The second presentation of respiratory physiology series

1. VENTILATION
PRESENTER: Keagan Kirugo
DISCUSSANTS:The Circle

5. OBJECTIVES
 Lung volumes
 Aspects of ventilation
 Regional differences in respiration

6. A. LUNG VOLUMES

7.  Lung volumes are measured by a spirometer.
 Using the original spirometer in the previous
slide for demonstration purposes; during
exhalation, the bell goes up and the pen goes
down marking a moving chart.

8.  Normal breathing is seen, the tidal volume.
 Next, the subject takes a maximum
inspiration followed by a maximum
expiration.The exhaled volume is the vital
capacity.
 However, some gas remains in the lung after
maximum expiration is the residual volume.
The volume of gas remaining in the lung after
a normal expiration is the functional residual
capacity (FRC)

10.  Spirometer is limited in the measurement of
residual volume, FRC andTLC.
 FRC can be measured by the Helium-dilution
method and plethysmography.

12.  The spirometer is filled with a small
concentration of helium (He). He is insoluble
thus cannot be absorbed by the blood.
 Valve is opened and the subject takes normal
breaths.The patient starts to breath at FRC.
 Breathing continues till there is equilibration
between the spirometer and the alveolar gas.

13.  Oxygen is added at this point to cater for the
O2 requirement of the subject. CO2 that is
exhaled is removed.
 FRC is thus obtained by
C1 xV1= C2 x (V1 + FRC)
 Plethysmography has replaced helium-
dilution method.

15. B. ASPECTS OF VENTILATION
 Total ventilation=Tidal volume x frequency
of breathing in a minute
 Thus change in tidal volume and frequency of
breathing will affect the total ventilation.
 Alveolar ventilation=Total ventilation –
(anatomic dead space x frequency of
breathing in one minute)

16. C. REGIONAL DIFFERENCES IN
VENTILATION
 Ventilation in lower zones > upper zones.
 This is demonstrated by inhalation of
radioactive xenon gas.The radiation emitted
is picked up by a radiation camera.
 The above is in upright posture. On supine
posture, the ventilation is relatively the same
at the different zones. On lateral posture, the
dependent side is greatly ventilated.