Heart rates of Atlantic salmon Salmo salar during a critical swim speed test and subsequent recovery.

In this study, heart rate (HR) bio-loggers were implanted in the abdominal cavity of 12 post-smolt Atlantic salmon Salmo salar weighing 1024 ± 31 g and acclimated to 12°C sea water. One week after the surgical procedure, a critical swim speed (Ucrit ) test was performed on tagged and untagged conspecifics, whereafter tagged fish were maintained in their holding tanks for another week. The Ucrit was statistically similar between tagged and untagged fish (2.67 ± 0.04 and 2.74 ± 0.05 body lengths s-1 , respectively) showing that the bio-logger did not compromise the swimming performance. In the pre-swim week, a diurnal cycle was apparent with HR peaking at 65 beats min-1 during the day and approaching 40 beats min-1 at night. In the Ucrit test, HR increased approximately exponentially with swimming speed until a plateau was reached at the final speed before fatigue with a maximum of 85.2 ± 0.7 beats min-1 . During subsequent recovery tagged fish could be divided into a surviving group (N = 8) and a moribund group (N = 4). In surviving fish HR had fully recovered to pre-swim levels after 24 h, including reestablishment of a diurnal HR cycle. In moribund fish HR never recovered and remained elevated at c. 80 beats min-1 for 4 days, whereafter they started dying. We did not identify a proximal cause of death in moribund fish, but possible explanations are discussed. Tail beat frequency (TBF) was also measured and showed a more consistent response to increased swimming speeds. As such, when exploring correlations between HR, TBF and metabolic rates at different swimming speeds, TBF provides better predictions. On the contrary, HR measurements in free swimming fish over extended periods of time are useful for other purposes such as assessing the accumulative burden of various stressors and recovery trajectories from exhaustive exercise.

Participation in exercise-based cardiac rehabilitation is related to reduced total mortality in both men and women: results from the SWEDEHEART registry.

AIMS: Participation in exercise-based cardiac rehabilitation (exCR) increases aerobic capacity and improves outcomes in patients following myocardial infarction (MI) and is therefore universally recommended. While meta-analyses consistently report that participation in exCR reduces cardiovascular mortality, there are conflicting results regarding effects on total mortality. Presently, many eligible patients do not receive exCR in clinical practice. We aimed to investigate the relation between participation in exCR post-MI and total mortality in men and women in a nationwide real-world cohort from the SWEDEHEART registry. DESIGN: Longitudinal, observational cohort study. METHODS AND RESULTS: In total, 20 895 patients from the SWEDEHEART registry were included. Mortality data were obtained from the Swedish National Population Registry. During a mean of 4.55 (±2.33) years of follow-up, 1000 patients died. Using Cox regression for proportional odds and taking a wide range of potential confounders into consideration, participation in exCR was related to significantly lower total mortality [hazard ratio (HR) 0.72, 95% confidence interval 0.62-0.83]. Excluding patients with shorter follow-up than 2 years did not alter the results. Exercise-based CR participation was related to lowered total mortality in most of the investigated subgroups. The risk reduction was more pronounced in women than in men (HR 0.54 vs. 0.81, respectively). CONCLUSION: Participation in exCR was associated with reduced total mortality, and more pronounced in women, compared with men. Our results further support the recommendations to participate in exCR, and hence we argue that exCR should be a mandatory part of comprehensive CR programmes, offered to all patients post-MI.