During inhalation, is the external atmospheric pressure greater or is the intrapulmonary pressure greater?

Sep 20, 2022 Source: Cainiu Health

Dr. Guo Xiheng

Introduction

The external atmospheric pressure is greater during inhalation. At the beginning of inhalation, the pressure inside the lungs is lower than the external atmospheric pressure, allowing outside air to flow into the lungs. Similarly, during exhalation, the pressure inside the lungs is higher than the external atmospheric pressure. Breathing movements are achieved due to pressure differences between the lungs and the atmosphere, caused by the contraction and relaxation of respiratory muscles. During inhalation, lung pressure decreases; during exhalation, it increases.

During inhalation, the external atmospheric pressure is higher. Inhalation begins when the air pressure inside the lungs is lower than the external atmospheric pressure, allowing outside air to flow into the lungs. Conversely, during exhalation, the air pressure within the lungs becomes higher than the external atmospheric pressure. Breathing movements are achieved through the contraction and relaxation of respiratory muscles, which create a pressure difference between the air inside the lungs and the outside atmosphere. Specifically:

Inhalation and exhalation are completed due to respiratory movements that create a pressure difference between the air in the lungs and the external atmosphere. When the intrapulmonary pressure (pressure inside the lungs) is higher than the external atmospheric pressure, air is expelled from the lungs. When the intrapulmonary pressure is lower than the external atmospheric pressure, outside air enters the lungs. When the external intercostal muscles and the diaphragm relax, the ribs and sternum return to their original positions due to their own weight and elasticity, resulting in a reduction of the thoracic cavity volume. The lungs consequently recoil, causing the intrapulmonary pressure to exceed the external atmospheric pressure, leading to the expulsion of air—a passive exhalation process. Exhalation ends when the intrapulmonary pressure equals the external atmospheric pressure. Therefore, at the very moment inhalation or exhalation ends, the lung pressure equals atmospheric pressure; however, for inhalation to occur, the external atmospheric pressure must be greater than the internal lung pressure.

During inhalation, lung volume increases and pressure decreases (not increases as inaccurately stated), while during exhalation, lung pressure increases as volume decreases. Practicing proper breathing techniques benefits overall health. Diaphragmatic (abdominal) breathing is recommended: inhale slowly through the nose, allowing the abdomen to expand, hold for a few seconds, then exhale slowly through the mouth. Abdominal breathing enables fresh air to reach deeper parts of the lungs, improves oxygen supply to the body, and may help reduce excess abdominal fat.

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There is obvious pain in the heart during exhalation, but not during inhalation.

There may be obvious heart pain during exhalation, while inhalation is painless. This could be caused by factors such as cold exposure, pleurisy, intercostal neuralgia, angina pectoris, or rib fractures, and treatment should be based on the specific condition. Additionally, it is commonly seen in diseases such as myocarditis, pericardial effusion, and myocardial ischemia, which require active treatment. Patients with heart problems should avoid staying up late, maintain a balance between work and rest, and consume more nutritious foods rich in vitamins.