Cardiopulmonary exercise testing (CPET) assesses the ability of the respiratory and cardiovascular systems to respond to exercise.  Reference values for CPET provide the terms of comparison for assessing the normalcy of patient?s response to exercise.

The aim of this study was to identify new cardiocirculatory response patterns, in terms of heart rate increase to oxygen consumption (HR/ V?O2) and carbon dioxide production (HR/V?CO2).

We performed a maximal symptom-limited CPET on cycle ergometer on 20 healthy subjects (15 males, 5 females; age 25-35) and analyzed the relationship between both V?O2 and V?CO2 and heart rate (HR) in terms of slope and y-intercept.

HR/ V?O2  slopes showed a median value of 50.6± 9.9 with a y-intercept of 68.1±19.4.  HR/V?CO2 slope median value was 32.7±6 with a y-intercept of 88±17.9.

We observed similar linear relationships between all subjects both for HR/ V?O2 and HR/ V?CO2, suggesting the existence of a ?normal reference? for these parameters.

HR/V?O2 slope showed also an inversely proportional relationship with BMI (Body Mass Index) and BSA (Body Surface Area) (p-value <0.05).

Assuming that we analyzed only fit subjects, this result seems to suggest that subjects with higher muscular mass have a better cardiovascular response to V?O2 (lower HR/ V?O2 slope) during exercise.

The identification of reference values for both HR/ V?O2 and HR/ V?CO2 may provide new evaluation tools for cardiopulmonary response to exercise. Further studies are needed to assess if these parameters increase the accuracy of CPET to identify abnormal cardiorespiratory response in subjects with cardiorespiratory chronic diseases.