Eva Závodná

Novel Method for Localization of Common Carotid Artery Transverse Section in Ultrasound Images Using Modified Viola-Jones Detector

This article describes a novel method for highly accurate and effective localization of the transverse section of the carotis comunis artery in ultrasound images. The method has a high success rate, approximately 97%. Unlike analytical methods based on geometric descriptions of the object sought, the method proposed here can cover a large area of shape variation of the artery under study, which normally occurs during examinations as a result of the pressure on the examined tissue, tilt of the probe, setup of the sonographic device, and other factors. This method shows great promise in automating the process of determining circulatory system parameters in the non-invasive clinical diagnostics of cardiovascular diseases. The method employs a Viola-Jones detector that has been specially adapted for efficient detection of transverse sections of the carotid artery. This algorithm is trained on a set of labeled images using the AdaBoost algorithm, Haar-like features and the Matthews coefficient. The training algorithm of the artery detector was modified using evolutionary algorithms. The method for training a cascade of classifiers achieves on a small number of positive and negative training data samples (about 500 images) a high success rate in a computational time that allows implementation of the detector in real time. Testing was performed on images of different patients for whom different ultrasonic instruments were used under different conditions (settings) so that the algorithm developed is applicable in general radiologic practice.

Influence of age, body mass index, and blood pressure on the carotid intima-media thickness in normotensive and hypertensive patients

Abstract We investigated whether body mass index and blood pressure have an additive influence on the carotid intima-media thickness (IMT). In 27 patients treated for hypertension (47.2±8.7 years) and 23 normotensive subjects (44.1±8.1 years), 24-h recording of blood pressure was performed. The carotid IMT was determined by ultrasonography and baroreflex sensitivity by a spectral method from 5-min recordings of blood pressure. Significant differences between hypertensive and normotensive subjects were observed for carotid IMT (0.60±0.08 vs. 0.51±0.07 mm; p<0.001) and baroreflex sensitivity (3.5±1.8 vs. 5.6±2.1 ms/mm Hg; p<0.001). Hierarchical multiple regression analysis (p<0.01) showed that carotid IMT was positively correlated with age (p<0.001) and body mass index (p<0.05) in normotensive subjects. The increased carotid IMT in hypertensive patients was not additively influenced by either age or body mass index. Baroreflex sensitivity decreased with age (p<0.01) and with carotid IMT (p<0.05) in normotensive subjects only. Multiregression analysis showed that an additive influence of age and body mass index on the development of carotid IMT is essential only in normotensive subjects. In hypertensive subjects the influence of blood pressure predominates, as documented by a comparison of the carotid IMT between hypertensive and normotensive subjects.

Is Low Baroreflex Sensitivity only a Consequence of Essential Hypertension or also a Factor Conditioning Its Development

Baroreflex sensitivity (BRS) is an individually characteristic index. It fluctuates spontaneously even at rest and therefore a particular value measured represents an approximate estimate of its size. Bearing in mind the fact that essential hypertension (EH) is a disease of higher age, the majority of studies done in previous years were naturally focused on BRS in older population. The increased arterial stiffness, increased IMT, and sympathetic activation in obesity represent indubitable factors which lead to hypertension and, consequently, result in a decrease of BRS. The hypothesis ensuing from these studies, which states that the drop in BRS accompanies the development of hypertension as a secondary manifestation of the disease, is proved by these studies. On the other hand, measurements of BRS in children and adolescents and the first genetic studies on the inborn conditionality of BRS have provided enough evidence that some individuals possess congenitally low BRS. Without a targeted study, we cannot even speculate on how this assumption will manifest itself in advanced age in terms of increased risk of sudden cardiac death, since in the meantime the long-term pathological influence of other mechanisms lowering BRS will have presented itself in the other risky patients. Low BRS will manifest itself as blood pressure hyperreactivity. It may lead to white coat hypertension in adolescents as a step in the development of EH. Therefore, congenitally low BRS may be considered as another risk factor for the development of EH. This is the reason why in the young population increased emphasis should be put on the prevention of obesity and sufficient physical activity as on easily influence able stimuli which additively increase blood pressure.

The development of LF/HF ratio and its dependence on the mean heart rate in children and adolescents

We have shown previously how the dependency of the baroreflex sensitivity on the inter-beat intervals (IBI) can cover up the developmental changes. Therefore we decided to analyse LF/HF ratio. We have calculated mean IBI and heart rate (HR) and their power spectra in 424 subjects (11 - 20 years) from the 5-min continuous blood pressure monitoring at rest. LF/HF ratios of IBI and HR spectra were determined. The statistic was done for a whole group (WG), and for subgroups of older children (C: 11 -1 5 years), adolescents (A:16-20 years), andfor 10 particular age-subgroups. In the WG and the A, we shown significant relationship between age and mean IBI or HR, but LF/HFIBI or LF/HFHR were age-independent. LF/HFIBI or LF/HFHR was also significantly age-dependent. Negative correlation of IBI vs. LF/HFIBIand a positive correlation of HR vs. LF/HFHR in the WG and in C or A was found. Relationship IBI vs. LF/HFIBI and HR vs. LF/HFHR were in particular age-subgroups from 11 to 14 years, but it was insignificant in subgroups from 15 to 20 years. Our analysis showed the increase of LF/HF ratio up to the age of 15 years when the development of sympathovagal balance seems to be finished. Strong relationship between IBI or HR and LF/HF ratios could cover the development changes.

Calculation of the pulse wave velocity from the waveform of the central aortic pressure pulse in young adults

Cardiovascular diseases are the most common causes of morbidity and mortality in developed countries. Therefore, the correct determination of the parameters indicating the disease condition is critical in effective treatment of patients. One of the parameters evaluating arterial stiffness is determining the pulse wave velocity (PWV), but the method of determining faces a number of problems. In the study was measured 20 healthy patients. Using applanation tonometry was measured pulse wave from a. radialis and a. carotis. PWV was measured by SphygmoCor and calculated by method of flow triangle using aortic pressure pulse for determination PWV. Average value of PWV calculated by method of flow triangle was 8.35 ± 0.86 m/ s and average value measured by SphygmoCor 7.2 ± 0.8 m/ s. The variance differences of measured and calculated values PWV was 0.785 ± 0.575 m /s. The average value of the a.radialis-a.carotis distance was 485 ± 43.4 mm. According to the results it can be assumed that the new method of analysis the forward and backward waves is relatively accurate, but it is very sensitive to standardize measurement. The results are affected by several factors, is necessary to propose further steps to accurate protocol for the more precise results.

CHANGES IN SYSTOLIC BLOOD PRESSURE AND PULSE INTERVAL VARIABILITY IN CHILDREN WITH TYPE 1 DIABETES MELLITUS: PP.27.363

Introduction: Polyneuropathy quite often accompanies diabetes mellitus and probably affects all organs. The aim of the study was to show differences in systolic blood pressure and heart rate variability in children with type 1 diabetes mellitus (T1DM). Methods: We examined 382 healthy (Co) children and adolescents (14.8 +- 2.6 years) and 34 patients with T1DM (15.0+- 3.2 years). We recorded systolic blood pressure (SBP) and pulse intervals (PI) beat-to-beat by non-invasive methods (Finapres) in all subjects for 5 min. The breathing was controlled by a metronome at a frequency of 0.33 Hz. The SBP and PI variability were determined as spectral power in the low frequency (LF) range (nSBPlf, nPIlf) and of respiratory (HF) range (nSBPhf, nPIhf) in normalised units, and in absolute values as well (vSBPlf, vPIlf, vSBPhf, vPIhf). Results: We did not find significant differences between controls and T1DM in SBP and PI variability LF range (nPIlf: Co=0.057 +- 0.031, T1DM=0.063 +- 0.027; nSBPlf: Co=0.046 +- 0.026, T1DM=0.046 +- 0.021; vPIlf: Co=15132 +- 14167, T1DM=16672 +- 16583 ms2/Hz; vSBPlf: Co=147 +- 119, T1DM=224 +- 242 mmHg2/Hz). However, there were significant differences in the HF range (nPIhf: Co=0.104 +- 0.064, T1DM=0.081 +- 0.056, p<0.05; nSBPhf: Co=0.058 +- 0.048, T1DM=0.035+-0.038, p<0.001; vPIhf: Co=30570+-39385, T1DM=17078+-16653 ms2/Hz, p<0.01; vSBPhf: Co=152+-145, T1DM=98+-63 mmHg2/Hz, p<0.05). Discussion: Decreased values of SBP and PI variability in children with T1DM in the high frequency region indicate early impairment of parasympathetic activity.

P2.6 Comparison of baroreflex sensitivity determined by cross-spectral analysis at respiratory and 0.1 Hz frequencies in man

Non-invasive methods of determination of baroreflex sensitivity (BRS, ms/mmHg) are based on beat-to-beat systolic blood pressure and inter-beat interval recording. Sequential methods and spectral methods at spontaneous breathing include transient superposition of breathing and 0.1 Hz rhythms. Previously, a cross-spectral method of analysis was used, at constant breathing rate using a metronome set at 0.33 Hz, enabling separate determination of BRS at 0.1 Hz (BRS(0.1Hz)) and respiratory rhythms (BRS(0.33Hz)). The aim of the present study was to evaluate the role of breathing in the spectral method of BRS determination with respect to age and hypertension. Such information would be important in evaluation of BRS at pathological conditions associated with extremely low BRS levels. Blood pressure was recorded by Finapres (5 minutes, controlled breathing at 0.33 Hz) in 118 healthy young subjects (YS: mean age 21.0+/-1.3 years), 26 hypertensive patients (HT: mean age 48.6+/-10.3 years) with 26 age-matched controls (CHT: mean age 46.3+/-8.6 years). A comparison of BRS(0.1Hz) and BRS(0.33Hz) was made. Statistically significant correlations were found between BRS(0.1Hz) and BRS(0.33Hz) in all groups: YS: r=0.52, p<0.01, HT: r=0.47, p<0.05, and CHT: r=0.70, p<0.01. The regression equations indicated the existence of a breathing-dependent component unrelated to BRS (YS: BRS(0.33Hz)=2.63+1.14*BRS(0.1Hz); HT: BRS(0.33Hz)=3.19+0.91*BRS(0.1Hz); and CHT: BRS(0.33Hz)=1.88+ +1.01*BRS(0.1Hz); differences between the slopes and the slope of identity line were insignificant). The ratios of BRS(0.1Hz) to BRS(0.33Hz) were significantly lower than 1 (p<0.01) in all groups (YS: 0.876+/-0.419, HT: 0.628+/-0.278, and CHT: 0.782+/-0.260). Thus, BRS evaluated at the breathing rate overestimates the real baroreflex sensitivity. This is more pronounced at low values of BRS, which is more important in patients with pathologic low BRS. For diagnostic purposes we recommend the evaluation of BRS at the frequency of 0.1 Hz using metronome-controlled breathing at a frequency that is substantially higher than 0.1 Hz and is not a multiple of 0.1 Hz to eliminate respiratory baroreflex-non-related influence and resonance effect on heart rate fluctuations.

Baroreflex open-loop gain at rest and during exercise in man

Baroreflex open-loop gain of heart rate, stroke volume and total peripheral resistance was deternined at rest and during exercise in 12 young adult subjects. The open-loop gain of the baroreflex decreased during exercise.

Changes in Blood Pressure Variability in Adolescents With Essential and Secondary Hypertension: P1.183

The aim of the present study was to determine the interrelationship among the baroreflex sensitivity (BRS), the variability in systolic blood pressure (varSBP) and pulse intervals (varPI) in adolescents with essential and secondary hypertension. The high systolic blood pressure variability in hypertensives could be explained by a primarily increased sympathetic vasomotor activity and by an inadequate dampening effect of baroreflex. The same low number of subjects with secondary hypertension and controls in subgroup with high varSBP, low varPI and low BRS and a high number of subjects with essential hypertension can indicate significantly greater influence of a baroreflex inadequacy in the development of essential hypertension.