Alterations of Cardiovascular Complexity during Acute Exposure to High Altitude: A Multiscale Entropy Approach

Abstract

Stays at high altitude induce alterations in cardiovascular control and are a model of specific pathological cardiovascular derangements at sea level. However, high-altitude alterations of the complex cardiovascular dynamics remain an almost unexplored issue. Therefore, our aim is to describe the altered cardiovascular complexity at high altitude with a multiscale entropy (MSE) approach. We recorded the beat-by-beat series of systolic and diastolic blood pressure and heart rate in 20 participants for 15 min twice, at sea level and after arrival at 4554 m a.s.l. We estimated Sample Entropy and MSE at scales of up to 64 beats, deriving average MSE values over the scales corresponding to the high-frequency (MSEHF) and low-frequency (MSELF) bands of heart-rate variability. We found a significant loss of complexity at heart-rate and blood-pressure scales complementary to each other, with the decrease with high altitude being concentrated at Sample Entropy and at MSEHF for heart rate and at MSELF for blood pressure. These changes can be ascribed to the acutely increased chemoreflex sensitivity in hypoxia that causes sympathetic activation and hyperventilation. Considering high altitude as a model of pathological states like heart failure, our results suggest new ways for monitoring treatments and rehabilitation protocols.

Associations between Cardiovascular Signal Entropy and Cognitive Performance over Eight Years

“…This was evident in the results from the BtB analyses reported herein, which provided mean SampEn values more than double those from the interpolated approach, as shown in Table 1. This is in line with previous cardiovascular entropy studies, which have reported mean SampEn values calculated in BtB data of >1.2; compared with mean sBP SampEn ~1.67 in the present study [23,49,50]. Despite this limitation, SampEn values calculated from both one and five minutes of 5 Hz interpolated data were significantly associated with cognitive performance, whereas SampEn values calculated from the BtB data were not.…”

Longitudinal Changes and Recovery in Heart Rate Variability of Young Healthy Subjects When Exposure to a Hypobaric Hypoxic Environment

“…This conclusion is supported by several studies ( Hughson et al, 1994 ; Perini et al, 1996 ; Saito et al, 2005 ) in which the balance of the ANS shifts toward relatively low parasympathetic and high sympathetic activity at high altitudes. Coherently with our result, a decrease of the heart-rate SampEn was observed during a real high-altitude environment ( Saito et al, 2005 ; Boos et al, 2018 ; Faini et al, 2019 ) and in a simulated high altitude ( Zhang et al, 2015 ). However, Vigo et al (2010) reported the opposite trend in a low-pressure chamber experiment simulating an altitude of 8,230 m asl, reflecting a rapid activation of defensive autonomic responses induced by the subjects’ sudden exposure to an extreme abnormal environment.…”

“…These spectral changes are in line with those repeatedly reported on the acute autonomic effects after an ascent at high altitude (Hughson et al, 1994;Perini et al, 1996;Saito et al, 2005;Chen et al, 2008;Faini et al, 2019) or a simulated altitude of 3,600 m asl in a hypobaric/hypoxic chamber. Similarly, Boos et al (2018) found an increase in LF power but without a change in HF power at relatively lower altitudes (3,000 m asl).…”

“…Particularly, linear parameters of HRV (both time and frequency domain metrics) have been widely used for hypoxia because the results of linear metrics are easy to interpret in physiological terms. Most studies have shown that LF and HF power decreases at high altitudes ( Hughson et al, 1994 ; Perini et al, 1996 ; Kanai et al, 2001 ; Sevre et al, 2001 ; Roche et al, 2002 ; Cornolo et al, 2004 ; Saito et al, 2005 ; Chen et al, 2008 ; Faini et al, 2019 ). However, it was also found that a decrease in HF power is accompanied by an increase in LF power ( Hughson et al, 1994 ), or no change in HF power but an increase in LF power ( Iwasaki et al, 2006 ; Boos et al, 2018 ).…”

Assessing Complexity in Physiological Systems through Biomedical Signals Analysis

“…Their results suggest that this entropy measure may distinguish diabetic patients with a satisfactory control of blood glucose from those with poor control, highlighting the feasibility of assessing autonomic dysfunctions of clinical relevance by the percussion entropy. Also Faini et al [ 10 ] considered a second cardiovascular signal in addition to the electrocardiogram: the finger arterial pressure. These authors calculated the multiscale sample entropy of the heart rate series and of the series of systolic and diastolic arterial pressure in volunteers at sea level and at high altitude and explained the alterations observed at high altitude by the increased chemoreflex sensitivity induced by hypoxia.…”