Oxygen supply, determining factors

The major determinants of myocardial oxygen demand (MVO2) are heart rate (HR), contractility, and intramyocardial wall tension during systole. Wall tension is thought to be the most important factor. Because the consequences of IHD usually result from increased demand in the face of a fixed oxygen supply, alterations in MVO2 are important in producing ischemia and for interventions intended to alleviate it. 

Tissue ischemia is a universal event in various forms of trauma and life-threatening emergencies. Reduced blood flow or disturbed oxygen supply results in the discrepancy of energy production and utilization. The cessation of blood flow not only halts the influx of oxygen and nutrients, but also stops carrying away toxic wastes. While many of the factors determining the flnal fate of the... 

Coronary blood flow is influenced by multiple factors however, the caliber of the resistance vessels delivering blood to the myocardium and MVO2 are the prime determinants in the occurrence of ischemia. The anatomy of the vascular bed will affect oxygen supply and, subsequently, myocardial metabolism and mechanical function. 

ADP is simultaneously phosphorylated to ATP. Oxidative phosphorylation requires a supply of NADH (or other source of electrons at high potential), O2, ADP, and Pj. The most important factor in determining the rate of oxidative phosphorylation is the level of ADP. The rate of oxygen consumption by mitochondria increases markedly when ADP is added and then returns to its initial value when the added ADP has been converted into ATP (Figure 18.42). 

Table 20.2-S presents the system parameters determined by Ward et al. for producing 10 x 10 SCFD of 30% oxygen with single-stage 1000 A ultrathin silicone-polycarbonate copolymer membranes. In addition to their thinness, these membranes had high permeabilities due to their silicone rubber component (57% on a mole basis) (see Fig. 20.2-7). The separation factor for the family of silicone-polycaibonate materials shown in Fig. 20.2-8 increases as the fraction of flexibilizing silicone decreases. If one considers the ratio of permeabilities at 0% silicone and at 57% silicone, it is clear that an aqrproximately lOO-foU increase in permeation area is required to achieve the same oxygen productivity far pure polycarbonate membranes as for the 57% copolymer. Thus, roughly 7.8 x 1(T ft of membrane area widi a 1(K)0 A thick separating layer would be required to supply the same absolute amoum of oxygen in the product gas for the polycarbonate case as compared to 78,CW0 ft for the copolymer case.

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