Background: This study quantifies hemodynamic and thoracic impedance (TI) changes with four levels of lower body negative pressure (LBNP) from - 15 to -65 mm Hg in seven healthy men in supine position 20 min before (pre- LBNP), 30 min during, and 20 min after suction (post-LBNP) as well as without suction (LBNP-0, rest control). Results: LBNP >15 mm Hg increased basic TI by up to 2.2 Ω (+9.5%). TI-computed stroke volume index (SVI) continuously decreased with time up to -12%, -28%, -36%, and -40% at the end of LBNP-15, - 35, -55, and -65. TI-computed cardiac index decreased most (-14%) at LBNP-15 and -35, resulting in a 19% increase of calculated total peripheral resistance index at those intensities. Mean arterial pressure (MAP) did not change in any systematic way with lower LBNP levels, but increased +4.7% and +7.4% at the end of LBNP-55 and -65, respectively. Heart rate remained unchanged at LBNP-15, but continuously increased to reach +22%, +42%, and +55% at the end of LBNP-35, -55, and -65. After finishing LBNP, heart rate fell to values below both pre-LBNP and rest control for ≤ 5 min (post-LBNP bradycardia). SVI transiently returned to, and MAP increased above, pre-LBNP levels after suction. Conclusion: In conclusion, different levels of lower body subatmospheric pressure produced quantitatively different time course and dose-response patterns and remained non-hypotensive up to -65 mm Hg suction. Further, heart rate was depressed after LBNP, while arterial BP and TI-computed total peripheral resistance exceeded pre-stimulus levels, indicating an altered cardiovascular state after 30 min of simulated orthostasis.
|Number of pages||8|
|Journal||Aviation Space and Environmental Medicine|
|Publication status||Published - jan. 1 1998|
ASJC Scopus subject areas
- Public Health, Environmental and Occupational Health