Evaluation of myocardial performance during wheelchair ergometer exercise

Since a relatively high incidence of cardiovascular disease is associated with wheelchair confinement, exercise stress testing techniques should be utilized to assess myocardial performance of wheelchair-dependent individuals. Therefore, the purpose of this study was to apply the techniques of impedance cardiography to graded wheelchair-type exercise. For this, 9 wheelchair-dependent volunteers completed a progressive intensity, discontinuous test on a wheelchair ergometer (WERG) at power outputs (PO) of 10, 20, and 30 watts. An impedance cardiogram (ZCG), electrocardiogram (ECG), and phonocardiogram (PCG) were recorded for 15 sec immediately following steady state exercise. Stroke volume (delta V) calculated from the ZCG was multiplied by steady state heart rate (HR) to estimate cardiac output (Q). The simultaneous recording of the ZCG, ECG, and PCG permitted calculation of systolic time intervals and impedance cardiography contractility indices. Values for delta V, HR, Q, arteriovenous oxygen difference, systolic and diastolic blood pressure, mean systolic ejection rate, the first derivative of the impedance change, and the Heather Index increased with increments in PO. The Q-S2 interval, left ventricular ejection time (LVET), the pre-ejection period (PEP), the ratio of PEP to LVET, and the R-Z interval decreased with increases in exercise intensity. A linear relationship was found between Q and oxygen uptake which was similar to that reported by other investigators for arm exercise. These data indicate that impedance cardiography may be used in conjunction with electrocardiography and phonocardiography for the non-invasive assessment of myocardial performance during wheelchair exercise testing.