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What is the maximal volume of all the airways in an adult? What structures does this include?
- 5-6 liters
- Nasopharynx, trachea, all the way to alveolar sacs
What does a simple spirometer measure?
- Volume of air inspired and expired.
- Measures the CHANGE in lung volume
What are the 4 standard lung volumes?
- 1) tidal volume
- 2) inspiratory reserve volume
- 3) expiratory reserve volume
- 4) residual volume
What are the 4 standard lung capacities?
- 1) inspiratory capacity: Vt + IRV
- 2) functional residual capacity: ERV + RV
- 3) total lung capacity: Vt + IRV + ERV + RV
- 4) Vital capacity: Vt + IRV + ERV
Define tidal volume
Volume of air entering and leaving the nose or mouth per NORMAL BREATH
What is the average adult Vt?
Define inspiratory reserve volume
ADDITIONAL volume of air a person can inhale ABOVE TIDAL VOLUME with maximal effort
What is normal IRV?
Define expiratory reserve volume
Volume FORCEFULLY exhaled below tidal volume AFTER a quiet exhalation
What is normal ERV?
1.2-1.5 liters in normal healthy adult
How is ERV mathematically determined?
FRC - RV
Define residual volume
- Volume of air left in the lungs AFTER forced exhalation
- Air that remains in lungs no matter what you do unless lungs collapse
What is the normal RV?
1.5 liters in healthy 70kg adult
What conditions will result in abnormally elevated RV?
Emphysema and COPD
What are 2 functions of residual volume?
- 1) prevents lungs from collapsing at very low lung volumes
- 2) maintains patency of alveoli
Can RV be measured with simple spirometry?
Define total lung capacity
Volume of air in the lungs after MAXIMAL INSPIRATORY EFFORT
What is normal volume of TLC?
How is TLC mathematically calculated?
Define functional residual capacity
Volume of gas remaining in lungs at the end of NORMAL TIDAL EXHALATION
What is the normal volume of FRC?
How is FRC mathematically calculated?
ERV + RV
What is the normal function of FRC?
Prevents dramatic changes in alveolar and arterial oxygen with each breath
What happens when FRC is significantly reduced?
PO2 increases with inspiration and decreases with expiration
How is denitrogenation related to FRC? How long should this take?
- Denitrogenation is replacement of FRC nitrogen with oxygen
- 5 minutes of denitrogenation is ideal; if not possible, have pt take 3-5 good, deep breaths
- Must have good mask seal
Define inspiratory capacity
After QUIET inspiration, IC is MAXIMAL inhalation that one can still inspire
What is normal volume of IC?
How can IC be mathematically calculated?
Vt + IRV
What is the difference between IC and IRV?
- IC begins at the end of normal EXPIRATION
- IRV begins at the end of normal INSPIRATION
Define vital capacity
Volume of air that can be EXHALED with MAXIMUM effort after MAXIMUM inspiration
What is the normal volume for VC?
How can VC be mathematically calculated?
- 1) TLC - RV
- 2) Vt + IRV + ERV
What does VC assess?
- 1) strength of thoracic muscles
- 2) pulmonary function
- Can identify residual NMBD
What conditions may increase VC?
- 1) body size
- 2) men
- 3) physical conditioning
What conditions may decrease VC?
- 1) smoking
- 2) obesity
- 3) supine positioning
- 4) poor posture: kyphoscoliosis or lordoscoliosis
What is FEV1?
- Forced expiratory volume in 1 second
- Volume of air exhaled in 1 second after MAXIMAL inspiratory effort and rapid, as complete as possible, exhalation
How is FEV1 related to VC?
FEV1 is about 80% of VC
What can simple spirometry measure?
- 1) tidal volume
- 2) IRV
- 3) ERV
- 4) IC
- 5) VC
What can simple spirometry not measure?
RV and any volume that includes it (TLC and FRC)
What are 2 types of gas-dilution techniques? What do they measure?
- 1) helium-dilution
- 2) nitrogen-washout
- Measure RV, TLC, and FRC
What does body plethysmography measure?
How does body plethysmography work?
- Application of Boyle's law
- At a constant temperature, increased volume decreases pressure and vise versa
- Patient placed in a closed chamber and makes inspiratory effort against CLOSED mouthpiece
- This measures pressure and volume changes
- Closed chamber resembles phone booth
What changes in FRC can be expected when moving from standing to supine?
Decreased FRC due to abdominal contents compressing diaphragm cephalad; decreased outward elastic recoil of the chest wall
What changes in lung volume can be expected in restrictive lung disease?
Everything is smaller, volumes and capacities
What are some examples of restrictive lung disease?
- 1) quadraplegic (can't expand/contract)
- 2) ascites
- 3) PULMONARY FIBROSIS - classic
- 4) kyphoscoliosis
- 5) lobectomy
- 6) phrenic nerve injury
- 7) rib fracture
- 8) pregnancy
What changes in lung volume can be expected in obstructive lung disease?
- RV is much larger and capacities that include RV are increased:
What is closing volume?
- Volume where airway closure begins to occur
- Bronchioles and alveoli
What is closing capacity?
Lung capacity where small airways begin to close
How can closing capacity be mathematically calculated?
CV + RV
What is the normal relationship between FRC and CC?
- Normal CC is less than FRC
- Increases with age
What is the relationship between FRC and CC at 44 years of age? At 66?
- At 44, they are equal when supine
- At 66, they are equal when standing
What is the relationship between FRC and CC in neonates?
CC > FRC
What is the normal change in PaO2 with age? Why?
Decreases with age due to increased CC
What factors increase CC and CV?
- 1) age
- 2) smoking
- 3) lung disease (asthma, emphysema, bronchitis)
- 4) body position (supine>standing, long-term ICU or nursing home patient)
- 5) decreased plasma oncotic pressure
- With any of these conditions, airways tend to close at higher volumes (more easily)
When lung volume is below CC, how is breathing affected?
- Work of breathing increases due to shunt
- Shunt = perfusion without gas exchange due to closed airways
What will cause airways to remain collapsed when CC > RV?
- 1) any pathological condition with lower tidal volume
- 2) patient does not sign or yawn
Alveoli in what region are most influenced by intrapleural pressure changes? Why?
- Alveoli in bases are most influenced due to lower intrapleural pressure in upright position (less negative)
- Apical alveoli are exposed to more negative intrapleural pressure that minimizes volumetric changes with respiration
Alveoli in what region are most prone to collapsing during active expiration?
What alveoli contribute most to V/Q mismatch?
What is the relationship between weight and deadspace?
Anatomical deadspace is approximately equal to the pt's weight in pounds
How is anatomic dead space measured?
What does Fowler's method do?
Plots nitrogen concentration against expired volume
What is physiologic dead space?
Anatomical dead space + alveolar dead space
What is the symbol for physiologic dead space?
What is physiologic dead space in healthy people?
- Anatomical dead space
- There is no alveolar dead space in normal, healthy people
How is physiologic dead space measured?
What does Bohr's method do?
- Assumes any measurable volume of CO2 in MIXED EXPIRED gas must come from alveoli that are BOTH perfused and ventilated
- It measures the volume that does NOT eliminate CO2
What is normal minute ventilation?
What is minute ventilation?
- Volume of gas EXPIRED per minute
- Vt + RR
- NOT equal to the volume of air entering and leaving the alveoli per minute
What is the symbol for minute ventilation?
What is alveolar ventilation?
Volume involved in gas exchange per minute
What is the symbol for alveolar ventilation?
How is alveolar ventilation related to PaCO2?
- Inversely related
- Hyperventilation will lower PaCO2
- Hypoventilation will increase PaCO2
What is a shunt?
Perfusion without ventilation
What is dead space?
Ventilation without perfusion
What is the normal Deadspace : tidal volume ratio?
- This is the dilution factor
- 30% of every tidal volume = deadspace
- 70% is alveolar ventilation
What are situations involving V/Q mismatch?
- 1) pulmonary emboli
- 2) low venous return causing low right heart output (hemorrhage)
- 3) high alveolar pressure
- 4) PEEP
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