Under what internal conditions does air tend to flow into the lungs? The simple answer is that air flows into the lungs because of a pressure gradient. But what creates this pressure gradient?

In this article, we’ll explore the different internal conditions that cause air to move from the environment into the lungs. There are two main forces at work: the atmospheric pressure and the diaphragm.

What Causes Air to Flow Into the Lungs?

The atmospheric pressure is the pressure of the air surrounding us. It’s what we feel when we put our hand out the car window or take a deep breath in. The atmospheric pressure is pushing down on our bodies constantly.

The diaphragm is a muscle located at the bottom of the lungs. When it contracts, it increases the volume of the thoracic cavity, which decreases the pressure inside the cavity. This decrease in pressure creates a gradient that causes air to flow into the lungs.

Process of Breathing

The act of breathing is an involuntary muscle movement controlled by the respiratory center in the brain. This center sends signals to the muscles that control the movement of the diaphragm and the intercostal muscles.

The diaphragm is a large, dome-shaped muscle that separates the chest cavity from the abdominal cavity. The intercostal muscles are a group of muscles that run between the ribs.

When the respiratory center sends signals to these muscles, they contract and cause the chest cavity to expand. This expansion of the chest cavity decreases the pressure inside the chest, which causes air to flow into the lungs.

Internal Conditions for Breathing

The main internal conditions that cause air to flow into the lungs are the pressure gradient, respiratory rate, and tidal volume.

The pressure gradient is the pressure difference between the atmospheric and intrapulmonary pressures. The atmospheric pressure is the pressure of the air surrounding the lungs, and the intrapulmonary pressure is the pressure inside the lungs.

The respiratory rate is the number of breaths taken per minute, and the tidal volume is the amount of air inhaled or exhaled with each breath.

What Drives Air Into the Lungs?

The pressure gradient is the main force that drives air into the lungs. The atmospheric pressure is greater than the intrapulmonary pressure, so air flows from the atmosphere into the lungs.

The respiratory rate and tidal volume also affect airflow into the lungs. When the respiratory rate increases, more air is exhaled, decreasing intrapulmonary pressure. This decrease in intrapulmonary pressure causes air to flow back into the lungs during the next inspiration.

The tidal volume that enters the lungs depends on the respiratory rate and the amount of air exhaled with each breath. When the tidal volume is large, more air is exhaled and

Types of Pressure That Control Breathing

Four types of pressure can affect the lungs and the process of breathing:

  1. Atmospheric pressure
  2. Intra-alveolar pressure
  3. Intrapleural pressure
  4. Transpulmonary pressure

Atmospheric Pressure

Atmospheric pressure is the pressure of the air surrounding the lungs. Atmospheric pressure at sea level is measured at 760 mmHg.

When the pressure drops below 760 mmHg, it is considered to be negative pressure. Positive pressure, on the other hand, is when the pressure is greater than 760 mmHg. When the pressure is equal to atmospheric pressure, it is expressed as 0 mmHg.

Intra-Alveolar Pressure

Intra-alveolar pressure is the pressure inside the alveoli, which are the tiny sacs in the lungs where gas exchange occurs. This pressure is affected by the respiratory rate and tidal volume.

The respiratory rate is the number of breaths taken per minute, and the tidal volume is the amount of air inhaled or exhaled with each breath.

When the respiratory rate increases, more air is exhaled, which decreases the intrapulmonary pressure. This decrease in intrapulmonary pressure causes air to flow into the lungs.

The tidal volume also affects the flow of air into the lungs. When the tidal volume increases, more air is inhaled, which increases the intrapulmonary pressure. This increase in intrapulmonary pressure decreases the pressure gradient, which causes air to flow into the lungs.

Intrapleural Pressure

Intrapleural pressure is the pressure inside the pleural cavity, which is the space between the lungs and the chest wall. This pressure is affected by the intercostal muscles and the diaphragm.

The intercostal muscles are the muscles between the ribs, and the diaphragm is a muscle that separates the thoracic cavity from the abdominal cavity.

When the intercostal muscles contract, they cause the ribs to move up and out, which increases the volume of the thoracic cavity. This increase in volume decreases the pressure inside the thoracic cavity, causing air to flow into the lungs.

Transpulmonary Pressure

Transpulmonary pressure is the difference in pressure between the intra-alveolar pressure and intrapleural pressure.

Like plateau pressure, it can be measured during mechanical ventilation by applying an inspiratory hold or occluding the exhalation port at end-inspiration for 0.5–2.0 seconds.

What is Pulmonary Ventilation?

Pulmonary ventilation is the process of moving air into and out of the lungs. The main force that drives pulmonary ventilation is the pressure gradient, which is the difference in pressure between the atmospheric pressure and intra-alveolar pressure.

This occurs when air naturally moves from an area of high pressure to an area of low pressure. When the atmospheric pressure is higher than the intra-alveolar pressure, air flows into the lungs.

Pulmonary ventilation is essential for gas exchange to occur. This is when the lungs take in oxygen while removing carbon dioxide during a breathing cycle.

Final Thoughts

The internal conditions that cause air to flow into the lungs are essential for breathing to occur. Without these conditions, the chest cavity would not expand, and air would not flow into the lungs.

Ventilation and oxygenation are essential for life, and the internal conditions that cause air to flow into the lungs play a vital role in these processes.

Check out some of our other similar articles on this topic if you want to learn more. Thanks for reading!

Written by:

John Landry, BS, RRT

John Landry is a registered respiratory therapist from Memphis, TN, and has a bachelor's degree in kinesiology. He enjoys using evidence-based research to help others breathe easier and live a healthier life.

References

  • Chen, Long, and Xia Zhao. “Characterization of Air Flow and Lung Function in the Pulmonary Acinus by Fluid-Structure Interaction in Idiopathic Interstitial Pneumonias.” National Library of Medicine, Mar. 2019, www.ncbi.nlm.nih.gov/pmc/articles/PMC6438611.
  • Campbell, Miles, and Amit Sapra. “Physiology, Airflow Resistance.” National Library of Medicine, 28 Apr. 2022, www.ncbi.nlm.nih.gov/books/NBK554401.
  • Powers, Kyle A., and Amit S. Dhamoon. “Physiology, Pulmonary Ventilation and Perfusion.” National Library of Medicine, StatPearls Publishing, Jan. 2022, ncbi.nlm.nih.gov/books/NBK539907.

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Medical Disclaimer: The information provided by Respiratory Therapy Zone is for educational and informational purposes only. It should not be used as a substitute for professional medical advice, diagnosis, or treatment. Please consult with a physician with any questions that you may have regarding a medical condition.