Chapter 2: Ventilation

What is ventilation?

The process of moving air in and out of the lungs

What is respiration?

The process of supplying the body with oxygen and ridding it of carbon dioxide.

What is driving pressure?

The difference of pressure/force of gas moving through the airways (between two points of a tube or vessel).

What is transairway pressure?

The barometric pressure difference between mouth pressure and alveolar pressure.

What is transpulmonary pressure?

The difference between alveolar pressure and pleural pressure.

What is transthoracic pressure?

The difference between alveolar and body surface pressure.

How do pressure differences and diaphragm contraction cause inspiration?

The diaphragm contracts and increases intrathoracic volume and decreasing intrapleural and alveolar pressures causing gas to flow to the low concentration lungs from the high concentration atmosphere.

How does the diaphragm assist in expiration?

The diaphragms relaxes and decreases thoracic volume and increases intrapleural and alveolar pressure which causes lung pressure to raise above mouth pressure causing gas to flow out until an equilibrium (end-expiration) is reached.

What is static lung condition?

The condition referring to the lungs at rest or without air movement.

What are natural tendencies of the lungs and chest wall?

The lungs naturally want to recoil inward or collapse while the chest wall naturally wants to move outward or expand due to the thorax and muscles.

What do the tendencies of the lungs and chest wall cause?

The opposing forces tend to cancel out and leave a residual volume in the lungs known as functional residual capacity.

What are the two static forces that causes inflated lungs to recoil?

The elastic properties of the tissue and the surface tension from the fluid layer inside the alveoli.

What is lung compliance?

How readily the elastic forces of the lungs accepts a volume of air; measured in Cl.

How is Cl calculated?

The change in lung volume (ΔV) per unit pressure change (ΔP).

Means the amount of volume an amount of pressure adds.

Normally 100mL/cm H2O; Cl= ΔV/ΔP

How does compliance change in normal and abnormal lungs when approaching alveoli filling capacity ?

Compliance progressively decreases.

What is elastance?

The natural ability of matter to respond to force and return to its original resting position or shape after the external force no longer exists. Elastance is the reciprocal of compliance: ΔP/ΔV

How does elasticity change when lung limits are reached?

The lungs no longer stretch and little or no volume changes occur in response to pressure change.

What is surface tension?

A molecular cohesive property that profoundly resists lung expansion due to the fluid lining the alveoli.

What is LaPlace's Law?

Distending pressure of a liquid sphere is directly proportional to liquid surface tension and inversely proportional to the radius of the sphere.

What does LaPlaces's Law correspond to alveoli?

Higher surface tension of water in the alveoli requires greater pressure to inflate, also the smaller the alveoli, the greater pressure is needed to inflate it.

What is critical opening pressure?

The pressure (with little to no volume change) that is required to overcome liquid molecular force and expand a sphere.

What is critical closing pressure?

A point where the molecular force of a bubble becomes greater than distending pressure and the bubble collapses.

What is pulmonary surfactant?

A phospholipid with both a hydrophobic and hydrophilic end that interrupts alveolar fluid at the alveolar gas-liquid interface. The presence of this avoids atelectasis.

How does pulmonary surfactant work?

The disruption of molecular fluid causes surface tension to decrease in proportion to the ratio of surfactant to alveolar surface area.

What can cause pulmonary surfactant deficiencies?

Acidosis, hypoxia or hyperoxia, atelectasis, RDS, pneumonia, pulmonary edema, and drowning.