Table 3.
Haemodynamic and neural responses to 15 mmHg lower body negative pressure (LBNP 15) performed under normothermic and heat stress conditions
| Normothermia | Heat stress | |||||||
|---|---|---|---|---|---|---|---|---|
| Young (n = 11) | Aged (n = 9) | Young (n = 10) | Aged (n = 9) | |||||
| Baseline | LBNP 15 | Baseline | LBNP 15 | Baseline | LBNP 15 | Baseline | LBNP 15 | |
| Heart rate (beats min−1) | 59 ± 5 | 60 ± 5 | 62 ± 5 | 63 ± 7 | 99 ± 13 | 108 ± 10# | 88 ± 8 | 93 ± 10 |
| MAP (mmHg) | 86 ± 6 | 87 ± 5 | 96 ± 5† | 101 ± 6*,† | 82 ± 9 | 85 ± 10 | 90 ± 6 | 83 ± 10 |
| Burst frequency (bursts min−1) | 15 ± 4 | 25 ± 5* | 31 ± 4† | 40 ± 7*,† | 48 ± 6 | 57 ± 7# | 59 ± 5 | 67 ± 8# |
| Burst incidence (bursts (100 CC)−1) | 26 ± 8 | 43 ± 10* | 52 ± 7† | 65 ± 12*,† | 49 ± 9 | 55 ± 7 | 65 ± 9† | 72 ± 9† |
| ΔTotal activity (units min−1) | 0 ± 0 | 247 ± 86* | 0 ± 0 | 246 ± 103* | 0 ± 0 | 236 ± 144 | 0 ± 0 | 227 ± 384 |
| Plasma [A] (pg ml−1) | 27 ± 16 | 16 ± 4 | 30 ± 26 | 27 ± 20 | 52 ± 13 | 75 ± 16# | 42 ± 21 | 67 ± 30# |
| Plasma [NA] (pg ml−1) | 145 ± 22 | 210 ± 37* | 282 ± 48† | 365 ± 53*,† | 317 ± 97 | 426 ± 88# | 401 ± 82 | 531 ± 106# |
Values are means ± 95% confidence intervals. MAP, mean arterial pressure; [A], adrenaline concentration; [NA], noradrenaline concentration.
*
Significantly different from normothermic baseline.
†
Significantly different from young for the indicated time point (P ≤ 0.05).
#
Significantly different from heat stress baseline for the indicated group. Note: the different baseline values in Tables4 are due to differences in the number of subjects from whom data were obtained throughout the applied perturbation.