Key result
Healthy adults with a high heart rate response to head-up tilt exhibited lower systolic pressure (120 vs 131 mmHg) and larger increases in plasma norepinephrine compared to low responders.
Why the study?
Does head-up tilt elicit different cardiovascular and neurohumoral responses in healthy subjects with high versus low heart rate responses?
Cross-Sectional (n=76)
No
Does head-up tilt elicit different cardiovascular and neurohumoral responses in healthy subjects with high versus low heart rate responses?
Absolute Event Rate: 120% vs 131%
p-value: p=<0.05
Healthy individuals with exaggerated heart rate responses to orthostatic stress exhibit greater blood pressure variability and norepinephrine release, sharing pathophysiological similarities with postural tachycardia syndrome (POTS).
May reflect distinct autonomic phenotypes; hypothesis-generating for POTS mechanisms, requires prospective validation before clinical relevance.
Orthostatic stress such as head-up tilt (HUT) elicits a wide range of heart rate (HR) and arterial pressure (AP) responses among healthy individuals. In this study, we evaluated cardiovascular dynamics in healthy subjects with different HR responses to HUT, but without autonomic dysfunction. We measured AP (brachial artery) and HR (ECG) during 5 min of 60 degrees HUT in 76 healthy normotensive individuals. We then chose individuals on the basis of the extremes of HR responses to HUT (high = DeltaHR > or = 20 beats/min, and low = DeltaHR < or = 10 beats/min; n = 15 per group). Peak HR during HUT was 87 +/- 10 beats/min in the high and 69 +/- 14 beats/min in the low group (P < 0.05). High HR responders had lower systolic pressure at baseline (121 +/- 9 vs. 129 +/- 11 mmHg, P < 0.05) and during HUT (120 +/- 10 vs. 131 +/- 13 mmHg, P < 0.05), and higher plasma norepinephrine (NE) response to HUT (DeltaNE: 156.9 +/- 17.8 vs. 89.0 +/- 17.2 pg/ml; P < 0.05). DeltaNE during HUT was also significantly correlated with DeltaHR when all 76 subjects were included in a regression analysis (r = 0.39; P < 0.001). Pulse pressure was lower during HUT in high HR responders compared with low HR responders (45 +/- 1 vs. 55 +/- 2 mmHg, P < 0.05). High HR responders also had larger fluctuations in systolic and pulse pressure during HUT (coefficient of variation = 10.7 +/- 0.7 vs. 5.7 +/- 0.3%; 7.9 +/- 0.5 vs. 4.1 +/- 0.4%, respectively, P < 0.05). Sex distribution was different between groups (high: 5 women, 10 men; low: 10 women, 5 men). Higher HR with lower AP during HUT is consistent with normal baroreflex mechanisms of integration. Although interindividual variability appears to be a fundamental part of cardiovascular regulation, the mechanisms of these differences and the sex discrepancy requires further investigation.
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Ramírez-Marrero et al. (2008) conducted a cross-sectional in Healthy subjects (n=76). High heart rate response to head-up tilt (ΔHR ≥ 20 beats/min) vs. Low heart rate response to head-up tilt (ΔHR ≤ 10 beats/min) was evaluated on Systolic pressure during head-up tilt (p=<0.05). Healthy adults with a high heart rate response to head-up tilt exhibited lower systolic pressure (120 vs 131 mmHg) and larger increases in plasma norepinephrine compared to low responders.
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