Biochemistry and Physiology of Breathing

Why do we breathe?
• To deliver oxygen to body cells
• To remove excess CO2

Oxygen
Body cell requirement 2-3%
Atmospheric content 21%
• Oxygen does not have to be stored. It is always available
• Its purpose is to provide energy and to regenerate cells

Carbon Dioxide
Body requirement 6.5% or 40mm Hg
Atmospheric content 0.03%
• It has to be produced by the body and stored
• It is stored in the lungs at 6.5%
• It is stored in arterial blood at 40mm Hg pressure
• It is produced as a by product of exercise and digestion

When the child breathes through the mouth the stored carbon dioxide in the lungs escapes. This results in reduced levels of carbon dioxide in the lungs and reduced levels of carboxy-haemoglobin in the blood.
Many of the problems associated with chronic mouth breathing are as a result of this lowered level of carboxy-haemoglobin in the body.

Carbon Dioxide
Has 4 major functions in the body
• It facilitates release of oxygen from haemoglobin
• It triggers breathing by activating the medullary sensor
• It maintains pH by buffering with bicarbonate or carbonic acid
• It prevents smooth muscle from going into spasm
All these functions are reduced or impaired in children who are chronic mouth-breathers.

What makes us breathe?

What is normal breathing?
• Gentle wave pattern
• 4-5 litres of air per minute
• 8-10 breaths per minute
• Breathing in and out through the nose
This is about one breath every six seconds

What goes wrong?
The Medullary Trigger resets itself
Through constant exposure to CO2 levels lower than 40mm Hg, mainly as a result of mouth breathing, the trigger is activated far earlier, causing over breathing or hyperventilation.
This is often results in an inhale every three seconds

The Problem with Mouth Breathing
The tongue no longer provides support for the upper jaw with resulting reduced upper arch size.

The vault rises leading to reduction in the size of the nasal passages contributing to congestion of nose.

The pH of saliva elevates leading to increased rate of caries A tendency to URT infections often resulting in tonsillitis and enlarged adenoids.

The medullary trigger resets at lower level leading to hyperventilation.

The alkalinity of blood increases so less oxygen released from the blood. This is known as the Bohr Effect. Oxygen circulates the blood in the form of oxy-haemoglobin but reduced levels of carboxyhaemoglobin mean that less oxygen is released from the oxy-haemoglobin to enter the tissues so cells
die.

Smooth muscle spasm. Gastric reflux, asthma and bed wetting are commonly associated with chronic mouth-breathing

Smooth muscle is found throughout the body

The Solution to Mouth Breathing
• Train the child to become a natural nose breather again
• Address the issues that caused the initial problem
• Institute a strategy to ensure this does not recur

Fixing the problem
The Medullary trigger can be reset, by reversing the process and sending messages of increasing CO2 levels it is possible to reset the trigger and return the breathing pattern to normal