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Discordance between direct (microneurographic) and indirect (heart rate variability) estimates of sympathetic activity in patients with pulmonary artery hypertension
Author(s) -
McGowan Cheri L,
Swiston John,
Granton John T,
Mak Susanna,
Morris Beverley L,
Notarius Cathy F,
Picton Peter E,
Floras John S
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.21.6.a888-b
Low frequency spectral power (P L ) may estimate the independent contributions of the sympathetic nervous system to heart rate variability in healthy subjects, but patients with heart failure (HF) due to systolic dysfunction (a state of generalized sympathetic activation) exhibit an inverse rather than direct relationship between muscle sympathetic nerve activity (MSNA) and P L . Patients with pulmonary artery hypertension (PAH) have normal left ventricular (LV) systolic function and low total power (P T ) due to right atrial tension secondary to high pulmonary vascular resistance. We therefore tested the hypothesis that P L relates inversely to MSNA in PAH. Heart rate (HR) and MSNA were recorded during 10 min of supine rest in 8 PAH patients (age: 45.6 ± 4.4 yrs, pulmonary capillary wedge pressure: 11 ± 2 mmHg, pulmonary artery mean pressure: 54 ± 4 mmHg, right atrial pressure: 7 ± 1 mmHg; mean ± SE). Coarse‐graining spectral analysis was used to determine P L and P T . HR was 87.3 ± 8.4 beats/min and MSNA was 47.9 ± 9.1 bursts/min (mean ± SE). MSNA related inversely to both P L (r = −0.73), and P T (r = −0.72) (p = 0.04). Thus, in PAH patients with normal LV pressures, P T relates inversely to MSNA, i.e., it is the absence of P L that indicates sympathetic activation. As with HF, reductions rather than elevations in low frequency power should be used to infer between‐subject differences in sympathetic outflow in PAH. Supported by funding from the Canada Research Chairs program, the Heart and Stroke Foundation of Ontario, and Actelion Pharmaceuticals.