Abstract
Baroreflex (BR) control is critically dependent of sympathetic and parasympathetic modulation. It has been documented that during acute hypobaric hypoxia there is a BR control impairment, however, the effect of a natural hypoxic environment on BR function is limited and controversial. Therefore, the aim of this study was to determine the effect of acute High-Altitude exposure on sympathetic/parasympathetic modulation of BR control in normal rats. Male Sprague Dawley rats were randomly allocated into Sea-Level (n = 7) and High-Altitude (n = 5) (3,270 m above sea level) groups. The BR control was studied using phenylephrine (Phe) and sodium nitroprusside (SNP) through sigmoidal analysis. The autonomic control of the heart was estimated using heart rate variability (HRV) analysis in frequency domain. Additionally, to determine the maximum sympathetic and parasympathetic activation of BR, spectral non-stationary method analysis, during Phe (0.05 μg/mL) and SNP administration (0.10 μg/mL) were used. Compared to Sea-Level condition, the High-Altitude group displayed parasympathetic withdrawal (high frequency, 0.6–2.4 Hz) and sympathoexcitation (low frequency, 0.04–0.6 Hz). Regarding to BR modulation, rats showed a significant decrease (p < 0.05) of curvature and parasympathetic bradycardic responses to Phe, without significant differences in sympathetic tachycardic responses to SNP after High-Altitude exposure. In addition, the non-stationary analysis of HRV showed a reduction of parasympathetic activation (Phe) in the High-Altitude group. Our results suggest that acute exposure to High-Altitude produces an autonomic and BR control impairment, characterized by parasympathetic withdrawal after 24 h of high-altitude exposure.
Highlights
The cardiac baroreflex (BR) function governs short-term fluctuations of blood pressure and, plays an important role in the regulation of several homeostatic functions (Stauss, 2002)
There were no significant differences between Sea-Level and High-Altitude exposure on body weight diastolic blood pressure (DBP), systolic blood pressure (SBP), MABP, PP, and heart rate (HR) (Table 1)
The autonomic control of the heart was estimated by heart rate variability (HRV) disturbances (Figure 1)
Summary
The cardiac baroreflex (BR) function governs short-term fluctuations of blood pressure and, plays an important role in the regulation of several homeostatic functions (Stauss, 2002). High-Altitude is amongst the most inhospitable environments on earth and it has been demonstrated that exposure to hypobaric hypoxia is strongly related to impairment of autonomic control (Lanfranchi et al, 2005; Hainsworth et al, 2007). It has been observed that BR control is compromised during hypobaric hypoxia, the evidence is limited and controversial; the major differences related to autonomic modulation could be related to the atmospheric pressure (Sagawa et al, 1997; Hainsworth et al, 2007). Human studies, using the neck chamber method, showed that hypobaric hypoxia had no effect on the BR set point, but reduce the BR gain (Sagawa et al, 1997). Considering that there are few evidences underpinning the acute effect of
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
