FAQ: Why Resistance Is Less During Inspiration Than Expiration?

As the radius of the airways increases, resistance to airflow is lower during this inspiratory phase. Conversely, in expiration, the intrathoracic pressure increases due to the lower volume of the thoracic cavity. This pressure leads to narrowing of the smaller airways, so resistance is higher during expiration.

What causes a decrease in airway resistance?

This turbulent airflow increases airway resistance. Helium is seven-times less dense than air, and when mixed with oxygen to form heliox, the lower density causes the turbulent airflow to revert to a state of laminar flow, decreasing airway resistance.

What happens during inspiration vs expiration?

The processes of inspiration (breathing in) and expiration (breathing out) are vital for providing oxygen to tissues and removing carbon dioxide from the body. Inspiration occurs via active contraction of muscles – such as the diaphragm – whereas expiration tends to be passive, unless it is forced.

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Which factors increase or decrease airway resistance?

Factors which affect airway resistance by affecting airway diameter

  • Increased smooth muscle tone. Bronchospasm. Irritants, eg. histamine. Parasympathetic nervous system agonists.
  • Decreased smooth muscle tone. Bronchodilators. Sympathetic nervous system agonists.

Why is resistance highest in medium sized bronchi?

While a single small airway provides more resistance than a single large airway, resistance to air flow depends on the number of parallel pathways present. For this reason, the large and particularly the medium-sized airways actually provide greater resistance to flow than do the more numerous small airways.

Why the airway resistance is more during expiration?

Inspiration vs Expiration On inspiration, the positive pressure within the alveoli and small airways causes their diameter to increase, and therefore resistance to decrease. The opposite is true for expiration, as airways narrow due to the reduced pressure, thus increasing resistance.

What factors increase airway resistance?

Multiple factors can influence airway resistance, including airflow velocity, the diameter of the airway, and lung volume. These are some of the most significant contributing factors and will be discussed further on how these variables exert change and why this is important for managing patient airways.

Why does inspiration decrease intrathoracic pressure?

Inspiration drops intrathoracic pressure, dilates the thoracic vena cava, and acutely decreases atrial filling. Cardiac output falls, and consequently arterial pressure falls. The drop in arterial pressure reduces stretch on the arterial baroreceptors, causing a reflex increase in heart rate.

Why is alveolar pressure negative during inspiration?

As the intrapleural and alveolar pressure become increasingly negative due to the expansion of the chest cavity during inspiration, air from the atmosphere flows into the lungs which allow the lung volume to increase and participate in gas exchange.

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What happens to the diaphragm during inspiration and expiration?

Upon inhalation, the diaphragm contracts and flattens and the chest cavity enlarges. This contraction creates a vacuum, which pulls air into the lungs. Upon exhalation, the diaphragm relaxes and returns to its domelike shape, and air is forced out of the lungs.

Does forced expiration increase airway resistance?

Airway resistance increases during expiration. During forced expiration, when intrapleural pressures become positive, small airways are compressed (dynamic compression) and may even collapse.

How does airway resistance affect pulmonary ventilation?

Another important fact is that airway resistance is inversely related to lung volumes because the airways expand a bit as they inflate, so the airways in a fully inflated lung will have lower resistance than a lung after exhalation.

Why is airway resistance insignificant in normal breathing?

The smallest airways contribute very little to resistance, because the combined cross-sectional area of these airways is much larger than that of the intermediate bronchi. Airway resistance is determined by lung volume, bronchial smooth muscle tone, and dynamic airway compression.

Why is airway resistance insignificant in relationship to gas flow?

Airway resistance is insignificant in relationship to gas flow because: the gas flow stops in the medium-sized bronchioles and diffusion takes over; therefore, airway resistance is no longer an issue.

What is the relationship between airflow resistance and airway diameter?

Since resistance is inversely proportional to the radius to the fourth power, anything that changes the radius or diameter of the airway will tremendously affect resistance to airflow.

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