Alveolar Dead Space Is Augmented During Exercise in Patients With Heart Failure With Preserved Ejection Fraction

BACKGROUND: Patients with heart failure with preserved ejection fraction (HFpEF) exhibit many cardiopulmonary abnormalities that could result in _V/Q_ mismatch, manifesting as an increase in alveolar dead space (VDalveolar) during exercise. Therefore, we tested the hy-pothesis that VDalveolar would increase during exercise to a greater extent in patients with HFpEF compared with control participants.RESEARCH QUESTION: Do patients with HFpEF develop VDalveolar during exercise?STUDY DESIGN AND METHODS: Twenty-three patients with HFpEF and 12 control participants were studied. Gas exchange (ventilation [_VE], oxygen uptake [_VO2], and CO2 elimination [_VCO2]) and arterial blood gases were analyzed at rest, twenty watts (20W), and peak exercise. Ventilatory effi- ciency (evaluated as the _VE/_VCO2 slope) also was measured from rest to 20W in patients with HFpEF. The physiologic dead space (VDphysiologic) to tidal volume (VT) ratio (VD/VT) was calculated using the Enghoff modification of the Bohr equation. VDalveolar was calculated as: (VD / VT x VT) - anatomic dead space. Data were analyzed between groups (patients with HFpEF vs control par-ticipants) across conditions (rest, 20W, and peak exercise) using a two-way repeated measures analysis of variance and relationships were analyzed using Pearson correlation coefficient.RESULTS: VDalveolar increased from rest (0.12 +/- 0.07 L/breath) to 20W (0.22 +/- 0.08 L/breath) in patients with HFpEF (P < .01), whereas VDalveolar did not change from rest (0.01 +/- 0.06 L/breath) to 20W (0.06 +/- 0.13 L/breath) in control participants (P = .19). Thereafter, VDalveolar increased from 20W to peak exercise in patients with HFpEF (0.37 +/- 0.16 L/breath; P < .01 vs 20W) and control participants (0.19 +/- 0.17 L/breath; P = .03 vs 20W). VDalveolar was greater in patients with HFpEF compared with control participants at rest, 20W, and peak exercise (main effect for group, P < .01). Moreover, the increase in VDalveolar correlated with the _VE/_VCO2 slope (r = 0.69; P < .01), which was correlated with peak _VO2peak (r = 0.46; P < .01) in patients with HFpEF.INTERPRETATION: These data suggest that the increase in _V/Q_ mismatch may be explained by increases in VDalveolar and that increases in VDalveolar worsens ventilatory efficiency, which seems to be a key contributor to exercise intolerance in patients with HFpEF.

Automated summary

Patients with heart failure with preserved ejection fraction (HFpEF) exhibit an increase in alveolar dead space (VDalveolar) during exercise, which worsens ventilatory efficiency and contributes to exercise intolerance.