Open AccessReliability and Physiological Interpretation of Pulmonary Gas Exchange by “Circulatory Equivalents” in Chronic Heart Failure
Author(s) -
Tan Chunting,
Rossiter Harry B.,
Porszasz Janos,
Bowen T. Scott,
Witte Klaus K.,
Stringer William W.,
Casaburi Richard,
Hansen James E.
Publication year - 2018
Publication title -
journal of the american heart association
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.494
H-Index - 85
ISSN - 2047-9980
DOI - 10.1161/jaha.117.008072
Subject(s) - algorithm , computer science
Background Peak ratios of pulmonary gas‐exchange to ventilation during exercise ( V ˙ O 2 / V ˙ EandV ˙ CO 2 / V ˙ E , termed “circulatory equivalents”) are sensitive to heart failure ( HF ) severity, likely reflecting low and/or poorly distributed pulmonary perfusion. We tested whether peakV ˙ O 2 / V ˙ EandV ˙ CO 2 / V ˙ Ewould: (1) distinguish HF patients from controls; (2) be independent of incremental exercise protocol; and (3) correlate with lactate threshold ( LT ) and ventilatory compensation point ( VCP ), respectively. Methods and Results Twenty‐four HF patients (61±11 years) with reduced ejection fraction (31±8%) and 11 controls (63±7 years) performed ramp‐incremental cycle ergometry. Eighteen HF patients also performed slow (5±1 W/min), medium (9±4 W/min), and fast (19±6 W/min) ramps. PeakV ˙ O 2 / V ˙ EandV ˙ CO 2 / V ˙ Efrom X‐Y plot, and LT and VCP from 9‐panel plot, were determined by 2 independent, blinded, assessors. PeakV ˙ O 2 / V ˙ E(31.2±4.4 versus 41.8±4.8 mL/L; P <0.0001) andV ˙ CO 2 / V ˙ E(29.3±3.0 versus 36.9±4.0 mL/L; P <0.0001) were lower in HF than controls. Within individuals, there was no difference across 3 ramp rates in peakV ˙ O 2 / V ˙ E( P =0.62) orV ˙ CO 2 / V ˙ E( P =0.97). Coefficient of variation ( CV ) in peakV ˙ O 2 / V ˙ Ewas lower than for LT (5.1±2.1% versus 8.2±3.7%; P =0.014), and coefficient of variation in peakV ˙ CO 2 / V ˙ Ewas lower than for VCP (3.3±1.8% versus 8.7±4.2%; P <0.001). In all participants, peakV ˙ O 2 / V ˙ Ewas correlated with, but occurred earlier than, LT ( r 2 =0.94; mean bias, −0.11 L/min), and peakV ˙ CO 2 / V ˙ Ewas correlated with, but occurred earlier than, VCP ( r 2 =0.98; mean bias −0.08 L/min). Conclusions Peak circulatory equivalents during exercise are strongly associated with (but not identical to) LT and VCP . Peak circulatory equivalents are reliable, objective, effort‐independent indices of gas‐exchange abnormality in HF .