ALE 3: Gas Transport and Exchange: A Quantitative Analysis

Vocabulary flashcards covering hemoglobin dissociation curves, right-to-left shunts, hypoventilation, pulmonary diffusion impairment, carbon monoxide poisoning, and carbon dioxide transport.

Right-to-left shunt

A condition in which blood moves from the right side of the heart directly to the left side without passing through the lungs, preventing the blood from becoming oxygenated.

Congenital conditions associated with right-to-left shunts

Cardiovascular anomalies that bypass pulmonary circulation, specifically including Tetralogy of Fallot, patent ductus arteriosus, patent foramen ovale, and atrial or ventricular wall defects.

Physiological right-shift of the $O_2$-hemoglobin dissociation curve

A shift in the hemoglobin-oxygen binding curve (dotted line) that decreases hemoglobin's affinity for oxygen, allowing significantly more $O_2$ to be delivered to metabolically active tissues (such as $16\,\text{ml O}_2$ delivered compared to $8\,\text{ml O}_2$ per $100\,\text{ml}$ of blood at a $PO_2$ of $30\,\text{mm Hg}$).

Oxygen therapy response in right-to-left shunts

A clinical phenomenon where administering $100\%$ oxygen does not effectively resolve hypoxemia because the shunted venous blood bypasses ventilated alveoli entirely without coming into contact with oxygen.

Fentanyl

A mu-opioid receptor agonist used for analgesia that, in excessive doses, induces hypoventilation by decreasing tidal volume, breath frequency, and total ventilation (e.g., by $30\%$).

Hypoventilation effects on $P_AO_2$ and $P_aO_2$

A state where decreased ventilation lowers alveolar $PO_2$ ($P_AO_2$), which consequently lowers arterial $PO_2$ ($P_aO_2$), while bronchial $PO_2$ and the A-a difference remain within normal limits.

Fibrotic lung disease (Diffusion impairment)

A respiratory disorder in which fibroblasts proliferate in the basal lamina membrane of the lungs, increasing the barrier thickness between the alveoli and blood (the $X$ variable in Fick's equation).

Diffusion impairment effects on $P_AO_2$ and $P_aO_2$

A pattern where alveolar $PO_2$ ($P_AO_2$) remains unchanged due to mild compensatory ventilation, but arterial $PO_2$ ($P_aO_2$) decreases because of a reduced rate of oxygen transfer across the thickened alveolar-capillary barrier.

Carbon monoxide ($CO$)

A colorless, odorless combustion byproduct that reversibly binds to hemoglobin with $230\times$ greater avidity than $O_2$, reducing oxygen-carrying capacity and increasing oxygen affinity at remaining sites (left-shifting the dissociation curve).

Carbon monoxide toxicity thresholds

Atmospheric exposure limits where human exposure to $35\,\text{ppm}$ induces headaches and dizziness, whereas exposure to $3{,}200\,\text{ppm}$ for $30\,\text{min}$ causes death.

Red blood cell $CO_2$ transport

The mechanism facilitating the removal of carbon dioxide from active tissues to the lungs via partial pressure gradients, binding to hemoglobin, and enzymatic conversion into bicarbonate transported in plasma.

A-a difference

The alveolar-arterial oxygen gradient, which stays within normal limits in cases of pure hypoventilation without diffusion impairment, distinguishing hypoventilation from a diffusion barrier defect.