Conversely, if metabolism is slowed but VA remains unchanged, PaCO 2 will fall. Thus PaCO 2 is directly proportional to VCO2. This conversion is achieved by the constant, 0.863. If only fats are eaten, the RQ is 0.71. There is an RQ for both metabolism in the tissues and gas exchange in the lungs.
Normal ventilation is governed by the body's metabolic demands.
From Equation 8 it can be seen that if VCO 2 rises proportionately more than VA, PaCO 2 will increase. If VCO 2 increases and if VA cannot rise proportionately, PaCO 2 will increase. In such cases the cause of hypercapnia is inadequate VA for the amount of carbon dioxide presented to the lungs for excretion. This inadequacy is discussed in the section on hypercapnia. This terminology is often confusing to neophytes for two reasons.