Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Spectral Analysis”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,189 records · Page 66Linked to original sources
PubMedDate not supplied

Cortical control of sinus arrhythmia in man studied by spectral analysis.

Eighteen healthy male volunteers, 21-26 years old, participated in a study intended to detect cortical control of beat-to-beat heart rate variability independent of the effects on breathing and mean heart rate. They were tested while seated and standing relaxed (baseline), and while performing tasks requiring concentrated attention while sitting. The mental concentration elicited a typical cardiorespiratory response manifested by moderate acceleration and shallowing of respiration with a small increase of mean heart rate (HR), a pattern already widely acknowledged as typically associated with concentration. With the aid of a variable tone delivered to the ear as a guide, the subjects were trained to breathe at the same rate without concentrating in order to test the influence of respiration on the concentration pattern. ECG, thermistor pneumogram and ear-lobe photo-plethysmogram were recorded and data reduction was performed on 3 minute or 1 minute data sequences selected for the best steady-state. Statistical treatment was limited to a subgroup of 10 subjects in whom there was no overlapping of the spectra of respiratory and Traube-Hering-Mayer sinus arrhythmia (RSA and THM-SA, respectively). Mental concentration elicited significant depression of both RSA and THM-SA even if the respiratory parameters were kept constant.

Adult↗
PubMed2004

Diversity of coexisting Planktothrix (cyanobacteria) chemotypes deduced by mass spectral analysis of microystins and other oligopeptides.

Cyanobacteria are reported to produce secondary metabolites of which toxic and bioactive peptides are of scientific and public interest. Many peptides are synthesized by the non-ribosomal peptide synthesis pathway and their presence is a stable feature of individual clones. We isolated 18 clonal strains of Planktothrix from a single water sample from lake Maxsee near Berlin and analyzed them by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry, HPLC, and PCR for their production of peptides and the presence of microcystin synthetase genes. Microcystins could be detected in seven of the strains with considerable variability of contents and numbers of structural variants. Other known peptides like anabaenopeptins B and E/F, microviridin I, and prenylagaramide B and new variants of known peptide classes like aeruginosins and cyanopeptolins were detected in some strains while lacking in others. The 18 strains represented 15 chemotypes with respect to their peptide patterns. In contrast, all strains were morphologically very similar with respect to cell dimensions and pigmentation. Given the diversity of chemotypes among the randomly selected isolates, an immense diversity of chemotypes in the entire population can be assumed.

Bacterial Proteins↗
PubMed2000

Comparison of different excitation methods for X-ray spectral analysis: the case of synchrotron radiation.

Different excitation means, protons, photons and electrons (PIXE, XRFA, and EPMA, respectively) have previously been compared with regard to the figures of merit, i.e. detection power, precision and accuracy. The aim in this article is to compare synchrotron radiation SR as another excitation method with the methods mentioned above. From this point of view the evaluation of (SR) was missing as an again independently optimized excitation method and was based as previously on practical problems of trace analysis, in this case on the determinations of traces in lead. The experiment has been performed with thick homogeneous samples of lead, the same samples already used in the former work, so that a direct comparison is possible. The calculation of the figures of merit is based on the measurements of the blank values and their relative standard deviation for the detection limit and on the random errors for the precision. Regarding the thick homogeneous target of lead XRFA still turns out to be the best method, whereas Synchrotron X-Ray Fluorescence SY-XRF compares favorably, at least for larger atomic numbers Z. Even PIXE is inferior to (SY-XRF) in the case of larger Z; when information on the lateral distribution of the elements is of interest, PIXE is indispensable.

Journal Article↗
PubMed1999

The effect of four different antihypertensive medications on cardiovascular regulation in hypertensive sleep apneic patients--assessment by spectral analysis of heart rate and blood pressure variability.

OBJECTIVE: To study the effect of antihypertensive medications on autonomic nervous system in patients with hypertension and sleep apnea syndrome using frequency domain measures of heart rate and blood pressure variabilities. METHODS: The beta-receptor blocking agent atenolol (50 mg), the calcium antagonist isradipine SRO (2.5 mg), the diuretic hydrochlorothiazide (25 mg) and the ACE inhibitor spirapril (6 mg) once daily were given in a double-blind crossover schedule for 8 weeks. Cardiovascular autonomic control was assessed using frequency domain measures of heart rate variability during the spontaneous and controlled breathing tests. During orthostatic maneuver and cold pressor test the blood pressure variability analysis also was performed. RESULTS: In general, the responses of heart rate and blood pressure variabilities were abnormal in the patients with arterial hypertension and sleep apnea syndrome compared to reference data. Of the four drugs, only atenolol effected heart rate and blood pressure variabilities as it shifted the autonomic regulation to the vagal direction. Other antihypertensive drugs did not change any parameter of heart rate or blood pressure variabilities. CONCLUSION: The short-term treatment with atenolol in patients with arterial hypertension and sleep apnea syndrome is associated with normalization of autonomic nervous control judged by heart rate and blood pressure variability. Thus, beta-receptor blockade may have adjunctive beneficial effects beyond blood pressure reduction in these patients. However, the long-term effects of blood pressure reduction on autonomic nervous control remain to be studied.

Adrenergic beta-Antagonists↗
PubMed2006

FTIR-spectral analysis of two photosynthetic hydrogen-producing [corrected] strains and their extracellular polymeric substances.

The Fourier transform infrared (FTIR) spectra of the cells of two photosynthetic H(2)-producing strains, Rhodoblastus acidophilus and Rhodobacter capsulatus, as well as their extracellular polymeric substances (EPS), were evaluated. The FTIR spectra of R. capsulatus and its EPS during its cultivation were also recorded. The main peaks in the spectra, including 1,080 cm(-1) (carbohydrates), 1,250 cm(-1) (nucleic acids), 2,830-2,930 cm(-1) (lipids), 1,660-1,535 cm(-1) (Amide I and II of proteins), were observed. The relative heights of these peaks in the spectra of the two strains were different, showing the difference in contents of various components in the cells or EPS. The ratios among the main components in the EPS obtained from the FTIR spectra were in good agreement with those from a conventional quantitative chemical analysis. As an easy, rapid, and direct technique, the FTIR spectroscopy could be used to characterize the components and their relative contents of EPS of photosynthetic bacteria.

Bacterial Proteins↗
PubMed2002

Evaluation of cold face test bradycardia by means of spectral analysis.

The cold face test (CFT) is a non-invasive challenge maneuver of the autonomic nervous system which activates the peripheral sympathetic and the cardiac parasympathetic nervous system and induces peripheral vasoconstriction and bradycardia. The physiology of CFT-induced bradycardia is still controversial. The heart rate decrease might result from a direct central up-regulation of cardiovagal activity or might be a secondary effect of baroreceptor activation or of changes of respiration. The purpose of this study was to analyze the origin of CFT-induced bradycardia. To evaluate the influence of respiration on bradycardia during CFT, we studied cardiac responses in 10 healthy volunteers during CFT (0-1 degrees C cold compresses for 60 s) with three different respiratory patterns: one with spontaneous and two with paced respiration (6 and 15 cycles/minute). We continuously monitored heart rate (HR), blood pressure (BP) and respiration and determined heart rate variability by assessment of coefficient of variation (CV), standard deviation (SD) and the root mean square of successive differences (RMSSD) of HR as well as low (LF) and high (HF) frequency spectra power of HR and BP. When coherence was above 0.5, we calculated the transfer function gain between HR and respiration in the HF band, as an index of respiratory sinus arrhythmia, and between HR and BP in the LF band, as an index of baroreflex sensitivity. HR decreased and BP increased significantly during the three types of CFT. The decrease of HR and the increase of BP, of time and frequency domain parameters did not differ between the three breathing patterns. Respiration, and HF and LF power of respiration did not change during CFT. The gain of the HF-transfer function between HR and respiration and the LF-transfer function gain between HR and BP increased significantly during CFT, but the increase did not differ between the three breathing patterns. The increase of the gain of both transfer functions is most likely due to an increase of vagal traffic and together with the unchanged respiratory pattern suggests that CFT-induced bradycardia is not due to baroreflex or respiratory influences, but seems to result from central vagal activation.

Adult↗
PubMed1989

Continuous spectral analysis of heart murmurs for evaluating stenotic cardiac lesions.

Severity of stenotic heart lesions affects timing, quality and pitch of associated heart murmurs. This quantitative study investigated the relation between instantaneous sound frequencies contained in heart murmurs and magnitudes of Doppler jet velocities measured distal to associated obstructions. Heart murmurs were recorded from 18 patients, ages 1 day to 23 years, with 21 separate murmurs resulting from abnormal valves (18 studies) or left-to-right shunts (3 studies). Recorded murmurs were digitized and divided into 12.3-ms time segments for computer frequency analysis using the maximum entropy method. Murmur spectra were plotted in gray scale against time. All murmurs contained dominant frequencies that varied with time. Dominant murmur frequencies and associated Doppler jet velocities at equivalent points in time were measured at 50-ms intervals. For 88 points analyzed, instantaneous dominant frequencies ranged from 130 to 410 Hz (mean +/- standard deviation 282 +/- 70 Hz) and instantaneous jet velocities ranged from 110 to 460 cm/s (290 +/- 80 cm/s). For the 21 murmurs studied, peak murmur frequencies ranged from 200 to 410 Hz (308 +/- 70 Hz) and peak jet velocities ranged from 165 to 460 cm/s (320 +/- 78 cm/s). Instantaneous dominant frequency correlated to instantaneous jet velocity (r = 0.85) and peak dominant frequency correlated to peak jet velocity (r = 0.89). This in vivo study demonstrates that dominant frequencies contained in heart murmurs are related to instantaneous jet velocities distal to associated obstructions.

Adult↗