Objective To analyze the quantitative relationship between respiratory effort and inferior vena cava (IVC) diameter variability in healthy adults, and explore the effects of respiratory effort on the fluid responsiveness with IVC diameter variability. Methods From October 2022 to May 2023, a cross-sectional study was conducted in healthy young subjects who met the criteria. Respiratory effort was evaluated by using portable pulmonary function to measure the subjects’ inspiratory conditions in three states (quiet breathing, moderate inspiration, and maximal inspiration). At the same time, the IVC internal diameter was measured by bedside ultrasound and the IVC diameter variability was calculated. The correlation between inspiratory volume and IVC diameter variation was analyzed, and the receiver operator characteristic (ROC) curve was drawn. The sensitivity and specificity of fluid responsiveness induced by inspiratory effort were predicted according to the area under the ROC curve (AUC). Results A total of 95 subjects were screened, aged 27.13±5.77 years, of whom 30 (32%) subjects were males. During quiet breathing, 41.1% of subjects had IVC inner diameter variation ≥50%. For moderate inspiration, it was 68.4%. At maximum inspiration, this proportion is more than 85%. Inspiratory volume was moderately positively correlated with IVC diameter variation, and the correlation coefficient r=0.45. With the IVC diameter variation ≥50% as the positive criterion for fluid responsiveness, the AUC of fluid responsiveness induced by inspiratory effort was 0.73 (95% confidence interval 0.67 - 0.78, P<0.001), and the inspiratory volume threshold was 13 mL/kg ideal body weight when the maximum Youden index was 0.41. That is, moderate force breathing can induce fluid responsiveness, with sensitivity of 79.57% and specificity of 61.62%. Conclusion The degree of respiratory effort significantly affects the IVC inner diameter variation, and there may be false positives in the evaluation of fluid responsiveness according to IVC inner diameter variation in the case of spontaneous breathing.
ObjectiveTo evaluate hepatic venous Doppler parameters under varying inspiratory effort levels in healthy adults using ultrasound, providing a theoretical basis for assessing the impact of inspiratory effort on hepatic venous blood return. MethodsA cross-sectional study was conducted from December 2024 to March 2025, enrolling 61 healthy adults. Inspiratory effort was quantified via portable pulmonary function testing, measuring inspiratory volume (IV) during quiet breathing, moderate inspiratory effort, and maximal inspiratory effort. Hepatic venous Doppler parameters (a-wave, s-wave, d-wave peak velocities) were assessed bedside under these three conditions. Correlation analyses and linear regression models were used to explore relationships between IV and hepatic venous flow parameters. ResultsA total of 61 participants completed screening, with a mean age of 27.03 ± 4.73 years (24 males, 39.0%). Although male participants had advantages in height and weight, no significant differences in inspiratory volume (IV), hepatic venous a-wave, s-wave, d-wave peak velocities, or s/d ratio were observed between men and women across all breathing states (all P>0.05). Significant negative correlations were identified between IV and a-wave (r=?0.68, 95%CI: ?0.75 to ?0.59), s-wave (r=?0.56, 95%CI: ?0.65 to ?0.45), and d-wave (r=?0.33, 95%CI: ?0.46 to ?0.20) velocities. Linear regression equations were established as follows:a-wave (cm/s) = 22.06 - 0.23 × IV (ml/kg ideal body weight); s-wave (cm/s) = 34.96 - 0.26 × IV (ml/kg ideal body weight); d-wave (cm/s) = 25.82 - 0.11 × IV (ml/kg ideal body weight).The s/d ratio decreased significantly with increasing inspiratory effort (1.37 ± 0.38 vs. 1.23 ± 0.24 vs. 1.15 ± 0.22; F=9.91, P<0.001). However, only a weak negative correlation (r=?0.28, P<0.001) was observed between inspiratory effort and s/d ratio. ConclusionInspiratory effort demonstrates a strong negative correlation with hepatic venous blood peak flow velocities in healthy adults. While the s/d ratio shows a downward trend with deeper inspiration, the association is weak.
