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Objectives: Patients with acute exacerbation of chronic obstructive pulmonary disease (AECOPD) combined with severe type II respiratory failure have a high probability of ventilation failure using conventional non-invasive positive pressure ventilation (NPPV). This study aims to investigate the clinical efficacy of high intensity NPPV (HI-NPPV) for the treatment of AECOPD combined with severe type II respiratory failure., Methods: The data of patients with AECOPD combined with severe type II respiratory failure (blood gas analysis pH≤7.25) treated with NPPV in the Second Affiliated Hospital of Chongqing Medical University from July 2013 to July 2023 were collected to conduct a retrospective case-control study. The patients were divided into 2 groups according to the inspired positive airway pressure (IPAP) used during the NPPV treatment: a NPPV group (IPAP<20 cmH 2 O, 1 cmH 2 O=0.098 kPa) and a HI-NPPV group (20 cmH 2 O≤IPAP< 30 cmH 2 O). Ninety-nine and 95 patients were included in the NPPV group and the HI-NPPV group, respectively. A total of 86 pairs of data were matched using propensity score matching (PSM) for data matching. The primary outcome indexes (mortality and tracheal intubation rate) and secondary outcome indexes [blood gas analysis pH, arterial partial pressure of oxygen (PaO 2 ) and arterial partial pressure of carbon dioxide (PaCO 2 ), adverse reaction rate, and length of hospitalization] were compared between the 2 groups., Results: The tracheal intubation rates of the NPPV group and the HI-NPPV group were 6.98% and 1.16%, respectively, and the difference between the 2 groups was statistically significant ( χ 2 =4.32, P <0.05); the mortality of the NPPV group and the HI-NPPV group was 23.26% and 9.30%, respectively, and the difference between the 2 groups was statistically significant ( χ 2 =11.64, P <0.01). The PaO 2 at 24 h and 48 h after treatment of the HI-NPPV group was higher than that of the NPPV group, and the PaCO 2 of the HI-NPPV group was lower than that of the NPPV group, and the differences were statistically significant (all P <0.05). The differences of pH at 24 h and 48 h after treatment between the 2 groups were not statistically significant (both P >0.05). The differences between the 2 groups in adverse reaction rate and hospitalization length were not statistically significant (both P >0.05)., Conclusions: HI-NPPV can reduce mortality and tracheal intubation rates by rapidly improving the ventilation of patients with AECOPD combined with severe type II respiratory failure. This study provides a new idea for the treatment of patients with AECOPD combined with severe type II respiratory failure.

Objective: To investigate the relationship between the existence of occlusal interference and masticatory muscle hyperalgesia by exploring the stimulus-response relationship between the duration of occlusal interference and masticatory muscle mechanical withdrawal threshold., Methods: Occlusal interference with 0.4 mm-thick crowns on rat molars was removed under anaesthesia at 2, 3, 4, 5, and 6 d after wear, and masticatory muscle mechanical withdrawal threshold was tested at 1, 3, 5, 7, 10, 14, 21 and 28 d., Results: Decreased mechanical withdrawal thresholds were detected in temporal muscles and masseter muscles on both sides following occlusal interference (P < 0.05). After removal of crowns at 2, 3, 4 and 5 d, rats exhibited the similar head withdrawal thresholds as the sham-application control in masticatory muscles on both sides at 10, 14, 14 and 21 d (P > 0.05). No significant differences were detected between the contralateral side with the ipsilateral side (P < 0.05). After removal of crowns at 6 d, rats still exhibited significantly decreased head withdrawal thresholds[right temporal muscle: (1.365±0.018) N; right masseter: (1.437 ± 0.024) N] in masticatory muscles on both sides until the last day of the experiment[the sham-application control: right temporal muscle: (1.554±0.040) N, P < 0.001; right masseter: (1.546±0.019) N, P < 0.001]., Conclusions: The mechanical hyperalgesia can disappear after removal of the occlusal interference at 5 d, and the existence of the occlusal interference is positively correlated with the duration of the mechanical hyperalgesia.