BPK 305 - Lecture 26

minute ventilation equation

tidal volume x respiratory rate

normal minute ventilation

7.5 L/min

what can't a spirometer measure?

- residual volume

- functional residual capacity

- total lung volume

inspiratory reserve volume

Amount of air that can be forcefully inhaled after a normal tidal volume inhalation

tidal volume

Amount of air that moves in and out of the lungs during a normal breath

expiratory reserve volume

Amount of air that can be forcefully exhaled after a normal tidal volume exhalation

residual volume

Amount of air remaining in the lungs after a forced exhalation

inspiratory capacity

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

functional residual capacity

volume of air remaining in the lungs after a normal tidal volume expiration

vital capacity

The total volume of air that can be exhaled after maximal inhalation.

FEV1

forced expiratory volume in 1 second

normal FEV1

over 0.7

asthmatic FEV1

0.45

what must spirometers correct for?

body temperature and pressure, saturated with water

Helium dilution method

used to measure residual volume;

uses helium because it has a poor water solubility and does not diffuse out of alveoli into plasma

done by connecting a patient to a closed system with a known volume of air containing and known concentration of helium

helium dilution equation

C1 x V1 = C2 x (V1 + V2)

residual volume equation

FRC-ERV

total lung capacity equation

IC + FRC

what is a normal functional residual capacity?

3L

what is tidal volume equal to?

dead space volume + alveolar volume

what is physiological dead space?

anatomical dead space + alveolar dead space

what is anatomical dead space?

conducting airways

what is alveolar dead space?

alveoli that are ventilated but not perfused

what does mismatch of ventilation and perfusion during lung disease do?

increased physiological dead space without affecting anatomical dead space

how can dead space be measured?

- Fowlers method (anatomical)

- Bohrs method (alveolar)

Fowlers method

1. inspire 100% O2. Dead space is fulled with O2 and alveolar N2 mixes with the O2

2. expire through a N2 meter

3. see where the slope reaches 50% height

Bohrs method

1. measure PaCO2 to estimate PACO2

2. measure PETCO2 which reflects the combination of perfused and non perfused alveolar CO2

3. plug into Bohr equation

Bohr equation

VD/Vt = PaCO2 - PECO2/PaCO2

alveolar ventilation rate

frequency x (tidal volume - dead space)

forced vital capacity

the maximum amount of air that can be removed from the lungs during forced expiration

FEV1/FVC less then 0.75

suggests obstructive pulmonary disease

Peak Expiratory Flow Rate (PEFR)

measure of the fastest flow of exhaled air after a maximal inspiration

FEF 25-75%

- Forced Expiratory Flow at 75, 50 or 25% FVC

- sensitive indicator of small airway function

what part of expiration is effort dependent?

20%

what happens at low VL?

- expiratory flow is

"effort independent" and "flow limited"

- airways begin to become compressed at low lung volumes

dynamic compression

airways close during forced exhalation

- greater in COPD

Normal flow volume loop

- upside down ice cream cone

- 5L to 1.8L

- max exhalation 10L/s

- max inhalation 8L/s

restrictive flow volume loop

- skinny and tall

- reduced volumes 3L to 1L

- similar FEV1 at 8L/s

- similar max inhalation flow

Obstructive flow volume loop

- short and wide

- reduced FEV1 at 3/s

- larger volumes 6L to 2L

what is PEFR used to monitor?

asthma, can detect abnormal functioning before symptoms

what do normal PEFR values depend on?

-age

-gender

-height

-weight

average PEFR

600 L/min

asthmatic PEFR

250 L/min

normal lung sounds

- a quiet "whoosh" distributed evenly over chest (vesicular sounds) "wind in

the trees"

- Sounds over large airways (bronchial sounds) more tubular "blowing in tube".

what do wheezes indicate?

narrowed airways

- asthma

what do crackles indicate?

fluid in the lungs

- heart failure, pneumonia

what do diminished or absent breathing noises indicate?

reduced flow

- pneumothorax

what does friction rub indicate?

inflamed pleural membranes

what does stridor indicate?

turbulent airflow in upper airway due to obstruction/inhaled foreign body

what does grunting indicate?

in premature infants with respiratory distress due to lack of surfactant