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M Smietanowski

Publications and source records attributed to M Smietanowski.

6 recordsLinked to original sources
PubMed2001

Non-linear dynamics of cardiovascular system in humans exposed to repetitive apneas modeling obstructive sleep apnea: aggregated time series data analysis.

OBJECTIVE: Testing the hypothesis that alterations in non-linear dynamics of the cardiovascular variability appear in healthy, awake subjects during voluntary apnea. SUBJECTS AND METHODS: Ten young subjects performed 20 apneas 60 s each separated by 1 min free breathing. Inter-beat interval (IBI) measured as RR-interval in ECG, systolic (SYS) and diastolic (DIAS) arterial blood pressure. stroke volume (SV), cardiac output (CO) and total peripheral resistance (TPR) were non-invasively recorded and computed by Portapress 2 system. Correlation dimension according to Grassberger-Proccacia algorithm (CD) and ratio of % determinism versus % recurrence (RDR) computed from recurrence plot according to Webber and Zbiluth [J. Appl. Physiol. 76 (1994) 965] were used as the indices of chaos and complexity. Sequential time series of cardiovascular variables in consecutive 60-s apneas and inter-apnea free breathings were separately windowed and aggregated. CD and RDR of aggregated apneic time series were compared with CD and RDR values of aggregated time series of inter-apnea free breathing, 10 min at rest and 10 min recovery. Reliability of the aggregation method of sequential time series was tested on transformed simulated data generated by Lorenz model. Error in CD and RDR estimation did not exceed 5% and 1%. respectively. RESULTS: CD of cardiovascular variables computed from aggregated apneas was significantly reduced and RDR augmented versus control and recovery periods. CD and RDR values of inter-apnea phases were in between those in control and during apneas. Time domain linear variance (SD) was increased during aggregated apneas. CONCLUSIONS: Signal dynamics dependent windowing and data aggregation could be a useful tool for non-linear analysis of short repeatable sequential time series; time domain linear variability of the cardiovascular dynamics is augmented while complexity reduced during apneic chemoreceptor stimulation; alterations in non-linear dynamics of cardiovascular variables during apneas in healthy normotensive subjects may suggest an early sign of a mechanism implicated in arterial hypertension in OSAS.

Adult↗
PubMed2001

Nonlinear parameters estimation from sequential short time data series.

Procedures of nonlinear parameter estimation require large samples of data. In stationary physiological situations, usually short time series are available. The method of dynamics-dependent windowing and data aggregation procedure are proposed. This technique was tested on chaotic signal generated by Lorenz model and applied to investigate beat-to-beat control of the cardiovascular system in 10 healthy volunteers. Nonivasively recorded blood pressure, respiratory activity and blood oxygen saturation were digitized and saved for further off-line analysis. The experimental procedure consisted of 10 min control--C, 20 voluntary apneas 1 min each-A, interapnea 20 periods of 1 min spontaneous breathing--B, and 10 min free-breathing recovery--R. Respiration signal served as a reference for apnea and interapnea free-breathing identification period. Correlation dimension-CD, according to Grassberger and Procaccia, and recurrence plot strategy, according to Webber and Zbilut, were applied to check dynamical properties of the signals. Results of numerical experiment on Lorenz model, original and transformed by segmentation and aggregation, support our assumption of similarity of their dynamics. Error in CD and recurrence parameters estimation strongly depended on segment length and was about 5% for 600 to 1,200 data points. However, even for segments of 75 to 100 samples, it did not exceed 10% for all, but one, periodic testing signal. Segmentation and aggregation applied to interbeat interval (IBI) and total peripheral resistance (TPR) data showed that CD and recurrence variables estimated separately for apneic and interapneic period and those calculated for mixed (apneic and interapneic) intervals were different. Average CD and recurrence parameters of IBI and TPR for 10 subjects during apnea and interapnea intervals were significantly different than during control and recovery. The lowest CD (mean +/- S.D.) of 6.38 +/- 0.4, 5.62 +/- 0.2 and %recurrence 10.35 +/- 0.8, 6.62 +/- 0.6 (highest ratio 4.95 +/- 0.2, 5.13 +/- 0.3) were observed in apnea for IBI and TPR, respectively. Low values of the estimates computed for mixed periods may suggest the influence of slowly varying, quasiperiodic driving force due to experimental procedure regime. Signal dynamics-dependent windowing and data aggregation regardless of the sequence of data could be a practical solution for nonlinear analysis of very short repeatable time series.

Adult↗
PubMed2001

Repetitive apneas reduce nonlinear dynamical complexity of the human cardiovascular control system.

We tested the hypothesis that intermittent apneas performed by awake subjects simulate obstructive sleep apnea (OSA) and change dynamic complexity of the cardiovascular control system by repetitive short time stimulation of arterial chemoreceptors. Correlation dimension (CD) and reccurent plot quantification calculated as ratio % determinism versus % recurrence (RDR) were used.as indices of chaotic dynamics. Thirty three normotensive subjects of mean age 21,58 +/- 4,1 performed 10 voluntary apneas 1 min. each separated by 1 min free breathing period. Systolic (SYS), diastolic (DIAS) arterial blood pressure was continuously recorded by finger volume clamp. Stroke volume (SV) was estimated by pulse pressure analysis. Cardiac output (CO) and total peripheral resistance (TPR) were calculated by Portapress system. Cardiac inter-beat interval (IBI) was measured from R-R intervals of ECG. Standard deviation (SD), an index of linear variability, was calculated in 1 min epoch. Dynamics of cardiovascular variables was computed in each subject during 20 min. rest (C), 20 min. of 10 apneas, 1 min each, separated by 1 min free breathing (A), and in 20 min. recovery free breathing (R). In A period CD of all circulatory variables was significantly reduced and RDR augmented. In 23 out of 33 subjects decreased nonlinear dynamics of TPR was carried over from A to R. In contrast, SD increased significantly in A. In conclusion, intermittent brief chemoreflex stimulations by repetitive apneas increase blood pressure and TPR and decrease chaotic behaviour and complexity of the cardiovascular autonomic control system, presumably by inhibition of some regulatory loops such as baroreflex, less vital for survival at oxygen deprivation. Reduced complexity could be implicated in the mechanism of arterial hypertension linked with OSA.

Adolescent↗
PubMed1996

Cardiovascular periodicities in healthy humans in the absence of breathing and under reduced chemical drive of respiration.

In 20 healthy human subjects (aged 20-24 years) power density spectra in 1-min time series were computed by modified MATLAB procedures from inter-beat heart intervals and systolic and diastolic finger blood pressure. High- (HF), mid- (MF) and low-frequency (LF) peaks (0.16-0.37 Hz, 0.08-0.12 Hz and 0.02-0.05 Hz, respectively) were distinguished in power density spectra (PDS). During 1-min voluntary apneas MF and LF power increased and in 18 out of 20 subjects HF peaks disappeared in PDS. Breath holding performed in hyperoxia or in hyperoxia accompanied by 1-min hyperventilation preceding apnea augmented power at MF and LF range and abolished marginal HF peaks present in the spectrum in two subjects. It is concluded that apneic PDS is characterized by augmented power of MF and LF rhythms, and represents endogenous free running cardiovascular periodicities released from feed-back mechanical, reflex and feed-forward central entrainment to respiratory rhythm.

Adult↗
PubMed1995

Changes in upper airway resistance during progressive normocapnic hypoxia in patients with obstructive sleep apnoea syndrome.

The responses of the upper airway to progressive normocapnic hypoxia were studied in 6 healthy men and in 6 patients with obstructive sleep apnoea syndrome (OSAS). The upper airway resistance was calculated by the ratio of the laryngeal pressure (measured using a catheter introduced into oesophagus) to the inspiratory flow. Additionally, genioglossal EMG activity (GG-EMG) was measured and analysed. The changes of all variables were analysed individually for each subject. The OSAS patients showed reduced ventilatory response, GG-reactivity and changes in upper airway resistance during progressive hypoxia. It is concluded that impaired reactivity to hypoxic activation (probably due to the process of adaptation of carotid chemoreceptors to nocturnal hypoxia), might reduce the defence abilities of OSAS patients against episodes of obturation in upper airway and obstructive apnoea events.

Journal Article↗