VENTILATION

PRESENTER: Keagan KirugoDISCUSSANTS: The Circle

OBJECTIVES

Lung volumes

Aspects of ventilation

Regional differences in respiration

A. LUNG VOLUMES

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.

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)

Spirometer is limited in the measurement of residual volume, FRC and TLC.

FRC can be measured by the Helium-dilution method and plethysmography.

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.

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 x V1= C2 x (V1 + FRC)

Plethysmography has replaced helium-dilution method.

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)

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.