Early Recovery of Oxygen Kinetics in Heart Failure: A Systematic Review of Oxygen Kinetics During the First Minute of Recovery after Cardiopulmonary Exercise Testing in Heart Failure

Abstract

Background: Cardiopulmonary exercise testing (CPET) is the gold standard for assessing functional capacity in heart failure (HF). Oxygen kinetics during the early recovery phase, particularly the VO₂/t-slope (the linear slope of oxygen uptake reduction during the first minute of recovery), are delayed in HF due to specific pathophysiological mechanisms. The hypothesis of a correlation between the VO₂/t-slope and peak oxygen uptake (VO₂peak) in HF remains debated. However, their parallel variation in HF patients, compared with healthy individuals and post-exercise interventions, suggests a common pathophysiological pathway. Since the VO₂/t-slope is independent of CPET duration and intensity, it may serve as a valuable alternative to VO₂peak, particularly for symptomatic HF patients.

Objective: To compare oxygen kinetics during the early CPET recovery phase in HF and healthy populations, evaluate VO₂/t-slope variations after exercise training, and propose the VO₂/t-slope as a complementary indicator to VO₂peak for HF diagnosis, classification, and prognosis.

Method: A systematic review was conducted on studies examining the correlation between the VO₂/t-slope and VO₂peak in HF patients, with or without structured training programs. The following keywords were used: "VO₂/t-slope," "oxygen kinetics," "recovery," "cardiopulmonary test," "VO₂peak," and "heart failure." Databases included PubMed, SciELO, Cochrane (CENTRAL), and ScienceDirect, following PRISMA (Preferred Reporting Items for Systematic Reviews and Meta- Analyses) guidelines. The PEDro scale (Clinimetric Tool Physiotherapy Evidence Database) was used to assess study quality. The systematic review is registered in INPLASY (DOI: 10.37766/inplasy2024.9.0111, registration number INPLASY: 202490111). Out of 542 articles, 10 were selected based on the study's eligibility criteria.

Results: A direct, positive, and statistically significant relationship was found between the VO₂/t-slope and VO₂peak after maximal CPET (r = 0.84, P < 0.001; VO₂peak = 10.5 + 16 × VO₂/t-slope) and after submaximal CPET (r = 0.87, P < 0.001; VO₂peak = 9.5 + 20 × VO₂/t-slope). Both parameters varied proportionally (indirect correlation) with HF severity and improved after exercise training, indicating shared metabolic pathways. Strength training combined with high-intensity aerobic exercise further enhanced cardiorespiratory recovery compared with aerobic training alone. HF-related histological and biochemical muscle changes, including mitochondrial adaptations, contribute to the observed VO₂/tslope delays and to the proportional variability of both the VO₂/t-slope and VO₂ peak.

Conclusion: VO2/t-slope is a promising diagnostic and prognostic indicator for HF, complementing VO2peak in maximal and submaximal CPET. Its proportional deterioration in HF and improvement post-exercise highlights its role in assessing functional status and disease progression. Unlike VO2peak, VO2/t-slope remains independent of CPET duration and intensity, making it particularly useful for advanced HF stages and revealing Clinical superiority. These findings support VO2/tslope as a valuable tool for HF diagnosis, classification, prognosis, and follow-up. DOI number: 10.37766/inplasy2024.9.0111, registration number INPLASY: 202490111.

Keywords: VO2/t-slope; VO2peak; cardiopulmonary test; heart failure; oxygen kinetics; recovery.