Ventilatory constraints influence physiologic dead space in heart failure.

NEW FINDINGS: What is the central question of this study? The goal of this study was to investigate the effect of alterations in tidal volume and alveolar volume to the elevated physiologic dead space and contribution of ventilatory constraints thereof in heart failure patients during submaximal exercise. What is the main findings and its importance? We found that physiologic dead space was elevated in heart failure via reduced tidal volume and alveolar volume. Furthermore, the degree of ventilatory constraints was associated with physiologic dead space and alveolar volume.

ABSTRACT: Introduction Heart failure patients with reduced ejection fraction (HFrEF) exhibit impaired ventilatory efficiency (i.e. greater ventilatory equivalent for carbon dioxide (VE /VCO2 ) slope), and elevated physiologic dead space (VD /VT ). However, the impact of breathing strategy on VD /VT during submaximal exercise in HFrEF is unclear. Methods HFrEF (n = 9) and control (CTL, n = 9)) participants performed constant load cycling exercise at similar ventilation (VE ). Inspiratory capacity (IC), operating lung volumes and arterial blood gases were measured during submaximal exercise. Arterial blood gases were used to derive VD /VT , alveolar volume, dead space volume, alveolar ventilation, and dead space ventilation. Results During submaximal exercise, HFrEF had greater VE /VCO2 slope and VD /VT than CTL (p = 0.01). At similar VE , HFrEF had smaller tidal volumes and alveolar volumes (HFrEF: 1.11 ± 0.33 vs. CTL: 1.66 ± 0.37 L) (both p≤0.01), while dead space volume was not different (p = 0.47). The augmented breathing frequency in HFrEF resulted in greater dead space ventilation compared to CTL (HFrEF: 15 ± 4; CTL: 10 ± 5 L min-1 ) (p = 0.048). HFrEF exhibited greater increases in expiratory reserve volume and lower IC (% predicted) than CTL (both p < 0.05), which were significantly related to VD /VT and alveolar volume in HFrEF (all p < 0.03). Conclusion In HFrEF, the reduced tidal volume and alveolar volume elevate physiologic dead space during submaximal exercise, which is worsened in those with the greatest ventilatory constraints. These findings highlight the negative consequences of ventilatory constraints on physiologic dead space during submaximal exercise in HFrEF. This article is protected by copyright. All rights reserved.