Lung Volumes And Capacities Flashcards
What is the alveolar capillary unit?
The physiologic unit of the lung
What is tidal volume (VT)?
The amount of air inspired/expired in a single breath
Varies under circumstances (ex. During aerobic exercises)
What is normal resting tidal volume?
500mL
What is residual volume (RV)?
Volume of air that cannot be forced out no matter how hard one tries
Cannot be determined by spirometry
What is inspiratory reserve volume (IRV)?
Additional volume that can be inhaled greater than tidal volume
Gap between inspiration during TV and max inspiration
What is expiratory reserve volume (ERV)?
Additional volume that can be exhaled greater than tidal volume
Does not include RV
What does ERV require?
Activation of expiratory muscles (i.e. active respiration)
What is total lung capacity (TLC)?
Maximal volume to which lungs can be expanded with greatest effort
Cannot be measured by spirometry
IC + FRC = VC + RV = ERV + RV + IRV + VT
What is functional residual capacity (FRC)?
Amount of air that remains in the lungs following a normal expiration
Cannot be determined by spirometry
ERV + RV
What is the function of FRC?
Helps prevent collapse of lungs, reduces workload, dilutes toxic inhaled gases
What is vital capacity (VC)?
Amount of air that can be maximally inspired following a maximal expiration
IRV + VT + ERV
What is VC influenced by?
Posture, ability of diaphragm to contract/relax, strength of respiratory muscles, thoracic wall expansibility, resistance to air flow, elasticity and disease
What is inspiratory capacity (IC)?
Capacity of air that can be maximally inspired following a normal exhalation
VT + IRV
FVC (TLC and VC) are largely impacted by what?
Disease
What are factors that can change pulmonary volumes and capacities?
Body size, age, posture, sex, ethnicity, obesity and pulmonary disease
Which capacities and volumes increase with age?
FVC, FRC and RV
Which capacity is reduced when supine?
FRC
What does obesity cause?
A reduction in all static long volumes (except for TV) particularly expiratory reserve volume and FRC
What are the main changes that occur when one ages?
TLC say similar
RV increases
VC goes down
What are other changes that can occur with age?
ERV decreases but RV increases to a greater extent so FRC increases
IC decreases
Both TLC and VC are greater in what position?
Seated (rather than supine)
Which volume has equal quantities when either seated or supine?
RV
Which other capacities are also greater when seated than when supine?
FRC and ERV
IC is greater in which position?
Supine (slightly)
What main changes occur with obesity?
Reduces TLC and VC
RV stays similar
Seated vs supine becomes very similar to one another
What other changes occur with obesity?
ERV largely reduces, IC less largely impacted and FRC is lower
What is emphysema?
Destruction of alveoli and capillaries
Obstructive lung disease characterized by limitations of airflow due to partial or complete obstruction
Hard to push air out often
What changes occur with emphysema?
TLC and RV increases
VC decreases
What is fibrosis?
A restrictive lung disease
Thickening of tissue between alveoli
Characterized by reduced expansion of lungs, hard to inflate or fill the lungs
What changes occur with fibrosis?
RV, TC and VC decreased
What are some techniques for measuring residual volume?
Helium (He) dilution, body plethysmography, nitrogen washout technique
What is helium (He) dilution?
Inhalation of a known concentration of helium (C1; insoluble in blood) from a known volume (V1)
Change in concentration (C2) allows for determination of V2 = FRC which allows you to calculate RV
What is body plethysmography?
Enclosed rigid box
Breath against shutter
Pressure in lungs change and pressure in box changes proportionally in opposite direction
Boyles Law (P1V1 = P2V2)
What does nitrogen washout determine?
Dead space
What is the nitrogen washout technique?
Individual breathes 100% oxygen through one way valve, all expired gas is collected and monitored until N2 reaches zero
Total volume of all gas expired is determined and multiplied by % of N2 in mixed expired air (usually 80%)
What is the basic model for pulmonary dead space?
VT = VA (volume that participates in gas exchange; alveolar) + VD (does not participate in gas exchange)
How much is anatomical dead space usually?
1 mL per lb in BW
