Signal processing procedures for the evaluation of the cardiovascular effects in the obstructive sleep apnea syndrome

A new index, the cross-power index (CPI), is proposed to quantify the severity of obstructive sleep apnea syndrome (OSAS) in terms of its cardiovascular effects. On the basis of the influences that recurring drops in oxygen saturation have on systolic blood pressure variability of OSAS patients, CPI is defined as the integral of the cross-spectrum modulus between systolic blood pressure and oxygen saturation. In a test group of 22 subjects, CPI correctly identified all 15 OSAS patients included in the pool. Moreover, evaluation of CPI in six OSAS patients sleeping with and without a CPAP (continuous positive airway pressure) device demonstrated that CPAP treatment substantially reduced the components of blood pressure variability that were correlated with oxygen saturation. These first applications of CPI support the use of this index to identify OSAS patients, to evaluate the efficacy of CPAP in their treatment and to quantify the cardiovascular effect of OSAS.