Lung ventilation and volume measurement intricately interweave to form the foundation of our understanding of respiration. With these processes, oxygen is exchanged for carbon dioxide, supporting the vital functions of every cell in our bodies.
Lung Ventilation
The Diaphragm
The diaphragm is a unique muscle, specially designed for the task of breathing.
- Structure & Location
- Thin, dome-shaped muscle.
- Sits below the lungs, dividing the thoracic and abdominal cavities.
- Role in Inhalation
- When it contracts, the diaphragm moves downwards.
- This increases the volume of the thoracic cavity, thereby decreasing the pressure inside.
- As a result, air rushes into the lungs to equalise the pressure.
- Role in Exhalation
- Relaxes and returns to its dome-shaped position.
- The thoracic cavity volume decreases, increasing the pressure, which forces air out of the lungs.
Image courtesy of VectorMine
Intercostal Muscles
These are groups of muscles that run between the ribs, assisting in the expansion and contraction of the chest wall during breathing.
- Types & Locations
- External intercostal muscles: Situated outwardly and assist in inhalation.
- Internal intercostal muscles: Located closer to the lungs and aid in exhalation.
- Functionality
- As the external muscles contract, the rib cage is elevated and pulled outward, aiding the diaphragm in expanding the thoracic cavity.
- Conversely, when the internal muscles contract, they pull the rib cage downward and inward, aiding in exhalation.
Abdominal Muscles
While these aren't primary muscles of respiration, they play an auxiliary role, especially during active or forced breathing.
- Contribution to Exhalation
- Contract during activities such as coughing, singing, or heavy exercise.
- This increases abdominal pressure, pushing the diaphragm upwards, leading to more forceful exhalation.
Ribs
The ribcage provides structural support to the thoracic cavity and plays a role in breathing.
- Composition & Structure
- 12 pairs of curved bones encasing the lungs and heart.
- Connected to the spine at the back and the sternum at the front.
- Functionality in Breathing
- Their flexibility allows them to move in conjunction with the intercostal muscles.
- During inhalation, they move upward and outward, and during exhalation, they move downward and inward.
Image courtesy of Cenveo
Measurement of Lung Volumes
Lung volumes offer a detailed perspective on respiratory health. Various components collectively paint a comprehensive picture of lung efficiency.
Tidal Volume (TV)
- Represents the regular volume of air displaced between normal inhalation and exhalation.
- Usually equates to about 500 mL in an average adult.
- Critical to everyday functioning as it's the air volume we breathe in and out while resting.
Vital Capacity (VC)
- Represents the total volume of air that can be expelled from the lungs after a deep inhalation.
- It’s the sum of inspiratory reserve volume, tidal volume, and expiratory reserve volume.
- Often used in clinical settings to determine respiratory health. A reduced VC might indicate respiratory muscle weakness or lung diseases.
Inspiratory Reserve Volume (IRV)
- This volume represents the additional air that can be inhaled with effort after a typical inhalation.
- In a healthy adult, this volume ranges from about 2,500 mL to 3,000 mL.
- It offers an understanding of the maximum amount one can inhale after a regular breath, which is crucial during physical exertion.
Expiratory Reserve Volume (ERV)
- Represents the extra volume of air that can be actively expelled after a passive exhalation.
- In a healthy adult, this usually lies between 1,000 mL to 1,500 mL.
- This volume gives insight into how much additional air can be exhaled when needed, such as during rigorous activities.
Methods of Measurement
- Spirometry: The gold standard for measuring lung volumes.
- Individuals breathe into a mouthpiece connected to a machine that records air volumes and flow rates.
- Often used to diagnose conditions like asthma, bronchitis, and emphysema.
- Can also track the progression of lung diseases and the efficacy of treatments.
Spirometer.
Image courtesy of BruceBlaus
Factors Influencing Measurements
Lung volumes can vary based on several factors:
- Age: As one ages, lung tissue loses elasticity, leading to a reduction in certain lung volumes.
- Physical Fitness: Athletes or those regularly engaged in aerobic activities often have greater lung capacities.
- Height: Taller individuals generally have larger lung capacities.
- Altitude: Those living at higher altitudes might develop increased lung capacities to compensate for reduced oxygen in the air.
- Smoking: Chronic smokers often have reduced lung capacities due to damaged lung tissue.
FAQ
When the diaphragm or intercostal muscles become fatigued or damaged, breathing can become impaired. The diaphragm, being the primary muscle of respiration, is responsible for the majority of lung expansion during inhalation. If it becomes weakened or damaged, the individual might experience shallow breathing and reduced lung capacity, making it difficult to get enough oxygen. Similarly, the intercostal muscles aid in the elevation and depression of the rib cage during breathing. Damage or fatigue to these muscles can restrict rib movement, again leading to shallow breaths. Chronic conditions or injuries affecting these muscles can necessitate the use of mechanical ventilation to support breathing.
The thinness and moisture of gas-exchange surfaces play pivotal roles in facilitating efficient gas diffusion. A thin surface, such as the thin walls of the alveoli in the lungs, ensures a short diffusion path for gases. This allows oxygen and carbon dioxide to move rapidly between the air in the alveoli and the blood in the surrounding capillaries. The moisture on these surfaces, on the other hand, aids in the dissolution of gases. Gases like oxygen dissolve more easily in a liquid medium before diffusing across cell membranes. Thus, having a moist surface optimises the rate at which gases can be exchanged, ensuring efficient respiratory function.
Regular exercise can have positive effects on lung volumes and capacities. Engaging in aerobic activities strengthens the respiratory muscles, particularly the diaphragm and intercostal muscles. This strength translates to increased efficiency during inhalation and exhalation. Over time, exercise can enhance tidal volume, enabling a larger volume of air to be exchanged during regular breathing. Furthermore, the inspiratory reserve volume and vital capacity might also see improvements, allowing for deeper breaths and more substantial exhalations. Regular exercise doesn't necessarily increase the total lung capacity; instead, it improves the efficiency and effectiveness of each breath, enhancing oxygen delivery to tissues and aiding in the removal of waste gases.
The ribcage, comprising 12 pairs of curved bones, is designed to protect vital organs such as the heart and lungs. Its structural elasticity aids in the breathing process. The rib bones are connected to the spine at the back and come together at the sternum in the front. This connection allows the ribs to move in a coordinated manner during inhalation and exhalation. As the external intercostal muscles contract during inhalation, the ribs are elevated and pulled outward, thus increasing the volume of the thoracic cavity. Conversely, during exhalation, the internal intercostal muscles cause the ribs to move downward and inward, decreasing the thoracic cavity volume and aiding in expelling the air.
A high surface area in the lungs, particularly in the alveoli, is essential for efficient gas exchange. The alveoli, tiny air sacs within the lungs, are where the actual exchange of oxygen and carbon dioxide occurs. The extensive surface area allows a greater amount of oxygen to diffuse from the alveoli into the surrounding blood capillaries and, simultaneously, permits a large quantity of carbon dioxide to diffuse from the blood into the alveoli to be exhaled. Without this vast surface area, the rate of gas exchange would be limited, hindering the body's ability to deliver sufficient oxygen to tissues and remove waste gases effectively.
Practice Questions
During inhalation, the diaphragm contracts and moves downwards, increasing the volume of the thoracic cavity. This results in a decrease in pressure inside the cavity, allowing air to be drawn into the lungs. Concurrently, the external intercostal muscles contract, elevating the rib cage and further augmenting the thoracic cavity’s volume. During exhalation, the diaphragm relaxes and reverts to its dome-shaped position, decreasing the thoracic cavity’s volume and increasing the pressure, which propels air out. Similarly, the internal intercostal muscles contract, pulling the rib cage downward and inward, further aiding in the expulsion of air from the lungs.
Tidal volume (TV) refers to the standard amount of air inhaled or exhaled during regular breathing, usually amounting to about 500 mL in an average adult. It signifies the volume of air exchanged during passive respiration when an individual is at rest. In contrast, vital capacity (VC) represents the total volume of air that can be forcefully expelled after a maximal inhalation. It is the cumulative sum of the inspiratory reserve volume, tidal volume, and expiratory reserve volume. Essentially, while TV denotes the routine volume of air exchanged during regular breathing, VC provides a comprehensive measure of the maximum amount of air the lungs can hold and expel.
