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

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 ( javax.xml.bind.JAXBElement@57c008e9 = 10) or ran ( javax.xml.bind.JAXBElement@7a503138 = 9) at 9, 11, 13, and 15 km.h javax.xml.bind.JAXBElement@189f9fd6 (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 javax.xml.bind.JAXBElement@270f0b82 ) were monitored continuously. During standing, LBPP increased SV [by +29 ± 13 (+41%) and +42 ± 15 (+60%) ml, at 15 and 40 mmHg, respectively ( javax.xml.bind.JAXBElement@705fd8ca < 0.05)] and decreased HR [by -15 ± 6 (-20%) and -22 ± 9 (-29%) bpm ( javax.xml.bind.JAXBElement@bfdfe08 < 0.05)] resulting in a transitory increase in CO [by +1.6 ± 1.0 (+32%) and +2.0 ± 1.0 (+39%) l.min javax.xml.bind.JAXBElement@6ff8b18e ( javax.xml.bind.JAXBElement@3074f4e8 < 0.05)] within the first seconds of LBPP. This was accompanied by a transitory decrease in end-tidal PO javax.xml.bind.JAXBElement@3e63f3a4 [by -5 ± 3 (-5%) and -10 ± 4 (-10%) mmHg ( javax.xml.bind.JAXBElement@5a8a47de < 0.05)] and increase in VO javax.xml.bind.JAXBElement@7054e9c0 [by +66 ± 53 (+26%) and +116 ± 64 (+46%) ml.min javax.xml.bind.JAXBElement@67908096 ( javax.xml.bind.JAXBElement@464fa113 < 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 javax.xml.bind.JAXBElement@4e73aab3 < 0.05]. After reaching steady-state exercise CO vs. VO javax.xml.bind.JAXBElement@19be4054 relationships remained linear with similar slope and intercept for each participant (mean javax.xml.bind.JAXBElement@7ac9e7c5 javax.xml.bind.JAXBElement@41b586b6 = 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