Central-peripheral respiratory chemoreflex interaction in humans

We investigated the interaction between the central and peripheral chemoreflexes in humans using a temporal separation technique in three tests. In two tests hyperventilation was used to reduce central P-CO2. In these tests the difference in the responses to the same step increases in P-CO2 to 45 mmHg at normoxic and hypoxic O-2 tensions provided a measure of the response to isocapnic hypoxia at a low central P-CO2. In a third test the response to a hypoxic step during sustained isocapnia at 45 mmHg provided a measure of the response to isocapnic hypoxia at a high central P-CO2. The responses to isocapnic hypoxia at high and low central P-CO2 were not significantly different, confirming the conclusion of previous studies that central and peripheral chemoreflex signals interact additively. This finding contrasts with those from recent animal experiments and emphasizes the need for caution when using animal experiments to make conclusions about the physiology of the respiratory chemoreflexes in humans. (C) 2011 Elsevier B.V. All rights reserved.