Respiratory Mechanics

airway increases with

• increased airway length

• increased velocity of air

• decreased diameter of airway

which of the 3 factors determining resistance do we have control over

diameter bc airways are covered in smooth muscle

what affects diameter in upper airways

physical obstruction bc trachea and bronchi surrounded by cartilage = can’t get bigger or smaller themselves

what affacts diametes of bronchioles

• bronchonconstriction - paraNS muscarinic receptors (acetylcholine)

• bronchodilation - SNS beta-2 receptors (adrenaline and noradrenaline)

work of breathing (difficulty) is affected by

1. airway resistance - decreased diameter = increased resistance = increased work

   1. lung compliance - ability to stretch

how does lung compliance affect work of breathing

decreased compliance = harder to stretch = increased work

lung elastance

ability of lung to spring back after being stretched

if lung compliance increases then lung elstance also increases. true or false

false bc inverse relationship

pulmonary fibrosis

tissue deep in lung becomes inelastic scar tissue = decreases lung compliance = harder to breath in and inflate lungs

emphysema

destorys elastin fibres in alveoli walls = lung elastance decreases = harder to breathe out bc lose recoil

alveoli structure

• very large surface area

• alveolar lining fluid - thin layer of fluid covers surface

problem caused by alveolar lining fluid

mostly water = hydrogen bonds between molecules creates surface tension = water molecules more attracted to other water than gases in air = resists forces that increase surface area

alveolar surface tension on lung compliance

attraction between water molecules opposes expansion = harder to inflate

law of LaPlace

smaller the sphere of alveolus = more inward pressure from alveolar surface tension till collapse

• increased resistance to stretch = harder to breath

factors preventing collapse

1. effect of surfactant

2. alveolar interdependence

surfactant

surface active agents

effect of surfactant

disrupts alveolar surface tension by injecting surfactant into fluid linning = disrupts hydrogen bonds

• decreased surface tension = decreased resistance to stretch

• more surfactant releasing cells in small alveoli = decreases pressure

effect of alveolar independence

when alveolus collapses surrounding alveoli stretch = surrounding then recoil pulling collopased alveolus open

2 categories of respiratory diseases

1. obstructive lung disease - limits airflow

2. restrictive lung disease - limits volume

obstructive lung disease

issues with paasage of airflow

• narrowing of lower airways

• increased airway resistance

• more difficult to expire

• e.g. asthma, emphysema, chronic bronchitis

restrictive lung disease

decrease in lung compliance = more difficult to inflate lung e.g. pulmonary fibrosis

spirometry

measurement of lung volumes and speed you can inhale and exhale

what does spirometer measures

1. tidal volume

2. expiratory reserve volume

3. inspiratory reserve volume

4. vital capacity

5. forced expiratory volume in 1 second (FEV1)

6. forced vital capacity

tidal volume

amount inhaled or exhaled during quiet breathing

• avg 500 mL

how much of total air is exchanged during normal breathing

10% - means most of air in lungs is stale (lower O2 and higher CO2 than in atmosphere)

expiratory reserve volume

extra amount of air you can forcefully exhale after finishing a normal breath

• male = 1.1 L

• female = 0.7 L

inspiratory reserve volume

maximum extra volume of air you can forcefully inhale after a normal breath

• male = 3 L

• female = 1.9 L

vital capacity

maximum amount of air a person can expel from the lungs after a maximum inhalation

• male = 4.6 L

• female = 3.1 L

residual voume

the amount of air that stays in your lungs after you breathe out as hard as you can

• spirometry can’t measure - only estimates

• male = 1.2 L

• female = 1.1 L

helium dilution method

used when residual volume and functional residual capacity is unknown

what can spirometry not measure

anything involving residual volume

• functional reserve capacity = expiration reserve volume + residual volume

• total lung capacity = vital capacity + residual volume

forced expiratory volume in one second

maximum amount of air you can forcefully exhale in one second

• males =4 L

• females = 3 L

forced vital capacity

total amount of air you can forcefully exhale after taking the deepest breath possible

• males = 5 L

• females = 3.5 L

FEV1/FVC ratio

average = 80%

• under 60% = somethings wrong in airway

how are spirometric measures are affected in obstructive lung disease

• FEV1 - biggest decrease

• FVC - slight decrease or normal

• FEV1/FVC ratio - decreases

• vital capacity decreases

• residual volume increases

• total lung capacity remains the same

how are spirometric measures are affected in restrictive lung disease

• FEV1 decreases

• FVC decreases

• FEV1/FVC ratio - same sometimes increase

• vital capacity significant decrease

• residual volume - stays same

• total lung capacity decreases - hallmark

anatomic dead space

volume of air in the conducting airways that does not take part in gas exchange e.g. trachea and bronchi

• wasted ventilation

• effects breathing efficiency

respiration cycle involving anatomic dead space

1. at end of inhale = dead space filled with 150 ml fresh air

2. exhale 500 ml of air = 1st 150 ml is from dead space and 350 ml from alveoli

3. end of exhale = dead space filled with 150 ml stale air

4. inhale 500ml = 1st 150ml into alveoli is stale air from dead space and 350ml fresh air = 150ml fresh air in dead space

minute ventilation (Ve)

total ventilation over a fixed time period (per minute)

• Ve = tidal volume x frequency of ventilation

• avg - 0.5L breath x 12 per minute = 6 L/min

alveolar ventilation (Va)

volume of alveolar air exchanged per unit of time (per minute)

• Va = (tidal volume - dead space) x breaths per minute

• avg 4.2 L/min

what is the functional difference is multiple Ve with different tidal volumes and frequency all equal the same total

difference in alveolar ventilation

what is the more effecient way of increasing alveolar ventilation

increasing tidal volume rather than frequency bc increasing TV makes dead space a smaller percentage of each breath

eupnea

normal quiet breathing

hyperpnea

increased respiratory rate and/or volume due to increased metabolism e.g. exercise

hyperventilation

increased respiratory rate and/or volume without increased metabolism e.g. blowing up balloon

hypoventilation

decreased alvoelar ventilation e.g restrictive lung disease, asthma

tachypnea

rapid breathing - increased rate with decreased depth e.g. panting

dyspnea

subjective feeling of difficulty breathing

apnea

cessation (stopping) of breathing e.g. voluntary holding breath

total lung capacity

maximum amount of air your lungs can hold after a deep, forced inhalation

• total lung capacity = vital capacity + residual volume

• males 6 L

• females 4.2 L