LAUSR

We determined for the first time whether individual differences in cardiovascular (CV) measures are observed after repeated baseline and recovery sleep (prior to and after exposure to total sleep deprivation) as well as the stability of such responses across 4-month and 8-month long-duration studies. We conducted a five-day experiment twice (at months 2 and 4) in a 4-month study (N=6 healthy adults; 3 females), and a similar five-day experiment three times (at months 2, 4, and 8) in an 8-month study (N=5 healthy adults; 2 females). During these repeated experiments, CV measures were collected via echocardiography at three assessment time points: 1) after two baseline 8h time in bed (TIB) nights (BL); 2) after a night of total sleep deprivation (TSD); and 3) after two recovery nights of 8-10h TIB (REC). Seated stroke volume (SV), heart rate (HR), cardiac index (CI), left ventricular ejection time (LVET), and systemic vascular resistance index (SVRI) were collected. Data did not significantly differ between the two studies and therefore were pooled together for analysis (N=11). Intraclass correlation coefficients (ICCs) assessed the stability of CV measures after BL and REC. Spearman’s rho assessed the relative rank of individuals’ averaged BL and REC responses across CV measures. BL ICCs (0.821-0.944) and REC ICCs (0.806-0.869) comparing months 2 and 4 for all CV measures were almost perfect. The ICCs comparing BL vs. REC measures at month 2 (0.816-0.969) and at month 4 (0.816-0.927) for all CV measures were similarly almost perfect. In the 8-month sample subset, BL ICCs (0.693-939) and REC ICCs (0.770-960) comparing months 2, 4 and 8 for all CV measures were substantial to almost perfect. The ICCs comparing BL vs. REC measures at month 8 for all CV measures were fair to almost perfect (0.314-0.960). Individuals also exhibited significant consistency of responses within CV measures across 2 months and 4 months during BL and REC. This is the first demonstration of remarkable robust phenotypic stability of a number of cardiovascular measures across repeated baseline and recovery sleep and across various CV measures in long-duration studies. NASA grants NNX14AN49G and 80NSSC20K0243 (NG)