Emergency ascent

Question:
Here comes my dive physiological question which I hope is not too silly:
It relates to a hypothetical out of air situation.
We assume that at a depth of 20 m a diver's second stages have all failed to deliver air (which to my knowledge can technically only happen if the first stage sinter filter has become clogged, e.g. Scubapro MK-20 ).
If the diver now immediately starts ascending - will the diver's urge to breathe be alleviated or even be suppressed by the expanding, residual air in his lungs ?
In other words, will the expanding air in his lungs sufficiently increase the gas exchange and thus affect and decrease the CO2/O2 ratio in the blood?
Will the decreased CO2 partial pressure in the blood (strictly speaking the " CO2 activity") delay the stimulus to breathe and thus prevent the feeling of suffocation ?

Answer:
If the regulator malfunction occurs on empty lungs, the initial air-hunger could indeed be first triggered by the lung inflation / deflation mechanical sensors and this would be eased by the expansion of the gas volume in the lungs.
The gas exchange processes are mainly guided by the partial pressures of the involved gases and not by the volume of a given gas mixture in the lungs.
The driving force for the CO2 or for oxygen will not be varied by their volume but mainly by their partial pressure, which will be more elevated at depth than at shallower levels during the ascent.
Even in a lung at the lower level of non-forced exhalation, the amount of gas retained is enough to assure adequate CO2 / O2 exchanges.
The volumetric expansion will not vary the driving force ( partial pressure ) which will be only affected by the changing hydrostatic pressure of the surrounding environment.
At depth, if an elevated partial pressure of CO2 is assumed, this will give rise to a diminished breathing urge, due to the balancing effect of the increased partial pressure of O2.
During ascent, irrispective of the volume increase, the CO2 partial pressure will itself decrease, and so will the related urge to breathe, even if the O2 partial pressure will also decrease. But the two effects will change parallely and their general balance will largely remain un-modified.
On the contrary, the lung deflation sensors will not be any longer triggered by a decreased lung volume and this will contribute to better resist a possible urge to breathe, while any extra volume is left free to escape the lungs through a patent airway during the ascent.