Quote: (Originally Posted by
womble)
Basically, If you stop and do nothing (lower VCO2) you will get a drop in arterial/alveolar CO2. This bit we all agree on. And as the loop is an extention of your lungs, will this result in a reduction of loop CO2 (if you dont bailout and dil flush instead)??
Mike has sort of addressed this.
If your problem is that you have retained CO2 by producing more than you "ventilate off", then by resting and producing less but maintaining your ventilation you will eventually lower your CO2. Technically speaking this will lower CO2 in the expiratory limb of the loop (because you are blowing less CO2 into it), but provided your scrubber is working, then there will be no CO2 in the inspiratory limb just as there never was. CO2 levels in the loop are essentially irrelevant in the context of a "CO2 retention" scenario.
If your problem is that the scrubber has failed and there is some CO2 breakthrough then predicting the effect of rest alone whilst staying on the loop is difficult. It depends on a number of things including the amount of CO2 breakthrough, and whether or not it is flow rate dependent (that is, just resting might stop the breakthrough).
Quote: (Originally Posted by
womble)
Secondly, alveolar ventilation (VA) changes you explain above also make sense. I also must apologise, I misread one of your earlier posts. You said Hypoventilation, I misread that as hyperventilation. So yes, If you are hypoventilating with regards to CO2 production (PACO2), you are just gonna get worse and worse. This would include, If I'm on the right track, shallow rapid breathing, as you may be experiencing with a CO2 hit.
Correct.
Quote: (Originally Posted by
womble)
High WOB on the unit (if still onloop) or high WOB on bailout (eg poor performance reg, dense gas etc) would affect both VCO2, as you are working harder to get the gas, AND it would affect VA. Is this assumption correct??
Absolutely. Diving provides the potential for situations in which CO2 production increases because of the work of breathing alone, and that same increase in work of breathing prevents an adequate response in VA. Rising CO2 drives greater respiratory effort, which produces more CO2 without generating a significant increase in VA. A spiralling crisis of increasing CO2 can result. And note, it may have nothing to do with the loop.... unless the loop is responsible for a significant component of the breathing resistance.
Hope this helps.
Simon M