Abstract
The goals of the current study were to compare leg blood flow, oxygen extraction and oxygen uptake (VO2) after constant load sub-maximal unilateral knee extension (ULKE) exercise in patients with heart failure with reduced ejection fraction (HFrEF) compared to those with preserved ejection fraction (HFpEF). Previously, it has been shown that prolonged whole body VO2 recovery kinetics are directly related to disease severity and all-cause mortality in HFrEF patients. To date, no study has simultaneously measured muscle-specific blood flow and oxygen extraction post exercise recovery kinetics in HFrEF or HFpEF patients; therefore it is unknown if muscle VO2 recovery kinetics, and more specifically, the recovery kinetics of blood flow and oxygen extraction at the level of the muscle, differ between HF phenotypes. Ten older (68±10yrs) HFrEF (n = 5) and HFpEF (n = 5) patients performed sub-maximal (85% of maximal weight lifted during an incremental test) ULKE exercise for 4 minutes. Femoral venous blood flow and venous O2 saturation were measured continuously from the onset of end-exercise, using a novel MRI method, to determine off-kinetics (mean response times, MRT) for leg VO2 and its determinants. HFpEF and HFrEF patients had similar end-exercise leg blood flow (1.1±0.6 vs. 1.2±0.6 L/min, p>0.05), venous saturation (42±12 vs. 41±11%, p>0.05) and VO2 (0.13±0.08 vs. 0.11±0.05 L/min, p>0.05); however HFrEF had significantly delayed recovery MRT for flow (292±135sec. vs 105±63sec., p = 0.004) and VO2 (95±37sec. vs. 47±15sec., p = 0.005) compared to HFpEF. Impaired muscle VO2 recovery kinetics following ULKE exercise differentiated HFrEF from HFpEF patients and suggests distinct underlying pathology and potential therapeutic approaches in these populations.
Highlights
The primary chronic symptom in heart failure patients with reduced or preserved ejection fraction (HFrEF and HFpEF, respectively), even when stable and well compensated, is severe exercise intolerance which is associated with their reduced quality of life [1]
Belardinelli et al [2] reported that pulm VO2 and skeletal muscle oxygenation recovery kinetics were significantly delayed in heart failure with reduced ejection fraction (HFrEF) patients compared to healthy controls after performing constant-load sub-maximal exercise
left ventricular (LV) EDV and ESV were significantly larger in HFrEF patients while LVEF and LVM/EDV were significantly reduced in HFrEF patients (Table 1)
Summary
The primary chronic symptom in heart failure patients with reduced or preserved ejection fraction (HFrEF and HFpEF, respectively), even when stable and well compensated, is severe exercise intolerance which is associated with their reduced quality of life [1]. Belardinelli et al [2] reported that pulm VO2 and skeletal muscle oxygenation recovery kinetics (measured with near infrared spectroscopy, NIRS) were significantly delayed in HFrEF patients compared to healthy controls after performing constant-load sub-maximal exercise. The independent contributions of blood flow and oxygen extraction to overall oxygen consumption during recovery following isolated muscle exercise, where the heart is not a major limiting factor as occurs during unilateral knee extension (ULKE) exercise [14], have not been previously been measured in HFrEF and HFpEF patients. The goals of the current study were to compare skeletal muscle blood flow, oxygen extraction and oxygen consumption recovery kinetics following ULKE exercise in HFrEF and HFpEF patients
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