Mechanics of breathing Practice Questions
20 free Mechanics of breathing practice questions for the Physiology. Tap an option to answer — you get instant feedback, the correct answer, and a detailed explanation for every question.
According to Boyle's Law, which of the following occurs during inspiration?
- A Thoracic volume decreases, increasing alveolar pressure
- B Thoracic volume increases, decreasing alveolar pressure
- C Thoracic volume increases, increasing alveolar pressure
- D Thoracic volume decreases, decreasing alveolar pressure
Correct answer: Thoracic volume increases, decreasing alveolar pressure
Boyle's Law states that pressure and volume are inversely proportional. When the diaphragm contracts and increases thoracic volume, the alveolar pressure drops below atmospheric pressure, allowing air to flow into the lungs.
Which of the following describes the 'Transpulmonary Pressure' (Ptp)?
- A The difference between atmospheric pressure and intrapleural pressure
- B The sum of alveolar pressure and intrapleural pressure
- C The difference between alveolar pressure and intrapleural pressure
- D The pressure within the bronchioles during forced expiration
Correct answer: The difference between alveolar pressure and intrapleural pressure
Transpulmonary pressure is the pressure gradient across the visceral pleura (Alveolar pressure minus Intrapleural pressure). It serves as the distending force that keeps the lungs inflated against their natural elastic recoil.
During a normal, quiet expiration (eupnea), which muscle contraction is primarily responsible for the exit of air?
- A Internal intercostal muscles
- B Contraction of abdominal rectus
- C External intercostal muscles
- D None; it is a passive process
Correct answer: None; it is a passive process
Quiet expiration is passive and results from the relaxation of the diaphragm and external intercostals. The elastic recoil of the lung tissue and thoracic wall provides the necessary force to decrease volume and increase pressure.
What is the typical value of intrapleural pressure relative to atmospheric pressure at Functional Residual Capacity (FRC)?
- A +5 cm H2O
- B 0 cm H2O
- C -5 cm H2O
- D -15 cm H2O
Correct answer: -5 cm H2O
At FRC, the lungs' tendency to recoil inward and the chest wall's tendency to recoil outward create a negative (sub-atmospheric) pressure in the intrapleural space. This vacuum-like effect is approximately -5 cm H2O.
Which of the following factors is the most significant contributor to lung compliance?
- A Airway resistance encountered within the bronchial passages
- B Surface tension at the alveolar air-liquid interface
- C The thickness of the parietal pleura
- D The total volume occupied by the anatomical dead space
Correct answer: Surface tension at the alveolar air-liquid interface
Lung compliance is determined by the elastic fibers of the lung and, more significantly, the surface tension of the fluid lining the alveoli. Pulmonary surfactant reduces this surface tension to increase compliance and make breathing easier.
How does the presence of pulmonary surfactant affect alveolar mechanics?
- A It significantly increases surface tension, which promotes alveolar collapse and instability
- B It decreases overall lung compliance in order to stabilize small alveoli
- C It reduces surface tension, preventing small alveoli from collapsing into larger ones
- D It increases the work of breathing by significantly thickening the respiratory membrane
Correct answer: It reduces surface tension, preventing small alveoli from collapsing into larger ones
According to the Law of Laplace, smaller alveoli have a higher pressure and tendency to collapse. Surfactant reduces surface tension more effectively in smaller alveoli, equalizing pressure and preventing atelectasis.
In a 'Pneumothorax,' what happens to the lung and the chest wall on the affected side?
- A The lung expands outward and the chest wall collapses inward
- B Both lung and chest wall collapse inward together
- C The lung collapses and the chest wall springs outward
- D Both lung and chest wall expand outward together
Correct answer: The lung collapses and the chest wall springs outward
A pneumothorax breaks the seal of the intrapleural space, allowing intrapleural pressure to equalize with atmospheric pressure. Without the negative pressure 'tether,' the lung's elastic recoil causes it to collapse, while the chest wall's recoil causes it to move outward.
Which of the following muscles are considered 'Accessory Muscles of Inspiration' used during heavy exercise?
- A Internal intercostals and abdominal muscles
- B Sternocleidomastoid and scalenes
- C Diaphragm and external intercostals
- D Diaphragm and rectus abdominis
Correct answer: Sternocleidomastoid and scalenes
While the diaphragm is the primary muscle of inspiration, the sternocleidomastoid and scalenes help lift the rib cage further during forced or labored breathing. This increases the thoracic volume even more than quiet breathing.
Airway resistance is highest in which part of the respiratory tree?
- A Trachea
- B Terminal bronchioles
- C Alveolar sacs
- D Medium-sized bronchi
Correct answer: Medium-sized bronchi
Although individual small airways have high resistance, their massive total cross-sectional area makes the aggregate resistance low. The medium-sized bronchi (generations 2-5) actually provide the greatest resistance to airflow.
During forced expiration, the intrapleural pressure can become positive. What is a potential consequence of this?
- A Dynamic compression of the airways
- B Alveolar hyper-expansion
- C A noticeable increase in lung compliance
- D A decrease in anatomical dead space volume
Correct answer: Dynamic compression of the airways
In forced expiration, high intra-abdominal and thoracic pressures can cause intrapleural pressure to exceed airway pressure. This results in the collapse of non-cartilaginous airways, limiting the maximum expiratory flow rate.
Which of the following would DECREASE lung compliance?
- A Emphysema
- B Aging
- C Increase in surfactant production
- D Pulmonary fibrosis
Correct answer: Pulmonary fibrosis
Pulmonary fibrosis involves the replacement of elastic lung tissue with stiff scar tissue, making the lungs harder to inflate. Emphysema actually increases compliance due to the destruction of elastic fibers.
The 'Bucket Handle' movement of the ribs during inspiration primarily increases the ________ diameter of the thorax.
- A Vertical
- B Anteroposterior
- C Oblique
- D Transverse
Correct answer: Transverse
The 'bucket handle' motion describes the lateral expansion of the lower ribs. The 'pump handle' motion refers to the elevation of the upper ribs which increases the anteroposterior diameter.
Hysteresis in a pressure-volume curve of the lung refers to the fact that:
- A The lung volume is higher during expiration than inspiration at the same pressure
- B Airway resistance is significantly higher during inspiration than during expiration throughout the cycle
- C The diaphragm moves considerably more during quiet breathing than during forced breathing efforts
- D Oxygen diffuses faster than carbon dioxide across the respiratory membrane
Correct answer: The lung volume is higher during expiration than inspiration at the same pressure
Hysteresis occurs because the surface tension forces differ during inflation and deflation. Because it takes more pressure to 'open' alveoli during inspiration, the volume for a given pressure is greater when the lung is deflating.
Which of the following describes the effect of Parasympathetic stimulation on the airways?
- A Bronchoconstriction via Muscarinic receptors
- B Bronchodilation of the airway smooth muscle via Beta-2 receptors
- C Increased surfactant production by type II alveolar cells
- D Inhibition of bronchial mucus secretion
Correct answer: Bronchoconstriction via Muscarinic receptors
The vagus nerve releases acetylcholine, which binds to muscarinic receptors on airway smooth muscle, causing bronchoconstriction. This increases airway resistance.
Functional Residual Capacity (FRC) is the volume of air remaining in the lungs after a:
- A Forced expiration
- B Quiet inspiration
- C Forced inspiration
- D Quiet expiration
Correct answer: Quiet expiration
FRC is the equilibrium point where the inward elastic recoil of the lungs is exactly balanced by the outward recoil of the chest wall. It is the sum of Expiratory Reserve Volume and Residual Volume.
What is the primary function of the pleural fluid?
- A To lubricate the pleural surfaces and provide surface tension for lung-chest wall coupling
- B To provide a continuous supply of oxygen and nutrients directly to the visceral pleura
- C To act as a chemical buffer that neutralizes carbon dioxide buildup in the pleural space
- D To trap and filter dust particles and pathogens that escape past the bronchi and bronchioles
Correct answer: To lubricate the pleural surfaces and provide surface tension for lung-chest wall coupling
The thin film of pleural fluid reduces friction between the moving lungs and the chest wall. Its high surface tension ensures the lungs follow the chest wall's expansion, similar to two wet pieces of glass sticking together.
Which physical law explains why smaller bubbles (alveoli) with the same surface tension would have higher internal pressure?
- A Poiseuille's Law
- B Fick's Law
- C Henry's Law
- D Law of Laplace
Correct answer: Law of Laplace
The Law of Laplace states that P = 2T/r (where P is pressure, T is surface tension, and r is radius). This illustrates why smaller alveoli require surfactant to lower their surface tension and prevent collapse into larger alveoli.
During inspiration, what happens to the 'Radial Traction' on the airways?
- A It increases, helping to pull the airways open
- B It decreases, causing the airways to narrow
- C It remains completely constant regardless of the current lung volume
- D It is present only during periods of forced expiration
Correct answer: It increases, helping to pull the airways open
As lung volume increases, the connective tissue fibers (parenchyma) surrounding the airways are stretched. This 'radial traction' pulls the airways open, which is why airway resistance is lower at high lung volumes.
A patient with Infant Respiratory Distress Syndrome (IRDS) lacks surfactant. This condition results in:
- A Decreased lung compliance and increased work of breathing
- B A significant increase in lung compliance and much easier breathing overall
- C Decreased surface tension and improved alveolar stability throughout the lungs
- D Excessive and persistent bronchodilation
Correct answer: Decreased lung compliance and increased work of breathing
Without surfactant, the surface tension in the alveoli is very high, making the lungs stiff (low compliance). This requires the infant to generate massive amounts of negative pressure to inflate the lungs, leading to exhaustion.
At which point in the respiratory cycle is the alveolar pressure equal to atmospheric pressure?
- A At the end of inspiration and the end of expiration
- B In the middle of the inspiratory phase before flow stops
- C During the pause following a maximal forced exhalation
- D Throughout the entire period of passive expiration
Correct answer: At the end of inspiration and the end of expiration
Airflow only occurs when there is a pressure gradient. At the static points (the end of inspiration and the end of expiration), air is not moving, indicating that alveolar pressure has equilibrated with atmospheric pressure.