Pulmonary Ventilation and Boyle's Law - Lecture Notes

Pulmonary Ventilation and Boyle's Law

Introduction

• Lecture by Dr. Malik Taradeh covering pulmonary ventilation and Boyle's law.
• Focuses on human physiology, pathophysiology, and therapeutics related to the respiratory system.

Chapter Content and Intended Learning Outcomes

• Objectives for students:
  • Describe the mechanics of pulmonary ventilation.
  • Define pleural pressure, alveolar pressure, and transpulmonary pressure.
  • Describe changes in lung volumes, alveolar pressure, pleural pressure, and transpulmonary pressure during normal breathing.
  • Define compliance of the lungs.
  • Describe the chemical composition and function of the surfactant.

Major Function of Respiratory System

• Respiratory system's primary function: supply oxygen to tissues and remove carbon dioxide (respiration).
• Major functional events of respiration:
  1. Pulmonary ventilation: movement of air in and out of the alveoli.
  2. Pulmonary gas exchange: diffusion of oxygen and carbon dioxide between blood and alveoli.
  3. Gas transportation: transport of oxygen and carbon dioxide to and from peripheral tissues.
  4. Cellular respiration: consumption of $O<em>2$ and production of $CO</em>2$.
  5. Regulation of respiration: respiratory centers in the brainstem.
• Respiration is divided into external and internal respiration.
  • External respiration involves the respiratory system, including inspiration and expiration.
  • Internal respiration involves the utilization of $O<em>2$ inside cells to produce energy, generating $H</em>2O$, $ATP$, and $CO_2$.

Pulmonary Ventilation

• Pulmonary ventilation: the process of moving air in and out of the lungs (breathing).
  • Inhalation (inspiration): air moves in.
  • Exhalation (expiration): air moves out.
• Air movement occurs due to pressure changes; gases move from high to low pressure areas (pressure gradient).
  • Inhalation: atmospheric pressure is higher than lung pressure.
  • Exhalation: lung pressure is higher than atmospheric pressure.

Physiological Anatomy of the Respiratory System

• Upper respiratory tract:
  • Nasal cavity, nostrils, oral cavity, pharynx (nasal pharynx, oropharynx, hypopharynx), epiglottis, larynx.
• Lower respiratory tract:
  • Trachea, right and left primary bronchus, bronchi, bronchioles, alveoli, diaphragm, superior lobe, middle lobe, inferior lobe

Functional Zones of the Respiratory System

• Two functional zones:
  1. Conducting zone: trachea to terminal bronchioles (first 16 levels of branching).
     • Function: filters, warms, and humidifies air, and conducts it to the lungs. Includes larynx and pharynx, nose.
  2. Respiratory zone: respiratory bronchioles, alveolar ducts, alveolar sacs.
     • Function: gas exchange.

Functional Units of Lungs: Alveoli

• Alveoli: sites for gas exchange, extending from respiratory bronchioles, alveolar ducts, and alveolar sacs.
• The wall of the alveoli consists of epithelial cells:
  • Type I: actual site for gas exchange.
  • Type II: produce surfactant.

Mechanics of Pulmonary Ventilation

• Principle: changing air pressure inside the lung by changing lung volume.
• Boyle’s Law: for a given quantity of gas, pressure is inversely proportional to volume.
• $P \propto 1/V$
• At rest, atmospheric pressure equals alveolar pressure.
• Increasing alveolar volume decreases alveolar pressure.
• Atmospheric pressure remains constant.
• Air moves until alveolar pressure equals atmospheric pressure.

Muscles That Cause Lung Expansion and Contraction

• Lung volume changes with thoracic cavity expansion and contraction.
• Main muscles of ventilation: diaphragm and intercostal muscles.
• Diaphragm movement changes the vertical diameter of the chest cavity.
• Rib elevation and depression by intercostal muscles change the anteroposterior diameter of the chest cavity.

Normal Quiet Breathing

• Accomplished primarily with the diaphragm.
• Inspiration: diaphragm contraction increases thoracic volume, expanding the lungs.
• Expiration (passive process): diaphragm relaxes, elastic recoil of lungs, chest wall, and abdominal structures compresses the lungs.

Raising and Lowering the Rib Cage

• Rib cage elevation moves the sternum forward and away from the spine, increasing the anteroposterior diameter of the chest.

Muscles of Inspiration and Expiration

• Inspiratory muscles: raise the rib cage.
  • External intercostals: move ribs upward and forward (deep inspiration with diaphragm).
  • Accessory muscles: sternocleidomastoid, anterior serrati, and scaleni.
  • Extra increase in lung volume leads to an increased pressure gradient, resulting in more air entering the lungs (deep inspiration)
• Expiratory muscles: depress the rib cage (deep expiration).
  • Internal intercostals and abdominal recti (primary).
  • Abdominal muscles compress abdominal contents upward toward the diaphragm, decreasing the vertical diameter of the chest cavity.

Pressures That Cause Movement of Air

• Atmospheric pressure:
  • Pressure exerted by the weight of air.
  • Considered to be 0 cmH2O (reference point).
• Alveolar pressure:
  • Pressure inside the alveoli.
  • No airflow: alveolar pressure = 0 cmH2O.
  • Inspiration: alveolar pressure becomes slightly negative (about -1 cm H2O), causing air to flow in (about 0.5 L in 2 seconds).
  • Expiration: alveolar pressure becomes slightly positive (about +1 cm H2O), causing air to flow out (about 0.5 L in 2-3 seconds).
• Alveolar pressure is lower than atmospheric pressure during inspiration.

Pleural Pressure (Intrapleural Pressure)

• Pressure in the pleural cavity (between visceral and parietal pleura).
• Normally negative relative to atmospheric pressure (about -4 to -5 cmH2O at rest).
• Inspiration: chest cage expansion pulls the lung surface, creating a more negative pressure (about -7 cmH2O).
• Negative pressure is due to the fluid in the pleural cavity.
• Pleural pressure is always less than alveolar pressure.
• In expiration, the air moves out of the lung and it might collapse.

Lung Elasticity and Pleural Pressure

• The lung is elastic and requires a force to keep it expanded.
• Lungs