Our colleagues skillfully addressed how peripheral chemoreceptors interact with systemic effects of CO2. Unfortunately, systemic CO2 affects oxyhemoglobin dissociation, sympathetic, endocrine and cardiovascular systems, and afferents from lungs and CO2‐sensitive upper airway receptors – all capable of having effects on ventilation independent of central chemoreceptors. Duffin's ingenious rebreathing studies add further concerns, namely psychological and physiological aspects of voluntary hyperventilation (e.g., Steinback et al. 2011). This article is protected by copyright. All rights reserved.