Pulmonary Physiology 1 (9/23a) [Biomedical Sciences 1] Flashcards
What is the main function of the pulmonary system?
Exchange oxygen and carbon dioxide between cells and the environment
Must adapt to changing demands
Ventilation, gas exchange, gas transport, ventilation-perfusion matching,
defense system
Respiratory demands - rest vs exercise
Rest: VO2 250 mL/min, minute ventilation 5 L/min
Exercise: VO2 5000 mL/min, minute ventilation 100 L/min
How do we assess ventilation?
use the spirometer to measure volumes and capacities
measure air flow
Tidal Volume (TV)
volume of air we are usually breathing
Normal amount is about ~½ L
can vary based on sex, age, height
Inspiratory Capacity (IC)
combination of TV and IRV
Vital Capacity (VC)
max inhale to max exhale
combination of IRV, TV, and ERV
Inspiratory/Expiratory Reserve Volume (I/ERV)
max inhalation/max exhalation
Reserve Volume (RV)
the little bit of air left in our lungs after an exhale
Functional Residual Capacity (FRC)
volume of air in the
lungs at the bottom of a normal exhale
combination of ERV and RV
Total Lung Capacity (TLC)
capacity of air from a max inhale to max exhale plus RV
combination of VC and RV
Ventilation
the bulk flow of air into/out of the lungs
Pin = alveolar pressure , Pout = barometric/atmospheric pressure
Air flows from high to low pressure
Mechanical ventilators are ___ ___ ventilation
positive pressure
How does air get into the lungs?
For air to flow into the lungs: Pin < Pout
Contraction of inspiratory muscles
Increased thoracic cavity
How does air get out of the lungs?
For air to flow out of the lungs: Pin > Pout
Air is expelled until Pin=Pout
Diaphragm relaxes and thoracic cavity decreases
Lungs recoil and compress alveoli
Properties of the thorax
Volume is large at equilibrium (Pin = Pout)
Usually wants to expand
Outside forces can cause the thorax to collapse or expand
Once outside force stops acting, thorax will return to equilibrium point
(ex: tennis ball)
Properties of the lungs
At equilibrium, volume is small ( Pin = Pout )
Outside forces (muscles) generally cause the lung to expand
Once the outside force stops acting, lung collapses back to equilibrium point
Compliance
Lung Compliance
Compliance = ΔV/ΔP (ex: slinky)
When volume is high → compliance is low (stiff)
When volume is low → compliance is high (stretchy)
The muscles will have to work much harder to stretch the lungs when
they are at high volume
Pleura
lines the inside of the pleural cavity and outside of the lungs
Pleural Coupling
pleural fluid that acts like glue and allows the lung and chest
wall to stick together
Cohesive force holds visceral and parietal pleura together
At new equilibrium point, lung partially expanded and thorax
partially collapsed
Tug of war creates produces negative Pip (because pulling apart)
Equilibrium point for lungs+thorax
functional residual capacity (FRC)- point where the collapsing force of the lung is balanced by the expanding force of the thorax
During inhalation, move right on curve
During exhalation, move left on curve
Pressure Gradient - Inspiration
Volume increases
Intrapleural pressure decreases
Alveolar pressure decreases
then increases back to its original point
Pressure Gradient - Expiration
Volume decreases
Intrapleural pressure increases then tapers off
Alveolar pressure increases then decreases back to its original point
Minute (total) ventilation
MV = tidal volume * respiratory rate
Some air stays in the conducting zone and doesn’t participate in gas exchange
Tidal Volume avg ~ 450 mL, RR 12 breaths/min → MV = 5.4 L/min
Conducting Zone
Conducting zone = anatomic dead space
Avg ~150 mL → can increase in disease states
Air has less oxygen and more carbon dioxide → already equilibrated
Alveolar ventilation
AV = (tidal volume - dead space volume) * respiratory rate
Alveolar ventilation (L/min) accounts for dead space
EX: (0.450 L - 0.150 L) * 12 breaths/min → AV = 3.6 L/min
Distribution of ventilation
When upright, the apex of the lung is more stretched and less compliant, due to gravity
The base is more compliant and can expand more during ventilation
We can use change in position to change degree of ventilation to the lungs
Measures of airflow
Obtained during a max inhalation
FVC, FEV1, and FEV1/FVC
Forced vital capacity (FVC)
telling pt to breathe as hard and as fast as they can
Forced Expiratory Volume in 1 second (FEV1)
volume of air exhaled in the first second
Strongest indicator of pulmonary disease
FEV1/FVC
useful indicator of pulmonary disease, and determining obstructive or restrictive pattern of disease
What affects the function of the pump?
Muscle weakness
Decoupling pleural membranes
Tissue compliance
Airway diameter
Surface tension and surfactant
Affecting Pump - Muscle Weakness (high cervical lesion)
C3 or above
Paralysis of diaphragm , requires mechanical ventilation
Affecting Pump - Muscle Weakness (low cervical lesion)
Diaphragm innervated but intercostals and abdominals are not
Contraction of diaphragm causes collapse of thoracic cage
-Upper chest paradoxical pattern
Loss of abdominals leads to flattening of diaphragm, expansion of
abdomen during inspiration → we can use abdominal binder or positioning
Affecting Pump - Decoupling Pleural Membrane
when the pleural membrane is decoupled, the thorax and lungs pull apart from each other and lose the equilibrium point
Pneumothorax = collapsed lung
Affecting Pump - Increased Tissue Compliance
Easier to expand lung, but it doesn’t snap back to normal resting volume
-Decreased elastic recoil
In severe cases, exhalation requires active contraction of abdominals
Destruction of airway support = airway collapse
Higher FRC (equilibrium)→ diaphragm flattened -Decreased mechanical advantage, less efficient
Increased work of breathing
-Up to 25% of VO2 (usually 5% in healthy people)
EX: emphysema → destroys elastic fibers in lung tissue
Affecting Pump - Decreased Tissue Compliance
Increased muscle effort required for inspiration and work of breathing
Lower FRC (equilibrium)→ low lung volume = smaller airway diameter
Increased resistance to flow, increased risk of airway collapse
EX: fibrosis, chest wall disorders (kyphosis, scoliosis, sarcoidosis, lupus)
Affecting Pump - Surface Tension
Surface tension pushes alveoli walls in toward collapse
Surfactant produced by lung epithelium
-Reduces surface tension to keep alveoli open
Respiratory distress syndrome=loss of surfactant leads to alveolar collapse/atelectasis
-Decreased lung compliance, decreased surface area for gas exchange
Affecting Pump - Airway Diameter
Resistance to airflow determined by airway diameter
Inspiration → airway diameter increases
Expiration → airway diameter decreases
- Dynamic compression - the harder we breathe, the more this airway collapse occurs
- Limits peak flow during expiration
Inspiration vs Expiration
INSPIRATION
- Volume of thorax increases
- Fall in alveolar pressure causes air to move into lung
EXHALATION
- Volume of thorax decreases
- Increase in alveolar pressure causes air to move out of lung
Air flow into/out of the lungs is driven by
the pressure gradient between the alveoli and the atmosphere
-Changes in the volumes of the thoracic cavity create those pressure gradients
