Estimating exercise Pa_CO 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 CO₂ (PJ_CO) equation (PJ_CO = 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 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 CO₂ ([Formula: see text]) and PJ_CO 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 (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 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 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 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.