Acute cardiovascular response to isocapnic hypoxia. I. A mathematical model

A mathematical model of the acute cardiovascular response to isocapnic hypo xia is presented. It includes a pulsating heart, the systemic and pulmonary circulation, a separate description of the vascular bed in organs with the higher metabolic need, and the local effect of O-2 on these organs. Moreov er, the model also includes the action of several reflex regulatory mechani sms: the peripheral chemoreceptors, the lung stretch receptors, the arteria l baroreceptors, and the hypoxic response of the central nervous system. Al l parameters in the model are given in accordance with the physiological li terature. The simulated overall response to a deep hypoxia (28 mmHg) agrees with the experimental data quite well, showing a biphasic pattern. The ear ly phase (8-10 s), caused by activation of peripheral chemoreceptors, exhib its a moderate increase in mean systemic arterial pressure, a decrease in h eart rate, a quite constant cardiac output, and a redistribution of blood f low to the organs with higher metabolic need at the expense of other organs . The later phase (20 s) is characterized by the activation of lung stretch receptors and by the central nervous system hypoxic response. During this phase, cardiac output and heart rate increase together, and blood flow is r estored to normal levels also in organs with lower metabolic need. The mode l may be used to gain a deeper understanding of the role of each mechanism in the overall cardiovascular response to hypoxia.