Mechanics of respiration:
Most people overlook respiration (breathing) because it is something that occurs in the background and outside of any conscious effort or consideration. The paradox is that breathing is a very complex mechanical marvel. It isn't merely a case of the lungs "inflating and deflating"...the lungs are elastic organs that are continuous with the entire thorax (chest wall). Therefore, the act of inflation / deflation involves more than the lungs...it involves an active contribution of the chest wall itself as well as the diaphragm. In other words, the ability for the lungs to draw in air (oxygen) is dependant on the integrity of the chest wall and the performance of the diaphgram.
In the newborn child, the relationship between the lungs and the chest wall is an exponentially more intimate one. To explain this with more clarity, we need to introduce a very important term:
COMPLIANCE.
Compliance is defined as the opposite of stiffness. In the context of respiration, the lungs AND the chest wall (ribs, sternum) are very compliant. What does this mean in practical terms?
When the newborn infant breathes, the lungs and the chest wall experience elastic deformation
In other words, the chest wall is essentially "soft" and is easily influenced by the mechanics of breathing. This characteristic of compliance becomes more relevant as the infant grows. To be precise, at approximately 18-24 months of age, the chest wall stiffens considerably. In essense, the chest wall loses compliance at a rapid rate as the child enters into this range of 18-24 months. This is perhaps the most significant and important process in a childs development. The gradual stiffening of the chest wall (which actually begins BEFORE 18 months and accelerates after) results in the increased development of what is called a "hydraulic pumping" stimulus that is directed up into the upper thorax and down into the pelvis and pelvic floor. To be precise, the reduced compliance of the chest wall causes the majority of the mechanical movement to be re-directed upwards and downwards.
Once again, what does this mean in practical terms? It means that the stffening of the chest wall is the primary catalyst for the development of the pelvis and the shoulder girdle. In other words, it is this precise hydraulic "pumping" of the pelvic floor and upper thorax that DRIVES the growth of the pelvis (crucial for the later development of the legs) and the shoulder girdle (crucial for the later development of function of the arms).
Altered mechanics in newborns / children with neurodevelopmental disorders:
The important reality to take away from part 1 of this discussion is the following:
All children / newborns with a neurodevelopmental disorder manifest altered respiratory mechanics and therefore are not fully exposed to this critical "hydraulic pumping" action.
Why is this?
One of the most prevalent characteristics of neurodevelopmental disorders is profound connective tissue weakness. In more laymans terms, everything from the tendons, ligaments, bones, organs, etc...are formally weak and remain weak throughout growth and maturation. In the context of respiration, this is represented explicitly in the chest wall...
The chest wall REMAINS compliant (elastic) long after 18-24 months...therefore the fundamentally critical hydraulic pump never reaches the pelvis and upper thorax. This is manifested almost unanimously in all affected children by the common characteristic of a small pelvis and small upper thorax. This ultimately reflects in the considerable delay (or arrest) or functional development of the arms and legs. Furthermore, it plays a significant role in the altered respiratory mechanics which lead to a multitude of systemic challenges due to altered oxygen saturation.
In summary, the vicious cycle of deterioration takes place as such:
1. Significant Prolonged Chest Wall Compliance (Thoracic Weakness)
2. Irregular Respiratory Mechanics and Altered Synchronicity (Active or Laboured Breathing)
3. Abnormal circulating Oxygen levels, Hypocapnia, Reduced cerebral blood flow, smooth muscle constriction in the intestines (constipation), Magnesium and Calcium imbalances in muscles (muscular tension)
**** The consequences of #3 can be a catalyst for further impaired neurological development ***
4. Repetitive deformation and subsequent distortion of the chest wall (sometimes manifested as a caved-in sternum or asymmetry)
5. Permanent structural distortion and chronic systemic distress
All of the above should represent some familiar challenge(s) in children with neurodevelopmental disorders. Regardless of the specific diagnosis, these challenges are universal because of the immediate impact on respiration. Paradoxically, this understanding actually improves our ability to positively affect the trajectory of improvement and essentially reduce the negative effects of this altered mechanism. The upcoming posts will further explain this process as well as (perhaps more importantly) introduce strategies to essentially "re-start" the respiratory "hydraulic pump" with some very safe and simple practical exercises.
Stay tuned!
