Phys: Lung Mechanics

Ventilation

The process of moving air into and out of the lungs.

Gas Exchange

The process involving oxygen uptake into the blood and carbon dioxide removal via diffusion and perfusion.

Acid-Base Balance

The regulation of blood pH through respiratory mechanisms.

Alveoli

The primary gas exchange units of the lung where oxygen enters the blood and carbon dioxide is removed.

Type I Pneumocytes

Thin, elongated alveolar epithelial cells that cover the majority of the alveolar surface and facilitate gas exchange.

Type II Pneumocytes

Cuboidal alveolar epithelial cells that constitute a small percentage of the alveolar surface, synthesize and secrete surfactant, and serve as progenitor cells for Type I pneumocytes.

Alveolar Macrophages

Phagocytic cells located within alveoli that ingest foreign material and remove it via the lymphatic system.

Alveolocapillary Membrane

The barrier formed by shared alveolar and capillary structures—including alveolar epithelium, alveolar basement membrane, interstitial space, capillary basement membrane, and capillary endothelium—across which gas exchange occurs.

Pulmonary Surfactant

A mixture of phospholipids synthesized by type II pneumocytes that reduces alveolar surface tension and increases lung compliance.

Atelectasis

Alveolar collapse resulting from reduced surfactant or elevated collapsing pressure.

Neonatal Respiratory Distress Syndrome

A condition in newborns caused by a deficiency or absence of surfactant, leading to high surface tension, alveolar collapse, hypoxemia, and decreased lung compliance.

Visceral Pleura

The serous membrane that adheres directly to the surface of the lungs.

Parietal Pleura

The serous membrane lining the inner wall of the thoracic cavity.

Compliance

A measure of the distensibility of the lungs and chest wall, representing the relative ease with which these structures stretch (the reciprocal of elasticity).

Elastic Recoil

The intrinsic elastic property of the lungs to return to their resting volume after inspiration, which opposes lung expansion.

Static Compliance

Compliance measured strictly under conditions accounting for the elastic properties of the lungs and chest wall without airflow.

Dynamic Compliance

Compliance measured during active breathing, which incorporates both elastic recoil properties and airway resistance.

Airway Resistance

The frictional opposition to airflow governed by Poiseuille’s Law, which increases with bronchoconstriction, lower lung volumes, higher gas viscosity, or longer airway length.

Reynolds Number

A calculated metric used to predict the likelihood of laminar versus turbulent airflow within the respiratory tract.

Minute Ventilation

The total volume of air moved through the respiratory system per minute, calculated as respiratory rate multiplied by tidal volume.

Tidal Volume

The volume of air inspired or expired with each normal breath.

Inspiratory Reserve Volume (IRV)

The maximal additional volume of air that can be inspired beyond a normal tidal inspiration.

Expiratory Reserve Volume (ERV)

The maximal additional volume of air that can be forcibly expired at the end of a normal tidal expiration.

Residual Volume (RV)

The volume of air remaining in the lungs after a maximal exhalation.

Total Lung Capacity (TLC)

The maximum volume to which the lungs can be expanded at the end of a maximal inspiration.

Functional Residual Capacity (FRC)

The volume of air remaining in the lungs at the end of a normal, resting exhalation.

Inspiratory Capacity (IC)

The maximum volume of air that can be inspired from the resting end-expiratory level.

Vital Capacity (VC)

The total volume of air available for active respiration, measured from maximal inspiration to maximal exhalation.

Forced Vital Capacity (FVC)

The maximal volume of air exhaled forcefully and rapidly following a maximal inspiration.

Restrictive Lung Disease

Pulmonary conditions characterized by reduced lung compliance or chest wall expansion (due to stiff lungs, chest wall deformities, or neuromuscular weakness) that increase the work of breathing.

Obstructive Lung Disease

Pulmonary conditions characterized by elevated airway resistance and dynamic airway closure (such as asthma, chronic bronchitis, or emphysema).