Effect of supine posture on airway blood flow and pulmonary function in stable heart failure

Abstract

Background: The aim of this study was to determine the relationship between body position, pulmonary function (PF) and bronchial blood flow (Q(aw)) in a group of heart failure (HF) and control subjects.

Methods: Thirty-six subjects were studied: 24 stable, ambulatory HF patients (HF: LVEF=27±6%, age=65±9 yr) and 12 age- and sex-matched controls (CTRL: LVEF=60±7%, age=62±8 yr). Measures of Q˙(aw) (soluble gas method) and PF were collected upright and following 30min in the supine position.

Results: Q˙(aw) was similar between groups and remained unchanged with body position. Declines in forced vital capacity (FVC) and forced expiratory volume in 1s (FEV1) with the supine position were observed in both groups; declines in forced expiratory flow 25-75% (FEF(25-75)) and FEF 75% (FEF75) with the supine position were observed in the HF group only. Changes in Q˙(aw) were related to changes in PF only in the HF patient groups (ΔFVC, % predicted, r = -0.45, p<0.04, ΔFEV1 r = -0.61, p<0.01, ΔFEV1% predicted, r = -0.45, p<0.04).

Conclusion: These data demonstrate that relationships between postural changes in Q˙(aw) and PF exist only in the HF population and that the bronchial circulation may contribute to postural PF decline in HF.

Figure 1. Airway blood flow and airway blood flow conductance in the upright and supine positions

Grey bars represent upright seated position, black bars represent supine position. Data reported as mean±SE. * p<0.05 when compared to CTRL.

Figure 2. Correlation between the ΔQ_aw ΔFVC (L), ΔFVC (%predicted), ΔFEV₁ (L) and ΔFEV₁ (%predicted) from the upright to the supine position for HF groups only

The center line (solid) represents the linear fit trendline, the outside lines (dotted) represents the 95% confidence interval to the linear fit line. FVC=forced vital capacity, FEV₁=forced expiratory volume in 1 second.