Our comments in reply to the arguments presented in the CrossTalks by Teppema and Smith (2013) and Wilson and Day (2013) are confined to experiments on humans, and in their CrossTalk Teppema and Smith (2013) cite two studies that found evidence supporting a hyperadditive interaction. First, carotid body denervation or removal in man has consequences for the central chemoreception of CO2. We agree that such denervation removes the tonic drive from the carotid bodies (Dahan et al., 2007); evident from their involvement in sympathetic tone. This article is protected by copyright. All rights reserved.