decay technique was the simplest, most reproducible method and was verified by the other two methods. It gave a pressure at zero flow of 5.8 +/- 0.4 mmHg (0.77 +/- 0.05 kPa). The critical closing pressure is discussed and related to the pressure at zero flow.     

Life expectancy for a class of life distributions having the "setting the clock back to zero" property

It is demonstrated that the expression for the life expectancy of an individual in biomedical investigations can be greatly simplified if the class of life distributions possesses what has been called the "setting the clock back to zero" property, studied previously by Raja Rao and Talwalker. It is shown that the Gompertzian growth process, Krane's family of life distributions, and the linear hazard exponential distribution have this property. To illustrate the use of this property, an individual's life expectancy is tabulated for several choices of the parameter values when the individual's life distribution belongs to a Gompertzian growth process. In addition, it is shown that a new survival model considered by Chiang and Conforti for the estimation of time to tumor has the "setting the clock back to zero" property. Its life expectancy is evaluated at any given time chi 0 using this property.     

Influence of "zero" magnetic field on the growth of embryonic cells and primary embryos of mouse in vitro

The present investigation reveals that a 250-fold screening of the geomagnetic field ("zero" geomagnetic fields, 200 nT) is a biologically active factor that adversely affects embryonic cells and the processes of early embryogenesis as a whole. In particular, the cultivation of primary embryonic fibroblasts in "zero" geomagnetic fields causes reduces the capacity for adhesion and proliferation, changes the monolayer morphology and increases cell death. In a more highly organized experimental model, two-celled mouse embryos, the exposure to the "zero" field results in an increase of plasma membrane permeability for dyes, a reorganization of the cytoskeleton because of alpha-actin redistribution, and the disturbance of the spatial orientation of blastomeres. As a result, the development of two-celled mouse embryos stops, and they do not reach the stage of blastocyst. These data show the significant role of geomagnetic fields in the normal growth of embryonic cells in vitro and the regulation of mammalian embryogenesis.