· Intro
· Inspiration
· Expiration
· Non-ventilatory function
· (Airway smooth muscle)
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Respiratory musculature |
· All muscle relevant to ventilation is skeletal and striated except airway smooth muscle · Primary ventilatory muscles mostly Type 1 = oxidative, fatigue-resistant o Diaphragm 55% in adult, 20% neonate o Intercostals 65% adult, 45% neonate |
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Control of breathing |
· Activity co-ordinated in medullary resp centre o Dorsal inspiratory group o Ventral expiratory group o Pre-Botzinger pacemaker cells · Normally involuntary. Can be controlled voluntarily by cortex. |
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Aims |
· Overall: ↓intrapleural pressure -> ↑transpulmonary pressure o ↑ AP diameter of chest (↑APD) o ↑ transverse diameter of chest (↑TD) o ↑ chest wall elevation (↑CWE) o Maintain airway patency (↑AP) |
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Diaphragm’s contribution |
· Upright adult: 50% · Supine adult: 66% · Neonate: ↑ (cartilaginous ribs = ineffective intercostals · Pregnant: ↑ (upward displacement = increased excursion) |
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Primary muscles |
· Diaphragm: o Dome shaped muscle between thorax and abdomen o Attachments: L and R crura to vertebral bodies, lower 6 ribs, xiphisternum o Central tendon fused to fibrous pericardium o Innervated by phrenic nerve C3-4-5 o Descends 1-2cm in quiet inspiration o Descends 10cm in max inspiration |
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· External intercostals: o ↑APD, ↑TD by “bucket handle” activity o From rib above space to rib below o Fibres in front pocket direction |
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· Scalenes: o ↑CWE, counteract inward movement of upper ribs by diaphragm o From cervical transverse processes to upper ribs |
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· Pharyngeal and laryngeal dilator muscles: o Maintain airway patency o Contraction timed with inspiration o CNIX (larynx) and X (larynx and pharynx) |
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· Dilators alae nasae: o Maintain airway patency o Contraction timed with inspiration o Important in neonates (obligate nose breathes, high total resistance) |
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Accessory muscles |
· Sternocleidomastoid: o ↑CWE |
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· Levator scapulae: o ↑CWE o Also: scapular elevation |
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· Trapezius: o ↑CWE, scapular elevation o Also: neck lateral flexion |
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· Pectoralis major (when upper limb fixed): o ↑CWE, ↑APD o Also: shoulder flexion and adduction |
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· Costal slips of latissimus dorsi (when upper limb fixed): o ↑CWE o Also: shoulder extension and adduction |
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· Serratus posterior superior o ↑CWE |
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Aims |
· Overall: ↑ intra-pleural pressure hence ↓ transpulmonary pressure · Opposite to inspiration |
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Passive |
· Relaxation of inspiratory muscles · Elastic recoil due to surface tension and elastic lung tissue · Energy stored during inspiration |
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Active |
· Internal intercostals o ↓ APD, ↓ TD by reverse Bucket handle activity o From rib below to rib above o Back pocket direction |
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· Abdominals o ↓ APD, ↓ TD, ↓CWE o Rectus, transversus, internal and external obliques o Pull down chest wall o ↑intra-abdo pressure, push up diaphragm |
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· Latissimus dorsi o ↓ APD, ↓ TD, ↓ CWE |
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· Serratus posterior inferior o ↓CWE |
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Quadratus lumborum o ↓CWE |
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Coughing |
· Inspiration, glottic closure, expiratory muscle contraction, glottic opening |
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Phonation |
· Expiration with partial glottic closure |
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Increased intra-abdominal pressure |
· Expiratory muscle contraction with closed glottis o Splint vertebral column during exertion o Abdominal or pelvic evacuation (e.g. vomiting, micturition, defecation, parturition) |