Achieve Mastery of Medical Concepts

Study for medical school and boards with Lecturio

Ventilation: Mechanics of Breathing

Human cells are primarily reliant on aerobic metabolism. Therefore, it is of vital importance to efficiently obtain oxygen from the environment and bring it to the tissues, while excreting the by-product of cellular respiration Respiration The act of breathing with the lungs, consisting of inhalation, or the taking into the lungs of the ambient air, and of exhalation, or the expelling of the modified air which contains more carbon dioxide than the air taken in. Nose and Nasal Cavity: Anatomy (carbon dioxide). Respiration Respiration The act of breathing with the lungs, consisting of inhalation, or the taking into the lungs of the ambient air, and of exhalation, or the expelling of the modified air which contains more carbon dioxide than the air taken in. Nose and Nasal Cavity: Anatomy involves both the respiratory and circulatory systems. There are 4 processes that supply the body with O2 and dispose of CO2. The respiratory system is involved in pulmonary ventilation and external respiration Respiration The act of breathing with the lungs, consisting of inhalation, or the taking into the lungs of the ambient air, and of exhalation, or the expelling of the modified air which contains more carbon dioxide than the air taken in. Nose and Nasal Cavity: Anatomy, while the circulatory system is responsible for transport and internal respiration Respiration The act of breathing with the lungs, consisting of inhalation, or the taking into the lungs of the ambient air, and of exhalation, or the expelling of the modified air which contains more carbon dioxide than the air taken in. Nose and Nasal Cavity: Anatomy. Pulmonary ventilation (breathing) represents movement of air into and out of the lungs Lungs Lungs are the main organs of the respiratory system. Lungs are paired viscera located in the thoracic cavity and are composed of spongy tissue. The primary function of the lungs is to oxygenate blood and eliminate CO2. Lungs: Anatomy. External respiration Respiration The act of breathing with the lungs, consisting of inhalation, or the taking into the lungs of the ambient air, and of exhalation, or the expelling of the modified air which contains more carbon dioxide than the air taken in. Nose and Nasal Cavity: Anatomy is represented by the O2 and CO2 exchange between the lungs Lungs Lungs are the main organs of the respiratory system. Lungs are paired viscera located in the thoracic cavity and are composed of spongy tissue. The primary function of the lungs is to oxygenate blood and eliminate CO2. Lungs: Anatomy and the blood.

Last updated: 28 Jun, 2022

Editorial responsibility: Stanley Oiseth, Lindsay Jones, Evelin Maza

Anatomy of the Respiratory System Involved in Ventilation

Ventilation, or breathing, involves the action and movements of structures found in the neck Neck The part of a human or animal body connecting the head to the rest of the body. Peritonsillar Abscess and thoracic cavity belonging to the pulmonary, musculoskeletal, and cardiac systems. 

  • Conducting zone: 
    • Function:
      • Provides conduit for air to flow Flow Blood flows through the heart, arteries, capillaries, and veins in a closed, continuous circuit. Flow is the movement of volume per unit of time. Flow is affected by the pressure gradient and the resistance fluid encounters between 2 points. Vascular resistance is the opposition to flow, which is caused primarily by blood friction against vessel walls. Vascular Resistance, Flow, and Mean Arterial Pressure into lungs Lungs Lungs are the main organs of the respiratory system. Lungs are paired viscera located in the thoracic cavity and are composed of spongy tissue. The primary function of the lungs is to oxygenate blood and eliminate CO2. Lungs: Anatomy
      • Humidifies and warms incoming air
    • Structures:
      • Pharynx Pharynx The pharynx is a component of the digestive system that lies posterior to the nasal cavity, oral cavity, and larynx. The pharynx can be divided into the oropharynx, nasopharynx, and laryngopharynx. Pharyngeal muscles play an integral role in vital processes such as breathing, swallowing, and speaking. Pharynx: Anatomy
      • Larynx Larynx The larynx, also commonly called the voice box, is a cylindrical space located in the neck at the level of the C3-C6 vertebrae. The major structures forming the framework of the larynx are the thyroid cartilage, cricoid cartilage, and epiglottis. The larynx serves to produce sound (phonation), conducts air to the trachea, and prevents large molecules from reaching the lungs. Larynx: Anatomy
      • Trachea Trachea The trachea is a tubular structure that forms part of the lower respiratory tract. The trachea is continuous superiorly with the larynx and inferiorly becomes the bronchial tree within the lungs. The trachea consists of a support frame of semicircular, or C-shaped, rings made out of hyaline cartilage and reinforced by collagenous connective tissue. Trachea: Anatomy
      • Right and left mainstem bronchi Bronchi The larger air passages of the lungs arising from the terminal bifurcation of the trachea. They include the largest two primary bronchi which branch out into secondary bronchi, and tertiary bronchi which extend into bronchioles and pulmonary alveoli. Bronchial Tree: Anatomy
      • Bronchioles Bronchioles The small airways branching off the tertiary bronchi. Terminal bronchioles lead into several orders of respiratory bronchioles which in turn lead into alveolar ducts and then into pulmonary alveoli. Bronchial Tree: Anatomy
  • Respiratory zone:
    • Function: location where gas exchange Gas exchange Human cells are primarily reliant on aerobic metabolism. The respiratory system is involved in pulmonary ventilation and external respiration, while the circulatory system is responsible for transport and internal respiration. Pulmonary ventilation (breathing) represents movement of air into and out of the lungs. External respiration, or gas exchange, is represented by the O2 and CO2 exchange between the lungs and the blood. Gas Exchange occurs
    • Structures:
      • Respiratory bronchioles Bronchioles The small airways branching off the tertiary bronchi. Terminal bronchioles lead into several orders of respiratory bronchioles which in turn lead into alveolar ducts and then into pulmonary alveoli. Bronchial Tree: Anatomy
      • Alveoli Alveoli Small polyhedral outpouchings along the walls of the alveolar sacs, alveolar ducts and terminal bronchioles through the walls of which gas exchange between alveolar air and pulmonary capillary blood takes place. Acute Respiratory Distress Syndrome (ARDS)
  • Musculoskeletal components:
    • Function: 
      • Provide sturdy framework for lungs Lungs Lungs are the main organs of the respiratory system. Lungs are paired viscera located in the thoracic cavity and are composed of spongy tissue. The primary function of the lungs is to oxygenate blood and eliminate CO2. Lungs: Anatomy
      • Generate mechanical forces necessary for breathing
    • Structures:
      • Rib cage Rib cage The bony thoracic enclosure consisting of the vertebral column; the ribs; the sternum; and the costal cartilage. Chest Wall: Anatomy
      • Respiratory muscles: diaphragm Diaphragm The diaphragm is a large, dome-shaped muscle that separates the thoracic cavity from the abdominal cavity. The diaphragm consists of muscle fibers and a large central tendon, which is divided into right and left parts. As the primary muscle of inspiration, the diaphragm contributes 75% of the total inspiratory muscle force. Diaphragm: Anatomy, external intercostals, portions of internal intercostals
      • Pleural membranes
      • Pleural cavity Pleural cavity Paired but separate cavity within the thoracic cavity. It consists of the space between the parietal and visceral pleura and normally contains a capillary layer of serous fluid that lubricates the pleural surfaces. Pleura: Anatomy: space between pulmonary and thoracic pleura Pleura The pleura is a serous membrane that lines the walls of the thoracic cavity and the surface of the lungs. This structure of mesodermal origin covers both lungs, the mediastinum, the thoracic surface of the diaphragm, and the inner part of the thoracic cage. The pleura is divided into a visceral pleura and parietal pleura. Pleura: Anatomy

Pressure Relationships in the Thoracic Cavity

  • Atmospheric pressure (Patm): 
    • Pressure exerted by air surrounding body 
    • At sea level, Patm is 760 mm MM Multiple myeloma (MM) is a malignant condition of plasma cells (activated B lymphocytes) primarily seen in the elderly. Monoclonal proliferation of plasma cells results in cytokine-driven osteoclastic activity and excessive secretion of IgG antibodies. Multiple Myeloma Hg.
  • Respiratory pressure: 
    • Relative to Patm
    • Negative respiratory pressure is < Patm.
    • Positive respiratory pressure is > Patm.
    • Zero respiratory pressure = Patm.
  • Intrapulmonary pressure (intra-alveolar) pressure (Ppul):
    • Pressure in alveoli Alveoli Small polyhedral outpouchings along the walls of the alveolar sacs, alveolar ducts and terminal bronchioles through the walls of which gas exchange between alveolar air and pulmonary capillary blood takes place. Acute Respiratory Distress Syndrome (ARDS)
    • Fluctuates with breathing
    • Always equalizes with Patm
  • Intrapleural pressure (Pip):
    • Pressure within pleural cavity Pleural cavity Paired but separate cavity within the thoracic cavity. It consists of the space between the parietal and visceral pleura and normally contains a capillary layer of serous fluid that lubricates the pleural surfaces. Pleura: Anatomy
    • Fluctuates with breathing
    • Always a negative pressure
    • Pip is generated by opposing forces:
      • 2 inward forces promoting lung collapse ( elastic Elastic Connective Tissue: Histology recoil Recoil Vessels can stretch and return to their original shape after receiving the stroke volume of blood ejected by the left ventricle during systole. Arteries: Histology of lungs Lungs Lungs are the main organs of the respiratory system. Lungs are paired viscera located in the thoracic cavity and are composed of spongy tissue. The primary function of the lungs is to oxygenate blood and eliminate CO2. Lungs: Anatomy and surface tension Surface tension The force acting on the surface of a liquid, tending to minimize the area of the surface. Acute Respiratory Distress Syndrome (ARDS) in alveoli Alveoli Small polyhedral outpouchings along the walls of the alveolar sacs, alveolar ducts and terminal bronchioles through the walls of which gas exchange between alveolar air and pulmonary capillary blood takes place. Acute Respiratory Distress Syndrome (ARDS))
      • 1 outward force ( elasticity Elasticity Resistance and recovery from distortion of shape. Skeletal Muscle Contraction of chest wall Chest wall The chest wall consists of skin, fat, muscles, bones, and cartilage. The bony structure of the chest wall is composed of the ribs, sternum, and thoracic vertebrae. The chest wall serves as armor for the vital intrathoracic organs and provides the stability necessary for the movement of the shoulders and arms. Chest Wall: Anatomy pulling thorax outward)
  • Transpulmonary pressure (Ppul – Pip):
    • Keeps airways open; lungs Lungs Lungs are the main organs of the respiratory system. Lungs are paired viscera located in the thoracic cavity and are composed of spongy tissue. The primary function of the lungs is to oxygenate blood and eliminate CO2. Lungs: Anatomy expand as transpulmonary pressure ↑
    • If Pip ≥ Ppul, lungs Lungs Lungs are the main organs of the respiratory system. Lungs are paired viscera located in the thoracic cavity and are composed of spongy tissue. The primary function of the lungs is to oxygenate blood and eliminate CO2. Lungs: Anatomy will collapse.

Inspiration and Expiration

Breathing consists of 2 phases:

  • Inspiration: flow Flow Blood flows through the heart, arteries, capillaries, and veins in a closed, continuous circuit. Flow is the movement of volume per unit of time. Flow is affected by the pressure gradient and the resistance fluid encounters between 2 points. Vascular resistance is the opposition to flow, which is caused primarily by blood friction against vessel walls. Vascular Resistance, Flow, and Mean Arterial Pressure of gases into lungs Lungs Lungs are the main organs of the respiratory system. Lungs are paired viscera located in the thoracic cavity and are composed of spongy tissue. The primary function of the lungs is to oxygenate blood and eliminate CO2. Lungs: Anatomy
  • Expiration: flow Flow Blood flows through the heart, arteries, capillaries, and veins in a closed, continuous circuit. Flow is the movement of volume per unit of time. Flow is affected by the pressure gradient and the resistance fluid encounters between 2 points. Vascular resistance is the opposition to flow, which is caused primarily by blood friction against vessel walls. Vascular Resistance, Flow, and Mean Arterial Pressure of gases out of lungs Lungs Lungs are the main organs of the respiratory system. Lungs are paired viscera located in the thoracic cavity and are composed of spongy tissue. The primary function of the lungs is to oxygenate blood and eliminate CO2. Lungs: Anatomy

Inspiration and expiration:

  • Mechanical processes caused by contraction of respiratory muscles
  • Cause volume changes in thoracic cavity 
  • Volume changes lead to gas movement according to Boyle’s law (pressure varies inversely with volume):
    • Volume changes cause pressure changes.
    • Pressure changes cause flow Flow Blood flows through the heart, arteries, capillaries, and veins in a closed, continuous circuit. Flow is the movement of volume per unit of time. Flow is affected by the pressure gradient and the resistance fluid encounters between 2 points. Vascular resistance is the opposition to flow, which is caused primarily by blood friction against vessel walls. Vascular Resistance, Flow, and Mean Arterial Pressure of gases to equalize pressure.
Changes in pressure relationships in the thoracic cavity during respiration

Changes in pressure relationships in the thoracic cavity during respiration Respiration The act of breathing with the lungs, consisting of inhalation, or the taking into the lungs of the ambient air, and of exhalation, or the expelling of the modified air which contains more carbon dioxide than the air taken in. Nose and Nasal Cavity: Anatomy:
During inspiration, muscles move to create negative intrapleural pressure (green line). This negative pressure is transferred to the lungs Lungs Lungs are the main organs of the respiratory system. Lungs are paired viscera located in the thoracic cavity and are composed of spongy tissue. The primary function of the lungs is to oxygenate blood and eliminate CO2. Lungs: Anatomy, making intrapulmonary pressure more negative (blue line) in relation to atmospheric pressure. Air flows into the lungs Lungs Lungs are the main organs of the respiratory system. Lungs are paired viscera located in the thoracic cavity and are composed of spongy tissue. The primary function of the lungs is to oxygenate blood and eliminate CO2. Lungs: Anatomy down this pressure gradient Pressure gradient Vascular Resistance, Flow, and Mean Arterial Pressure, increasing the breath volume (purple line). With exhalation, the process reverses, leading to airflow out of the lungs Lungs Lungs are the main organs of the respiratory system. Lungs are paired viscera located in the thoracic cavity and are composed of spongy tissue. The primary function of the lungs is to oxygenate blood and eliminate CO2. Lungs: Anatomy.

Image by Lecturio. License: CC BY-NC-SA 4.0

Inspiration

Inspiration is an active process:

  • Inspiratory muscles contract, pulling the rib cage Rib cage The bony thoracic enclosure consisting of the vertebral column; the ribs; the sternum; and the costal cartilage. Chest Wall: Anatomy out, decreasing the Pip, and increasing thoracic volume.
  • Adhesive forces pull on the pleural membrane, which in turn, pull on lung parenchyma.
  • Lungs Lungs Lungs are the main organs of the respiratory system. Lungs are paired viscera located in the thoracic cavity and are composed of spongy tissue. The primary function of the lungs is to oxygenate blood and eliminate CO2. Lungs: Anatomy are stretched and intrapulmonary volume ↑.
  • Ppul drops, becoming lower than Patm.
  • Air flows into lungs Lungs Lungs are the main organs of the respiratory system. Lungs are paired viscera located in the thoracic cavity and are composed of spongy tissue. The primary function of the lungs is to oxygenate blood and eliminate CO2. Lungs: Anatomy down pressure gradient Pressure gradient Vascular Resistance, Flow, and Mean Arterial Pressure until Ppul = Patm.

Expiration

Expiration (at rest) is a passive process:

  • Inspiratory muscles relax.
  • Thoracic cavity volume ↓ owing to elastic Elastic Connective Tissue: Histology recoil Recoil Vessels can stretch and return to their original shape after receiving the stroke volume of blood ejected by the left ventricle during systole. Arteries: Histology.
  • Intrapulmonary volume ↓
  • Ppul rises above Patm.
  • Air flows out of lungs Lungs Lungs are the main organs of the respiratory system. Lungs are paired viscera located in the thoracic cavity and are composed of spongy tissue. The primary function of the lungs is to oxygenate blood and eliminate CO2. Lungs: Anatomy down pressure gradient Pressure gradient Vascular Resistance, Flow, and Mean Arterial Pressure until Ppul = Patm.
  • Forced expiration: 
    • Active process 
    • Expiratory muscles used to ↓ thoracic volumes
    • ↑ Airflow speed out of lungs Lungs Lungs are the main organs of the respiratory system. Lungs are paired viscera located in the thoracic cavity and are composed of spongy tissue. The primary function of the lungs is to oxygenate blood and eliminate CO2. Lungs: Anatomy

Lung Volumes and Capacities

Lung volumes

Lung volumes are specific volumes of air contained by different portions of lungs Lungs Lungs are the main organs of the respiratory system. Lungs are paired viscera located in the thoracic cavity and are composed of spongy tissue. The primary function of the lungs is to oxygenate blood and eliminate CO2. Lungs: Anatomy at specific points in the respiratory cycle Cycle The type of signal that ends the inspiratory phase delivered by the ventilator Invasive Mechanical Ventilation.

  • Tidal volume (TV): volume of air inhaled or exhaled with each breath under resting conditions
  • Residual volume (RV): volume of air left in lungs Lungs Lungs are the main organs of the respiratory system. Lungs are paired viscera located in the thoracic cavity and are composed of spongy tissue. The primary function of the lungs is to oxygenate blood and eliminate CO2. Lungs: Anatomy after forced exhalation
  • Expiratory reserve volume (ERV): volume of air that can be forcefully exhaled after normal tidal volume exhalation
  • Inspiratory reserve volume (IRV): volume of air that can be forcefully inhaled after normal tidal volume inhalation
Respiratory physiology_lung volumes and capacities

Lung volumes and capacities

Image by Lecturio. License: CC BY-NC-SA 4.0

Lung capacities

Lung capacities are a combination of 2 or more volumes.

  • Total lung capacity (TLC): 
    • Maximum volume of air contained in lungs Lungs Lungs are the main organs of the respiratory system. Lungs are paired viscera located in the thoracic cavity and are composed of spongy tissue. The primary function of the lungs is to oxygenate blood and eliminate CO2. Lungs: Anatomy after maximum inspiratory effort
    • TLC = TV + RV + ERV + IRV
  • Vital capacity (VC): 
    • Maximum volume of air that a person can move in or out of lungs Lungs Lungs are the main organs of the respiratory system. Lungs are paired viscera located in the thoracic cavity and are composed of spongy tissue. The primary function of the lungs is to oxygenate blood and eliminate CO2. Lungs: Anatomy
    • VC = TV + IRV + ERV
  • Functional residual capacity (FRC): 
    • Volume of air remaining in lungs Lungs Lungs are the main organs of the respiratory system. Lungs are paired viscera located in the thoracic cavity and are composed of spongy tissue. The primary function of the lungs is to oxygenate blood and eliminate CO2. Lungs: Anatomy after tidal expiration
    • FRC = ERV + RV
  • Inspiratory capacity ( IC IC Inhaled Anesthetics): 
    • Maximum volume of air that can be inspired after normal expiration 
    • IC IC Inhaled Anesthetics = TV + IRV

Dead space

Dead space is air that enters and exits lungs Lungs Lungs are the main organs of the respiratory system. Lungs are paired viscera located in the thoracic cavity and are composed of spongy tissue. The primary function of the lungs is to oxygenate blood and eliminate CO2. Lungs: Anatomy but does not make it to areas where gas exchange Gas exchange Human cells are primarily reliant on aerobic metabolism. The respiratory system is involved in pulmonary ventilation and external respiration, while the circulatory system is responsible for transport and internal respiration. Pulmonary ventilation (breathing) represents movement of air into and out of the lungs. External respiration, or gas exchange, is represented by the O2 and CO2 exchange between the lungs and the blood. Gas Exchange can occur.

  • Anatomical dead space: air in airways that does not reach alveoli Alveoli Small polyhedral outpouchings along the walls of the alveolar sacs, alveolar ducts and terminal bronchioles through the walls of which gas exchange between alveolar air and pulmonary capillary blood takes place. Acute Respiratory Distress Syndrome (ARDS) or respiratory bronchioles Bronchioles The small airways branching off the tertiary bronchi. Terminal bronchioles lead into several orders of respiratory bronchioles which in turn lead into alveolar ducts and then into pulmonary alveoli. Bronchial Tree: Anatomy
  • Alveolar dead space Alveolar dead space Respiratory Acidosis: air in alveoli Alveoli Small polyhedral outpouchings along the walls of the alveolar sacs, alveolar ducts and terminal bronchioles through the walls of which gas exchange between alveolar air and pulmonary capillary blood takes place. Acute Respiratory Distress Syndrome (ARDS) that cannot be absorbed into bloodstream due to lung disease or blood flow Flow Blood flows through the heart, arteries, capillaries, and veins in a closed, continuous circuit. Flow is the movement of volume per unit of time. Flow is affected by the pressure gradient and the resistance fluid encounters between 2 points. Vascular resistance is the opposition to flow, which is caused primarily by blood friction against vessel walls. Vascular Resistance, Flow, and Mean Arterial Pressure issues
  • Total dead space = alveolar dead space Alveolar dead space Respiratory Acidosis + anatomical dead space

Ventilation and Work of Breathing

Ventilation

Ventilation is the process of moving air in and out.

  • Minute ventilation (VE):
    • Volume of air moved in and out of lungs Lungs Lungs are the main organs of the respiratory system. Lungs are paired viscera located in the thoracic cavity and are composed of spongy tissue. The primary function of the lungs is to oxygenate blood and eliminate CO2. Lungs: Anatomy per minute
    • VE =  breathing frequency expressed in breaths/minute (Bf) × tidal volume (TV)
  • Alveolar ventilation (VA):
    • Volume of air reaching alveoli Alveoli Small polyhedral outpouchings along the walls of the alveolar sacs, alveolar ducts and terminal bronchioles through the walls of which gas exchange between alveolar air and pulmonary capillary blood takes place. Acute Respiratory Distress Syndrome (ARDS) per minute and is available for gas exchange Gas exchange Human cells are primarily reliant on aerobic metabolism. The respiratory system is involved in pulmonary ventilation and external respiration, while the circulatory system is responsible for transport and internal respiration. Pulmonary ventilation (breathing) represents movement of air into and out of the lungs. External respiration, or gas exchange, is represented by the O2 and CO2 exchange between the lungs and the blood. Gas Exchange
    • VA = Bf × (TV – total dead space)

“Work of breathing”

The work of breathing Work of breathing Respiratory muscle contraction during inhalation. The work is accomplished in three phases: lung compliance work, that required to expand the lungs against its elastic forces; tissue resistance work, that required to overcome the viscosity of the lung and chest wall structures; and airway resistance work, that required to overcome airway resistance during the movement of air into the lungs. Work of breathing does not refer to expiration, which is entirely a passive process caused by elastic recoil of the lung and chest cage. Pulmonary Examination is the amount of energy a person needs to breathe.

  • Elastic Elastic Connective Tissue: Histology work: done to overcome elastic Elastic Connective Tissue: Histology recoil Recoil Vessels can stretch and return to their original shape after receiving the stroke volume of blood ejected by the left ventricle during systole. Arteries: Histology of chest wall Chest wall The chest wall consists of skin, fat, muscles, bones, and cartilage. The bony structure of the chest wall is composed of the ribs, sternum, and thoracic vertebrae. The chest wall serves as armor for the vital intrathoracic organs and provides the stability necessary for the movement of the shoulders and arms. Chest Wall: Anatomy and pulmonary parenchyma and surface tension Surface tension The force acting on the surface of a liquid, tending to minimize the area of the surface. Acute Respiratory Distress Syndrome (ARDS) of alveoli Alveoli Small polyhedral outpouchings along the walls of the alveolar sacs, alveolar ducts and terminal bronchioles through the walls of which gas exchange between alveolar air and pulmonary capillary blood takes place. Acute Respiratory Distress Syndrome (ARDS)
  • Resistive work: done to overcome resistance of airways and tissues

Factors Influencing Pulmonary Ventilation

Aside from the pressures that the thoracic musculature is capable of creating, ventilation is limited by the physical properties of the structures of the lungs Lungs Lungs are the main organs of the respiratory system. Lungs are paired viscera located in the thoracic cavity and are composed of spongy tissue. The primary function of the lungs is to oxygenate blood and eliminate CO2. Lungs: Anatomy. The most important physical properties to be taken into account are:

  • The resistance of the airways
  • The compliance Compliance Distensibility measure of a chamber such as the lungs (lung compliance) or bladder. Compliance is expressed as a change in volume per unit change in pressure. Veins: Histology of the lung tissue
  • The surface tension Surface tension The force acting on the surface of a liquid, tending to minimize the area of the surface. Acute Respiratory Distress Syndrome (ARDS) of the alveoli Alveoli Small polyhedral outpouchings along the walls of the alveolar sacs, alveolar ducts and terminal bronchioles through the walls of which gas exchange between alveolar air and pulmonary capillary blood takes place. Acute Respiratory Distress Syndrome (ARDS)

Resistance

  • Definition:
    • Resistance: force that opposes flow Flow Blood flows through the heart, arteries, capillaries, and veins in a closed, continuous circuit. Flow is the movement of volume per unit of time. Flow is affected by the pressure gradient and the resistance fluid encounters between 2 points. Vascular resistance is the opposition to flow, which is caused primarily by blood friction against vessel walls. Vascular Resistance, Flow, and Mean Arterial Pressure (in this case of air)
    • Poiseuille’s law: Flow Flow Blood flows through the heart, arteries, capillaries, and veins in a closed, continuous circuit. Flow is the movement of volume per unit of time. Flow is affected by the pressure gradient and the resistance fluid encounters between 2 points. Vascular resistance is the opposition to flow, which is caused primarily by blood friction against vessel walls. Vascular Resistance, Flow, and Mean Arterial Pressure of air is inversely proportional to resistance.
  • Effect on the pulmonary system:
    • Resistance impedes airflow into lungs Lungs Lungs are the main organs of the respiratory system. Lungs are paired viscera located in the thoracic cavity and are composed of spongy tissue. The primary function of the lungs is to oxygenate blood and eliminate CO2. Lungs: Anatomy.
    • ↑ Resistance = ↑ energy needed to breathe in.
    • Airways generate 80% of resistance.
    • Diameter of airway Airway ABCDE Assessment is inversely proportional to the resistance it produces.
  • Physiologic implications:
    • In healthy patients Patients Individuals participating in the health care system for the purpose of receiving therapeutic, diagnostic, or preventive procedures. Clinician–Patient Relationship, resistance is insignificant, as total diameter of airways is large:
      • Large airway Airway ABCDE Assessment diameters in beginning of conducting zone
      • Smaller airways maintain high total cross-sectional area because there are so many.
      • Resistance disappears in terminal bronchiole → diffusion Diffusion The tendency of a gas or solute to pass from a point of higher pressure or concentration to a point of lower pressure or concentration and to distribute itself throughout the available space. Diffusion, especially facilitated diffusion, is a major mechanism of biological transport. Peritoneal Dialysis and Hemodialysis drives gas exchange Gas exchange Human cells are primarily reliant on aerobic metabolism. The respiratory system is involved in pulmonary ventilation and external respiration, while the circulatory system is responsible for transport and internal respiration. Pulmonary ventilation (breathing) represents movement of air into and out of the lungs. External respiration, or gas exchange, is represented by the O2 and CO2 exchange between the lungs and the blood. Gas Exchange
    • In certain ailments, ↓ total airway Airway ABCDE Assessment diameter, ↑ resistance to overcome to breathe:
      • Smooth muscle of airway Airway ABCDE Assessment constricts (e.g., asthma Asthma Asthma is a chronic inflammatory respiratory condition characterized by bronchial hyperresponsiveness and airflow obstruction. The disease is believed to result from the complex interaction of host and environmental factors that increase disease predisposition, with inflammation causing symptoms and structural changes. Patients typically present with wheezing, cough, and dyspnea. Asthma)
      • Mucous plugging of airways (e.g., chronic obstructive pulmonary disease Chronic obstructive pulmonary disease Chronic obstructive pulmonary disease (COPD) is a lung disease characterized by progressive, largely irreversible airflow obstruction. The condition usually presents in middle-aged or elderly persons with a history of cigarette smoking. Signs and symptoms include prolonged expiration, wheezing, diminished breath sounds, progressive dyspnea, and chronic cough. Chronic Obstructive Pulmonary Disease (COPD) ( COPD COPD Chronic obstructive pulmonary disease (COPD) is a lung disease characterized by progressive, largely irreversible airflow obstruction. The condition usually presents in middle-aged or elderly persons with a history of cigarette smoking. Signs and symptoms include prolonged expiration, wheezing, diminished breath sounds, progressive dyspnea, and chronic cough. Chronic Obstructive Pulmonary Disease (COPD)), bronchitis)
      • Obstruction of bronchioles Bronchioles The small airways branching off the tertiary bronchi. Terminal bronchioles lead into several orders of respiratory bronchioles which in turn lead into alveolar ducts and then into pulmonary alveoli. Bronchial Tree: Anatomy and alveoli Alveoli Small polyhedral outpouchings along the walls of the alveolar sacs, alveolar ducts and terminal bronchioles through the walls of which gas exchange between alveolar air and pulmonary capillary blood takes place. Acute Respiratory Distress Syndrome (ARDS) by infectious Infectious Febrile Infant material (e.g., pneumonia Pneumonia Pneumonia or pulmonary inflammation is an acute or chronic inflammation of lung tissue. Causes include infection with bacteria, viruses, or fungi. In more rare cases, pneumonia can also be caused through toxic triggers through inhalation of toxic substances, immunological processes, or in the course of radiotherapy. Pneumonia)

Alveolar surface tension Surface tension The force acting on the surface of a liquid, tending to minimize the area of the surface. Acute Respiratory Distress Syndrome (ARDS)

  • Definition:
    • Property derived from adhesion Adhesion The process whereby platelets adhere to something other than platelets, e.g., collagen; basement membrane; microfibrils; or other ‘foreign’ surfaces. Coagulation Studies of water molecules
    • Water molecules stick to other water molecules.
    • Resists any force that tends to ↑ surface area of liquid
  • Effect on the pulmonary system:
    • Occurs in alveoli Alveoli Small polyhedral outpouchings along the walls of the alveolar sacs, alveolar ducts and terminal bronchioles through the walls of which gas exchange between alveolar air and pulmonary capillary blood takes place. Acute Respiratory Distress Syndrome (ARDS) owing to the water molecules inside them
    • If left unchecked, keeps alveoli Alveoli Small polyhedral outpouchings along the walls of the alveolar sacs, alveolar ducts and terminal bronchioles through the walls of which gas exchange between alveolar air and pulmonary capillary blood takes place. Acute Respiratory Distress Syndrome (ARDS) from stretching during inspiration
  • Physiologic implications:

Compliance Compliance Distensibility measure of a chamber such as the lungs (lung compliance) or bladder. Compliance is expressed as a change in volume per unit change in pressure. Veins: Histology

  • Definition:
    • Measure of volume change with given change in transpulmonary pressure
    • Determined by tensile properties of lung tissue
    • Simply: how stiff the lungs Lungs Lungs are the main organs of the respiratory system. Lungs are paired viscera located in the thoracic cavity and are composed of spongy tissue. The primary function of the lungs is to oxygenate blood and eliminate CO2. Lungs: Anatomy are
  • Effect on the pulmonary system:
    • Lungs Lungs Lungs are the main organs of the respiratory system. Lungs are paired viscera located in the thoracic cavity and are composed of spongy tissue. The primary function of the lungs is to oxygenate blood and eliminate CO2. Lungs: Anatomy stiffness, ↑ energy to stretch them during inspiration:
      • Ventilation is more efficient in areas of lung with ↑ compliance Compliance Distensibility measure of a chamber such as the lungs (lung compliance) or bladder. Compliance is expressed as a change in volume per unit change in pressure. Veins: Histology.
      • Areas with ↓ compliance Compliance Distensibility measure of a chamber such as the lungs (lung compliance) or bladder. Compliance is expressed as a change in volume per unit change in pressure. Veins: Histology expand less.
    • Compliance Compliance Distensibility measure of a chamber such as the lungs (lung compliance) or bladder. Compliance is expressed as a change in volume per unit change in pressure. Veins: Histology of lungs Lungs Lungs are the main organs of the respiratory system. Lungs are paired viscera located in the thoracic cavity and are composed of spongy tissue. The primary function of the lungs is to oxygenate blood and eliminate CO2. Lungs: Anatomy also influenced by gravity:
      • Apex is ↓ compliant.
      • Base is ↑ compliant.
  • Physiologic implications:
    • In healthy lungs Lungs Lungs are the main organs of the respiratory system. Lungs are paired viscera located in the thoracic cavity and are composed of spongy tissue. The primary function of the lungs is to oxygenate blood and eliminate CO2. Lungs: Anatomy, ↑ compliance Compliance Distensibility measure of a chamber such as the lungs (lung compliance) or bladder. Compliance is expressed as a change in volume per unit change in pressure. Veins: Histology because of:
    • ↓ Lung compliance Compliance Distensibility measure of a chamber such as the lungs (lung compliance) or bladder. Compliance is expressed as a change in volume per unit change in pressure. Veins: Histology appears in:
      • Fibrosis Fibrosis Any pathological condition where fibrous connective tissue invades any organ, usually as a consequence of inflammation or other injury. Bronchiolitis Obliterans (e.g., acute respiratory surfactant Surfactant Substances and drugs that lower the surface tension of the mucoid layer lining the pulmonary alveoli. Acute Respiratory Distress Syndrome (ARDS) distress syndrome, scarring Scarring Inflammation after chemotherapy Chemotherapy Osteosarcoma)
      • ↓ Production of surfactant Surfactant Substances and drugs that lower the surface tension of the mucoid layer lining the pulmonary alveoli. Acute Respiratory Distress Syndrome (ARDS) (e.g., premature Premature Childbirth before 37 weeks of pregnancy (259 days from the first day of the mother’s last menstrual period, or 245 days after fertilization). Necrotizing Enterocolitis lungs Lungs Lungs are the main organs of the respiratory system. Lungs are paired viscera located in the thoracic cavity and are composed of spongy tissue. The primary function of the lungs is to oxygenate blood and eliminate CO2. Lungs: Anatomy, COPD COPD Chronic obstructive pulmonary disease (COPD) is a lung disease characterized by progressive, largely irreversible airflow obstruction. The condition usually presents in middle-aged or elderly persons with a history of cigarette smoking. Signs and symptoms include prolonged expiration, wheezing, diminished breath sounds, progressive dyspnea, and chronic cough. Chronic Obstructive Pulmonary Disease (COPD))
      • ↓ Flexibility of thoracic cage (e.g., scoliosis Scoliosis Scoliosis is a structural alteration of the vertebral column characterized by a lateral spinal curvature of greater than 10 degrees in the coronal plane. Scoliosis can be classified as idiopathic (in most cases) or secondary to underlying conditions. Scoliosis, cerebral palsy Cerebral palsy Cerebral palsy (CP) refers to a group of conditions resulting in motor impairment affecting tone and posture and limiting physical activity. Cerebral palsy is the most common cause of childhood disability. It is caused by a nonprogressive CNS injury to the fetal or infant brain. Cerebral Palsy)

Clinical Relevance

  • Obstructive lung disease: group of conditions that increase resistance of airways, either small or large: Obstructive lung disease causes narrowing of the airways. The increased resistance creates more work that needs to be overcome, so patients Patients Individuals participating in the health care system for the purpose of receiving therapeutic, diagnostic, or preventive procedures. Clinician–Patient Relationship often present with increased respiratory rates and work of breathing Work of breathing Respiratory muscle contraction during inhalation. The work is accomplished in three phases: lung compliance work, that required to expand the lungs against its elastic forces; tissue resistance work, that required to overcome the viscosity of the lung and chest wall structures; and airway resistance work, that required to overcome airway resistance during the movement of air into the lungs. Work of breathing does not refer to expiration, which is entirely a passive process caused by elastic recoil of the lung and chest cage. Pulmonary Examination. Patients Patients Individuals participating in the health care system for the purpose of receiving therapeutic, diagnostic, or preventive procedures. Clinician–Patient Relationship often are unable to completely expel air during exhalation. Unless obstruction is widespread, these patients Patients Individuals participating in the health care system for the purpose of receiving therapeutic, diagnostic, or preventive procedures. Clinician–Patient Relationship can continue to have normal or near-normal oxygen saturation Oxygen Saturation Basic Procedures. Pulmonary exam findings depend on where the obstruction is along the airway Airway ABCDE Assessment. Examples include asthma Asthma Asthma is a chronic inflammatory respiratory condition characterized by bronchial hyperresponsiveness and airflow obstruction. The disease is believed to result from the complex interaction of host and environmental factors that increase disease predisposition, with inflammation causing symptoms and structural changes. Patients typically present with wheezing, cough, and dyspnea. Asthma, chronic bronchitis Chronic bronchitis A subcategory of chronic obstructive pulmonary disease. The disease is characterized by hypersecretion of mucus accompanied by a chronic (more than 3 months in 2 consecutive years) productive cough. Infectious agents are a major cause of chronic bronchitis. Rhinovirus, emphysema Emphysema Enlargement of air spaces distal to the terminal bronchioles where gas-exchange normally takes place. This is usually due to destruction of the alveolar wall. Pulmonary emphysema can be classified by the location and distribution of the lesions. Chronic Obstructive Pulmonary Disease (COPD), obstructive sleep Sleep A readily reversible suspension of sensorimotor interaction with the environment, usually associated with recumbency and immobility. Physiology of Sleep apnea, and airway Airway ABCDE Assessment foreign bodies
  • Restrictive lung disease: group of conditions that causes decrease in compliance Compliance Distensibility measure of a chamber such as the lungs (lung compliance) or bladder. Compliance is expressed as a change in volume per unit change in pressure. Veins: Histology of lungs Lungs Lungs are the main organs of the respiratory system. Lungs are paired viscera located in the thoracic cavity and are composed of spongy tissue. The primary function of the lungs is to oxygenate blood and eliminate CO2. Lungs: Anatomy, increasing amount of work needed to expand and contract lungs Lungs Lungs are the main organs of the respiratory system. Lungs are paired viscera located in the thoracic cavity and are composed of spongy tissue. The primary function of the lungs is to oxygenate blood and eliminate CO2. Lungs: Anatomy: Patients Patients Individuals participating in the health care system for the purpose of receiving therapeutic, diagnostic, or preventive procedures. Clinician–Patient Relationship are unable to completely stretch the lungs Lungs Lungs are the main organs of the respiratory system. Lungs are paired viscera located in the thoracic cavity and are composed of spongy tissue. The primary function of the lungs is to oxygenate blood and eliminate CO2. Lungs: Anatomy to breathe in sufficient air. Restrictive lung disease usually affects the entire lung parenchyma and presents with increased respiratory rate Respiratory rate The number of times an organism breathes with the lungs (respiration) per unit time, usually per minute. Pulmonary Examination and work of breathing Work of breathing Respiratory muscle contraction during inhalation. The work is accomplished in three phases: lung compliance work, that required to expand the lungs against its elastic forces; tissue resistance work, that required to overcome the viscosity of the lung and chest wall structures; and airway resistance work, that required to overcome airway resistance during the movement of air into the lungs. Work of breathing does not refer to expiration, which is entirely a passive process caused by elastic recoil of the lung and chest cage. Pulmonary Examination, as well as decreased oxygen saturations. Examples include neonatal respiratory distress syndrome Neonatal Respiratory Distress Syndrome Respiratory distress syndrome (RDS), also known as hyaline membrane disease, is caused by the lack of adequate pulmonary surfactant production in an immature lung. The syndrome is most commonly seen in preterm infants. Neonatal Respiratory Distress Syndrome, pulmonary fibrosis Pulmonary Fibrosis Idiopathic pulmonary fibrosis is a specific entity of the major idiopathic interstitial pneumonia classification of interstitial lung diseases. As implied by the name, the exact causes are poorly understood. Patients often present in the moderate to advanced stage with progressive dyspnea and nonproductive cough. Pulmonary Fibrosis, and sarcoidosis Sarcoidosis Sarcoidosis is a multisystem inflammatory disease that causes noncaseating granulomas. The exact etiology is unknown. Sarcoidosis usually affects the lungs and thoracic lymph nodes, but it can also affect almost every system in the body, including the skin, heart, and eyes, most commonly. Sarcoidosis.
  • Mixed lung disease: Lung diseases often have elements of both restrictive and obstructive pathologies. The most common example of mixed lung disease is cystic fibrosis Cystic fibrosis Cystic fibrosis is an autosomal recessive disorder caused by mutations in the gene CFTR. The mutations lead to dysfunction of chloride channels, which results in hyperviscous mucus and the accumulation of secretions. Common presentations include chronic respiratory infections, failure to thrive, and pancreatic insufficiency. Cystic Fibrosis, where airways are narrowed and the lung parenchyma is stiffened.

References

  1. Hall, J. E. (2015). Guyton and hall textbook of medical physiology, 13th ed.. W. B. Saunders.
  2. OpenStax College. (2013). Anatomy and physiology. OpenStax. http://cnx.org/content/col11496/latest/ 
  3. Levitzky, M. G. (2017). Mechanics of breathing. Chapter 2 in Pulmonary Physiology, 9th ed. New York: McGraw-Hill Education. https://accessmedicine.mhmedical.com/content.aspx?bookid=2288&sectionid=178856534
  4. Levitzky, M. G. (2017). Alveolar ventilation. Chapter 3 in Pulmonary Physiology, 9th ed. New York, NY: McGraw-Hill Education. https://accessmedicine.mhmedical.com/content.aspx?bookid=2288&sectionid=178856748

USMLE™ is a joint program of the Federation of State Medical Boards (FSMB®) and National Board of Medical Examiners (NBME®). MCAT is a registered trademark of the Association of American Medical Colleges (AAMC). NCLEX®, NCLEX-RN®, and NCLEX-PN® are registered trademarks of the National Council of State Boards of Nursing, Inc (NCSBN®). None of the trademark holders are endorsed by nor affiliated with Lecturio.

Study on the Go

Lecturio Medical complements your studies with evidence-based learning strategies, video lectures, quiz questions, and more – all combined in one easy-to-use resource.

Learn even more with Lecturio:

Complement your med school studies with Lecturio’s all-in-one study companion, delivered with evidence-based learning strategies.

User Reviews

¡Hola!

Esta página está disponible en Español.

🍪 Lecturio is using cookies to improve your user experience. By continuing use of our service you agree upon our Data Privacy Statement.

Details