Changes in peripheral blood flows in response to 48 hours of 6° head down bed rest

Nine young, healthy men (171±4.4 cm, 77.4±3.9 kg, 23.1±1.8 yr) were studied before and after 48 hours of 6° head down bed rest (HDBR). Arterial pressure (AP, Finapress), heart rate (HR, BoMed), stroke volume (SV, BoMed), cardiac output (CO, BoMed), radial artery flow (RF, BoMed), skin perfusion of palm and calf (SP1, SP2, Perimed) and peripheral vascular resistance (TPR, calculated) were acquired non-invasively for 20 minutes of supine rest and up to 20 minutes of lower body negative pressure (LBNP), less if syncopal. A two factor analysis of variance was used to assess responses to -50 mmHg LBNP and 6° HDBR. As expected, LBNP elicited significant (p<0.02) decreases in mean values of SV, RF, CO, and SP1 and increased mean values of HR and TPR. HDBR elicited decreased mean values of RF and SP1 to less than half of control (p<0.01). In addition, total spectral power of RF decreased with LBNP (p<0.06) while total spectral power of SP1 decreased with both HDBR (p<0.02) and LBNP (p<0.08). These data suggest that HDBR and LBNP evoke decreases in both the absolute values of peripheral flows as well as total spectral power associated with vasomotion. These data also indicate that the effects of HDBR are more apparent in peripheral than in central variables.