Ventilation – Introduction

Ventilation

The term ventilation refers purely to the movementA fundamental property of life involving motion of the body or its parts. of air. It does not refer to the exchange of gases. I have pictured here a fan that only moves air Similar to the process of ventilation. I also have pictured here a protist which is a one-celled organismA living individual made up of cells. that is essentially a parasite. It gets delivered to human via a mosquito bite from a mosquito carrying the eggs of this parasite. They then grow and multiply in your blood. This is a species called Trypanosomas, known to cause sleeping-sicknesses. Basically this little protist likes to hug your red blood cellsThe basic structural and functional units of life.. It hugs them so tightly that they burst. So, as you sleep, you keep ventilating. However, the oxygen you get during external or alveolar respirationThe process of gas exchange, including ventilation, external and internal respiration. never reaches your cells.

Respiratory Muscles

Listen to yourself take a few breaths. Right now, you are probably doing quiet breathingNormal, passive breathing at rest., if you are sitting and studying.  If you are exercising and listening to this, you are probably doing active breathingA type of breathing that involves conscious effort, engaging accessory muscles for deeper or more fo.  I assigned these names not based on your state of exertion. They are based on the use of muscles to achieve both types of breathing.

In quiet breathing, which is what you do all the time, you are only using your diaphragm. You are also using the external intercostal muscles between your ribsCurved bones forming the rib cage; articulate with thoracic vertebrae and most with the sternum..  You use these two for inhalation and you use nothing for exhalation.  Nothing.  The lung’s elasticity and its ability to recoil facilitate exhalation. This means you don’t need to use any muscles to exhale.  Quite efficient. 

In active or forced breathing, you continue to use the diaphragm and the external intercostal muscles to inhale. However, you also use accessory muscles to aid the diaphragm and external intercostalsElevator Between ribs; lifts rib cage during breathing in. in inhaling. The muscles you use in quiet breathing to inhale are called your primary respiratory muscles. Additional muscles come into play. They include the scalenes or the sternocleidomastoidFlexor / Rotator From sternum and clavicle to skull behind the ear; turns and bends the head. from the neckNarrow region just below the head; common fracture site., the pectoralis minorDepressor / Protractor Under pectoralis major; pulls shoulder blade forward and downward. from the chest, and the rectus abdominis from the belly. These are called accessory muscles. These muscles can be recruited to help. You do not need to consciously recruit these accessory muscles. The centers of your brain that control respiration will recruit these muscles as needed.

 It is possible to be doing active or forced breathing and not realize it. In conditions such as asthmaA chronic condition characterized by airway inflammation, narrowing, and excessive mucus production, and bronchitisInflammation of the bronchi, leading to mucus buildup, coughing, and breathing difficulties., accessory muscles are usually recruited for breathing. However, it is not noticeable. These accessory muscles in active or forced breathing can contribute to the work of the diaphragm and external intercostals. These accessory muscles can also be used in exhalation. But remember again that there are no primary musclesThe diaphragm and external intercostals, responsible for quiet breathing. for exhalation. This is because exhalation happens due to the elasticity of your lungs.

Pressures

What I just explained in the previous slide makes sense now. I guarantee this. However, I will soon make it more complicated.  Let’s give a few things some abbreviations so you don’t have to keep writing it out in your notes.  Dalton’s lawStates that the total pressure of a gas mixture is the sum of the partial pressures of its individua told us about pressures in the atmosphere.  Let’s call that Patm.  There is also pressureThe force exerted by gases in the respiratory system, affecting airflow and gas exchange. in the alveoliMicroscopic air sacs in the lungs where gas exchange occurs between air and blood. of the lung.  I’m going to call that Ppul.  The pul stands for pulmonary.  But to make this more complicated, we also have to consider the pressure in the intrapleural space or Pip.  No, we don’t move any air into the intrapleural space. Remember that it is a closed cavity bounded by the pleuraThe double-layered membrane surrounding the lungs and lining the thoracic cavity..  But, I will use this space to create a pressure gradient to inflate the alveoli.’’

Here is a very important thing to remember.  You can’t manipulate pressures, especially not atmospheric pressure!  But, you can manipulate the volume on your lungs.  Do that right now by taking an extra large breath or exhaling for a few seconds longer.  You may not be able to change air pressure directly. However, you can control the volume of your lungs. According to Boyle’s Law, this will create an inverse effect on pressure.