The role of pulse transit time as an index of arterial stiffness during exercise

The aim of the present study was to investigate, whether pulse transit time (PTT), a popular index of arterial stiffness at rest, can be also used as such, during steady state exercise. For this purpose, twelve male volunteers exercised on a cycle ergometer for 70 min on three separate occasions whereas, cycling cadence and workload were manipulated in order to produce diverse cardiorespiratory responses. PTT, blood pressure, cardiac output and respiratory frequency were measured during exercise. Resistance to systole and total peripheral resistance were calculated by the ratio of systolic pressure, and mean arterial pressure over cardiac output, respectively. All subjects across all conditions, showed a negative linear correlation (P < 0.01) between changes in PTT and systolic pressure (SP) (r = -0.66), changes in cardiac output (r = -0.76), and respiratory frequency (r = -0.40), whereas PTT was positively correlated (P < 0.05) with total peripheral resistance (r = 0.31), the SP to cardiac output ratio (r = 0.30) and plasma volume changes (r = 0.29). However, forward stepwise multiple regression analysis revealed that 71% (P < 0.001) of PTT changes from rest (DeltaPTT) variability was attributed to changes in cardiac output, SP and SP to cardiac output ratio. In the same model, total peripheral resistance did not exert significant influence on DeltaPTT variability. In conclusion, PTT is a reflection not only of SP but also of cardiac output changes per se and in combination with cardiac output (SP to cardiac output ratio) and should not be used as a pure marker of arterial stiffness under marked exercise cardiovascular and respiratory perturbations.