Non-Invasive Determination of Hemodynamic Variables and their Relationship to the Anaerobic Threshold

Abstract

Determination of non-invasive homodynamic monitoring using impedance cardiography has been shown to be possible at rest and during exercise. PURPOSE: To determine the relationship of various homodynamic variables to the anaerobic threshold during upright cycle ergometry. METHODS: Twenty-five moderately trained healthy young male subjects (mean±SD) age: 24±4 yrs; weight: 78±7 kg; height: 182±6 cm) performed an incremental cycle ergometer test in an upright position. Two submaximal markers of energy supply were denned by means of blood lactate concentration (LA): aerobic threshold (AeT): first abrupt increase of LA above resting levels; anaerobic threshold (AnT): second abrupt increase of LA between AeT and maximal workload (Pmax). Non-invasive homodynamic monitoring was performed in supine position prior to the test and during the exercise test using a combination of impedance cardiography and vascular unloading technique to measure stroke volume (SV), cardiac output (CO), systolic blood pressure (BP) and total peripheral resistance index (TPRI) (Task Force® Monitor, CNSystems, Graz, Austria). The determination of break points in all measured variables was conducted by means of computer-aided linear regression break point analysis between AeT and Pmax. RESULTS: Workload (P) and heart rate (HR) at Pmax were 331±35 W and 185±10 min−1, respectively. SV was significantly higher, BP and TPRI were significantly lower at supine compared to the upright position at rest. SV, BP, CO increased, TPRI decreased steadily from resting values to Pmax. BP showed a plateau at workload above AnT. A break point was observed in measured variables in most of the subjects. One-way ANOVA revealed no statistical significant difference (P>0.05) for workload at AnT of 242±29 W, (N=25) and at workload of the breakpoint for SV 247±41 W (N=19), CO of 249±40 W, N=18), TPRI of 232±37 W (N=22) and BP of 239±36 W (N=25). Significant correlations (P<0.001) were observed between workload at AnT and at workload of the breakpoint for SV (r=0.76), CO (r=0.80), TPRI (r=0.65) and BP (r=0.63). CONCLUSIONS: We conclude that there is a strong relationship between the AnT and multiple homodynamic variables. Non-invasive homodynamic monitoring using impedance electrocardiography and vascular unloading technique seems to be useful for application during upright cycle ergometry.