Table 4.
Haemodynamic and neural responses to 30 mmHg lower body negative pressure (LBNP 30) performed under normothermic and heat stress conditions
| Normothermia | Heat stress | |||||||
|---|---|---|---|---|---|---|---|---|
| Young (n = 11) | Aged (n = 6) | Young (n = 8) | Aged (n = 5) | |||||
| Baseline | LBNP 30 | Baseline | LBNP 30 | Baseline | LBNP 30 | Baseline | LBNP 30 | |
| Heart rate (beats min−1) | 59 ± 5 | 70 ± 4* | 61 ± 8 | 67 ± 9* | 103 ± 13 | 122 ± 12# | 85 ± 14 | 95 ± 20# |
| MAP (mmHg) | 86 ± 6 | 87 ± 5 | 94 ± 7 | 98 ± 6† | 83 ± 10 | 79 ± 12 | 89 ± 12 | 73 ± 16# |
| Burst frequency (bursts min−1) | 15 ± 4 | 30 ± 6* | 29 ± 4† | 46 ± 6*,† | 49 ± 8 | 66 ± 9# | 53 ± 9 | 62 ± 12# |
| Burst incidence (bursts (100 CC)−1) | 26 ± 8 | 44 ± 8* | 49 ± 9† | 72 ± 17*,† | 51 ± 11 | 57 ± 10 | 60 ± 10 | 66 ± 12 |
| ΔTotal activity (units min−1) | 0 ± 0 | 359 ± 105* | 0 ± 0 | 501 ± 412* | 0 ± 0 | 334 ± 326 | 0 ± 0 | 287 ± 483 |
| Plasma [A] (pg ml−1) | 27 ± 16 | 19 ± 6 | 39 ± 41 | 29 ± 20 | 48 ± 12 | 235 ± 198 | 39 ± 28 | 87 ± 37 |
| Plasma [NA] (pg ml−1) | 145 ± 22 | 278 ± 47* | 268 ± 64† | 402 ± 85*,† | 307 ± 121 | 476 ± 161 | 339 ± 114 | 619 ± 271 |
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.