Egan Chapter 11: Ventilation Lecture Notes

Practice flashcards covering the mechanics of ventilation, pressure gradients, lung compliance, resistance, and clinical applications from Egan Chapter 11.

Ventilation

The process of moving gas (usually air) in and out of the lungs.

Respiration

The physiologic processes of oxygen use at the cellular level.

Tidal volume ($V_T$)

The volume of gas moved per phase, measured during either inspiration or expiration.

Transrespiratory pressure ($P_{TR}$)

The pressure gradient between the airway opening ($P_{AO}$) and the body surface ($P_{BS}$), calculated as $P_{TR} = P_{AO} \text{ – } P_{BS}$, which causes gas flow in and out of the lungs.

Transairway pressure ($P_{TAW}$)

The pressure difference between the airway opening and the alveoli of the lungs, calculated as $P_{TAW} = P_{AO} \text{ – } P_A$.

Transalveolar pressure ($P_{TA}$)

The pressure difference between the model alveolus and the pleural space ($P_{pl}$), calculated as $P_{TA} = P_A \text{ – } P_{pl}$.

Transchestwall pressure ($P_{TCW}$)

The pressure difference between the pleural space and the body surface, calculated as $P_{TCW} = P_{pl} \text{ – } P_{BS}$.

Transpulmonary pressure difference ($P_{TP}$)

The pressure gradient that maintains alveolar inflation, defined as $P_{TP} = P_{AO} \text{ – } P_{pl}$ (or $P_A \text{ – } P_{pl}$).

Transthoracic pressure difference ($P_{TT}$)

The pressure difference between the alveoli and the body surface ($P_{TT} = P_A \text{ – } P_{BS}$) that causes gas to flow into and out of alveoli during breathing.

Boyle’s Law

The principle stating that increasing thoracic volume causes fewer collisions between gas molecules, thereby decreasing pleural pressure.

Positive Pressure Ventilation (PPV)

A method of inspiration that raises the $P_{pl}$, which tends to compress veins returning blood to the heart and may impede cardiac output.

Flail Chest

A condition resulting from unstable broken ribs where the chest wall sinks in during inhalation and bulges outward during exhalation due to pressure gradients.

Functional Residual Capacity (FRC)

The resting lung volume established where the inward recoil of the lungs equals the outward tendency of the chest wall to expand, occurring at approximately $40\%$ of Total Lung Capacity (TLC).

Hysteresis

The difference between lung inflation and deflation curves, partly caused by surface tension, where lung volume at any given pressure is slightly greater during deflation.

Pulmonary Surfactant

A substance produced in alveolar type II pneumocytes that reduces lung surface tension and stabilizes alveoli by preventing collapse.

Elastance

The natural ability of matter to respond to force and return to its original shape; defined in pulmonary physiology as the change in pressure per change in volume.

Hooke’s Law

The principle that volume varies directly with pressure until the elastic limit of the lung unit is reached, beyond which rupture (e.g., pneumothorax) may occur.

Lung Compliance ($C_L$)

A measure of the lung's ability to stretch and expand, defined as $C_L = \frac{\Delta V}{\Delta P}$ with a normal value of approximately $0.2\,L/cm\,H_2O$.

Emphysema

An obstructive lung disease that increases compliance due to the loss of elastic tissue, resulting in lungs that are more distensible or hyperinflated.

Fibrosis

A restrictive lung disease that decreases compliance due to increased elastic tissue, resulting in stiffer lungs and reduced volume.

Tissue Viscous Resistance

The impeded motion caused by tissue displacement of the lungs, rib cage, diaphragm, and abdominal organs, accounting for approximately $20\%$ of total resistance.

Airway Resistance ($R_{aw}$)

The frictional resistance to gas flow through the airways, accounting for approximately $80\%$ of frictional resistance; it is highest at the nose ($50\%$) and falls to about $20\%$ in the small airways.

Pursed Lip Breathing

A technique used by patients with emphysema to create gentle back pressure that counters small airway collapse by moving the Equal Pressure Point (EPP) toward larger airways.

Oxygen Cost of Breathing (OCB)

An indirect measurement of the work of breathing reflecting the O2 consumption ($VO_2$) of respiratory muscles; normally $<5\%$ but can exceed $30\%$ in disease.

Dependent Area

The bases of the upright lung where ventilation and perfusion ($V/Q$) are best matched and where approximately 4 times as much ventilation occurs compared to the apexes.

Time Constant

The time in seconds necessary to inflate a particular lung region to approximately $60\%$ of its potential filling capacity; determined by the product of resistance ($R_{aw}$) and compliance ($C_L$).

Minute Ventilation ($V_E$)

The total volume moved in and out of the lungs per minute, calculated as $V_E = f_B \times V_T$; normal range is $5–10\,L/min$.

Alveolar Dead Space ($V_{Dalv}$)

The volume of gas ventilating unperfused alveoli or alveoli where ventilation exceeds perfusion.