Upper trunk flexion versus whole trunk elevation in semi-Fowler's position: Effects on ventilation and heart rate responses

Abstract

Study aim: The semi-Fowler's position is widely used to support respiratory function and reduce cardiovascular stress. Despite the known cardiovascular benefits of upper trunk flexion in Fowler's position, its effects in the semi-Fowler's position remain uninvestigated. This study aimed to compare the effects of upper trunk flexion (UT30) and whole-trunk elevation (WT30) at 30° on ventilation and cardiac chronotropy in healthy young women. Material and methods: Fourteen healthy young women (age: 20.6 ± 0.7 years; height: 162.1 ± 5.4 cm; weight: 53.1 ± 5.6 kg) participated in a randomized crossover design comparing supine, 30° whole-trunk elevation (WT30), and 30° upper trunk flexion at T10 (UT30). Tidal volume (TV), minute ventilation (MV), respiratory rate, and RR intervals were measured using a pneumotachograph and ECG (BIOPAC MP150) after 5-min equilibration. Data were analyzed using Linear Mixed Models (R version 4.3.3). Results: Both UT30 and WT30 increased TV (Δ+ 79 and + 94 mL) and MV (Δ+ 0.89 and + 1.18 L/min) versus supine (all p < 0.001), with no UT30-WT30 differences. RR interval decreased in WT30 versus supine (Δ- 0.029 s, ≈ +2.1 bpm, p = 0.038) but not in UT30 (p > 0.05); the direct UT30-WT30 comparison was not significant. Conclusions: These findings suggest that UT30 may be an efficient low-burden posture in healthy young women; applicability to populations with limited cardiovascular reserve requires direct clinical validation.