Effect of Acute β-blocker Withholding on Ventilatory Efficiency in Patients With Advanced Chronic Heart Failure

Abstract

Background This is the first study to examine the effect of acute (24-hour) β-blocker withholding on ventilatory efficiency in patients with advanced chronic heart failure (CHF) during maximal incremental treadmill cardiopulmonary exercise test. Methods and Results Seventeen CHF patients were studied either 3 hours after administration of β-blocker (BB ON) or 27 hours after the last β-blocker ingestion (BB OFF). The ventilatory efficiency was measured via the slope of the linear relationship between ventilation (V′ E) and carbon dioxide production (V′CO 2) (ie, V′ E/V′CO 2 slope). Measurements were also made at rest, anaerobic threshold (AT), maximal end-tidal pressure for carbon dioxide (P ETCO 2max), respiratory compensation point (RC), and peak exercise. Compared with BB ON, the V′ E/V′CO 2 slope was significantly increased during BB OFF (30.8 ± 7.4 vs. 29.1 ± 5.4, P = .04). At peak exercise, oxygen uptake (V′O 2, 16.0 ± 2.7 vs. 15.6 ± 2.8 mL·kg·min) and V′CO 2 (1458 ± 459 vs. 1414 ± 429 mL/min) were not different between the 2 conditions, whereas V′ E was higher during BB OFF (49.5 ± 10.7 vs. 46.1 ± 9.6 L/min, P = .04). No differences were noted at AT and RC in V′O 2, V′CO 2, V′ E, V′ E/V′O 2, and V′ E/V′CO 2 ratios during the 2 conditions. At P ETCO 2max, used to noninvasively estimate the CO 2 set point, V′ E was higher (33.9 ± 7.6 vs. 31.7 ± 7.3 L/min, P = .002) and P ETCO 2 was lower (37.4 ± 4.8 vs. 38.5 ± 4.0 mm Hg, P = .03), whereas V′CO 2 was unchanged (1079 ± 340 vs. 1050 ± 322 mL/min) during BB OFF. Conclusion Acute β-blocker withholding resulted in decreased ventilatory efficiency mostly from an increase of V′CO 2-independent regulation of V′ E and less likely from a change in ventilation/perfusion mismatching.