Abstract
IntroductionBaroreflex sensitivity (BRS) is essential to ensure rapid adjustment to variations in blood pressure (BP). Spontaneous baroreflex function can be assessed using continuous recordings of blood pressure. The goal of this study was to compare four methods for BRS quantification [the sequence, Bernardi’s (BER), frequency and transfer function methods] to identify the most consistent method across an extreme range of conditions: rest and exercise, in normoxia, hypoxia, hypocapnia, and hypercapnia.MethodsUsing intra-radial artery BP in young healthy participants, BRS was calculated and compared using the four methods in normoxia, acute and chronic hypoxia (terrestrial altitude of 5,260 m) in hypocapnia (hyperventilation), hypercapnia (rebreathing) and during ramp exercise to exhaustion.ResultsThe sequence and BER methods for BRS estimation showed good agreement during the resting and exercise protocols, whilst the ultra- and very-low frequency bands of the frequency and transfer function methods were more discrepant. Removing respiratory frequency from the blood pressure traces affected primarily the sequence and BER methods and occasionally the frequency and transfer function methods.Discussion/ConclusionThe sequence and BER methods contained more respiratory related information than the frequency and transfer function methods, indicating that the former two methods predominantly rely on respiratory effects of BRS. BER method is recommended because it is the easiest to compute and even though it tends to overestimate BRS compared to the sequence method, it is consistent with the other methods, whilst its interquartile range is the smallest.
Highlights
Baroreflex sensitivity (BRS) is essential to ensure rapid adjustment to variations in blood pressure (BP)
Resting heart rate increased in hypoxic conditions (77 ± 17; 90 ± 12, p < 0.05; 97 ± 15, p < 0.05, bpm SL, ALT1, and ALT16, respectively, all p-values vs. SL) whilst heart rate at maximal exercise decreased (185 ± 14; 170 ± 12, p < 0.05; 166 ± 13, p < 0.05, bpm, SL, ALT1, and ALT16, respectively, all p-values vs. SL)
Mean resting Blood pressure (BP) was unchanged in hypoxic conditions (95 ± 11; 94 ± 9; 92 ± 9 mmHg, SL, ALT1, and ALT16, respectively), whilst it decreased at maximal exercise (121 ± 8; ± 10, p < 0.05; ± 11, p < 0.05, mmHg, SL, ALT1, and ALT16, respectively, all p-values vs. SL)
Summary
Baroreflex sensitivity (BRS) is essential to ensure rapid adjustment to variations in blood pressure (BP). Spontaneous baroreflex function can be assessed using continuous recordings of blood pressure. The goal of this study was to compare four methods for BRS quantification [the sequence, Bernardi’s (BER), frequency and transfer function methods] to identify the most consistent method across an extreme range of conditions: rest and exercise, in normoxia, hypoxia, hypocapnia, and hypercapnia. Altitude induces hypoxemia, leading to vasodilation and BP reduction (Bourdillon et al, 2018). During dynamic exercise (walking, running, cycling), cardiac output increases and systemic vascular resistances change (vasodilation in working muscle, vasoconstriction of renal and gastro-intestinal vascular beds) leading to an increased BP, which triggers the baroreflex (Michelini et al, 2015). Mean BP only increases moderately, because there is a resetting of the baroreflex to increased arterial BP as a function of exercise intensity (Bevegård and Shepherd, 1966; Eckberg et al, 1975; Pawelczyk and Raven, 1989; Joyner, 2006) from rest to 75% of maximum oxygen consumption (Potts et al, 1993; Papelier et al, 1994)
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