RET 1026: Oxygen Transport and Hemodynamics

Vocabulary terms and definitions covering oxygen transport, hemoglobin properties, hypoxia classifications, the oxyhemoglobin dissociation curve, and pulmonary hemodynamics.

Oxyhemoglobin ($HbO_2$)

Hemoglobin with oxygen attached to its iron atoms, exhibiting a bright red appearance characteristic of arterial blood.

Deoxyhemoglobin ($Hb$)

Hemoglobin that has released its oxygen, exhibiting a deep purple appearance characteristic of venous blood.

Hypoxemia

A low tension or partial pressure of oxygen in arterial blood, identified by a decreased $PaO_2$ on an arterial blood gas ($ABG$).

Hypoxia

A deficiency of oxygen at the tissue or cellular level, evidenced by clinical signs such as confusion, tachycardia, elevated lactic acid, and decreased mixed venous oxygen.

Hypoxic Hypoxia

A form of hypoxia characterized by a low level of oxygen in the alveoli leading to a decreased $PaO_2$; it is the only type of hypoxia presenting with low arterial $PO_2$.

Anemic Hypoxia

Hypoxia resulting from a reduced oxygen-carrying capacity of the blood due to decreased hemoglobin concentration or hemoglobin dysfunction, despite a normal $PaO_2$.

Circulatory Hypoxia

Hypoxia caused by reduced tissue blood flow from conditions such as hypotension, shock, or heart failure, resulting in normal $PaO_2$ and $CaO_2$ but low $CvO_2$.

Histotoxic Hypoxia

Hypoxia where cellular oxygen delivery is unimpaired, but intracellular poisoning (such as cyanide poisoning) renders the cells unable to utilize oxygen, causing a high $CvO_2$.

Hematocrit

The proportion of total blood volume occupied by red blood cells, with a normal value of approximately $45\%$.

Polycythemia

An elevated concentration of hemoglobin and red blood cells, often developing as a compensatory physiological response to chronic arterial hypoxemia.

Arterial Oxygen Content ($CaO_2$)

The total volume of oxygen contained in $100\,\text{mL}$ of arterial blood, calculated using the formula $(Hb \times 1.34 \times SaO_2) + (PaO_2 \times 0.003)$ and normally equaling about $20.2\,\text{vol\%}$.

Mixed Venous Oxygen Content ($CvO_2$)

The total volume of oxygen contained in $100\,\text{mL}$ of mixed venous blood, calculated using the formula $(Hb \times 1.34 \times SvO_2) + (PvO_2 \times 0.003)$ and normally equaling about $15.2\,\text{vol\%}$.

Arterial-Venous Oxygen Difference ($a\text{-}v\ O_2\ \text{difference}$)

The quantity of oxygen extracted by peripheral tissues from each $100\,\text{mL}$ of passing blood, calculated as $CaO_2 - CvO_2$ with a standard normal value of $5\,\text{vol\%}$.

Fick Equation

The physiological formula used to calculate cardiac output based on oxygen consumption and tissue extraction: $CO = \frac{VO_2}{a\text{-}v\ O_2\ \text{difference} \times 10}$.

Cooperative Binding

The conformational mechanism where oxygen binding to one of hemoglobin's four heme groups alters the molecular structure to facilitate successive oxygen binding, producing an S-shaped dissociation curve.

$$P_{50}$$

The partial pressure of oxygen in plasma at which hemoglobin reaches $50\%$ oxygen saturation, normally $27\,\text{mmHg}$ at standard body temperature, $PCO_2$, and $\text{pH}$.

Bohr Effect

The physiological shift of the oxyhemoglobin dissociation curve in response to carbon dioxide and hydrogen ion concentrations, enhancing oxygen delivery to tissues and uptake in the lungs.

2,3-Diphosphoglycerate ($2,3\text{-}DPG$)

An intraerythrocytic chemical compound that binds to deoxygenated hemoglobin, reducing its affinity for oxygen and promoting oxygen release to the tissues.

Carboxyhemoglobin ($COHb$)

A hemoglobin compound formed with carbon monoxide, which binds with an affinity $210$ times that of oxygen, induces functional anemia, and shifts the remaining dissociation curve to the left.

Methemoglobin ($MetHb$)

An altered hemoglobin molecule whose iron has oxidized to the ferric ($Fe^{3+}$) state, preventing oxygen unloading and imparting a brown rusty color to the skin.

Cyanosis

A bluish skin discoloration that becomes perceptible when capillary blood contains at least $5\,\text{g/dL}$ of desaturated hemoglobin.

Pulmonary Shunt

Portion of cardiac output that passes from the right side of the heart to the left without participating in alveolar gas exchange ($V/Q = 0$).

Henry's Law

A physical law establishing that the volume of gas dissolved in a liquid is proportional to the partial pressure of that gas and its solubility coefficient in that liquid.

Hypoxic Pulmonary Vasoconstriction

A compensatory vascular reflex where small pulmonary arterial vessels constrict in regions of low alveolar oxygen to redistribute perfusion toward well-ventilated areas.

West Zone 1

The superior pulmonary region where alveolar pressure exceeds arterial pressure and venous pressure ($PA > Pa > Pv$), collapsing capillary beds and preventing blood flow.