Airway Resistance – Factors Affecting Pulmonary Ventilation (Nursing)

00:02 So there are three physical factors that are going to influence our pulmonary ventilation.

00:09 These factors are going to influence how easy it is for air passage in and out of our respiratory system.

00:18 The first is our airway resistance.

00:21 Second is going to be alveolar surface tension, and third is going to be lung compliance.

00:28 So let's take a look at each of these three.

00:32 So starting with airway resistance, friction is a major non-elastic source of resistance to gas flow and friction does occur in our airways.

00:45 The relationship between air flow pressure and resistance can be described in the following mathematical equation.

00:54 Flow is equal to the change in pressure divided by the resistance.

01:01 Because the resistance is in the denominator the higher the resistance the lower the air flow.

01:09 So in this equation our change in pressure is going to be the pressure gradient between the atmosphere and the alveoli.

01:19 And this change is usually about 2 millimeters of mercury, But even this very small difference is sufficient enough to move in about 500 milliliters of air.

01:32 Also gas flow is going to be inversely related to resistance again, because the higher the resistance the lower the hair airflow and this kind of makes sense the more you resist that ability for air to flow then the less flow there will be.

01:51 So resistance in the respiratory tree is usually insignificant for two major reasons.

01:58 The first reason is that the diameters of the airways in the first part of the conducting zone are pretty big they're pretty large and there's just not a lot of friction or resistance.

02:09 Secondly, because of the progressive branching of the airways as they get smaller even though they're getting smaller there's still an increase in the total cross-sectional area are places where the air can go.

02:26 So any resistance is usually going to occur in the medium sized bronchi, but this resistance is going to start to disappear at the terminal bronchioles where diffusion is what drives gas movement instead of the actual air flow.

02:44 So in these terminal bronchioles, the resistance is actually going to be controlled more so byour autonomic nervous system and the smooth muscles which are going to allow for constriction and dilation, so it's not really being controlled by the airflow but more so by the our autonomic nervous system instead.

03:06 All right.

03:07 So if we look at the relationship of resistance as the airwaves branch, we find that most of the resistance that we have in our airways will beat the medium sized bronchi.

03:19 But this is quickly dissipated as more branching occurs.

03:24 But once we reach the respiratory zone, resistance is going to be zero because again now it is our autonomic nervous system and smooth muscles that are controlling resistance or airflow and not necessarily the air coming in from outside.