Respiratory Physiology: Intrapleural Pressure & Compliance

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Questions and Answers

What is the relationship between intrapleural pressure and intra-alveolar pressure?

Intrapleural pressure is always equal to intra-alveolar pressure.

Intrapleural pressure varies with atmospheric pressure.

Intrapleural pressure is always greater than intra-alveolar pressure.

Intrapleural pressure is always less than intra-alveolar pressure. (correct)

What occurs when intrapleural pressure equilibrates with atmospheric pressure?

Pneumothorax occurs. (correct)

Intrapleural pressure becomes negative.

Lung compliance increases.

The lung expands normally.

What is the formula for lung compliance?

Compliance = ΔV × ΔP

Compliance = ΔV/ΔP (correct)

Compliance = ΔV + ΔP

Compliance = ΔP/ΔV

Which factor contributes to decreased lung compliance?

Deficiency of surfactant. Signup and view all the answers

How does lung compliance generally change with lower lung volumes?

It increases. Signup and view all the answers

What is the effect of pulmonary congestion on lung compliance?

It decreases compliance. Signup and view all the answers

What differentiates the deflation limb from the inflation limb in lung compliance measurement?

Surface tension is higher during inflation. Signup and view all the answers

In restrictive lung disease, what change occurs in lung compliance?

Lung compliance is decreased. Signup and view all the answers

What can be inferred about lung compliance in advanced age?

Lung compliance increases with age. Signup and view all the answers

What characterizes obstructive diseases like emphysema?

Airway obstruction Signup and view all the answers

What effect does the loss of elastic lung fibers have on lung compliance in emphysema?

Compliance increases Signup and view all the answers

What is the primary consequence of surface tension in the alveoli?

Tendency to collapse alveoli Signup and view all the answers

Which condition is associated with restrictive lung disease?

Fibrosis Signup and view all the answers

How does increased alveolar surface tension affect lung function?

Reduces compliance Signup and view all the answers

What happens to lung compliance when there is stiffening of lung tissues?

Compliance decreases Signup and view all the answers

What leads to airway obstruction in chronic obstructive pulmonary disease?

Inflammation of lung tissues Signup and view all the answers

In emphysema, how is the slope of the volume/pressure curve affected?

The slope increases Signup and view all the answers

Which of the following is a feature of cystic fibrosis related to lung function?

Thickened mucus production Signup and view all the answers

What condition is characterized by a loss of elastic fibers leading to increased lung compliance?

Emphysema Signup and view all the answers

According to Boyle's Law, what happens to pressure when gas volume increases?

Pressure decreases Signup and view all the answers

What is the primary function of the diaphragm during inspiration?

It pushes abdominal contents downwards Signup and view all the answers

What occurs to intrathoracic volume when the diaphragm contracts?

It increases Signup and view all the answers

Which accessory muscles are recruited during heavy exercise for inspiration?

Sternocleidomastoid and scalenus Signup and view all the answers

When does air stop moving into the alveoli?

When Palv = Patm Signup and view all the answers

What characterizes expiration during eupnea?

It is a passive process due to relaxation of muscles Signup and view all the answers

What happens to the lungs during expiration?

The lungs recoil due to elasticity Signup and view all the answers

What does the contraction of external intercostal muscles assist with?

Supporting rib movement upward and outward Signup and view all the answers

What is the role of the pressure gradient during inspiration?

It drives air to flow into the lungs Signup and view all the answers

How does the volume of the chest cavity change during eupnea?

It increases due to muscle contraction Signup and view all the answers

What primarily causes air to move out of the lungs during expiration?

Intra-alveolar pressure is greater than atmospheric pressure Signup and view all the answers

During active expiration, which muscles are primarily responsible for decreasing the volume of the thoracic cavity?

Internal intercostals and abdominal muscles Signup and view all the answers

What happens to the diaphragm during passive expiration?

It relaxes Signup and view all the answers

What occurs when the phrenic nerve stops firing?

Diaphragm relaxes Signup and view all the answers

What is the relationship between thorax volume and lung volume?

They are coupled through intrapleural fluid Signup and view all the answers

What factor is NOT involved in causing air to move from the alveoli to the atmosphere?

When Palv is equal to Patm Signup and view all the answers

Why is the expansion and contraction of the lungs not directly controlled by muscles that attach to the lung surface?

They rely on pleural fluid for mechanical coupling Signup and view all the answers

Active expiration involves all of the following actions EXCEPT:

Diaphragm relaxation Signup and view all the answers

What causes the size of alveoli to decrease during expiration?

Elasticity of the thorax and lungs Signup and view all the answers

What is the total lung capacity (TLC) calculated from?

Inspiratory Reserve Volume (IRV) + Tidal Volume (VT) + Expiratory Reserve Volume (ERV) + Residual Volume (RV) Signup and view all the answers

Which lung volume cannot be measured by spirometry?

Residual Volume (RV) Signup and view all the answers

What occurs during the mechanics of expiration?

Elastic recoil of lung tissue helps push air out Signup and view all the answers

What is Functional Residual Capacity (FRC)?

Volume of air in the lungs at the end of a normal passive expiration Signup and view all the answers

Which factor typically decreases lung compliance?

Increased surface tension in the alveoli Signup and view all the answers

What characterizes obstructive lung diseases compared to restrictive lung diseases?

Difficulty in exhaling air effectively Signup and view all the answers

Study Notes

Intrapleural Pressure

Intrapleural pressure is always less than intra-alveolar pressure.
The lung is always stretched, even during expiration.
If intrapleural pressure equilibrates with atmospheric pressure, a pneumothorax occurs.

### Lung Compliance

Lung compliance refers to the change in lung volume for a given pressure change.
High lung compliance means the lung is easy to expand.
Lung compliance is decreased with a deficiency of surfactant, at high lung volumes, and with pulmonary congestion.
Lung compliance is increased at lower lung volumes and with advancing age.
During inflation, surface tension is higher than during deflation.
The exact mechanism of this difference is unclear, but it is thought to involve surfactant redistribution.
Filling the lungs with saline can eliminate surface tension forces, allowing for measurement of lung compliance.
Lung compliance is increased at low lung volumes and decreased at high lung volumes.

Lung Compliance and Lung Disease

Pulmonary disorders are classified as obstructive or restrictive.
Restrictive diseases involve increased fibrous tissue, which decreases lung compliance.
Examples of restrictive diseases include pulmonary fibrosis, often caused by asbestos exposure.
Obstructive diseases involve airway obstruction.
Examples of obstructive diseases include Chronic Obstructive Pulmonary Disease (COPD), which includes emphysema and chronic bronchitis, asthma, and cystic fibrosis.
In fibrosis, the lung tissue stiffens, decreasing compliance and the slope of the volume/pressure curve.
In emphysema, the loss of elastic lung fibers increases compliance and the slope of the volume/pressure curve.

Alveolar Surface Tension

Alveoli are lined with a thin film of fluid.
Fluid molecules are more attracted to each other than to air, producing surface tension.
Surface tension minimizes alveolar size and resists inflation, reducing compliance.
Pressure exerted by a gas is inversely proportional to its volume (Boyle’s Law).

Respiratory Muscles

The diaphragm is the most important muscle of inspiration.
Diaphragm contraction pushes abdominal contents downwards and lifts ribs upwards and outwards.
External intercostal contraction supports rib movement upwards and outwards.
Contraction of inspiratory muscles increases intrathoracic volume and decreases intrathoracic pressure.
Air flows into the lungs due to this pressure gradient.
During eupnea, the diaphragm is sufficient for inspiration.
Accessory muscles (sternocleidomastoid, scalenes) are recruited during heavy exercise.
During eupnea, inspiration occurs due to diaphragm contraction, which moves the ribs upwards and sternum outwards.
Inspiration continues until the air pressure in the alveoli equals atmospheric pressure (Palv = Patm).

### Expiration

During eupnea, expiration is passive.
Diaphragm and external intercostals relax.
Stretched lung recoil decreases volume, increasing intra-alveolar pressure.
Air moves out of the lungs down the resulting pressure gradient.
Active expiration involves contraction of abdominal muscles (forcing the diaphragm upward) and internal intercostals (depressing ribs and sternum).
Expiration is passive due to the relaxation of the diaphragm and elastic recoil of the lung and thorax.
This decreases the size of the alveoli, increasing Palv above Patm.
Air moves from the alveoli to the atmosphere until Palv = Patm.

Lung Volume and Thorax Volume

There are no muscles attached to the lung surface.
Changes in thorax volume are linked to changes in lung volume due to the coupling of the lungs and thoracic wall.
This coupling occurs due to intrapleural fluid and cohesion between the parietal and visceral pleura.

### Lung Volumes and Capacities

Lung volumes are measured with a spirometer.
Inspiratory reserve volume (IRV) is the amount of air that can be inhaled after a normal inspiration, typically 3000 ml.
Tidal volume (VT) is the amount of air inhaled or exhaled during a normal breath, typically 500 ml.
Expiratory reserve volume (ERV) is the amount of air that can be exhaled after a normal expiration, typically 1200 ml.
Residual volume (RV) is the amount of air remaining in the lungs after a maximal expiration, typically 1200 ml.
Residual volume cannot be exhaled and cannot be measured by spirometry.
Total lung capacity (TLC) is the maximum amount of air the lungs can hold, including all volumes, and is equal to IRV + VT + ERV + RV.
Inspiratory capacity is the maximum amount of air that can be inhaled after a normal expiration, and is equal to IRV + VT.
Vital capacity is the maximum amount of air that can be exhaled after a maximal inspiration, and is equal to ERV + IRV + VT.
Functional residual capacity is the volume of air remaining in the lungs at the end of a normal passive expiration, and is equal to ERV + RV.

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Description

This quiz covers key concepts related to intrapleural pressure and lung compliance. Understand the relationships between lung expansion, pressure gradients, and the factors affecting lung compliance. Test your knowledge on how these physiological principles impact respiratory function.