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A step in the right direction: pressure‐volume relationships provide insight into right ventricular performance during exercise in healthy adults

The right ventricle (RV) is critically involved in endurance training and cardiopulmonary disease, yet important knowledge gaps persist regarding normal function which limit our ability to detect and improve RV dysfunction. The pressure-volume loop describes ventricular pump performance over the cardiac cycle, including four main temporal phases; ventricular filling, isovolumic contraction, ejection and isovolumic relaxation. From the pressure-volume loop, quantitative descriptions can be derived for diastolic and systolic ventricular performance, as well as the effective pulmonary arterial (PA) load (Ea) (Sunagawa et al. 1984). The end-systolic pressure-volume relationship, particularly for the left ventricle (LV), is approximately linear within physiological ranges, load independent, and closely related to inotropic state. As such, its slope, end-systolic elastance (Ees), is the gold-standard index of systolic contractile performance for the intact ventricle. Pressure-volume analysis has clear value for studying conditions that have an impact on the RV-PA circulatory unit, which is highly load sensitive. Substantial advances have been made to enable RV pressure-volume analysis in adults with cardiopulmonary disease. To provide context, comprehensive descriptions of RV performance in health are needed to understand the functional changes that occur with the development of cardiopulmonary disease, as well as recognize the normal limits of systolic RV reserve to respond to acute challenges. Cornwell et al. (2020) have contributed to filling these knowledge gaps in a recent article in The Journal of Physiology. The study aimed to comprehensively describe systolic and diastolic RV performance and reserve in healthy individuals using pressure-volume relationships at rest and during exercise. Nine middle-aged individuals (22% female) without evidence of cardiopulmonary disease were recruited within a broader study examining RV function in health and heart failure. A pressure-volume catheter, which combines high-fidelity pressure sensors and multiple electrodes to estimate volume into a single device, was used to acquire pressure-volume loops, and breath-by-breath gas exchange measurements were recorded to determine metabolic parameters. Subjects performed upright cycle ergometry in a hybrid protocol comprising two constant work-rates, then an incremental maximal exercise test. Ees was derived from pressure-volume data using a single-beat approach, which estimates the theoretical maximal RV pressure developed in isovolumic contraction and subtracts the end-systolic pressure to determine the ‘rise’ of the slope, which is divided by stroke volume (the ‘run’). The ratio of Ees:Ea was calculated to assess ventricular-vascular coupling (VVC), and pressure-volume area bounded by the end-systolic and end-diastolic pressure-volume relations was calculated as an index of myocardial energy expenditure. The main findings were that the 3-fold increase in Ea at peak exercise was well matched by augmented Ees, indicating that RV contractile reserve is normally substantial, compared to individuals with pulmonary hypertension who have little reserve (Spruijt et al. 2015). These changes resulted in well-preserved VVC and suggest a 3-fold increase in myocardial energy expenditure at peak exercise. Additionally, progressive increases in the maximal rate of diastolic RV pressure decay reflected diastolic reserve. The authors concluded that the healthy RV has substantial reserve which can be recruited to maintain efficient VVC during exercise. Methodological considerations