Part III: Muscles of Ventilation

Reference & Reading: Egan's p.158-163

Primary Muscles

Diaphragm Intercostal muscles

Accessory Muscles

Scalenes Sternocleomastoid Pectoralis Major Abdominals

Rises from costal margin

Connects at central tendon

Hemidiaphragms

Separates thorax from abdomen

Resting Position

When muscle contracts, drops floor of thoracic cavity down

Pulls air in

Located between each rib pair

External Intercostals

Internal Intercostals

Active during quiet breathing

Elevates ribs, ↑ thoracic volume - occurs closer to exhalation

At increased lung volumes, ribs are lowered

Stabilizes chest wall during large pressure changes

Quiet Breathing

– from www.gettyimages.com

Also called intercostal retractions

There is increased amount of negative pressure generated

Clinical sign of increased WOB; look at suprasternal notch

Retractions on infant

Collection of chest wall muscles

Help to increase thoracic space, by assisting the primary muscles:

Includes:

Scalene Sternocleomastoid Pectoralis Trapezius

3 muscles

Anterior Medial Posterior

Arise from lower 5 cervical vertebrae & connect to 2nd rib anteriorly

Function:

Normal With increased WOB

Rise from manubrium & medial end of clavicle

Insert into the skull

Function:

Primary: supports head Increased WOB: raises

sternum up & out

Rises from clavicle & anterior surface of sternum

Function:

Primary: hugging motion With increased WOB:

pulls opposite of primary function

Arise from the occipital bone in the skull & all thoracic vertebrae; insert into clavicle

Function:

Primary: shrug shoulders; raise or lower arms

Increased WOB: Raises rib cage

Used to forcibly exhale (cough, sneeze, etc)

Muscles used are the abdominal muscles

Collectively compress abdominal contents to push diaphragm up

Includes:

External & internal obliques Transverse abdominals Rectus abdominus

External Oblique: arise from lower 8 ribs

Internal Oblique: Arise from iliac crest& inguinal ligament

Fibrous aponeurosis

Arises from:

costal cartilages Iliac crest Part of inguinal

ligament

Connects to a aponeurosis

Arises from pubic bones

Inserts into costal cartilages 5 -7

Contraction ↓ distance from xiphoid to pubis