Influence of sympathetic activation on myocardial contractility measured with ballistocardiography and seismocardiography during sustained end-expiratory apnea.

Ballistocardiography (BCG) and seismocardiography (SCG) assess vibrations produced by cardiac contraction and blood flow, respectively, through micro-accelerometers and micro-gyroscopes. BCG and SCG kinetic energies (KE), and their temporal integrals (iK) during a single heartbeat are computed in linear and rotational dimensions. Multiunit muscle sympathetic nerve traffic (BF, burst frequency; tMSNA, total muscular sympathetic nerve activity) was measured by microneurography during normal breathing and apnea (n=28, healthy men). iK of BCG and SCG were simultaneously recorded along with oxygen saturation (SatO2) and systolic blood pressure (SBP).The mean duration of apneas was 25.4±9.4s. SBP, BF, tMSNA increased during the apnea compared to baseline (p=0.01, p=0.002, p=0.001, respectively), while SatO2 decreased (p=0.02). At the end of the apnea compared to normal breathing, changes of iK computed from BCG were related to changes of tMSNA and BF only in the linear dimension (r=0.85, p<0.0001; r=0.72, p=0.002, respectively), while changes of linear iK of SCG were related only to changes of tMSNA (r=0.62, p=0.01).Maximal end expiratory apnea increases cardiac kinetic energy computed from BCG and SCG, along with sympathetic activity. The novelty of the present investigation is that linear iK of BCG is directly and more strongly related to the rise in sympathetic activity than the SCG, mainly at the end of a sustained apnea, likely because the BCG is more affected by the sympathetic and hemodynamic effects of breathing cessation. BCG and SCG may prove useful to assess sympathetic nerve changes in patients with sleep disturbances.