VO2peak and phase angle in heart failure

Background The phase angle (PhA) serves as an indirect marker of cellular health, membrane integrity, and hydration status. Higher PhA values are typically observed in well-nourished individuals with metabolically active, structurally intact cells, whereas lower values are indicative of malnutrition, systemic inflammation, and compromised cellular integrity. Since peak oxygen uptake (VO2peak) is determined by both central cardiovascular function and peripheral muscle oxygen extraction, impairments in cellular health—as reflected by lower PhA—may negatively affect VO2peak. Purpose Therefore, we hypothesize that higher VO2peak is associated with higher whole-body PhA in heart failure patients. Methods Retrospective data of heart failure patients who underwent in-patient exercise-based cardiac rehabilitation between December 2022 and June 2024 was analyzed. Whole-body PhA was assessed using BIA. VO2peak was measured via cardiopulmonary exercise testing (CPET) on a cycle ergometer with breath-by-breath gas exchange analysis. Participants were encouraged to exercise to volitional fatigue. The CPET protocol was individualized by the attending physician to achieve an expected exercise duration of 8–12 minutes. Results A total of 39 adults were included (median age = 61 years, IQR = 54.0–73.0; 10% female). Median BMI was 25.2 kg/m² (IQR = 23.7–29.9), mean PhA was 4.6° (SD = 0.7), and mean VO2peak was 22.8 ± 7.8 mL/kg/min (Table 1). A Pearson correlation analysis revealed a statistically significant positive association between VO2peak and whole-body PhA, r(37) = .432, p = .006 (Figure 1). A non-significant negative correlation was observed between VE/VCO2 slope and PhA (Pearson’s r = –0.251, p = 0.123). Conclusion The positive association between VO2peak and whole-body PhA suggests that greater aerobic capacity is linked to better cellular health and membrane integrity in this population. These findings support the physiological premise that PhA, as a marker of cellular integrity, may contribute to oxygen uptake capacity. Although a non-significant negative correlation between PhA and VE/VCO2 slope was observed, the direction of the relationship suggests that better cellular health may be linked to more efficient ventilation. However, this potential connection is likely indirect and possibly influenced by various clinical factors. Phase angle may serve as a valuable complementary marker for evaluating functional status, particularly in heart failure patients during the acute post-hospitalization phase when maximal exercise testing may not be feasible. Further research with larger cohorts and adjustment for key confounders is warranted to determine whether PhA could serve as an additional for ventilatory efficiency, or whether it primarily reflects a distinct physiological domain relevant to functional capacity in heart failure.For image description, please refer to the figure legend and surrounding text. For image description, please refer to the figure legend and surrounding text.