Table 1. Cardiovascular and Cerebrovascular Responses to Different Exercises Performed in −15° HDT Position.
| Response | Estimated Marginal Means | Exercise Conditions | |||||
|---|---|---|---|---|---|---|---|
| Mean (SD) | Change With Exercise (95% CI)a | Mean (SD) | P Valueb | ||||
| −15° HDT | −15° HDT With Exercise | Moderate | Resistance | High | |||
| Cardiovascular responses | |||||||
| Heart rate, /min | 59 (9) | 107 (21) | 48 (45 to 52)c | 98 (15) | 100 (18) | 123 (18)d,e | <.001 |
| Stroke volume, mL | 91 (15) | 101 (22) | 10 (6 to 13)c | 96 (22) | 101 (21) | 106 (22) | .47 |
| Cardiac output, L/min | 5.4 (1.0) | 10.8 (3.0) | 5.4 (4.8 to 6.0)c | 9.4 (2.3) | 10.0 (2.2) | 13.0 (3.1)d,e | .003 |
| V̇o2, L/min | 0.3 (0.1) | 1.7 (0.5) | 1.4 (1.3 to 1.6)c | 1.7 (0.4) | 1.4 (0.5) | 2.2 (0.4)d,e | .003 |
| V̇o2, mL/kg/min | 3.7 (0.9) | 21.9 (6.4) | 18.2 (16.1 to 20.3)c | 21.2 (5.3) | 17.2 (5.4) | 27.2 (4.6)d,e | .001 |
| V̇e, L/min | 11.2 (3.0) | 59.1 (19.4) | 47.9 (41.9 to 53.8)c | 54.3 (16.4) | 45.0 (11.3) | 78.0 (14.7)d,e | <.001 |
| MAP, mm Hg | 95 (8) | 119 (12) | 24 (22 to 27)c | 117 (8) | 112 (9) | 128 (11)d,e | .002 |
| SBP, mm Hg | 127 (12) | 188 (29) | 61 (55 to 67)c | 188 (22) | 167 (20) | 208 (29)e | .001 |
| DBP, mm Hg | 78 (7) | 84 (8) | 6 (4 to 8)c | 82 (7) | 84 (7) | 88 (8)d | .04 |
| Cerebrovascular responses | |||||||
| Intraocular pressure, mm Hg | 21.6 (4.1) | 20.0 (3.9) | −1.6 (−2.6 to −0.6)f | 20.0 (4.5) | 19.2 (3.7) | 20.9 (3.3) | .51 |
| Venous pressure, mm Hg | |||||||
| Internal jugular pressure, mm Hg | 31.8 (6.9) | 33.9 (10.5) | 2.1 (−0.4 to 4.4) | 33.7 (8.6) | 33.1 (8.8) | 34.7 (13.9) | .98 |
| External jugular pressure, mm Hg | 17.6 (5.7) | 18.0 (7.2) | 0.4 (−1.5 to 2.2) | 16.8 (4.6) | 19.5 (8.7) | 17.5 (7.5) | .50 |
| Estimated translaminar pressure gradient, mm Hg | −10.6 (8.4) | −14.1 (11.3) | −3.5 (−6.2 to −0.7)f | −14.0 (9.7) | −14.5 (9.9) | −13.9 (14.2) | .87 |
| Estimated cerebral transmural pressure, mm Hg | 62.8 (8.1) | 85.6 (14.8) | 22.8 (19.7 to 25.9)c | 85.3 (11.4) | 78.4 (11.0) | 93.1 (18.0)e | .04 |
| OPP, mm Hg | 73.6 (10.3) | 99.5 (11.6) | 25.9 (23.2 to 28.7)c | 98.2 (10.0) | 93.2 (9.2) | 107.0 (11.6) | .09 |
| Global CBF, mL/min | 1247 (236) | 1337 (325) | 90 (2 to 179)f | 1396 (287) | 1250 (365) | 1364 (325) | .54 |
| Total head blood flow, mL/min | 1844 (284) | 2350 (521) | 506 (360 to 651)c | 2456 (580) | 2134 (422) | 2462 (503) | .40 |
| CO to head, % | 35.0 (7.1) | 22.0 (7.3) | −13.0 (−15.4 to −10.3)c | 26.2 (8.6) | 21.3 (5.5) | 18.6 (5.1) | .45 |
Abbreviations: CBF, cerebral blood flow; CO, cardiac output; DBP, diastolic blood pressure; EMM, estimated marginal means; HDT, head-down tilt; MAP, mean arterial pressure; OPP, ocular perfusion pressure; SBP, systolic blood pressure; V̇e, expired volume per unit time; V̇o2, oxygen consumption.
Change with exercise was calculated as EMM for −15° HDT with exercise minus EMM for −15° HDT during rest.
P values reflect between-condition main effects.
P < .001 for −15° HDT with exercise vs −15° HDT during rest.
P < .05 for high-intensity aerobic exercise vs moderate-intensity aerobic exercise.
P < .05 for high-intensity aerobic exercise vs resistance exercise. All statistical tests are Bonferroni adjusted.
P < .05 for −15° HDT with exercise vs −15° HDT during rest.