Mechanics of Breathing - Lecture 18 Flashcards
What is the first step of respiration?
Pulmonary ventilation (breathing): Inspiration and expiration of air between atmosphere and lungs (alveoli)
What is the second step of respiration?
External (pulmonary) respiration: exchange of gases between alveoli and blood in pulmonary capillaries
What is the third step of respiration?
Exchange of gases between blood in systemic capillaries and tissue cells
What is Boyle’s law?
When the temperature of a gas is constant , the volume of the gas varies inversely with volume
What is the atmospheric and intrapulmonary pressure like during inspiration?
Intrapulmonary pressure is lower than atmospheric pressure
What is the atmospheric and intrapulmonary pressure like during expiration?
Intrapulmonary pressure is higher than atmospheric pressure
What is intrapleural pressure?
○ Refers to the pressure within the pleural cavity
○ Always lower than atmospheric and intrapulmonary pressures (always negative)
○ Created by elastic recoil of the lungs
○ Keeps lungs inflated
What forces need to be overcome during breathing?
○ Lung compliance (how easily the lungs can expand):
- Elasticity of the lung tissue
- Surface tension of alveoli
- Mobility of chest wall
○ Airway resistance
How does each force affect breathing?
○ Elastic recoil: opposes inspiration and aids expiration
○ Airways resistance opposes both
What does lung compliance relate to?
Change in volume/Change in pressure
What is Laplace’s law?
○ P = 2T/r
○ P - Pressure
○ T = surface tension
○ r = radius of a alveolus
How does the surfactant in the alveoli prevent them collapsing?
○ Greatly reduces surface tension and increases compliance
○ Equalises the pressure difference between small and large alveoli (smaller alveoli have more surfactant)
What is neonatal respiratory distress syndrome?
○ Lack of surfactant secretion in premature babies
○ Reduced compliance
○ Alveoli collapse on exhalation
○ Difficult to inflate lungs
○ 50% die without rapid treatment
What factors can affect airway resistance?
○ Lung volume: bronchi dilate as lung expands
○ Bronchial smooth muscle:
- Parasympathetic nerves: bronchoconstriction
- Sympathetic nerves: bronchodilation
What stimuli can cause bronchoconstriction?
○ Smoke, dust, irritants
○ Histamine
What is forced vital capacity and vital capacity?
○ VC = Maximum amount of air that can be expired after a maximum inspiratory effort
○ FVC = Forceably breathing out VC
What is FEV1?
○ Forced expiratory volume in 1 second: the volume of air expired in 1 second
○Used to assess changes in resistance to airflow e.g. asthma patients
○ Above 70% = healthy adult
What does it mean if there are no breath sounds?
Collapsed lung
What is a peak flow meter?
○ Measures the speed at which you are able to breathe air out
○ Used by chronic asthmatics on a regular basis: not good if value decreases
What does a spirometer measure?
Lung volume and capcacities
What is tidal volume?
○ The volume of air moved per breath
○ 500ml in both men and women
What is functional residual capacity?
○ Helps to stabilise the composition of alveolar air
○ Volume of air left in the lungs after a normal, passive exhalation
○ Cannot be measured by spirometry as it includes the residual volume
What is expiratory reserve volume?
○ The amount of air that can be forcibly exhaled after a normal tidal volume exhalation
○ Males = 1000ml, Females = 700ml
What is inspiratory reserve volume?
○ Amount of air that can be forcibly inhaled after a normal tidal volume inhalation
○ Males = 3300ml, Females = 1900ml
