To examine cardiac performance during rhythmic handgrip exercise in the supine versus head-down tilt positions.
Continuous measures of arterial pressure, thoracic bio-impedance, heart sounds, and an electrocardiogram were collected in 12 participants (age:26±2 yr) during 5 minutes of rest (R) and 3 minutes of rhythmic handgrip exercise (HG) performed while lying supine (S) and during 6 degrees of head-down tilt (Dn). Contractions were performed at an intensity of 70% of maximal voluntary contraction and at a rate of 1 contraction per 4 seconds. The following variables were calculated, recorded, and averaged during the last 10 heart beats of each condition: stroke volume (SV), heart rate (HR), mean arterial pressure (MAP), total peripheral resistance (TPR), pre-ejection period (PEP), diastolic time (DT), left ventricular ejection time (LVET), diastolic filling rate (DFR), and left ventricular ejection rate (LVER). A 2 × 2 ANOVA was used to examine differences in the 10-beat average of each variable between conditions. All tests were considered significant at the 0.05 level.
Data are shown in Table 1. There were main effects of Condition such that MAP, HR, and TPR were greater during HG, and SV, DT, and LVER were lower during HG. Furthermore, there was a main effect of Position such that DT was greater during Dn. Lastly, there was a trend toward a Position × Condition interaction (p =0.07) such that DT was reduced more during Dn-HG compared to S-HG.
HG results in increased MAP, HR, and TPR, and reduced SV, DT, and LVER. Furthermore, these responses appear to be similar in the S and Dn positions, with the possible exception of DT. These data suggest the reduced SV is due to an increased afterload during HG.
Posters Displayed One and one-half hour author presentation times are staggered among authors from2:00–3:30 p.m. and 3:30–5:00 p.m.