OSAS


Obstructive Sleep Apnea Screening (OSAS) software which makes possible a direct comparison between quantitative heart rate variability parameters in the time and frequency domains during the wakeful state and sleep, thus enabling the doctor to determine whether suspicion of sleep apnea is grounded and thus whether an indication for further diagnostic procedures (i.e., polysomnography) in a sleep laboratory exists.

The first step is a 24-hour ECG Holter recording by means of a compatible ECG recording system (Nevrokard OSAS is at present compatible with Cardiac Science Burdick, Mortara, Rozinn, Philips Zymed, Forest Medical, DelMar Reynolds and Mini Mitter systems, further compatibilities to be added later at customers' request).

During the second step the RRI file derived from the Holter recording is submitted to analysis by the Nevrokard OSAS software. The AWAKE and SLEEP sections of each recording are separately analyzed and directly compared in the same screen. A set of quantitative parameters describing the patient's heart rate variability in both time and frequency domains is obtained and easily compared. Differences between some of these parameters are proportional to the probability that the patient has sleep apnea.

Nevrokard OSAS consists of two software modules:
  • The Nevrokard HRV File Preparation software module is used to obtain an RRI file from ECG recordings of different compatible formats (see also Data Formats). This step is not required with Holter recordings of the brands listed above, because the Holter systems perform this step themselves and output an RRI file.

  • The Nevrokard OSAS (=Obstructive Sleep Analysis Software) is then used to analyze RRI data series obtained from the compatible Holter systems (see Data Formats) (or, more rarely, from the Nevrokard HRV File Preparation software module) and compare the AWAKE and SLEEP sections of recordings.

 

   
An ECG file recorded by any compatible acquisition system or an RR interval file recorded by a compatible Holter system (see above and Data Formats) is required
AWAKE and SLEEP sections are clearly color-coded (see below).

Recordings can be displayed and analyzed either in the RRI (below left) or HR mode (below right).



 
  TIME DOMAIN ANALYSIS
 
All time-domain displays and calculations will be done either in the RR or HR mode.
 

Statistics: Max., Min., Max./Min., Range, Mean NN, Mean dNN (MSD), Median, 95% Conf. Interval, 99% Conf. Interval, lnHRV, Coef. of Variance, Variance, SDNN, SENN, SDSD, RMSSD, NN50 Count, pNN50, SDANN, SDNN Index, SDASD.                                          The AWAKE and SLEEP results are directly compared in the table.

Segmented statistics: SDANN, SDNN Index, SDASD, t-test between segments; Mean, STD, SE, 95% Confidence Interval and 99 % Confidence Interval for each segment.

Histogram: Mean, SD, Median, Modus, Dispersion, Upper F(X), Uncertainty, Skeweness, Kurtosis and Variability Index (HRV Triangular Index with a freely adjustable Class Interval (bin value)).

Poincare Analysis: SD1, SD2 in both absolute and normalized units, SD1/SD2 Ratio, CSI (Cardiac Sympathetic Index), CVI (Cardiac Vagal Index), dRRt, dRRr in both absolute and normalized units, dRRt/dRRr, Centroid, Ellipse Area, R2 and SEE.

 
  FREQUENCY DOMAIN ANALYSIS
 

Based on the autoregressive model (parametric method):

  • Spectral density units: absolute, normalized.
  • Freely adjustable model order.
  • Graphic presentation and calculation of integrals of up to three preset frequency bands (ULF, VLF, LF, HF,VHF) which represent the quantitative, numeric results of spectral analysis and give a non-invasive estimate of the function of the sympathetic and parasympathetic autonomic nervous systems in patients in absolute or normalized units (absolute power of given component/[sum of absolute powers of all components-F*] x 100, *F=adjustable low frequency limit for n.u. calculation).
  • On-screen determination of spectral density at any frequency.
  • LF/HF ratio, LF/(LF+HF) ratio, HF/(LF+HF) ratio, CCVLF (Coefficient of Component Variance for LF) and CCVHF (Coefficient of Component Variance for HF).



Based on the FFT Algorithm (non-parametric method):
  • FFT spectra types: Amplitude (=Magnitude), RMS, Power.

  • FFT window types: Rectangular, Hanning, Hamming, Flat Top, Bartlet, Blackman, Exponent, Blackman Exact, Blackman Harris, Chebyshev, Cosine Tappered, Kaiser.

  • Spectral density units: absolute, normalized.

  • Absolute units: linear, logarithmic (absolute, relative).

  • Smoothing with triangular window (freely adjustable smooth index).

  • Graphic presentation and calculation of integrals of up to three preset frequency bands (ULF, VLF, LF, HF,VHF) which represent the quantitative, numeric results of spectral analysis and give a non-invasive estimate of the function of the sympathetic and parasympathetic autonomic nervous systems in patients in absolute or normalized units (absolute power of given component/[sum of absolute powers of all components-F*] x 100, *F=adjustable low frequency limit for n.u. calculation).

  • On-screen determination of spectral density at any frequency.

  • LF/HF ratio, LF/(LF+HF) ratio, HF/(LF+HF) ratio, CCVLF (Coefficient of Component Variance for LF) and CCVHF (Coefficient of Component Variance for HF).


FFTSPECTRUM


 
  RESULTS OF ANALYSIS
 
  • Heart rate variability results in the time domain are directly compared in the Statistics table.

  • Results of analysis can be printed, exported, directly converted into graphic formats or presentation slides, transferred to clipboard etc.

  • Chart Editor is available for all modes of analysis.