The effect of the width of the ventilation-perfusion distribution on arterial blood oxygen content

We investigate the effect of the width of ventilation-perfusion distributio ns on arterial blood oxygen content. We assume that the perfusion within th e alveolar volume is a continuous function of ventilation-perfusion ratio, known as the continuous ventilation-perfusion distribution, and then write down the conservation of mass equations in the lung incorporating the nonli near relationship between oxygen concentration in the gas phase and blood o xygen content. We solve these equations for various unimodal and bimodal ve ntilation-perfusion distributions believed to occur in practice and calcula te the arterial blood oxygen content in each case. When a subject has a uni modal ventilation-perfusion distribution we show that the fraction of cardi ac output to that mode (i.e. the fraction of non-shunted blood) has a large effect on arterial oxygen blood content. However, the width of the distrib ution has only a negligible effect on arterial oxygen blood content. For a bimodal ventilation-perfusion distribution the location and fraction of car diac output to each mode has a large effect on arterial oxygen blood conten t. Again, the width of each mode of the distribution has little effect on a rterial oxygen blood content. As a result there is little point, from a cli nical perspective, in developing techniques for investigating the width of modes of these distributions since all relevant clinical information is con tained in the nature (i.e. unimodal or bimodal) and in the location of the modes. (C) 1999 Academic Press.