Lung Physiology 1- General Principles Flashcards
Respiratory pump
Requirement to move 5 litres / minute of inspired gas [cardiac output 5 litres / min]
Generation of negative intra-alveolar pressure
Inspiration active requirement to generate flow
Bones, muscles, pleura, peripheral nerves, airways all involved
Bony structures support respiratory muscles and protect lungs
Rib movements; pump handle and water handle
Muscles of respiration
Inspiration
-Largely quiet and due to diaphragm (C3/4/5) contraction
-External intercostals (nerve roots at each level)
Expiration
-Passive during quiet breathing
During normal breathing diaphragm is what allows breathing. C3, C4, C5 spinal nerves allow the diaphragm to contract and relax for breathing
Pleura
2 layers, visceral and parietal
Potential space only between these, few millilitres of fluid
Nerves
Sensory;
Sensory receptors assessing flow, stretch etc..
C fibres
Afferent via vagus nerve (10th cranial nerve)
Autonomic sympathetic, parasympathetic balance
Static lungs
Both chest wall and lungs have elastic properties, and a resting (unstressed) volume
Changing this volume requires force
Release of this force leads to a return to the resting volume
Pleural plays an important role linking chest wall and lungs
Gas exchange
VENTILATION; Bulk flow in the airways allows;
O2 and CO2 movement
Large surface area required, with minimal distance for gases to move across. Total combined surface area for gas exchange 50-100 m2
300,000,000 alveoli per lung
PERFUSION; Adequate pulmonary blood supply also needed
Alveolar ventilation
Dead space
Volume of air not contributing to ventilation
Made up of two parts:
Anatomic; Approx 150mls (last part of the breath does not enter the alveoli for gas exchange- stays in trachea and bronchi)
Alveolar; Approx 25mls (the part of the air that stays in the alveoli but isn’t involved in gas exchange)
Physiological
(Anatomic+Alveolar) = 175mls
When hyperventilating, increase in the alveolar dead space
Circulation- bronchial
Blood supply to the lung; branches of the bronchial arteries
Paired branches arising laterally to supply bronchial and peri-bronchial tissue and visceral pleura
Systemic pressures (i.e. LV/aortic pressures)
Venous drainage; bronchial veins draining ultimately into the superior vena cava
Circulation- pulmonary
Normal pulmonary pressure is 24 systolic and 10 diastolic (24/10)
Left and right pulmonary arteries run from right ventricle
Low(er) pressure system (i.e. RV / pulmonary artery pressures)
17 orders of branching
Elastic (>1mm ) and non elastic
Muscular (<1mm )
Arterioles (<0.1mm )
Capillaries
Broncho- vascular bundle
Pulmonary artery and bronchus run in parallel
1000 capillaries per alveolus
Each erythrocyte may come into contact with multiple alveoli
Erythrocyte thickness an important component of the distance across which gas has to be moved
At rest, 25% the way through capillary, haemoglobin is fully saturated
Alveolar perfusion
Capillaries at the most dependent parts of the lung are preferentially perfused with blood at rest
Perfusion of capillaries also depends on;
Pulmonary artery pressure
Pulmonary venous pressure
Alveolar pressure
Ventilation and perfusion
Matching ventilation and perfusion important
Hypoxic pulmonary vasoconstriction occurs in response to alveolar hypoxia
Involves the vasoconstriction of pulmonary vessels to:
1) Divert the direction of the blood to ensure the blood is reaching areas of high oxygen in the lung
2) To get Oxygen faster
Pulmonary vessels have high capacity for
cardiac output
30% of total capacity at rest
Recruiting of alveoli occurs as a consequence of exercise
Nomenclature
Slide 16
Increase in alveolar ventilation
CO2 levels drop
Important in acid base balance
Slide 18
Oxygenation
Alveolar gas equation on slide 19
