<p>We first reported a characteristic “chair-back” capnogram with an α angle &lt; 90° during sleeve lobectomy, suggesting impaired pulmonary artery perfusion. However, whether this waveform can be consistently reproduced in the setting of pulmonary artery perfusion impairment and the possible factors contributing to its appearance remain unclear. This study comprised one animal experiment and two clinical investigations. In the animal experiment, 6 pigs were randomly assigned to either the single-lumen endotracheal tube (SLT) group (<i>n</i> = 3) or the double-lumen endotracheal tube (DLT) group (<i>n</i> = 3). The clinical investigation included a pneumonectomy cohort (<i>n</i> = 10), in which all patients were managed with DLT, and a randomized lobectomy trial (<i>n</i> = 50), in which patients were allocated (1:1) to allocated (1:1) to either the SLT plus bronchial blocker (BB) group or the DLT group. Capnogram, end-tidal carbon dioxide (PetCO₂), and arterial blood gas measurements were obtained before and after pulmonary artery or lobar pulmonary artery ligation, and the arterial-to-end-tidal carbon dioxide gradient (Pa–etCO₂) was calculated. Following pulmonary artery or lobar pulmonary artery ligation, the characteristic “chair-back” capnogram with α angle &lt; 90° was consistently observed in all pigs intubated with DLT and patients in the pneumonectomy cohort, whereas the capnogram remained rectangular in all pigs managed with SLT. In the randomized lobectomy trial, the α angle &lt; 90° occurred in 16 of 25 patients (64%) patients intubated with DLT but in none of the patients with SLT plus BB (<i>P</i> &lt; 0.001). Pulmonary artery occlusion consistently reduced PetCO₂ and increased the Pa–etCO₂ gradient across all experimental and clinical groups (all <i>P</i> &lt; 0.05), irrespective of the airway device. Pulmonary artery occlusion is associated with characteristic capnographic changes during pulmonary surgery. The double-lumen endotracheal tube facilitates recognition of the characteristic “chair-back” capnogram, whereas this waveform is not observed with a single-lumen tube plus bronchial blocker. When interpreted together with decreases in PetCO₂ and increases in the Pa–etCO₂ gradient, the “chair-back” capnogram may serve as a potential real-time capnographic sign of pulmonary perfusion impairment when DLT is used.</p><p>Trial registration</p><p>Chinese Clinical Trial Registry <a href="http://www.chictr.org.cn">http://www.chictr.org.cn</a> (November 1, 2022; ChiCTR2200065248 and December 18, 2025; ChiCTR2500114855).</p>