Anatomy and Physiology Series: Respiratory physiology at rest and during speech (or singing)

Most A&P classes typically start off with anatomy, but I feel that some introduction into physiology at the start can be a big help bringing the "big picture" together as you learn. So here we go! 

Now, the very most basic biological function of respiration is pretty obvious to most of us today: It takes in oxygen and diffuses it to the blood stream while getting rid of carbon dioxide during the gas exchange in the lungs. So how does the gas get into the lungs to begin with? Physics, of course!...okay, there's some muscular effort that takes place too, but we'll get to that later...

The lungs are a very spongy tissue that would deflate if they weren't attached to the surrounding tissue in some way. The lungs, inner thorax*, and the diaphragm are all covered in pleural (connective tissue) lining, but the lining around the lungs maintains a strong negative pressure, called intrapleural pressure, which sort of "suction cups" the lungs to the tissue. This pressure is always negative...which is a good thing. If it ever changes, you end up with a collapsed lung, and, as anyone who's watched House one too many times knows, a collapsed lung ain't a very good thing to have. 

*Quick anatomy side-note, if you didn't click the link: The thorax is the name given the space between our head and our abdomen, minus the neck...so basically our chest. See? It's that "name something fancy for specificity's sake" coming back to bite us!

Thanks to this intrapleural pressure, the lungs both expand when the thorax expands and decrease in size as the thorax decreases. That is very convenient for us, because it means we can take in air during our resting state relatively easily. How do we do that? (Warning: You're about to be physics-ed...um, yeah.) In a state of rest, inhalation is where we exert force, i.e. muscular effort, to overcome the effects of gravity on pulling our chest down. So we've got to contract something to expand our thorax (hint: This is where the diaphragm and external intercostals come into play). Expiration, while at rest, utilizes the principles of elasticity and gravity which make it a passive act. (Elasticity is also a principle from physics where a material put under strain or stress will return to it's original state after the stress is removed. We'll come back to it when we talk about the physics of sound in the future. But what's most important for now is to understand that your muscles are put under strain by your nervous system when they are told to contract, and they will return to their original resting state once active contraction ceases.) 

The fancy-pants name for the principle governing the intake of air into the lungs is called Boyle's law, which states that as the as the volume of a chamber (for us, the lungs) increases, the pressure inside the chamber will decrease. So when you expand your thorax through use of your diaphragm and external intercostal muscles (among others), the volume of the lungs increases, air pressure inside the lungs decrease and becomes more negative than atmospheric pressure. Air will always move from areas of high pressure to areas of lower pressure, and so, when negative (less) pressure is created in the lungs, air rushes in. This is inhalation at work when you're just sitting and hanging out on your couch, like I am. Exhalation, in my current state, involves the relaxation of my diaphragm and external intercostal muscles, which, due to gravity, decreases the volume of my lungs by decreasing their size. This causes air pressure in my lungs to increase and become more positive than atmospheric pressure, which then causes the air molecules to rush out to freedom!(...or where ever those air molecules like to go on a Saturday night. I'm not judging.) The key to this: Air will always move from an area of higher pressure (smaller cavity) to an area of lower pressure (larger cavity). Might want to remember that for later, cause pressure is a big deal when we get to laryngeal physiology too.

Big farting deal, right? What the heck does this have to do with breathing for singing or speech, or whichever it is I do on a daily basis? Well, it does have a good amount to do with how we want to use our muscles, and which muscles we want to use while we sing. Here's a fun little exercise from my A&P textbook I sighted below*: "Close your eyes and breathe in as deeply as you can and hold it for a few seconds. Feel how much pressure you are fighting to hold your chest in that position. Next, take a quiet breath (interjection: Like me sitting on the couch) and hold it: Do you feel the difference in pressure?" Yes. Yes I do. Thank you Drs. Seikel, King, and Drumright!

So why does that happen? Well, the forces that restore your thorax to it's resting position, elasticity and gravity, generate their own pressure on the situation, much like when your manager's manager shows up at your crummy day job. The recoil that happens on exhalation obeys those forces rather well when left alone, but if you want to extend that exhalation, you've got to exert more effort. Like my lovely little text book says here, "The greater you distend or distort the material, the greater is the force required to hold it in that position and the greater is the force with which it returns to rest." So the more you want to hold back your exhale, the more muscular effort you will need to hold it back, and if you want to keep it at a steady flow while extending it, you've got to exert a great deal of flexible yet strong control, since what your body really wants is to give in to elasticity and gravity and let out a fast, big "sigh" of breath (much like what I was doing in my my-teacher-is-in-such-great-shape-that-she-has-no-idea-how-much-she-is-kicking-our-butts yoga class earlier today). 

This is why "breath support" is such a HUGE deal in the singing world. This, and little bit of the relationship between the abdomen and the larynx that we'll go over later, is the key basis of any excellent vocal technique. 

*And if you guys would love to have this material in the oh-so-user-friendly format of a $100+ textbook, here it is: Seikel, J. A., King, D. W., & Drumright, D. G. (2010). Anatomy and physiology for speech, language, and hearing. Clifton Park, NY: Delmar.

--But all joking aside, this is a fantastic book that I highly recommend to any serious voice-user and/or teacher of voice. I'm not ever selling my copy to anyone...unless I'm just upgrading to the next edition when they come out with it.