Lung diseases that primarily cause abnormality in alveolar gas exchange usually do not cause hypoventilation but tend to cause stimulation of ventilation and hypocapnia secondary to hypoxia.
12.
The second mechanism requires hyperventilation ( forced overbreathing ) until symptoms of hypocapnia such as tingling, light-headedness or dizziness are felt, followed by a breath-hold.
13.
Hyperventilation depletes the blood of carbon dioxide ( hypocapnia ), which causes respiratory alkylosis ( increased pH ), and causes a leftward shift in the oxygen hemoglobin dissociation curve.
14.
This confusion is exacerbated by the fact that in the case of blackout on ascent, hyperventilation induced hypocapnia also may be a contribitory factor even if depressurisation on ascent is the actual precipitator.
15.
The absence of any symptoms of hypocapnia is not an indication that the diver s carbon dioxide is within safe limits and cannot be taken as an indication that it is therefore safe to dive.
16.
Hyperventilation before any dive, deep or shallow, flushes out carbon dioxide in the blood resulting in a dive commencing with an abnormally low carbon dioxide level; a potentially dangerous condition known as hypocapnia.
17.
The absence of any symptoms of hypocapnia is not an indication that the diver s carbon dioxide level is within safe limits and cannot be taken as an indication that it is therefore safe to dive.
18.
Where these terms are used in this manner there is usually little or no discussion of the phenomenon of blackouts not involving depressurisation and the cause may be variously attributed to either depressurisation or hypocapnia or both.
19.
In reality, they have about the same oxygenation in the arterial blood ( normal values are about 98 % for hemoglobin saturation ) and too little carbon dioxide ( hypocapnia ) in their blood and other tissues.
20.
Blackout during a shallow dive differs from blackout during ascent from a deep dive in that deep water blackout is precipitated by depressurisation on ascent from depth while shallow water blackout is a consequence of hypocapnia following hyperventilation.
