Ventilatory limitations in patients with HFpEF and obesity

Abstract

Heart failure with preserved ejection fraction (HFpEF) patients have an increased ventilatory demand. Whether their ventilatory capacity can meet this increased demand is unknown, especially in those with obesity. Body composition (DXA) and pulmonary function were measured in 20 patients with HFpEF (69 ± 6 yr;9 M/11 W). Cardiorespiratory responses, breathing mechanics, and ratings of perceived breathlessness (RPB, 0-10) were measured at rest, 20 W, and peak exercise. FVC correlated with %body fat (R² =0.51,P = 0.0006), V̇O_2peak (%predicted,R² =0.32,P = 0.001), and RPB (R² =0.58,P = 0.0004). %Body fat correlated with end-expiratory lung volume at rest (R² =0.76,P < 0.001), 20 W (R² =0.72,P < 0.001), and peak exercise (R² =0.74,P < 0.001). Patients were then divided into two groups: those with lower ventilatory reserve (FVC<3 L,2 M/10 W) and those with higher ventilatory reserve (FVC>3.8 L,7 M/1 W). V̇O_2peak was ∼22% less (p < 0.05) and RPB was twice as high at 20 W (p < 0.01) in patients with lower ventilatory reserve. Ventilatory reserves are limited in patients with HFpEF and obesity; indeed, the margin between ventilatory demand and capacity is so narrow that exercise capacity could be ventilatory limited in many patients.

Keywords: Aging; Breathing mechanics; Breathlessness; Exercise capacity; Exercise intolerance; Operational lung volumes; Pulmonary function.

Fig. 1.

Relationship between forced vital capacity (FVC) in liters and total body fat (%) (N = 19).

Fig. 2.

Relationship between total body fat (%) and end-expiratory lung volume (EELV, L) at rest, during exercise at 20 W, and during peak exercise.

Fig. 3.

Relationship between forced vital capacity (FVC) in liters and peak oxygen uptake (%predicted) (N = 20).

Fig. 4.

Relationships between inspiratory capacity (IC) and peak oxygen uptake (%predicted) and rating of perceived breathlessness (RPB, Borg scale 0–10) during exercise at 20 W.

Fig. 5.

Individual data (N = 20) for forced vital capacity (FVC) in liters and percent predicted.

Fig. 6.

Demonstrates the constraints on tidal volume (V_T) during exercise in patients with an FVC< 3 L and an FVC> 3.8 L (FVC=forced vital capacity). Left bar, lung volume subdivisions measured during pulmonary function testing (TLC, total lung capacity; FRC, functional residual capacity; IC, inspiratory capacity). EELV, end-expiratory lung volume; V_T, tidal volume; IRV, inspiratory lung volume measured at rest on the cycle ergometer, during exercise cycling at 20 W, and during peak exercise. Note: IC = V_T + IRV and progressively declines with exercise reducing potential for V_T augmentation and increasing the encroachment on TLC. End-inspiratory lung volume (EILV) = V_T + EELV. As EILV approaches TLC 1) work of breathing increases remarkably, 2) V_T cannot increase further, and 3) patients usually experience increased breathlessness. Both groups display marked mechanical ventilatory constraints during exercise. *Significant differences between groups within conditions, P < 0.05. Comparisons were not made between conditions.

Fig. 7.

Maximal and tidal flow-volume loops from typical subject with forced vital capacity less than 3 liters (FVC< 3 L) and typical subject with forced vital capacity greater than 3.8 liters (FVC> 3.8 L). Black maximal flow-volume loop from pulmonary function testing (mouth flow vs. mouth volume) and the blue curve is maximal flow-volume loop corrected for gas compression artifact (mouth flow vs. box volume). Tidal flow-volume loops measured during rest, at 20 W, and during peak exercise as marked.