Smooth muscle cells are located in collagen within intervertebral discs, ligaments, fascia and menisci.
Thus alterations in breathing mechanics may affect the function of the passive system.
Furthermore, respiratory alkalosis alters neuronal excitability, muscle function and emotional state.
Through these mechanisms respiratory rate may at times affect the function of the entire musculoskeletal system.
Breathing mechanics may affect dentofacial and craniorofacial structure.
Harari et al. [5] retrospectively analysed the changes in 116 pediatric patients, 55 of which showed signs and symptoms of mouth breathing and 61 controls that were normal nasal breathers.
Mouth breathing was assessed using subjective history and physical exam.
These findings were confirmed with a mouth-breathing questionnaire.
Mouth breathers demonstrated considerable backwards and downward rotation of the mandible, increased over-jet, increased mandible plane angle, a higher palatal plane and narrowing of both the upper and lower arches compared to nasal breathers.
Furthermore, a posterior cross bite was more prevalent in the mouth breathers at 49% compared with 26% in controls.
As was an abnormal lip to tongue seal, 56% in mouth breathers as opposed to 30% in controls.
This could be viewed as the CNS prioritising respiration over the stomatognathic system.
Mouth breathing is also associated with compensatory changes throughout the kinetic chain.
In children, mouth breathers have been found to have significant increases in cervical protraction and thoracic curvature in the sagittal plane measured with biophotogrammetry [2].
These changes lead to measureable reductions in thoracic rotation and winging scapula.
At the lumbar spine subjects compensated most frequently with an anteriorly rotated pelvis, although others used a posterior pelvic tilt strategy [2].
In the lower limb the knees hyperextend and the ankles dorsiflex.
These findings suggest a possible link between posture and mouth breathing.
The respiratory function of muscles is prioritised over their stabilization function.
The postural and respiratory function of the diaphragm is coordinated with the respiratory and postural inputs summated at the phrenic motorneurons [6].
Further integration of respiratory and postural roles has been demonstrated for the transversus abdominis and the intercostals. Hodges et al. [6] assessed the effects of increasing respiratory demand on the postural function of the diaphragm.
Six participants had to oscillate an arm whilst breathing through a tube, which increased dead space in the lungs for 4 min.
As participants reached the final minutes, their respiratory rates increased and CO2 levels had decreased.
Their results showed that as respiratory demand increased, the postural function of the diaphragm declined.
They concluded:
“To maintain homeostasis, the CNS must prioritise respiratory drive over other functions of the respiratory muscles, such as postural control” [6, p.1006].
The clinical application of this statement is clear.
Patients need to be cleared for respiratory dysfunctions, such as breathing pattern disorder or mouth breathing.