Discriminating circulatory problems with reduced stroke volume (SV) from deconditioning, in which the muscles cannot consume oxygen normally, by gas exchange parameters is difficult.Methods:
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-Symbolo2 Diff) in four predefined activity levels to assess which of the gas measures may help in the discrimination.Results:
Reduced anaerobic threshold (AT), low unchanging peak oxygen pulse, periodic breathing, shallow Δ peak oxygen consumption (Symbolo2)/Δwork rate (WR) ratio, and high expired volume per unit time/carbon dioxide production (Symbole/Symbolco2) slope were all associated with abnormal SV response (P < .05 for all). The best discriminator was Symbole/Symbolco2 slope to Symbolo2 ratio (≥ 2.7; area under the curve [AUC], 0.79; P < .0001). The optimal gas exchange model included ΔSymbolo2/ΔWR < 8.6; Symbole/Symbolco2 slope to peak Symbolo2 ratio ≥ 2.7, and periodic breathing (AUC of 0.84; P < .0001).Conclusions:
The best single gas exchange parameter to discriminate between circulatory problems and deconditioning is Symbole/Symbolco2 slope to peak SymbolO2 ratio. Combining it with ΔSymbolo2/ΔWR and periodic breathing improves the discriminative ability.