Ventilation / Ventilation Control Tests
RET 2414
Pulmonary Function Testing
Module 5.0
Ventilation / Ventilation Control Tests

Objectives



Calculate tidal volume and minute
ventilation
Describe two causes of increased
ventilation
Identify an abnormal VD/VT ratio
Ventilation / Ventilation Control Tests

Objectives



Calculate dead space and alveolar
ventilation
Describe one method for measuring
breathing response to O2
Identify the normal breathing
response to carbon dioxide (CO2)
Ventilation / Ventilation Control Tests

VT, Rate, Minute Ventilation

Tidal volume (VT) is


Respiratory rate (f)


Volume of gas inspired or expired during
each respiratory cycle
Number of breaths per unit of time
Minute ventilation (

)
Total volume of gas expired per minute

alveolar ventilation (
)

dead space ventilation (
)
Ventilation / Ventilation Control Tests

VT, Rate, Minute Ventilation
.
VE = f x VT

Measured with volume displacement
or flow-sensing spirometer
Ventilation / Ventilation Control Tests

VT, Rate, Minute Ventilation

VT decreased in:



Severe restrictive patterns
Neuromuscular disorders
Decreased VT is usually accompanied by
an increase in respiratory rate in order to
maintain alveolar ventilation (
)
Ventilation / Ventilation Control Tests

VT, Rate, Minute Ventilation

Decreases in both VT and respiratory
rate are often associated with
respiratory center depression

Alveolar hypoventilation
Ventilation / Ventilation Control Tests

VT, Rate, Minute Ventilation

Normal respiratory rates ranges:

10 – 20 breaths/min

Increased in:





Hypoxia
Hypercapnia
Metabolic acidosis
Decrease lung compliance
Exercise
Ventilation / Ventilation Control Tests

VT, Rate, Minute Ventilation

Normal respiratory rates ranges:

10 – 20 breaths/min

Decreased in:


Central nervous system depression
CO2 narcosis; a condition resulting from
high levels of carbon dioxide in the blood.
Confusion, tremors, convulsions, and coma
may occur if blood levels of carbon dioxide
are too high (>70 mm Hg or higher).
Ventilation / Ventilation Control Tests

VT, Rate, Minute Ventilation

Normal minute ventilation ranges:


5 – 10 L/min
When used in conjunction with
arterial blood gases,
indicates the
adequacy of ventilation
Ventilation / Ventilation Control Tests

VT, Rate, Minute Ventilation

Normal minute ventilation ranges:

5 – 10 L/min
increases in response to:






Hypoxia
Hypercapnia
Metabolic acidosis
Anxiety
Exercise
Ventilation / Ventilation Control Tests

Dead Space /Alveolar Ventilation

Dead space is the lung volume that
is ventilated but not perfused by
pulmonary capillary blood flow


Anatomic (conducting airways) VDan
Alveolar (non-perfused alveoli) VDA
VDan + VDA = VD

VD
(Respiratory or Physiologic Dead Space)
Ventilation / Ventilation Control Tests

Anatomic Dead Space
Ventilation / Ventilation Control Tests

Dead Space /Alveolar Ventilation

The portion of ventilation wasted on
the conducting airways and poorly
perfused alveoli is usually expressed
as a ratio:
VD/VT =
(PaCO2 – PECO2)
PaCO2
Modification of Bohr’s equation
X 100
Ventilation / Ventilation Control Tests

Dead Space /Alveolar Ventilation

For convenience VD is often estimated as
equal to anatomic deadspace;
VD = 1 ml/lb of ideal body weight
Valid only if little or no alveolar dead space
exists due to pulmonary disease
Ventilation / Ventilation Control Tests

Dead Space /Alveolar Ventilation

Normal VD/VT ratio in adults:
 0.3 or 30% (0.2–0.4 or 20%–40%)

Increases with:




Pulmonary embolism
Acute pulmonary hypertension
Decreased cardiac output
Decreases with:

Exercise (increase cardiac output and
perfusion of lung apices)
Ventilation / Ventilation Control Tests

Dead Space /Alveolar Ventilation

Alveolar ventilation is the volume of
gas that participates in gas
exchange in the lungs per minute
Ventilation / Ventilation Control Tests

Dead Space /Alveolar Ventilation


Alveolar ventilation at rest is
approximately 4 – 5 L/min
The adequacy of
can only be
determined with an arterial blood gas
(ABG)
Hypoventilation = PCO2 >45 with a pH <7.35
Hyperventilation = PCO2 <35 with a pH >7.45
Ventilation / Ventilation Control Tests

Dead Space /Alveolar
Ventilation

Decreased

Increases in VD




can result from:
Destruction/dilation airway walls
>FRC (air trapping/hyperinflation)
Bronchodilators
Decreases in
Ventilation / Ventilation Control Tests

Ventilatory Response to CO2

Ventilatory response to CO2 is a
measurement of the increase or
decrease in
caused by breathing
various concentration of carbon
dioxide while PaO2 is kept normal
Ventilation / Ventilation Control Tests

Ventilatory Response to CO2
Procedure
1-7% CO2 is breathed
through either an open or
closed circuit while the
following are measured:
•
•PeTCO2
•SaO2
•P100
Ventilation / Ventilation Control Tests

Ventilatory Response to CO2

Normal response to an increased PACO2 is a
linear increase in ventilation (
)


Approximately 3 L/min/mm Hg (PCO2)
Ventilation / Ventilation Control Tests

Ventilatory Response to CO2

Decreased in patients with:
 COPD

Increased airway resistance (Raw)

Lesions in the CNS

Chemoreceptor dysfunction
Ventilation / Ventilation Control Tests

Ventilatory Response to Oxygen

Ventilatory response to O2 is a
measurement of the increase or
decrease in
causes by breathing
various concentration of O2 while
PaCO2 is kept normal
Ventilation / Ventilation Control Tests

Ventilatory Response to Oxygen
Procedure
20%-12% O2 is breathed
through either an open or
closed circuit while the
following are measured:
, PaO2, P100, PetCO2
The test is repeated with
decreasing concentrations
of O2
Ventilation / Ventilation Control Tests

Ventilatory Response to Oxygen

Normal response to a decreasing PaO2 is an
exponential increase in ventilation (
) once
the PaO2 is less than 60 mm Hg (SaO2
<90%)
60 torr/90% Saturation
O2
Ventilation / Ventilation Control Tests

Ventilatory Response to Oxygen

Significance and Pathology

Patients with obesity-hypoventilation
syndrome, obstructive sleep apnea,
and idiopathic hypoventilation will
show a marked decrease response to
hypoxemia
Ventilation / Ventilation Control Tests

Occlusion Pressure (P100 or P0.1)


P100 is the pressure generated during
the first 100 milliseconds of
inspiratory effort against an occluded
airway.
It is a measurement of the neural
output from the medullary centers
that drive ventilation rate and volume
Ventilation / Ventilation Control Tests

Occlusion Pressure (P100 or P0.1)
Normally P100 values
are:
1.5 – 5.0 cm H2O
Usually measured at
varying PetCO2 values
or levels of O2
desaturation to assess
the effect of changing
stimuli to ventilation
Ventilation / Ventilation Control Tests

Occlusion Pressure (P100 or P0.1)
P100 is usually
plotted against
PetCO2
Ventilation / Ventilation Control Tests

Occlusion Pressure (P100 or P0.1)

P100 values will normally increase with
PaCO2 (hypercapnia) or PaO2
(hypoxemia)


Healthy patients typically increase occlusion
pressure 0.5 to 0.6 cm H2O/mm Hg PCO2
Patients with COPD will not increase the
P100 when the PaCO2 in increased