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* From the Departments of Psychiatry (Drs. Neleson, Mills, and Dimsdale, and Mr. Yu) and Medicine (Drs. Ziegler and Clausen), University of California San Diego, La Jolla, CA.
Correspondence to: Richard A. Nelesen, PhD, Department of Psychiatry, University of California San Diego, 9500 Gilman Dr, La Jolla, CA 92093-0804; e-mail: rnelesen{at}ucsd.edu
Objectives: We examined the effect of continuous positive airway pressure (CPAP) treatment for sleep apnea on cardiac contractility, heart rate variability, and hemodynamics at rest and in response to a laboratory stressor.
Subjects and instrumentation: Forty-one apneic patients were studied on three occasions: before treatment, after 1 full night of CPAP treatment, and after 1 week of CPAP treatment. The subjects were randomly assigned to receive effective treatment or placebo. Contractility and hemodynamics were determined with impedance cardiography, and parasympathetic activity was assessed by analysis of heart rate variability. Measures were determined at rest and in response to a stressor.
Design and results: For the cardiac sympathetic
(contractility) measures (preejection period, cardiac acceleration
index [CAI], and low-frequency/high-frequency ratio) significant
interactions were found in the combination treatment (CPAP vs placebo)
by study day (day 1, day 3, day 11) by test period (baseline,
preparation, talking) [p < 0.01]. For these measures, there were
no differences between the treatment groups or responses to the
stressor on day 1. Levels in placebo-treated subjects did not change or
respond on the subsequent study days. In the CPAP-treated subjects,
there was a decrease in these indexes at baseline, which became
significantly lower by day 11 (ie, CAI levels were 24
/s2, 22 /s2, and 14 /s2 on
day 1, day 3, and day 11, respectively). These measures also became
responsive to the stressor by showing increased sympathetic activity
(CAI levels on day 11 were 14 /s2 at baseline, 32
/s2 during speech preparation, and 36 /s2
while speaking). The parasympathetic indexes, such as high-frequency
power or band of heart rate variability as determined by spectral
analysis, showed a significant day-by-treatment interaction
(p < 0.005), whereas the CPAP- treated group had significantly more
parasympathetic activity after 1 week of treatment. For the hemodynamic
measures (stroke volume [SV], cardiac output, and systemic vascular
resistance [SVR]), there were significant treatment-by-study
day-by-test-period interactions (p < 0.01). SV and cardiac output
increased across days, and SVR decreased in the CPAP-treated
patients.
Conclusions: These results indicate that CPAP normalizes contractility, increases cardiac vagal tone, and changes hemodynamic regulation from being resistance dominated to being cardiac dominated. Thus, after 1 week of treatment with CPAP, many of the indicators of poor cardiac functioning in apnea patients are improved.
Key Words: autonomic nervous system • continuous positive airway pressure • contractility • heart rate variability • hemodynamics • sleep apnea
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