Week 7: Pulm Patho

HbA

The most common adult hemoglobin consisting of two $\alpha$ chains, two $\beta$ chains, and four heme groups, each containing an iron-binding site for an $O_2$ molecule.

Hemoglobin equilibrium reaction

The reversible process by which oxygen binds to heme iron, expressed as: $Hb (\text{free}) + O_2 \rightleftharpoons HbO_2 (\text{bound})$.

$$PO_2$$

The partial pressure of oxygen found in alveolar air, pulmonary capillary plasma, or tissues.

Hemoglobin % saturation

The ratio of oxygen-bound hemoglobin to total hemoglobin, calculated as: $\frac{HbO_2}{\text{Total Hb}}$.

Right shift (HbO2 dissociation curve)

A movement occurring in tissues with high activity (e.g., cardiac muscle) where lower $pH$, higher $CO_2$, and higher temperature decrease hemoglobin's affinity for oxygen, indicating greater oxygen delivery.

Left shift (HbO2 dissociation curve)

A movement where hemoglobin has a higher affinity for oxygen molecules, occurring in conditions such as hypothermia.

Ventilation (V)

The inspiration of atmospheric air with a $PO_2 \thicksim 150 \text{ mm Hg}$ which replenishes alveolar oxygen.

Perfusion (Q)

The flow of blood arriving in the alveolar capillary with an initial $PO_2 \thicksim 40 \text{ mm Hg}$ and 75 \text{ %} hemoglobin saturation.

Pulse oximetry

A method used to estimate blood oxygen levels by placing a sensor over a fingernail, though accuracy can be affected by nail polish, artificial nails, or darker skin tones.

Hypoxemia

Low oxygen levels specifically in arterial blood, distinguished from hypoxia, which is a generalized lack of oxygen.

Generalized hypoventilation

A state where minute ventilation ($\text{tidal volume} \times \text{respiratory rate}$) is insufficient to maintain alveolar $O_2$ and clear $CO_2$, often caused by CNS-suppressant drugs or neuromuscular disorders.

Ventilation/Perfusion (V/Q) Mismatch

A condition caused by lung diseases like pneumonia or bronchoconstriction where some alveoli do not receive enough $O_2$ or remove enough $CO_2$, resulting in low $O_2$ and high $CO_2$ in the blood traveling to the left atrium.

Shunt

A condition of zero ventilation in some alveoli due to mucus plugging or alveolar flooding where oxygen administration does not improve blood gases because blood bypassed gas exchange.

Diffusion limitation

Hypoxemia caused by the thickening of the alveolar/capillary membrane (e.g., pulmonary fibrosis, edema) where gas exchange is insufficient, especially during exercise when blood circulation rate increases.

DlCO

Diffusing capacity of the lung for carbon monoxide, which is the major pulmonary function test used to assess diffusion impairment.

Hypoxic vasoconstriction

A local regulatory mechanism where pulmonary blood vessels constrict in response to low lung tissue $PO_2$, redirecting blood flow to better-ventilated regions.

Cor pulmonale

Right heart failure specifically caused by lung disease and the resulting pulmonary hypertension.

Dead space

Also known as 'wasted ventilation', these are blocked lung regions with no perfusion (such as in pulmonary embolism) where gas exchange cannot occur despite ventilation.

Saddle emboli

Large thrombi that block major lung vessels, potentially causing immediate death due to right heart overload and hypotensive shock.

Starling forces

The capillary filtration forces that control fluid movement; pulmonary edema forms when these are imbalanced, such as in left heart failure.

Acute respiratory distress syndrome (ARDS)

A condition where inflammatory mediators damage alveolar epithelial cells (AECs), leading to increased capillary permeability, alveolar flooding, loss of surfactant, and decreased lung compliance.

Neonatal respiratory distress syndrome

A disorder in infants born before adequate surfactant production, resulting in stiff and noncompliant lungs.

Bronchopulmonary dysplasia

Lung damage in preterm infants resulting from interventions, infections, or complications of delayed lung development.

Bronchiolitis

A condition in infants, often caused by RSV, that can cause severe lung compromise due to very small airway diameters.

Surfactant

A phospholipid–protein liquid secreted by type 2 alveolar epithelial cells (AEC) that reduces surface tension, makes inflation easier, and resists alveolar collapse.

Lung Compliance

The lung's ability to accommodate addition of volume with a small distending pressure; for example, accommodating a tidal volume of $500\,mL$ with $3\,cm\,H_2O$ pressure.

Tidal Volume

The volume of air moved in a normal breath.

Residual Volume (RV)

The amount of air remaining in the lungs after a maximal expiration; it cannot be measured by spirometry alone.

Functional Residual Capacity (FRC)

The amount of air in the lungs after a normal, quiet expiration, representing the equilibrium position where the inward recoil of the lungs and outward expansion of the chest wall are equal.

Total Lung Capacity (TLC)

The total volume of air in the lungs after a maximal inspiration.

Vital Capacity (VC)

The volume of air moved during a complete expiration from total lung capacity; calculated as $TLC - RV$.

Transpulmonary Pressure (PT)

The distending pressure holding the lungs open, equaling the pressure inside the lung minus the pressure outside ($P_A - P_{pl}$).

Pneumothorax

A condition where pleural pressure ($P_{pl}$) equilibrates with atmospheric pressure ($P_{atm}$), causing the loss of the pressure gradient and allowing the lung to collapse.

Elastance

The inverse of compliance; it refers to the ability of the lung to spring back (elastic recoil) after changing size, due in part to elastin fibers.

Alpha-1 Antiprotease (Alpha-1 Antitrypsin)

A protective substance made by the liver that blocks leukocyte proteases from damaging self cells and tissues.

Emphysema

A condition characterized by the breakdown of alveolar walls and small airways, leading to increased compliance, decreased elastance, and air trapping (blebs and bullae).

Restrictive Lung Diseases

Infiltrative processes like pulmonary fibrosis or sarcoidosis that cause accumulation of connective tissue and fluid, making lungs stiff and reducing $RV$, $FRC$, $VC$, and $TLC$.

$$FEV_1$$

Forced expiratory volume in the first second of a forcer vital capacity maneuver; typically about $80\%$ of the total $FVC$ in a healthy adult.

Flow-Volume Loop

A graph of airflow rate relative to lung volume during inspiration and expiration, used to demonstrate obstructive lung disease when the expiratory curve is 'scooped out'.

Peak Flow

The initial peak airflow rate reached after starting a forced expiration.

Asthma

A type 1 hypersensitivity disorder where allergen exposure triggers Th2-type lymphocyte sensitization, IgE binding to mast cells, and reversible airway obstruction.

COPD (Chronic Obstructive Pulmonary Disease)

A persistent, non-reversible airway obstruction often characterized by chronic bronchitis, productive cough, and decreased $FEV_1/FVC$ ratio.

Obstructive Sleep Apnea

A reversible upper airway obstruction during sleep, often associated with obesity, that produces excessive daytime sleepiness and is managed with CPAP.

Phospholipase C System

The cellular pathway used by Acetylcholine (ACh) and other bronchoconstrictors to increase intracellular calcium and activate smooth muscle contraction.

Cyclic AMP System

The cellular pathway used by Epinephrine (Epi) and other bronchodilators to inhibit bronchial smooth muscle contraction.

Elastic recoil

The property of the lung, chest wall, and diaphragm that stores and releases energy, allowing normal expiration to occur passively.

Alveoli

The thin-walled interface between lung air and pulmonary capillary blood where gas exchange occurs via the diffusion of oxygen and carbon dioxide.

Minute ventilation

The product of $Tidal\,volume \times Respiratory\,rate$, which typically measures $5-8\,L/min$ in adults at rest.

Dead space

The volume in conducting airways that do not have a surface for gas exchange.

Cystic fibrosis

A genetic disorder of lung protection caused by mutations in the CFTR gene leading to thick mucus and failure of mucociliary clearance.

Pleural effusion

A specific type of pleural disorder mentioned alongside lung compliance and airway resistance issues.

Decreased compliance disorders

Chronic conditions such as interstitial lung disease, pulmonary fibrosis, and pneumoconiosis, or acute conditions like lack of surfactant and generalized pneumonia.

Emphysema

A lung disorder characterized by increased compliance and chronic airway obstruction, categorized under COPD.

Airway resistance/obstructive diseases

Conditions including asthma, obstructive sleep apnea, and chronic obstructive pulmonary disease (COPD).

Cor pulmonale

A lung vascular disorder mentioned alongside pulmonary embolism and pulmonary hypertension.

Upper respiratory tract

The part of the respiratory system that includes the pharynx and is prone to infections and allergic reactions.

Lower respiratory tract

The part of the respiratory system starting at the larynx, subject to infections, allergic reactions, and alterations of mechanical properties.

Conducting zone

The initial section of the airway tree containing no alveoli.

Respiratory zone

The area where branching continues to alveolar sacs (generation 23) and alveoli bud off from bronchioles for gas exchange.

Visceral pleura

The layer of tissue that covers the lungs.

Parietal pleura

The layer of tissue that lines the chest wall.

Pleural space

A thin section containing a small layer of fluid where negative pressure keeps the lungs in close contact with the chest wall and diaphragm.

Phrenic nerve

The nerve stimulated by medullary respiratory neurons to control the diaphragm during inspiration.

Mucociliary clearance

A protective mechanism where cilia move mucus (secreted by goblet cells) toward the mouth for removal by coughing or expectoration.

CFTR

The cystic fibrosis transmembrane conductance regulator, which is a cyclic adenosine monophosphate (cAMP)-stimulated ion channel responsible for chloride transport.

Phenylalanine

The amino acid whose deletion from the CFTR protein is the most common cause of mutated CFTR in cystic fibrosis.