Higher Respiratory Muscle Oxygen Cost of Breathing During Exercise in Heart Failure With Preserved Ejection Fraction.

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.