RP - Dynamic Lung Mechanics Flashcards
Describe the movements of breathing:
Pump handle movement:
- Refers to anterior-posterior expansion of the thorax
- as external intercostal muscles contract ribs elevate upward and outward
- The sternum moves anteriorly and superiorly, like a pump handle
- Increases anteroposterior diameter of thorax
Bucket handle movement:
- refers to lateral expansion of the lower ribcage
- On inspiration, the ribs elevate laterally like a bucket handle swinging up
- increases transverse diameter of thorax
In obstructive diseases (e.g., COPD), accessory muscles (like sternocleidomastoid) become overactive to assist these movements
Define and Explain Airway Resistance:
Ohm’s law:
AWR = Pressure in alveoli/ flow
Influenced by airway radius, length, flow pattern, and air viscosity.
Small changes in radius (as per Poiseuille’s Law) → large changes in resistance
Greatest resistance: medium-sized bronchi, not small airways (due to high parallel branching)
Describe the phases of the respiratory cycle:
Inspiration:
- active
- Diaphragm contracts → thoracic volume ↑ → intrathoracic pressure ↓ → air flows in
Expiration:
- usually passive
- Elastic recoil of lungs → pressure ↑ → air expelled
Pause between breaths
Describe the different types of flow:
Laminar:
- Streamlined
- occurs in small bronchioles
- Described by Poiseuille’s Law
Turbulent:
- Chaotic
- occurs in trachea, main bronchi, during exercise or obstruction
- Resistance increases non-linearly with flow
Transitional flow - At bifurcations; mixture of both
Reynold’s number:
Re = VPD/ u
Re > 2000 → turbulence likely
Describe quiet inspiration and quiet expiration:
Quiet inspiration:
- active process
- diaphragm contracts and flattens → increases vertical thoracic dimension
- external intercostal muscles elevate ribs and facilitate bucket and pump handle movements
- scalene stabilises ribs 1 + 2
Quiet expiration:
- passive process
- relies on elastic recoil of the lungs and Relaxation of diaphragm and intercostals
Describe forced inspiration and expiration:
Forced inspiration:
- occurs during exercises and respiratory distress
- additional muscles are recruited to aid
- sternocleidomastoid, scalenes, pectoralis minor and major, Serratus anterior and posterior superior
Forced expiration:
- active process
- internal intercostal muscles depress ribs → reduce thoracic volume
- Transversus abdominis , rectus abdomens and transverse obliques → Increase intra-abdominal pressure → push diaphragm upward
Describe the Effect of Airway Generation on Resistance:
Large airways:
- lower cross sectional area
- more turbulent flow → ↑ Raw
Smaller airways:
- High individual R, but arranged in parallel.
- Collective resistance = very low, unless diseased
Describe the secretion, action and removal of bronchial secretions:
Secretion:
- goblet cells (epithelium) & submucosal glands (serous + mucous)
- controlled by Parasympathetic (ACh): ↑ secretion and Irritants, allergens: reflex increase
Composition - Mucins (MUC5AC, MUC5B), water, electrolytes, IgA, lysozyme, lactoferrin
Function:
- traps pathogens, particles and dirt
- lubricates the epithelium
Mucociliary clearance:
- Sol layer (periciliary) and gel layer (mucus)
- cilia beat mucus towards pharynx
Cough reflex:
- activated if excessive load
- High airflow helps expel
Describe the different factors affecting airway resistance:
Intraluminal factors:
- secretions of mucus
- foreign bodies and tumours
Mural (wall) factors:
- inflammation
- smooth muscle contraction
- oedema
Extramural factors:
- Lymphadenopathy
- External compression (tumour, vessel)
Describe how the upper airways, extrathoracic and intrathoracic lower airways are affected by the factors:
Upper airways:
- larynx, pharynx
- Primary site of resistance during normal breathing due to narrow, convoluted anatomy and turbulent flow
- Resistance is fixed and largely independent of lung volume
- Diseases: OSA, laryngeal oedema, foreign body
Extrathoracic Lower Airways:
- trachea
- During inspiration, negative intraluminal pressure can cause dynamic narrowing or collapse if airway wall is floppy or obstructed
- During expiration, walls are stabilized due to positive intraluminal pressure, so collapse is less likely
- affected by Laryngeal edema or paralysis, Tumors or structural narrowing
Intrathoracic airways:
- below thoracic inlet
- Dynamic airway compression is prominent during forced expiration due to positive pleural pressure exceeding intrabronchial pressure → airway narrowing/collapse
- Airway resistance is highly dependent on lung volume: Low lung volumes → decreased radial traction → airway narrowing → increased resistance
- affeted by asthama and COPD
Outline non-specific immune mechanisms in the respiratory tract:
Mechanical:
- epiglottis
- nasal hairs trap large airborne particles and increase turbulence
- mucus
- cough and sneeze reflex is a powerful expiratory maneuver
- Mucociliary escalator, coordinated ciliary beating moves mucus toward the pharynx to be swallowed or expelled
Cellular:
- alveolar macrophages engulf and destroy pathogens via phagocytosis
- dendritic cells activate adaptive immune responses
- neutrophils Kill pathogens via oxidative burst and enzymatic granules
Molecular:
- IgA (secretory antibody)
- lysozyme breakds down bacteria cell walls (gram positive)
- lactoferrin sequesters iron, depriving bacteria of a critical growth factor
Describe the neural mediators:
Parasympathetic nervous system:
- vagus
- acetylcholine acting on M3 muscarinic receptors
- effect is bronchoconstriction
and ↑ secretion
Sympathetic nervous system:
- adrenal
- adrenaline acting on β2 (via cAMP)
- effect is bronchodilation
Describe the inflammatory mediators:
IL-4, IL-5, IL-13 (Th2 cytokines): promote eosinophilic inflammation in asthma.
TNF-α, IL-1: promote vascular permeability, immune cell recruitment.
Describe hormonal mediators:
Adrenaline - Bronchodilation (β2)
Histamine - Bronchoconstriction, oedema
Leukotrienes (C4, D4) - potent bronchoconstriction
