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Higher Respiratory Muscle Oxygen Cost of Breathing During Exercise in Heart Failure With Preserved Ejection Fraction
Tarin C Phillips1, Eric J Bruhn1, Gizem Cifci1
1Department of Cardiovascular Medicine, Mayo Clinic, Rochester, MN.
Background:
Patients with heart failure with preserved ejection fraction (HFpEF) have pulmonary system abnormalities resulting in impaired ventilatory reserve and heightened respiratory muscle work during submaximal exercise.
Research Question:
Do patients with HFpEF have higher respiratory muscle oxygen uptake (V˙o2) during submaximal exercise than control participants?
Study Design And Methods:
Patients with HFpEF (n = 13) and control participants (n = 16) completed 2 visits. The first visit included pulmonary function tests and an incremental exercise test. On the second visit, participants mimicked their exercise breathing patterns across a range of work rates (voluntary hyperpnea) in the absence of exercise to quantify respiratory muscle V˙o2. Respiratory muscle V˙o2 was reported during exercise at 40 W and approximately 65% peak work rates.
Results:
During exercise at 40 W, patients with HFpEF had higher respiratory muscle V˙o2 expressed as % of whole-body V˙o2 (control participants, 4.6% of whole-body V˙o2; interquartile range [IQR], 2.0-5.7 vs HFpEF, 8.3% of whole-body V˙o2; IQR, 6.1-9.2; P < .01) and mL/kg/min (control participants, 0.53 mL/kg/min; IQR, 0.24-0.68 vs HFpEF, 0.79 mL/kg/min; IQR, 0.69-1.10; P < .01). During exercise at 40 W, respiratory muscle V˙o2 was related to FVC % predicted (r = -0.64; P = .02) and breathing frequency during exercise (r = 0.70; P = .01) for patients with HFpEF, but not control participants (both r > 0.19; P > .40). During exercise at approximately 65% peak work rate, patients with HFpEF had higher respiratory muscle V˙o2 expressed as % of whole-body V˙o2 (control participants, 4.6% of whole-body V˙o2; IQR, 2.8-6.3 vs HFpEF, 7.2% of whole-body V˙o2; IQR, 6.0-8.8; P < .01). When accounting for ventilation, patients with HFpEF had higher respiratory muscle V˙o2 during exercise at 40 W and approximately 65% peak work rates (all P < .03).
Interpretation:
Our results show that respiratory muscle V˙o2 is significantly elevated in patients with HFpEF compared with control participants during submaximal exercise.
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