Critical oxygen refers to the minimum level of oxygen supply needed to meet an organism's metabolic demands. This level varies greatly depending on the organism and its activity level. There isn't a single, universally applicable value.
Defining Critical Oxygen Levels: Different Contexts, Different Values
The concept of "critical oxygen" manifests differently across various fields:
1. Critical Oxygen Delivery (DO2) in Humans:
Research in conscious, healthy humans suggests that a decrease in oxygen delivery (DO2) to 7.3 ± 1.4 ml O2·kg⁻¹·min⁻¹ does not show signs of inadequate systemic oxygenation. https://pubs.asahq.org/anesthesiology/article/92/2/407/38157/Critical-Oxygen-Delivery-in-Conscious-Humans-Is This means that below this level, oxygen delivery is insufficient to meet metabolic needs, thus indicating a critical level. However, this value is context-specific and based on resting, healthy individuals.
2. Critical Oxygen Concentration in Microbiology:
In bacteria and yeast, the critical oxygen concentration is significantly lower, ranging from approximately 5-10% of the saturated dissolved oxygen (DO) concentration. For other organisms, this percentage can be higher, reaching 10-50% of the saturated DO concentration. https://www.sciencedirect.com/topics/engineering/critical-oxygen-concentration This lower value reflects the different metabolic requirements of these microorganisms.
3. Critical Oxygen Partial Pressure (Pcrit) in Aquatic Organisms:
In aquatic organisms, Pcrit is defined as the oxygen partial pressure below which an animal's standard metabolic rate (SMR) cannot be maintained. This value is heavily influenced by the organism's oxygen supply capacity. https://journals.biologists.com/jeb/article/224/8/jeb242210/237810/Oxygen-supply-capacity-breathes-new-life-into Pcrit serves as a measure of an organism's hypoxia tolerance.
4. Critical Congenital Heart Defects (CCHD):
In the context of medicine, "critical oxygen" can also refer to situations where critical congenital heart defects (CCHD) prevent the heart from effectively pumping blood, thus reducing blood oxygen levels. This can lead to insufficient oxygen delivery to vital organs. https://www.cdc.gov/heart-defects/screening/index.html
In summary, "critical oxygen" isn't a single number but a concept representing the minimum oxygen level required to sustain life or a specific function, and its value depends heavily on the context.
