Volumes and Capacities

What does spirometry measure?

The pattern of air movement into and out of the lungs during controlled ventilatory maneuvers

How is spirometry performed?

As a maximal expiratory maneuver, either forced or slow

During an SVC, when is the patient at TLC?

When the curve plateaus at maximal inspiration

Why is spirometry important if physical exam findings can be misleading?

It provides objective evidence to identify patterns of lung disease

Why can spirometry be more useful than relying only on physical exam?

Patients and physicians may inaccurately estimate the severity of airflow obstruction or lung disease by physical exam alone

What two main structures are the lungs composed of?

Airways and alveoli

What happens in the conducting zone?

No gas exchange occurs

What does the conducting zone represent?

Anatomic dead space

What happens in the transitional zone?

Alveoli begin to appear, but they are not present in large numbers

What is found in the respiratory zone?

Alveolar sacs

Is inspiration active or passive?

Active

Is expiration during quiet breathing active or passive?

Passive

Can expiration become active?

Yes

What two lung factors affect spirometry?

Mechanical properties and resistive elements

What does lung compliance describe?

The stiffness of the lungs

What is the relationship used to describe compliance?

Change in volume divided by change in pressure

What is elastic recoil?

The tendency of the lung to return to its resting state

What happens to elastic recoil when the lungs are fully stretched?

Elastic recoil increases

How does greater elastic recoil affect maximal flows?

It produces larger maximal flows

Which direction represents inspiration?

Downward

Which direction represents exhalation?

Upward

What does easy, normal breathing represent on the tracing?

Tidal volume breathing

What maneuver is performed to obtain the volume/capacity tracing?

A vital capacity maneuver, specifically an SVC

What should the patient do first during an SVC test?

Breathe normally to establish tidal breathing and baseline FRC

What does the patient do after establishing baseline FRC?

Inspire maximally, then exhale completely

How is an SVC maneuver performed compared with an FVC?

SVC is slow and complete; FVC is hard and fast

What indicates a good start to an SVC test?

Stable tidal volume breathing and an established FRC baseline

Is coughing acceptable during an SVC maneuver?

No

Is variable flow acceptable during an SVC maneuver?

No

Is early termination acceptable during an SVC maneuver?

No

What should be seen at maximal inspiration and at the end of expiration during SVC?

A slight plateau at each

What is required for SVC repeatability?

Two acceptable SVC maneuvers within 150 ml

How many lung volumes are listed?

Four

How many lung capacities are listed?

Four

What is a lung capacity?

The sum of two or more lung volumes

What are the four lung volumes?

IRV, TV, ERV, and RV

What are the four lung capacities?

IC, FRC, VC, and TLC

What is vital capacity?

The maximum volume of gas that can be exhaled after a maximal inhalation

What normal VC value is listed?

4800 cc

What is the main VC equation?

VC = IRV + TV + ERV

How can VC be calculated using TLC and RV?

VC = TLC − RV

How can VC be calculated using IC and ERV?

VC = IC + ERV

What is an FVC?

Vital capacity exhaled forcefully

What is an SVC?

Vital capacity exhaled slowly

What is the main difference between FVC and SVC?

FVC is forceful; SVC is slow

What is tidal volume?

The amount of gas inhaled or exhaled during a normal respiratory cycle

What normal tidal volume is listed?

500 cc

What weight-based tidal volume value is listed?

10 cc/kg

What type of breathing does tidal volume represent?

Normal quiet breathing

What is IRV?

The maximum amount of air that can be inhaled after a normal tidal inspiration

What normal IRV value is listed?

3100 ml

Where does IRV begin?

After a normal tidal volume inspiration

What is FRC?

The amount of gas remaining in the lungs after a normal tidal exhalation

What normal FRC value is listed?

2400 ml

What is the FRC equation?

FRC = RV + ERV

At what point in breathing is FRC measured?

At the end of a normal tidal expiration, or resting expiratory level

What mechanical balance exists at FRC?

The elastic force of the chest wall exactly balances the elastic force of the lungs

What is TLC?

The total volume of gas in the lungs after maximal inspiration

What normal TLC value is listed?

6000 ml

What is the full-volume equation for TLC?

TLC = IRV + TV + ERV + RV

How can TLC be calculated using IC and FRC?

TLC = IC + FRC

How can TLC be calculated using VC and RV?

TLC = VC + RV

At what point in breathing is TLC reached?

After a maximum inspiration

What is ERV?

The maximum amount of gas that can be exhaled after a normal tidal exhalation

What normal ERV value is listed?

1200 ml

What is the ERV equation?

ERV = FRC − RV

From what point does ERV begin?

The resting expiratory level

What is IC?

The maximum amount of gas that can be inhaled from resting expiratory level

What normal IC value is listed?

3600 ml

What is the IC equation?

IC = VT + IRV

From what point does IC begin?

At the end of a tidal-volume expiration

What is RV?

The volume of gas remaining in the lungs after maximal exhalation

Can residual volume be voluntarily exhaled?

No

How must RV be measured?

Indirectly

What normal RV value is listed?

1200 cc

How can RV be calculated using FRC and ERV?

RV = FRC − ERV

How can RV be calculated using TLC and VC?

RV = TLC − VC

What equation gives vital capacity?

VC = IRV + TV + ERV

What equation gives FRC?

FRC = ERV + RV

What equation gives IC?

IC = IRV + TV

What equation includes every lung volume to calculate TLC?

TLC = IRV + TV + ERV + RV

What patient factors can affect lung volumes?

Age, sex, height, weight, race, and disease

Do SVC and FVC normally differ?

No, except in severe airway obstruction

Why may FVC and SVC differ in severe airway obstruction?

The forceful FVC maneuver may cause airway collapse

Which maneuver is more likely to cause airway collapse in severe obstruction?

FVC because it is forceful

What does an increased VC usually mean?

It is rarely seen and is usually due to underestimation of predicted values

How do lung volumes/capacities generally change in restrictive disease?

They are less than normal

How do lung volumes/capacities generally change in obstructive disease?

They are more than normal

Looking at the disease diagram, which pattern shows overall smaller lung compartments?

Restrictive

Looking at the disease diagram, which pattern shows overall larger lung compartments?

Obstructive