Pulse oximetry during breath holding (BH) in normal
residents at high altitude (3510 m) gives a characteristic graph.
Following a deep inspiration to total lung capacity (TLC) and subsequent breath holding, at around 18 seconds, a descent of saturation (SaO2), is observed. This down pointed peak, prior to the elevation of SaO2 to sea level values, as previously described, corresponds to the blood circulation time from the alveoli to the finger where the pulse oximeter probe is placed. Such a simple maneuver corroborates the measurement of circulation time by other methods.
This independent phenomenon is even observed when the subject breathes 100% oxygen. (PIO2 = 403 mmHg for a barometric pressure of 495 mmHg). BH time is, as expected, prolonged under these circumstances.
The possible explanation is as follows: Once BH is initiated, there is no renewal of alveolar air. Oxygen consumption, due to inspiratory muscles contraction work, is seen as a descent of SaO2. However, since oxygen incoming from the TLC inspiration arrives, saturation begins to rise. This corresponds to the vertex of the graph formed by the descent and subsequent rise of the SaO2 detected by the pulse oximetry. Thus the time delay of blood circulation from the pulmonary alveoli to the finger is measured.
This phenomenon is observed at different levels of inspiratory oxygen pressure in the lungs traduced by the percentage of saturation, in both natives and normal residents at this altitude.
BREATH HOLDING AND PULSE OXIMETRY AS A DIAGNOSTIC
TOOL AT HIGH ALTITUDE
G. Zubieta-Castillo, G.R. Zubieta-Calleja
IPPA * High Altitude Pathology Institute
As presented in the 4th WORLD CONGRESS ON MOUNTAIN MEDICINE AND HIGH ALTITUDE PHYSIOLOGY held in Arica, Chile Oct 1-6, 2000.
Since the time of Haldane, Douglas and Fitzgerald
(1913), when they used a tube and a simple gas analyzer to study the changes
in alveolar concentration of CO2 and O2 during breath holding (BH), modern
technology makes this a simple but very effective method of studying several
additional aspects of respiratory physiology. Now with pulse oximetry together
with fast O2 and CO2 analyzers along with the adequate software, a computer
shows the changes on-line during breath holding. This procedure can be
used to diagnose pulmonary and circulatory disease at high altitude.
Breath holding, a simple maneuver, can be studied at different altitudes and during different functional states, and oxygen concentrations.
The computer graphs, allow us to:
1) evaluate pulmonary diffusion.
2) measure circulation time of blood from the alveoli to the fingers.
3) differentiate the normal SaO2 in natives and residents from low SaO2 in heart and pulmonary disease as for example in chronic mountain sickness.
4) detect pulmonary shunts breathing 100 % oxygen prior to BH.
5) observe chronic hypercapnia in end tidal CO2.
Finally, we think that in the future, unpredictable
approaches to other aspects of pulmonary function will surface with the
use of this technique.