How much effect has this drop had on 1) the PO2 2) the O2 content?
While there is less hemoglobin available all of it that is still present gets well-oxygenated. Therefore PO2 (mmHg) does not drop. O2 content (i.e. how much O2 is carried per ml of blood), on the other hand, does drop simply because there is less hemoglobin present to bind it. Examine the ventilation response. Why has it not risen in response to the O2 content hypoxia? While there is a developing tissue hypoxia due to the low arterial O2 content the respiratory O2 chemoreceptors sense PO2, not content, and thus are perfectly “happy” They thus do not increase ventilation. Estimate what has happened to O2 extraction by the tissues (O2A-O2V). [O2A – O2V] narrows progressively from its original 0.04 ml/ml value because arterial content (O2A) drops progressively but the tissues continue to consume O2 at a near normal rate. Note the response of cardiac output. It rises dramatically and progressively. Tissue hypoxia causes peripheral vasodilation (note the rise in vascular ease of flow – COND
