29 - Lung Volumes Flashcards
o Tidal Volume (Vt):
500 ml during quiet breathing
Volume of air leaving/entering nose/mouth per breath
Determined by mechanics of chest wall, lungs, and activity of respiratory control centers in brain (b/c control center affects respiratory muscles)
o Residual Volume (RV):
1.5 L (emphysema ↑ this)
Volume of gas left in lungs after max. forced expiration
Determined by force generated by expiration muscles, inward elastic recoil of lungs…airway collapse occurs allowing for trapped gas in alveoli
Prevents lung from collapsing at low lung volumes
o Expiratory Reserve Volume (ERV):
1.5 L
Volume of gas expelled from lungs during maximum forced expiration (starts @ end of normal tidal expiration)
Determined by the difference between functional residual capacity (FRC) and Residual volume (RV)
o Inspiratory Reserve Volume (IRV):
2.5 L
Volume of gas inhaled into lungs during maximum forced inspiration (starts @ end of normal tidal inspiration)
Determined by strength of contraction of inspiratory muscles, inward elastic recoil of lung and chest wall and starting point
o Functional Residual Capacity (FRC):
3L
Volume of gas remaining in lungs at end of normal tidal expiration
Represents the balance of inward/outward elastic recoil
o Inspiratory Capacity (IC):
3L
Volume of air inhaled into lungs during maximum inspiratory effort beginning at FRC
o Total Lung Capacity (TLC):
6L
Volume of air in lungs after maximum inspiratory effort
Determined by strength of contraction of inspiratory muscles, inward elastic recoil of lung and chest wall
o Vital Capacity (VC):
4.5 L
Volume of air expelled from lungs during maximum forces exhalation starting after a maximum forced inspiration
• Not measured by spirometry:
o Residual volume
o Functional reserve capacity
o Total lung capacity
o Everything else can be measured by spirometry
• Forced Vital Capacity (FVC)
o Total volume of air that can be forcibly expired after max. inspiration (same thing as VC)
• Forced Expiratory volume in 1st second of exhalation (FEV1)
o Cumulative volume can be measure for the 2nd and 3rd seconds, too.
• FEV1/FVC ratio
o Fraction of total forced vital capacity that can be expelled in the 1st second
o 80% is typical
o Ratio reflects resistance to airflow***
• Forced Expiratory Flow in the middle of expiration (FEV25-75)
o Parameter obtained from flow-volume curve
o It is the flow rate at 25-75% of exhaled vital capacity
o Parameters useful in assessment of obstructive/restrictive lung diseases
o Obstructive LD (Ex. Asthma):
↓ in FVC and FEV1, but FEV1 is reduced more. So, would create a decreased ratio
o Restrictive LD (Ex. alveolar fibrosis):
↓ in compliance, ↓ FVC and FEV1, but FVC is reduced more. So, would create an increased ratio
4) Recognize different patterns of flow volume curve in typical cases of obstructive lung disease, restrictive lung disease, and upper airway obstruction
Asthma (obstructive) - has a steep decline between 25-75
Upper airway obstruction has decreased total volume and does not reach any peaks, simply plateaus
Restrictive lung disease also has a decreased volume and it is shifted far to the right… the flow must be high for the volume to increase at all and when it does increase, it has a similar shape, but smaller size
• Dead Space
o Volume of airways and lungs that don’t participate in gas exchange
• Anatomic Dead Space (~150 mL)
o Volume of the conducting airways (nose, trachea, bronchi, bronchioles).
o At the end of expiration, conducting airways are filled with alveolar air.
• Functional Dead Space
o Alveoli that do not participate in gas exchange due to mismatch in ventilation/perfusion.
o Typically ~0 mL in normal people.
• Physiologic Dead Space (VD)
o Total volume of the lungs that does not participate in gas exchange.
VD = Anatomical Dead Space + Functional Dead Space
So, b/c Functional DS in healthy people ~ 0…Anatomical Dead Space = VD • If physiological is larger than anatomical = suggests ventilation/perfusion defect • Vd/Vt determines estimate of wasted ventilation
6) Calculate minute ventilation
• Minute Ventilation: total rate of air movement into and out of lungs
MV = tidal volume x Respiration Rate
Calculate alveolar ventilation
• Alveolar Ventilation (VA): rate at which new air reaches gas-exchange areas of lung (takes into account physiologic dead space)
VA = (tidal volume – dead space) x Respiration Rate
• Alveolar Ventilation Equation:
describes the inverse relationship between alveolar ventilation and alveolar pressure of CO2
VA = (VCO2 x K) / PACO2
7) Describe alveolar ventilation equation and its meanings with respect to the relationship between tissue CO2 production, alveolar ventilation, and alveolar partial pressure of CO2
- Alveolar Ventilation Equation: describes the inverse relationship between alveolar ventilation and alveolar pressure of CO2
- CO2 production rate can be determined by knowing alveolar ventilation and alveolar pressure of CO2
- If you breath out air faster (alveolar ventilation ↑) then it would make sense that the pressure of CO2 in the alveolar would ↓ b/c you’re getting rid of it faster.
