The Effect of Posture on the Diaphragm

Original Editor - Carin Hunter based on the course by Rina Pandya
Top Contributors - Ewa Jaraczewska, Carin Hunter, Jess Bell, Lucinda hampton, Merinda Rodseth and Kim Jackson

Introduction

The diaphragm is a fibromuscular sheet that lies between the thorax and abdomen and attaches to the xiphoid process of the sternum, ribs sixth to 12th ribs, and the vertebral bodies of L1 to L3. Its primary function is in respiration. The second important role of the diaphragm is to provide dynamic spinal stabilisation in collaboration with deep stabilisation muscles of the body. This function is possible due to the diaphragm's contribution to increasing intra-abdominal pressure, which plays an important role in spinal stability. Disorders of the diaphragm and postural deficiencies can negatively affect respiration, spinal stability, endurance and patient's abilities to complete functional tasks. This article will discuss the relationship between postural malalignment and diaphragm function.

The Effect of Posture on the Diaphragm

Posture significantly impacts the function of the diaphragm. To optimise diaphragm function, vertical length is needed - i.e. the thoracic and abdominal cavities need to be long enough for the diaphragm to create negative and positive pressure during inspiration and expiration. A patient must be able to take a deep breath down to the base of the lungs so that the ribs can flare out and the diaphragm can descend. A detailed discussion of breathing is available here and here. However, specific postures such as forward head posture (FHP) and kyphosis have been found to affect breathing mechanics, including diaphragm mobility.

Forward Head Posture

FHP

FHP is "a poor habitual neck posture that is defined by hyperextension of the upper cervical vertebrae and forward translation of the cervical vertebrae".This postural malalignment can also become a compensatory pain relieving adaptation in chronic neck pain, an adaptation to improve lung capacity in obstructive lung condition or in response to postural changes in the thoracic spine.

FHP affects chest expansion and the activity of the respiratory muscles, which can lead to reduced alveolar ventilation. Zafar et al. found that induced FHP in healthy subjects has an immediate impact on respiratory function. They suggested that this could be caused by a temporary entrapment of the phrenic nerve (i.e. the nerve, which supplies the diaphragm). This entrapment decreases neural activity and ultimately weakens the diaphragm.

Patients with forward head posture have reduced diaphragmatic excursion. The abdominal muscle shortening and changes in the shape and expansion of the anteroposterior aspect of the lower thorax can explain this. As a result, diaphragm excursion becomes limited. Hodges et al deduced that altered diaphragm function leads to core muscle instability, which can result in other systemic and musculoskeletal disorders, including spinal instability.

A FHP has an impact on respiratory biomechanics. A prolonged forward head posture can lead to kyphotic posture, reduction in the mobility of ribcage, and modification in function of all respiratory muscular attachments such as sternocleidomastoids, intercostals, and the diaphragm. It results in an expansion of the upper thorax and a contraction of the lower thorax. Thoracic elevation observed in forward head posture and decreased mobility of the thoracolumbar region is caused by an increased tone in the sternocleidomastoid muscle. The biomechanical impacts of forward head posture on respiratory function include development of restrictive lung disorder , decreased respiratory function, and decreasing the primary respiratory parameters: vital capacity (FVC), forced expiratory volume in the 1st second (FEV1), expiratory reserve volume (ERV), inspiratory reserve volume (iRV), and peak expiratory flow (PEF). Additionally, the forward head posture tends to decrease the SNIP values compared to the normal upright sitting, indicating a reduction in the diaphragm strength.

Interventions

For the diaphragm of patients with an FHP to be more effective during breathing, we need to:

• Restore the normal length-tension relationship
  • Postural alignment is necessary for effective respiratory muscle training as trunk rotation posture may limit chest wall movement. Diaphragm asymmetry is consistent with trunk rotation, negatively affecting lung volume.
  • Myofascial release of the diaphragm to indirectly stretch the diaphragm muscle fibres for muscle tension reduction, normalising fibre length, and promoting muscle contraction efficiency.

The following video demonstrates a self-release technique for the diaphragm:

• Improve mobility and expansion in the chest wall
  • Increase strength and mobility of the intercostal muscles through chest expansion exercises, rotation movement, swimming and various ball games (use of upper limbs).
  • Chest mobilisation: The patient sits and bends away from the tight side. Next, the patient inhales to expand that side of the chest. Then, the patient bends toward the tight side during expiration. Repeat multiple times for a total of 6 minutes of exercises.
  • The upper chest mobilisation and stretching of the pectoralis muscles: The patient sits in a chair with hands clasped behind the head. The patient horizontally abducts the arms during a deep inspiration followed by bringing the elbows together and bending forward during expiration. Repeat multiple times for a total of 6 minutes of exercises.
  • Chest mobilisation and core stabilisation exercises improve forced expiratory volume and vital capacity.
• Relieve the load on accessory respiratory muscles in the neck
  • The accessory inspiratory muscles consist of the sternocleidomastoids (SCM), scalenes, pectoralis major and minor, and inferior fibres of the serratus anterior and latissimus dorsi
  • Forward head posture induces muscle imbalances. Levator scapulae, sternocleidomastoid, anterior scalene, posterior cervical extensor, upper trapezius and pectoralis muscles become short or stiff. The deep cervical neck flexor, rhomboid, and serratus anterior muscles become inhibited or weak. These postural changes lead to overactivity of accessory respiratory muscles.
  • Weak, overactive, or tight accessory muscles of respiration, especially SCM and anterior scalenus, can increase respiratory inefficiency
  • Diaphragm myofascial release combined with an exercise program can improve FHP and chest mobility compared to exercises alone.

Watch this 6-minute video on how to measure and correct FHP.

Kyphotic Posture

Osteoporotic kyphosis in elderly women

Kyphosis is "an increase in the forward curvature of the spine that is seen along the sagittal plane".

It can be caused by torticollis (i.e. when the neck twists to one side) and FHP leading to the development of a secondary thoracic curve to compensate for the flattening of the cervical spine curve. Altered cervicothoracic mobility impairs normal breathing mechanics by reducing diaphragm mobility and strength.

There is an approximation of the ribs and pelvis in individuals who are slumped in a kyphotic posture. This approximation can increase intra-abdominal pressure, which affects diaphragmatic movement. This can lead to the following:

1. Reduced lung capacity
2. Reduced inspiratory flow
3. Decreased forced vital capacity

Watch this 1-minute video on Kyphosis symptoms.

Respiratory function should be assessed in patients with postures such as FHP and torticollis. Zafar et al. recommend that clinicians use the SNIP tool (Sniff Nasal Inspiratory Pressure) to assess respiratory function as it is a simple, easy-to-use method to screen patients with postural dysfunction. It is considered a good measure of global inspiratory muscle strength. The disadvantages of using the test include poor pressure transmission with nasal or airway obstruction, and the test is difficult to perform for patients with bulbar involvement (ALS).

A nasal“Bung” with a pressure catheter is needed to perform the test. The patient performs a maximum sniff through the unoccluded nostril. Multiple test attempts are completed: ten attempts are usually sufficient to reach a plateau in SNIP values. Greater than ten tests need to be completed if SNIP falls below normal. The rest period between intervals does not significantly impact the results of the SNIP test, and 30 seconds of rest time is tolerable for patients.

Normal values of maximal SNIP can be predicted from age and sex. Sitting or supine during testing does not affect the values, as the maximal SNIP is similar in both positions. The table below shows a normal value and lower limit of normal (LLN) value for the SNIP test in men and women of different ages:

	Men		Women
Age (years)	SNIP (cmH2O)	LLN (cmH2O)	SNIP (cmH2O)	LLN (cmH2O)
20	118	79	91	62
30	114	75	88	60
40	110	71	86	58
50	106	67	84	56
60	102	62	82	54
70	97	58	80	51
80	93	54	77	49
90	89	50	75	47

Adapted from: Rafferty G. Respiratory Muscle Testing Reference Equations. ARTP 2020

The below 4-minute video shows how to use an SNIP tool.

Positioning in an Intensive Care Unit (ICU) Bed

Pillows are often placed under patients' heads and knees in ICU settings to make them comfortable in bed. However, this positioning causes them to lie in a 'hammock' position, which reduces the ability of the diaphragm to function optimally.

Poor ICU positioning results in:

• Increased forward head angle
• Increased apical breathing
• Decreased diaphragmatic breathing

The consequences of poor ICU positioning include:

• Anterior neck muscle tightness
• Cervical extensor muscle weakness
• Diaphragmatic weakness

ICU Positioning Recommendations

• Supine or side lying positions do not improve the respiratory mechanics of critically ill patients.
• The optimum position is sitting with thorax greater than 30° from the horizontal plane. This position improves functional residual capacity (FRC), increases tissue oxigenation, and facilitates breathing.
• Frequent and regular changes to patient positioning and high angles of body rotation contribute to reducing ventilator-associated pneumonia (VAP).
• Prone position can improve oxygenation in awake patients

Other Factors to Consider

The diaphragm influences:

1. Oesophageal function
   • The diaphragm helps to stop gastric contents from refluxing into the oesophagus.
2. Digestive function
   • Peristaltic movements, massaging of the abdominal contents
3. Vascular and lymphatic function. The diaphragm acts as a respiratory pump. Its motion drives changes in intrathoracic pressure during inspiration and expiration.
   • Inspiration: reduces intrathoracic pressure and increases intra-abdominal pressure. It creates a pressure gradient, thus enhancing venous return to the right atrium. The pressure gradient drives the passive lymphatic drainage process into the venous system.
   • Expiration: increase of the blood flow to the left atrium and aortic diastolic pressure drops
4. Immune system
   • The diaphragm helps with immunity because it creates "fresh flow" and assists with the absorption of nutrients and vitamins
   • Resistive breathing activates an immune response, which includes the elevation of plasma cytokines and the recruitment and activation of lymphocyte subpopulations.

More information on the roles of the diaphragm is available here.

Summary

1. Postural malalignment significantly impacts the function of the diaphragm.
2. Forward head posture affects chest expansion, reduces alveolar ventilation, reduces diaphragmatic excursion.
3. Thoracic kyphosis can lead to reduction in lung capacity, inspiratory flow , and forced vital capacity.
4. SNIP test should be considered in the assessment of respiratory function.
5. When tolerated, a semi-sitted position with trunk at 30 degrees angle from the horizontal plane is recommended for patients on the ICU as it improves functional residual capacity, increases tissue oxigenation, and facilitates breathing.