Cardiorespiratory responses to cyclic triangular ramp forcings in work load

The dynamic responses of minute ventilation, heart rate, cardiac output, oxygen uptake, and carbon dioxide output to cyclic ramp exercise were studied on six healthy male subjects. Exercise was performed in the sitting position using a cycle ergometer. On separate occasions, three different ramp slopes, i.e. 33.3 (repeated for three cycles), 20 (two cycles), and 14.3 W/min (one cycle), were applied over the load range from 0 to 100 W. Mean response times (MRTs) were determined by adopting an exponential function with a time delay to the transient responses. The MRTs of the ascending phase of the first cycle were elongated with a decreasing ramp slope in almost all variables, while those for the descending phase remained unchanged. This resulted in notable asymmetry of the responses in the first cycle. However, there was negligible asymmetry observed in subsequent cycles and the MRTs gradually attained their proper values. Asymmetry in cardiac output was less noticeable compared with that of the respiratory variables. The correlation between the MRTs for ventilation and carbon dioxide output was highly significant, suggesting that a cardiodynamic or humoral mechanism may be related to this phenomenon.