High-altitude hypoxemia increased MSNA burst frequency by a greater extent (MD +22.5 bursts/min; 95% CI -19.20 to 25.84; P<0.001) compared with acute poikilocapnic and isocapnic hypoxemia.
Meta-Analysis
Does hypoxemia type and severity affect muscle sympathetic nerve activity and cardiovascular function in healthy individuals?
Different types and severities of hypoxemia elicit distinct sympathetic and cardiovascular responses in healthy humans, with high-altitude hypoxemia causing the greatest increase in MSNA burst frequency.
Effect estimate: MD +22.5 bursts/min (95% CI -19.20 to 25.84)
p-value: p=< 0.001
We conducted a systematic review and meta-analysis to determine the effect of acute poikilocapnic, high-altitude, and acute isocapnia hypoxemia on muscle sympathetic nerve activity (MSNA) and cardiovascular function. A comprehensive search across electronic databases was performed until June 2021. All observational designs were included: population (healthy individuals); exposures (MSNA during hypoxemia); comparators (hypoxemia severity and duration); outcomes (MSNA; heart rate, HR; and mean arterial pressure, MAP). Sixty-one studies were included in the meta-analysis. MSNA burst frequency increased by a greater extent during high-altitude hypoxemia P < 0.001; mean difference (MD), +22.5 bursts/min; confidence interval (CI) = −19.20 to 25.84 compared with acute poikilocapnic hypoxemia ( P < 0.001; MD, +5.63 bursts/min; CI = −4.09 to 7.17) and isocapnic hypoxemia ( P < 0.001; MD, +4.72 bursts/min; CI = −3.37 to 6.07). MSNA burst amplitude was only elevated during acute isocapnic hypoxemia ( P = 0.03; standard MD, +0.46 au; CI = −0.03 to 0.90), and MSNA burst incidence was only elevated during high-altitude hypoxemia P < 0.001; MD, 33.05 bursts/100 heartbeats; CI = −28.59 to 37.51. Meta-regression analysis indicated a strong relationship between MSNA burst frequency and hypoxemia severity for acute isocapnic studies ( P < 0.001) but not acute poikilocapnia ( P = 0.098). HR increased by the same extent across each type of hypoxemia P < 0.001; MD +13.81 heartbeats/min; 95% CI = 12.59–15.03. MAP increased during high-altitude hypoxemia ( P < 0.001; MD, +5.06 mmHg; CI = 3.14–6.99), and acute isocapnic hypoxemia ( P < 0.001; MD, +1.91 mmHg; CI = 0.84–2.97), but not during acute poikilocapnic hypoxemia ( P = 0.95). Both hypoxemia type and severity influenced sympathetic nerve and cardiovascular function. These data are important for the better understanding of healthy human adaptation to hypoxemia.
Tymko et al. (Tue,) conducted a meta-analysis in Healthy individuals exposed to hypoxemia. Hypoxemia (acute poikilocapnic, high-altitude, and acute isocapnic) vs. Different types and severities of hypoxemia was evaluated on Muscle sympathetic nerve activity (MSNA) burst frequency (MD +22.5 bursts/min, 95% CI -19.20 to 25.84, p=< 0.001). High-altitude hypoxemia increased MSNA burst frequency by a greater extent (MD +22.5 bursts/min; 95% CI -19.20 to 25.84; P<0.001) compared with acute poikilocapnic and isocapnic hypoxemia.
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