# 1.3.1 Mechanism of Ventilation 2 Flashcards

What is the formula for resistance?

R = Pressure difference/flow

What is the formula for total airway resistance?

What is the site of highest airway resistance?

Nose

Pulmonary capillaries make up how much of the total resistance?

less than 10% due to high cross sectional area

What are the two factors that control the cross-sectional area of the airways?

Neurohumoral factors affeting the tone of bronchial smooth muscle

Factors influencing the pressure difference across the airway wall

What are the affectors of bronchial smooth muscle tone?

What are each of the shaded areas?

What is the vital capacity?

the volume of air that can be exhaled in a maximal expiration after having inhaled maximally

What is the VC normally measured as?

The vital capacity is usually measured as the Forced Vital Capacity (FVC). In the FVC the patient is not only asked to empty the lungs as completely as possible, but also to do it as rapidly as possible.

What is important about the FEV1/FVC? What can it indirectly determine?

The FEV1 is the volume that can be exhaled during the first second of an FVC maneuver. The normal value for an FEV1/FVC is roughly 0.7 to 0.8. Deviations from this value can provide an indirect estimate of airway resisitance.

For a patient with increased airway resistance, how will this effect their value for FEV1?

They will have a lower value for FEV1 due to the increased airway resistance.

What is the reason for airflow decreasing with lung volume?

The reason that the airflow decreases with lung volume is that the **airway resistance increases throughout expiration**. **This is due to narrowing of the airways as the lungs become smaller**. This means that, if airway resistance is increased by disease, it is always more difficult to get air out of the lungs than get air into the lungs.

Is both of these graphs of differing effort levels, which point has the highest flow?

Explain what is also going on between the effort dependent and effort independent section.

At high lung volumes, expiratory flow depends on the expiratory effort, i.e. **flow is highest in a**, lower in b and lowest of all in c.

As expiration proceeds, and the lungs get smaller, expiratory flow becomes independent of effort. In the effort-independent part of expiration, at any given lung volume, the flow is the same no matter what the effort is.

The mechanism responsible for this is known as **dynamic airway compression, and is due to the fact that the high PPL needed to generate a high expiratory airflow tends to narrow the airways and limit the flow.**

What is the formula for flow?

Airway resistance is determined by?

Airway diameter - inverse proportion