Altered Cardiovascular Variability in Obstructive Sleep Apnea

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Abstract

Altered cardiovascular variability is a prognostic indicator for cardiovascular events. Patients with obstructive sleep apnea (OSA) are at an increased risk for cardiovascular disease. We tested the hypothesis that OSA is accompanied by alterations in cardiovascular variability, even in the absence of overt cardiovascular disease. Spectral analysis of variability of muscle sympathetic nerve activity, RR interval, and blood pressure were obtained during undisturbed supine rest in 15 patients with moderate-to-severe OSA, 18 patients with mild OSA, and 16 healthy control subjects in whom sleep disordered breathing was excluded by complete overnight polysomnography. Patients with OSA were newly diagnosed, never treated for OSA, and free of any other known diseases. Patients with moderate-to-severe OSA had shorter RR intervals (793+/-27 ms) and increased sympathetic burst frequency (49+/-4 bursts/min) compared with control subjects (947+/-42 ms; 24+/-3 bursts/min; P=0.008 and P<0.001, respectively). In these patients, total variance of RR was reduced (P=0.01) and spectral analysis of RR variability showed an increase in low frequency normalized units, a decrease in high frequency normalized units, and an increase in the ratio of low to high frequency (all P<0.05). Even though blood pressure was similar to that of the control subjects, blood pressure variance in patients with moderate-to-severe OSA was more than double the variance in control subjects (P=0.01). Patients with mild OSA also had a reduction in RR variance (P=0.02) in the absence of any significant difference in absolute RR interval. For all patients with OSA, linear regression showed a positive correlation (r=0.40; P=0.02) between sleep apnea severity and blood pressure variance. Cardiovascular variability is altered in patients with OSA. This alteration is evident even in the absence of hypertension, heart failure, or other disease states and may be linked to the severity of OSA. Abnormalities in cardiovascular variability may be implicated in the subsequent development of overt cardiovascular disease in patients with OSA.

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Most cited references 23

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Important influence of respiration on human R-R interval power spectra is largely ignored.

Timothy J. Koh, L Beightol, Dwain Eckberg … (1993)

Frequency-domain analyses of R-R intervals are used widely to estimate levels of autonomic neural traffic to the human heart. Because respiration modulates autonomic activity, we determined for nine healthy subjects the influence of breathing frequency and tidal volume on R-R interval power spectra (fast-Fourier transform method). We also surveyed published literature to determine current practices in this burgeoning field of scientific inquiry. Supine subjects breathed at rates of 6, 7.5, 10, 15, 17.1, 20, and 24 breaths/min and with nominal tidal volumes of 1,000 and 1,500 ml. R-R interval power at respiratory and low (0.06-0.14 Hz) frequencies declined significantly as breathing frequency increased. R-R interval power at respiratory frequencies was significantly greater at a tidal volume of 1,500 than 1,000 ml. Neither breathing frequency nor tidal volume influenced average R-R intervals significantly. Our review of studies reporting human R-R interval power spectra showed that 51% of the studies controlled respiratory rate, 11% controlled tidal volume, and 11% controlled both respiratory rate and tidal volume. The major implications of our analyses are that breathing parameters strongly influence low-frequency as well as respiratory frequency R-R interval power spectra and that this influence is largely ignored in published research.

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Prognostic value of 24-hour blood pressure variability.

A Frattola, G. Parati, C Cuspidi … (1993)

Evaluation of the prognostic value of 24-h blood pressure averages and 24-h blood pressure variability. After an initial thorough clinical and laboratory evaluation which included 24-h continuous ambulatory blood pressure monitoring, a group of hypertensive patients were re-examined after an average of 7.4 years. End-organ damage at the follow-up visit was related to different measures of blood pressure levels and variability obtained at the initial or the follow-up visit or both. Seventy-three patients with essential hypertension of variable severity, in whom ambulatory blood pressure was monitored intra-arterially for 24 h (Oxford technique) were re-examined at a follow-up visit (including echocardiographic assessment of left ventricular mass index) 1-13 years later (mean 7.4 years). The severity of end-organ damage was quantified by a score and related to clinic blood pressure at follow-up and to (1) clinic blood pressure, (2) 24-h blood pressure mean, (3) 24-h short-term and long-term blood pressure variability, and (4) end-organ damage, all assessed at the initial visit (multiple regression analysis). The set of independent variables considered was significantly related to end-organ damage at follow-up (R = 0.51). The individual variables most important in determining end-organ damage at follow-up were clinic blood pressure at the follow-up visit (P < 0.01), the initial level of end-organ damage (P < 0.05) and long-term blood pressure variability (among half-hour standard deviation of 24-h mean blood pressure) at the initial evaluation (P < 0.05). The prognostic individual weight of the other haemodynamic parameters considered was less and not statistically significant. The results confirm that the level of blood pressure achieved by treatment and the degree of end-organ damage at the time of initial evaluation are important determinants of future end-organ damage related to hypertension. They also constitute the first longitudinal evidence that the cardiovascular complications of hypertension may depend on the degree of 24-h blood pressure variability.

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Author and article information

Journal

Title: Circulation

Abbreviated Title: Circulation

Publisher: Ovid Technologies (Wolters Kluwer Health)

ISSN (Print): 0009-7322

ISSN (Electronic): 1524-4539

Publication date Created: September 15 1998

Publication date (Print): September 15 1998

Volume: 98

Issue: 11

Pages: 1071-1077

Affiliations

[1 ]From the Departments of Internal Medicine (K.N., P.J.H. v. d. B., V.K.S.) and Neurology (M.E.D.), Cardiovascular Division, University of Iowa, Iowa City, and Centro L.I.T.A.-Vialba (N.M., C.C.), Centro Ricerche Cardiovascolari, CNR, Medicina Interna II, Ospedalè “L. Sacco”, Università degli Studi di Milano (Italy).