To validate the pressure–time index of the inspiratory muscles as a non-invasive index of inspiratory muscle function in spontaneously breathing infants by comparing it against the gold-standard pressure–time index of the diaphragm. Prospective observational cohort study of consecutive infants breathing unsupported in room air in a tertiary neonatal intensive care unit, studied prior to discharge from neonatal care. The invasive pressure–time index of the diaphragm was calculated using a transdiaphragmatic dual-pressure catheter that measured transdiaphragmatic pressure by subtraction of the oesophageal from the gastric pressure. The non-invasive pressure–time index of the inspiratory muscles was calculated using pressure measurements at the level of the mouth via a differential pressure transducer connected to a face mask. Both indices were calculated as the product of the ratio of the mean inspiratory pressure divided by the maximum inspiratory pressure and the ratio of the inspiratory time divided by the total time of a respiratory cycle. One hundred and thirty infants (79 male) were included with a mean (SD) gestational age of 35.2 (3.2) weeks, studied at a median (IQR) postnatal age of 9 (6–20) days. The mean (SD) pressure–time index of the diaphragm was 0.063 (0.019) and the mean (SD) pressure–time index of the inspiratory muscles was 0.065 (0.023). The correlation coefficient for the two indices was 0.509 (p < 0.001). The mean (SD) absolute difference between the pressure–time index of the inspiratory muscles and pressure–time index of the diaphragm was 0.002 (0.021). In convalescent infants, the non-invasive pressure–time index of the inspiratory muscles had a moderate degree of correlation with the invasively derived pressure time index of the diaphragm measured with a transdiaphragmatic catheter.

通过将吸气肌压力-时间指数与膈肌的金标准压力-时间指数进行比较，验证吸气肌压力-时间指数作为自主呼吸婴儿吸气肌功能的非侵入性指标。在新生儿护理出院前对三级新生儿重症监护病房中在室内空气中无支持呼吸的连续婴儿进行前瞻性观察队列研究。使用经膈双压导管计算膈肌的侵入性压力-时间指数，该导管通过从胃压中减去食管压力来测量经膈压。吸气肌的无创压力-时间指数是通过连接到面罩的压差传感器使用口腔水平的压力测量来计算的。两个指数均计算为平均吸气压力除以最大吸气压力之比与吸气时间除以呼吸周期总时间之比的乘积。130 名婴儿（79 名男性）被纳入平均 (SD) 胎龄为 35.2 (3.2) 周，研究的中位 (IQR) 产后年龄为 9 (6–20) 天。横膈膜的平均 (SD) 压力-时间指数为 0.063 (0.019)，吸气肌的平均 (SD) 压力-时间指数为 0.065 (0.023)。两个指数的相关系数为 0.509 (p < 0.001)。吸气肌压力-时间指数与隔膜压力-时间指数之间的平均 (SD) 绝对差为 0.002 (0.021)。在恢复期的婴儿中，