Study sheet: Pulmonary Ventilation

📋 Course Outline

1. Respiration and Ventilation Overview
2. Inspiratory and Expiratory Mechanics
3. Pressure Gradients and Lung Compliance
4. Surfactant and Surface Tension
5. Work of Breathing
6. Pulmonary Volumes and Capacities
7. Alveolar Ventilation and Dead Space
8. Airway Structure and Regulation

📖 1. Respiration and Ventilation Overview

🔑 Key Concepts & Definitions

• Respiration : has the main purpose of supplying tissues with O2 and removing CO2 from the organism
• Pulmonary ventilation : is the movement of air into and out of the lungs between the atmosphere and the alveoli

📝 Essential Points

• Respiration consists of: pulmonary ventilation, diffusion of O2 and CO2 between alveoli and blood, transport of O2 and CO2 in blood and body fluids, regulation of ventilation

💡 Memory Hook

Ventilation → diffusion → transport → regulation

📖 2. Inspiratory and Expiratory Mechanics

★ Must-know

• 🔄 During inspiration:

  1. inspiratory muscles elevate the ribs
  2. the diaphragm lowers
  3. thoracic volume increases
  4. air is drawn into the lungs

• External intercostal muscle contraction contributes approximately 25% of lung volume change during quiet breathing, whereas diaphragm contraction accounts for approximately 75% of air movement.

Further detail

• During active expiration, the internal intercostals and transversus thoracis lower the ribs, while the accessory expiratory muscles push the relaxed diaphragm upward into the thorax.

💡 Memory Hook

Inspiration expands the thorax; active expiration compresses it

📖 3. Pressure Gradients and Lung Compliance

🔑 Key Concepts & Definitions

• Pleural pressure : Pleural pressure is the pressure of fluid in the thin space between the visceral and parietal pleura and is approximately $-5\ \mathrm{cmH_2O}$ at rest and $-7.5\ \mathrm{cmH_2O}$ during inspiration.
• Alveolar pressure : Alveolar pressure is the pressure of air in the alveoli; it is $0\ \mathrm{cmH_2O}$ without airflow, falls to $-1\ \mathrm{cmH_2O}$ during inspiration, and rises to $+1\ \mathrm{cmH_2O}$ during expiration.
• Lung compliance : Lung compliance is the increase in lung volume per unit increase in transpulmonary pressure and is normally approximately 200 ml of air for each $1\ \mathrm{cmH_2O}$ increase.

📝 Essential Points

📐 Formula — Transpulmonary pressure equals alveolar pressure minus pleural pressure: $P_{el}=P_{alv}-P_{pl}$.

💡 Memory Hook

More negative pleural pressure → larger thoracic volume → airflow inward

📖 4. Surfactant and Surface Tension

🔑 Key Concepts & Definitions

• Surfactant : is a surface-active substance secreted by type II alveolar epithelial cells that markedly reduces the surface tension of alveolar fluid

★ Must-know

• Surface tension is approximately 0.072 N/m in pure water, 0.050 N/m in alveolar fluid without surfactant, and 0.005–0.030 N/m in alveolar fluid with surfactant.

📐 Formula — The pressure generated by alveolar surface tension is given by $P=\frac{2T}{r}$, where pressure increases as alveolar radius decreases.

Further detail

• Its most important components include:

  • dipalmitoyl phosphatidylcholine
  • surfactant apoproteins
  • Ca++ ions

• For an alveolus with an average diameter of 100 µm and normal surfactant, surface-tension pressure is 0.4 kPa, whereas with pure water it is 1.8 kPa.

💡 Memory Hook

Air-filled lungs face surface tension; saline-filled lungs do not

📖 5. Work of Breathing

★ Must-know

📌 During normal breathing, inspiration is an active process requiring work, whereas expiration is passive and results from the elastic forces of the lungs and chest wall.

• Inspiratory work is divided into:
  • work against elastic forces
  • work against tissue resistance
  • work against airway resistance

Further detail

• Pulmonary ventilation accounts for 3–5% of total energy expenditure during normal breathing, and the energy required for breathing can increase 50-fold during physical activity.

💡 Memory Hook

Compliance work → tissue resistance work → airway resistance work

📖 6. Pulmonary Volumes and Capacities

🔑 Key Concepts & Definitions

• Spirometry : is the recording of the volume of air entering and leaving the lungs and produces a spirogram

📝 Essential Points

• The four pulmonary volumes are:

  • tidal volume
  • inspiratory reserve volume
  • expiratory reserve volume
  • residual volume

• Tidal volume is 500 ml, inspiratory reserve volume is 3000 ml, expiratory reserve volume is 1100 ml, and residual volume is 1200 ml.

📐 Formula — Inspiratory capacity equals $IC=TV+IRV=3500\ \mathrm{ml}$, functional residual capacity equals $FRC=ERV+RV=2300\ \mathrm{ml}$, vital capacity equals $VC=IRV+TV+ERV=4600\ \mathrm{ml}$, and total lung capacity equals $TLC=VC+RV=5800\ \mathrm{ml}$.

💡 Memory Hook

TV, IRV, ERV, RV form the four volumes

📖 7. Alveolar Ventilation and Dead Space

🔑 Key Concepts & Definitions

• Alveolar ventilation : is the amount of new air reaching the gas-exchange areas per unit time, including the alveoli, alveolar ducts, alveolar sacs, and respiratory bronchioles
• Anatomical dead space : Anatomical dead space consists of the conducting airways without gas exchange and has a volume of approximately 150 ml.
• Physiological dead space : Physiological dead space includes anatomical dead space plus alveolar dead space formed by alveoli with absent or insufficient perfusion.

📝 Essential Points

📐 Formula — Minute alveolar ventilation equals respiratory frequency multiplied by tidal volume minus dead-space volume: $V_A=f\times(V_T-V_D)=12\times(500-150)=4200\ \mathrm{ml/min}$.

💡 Memory Hook

Anatomical dead space conducts air; alveolar space exchanges gases

📖 8. Airway Structure and Regulation

★ Must-know

• Conducting airways are kept open by cartilage from the trachea to the bronchi, whereas cartilage disappears completely in the bronchioles.

📌 Sympathetic stimulation through norepinephrine and epinephrine acting on beta-adrenergic receptors dilates the bronchi, whereas parasympathetic vagal acetylcholine causes mild to moderate bronchiolar constriction.

• Mucus secreted by goblet cells and submucosal glands traps particles, and cilia beat approximately 20 times per second to move the mucus toward the pharynx for swallowing or coughing.

Further detail

• The main resistance to airflow is located in the larger bronchi and bronchi near the trachea rather than in the terminal bronchioles, of which there are approximately 65,000.

• Histamine and the slow-reacting substance of anaphylaxis released by mast cells during allergic reactions constrict bronchioles and can obstruct the airways.

💡 Memory Hook

Bronchial muscle contraction or mucus → increased airway resistance

📊 Synthesis Tables

Pulmonary Volumes and Capacities

Measure	Definition or formula	Value
Tidal volume (TV)	Air inspired or expired in a normal breath	500 ml
Inspiratory reserve volume (IRV)	Extra air inspired after a normal inspiration	3000 ml
Expiratory reserve volume (ERV)	Extra air expired after a normal expiration	1100 ml
Residual volume (RV)	Air remaining after maximal expiration	1200 ml
Vital capacity (VC)	IRV + TV + ERV	4600 ml
Total lung capacity (TLC)	VC + RV	5800 ml