Breathing

Technically, the physical act of breathing is called ventilation. This includes two phases: inspiration and expiration (to be discussed later). Breathing, therefore, is just the movement of air in and out of the lungs. Some facts:

3. Breathing also helps to vent about 350 ml of water from the body each day.

1. The average resting person breathes in and out about 10 to 16 times per minute.

2. An average volume of air inspired in a “resting” breath is about 500 ml.

The lungs can expand and retract through two different ways. The first is by the downward and upward motion of the diaphragm which either lengthens or shortens the chest cavity.

contracted

relaxed

When the diaphragm contracts it moves downward so the cavity lengthens

When the diaphragm relaxes it moves upward so the cavity shortens

Intercostal musclesThe second is by elevation and depression of the ribs which is produced by the external & internal intercostal muscles. This motion increases or decreases the circumference of the chest cavity.

Contraction of the external intercostal muscles pulls the ribs

up and out thus increasing the

circumference of the chest cavity

Contraction of the internal intercostal

muscles pulls the ribs down and in thus

decreasing the circumference of the

chest cavity

At rest, ventilation is mostly diaphragm breathing but extreme conditions like strenuous exercise will increase the proportion of costal breathing to more than half. The greater the volume of inspiration &/or expiration, the greater the ratio of costal breathing.

The two breathing mechanisms are called diaphragm breathing and costal breathing and they usually work together to some degree.

diaphragmcostal costal

“Breathing in” is called inspiration while “breathing out” is called expiration. In inspiration, for example, a sequence of muscular contractions takes place that has one goal: to decrease the pressure inside the lungs below that of atmospheric pressure. Why do this?

To create a vacuum by increasing the volume of the chest cavity.

Which gas law studied in Chemistry related volume to pressure?

Boyle’s law: the volume of a given gas in inversely proportional to the pressure applied to the gas. Simply stated: Pressure goes up, Volume goes down or Pressure goes down, Volume goes up

“Active” Inspiration includes all inhalation (“normal” & “forced”)

involving muscular contraction. This is referred to as an active phase of ventilation, since it is initiated by the contraction of the diaphragm and external intercostal muscles.

Expansion of the chest cavity causes the pressure inside the lungs to drop which causes air to rush in and compensate for the partial vacuum. This makes it “active muscle”, but “passive air”.

Diaphragm

All muscles relaxed

Maximum Expiration

Maximum inspiration

Contraction of:Diaphragm &External Intercostal

“Active” muscle“Passive” air

“Passive” Expiration includes all exhalation involving muscular relaxation. This is referred to as a passive phase of ventilation, since it is initiated by the relaxation of the diaphragm and external intercostal muscles. Diaphragm

The volume of the chest cavity decreases causing the pressure inside the lungs to increase. This combined with the elastic recoil of the alveoli puts a force on the air pushing it out of the lungs thus equalizing the pressures. This makes it “passive muscle”, but “active air”.

All muscles relaxed

Maximum Expiration

Maximum inspiration

Relaxation of:Diaphragm &External Intercostal

“Passive” muscle“Active” air

All muscles relaxed

Maximum Expiration

Maximum inspiration

Contraction of:Diaphragm &External Intercostal

“Active” muscle“Passive” air

Relaxation of:Diaphragm &External Intercostal

“Passive” muscle“Active” air

“Active or Forced” Expiration is an active muscular process. In this case the internal intercostal muscles contract and pull the ribs inward & downward while the abdominal muscles contract to raise the pressure in the abdominal cavity which forces the diaphragm up even more.

Abdominal Muscles

These actions further decrease the volume of the chest cavity, forcing additional air out. This makes it “active muscle” and “active air”.

All muscles relaxed

Maximum Expiration

Maximum inspiration

Contraction of:Internal Intercostal &Abdominals“Active” muscle“Active” air

All muscles relaxed

Maximum Expiration

Maximum inspiration

Contraction of:Diaphragm &External Intercostal

“Active” muscle“Passive” air

Relaxation of:Diaphragm &External Intercostal

“Passive” muscle“Active” air

Contraction of:Internal Intercostal &Abdominals“Active” muscle“Active” air

“Passive” Inspiration is a passive muscular process. In this case the internal intercostal muscles relax allowing the ribs to return to their resting position while the abdominal muscles also relax lowering the pressure in the abdominal cavity which drops the diaphragm down to its resting position.

Abdominal Muscles

These actions increase the volume and decrease the pressure causing air to rush in to fill the partial vacuum. This makes it “passive muscle” and “passive air”.

All muscles relaxed

Maximum Expiration

Maximum inspiration

Relaxation of:Internal Intercostal &Abdominals“Passive” muscle“Passive” air

All muscles relaxed

Maximum Expiration

Maximum inspiration

Contraction of:Diaphragm &External Intercostal

“Active” muscle“Passive” air

Relaxation of:Diaphragm &External Intercostal

“Passive” muscle“Active” air

Contraction of:Internal Intercostal &Abdominals“Active” muscle“Active” air

Relaxation of:Internal Intercostal &Abdominals“Passive” muscle“Passive” air