Describe the structure & function of lungs
I've described the lungs, the pleural membranes, the pleural cavity and the thoracic cavity that they sit in in a previous post for ANHB2212. That post didn't cover the structure of the airways though, so a quick note here. As you probably well know, the airways get thinner and thinner as you go down the pulmonary "tree," until you get to the alveoli where the walls are only one cell thick so as to facilitate gas exchange. As you move back up the "tree" the walls become thicker, have more smooth muscle and ciliated cells (cilia are like little "hairs" that can beat to get dust and bacteria and other unwanted crap out of our lungs) and eventually also have cartilaginous rings to stop the airways from collapsing. The bronchioles are the level at which the highest resistance occurs, kinda like how the arterioles are the level at which the highest resistance occurs in the pulmonary circuit. This is because bronchioles are relatively thin (compared to the bronchi and trachea), but they don't have as large a surface area as alveoli do.
Discuss inspiration & expiration
I've pretty much already done this in my post for ANHB2212. Moving on...
List lung volumes & average values
There's lots of important terminology that you need to know here.
Firstly, the total lung capacity is basically the number of litres that your lungs can hold at full volume. This is usually around 5700mL (for a healthy young adult male). (Yes, pretty much all the values I'm going to give are the averages for a healthy young adult male.)
The next important term is... eh, screw it, here's a table because I feel like showing off my madddd HTML skillz.
| Term | Definition | Average value |
| Tidal volume (VT) | The amount of air moved in and out of the lungs with each normal breath | 400-500mL |
| Inspiratory reserve volume (IRV) | The amount of air that can be inspired above and beyond the tidal volume during maximum inspiration. | 3000mL |
| Inspiratory capacity (IC) | The total amount of air that can be expired into the lungs following a normal quiet expiration. Equal to IRV + VT. | 3500mL |
| Expiratory reserve volume (ERV) | The amount of air that can be expired past the tidal volume. | 1000mL |
| Residual volume (RV) | The amount of air remaining after maximum forced expiration. | 1200mL |
| Functional residual capacity (FRC) | The amount of air remaining after a normal tidal expiration. Equal to RV + ERV. | 2200mL |
| Vital capacity (VC) | The total amount of air that can be moved in and out of the lungs. Equal to IRV + VT + ERV. | 4500mL |
| Forced expiratory volume in 1 second (FEV1) | The maximum amount of air that can be expired in one second following a forced inspiration. | 80% of VC |
Describe spirometry
Spirometry is a useful tool for testing someone's lung function. It basically involves breathing into a tube which is linked up to a computer that records how much air is moved in and out. I'm not 100% sure on the mechanics on how it works, but I don't think that's super important for now. Conventional spirometry can determine all of the above values except for residual volume and functional residual capacity. Functional residual capacity can be determined by the helium dilution technique, however, and once that's determined, residual volume can also be determined (as residual volume is simply FRC - ERV).
So what is this helium technique? The helium dilution technique involves first adding a known amount of helium to a closed system while the subject breathes normally through another tube. The concentration of helium in this system is then recorded. Then the tube that the subject is breathing through is added to the closed system, so that their lungs essentially become part of the system. The new concentration of helium is then recorded. A variant on the old faithful C1V1 = C2V2 can then be used to work out the functional residual capacity of the subject's lungs.
This variant is, quite simply, C1V1 = C2(V1 + V2) as the second volume is the original volume plus the FRC (which is V2).
Discuss the determinants of lung volume
There are many determinants of lung volume, such as age, gender, disease states, altitude (I guess people develop bigger lungs in order to deal with the lower oxygen concentration?) and so on. Body size also matters (though that's determined by age and gender as well). I feel like I've been kinda unfairly shafted here because I'm a little girl who plays clarinet. Oh well.
Determine pulmonary & alveolar ventilation
Pulmonary ventilation is, quite simply, how much air is moving in and out of the lungs. The amount of air moved in and out per minute can be denoted by VE, except that V is meant to have a dot on top (unfortunately my epic mad skillz in HTML don't go that far). Under resting conditions, this is simply the tidal volume VT multiplied by the breathing frequency, Bf (which is normally around 12 breaths per minute). Therefore, VE = VT * Bf.
Alveolar ventilation is pretty similar, but with one difference: alveolar ventilation is about the amount of air that actually takes place in gas exchange. You see, not all the air inspired gets to take place in gas exchange. About 150mL per breath is "anatomical dead space," in that it's inspired, but doesn't actually do anything. It's denoted by VA, again with a dot on top of the V. (Just use your imagination, I guess.) The equation for this is pretty similar for that of pulmonary respiration, but you have to take the 150mL of anatomical dead space into account: VA = (VT - 150mL) * Bf.
First post done! If there's anything that you still don't understand, check out http://nutrition.uvm.edu/bodycomp/uww/lung-vol.html: it explains a lot of the basic terminology and spirometry stuff pretty well.
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