Discriminating circulatory problems with reduced stroke volume (SV) from deconditioning, in which the muscles cannot consume oxygen normally, by gas exchange parameters is difficult.
We performed combined stress echocardiography (SE) and cardiopulmonary exercise tests (CPET) in 110 patients (20 with normal effort capacity, 54 with attenuated SV response, and 36 with deconditioning) to evaluate multiple hemodynamic parameters and oxygen content difference (A-o2 Diff) in four predefined activity levels to assess which of the gas measures may help in the discrimination.
Reduced anaerobic threshold (AT), low unchanging peak oxygen pulse, periodic breathing, shallow Δ peak oxygen consumption (o2)/Δwork rate (WR) ratio, and high expired volume per unit time/carbon dioxide production (e/co2) slope were all associated with abnormal SV response (P < .05 for all). The best discriminator was e/co2 slope to o2 ratio (≥ 2.7; area under the curve [AUC], 0.79; P < .0001). The optimal gas exchange model included Δo2/ΔWR < 8.6; e/co2 slope to peak o2 ratio ≥ 2.7, and periodic breathing (AUC of 0.84; P < .0001).
The best single gas exchange parameter to discriminate between circulatory problems and deconditioning is e/co2 slope to peak O2 ratio. Combining it with Δo2/ΔWR and periodic breathing improves the discriminative ability.