Experimental physiology
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Experimental physiology · May 2016
Maximal expiratory pressure and Valsalva manoeuvre do not produce similar cardiovascular responses in healthy men.
What is the central question of this study? This is the first study to evaluate and describe the cardiovascular responses during maximal expiratory pressure compared with the Valsalva manoeuvre, and whether those responses are similar. What is the main finding and its importance? This study showed that the duration of the manoeuvres appears to be responsible for the different physiological mechanisms involved in the cardiovascular responses to each manoeuvre and that the intensity of expiratory effort was related to the response in maximal expiratory pressure. These results are important to identify the risks to which subjects are exposed when performing these manoeuvres. ⋯ The execution time of the manoeuvres (VM ∼15 s and MEP ∼5 s) appears to be largely responsible for the activation of different physiological mechanisms involved in the cardiovascular control for each manoeuvre, and the intensity of expiratory effort is related to the higher response of MAP and peripheral vascular resistance (PVRIsotime and ΔPVRIsotime ) during MEP (P < 0.05). Moreover, it appears that age affects only the heart rate and PVR responses (P < 0.05), which were higher in the young and middle-aged group, respectively. Based on these findings, we can conclude that MEP and the VM do not generate similar cardiovascular responses, except for cardiac output.
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Experimental physiology · May 2016
Haemoglobin mass alterations in healthy humans following four-day head-down tilt bed rest.
What is the central question of this study? Is haemoglobin mass (Hbmass) decreased following 4 days of head-down tilt bed rest (HDTBR), and does increased red blood cell (RBC) destruction mediate this adaptation? What is the main finding and its importance? Haemoglobin mass was increased immediately following HDTBR, before decreasing below baseline 5 days after return to normal living conditions. The transient increase in Hbmass might be the result of decreased RBC destruction, but it is also possible that spleen contraction after HDTBR contributed to this adaptation. Our data suggest that the decreased Hbmass 5 days following HDTBR resulted from decreased RBC production, not increased RBC destruction. ⋯ From PRE to POST5, the concentration of soluble transferrin receptor decreased from 20.7 ± 3.9 to 17.1 ± 3.3 nmol l(-1) (P = 0.018) but the concentrations of ferritin, haptoglobin and bilirubin were not significantly altered, suggesting that the decrease in Hbmass was mediated by decreased RBC production rather than increased RBC destruction. Peak oxygen uptake decreased by 0.31 ± 0.16 l min(-1) from PRE to POST (P = 2 × 10(-4) ) but was not significantly altered at POST5 compared with PRE. Overall, these findings indicate that 4 days of HDTBR does not increase RBC destruction and that re-examination of the time course and mechanisms of Hbmass alterations following short-term spaceflight and simulated microgravity is warranted.