Table 1.

Muscle sympathetic nerve activity during progressive lower-body negative pressure to presyncope performed under hyperthermic conditions after intravenous infusion of either iso-osmotic or hyperosmotic saline

Pre-LBNP20%40%60%80%100%
Burst frequency, bursts/min
All subjects (n = 6)
 ISO50 ± 2371 ± 1277 ± 1975 ± 2271 ± 1956 ± 24
 HYPER61 ± 1576 ± 1683 ± 1187 ± 1184 ± 1864 ± 10
Responders (n = 3)
 ISO44 ± 1269 ± 1167 ± 960 ± 660 ± 1235 ± 12
 HYPER65 ± 1178 ± 1983 ± 1287 ± 1278 ± 659 ± 7
Nonresponders (n = 3)
 ISO56 ± 3273 ± 1486 ± 2391 ± 2281 ± 2076 ± 7
 HYPER56 ± 2073 ± 1682 ± 1287 ± 1490 ± 2669 ± 10
Burst incidence, bursts/100 heartbeats
All subjects (n = 6)
 ISO50 ± 2163 ± 1468 ± 1765 ± 1960 ± 1753 ± 12
 HYPER61 ± 1968 ± 1770 ± 1371 ± 1569 ± 1661 ± 16
Responders (n = 3)
 ISO49 ± 1368 ± 1172 ± 1168 ± 1667 ± 854 ± 14
 HYPER71 ± 1277 ± 1377 ± 1280 ± 876 ± 072 ± 4
Nonresponders (n = 3)
 ISO51 ± 3158 ± 1663 ± 2362 ± 2554 ± 2352 ± 14
 HYPER50 ± 2059 ± 1662 ± 1162 ± 1563 ± 2250 ± 15
  • Values are means ± SD and presented as a percentage of total lower-body negative pressure (LBNP) time for three subgroups: 1) all subjects from whom appropriate muscle sympathetic nerve activity (MSNA) signals were obtained (n = 6); 2) subjects in whom LBNP tolerance improved during hyperosmotic (HYPER) (responders, n = 3), and; 3) subjects in whom LBNP tolerance did not improve during HYPER (nonresponders, n = 3). Pre-LBNP: values immediately before the LBNP protocol. ISO, iso-osmotic.