Mechanics of Respiration – Pulmonary Ventilation

These question-and-answer flashcards cover key concepts from the lecture on pulmonary ventilation, including respiratory pressures, mechanics of inspiration and expiration, Boyle’s law, and physical factors influencing breathing.

What are the four major processes of respiration?

1) Pulmonary ventilation 2) External respiration 3) Transport of respiratory gases 4) Internal respiration

Define pulmonary ventilation.

The movement (exchange) of air between the atmosphere and the alveoli.

During which phase do gases flow into the lungs?

Inspiration (inhalation).

During which phase do gases exit the lungs?

Expiration (exhalation).

What muscle is the most important for quiet inspiration?

The diaphragm.

Name the primary inspiratory muscles.

Diaphragm and external intercostal muscles.

List three accessory muscles recruited during forced inspiration.

Scalenes, sternocleidomastoid, and pectoralis minor.

Which muscles contract during forced expiration?

Abdominal wall muscles (e.g., obliques, transversus) and internal intercostals.

State Boyle’s Law as it applies to breathing.

The pressure of a gas is inversely proportional to the volume of its container; as thoracic volume increases, intrapulmonary pressure decreases, and vice-versa.

What is atmospheric pressure (Patm) at sea level?

760 mm Hg (1 atmosphere).

Define intrapulmonary (intra-alveolar) pressure (Ppul).

The pressure inside the alveoli that fluctuates with breathing and eventually equalises with Patm at the end of each breath.

Define intrapleural pressure (Pip).

The pressure within the pleural cavity; it is always negative relative to Patm and Ppul.

What keeps the lungs from collapsing under normal conditions?

A negative intrapleural pressure (Pip) and a positive transpulmonary pressure (Ppul – Pip).

Give the formula for transpulmonary pressure.

Transpulmonary pressure = Ppul – Pip.

What happens if Pip equals Ppul or Patm?

The lungs collapse (atelectasis).

List two inward forces that promote lung collapse.

1) Elastic recoil of lung tissue 2) Surface tension of alveolar fluid.

What is pneumothorax?

Air in the pleural cavity, often producing lung collapse; treated by removing the air with chest tubes.

State two common causes of atelectasis.

Plugged bronchioles (collapse of alveoli) and pneumothorax (air in pleural cavity).

During quiet inspiration, how much does intrapulmonary pressure drop?

About –1 mm Hg below atmospheric pressure.

During quiet expiration, intrapulmonary pressure rises to approximately what value?

+1 mm Hg above atmospheric pressure.

How large is the pressure gradient (∆P) that moves air during quiet breathing?

About 2 mm Hg or less between Patm and alveoli.

What three physical factors hinder pulmonary ventilation?

1) Airway resistance 2) Alveolar surface tension 3) Lung compliance.

Write the relationship among gas flow (F), pressure gradient (∆P), and resistance (R).

F = ∆P / R (gas flow changes inversely with resistance).

How do bronchodilators such as albuterol or epinephrine affect airway resistance?

They dilate bronchioles, decreasing airway resistance and easing ventilation.

Define surface tension in the lungs.

The inward force created by molecular attraction at the liquid-gas interface lining the alveoli, tending to reduce alveolar size.

What is pulmonary surfactant and which cells secrete it?

A lipid-protein complex that reduces alveolar surface tension, secreted by type II alveolar cells.

Why do premature infants often develop infant respiratory distress syndrome (IRDS)?

They produce insufficient surfactant, causing alveoli to collapse after each breath.

Define lung compliance.

The measure of the change in lung volume that occurs with a given change in transpulmonary pressure; high compliance means the lungs expand easily.

Give two reasons normal lungs have high compliance.

1) Distensibility (elasticity) of lung tissue 2) Presence of surfactant that lowers surface tension.

List three factors that diminish lung compliance.

1) Fibrosis/scar tissue (e.g., chronic inflammation, TB) 2) Reduced surfactant production 3) Decreased flexibility of the thoracic cage.

Name three homeostatic imbalances that lower thoracic flexibility and thus compliance.

Thoracic deformities, ossification of costal cartilage, paralysis of intercostal muscles.

What is the main equation linking pressure changes and gas flow during breathing?

Volume changes → pressure changes → gases flow down pressure gradients until equalisation.

During forced inspiration, why does thoracic cavity volume increase more than during quiet inspiration?

Additional accessory muscles lift and expand the rib cage further, creating a larger drop in intrapulmonary pressure.

How does contraction of abdominal muscles aid forced expiration?

It pushes abdominal organs against the diaphragm, reducing thoracic volume and raising pressure to expel air forcefully.