Normal Mechanics of Spontaneous Ventilation and Mechanical Ventilation

Flashcards on normal mechanics of spontaneous ventilation, pressure gradients, equations, compliance, resistance, and mechanical ventilation modes based on the lecture transcript.

Ventilation

The active movement of air into and out of the lungs involving work performed by respiratory muscles to establish a pressure differential between the atmosphere and the lungs.

Respiration

The exchange of $O_2$ and $CO_2$ as part of primary respiratory function, divided into external and internal respiration.

External Respiration

The diffusion of $O_2$ and $CO_2$ between the alveoli and the pulmonary capillaries.

Internal Respiration

The exchange of $O_2$ and $CO_2$ at the cellular level between systemic capillaries and the cells of the body.

Airway Opening Pressure ($P_{awo}$)

Also called mouth pressure, upper airway pressure, mask pressure, or proximal airway pressure; assigned a baseline value of $0$ relative to atmospheric pressure unless external pressure is applied.

Body Surface Pressure ($P_{bs}$)

The pressure at the body surface, equal to atmospheric pressure unless a person is in a hyperbaric chamber or negative pressure ventilator.

Intrapleural Pressure ($P_{pl}$)

The pressure in the potential space between parietal and visceral pleura, measuring approximately $-503420$ (or $-5$) $cmH_2O$ at the end of expiration and $-10$ $cmH_2O$ at the end of inspiration.

Esophageal Pressure

A pressure measurement obtained via a specialized esophageal balloon used to estimate intrapleural pressure and its changes.

Alveolar Pressure ($P_{alv}$)

Also called intrapulmonary pressure or lung pressure; changes as intrapleural pressure changes, measuring approximately $-1$ $cmH_2O$ during spontaneous inspiration and $+1$ $cmH_2O$ during expiration.

Transairway Pressure ($P_{ta}$)

The pressure difference between the airway opening and the alveolus; the gradient required to produce airflow and overcome resistance in the conductive airways.

Transthoracic Pressure ($P_{tt}$)

The pressure difference between the alveolar space and the body's surface ($P_{alv} - P_{bs}$), representing the pressure needed to expand or contract the lungs and chest wall together.

Transpulmonary Pressure ($P_{tp}$ or $P_L$)

Also called transalveolar or alveolar distending pressure; the pressure difference between the alveolar space and the pleural space ($P_{alv} - P_{pl}$) required to maintain alveolar inflation.

Transrespiratory Pressure

The pressure difference between the airway opening and the body surface ($P_{awo} - P_{bs}$) required to inflate the lungs during positive pressure ventilation; consists of transthoracic and transairway pressures.

Compliance ($C$)

A measure of elastic forces opposing inflation defined as $C = \frac{\text{Volume}}{\text{Pressure}}$, reflecting the relative ease with which lung structures distend.

Elastance ($E$)

The inverse of compliance, defined as the tendency of a structure to return to its original form after being stretched or acted upon by an outside force.

Normal Lung Compliance

A value typically averaging $0.1$ $L/cmH_2O$ (ranging from $0.05$ to $0.17$ $L/cmH_2O$), depending on posture, position, and phase of respiration.

Airway Resistance ($R_{aw}$)

The frictional forces opposing gas flow through conductive airways, calculated as $R_{aw} = \frac{P_{ta}}{\text{flow}}$, with normal values ranging from $0.6$ to $2.4$ $cmH_2O/L/s$.

Fast Lung Units

Pulmonary units that have short time constants and take less time to fill and empty.

Slow Lung Units

Pulmonary units that have increased resistance or compliance (such as in pulmonary emphysema) and require more time to fill and empty.

Negative Pressure Ventilation

A type of ventilation (e.g., Iron Lung) that mimics respiratory muscles to allow breathing through normal physiological mechanisms without an artificial airway.

Positive Pressure Ventilation

Ventilation delivered via mechanical ventilator air delivery through an endotracheal tube or mask by creating positive pressure at the airway opening.

High Frequency Jet Ventilation

A ventilation method using above-normal rates and below-normal volumes with frequencies from $4$ to $10$ $Hz$.

High Frequency Oscillatory Ventilation

A ventilation method using above-normal rates and below-normal volumes with frequencies from $3$ to $15$ $Hz$.

High Frequency Percussive Ventilation

A ventilation method using above-normal rates and below-normal volumes with frequencies from $3$ to $15$ $Hz$.

PEEP (Positive End-Expiratory Pressure)

A set positive baseline airway pressure higher than $0$ that prevents complete exhalation to baseline, increasing volume remaining in lungs at end-exhalation.

Auto-PEEP

Accidental or unintentional air trapping in the lungs occurring when a patient lacks sufficient time to complete exhalation before the next breath delivery.

Peak Inspiratory Pressure (PIP)

The highest airway pressure recorded at the end of inspiration, equaling the combined pressure to overcome airway resistance and inflate alveoli.

Plateau Pressure

An end-inspiratory pressure measured during a $0.5$ to $1.5$ second breath-hold before exhalation, reflecting elastic recoil force on alveolar volume without gas flow.