Skeletal Muscle Oxidative Capacity And Muscle Fat Content In Heart Failure With Preserved Ejection Fraction
Bibliographic record
Abstract
PURPOSE Exercise intolerance is the hallmark symptom of heart failure with preserved ejection fraction (HFpEF), the most common form of heart failure among older individuals. Initially considered to be a central limitation (i.e. abnormal left ventricular relaxation and impaired cardiac output), emerging evidence supports a peripheral limitation to exercise. However, direct evaluation of the quadriceps (the primary locomotor muscle group) remains limited. METHODS HFpEF patients (n = 23, 12F, 68.1 ± 6.4 yrs) and age-matched controls (n = 23, 14F, 69.2 ± 6.6 yrs) completed: 1) an incremental cycle test to assess VO2max, 2) T2- magnetic resonance imaging to quantify thigh muscle volume and fat content, and 3) 31P magnetic resonance spectroscopy of the quadriceps to quantify muscle oxidative capacity; measured as the Tau (τ) of phosphocreatine recovery (τPCr) immediately following knee extension exercise. Whole-body arterial-venous oxygen difference and cardiac output were also measured in HFpEF patients (but not controls) to further sub-divide HFpEF patients as being centrally- (Type A) versus peripherally-limited (Type-B). RESULTS HFpEF had greater body mass (p = 0.001) and BMI (p = 0.001) than Controls, and a lower VO2max when normalized to body mass (14.3 ± 4.5 vs 18.9 ± 4.6 ml/kg/min; p = 0.006), but no differences were observed for VO2max normalized to leg lean mass (899.5 ± 168.3 vs 982.8 ± 164.1 ml/kg/min; p = 0.096), τPCr (57.1 ± 11.8 vs 54.4 ± 14.9 s; p = 0.518), or muscle- (22.5 ± 7.0 vs 19.9 ± 4.0 %; p = 0.127) and thigh-fat percentages (56.1 ± 16.0 vs 51.4 ± 12.4 %; p = 0.287). After separating Type-A (n = 8, 1F) and Type-B (n = 15, 11F) HFpEF patients, VO2max normalized to leg mass (main effect p = 0.115) and τPCr (main effect p = 0.481) were still not different between groups, but Type-B HFpEF patients did exhibit greater muscle- (24.9 ± 7.0 %) and thigh-fat (62.3 ± 13.7 %) percentages than Type-A HFpEF patients (18.1 ± 4.6 and 44.5 ± 14.0 %; p < 0.015) and Controls (p < 0.05). CONCLUSION The results of the present study do not support impairments in intrinsic skeletal muscle oxidative capacity as a major source of exercise intolerance in HFpEF but highlight potentially important roles for differences in skeletal muscle- and thigh-fat content. This study was funded by the National Institutes of Health (P01 HL137630).
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".