Respiratory Physiology: Ventilation, Pressures, and Gas Laws

Comprehensive vocabulary flashcards covering pulmonary ventilation mechanics, Boyle's Law, lung compliance, surfactant, pulmonary volumes, and Dalton's Law based on lecture notes.

Boyle's Law

A physical law stating that pressure and volume are inversely related; within the respiratory system, expanding lung volume during inhalation decreases intrapulmonary pressure below atmospheric pressure, causing air to flow into the lungs.

Atmospheric Pressure

The pressure exerted by the weight of atmospheric gases pushing down at standard sea level conditions, measuring $760\,\text{mmHg}$ (or approximately $29.92\,\text{inches}$ of mercury in aviation and meteorology).

Compliance (Lung Compliance)

The ability of the lungs to expand, stretch, and recoil; it depends on the integrity of lung tissue (collagen and elastin fibers), the mobility of the thoracic cage/chest wall, and the presence of surfactant.

Surfactant

A soapy, sudsy substance secreted within the alveoli starting around gestational weeks $30$ to $33$ that breaks the surface tension of water, preventing smaller alveoli from collapsing during exhalation.

Respiratory Distress Syndrome

A condition seen frequently in premature infants (often delivered near $24\,\text{weeks}$ gestation) who lack sufficient surfactant, leading to widespread alveolar collapse that requires mechanical ventilation and exogenous surfactant lavage.

Intrapleural Pressure

The pressure measurement inside the pleural cavity, which is normally around $756\,\text{mmHg}$ (often referred to as a negative pressure of $-4\,\text{mmHg}$ relative to atmospheric pressure) due to surface tension and pleural mechanics.

Intrapulmonary (Intra-alveolar) Pressure

The pressure within the alveoli of the lungs that drops below atmospheric pressure during inhalation (directing air inward) and rises above atmospheric pressure during exhalation (directing air outward).

Tidal Volume ($V_t$)

The volume of air inhaled or exhaled during a single, quiet, resting respiratory cycle under autonomic control, averaging roughly $500\,\text{mL}$ (half a liter) in a healthy adult.

Primary Muscles of Respiration

The diaphragm and the external intercostal muscles, which actively contract to enlarge the thoracic cavity during normal resting inspiration.

Passive Exhalation

The quiet expiration during resting tidal breathing that requires zero active muscle contraction, driven entirely by the elastic recoil of stretched proteins (such as titin, collagen, and elastin) returning to their resting positions.

Inspiratory Reserve Volume

The maximal amount of air that can be inhaled above and beyond resting tidal volume (typically about $1.2\,\text{L}$ to $1.3\,\text{L}$ above normal tidal volume) using accessory inspiratory muscles.

Expiratory Reserve Volume

The additional volume of air that can be forcefully exhaled past normal resting exhalation by actively recruiting abdominal and internal thoracic muscles to compress the lungs.

Hyperpnea

A forced breathing pattern requiring conscious or forceful muscular exhalation—recruiting abdominal and chest muscles to squeeze air out—utilized during heavy exercise or pressurized aviation breathing.

Respiratory Rate

The number of breaths taken per minute under resting conditions, normally ranging between $12$ and $18\,\text{breaths per minute}$ and coordinated with heart rate (roughly one breath for every four heartbeats) by the medulla oblongata.

Respiratory Minute Ventilation

The total volume of air moved across the nose and mouth per minute, calculated by multiplying tidal volume by the respiratory rate (e.g., $500\,\text{mL} \times 12\,\text{breaths/min} = 6{,}000\,\text{mL/min}$, or $6\,\text{L/min}$).

Residual Volume

The permanent leftover volume of air remaining inside the non-collapsible conducting airways and alveoli even after maximal forced expiration, which progressively increases with age and pulmonary disease.

Alveolar Ventilation

The actual volume of fresh air reaching the alveoli to participate in gas exchange each minute, calculated by subtracting dead airspace (residual volume) from tidal volume and multiplying by the respiratory rate (averaging about $4.2\,\text{L/min}$).

Dalton's Law

A gas law (nicknamed the addition law) stating that the total pressure of a gas mixture is equal to the sum of the partial pressures of each individual gas component ($P_{\text{total}} = P_{N_2} + P_{O_2} + P_{\text{other}}$).

Partial Pressure of Water Vapor ($P_{H_2O}$)

The pressure contributed by water vapor added as air is humidified within the airways, exerting approximately $47\,\text{mmHg}$ toward the total pressure and reducing the partial pressures of other inspired gases.

Alveolar Partial Pressure of Oxygen ($P_{A{O_2}}$) at Sea Level

The target oxygen partial pressure within alveoli at sea level, which drops from $161\,\text{mmHg}$ in atmospheric air down to approximately $100\,\text{mmHg}$ due to the addition of water vapor ($47\,\text{mmHg}$) and carbon dioxide from dead airspace ($40\,\text{mmHg}$).

Hypoxia

A state of insufficient tissue oxygenation characterized clinically by pulse oximetry readings dropping below $92\%\text{--}94\%$, which results in cognitive confusion, impaired motor control, and reduced physiological function.