FIG. 45:  This is a repeat of Figure 16, showing the acute responses to apnea and illustrating that at the end of an apnea, there are a number of very significant stressors, namely severe hypoxemia, hypercapnia, significant sympathetic vasoconstriction with high levels of catecholamines in the bloodstream, and very high pressure levels.^[5]  In other words, the heart is having to deal with a high afterload in the setting of a high catecholamine, hypercapnic, and hypoxic environment.