Effects of cryo-parameters and retrieval methods on specimen acquisition and quality for ultrathin cryoprobe transbronchial cryobiopsy in porcine models

Ultrathin cryoprobes enable direct retraction through the working channel during transbronchial cryobiopsy. However, key factors of biopsy performance remain insufficiently characterized. This study evaluates cryo-parameters and retrieval methods across different working channels in a porcine model to define parameter strategies that balance specimen acquisition, quality and complication risk. Transbronchial cryobiopsy using an ultrathin cryoprobe under different cryo-parameters was compared with standard forceps biopsy (sFB) in ex vivo and in vivo models. Biopsy approaches were classified into five groups: P290 (BF-P290, cryoprobe retracted through 2.0 mm diameter working channel), EWC (BF-1TQ290 combined with a 2.0 mm diameter extending working channel (EWC), cryoprobe retracted through the EWC), 1TQ290-IN (BF-1TQ290, cryoprobe retracted through 3.0 mm diameter working channel), 1TQ290-OUT (BF-1TQ290, cryoprobe retracted en bloc with the bronchoscope), and sFB (standard forceps biopsy with BF-1TQ290). Acquisition rates, specimen quality and complications were assessed. In ex vivo experiments at 55 and 60 bar, a 3 s cryo-activation time was sufficient to produce specimens of greater size than those obtained with sFB. In vivo, cryo-activation times of 3–7 s achieved acquisition rates > 60% across all groups. At 9 s, acquisition rates declined to < 60% for EWC and P290, whereas the 1TQ290-IN and 1TQ290-OUT groups maintained rates > 60%. Except for the EWC group at 3 s, all groups had greater specimen weight, macroscopic cross-sectional areas, and microscopic section areas than sFB ( P < 0.05). No severe complications (grade ≥ 3 bleeding) occurred; grade 2 bleeding and pneumothorax were predominantly observed in the 1TQ290-IN and 1TQ290-OUT groups at cryo-activation times 7 and 9 s. For ultrathin cryoprobe transbronchial cryobiopsy with retraction through the EWC, a cryo-activation time of 5–7 s appears to yield increased specimen size compared with sFB, while maintaining a high specimen acquisition rate (> 60%) and procedural safety. For withdrawal via P290 and 1TQ290 bronchoscope’s working channels, a 3–7 s appears to provide a favorable balance between specimen acquisition rate, quality and procedural safety.