Ventilation and Compliance 2 Flashcards
What are the 2 kinds of cells that makes up alveolar walls?
Type 1 (gas exhange)
Type 2 (secretes surfactant fluid)
What do type 1 cell of alveoli do?
Allows gas exchange
What do type 2 cells of alveoli do?
Secretes surfactant fluid
What is surfactant?
Detergent like fluid produced by type 2 alveolar cells
What does surfactant do?
Reduces surface tension on alveolar surface membranes, reducing tendancy for alveoli to collapse
What is surface tension?
Attraction between water molecules, occurs wherever there is an air-water interface
What does surfactant do to the compliance of the lung?
Increases it
What does surfactant do to the lungs tendency to recoil?
Reduces it
Is surfactant more effective in small or large alveoli, and why?
Small because surfactant molecules come closer together and are therefore more concentrated
Why does air spread evenly between small and large alveoli although there would be a pressure difference?
Surfactant reduces surface tension better in small alveoli, making the pressure in small and large equal
When does surfactant production begin and is completed by?
About 25 weeks gestation and is completed by 36 weeks
What is production of surfactant stimulated by?
Thyroid hormones which increase towards the end of pregnancy
What do premature babies often suffer from due to surfactant production being complete at week 36?
Infant respiratory distress syndrome
What is a saline filled lung similar to?
A lung in utero
Why does a lung in utero require a smaller change in pressure to inflate?
Does not need to overcome surface tension (no air-water interface)
What is compliance?
Change in volume relative to change in pressure
What does compliance of the lung represent?
Stretch ability of the lung (not elasticity)
What does a high compliance mean?
Large increase in lung volume for a small increase in ip pressure
What does a low compliance mean?
Small increase in lung volume for a large decrease in ip pressure
What does compliance change with?
Disease and age
Does it require a greater change in pressure from fictional residual capacity to reach a lung volume during inspiration or expiration?
Greater change in pressure is required during inspiration
Why is expiration passive?
Work on inspiration is recovered as elastic recoil during expiration
What is emphysema?
Loss of elastic tissue means expiration requires effort (image c)
What is loss of elastic tissue called?
Emphysema
What is fibrosis?
Inert fibrous tissue means effort of inspiration increases (image d)
What is inert fibrous tissue called?
Fibrosis
What does inert mean?
Lacking the ability or strength to move
Does emphysema make inspiration or expiration more difficult?
Expiration (image c)
Does fibrosis make inspiration or expiration more difficult?
Inspiration (image d)
What does the pressure/volume curve vary between?
The apex and the base of the lung
Is the volume change (compared to change in pressure) greater at the base or the apex of the lung?
Base
How does alveolar ventilation and compliance change with height from the base to the apex and why?
Decreases due to alveolar at the apex being more inflated at functional residual capacity
Why are the alveoli at the base more compliant during inspiration?
They are compressed between the lung above and the diaphragm below
How does the change in intrapleural pressure affect the change in volume at the base of the lung compared to the apex?
Brings about a larger change at the base compared to the apex
What are the 2 categories of lung disease?
Obstructive
Restrictive
What does an obstructive lung disease mean?
Obstruction of airflow, especially on expiration
What could an obstructive lung disease be due to?
Increased airway resistance
What does a restrictive lung disease mean?
Restriction of lung expansion
What could a restrictive lung disease be due to?
Loss of lung compliance, leading to lung stiffness and incomplete lung expansion
What are examples of obstructive lung diseases?
Asthma
Chronic obstructive pulmonary disease (COPD)
What are examples of chronic obstructive pulmonary diseases?
Chronic bronchitis
Emphysema
What is chronic bronchitis?
Inflammation of the bronchi
What is emphysema?
Destruction of alveoli, loss of elasticity
What is destruction of the alveoli known as?
Emphysema
How many people suffer from moderate to severe chronic obstructive pulmonary disease (COPD) worldwide?
80 million people
What percent of the UK population suffers from chronic obstructive pulmonary disease (COPD) and how does this change with age?
About 1%, which increases with age
What percent of men older than 75 suffer from chronic obstructive pulmonary disease (COPD)?
10%
What are examples of restrictive lung diseases?
Fibrosis
Infant respiratory distress syndrome
Oedema
Pneomothorax
What is infant respiratory distress syndrome?
Insufficient surfactant production
What is spirometry?
Technique used to measure lung function
What can the measurements from spirometry be classed as?
Static (where the only consideration made is the volume exhaled)
Dynamic (where the time taken to exhale a certain volume is what is being measured)
What are static spirometry measurements?
Ones where the only consideration made is the volume exhaled
What are dynamic spirometry measurements?
Ones where the time taken to exhale a certain volume is what is being measured
What measurements can be made directly from spirometry?
Tidal volume
Inspiratory reserve volume
Expiratory reserve volume
Inspiratory capacity
Vital capacity
What is FEV1?
Forced expiratory volume in 1 second
What is FEV1 for a fit, healthy, young adult male?
4L
What is FVC?
Forced vital capacity
What is forced vital capacity for a fit, healthy young adult male?
5L
What is the normal FEV1/FVC ratio for healthy young men?
80%
How does the FEV1/FVC ratio change with obstructive and restrictive diseases?
Restrictive - FEV1 and FVC decrease, ratio decreases
Obstructive - FEV1 and FVC decrease, ratio increases
Why is FEV1 reduced by a much greater extent than FVC for obstructive lung diseases?
Because major effect on airways
Why is FVC decreased in restrictive lung diseases?
Due to limitations on lung expansion
Why is the FEV1/FVC ratio not always a good indicator of health?
Because disease can cause it to decrease or increase, as seen with obstructive and restrictive lung disease
What is forced expiratory flow (FEF25-75)?
Average expired flow over the middle of an FVC
How do changes for forced expiratory flow compare to FEV1 with disease?
They correlate but changed for forced expiratory flow are more striking
