Estimating exercise Pa CO 2 in patients with heart failure with preserved ejection fraction.

Patients with heart failure with preserved ejection fraction (HFpEF) exhibit cardiopulmonary abnormalities that could affect the predictability of exercise [Formula: see text] from the Jones corrected partial pressure of end-tidal CO ₂ (PJ _{CO 2} ) equation (PJ _{CO 2}  = 5.5 + 0.9 × [Formula: see text] - 2.1 × V _T ). Since the dead space to tidal volume (V _D /V _T ) calculation also includes [Formula: see text] measurements, estimates of V _D /V _T from PJ _{CO 2} may also be affected. Because using noninvasive estimates of [Formula: see text] and V _D /V _T could save patient discomfort, time, and cost, we examined whether partial pressure of end-tidal CO ₂ ([Formula: see text]) and PJ _{CO 2} can be used to estimate [Formula: see text] and V _D /V _T in 13 patients with HFpEF. [Formula: see text] was measured from expired gases measured simultaneously with radial arterial blood gases at rest, constant-load (20 W), and peak exercise. V _D /V _T[art] was calculated using the Enghoff modification of the Bohr equation, and estimates of V _D /V _T were calculated using [Formula: see text] (V _D /V _T[ET] ) and PJ _{CO 2} (V _D /V _T[J] ) in place of [Formula: see text]. [Formula: see text] was similar to [Formula: see text] at rest (-1.46 ± 2.63, P = 0.112) and peak exercise (0.66 ± 2.56, P = 0.392), but overestimated [Formula: see text] at 20 W (-2.09 ± 2.55, P = 0.020). PJ _{CO 2} was similar to [Formula: see text] at rest (-1.29 ± 2.57, P = 0.119) and 20 W (-1.06 ± 2.29, P = 0.154), but underestimated [Formula: see text] at peak exercise (1.90 ± 2.13, P = 0.009). V _D /V _T[ET] was similar to V _D /V _T[art] at rest (-0.01 ± 0.03, P = 0.127) and peak exercise (0.01 ± 0.04, P = 0.210), but overestimated V _D /V _T[art] at 20 W (-0.02 ± 0.03, P = 0.025). Although V _D /V _T[J] was similar to V _D /V _T[art] at rest (-0.01 ± 0.03, P = 0.156) and 20 W (-0.01 ± 0.03, P = 0.133), V _D /V _T[J] underestimated V _D /V _T[art] at peak exercise (0.03 ± 0.04, P = 0.013). Exercise [Formula: see text] and V _D /V _T[ET] provides better estimates of [Formula: see text] and V _D /V _T[art] than PJ _{CO 2} and V _D /V _T[J] does at peak exercise. Thus, estimates of [Formula: see text] and V _D /V _T should only be used if sampling arterial blood during CPET is not feasible. NEW & NOTEWORTHY  [Formula: see text] provides a better estimate of [Formula: see text] than PJ _{CO 2} at peak exercise, and V _D /V _T[ET] provides a better estimate of V _D /V _T[art] than V _D /V _T[J] at peak exercise. Although we reported significant correlations, we did not find an identity between [Formula: see text] and estimates of [Formula: see text], nor did we find an identity between V _D /V _T[art] and estimates of V _D /V _T[art] . Thus, caution should be taken and estimates of [Formula: see text] and V _D /V _T should only be used if sampling arterial blood during CPET is not feasible.