Effects of Upper Trunk Flexion on Ventilation Volume in Semi-Fowler's Position

The semi-Fowlers position, in which the trunk is elevated 30{degrees} 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 Fowlers position, its effects in the semi-Fowlers 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{degrees} 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, p<0.001) and MV (>0.9 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 (p<0.05), indicating compensatory heart rate elevation, whereas the UT30 group maintained RR intervals equivalent to the supine position (p>0.05), 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.