AUTHOR=Stucky Frédéric , Vesin Jean-Marc , Kayser Bengt , Uva Barbara 

TITLE=The Effect of Lower-Body Positive Pressure on the Cardiorespiratory Response at Rest and during Submaximal Running Exercise

JOURNAL=Frontiers in Physiology

VOLUME=9

YEAR=2018

URL=https://www.frontiersin.org/journals/physiology/articles/10.3389/fphys.2018.00034

DOI=10.3389/fphys.2018.00034

ISSN=1664-042X

ABSTRACT=<p>Anti-gravity treadmills facilitate locomotion by lower-body positive pressure (LBPP). Effects on cardiorespiratory regulation are unknown. Healthy men (30 ± 8 y, 178.3 ± 5.7 cm, 70.3 ± 8.0 kg; mean ± SD) stood upright (<italic>n</italic> = 10) or ran (<italic>n</italic> = 9) at 9, 11, 13, and 15 km.h<sup>−1</sup> (5 min stages) with LBPP (0, 15, 40 mmHg). Cardiac output (CO), stroke volume (SV), heart rate (HR), blood pressure (BP), peripheral resistance (PR), and oxygen uptake (VO<sub>2</sub>) were monitored continuously. During standing, LBPP increased SV [by +29 ± 13 (+41%) and +42 ± 15 (+60%) ml, at 15 and 40 mmHg, respectively (<italic>p</italic> &lt; 0.05)] and decreased HR [by −15 ± 6 (−20%) and −22 ± 9 (−29%) bpm (<italic>p</italic> &lt; 0.05)] resulting in a transitory increase in CO [by +1.6 ± 1.0 (+32%) and +2.0 ± 1.0 (+39%) l.min<sup>−1</sup> (<italic>p</italic> &lt; 0.05)] within the first seconds of LBPP. This was accompanied by a transitory decrease in end-tidal PO<sub>2</sub> [by −5 ± 3 (−5%) and −10 ± 4 (−10%) mmHg (<italic>p</italic> &lt; 0.05)] and increase in VO<sub>2</sub> [by +66 ± 53 (+26%) and +116 ± 64 (+46%) ml.min<sup>−1</sup> (<italic>p</italic> &lt; 0.05)], suggesting increased venous return and pulmonary blood flow. The application of LBPP increased baroreflex sensitivity (BRS) [by +1.8 ± 1.6 (+18%) and +4.6 ± 3.7 (+47%) at 15 and 40 mmHg LBPP, respectively <italic>P</italic> &lt; 0.05]. After reaching steady-state exercise CO vs. VO<sub>2</sub> relationships remained linear with similar slope and intercept for each participant (mean <italic>R</italic><sup>2</sup> = 0.84 ± 0.13) while MAP remained unchanged. It follows that (1) LBPP affects cardiorespiratory integration at the onset of exercise; (2) at a given LBPP, once reaching steady-state exercise, the cardiorespiratory load is reduced proportionally to the lower metabolic demand resulting from the body weight support; (3) the balance between cardiovascular response, oxygen delivery to the exercising muscles and blood pressure regulation is maintained at exercise steady-state; and (4) changes in baroreflex sensitivity may be involved in the regulation of cardiovascular parameters during LBPP.</p>