Upper Trunk Flexion Versus Whole Trunk Elevation in Semi-Fowler’s Position: Effects on Ventilation and Cardiac Chronotropy

ABSTRACT The semi-Fowler’s position, in which the trunk is elevated 30° from the supine position, is widely used in clinical practice to manage respiratory function and reduce cardiovascular stress. Despite the known cardiovascular benefits of upper trunk flexion in the Fowler’s position, its effects in the semi-Fowler’s position remain uninvestigated. This study provides the first direct comparison of upper trunk flexion (UT30) and conventional whole-trunk elevation (WT30) at an identical 30° angle. Fourteen healthy young women participated in a randomized crossover design comparing three positions: supine, WT30 (standard bed angle elevation), and UT30 (isolated flexion at the T10 vertebral level using cushions). Tidal volume (TV), minute ventilation (MV), respiratory rate, and RR intervals were measured after 5-minute equilibration in each position. Both UT30 and WT30 significantly increased TV (>80 mL, p0.9 L/min, p<0.001) compared to the supine position, with no differences between the positioning variants. Critically, RR intervals significantly decreased in the WT30 group compared to the supine position (p0.05), demonstrating a preserved hemodynamic baseline. Although the direct comparison between UT30 and WT30 did not reach statistical significance, the distinct response patterns—hemodynamic perturbation in WT30 versus baseline stability in UT30—suggest that UT30 achieves ventilatory improvements without the associated orthostatic cardiac cost. These findings highlight UT30 as a potential strategy for decoupling respiratory support from cardiovascular stress, warranting validation in clinical populations with limited cardiac reserves. Competing Interest Statement The authors have declared no competing interest. Funding Statement This work was supported by Grants-in-Aid for Scientific Research from the Japan Society for the Promotion of Science (C Grant No. 23K09795). Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: The study was conducted in accordance with the Declaration of Helsinki and was approved by the Ethics Committee of International University of Health and Welfare (approval number: 21-lg-16). I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes Footnotes We have changed the title and revised the manuscript. Data Availability Statement The authors will make the data supporting the conclusions of this article available upon reasonable request.