15 research outputs found

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

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    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

    The menthol receptor TRPM8 is the principal detector of environmental cold

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    Sensory nerve fibres can detect changes in temperature over a remarkably wide range, a process that has been proposed to involve direct activation of thermosensitive excitatory transient receptor potential (TRP) ion channels. One such channel--TRP melastatin 8 (TRPM8) or cold and menthol receptor 1 (CMR1)--is activated by chemical cooling agents (such as menthol) or when ambient temperatures drop below approximately 26 degrees C, suggesting that it mediates the detection of cold thermal stimuli by primary afferent sensory neurons. However, some studies have questioned the contribution of TRPM8 to cold detection or proposed that other excitatory or inhibitory channels are more critical to this sensory modality in vivo. Here we show that cultured sensory neurons and intact sensory nerve fibres from TRPM8-deficient mice exhibit profoundly diminished responses to cold. These animals also show clear behavioural deficits in their ability to discriminate between cold and warm surfaces, or to respond to evaporative cooling. At the same time, TRPM8 mutant mice are not completely insensitive to cold as they avoid contact with surfaces below 10 degrees C, albeit with reduced efficiency. Thus, our findings demonstrate an essential and predominant role for TRPM8 in thermosensation over a wide range of cold temperatures, validating the hypothesis that TRP channels are the principal sensors of thermal stimuli in the peripheral nervous system
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