Assessment of heart rate and oxygen consumption during and following a six-minute walk test in patients awaiting liver transplant (2024)

Background

People with liver cirrhosis (LC) who are awaiting liver transplant have reduced physical function and quality of life [1,2]. However, the physiologic factors contributing to decreased physical function remain unclear.

Purpose

To test the hypothesis that people with LC will have worse exercise efficiency during a standardized six-minute walk test (6MWT) defined as a shorter walk distance at a higher energy cost (e.g., higher oxygen consumption; VO2). We further hypothesized that patients with LC will have prolonged post-exercise heart rate and VO2 kinetics compared to adults of similar age without LC.

Methods

Nine participants with LC who are being assessed for transplantation (60±7 years, 2 female, 31.3±6.9 kg/m2) and seven age- and sex-matched healthy adults (HA; 60±9 years, 1 female, 27.6±3.9 kg/m2) were recruited for this study. Participants with LC were enrolled as part of a larger pre-habilitation exercise and nutrition intervention and were classified as pre-frail according to the liver frailty index (LFI: 3.8±0.4). The LC group had Child-Pugh scores between 9-12 (Class B and C; n=3 and n=6, respectively) and MELD-Na score of 16.8±4.9. We measured heart rate and VO2 (VO2 Master portable analyzer) prior to (five-minutes seated rest), during the last two-minutes of the 6MWT (i.e., at steady-state exercise), and immediately post-exercise (five- minutes of seated recovery; Figure 1). Blood pressure was also measured at rest and two-minutes after the 6MWT. Post-exercise heart rate and VO2 recovery kinetics were determined using monoexponential modelling (OriginLab, 2023b). Specifically, we determined the time delay to the start of the exponential decline in heart rate or VO2 following exercise termination, and the time to reach 63% of the recovery (τ) during the five-minutes of seated rest. From this, the mean response time (MRT) was computed as MRT= time delay + τ.

Results

Resting heart rate, blood pressure, and VO2 were not different between groups (Table 1). During the last two-minutes of the 6MWT, heart rate was not different between groups. However, owing to a greater total distance walked (HA: 629±50m vs LC: 397±133m; p<0.001), VO2 was higher in the HA group (Table 1). The heart rate MRT was not different between groups (HA: 66±34s vs LC: 46±17s; p=0.164) but VO2 MRT was 25% slower in LC (85±22s) compared to HA (64±14s; p=0.045).

Conclusion