3.2.2 Ventilation and Perfusion Flashcards
What is compliance?
Change in volume / Change in pressure
if small change in pressure > large change in volume, tissue has HIGH compliance
What muscles are used in inspiration?
Diaphragm
External intercostal muscles
Scalene muscles (accessory)
What muscles are used in expiration?
Passive so no musches
Abdominal muscles (accessory)
Internal intercostal (accessory)
Explain a horse’s biphasic manner of breating
Both inspiration and expiration have a biphasic manner which is initially passive and then active
What is elastic resistance?
Resistance of lung tissue and chest wall (compliance)
What is surface tension?
Resistance from surface forces at alveolar gas-liquid interphase
What is viscoelastic tissue resistance?
Frictional resistance from deformation of thoracic tissue
Explain elastic recoil
Elastin and collagen fibres in alveolar walls, airways, vessels
Lung returns to resting volume after distension
Chester wall is under tension too (intercostal muscles and ribcage ‘spring out’)
Intrapleural pressure is subatmospheric
How is lung compliance measured?
Volume change per unit pressure change
What is pulmonary surfactant and what are its effects?
DPPC, secreted from type II alveolar cells (pneumocytes)
- increases compliance (reduces work of expansion)
- Promotes stability of each alveolus
- Keeps alveoli dry(er)
What are the consequences of brochodilation?
- ↑ airflow due to ↓ resistance
- ↑ alveolar ventilation
- ↓ physiological dead space
- Physiologically occurs during exercise (sympathetic stim. of β receptors
What are the consequences of bronchoconstriction?
- ↑ resistance
- ↓ alveolar ventilation
- ↓PaO2, ↑PaCO2
- ↓pH
- If chronic leads to SM cell proliferation, fibrosis
Describe bronchial circulation
Low volume, high pressure (from aorta)
Carries O2 blood to lungs (metabolic needs)
Describe pulmonary circulation
Large volume system, low pressure (pulmonary trunk)
Carries venous blood to lungs
Factors effecting perfusion
Excersise - ↑open capillaries, ↑ bloodflow, lungs cope with increasing pulmonary arterial pressure and CO
Hypoxia - low alveolar O2, blood vessels constrict, allows distribution of blood from to most effective places
