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.