M103 T4 L1 Flashcards
What are the three inspiratory muscles?
diaphragm
intercostals
accessory muscles
Which inspiratory muscle is primarily responsible for inspiration? What proportion of volume change is it responsible for?
The diaphragm, 75%
How far down does the diaphragm push during tidal breathing and during forced inspiration?
inspiration - 1cm
forced - 10cm
What happens when the external intercostal muscles contract?
pulled upwards and forwards
(act like a bucket handle)
increases thoracic volume
What is a clinical sign of respiratory distress?
The accessory muscles being involved in respiration
particularly the scalene and sternomastoid muscles
Describe the process of inspiration
Contraction of inspiratory muscles Intrathoracic volume increases Decrease in intrapleural pressure Lungs pulled into more expanded position Pressure in the airways becomes negative Air moves in down the concentration gradient Pressures are now equal Lungs recoil
What is the standard intrapleural pressure?
-2.5 mmHg
Describe the process by which transpulmonary pressure is generated
The chest wall exerts a distending pressure on the pleural space
This pressure is transmitted to the alveoli to increase its volume, lower its pressure and generate airflow backwards
What is the relationship between transpleural and the elastic recoil pressure?
For any given value, the transpleural pressure is equal to and opposite to elastic recoil pressure of the lung
What is the average lung capacity among healthy adults?
about 6 liters
Describe compliance in the normal lung
compliance is just right
Good compliance for low work of inhalation
Good retention of elasticity of alveolar units
allows for effective exhalation
Describe compliance in a lung suffering from interstitial fibrosis
compliance is decreased
alveolar walls are more stiff due to fibrosis
Describe compliance in a lung suffering from emphysema
complience is increased due to loss of alveolar interdependence
Why can surface tension lead to the collapse of alveolar?
due to the tendency of water molecules to form spheres due to surface tension pressures
surface tension can increase with emphysema and age
How does DPPC work to reduce surface tension?
the hydrophobic and hydrophilic ends repel eachother and interfere with lipid molecule attraction resulting in lower surface tension
What are the two main clinical syndromes of surfactant deficiency?
neonatal respiratory distress syndrome
Surfactant dysfunction
Why is surfactant important?
Increases lung compliance
Promotes alveolar stability
Prevents alveolar collapse
tends to suck fluid from the capillaries into the alveoli
What causes airway resistance?
Friction between the air and the mucosa
What does normal lung compliance look like on a graph?
Hysteresis loop. Difference in compliance is due to the increased level of energy required for inspiration. More volume in deflation than inflation, as some of the pressure in inflation is being used to recruit and inflate the alveoli
What are the two elastic components of the lung?
Elastin fibres in the alveolar walls, bronchioles and capillaries, and alveolar surface tension
What is the functional residual capacity?
Balance point where lungs and chest are in equilibrium (after exhaling); lungs sit at this position naturally
What do inspiration and expiration do to the intrapleural pressure?
Makes it more negative, and expiration makes it more positive so air is forced out of the lungs as chest wall and diaphragm relax
How does pressure change during the quiet breathing cycle in inspiration?
- Flow line before breathing = 0, increases inwards and RR slows and stops
- to generate flow, create pressure gradient through a change in alveolar pressure; this drives flow and changes lung volume
- reflects static compliance of lungs + generation of driving force of negative alveolar pressure
How does pressure change during expiration in the quiet breathing cycle?
- Flow increases, going outwards, rate slows + stops - back to zero
- At end of breath, alveolar pressure back to 0. Changing pressure down drives flow out
- Intrapleural pressure again reflects the compliance and pressure creating this alveolar pressure. Faster lung contraction creates an increase in alveolar pressure
What is the Poiseuille equation and what does it represent?
Resistance is inversely proportional to 4th power of radius; flow is inversely proportional to the viscosity of a fluid. I.e more flow for less viscous liquid
What are the factors in airway resistance?
Inflammation, mucus, bronchodilators, steroids, gas density
What increases the likelihood of turbulent flow?
High velocity, large tube diameter
Where does turbulent flow occur?
Trachea
