Lung physiology Flashcards
What are muscles involved in inspiration?
Diaphragm- 70% of volume change phrenic C3-5
innervation
External intercostals- lift ribs 2-12
widen thoracic cavity
Scalenes- lift ribs 1&2
Pectoralis major- lift ribs 3-5
Sternocleido.- elevates sternum
Muscles relax to allow passive expiration
What innervates the diaphragm?
C3, 4, 5
Phrenic
Keep the diaphragm alive
Function external intercostal?
Lift ribs 2-12
Widen thoracic cavity
Function scalenes?
Lift ribs 1 and 2
Function pectoralis major?
Lift ribs 3-5
Function sternocleidomastoids?
Elevate sternum
What occurs to achieve passive expiration?
Muscle relaxation
What muscles used during active expiration?
Internal intercostals- depress ribs 1-11
Rectus abdominis- depress lower ribes
- compress abdominal organs and diaphragm
What muscles used during active expiration?
Internal intercostals- depress ribs 1-11
Rectus abdominis- depress lower ribes
- compress abdominal organs and diaphragm
Define:
PaCO2
PACO2
PaO2
PAO2
PIO2
V’A
V’CO2
PaCO2 arterial CO2
PACO2 Alveolar CO2
PaO2 arterial O2
PAO2 Alveolar O2 (~14kPa)
PIO2 Pressure of inspired O2
V’A Alveolar ventilation
V’CO2 CO2 production
What does ‘a’ represent?
arterial
What does ‘A’ represent
Alveolar
At what point is Hb fully saturated through capillary bed?
Fully sat 25% WAY THROUGH
What occurs when hypoxia?
Hypoxia
Pulmonary vasoconstriction
Maximise ventilation-perfusion
Optimal gas exchange
Altered posture
How is CO2 transported?
Bound haemoglobin
In plasma (dissolved CO2 as HCO3-)
Define Boyle’s law?
Boyle’s Law: P1V1=P2V2
How does Boyle’s law apply to ventilation?
Inspiritary muscles contract
Thoracic cavity volume increases
Allows air to flow into lungs:
1) increased transpulmonary pressure (Palveolar – Pintraplueral)
2) alveolar pressure lower than atmospheric
3) expiration caused by decreasing transpulmonary pressure
4) ribcage pressing down on lungs
5) alveolar pressure increases above atmospheric
6) air flow out
What limits lung expansion?
Compliance- ability stretch and expand
Determined by amount elastic tissue and surface tension in alveoli
What reduces surface tension in alveoli?
Surfactant
Define normal pH?
7.35-7.45
What is Henderson Hasellback equation for pH?
pH = pKₐ + log([A⁻]/[HA])
pH=6.1 + log10([HCO3-]/[0.03PCO2])
Equation for dissociation of CO2?
CO2 + H2O to H2CO3 to H+ + HCO3-
What enzyme is involved in the dissociation of CO2?
Carbonic anhydrase
How is pH maintained?
CO2 dissociation
renal secretion/reabsorption
protein buffers
Characteristics of respiratory acidosis?
Low pH
High HCO3-
High pCO2
What are causes of respiratory acidosis?
Lack respiratory drive
Restriction airways
Hypoventilation
COPD2
Impaired CO2 elimination cause hypercapnia (smaller 6kPA)
What compensates respiratory acidosis?
Retention and production HC03-
H+ secretion
Characteristics of respiratory alkalosis?
High pH
Low HCO3-
Low CO2
What is the cause of respiratory alkalosis?
Hyperventilation, fever
Loss CO2 causes hypocapnia
H2CO3 converted CO2 meaning less H+
pH raised
Define tidal volume?
Volume inhaled/exhaled in normal breath
500ml
Define inspiratory reserve?
Max air that can be inhaled minus tidal volume
3L
Define expiratory reserve volume?
Mac air that can be exhaled minus tidal volume
1.2L
Define residual volume?
Air remaining in lungs after max expiration to prevent collapse
1.2L
Define vital capacity?
Max air expired after max inspiration
4.7L
(ERV +TV + IRV)
Define inspiratory capacity?
Max inhalation after normal tidal expiration
3.5L
(IRV + TV)
Define functional residual capacity?
Air in lungs after tidal expiration
2.4L
(RV+ERV)
Define total lung capacity
Total volume of air in lungs after maximal inspiration
5.9L
(RV+VC)
Define FEV1? Amount?
Forced exp. Volume in 1 second
80% of vital capacity in healthy person
Define FVC?
forced vital capacity- max air expired under max force after max inspiration
Define PEF?
Peak air flow
Highest velocity of air measured during FVC
Flow will decrease linearly in healthy person after PEF
Define DLCO?
Diffusing capacity of lung for carbon dioxide
Measure efficiency gas exchange
Known [CO] inhaled, 10 sec breath hold, expired [CO] measured
Reduced with COPD
What will an airway obstruction cause? (Lung vol)
Causes
Ratio?
Decreasing FEV1
Increasing RV
Increasing TLC
FVC similar
Ratio FEV1/FVC reduced below 0.7
e.g. COPD, asthma
Define airway restriction?
Causes?
Ratio?
Reduced compliance of lungs
Reduce FEV1 and FVC- ratio same
Everything else reduced
Pulmonary fibrosis
Define airway restriction?
Causes?
Ratio?
Reduced compliance of lungs
Reduce FEV1 and FVC- ratio same
Everything else reduced
Pulmonary fibrosis
Label:
Tidal volume
Inspiratory reserve
Expiratory reserve
Residual volume
Vital capacity
Insp. capacity
Functional residual capacity
Total lung capacity
How to calculate vital capacity?
ERV+TV+IRV
4.7L
How to calculate inspiratory capacity?
IRV+TV
3.5L
How to calculate functional residual capacity?
ERV+VC
2.4L
How to calculate total lung capacity?
RV+VC
5.9L
State process of inspiration?
Diaphragm- flattens
External intercostal muscles- elevate ribs and sternum- extend thoracic
Increase volume thoracic cavity- lungs increase
Decrease pressure in lungs- Boyles law
Pressure higher environment than lungs
Air move down pressure gradient
Explain process passive expiration?
Relaxation inspiratory muscles
Diaphragm- return resting position- reduce thoracic cavity
External intercostal relax- depress rib and sternum
Decrease volume thoracic cavity- increase pressure
Pressure inside lungs greater external environment
Air moves out lung
Down pressure gradient
Explain forced breathing? When used?
Exercise
Active inspiration- contraction accessory muscles
Scalenes – elevates the upper ribs.
Sternocleidomastoid – elevates the sternum.
Pectoralis major and minor – pulls ribs outwards.
Serratus anterior – elevates the ribs (when the scapulae are fixed).
Latissimus dorsi – elevates the lower ribs
Increase volume thoracic cavity
Outline how active expiration occurs?
Anterolateral abdominal wall – increases the intra-abdominal pressure, pushing the diaphragm further upwards into the thoracic cavity.
Internal intercostal – depresses the ribs.
Innermost intercostal – depresses the ribs.
Decrease volume thoracic cavity
