Nasal breathing difficulties (NBD) are widespread and difficult to diagnose; the failure rate of their surgical corrections is high. Computational fluid dynamics (CFD) enables diagnosis of NBD and surgery planning, by comparing a pre-operative (pre-op) situation with the outcome of virtual surgery (post-op). An equivalent comparison is involved when considering distinct anatomies in the search for the functionally normal nose. Currently, this comparison is carried out in more than one way, under the implicit assumption that results are unchanged, which reflects our limited understanding of the driver of the respiratory function. The study describes how to set up a meaningful comparison. A pre-op anatomy, derived via segmentation from a CT scan, is compared with a post-op anatomy obtained via virtual surgery. State-of-the-art numerical simulations for a steady inspiration carry out the comparison under three types of global constraints, derived from the field of turbulent flow control: a constant pressure drop (CPG) between external ambient and throat, a constant flow rate (CFR) through the airways and a constant power input (CPI) from the lungs can be enforced. A significant difference in the quantities of interest is observed depending on the type of comparison. Global quantities (flow rate, pressure drop and nasal resistance) as well as local ones are affected. The type of flow forcing affects the outcome of the comparison between pre-op and post-op anatomies. Among the three available options, we argue that CPG is the least adequate. Arguments favouring either CFR or CPI are presented.

鼻呼吸困难 (NBD) 很普遍且难以诊断；他们的手术矫正失败率很高。计算流体动力学 (CFD) 通过将术前（术前）情况与虚拟手术（术后）结果进行比较，实现 NBD 诊断和手术计划。在寻找功能正常的鼻子时考虑不同的解剖结构时，涉及等效的比较。目前，这种比较是在结果不变的隐含假设下以不止一种方式进行的，这反映了我们对呼吸功能驱动因素的理解有限。该研究描述了如何进行有意义的比较。将通过 CT 扫描分割得出的术前解剖结构与通过虚拟手术获得的术后解剖结构进行比较。最先进的稳定吸气数值模拟在源自湍流控制领域的三种全局约束下进行比较：外部环境和喉部之间的恒定压降 (CPG)、恒定流速（CFR）通过气道和来自肺部的恒定功率输入（CPI）可以被强制执行。根据比较类型的不同，可以观察到感兴趣数量的显着差异。全局量（流量、压降和鼻阻力）以及局部量都会受到影响。血流强迫的类型影响术前和术后解剖结构之间的比较结果。在三个可用选项中，我们认为 CPG 是最不充分的。提出了支持 CFR 或 CPI 的论点。