Background:
Right heart failure (RHF) drives morbidity and mortality regardless of the primary condition. In the context of basic research in this field and the desired translation of results from animal models to humans, thorough and adequate phenotyping of the animals for the assessment of disease severity is indispensable. Here, we show a comprehensive analysis of data derived from echocardiography as well as cardiopulmonary exercise testing (CPET) focusing on respiratory gas measurement and its link to mitochondrial integrity in a mouse model of RV pressure overload.
Methods and Results:
RV pressure overload was induced in C57BL/6N male mice by constricting the pulmonary artery to a diameter of 300 µm for a period of 6 weeks. At 2, 4 and 6 weeks mice were subjected to CPET following a standardized protocol of graded maximal exercise testing. At the same time, cardiac function was assessed by echocardiography. Mice upon PAB showed significantly reduced distance, work rate, and peak oxygen consumption (VO2) compared to control mice (6 wks, n=14/19, for each respective parameter: p<0.0001). Furthermore, the anaerobic threshold was determined using the Beaver method to evaluate metabolic response during exercise, and, notably, PAB mice had a lower oxygen uptake at the AT (6 wks, n=7/7: p<0.01). All of these parameters exhibited a strong correlation with functional parameters derived from echocardiography (6 wks, n=26, most importantly endsystolic RA area with distance, p<0.0001; with peak VO2, p<0.0001).
To shed light on the relevance of mitochondrial integrity in this context, we isolated murine cardiomyocytes following the final exercise test and conducted high-resolution respirometry using the Oroboros O2k. Both parameters reflecting mitochondrial respiratory chain integrity and those evaluating the efficiency of energy production were reduced in right ventricles of PAB mice, suggesting impaired mitochondrial function (6 wks, n=19/24, most importantly respiratory control ratio (RCR), p<0.0001 and ATP production, p<0.0001). These parameters also correlated with parameters from echocardiography (6 wks, n=17, e.g. RA area with RCR, p<.0.05 and with ATP production, p<0.01) and CPET (6 wks, n=24, most importantly RCR with distance, p<0.01; with peak VO2, p<0.01). Next, the murine data described above will be compared with spiroergometric and echocardiographic measurements obtained from a cohort of patients with right heart dysfunction caused by pulmonary arterial hypertension or tricuspid regurgitation. By doing so, we aim to gain insights into the translatability of the PAB model.
Conclusion:
CPET focusing on respiratory gas analysis allows for a detailed characterization of disease severity in mice, as demonstrated here using a model of RHF. By assessing peak VO2 as well as submaximal exercise capacity parameters such as VO2 at the anaerobic threshold, a comprehensive overview of cardiopulmonary function can be achieved. Added to that, these parameters seem to provide an adequate representation not only of cardiac consequences, as indicated by altered echocardiographic parameters, but also of subcellular processes at the cardiomyocyte level, reflected by changes in cellular respiration.
