Kinetics of Cardiac Output at the Onset of Exercise in Precapillary Pulmonary Hypertension

Abstract

Purpose. Cardiac output (CO) is a cornerstone parameter in precapillary pulmonary hypertension (PH). The Modelflow (MF) method offers a reliable noninvasive determination of its beat-by-beat changes. So MF allows exploration of CO adjustment with the best temporal resolution. Methods. Fifteen subjects (5 PH patients, 10 healthy controls) performed a submaximal supine exercise on a cycle ergometer after 5 min of rest. CO was continuously determined by MF (CO_MF). Kinetics of heart rate (HR), stroke volume (SV), and CO were determined with 3 monoexponential models. Results. In PH patients, we observed a sudden and transitory drop of SV upon exercise onset. This implied a transitory drop of CO whose adjustment to a new steady state depended on HR increase. The kinetics of HR and CO for PH patients was slower than that of controls for all models and for SV in model 1. SV kinetics was faster for PH patients in models 2 and 3. Conclusion. This is the first description of beat-by-beat cardiovascular adjustments upon exercise onset in PH. The kinetics of HR and CO appeared slower than those of healthy controls and there was a transitory drop of CO upon exercise onset in PH due to a sudden drop of SV.

Figure 1

Graphical representation of the 3 models used for CO data analysis. CO, cardiac output; time 0 (black dotted line) corresponds to exercise onset; the red line in panels (a), (b), and (c) corresponds to the 3 models description; the green point in panels (b) and (c) corresponds to the minimal CO output (CO_min) determined for models 2 and 3, respectively. CO data of the PH patients were temporally aligned and superimposed. Analysis was performed individually for all subjects.

Figure 2

Time course of beat-by-beat heart rate (HR) and stroke volume (SV) upon exercise onset. Time 0 corresponds to exercise start. Data were temporally aligned and superimposed for both groups.

Figure 3

Time course of beat-by-beat heart rate (HR), stroke volume (SV), and cardiac output (CO) upon the onset of exercise. Data are superimposed for all PH patients (black, n = 5) and control subjects (grey, n = 10) and represented as relative values from 0 (baseline) to 100% (steady-state exercise). Time 0 corresponds to exercise start. Data were temporally aligned and superimposed for both groups.

Figure 4

Time course of systemic vascular resistances (SVR) upon exercise onset. Time 0 corresponds to exercise start. Data were temporally aligned and superimposed for both groups.