Biomedical subjects

Alan Murray

Publications and source records attributed to Alan Murray.

At least 19 recordsLinked to original sources

PubMed2006

Comparison of magnetocardiography and electrocardiography: a study of automatic measurement of dispersion of ventricular repolarization.

AIMS: There is some dispute over the clinical significance of dispersion of ventricular repolarization measurements from the electrocardiogram. Recent studies have indicated that multichannel magnetocardiograms (MCGs), which non-invasively measure cardiac magnetic field strength from many sites above the body surface, may provide independent information from ECGs about ventricular repolarization dispersion. For this study, magnetocardiography and electrocardiography were compared from automatic measurements of dispersion of ventricular repolarization. METHODS AND RESULTS: Dispersion of ventricular repolarization time was determined in MCGs and standard ECGs recorded simultaneously from 27 healthy volunteers and 22 cardiac patients. Two automatic techniques were used to determine the interval of ventricular repolarization. There were significant differences in ventricular dispersion between ECG and MCG measurements, with multichannel MCG greater than ECG by 52 (47) ms [mean (SD)] (P<0.00001) and 12-channel MCG greater by 17 (40) ms (P<0.004) across techniques and all subjects. Magnetocardiograms had the greater discriminating power between normal and cardiac patients with differences of 46 (18) ms (P<0.017) for multichannel MCG and 44 (16) ms (P<0.005) for 12-channel MCG, compared with 16 (7) ms (P<0.04) for ECG. CONCLUSION: Magnetocardiography has the power to discriminate regional cardiac conduction differences.

Electrocardiography↗

PubMed2006

Analysis of surface electrocardiograms in atrial fibrillation: techniques, research, and clinical applications.

Atrial fibrillation (AF) is the most common arrhythmia encountered in clinical practice. Neither the natural history of AF nor its response to therapy is sufficiently predictable by clinical and echocardiographic parameters. The purpose of this article is to describe technical aspects of novel electrocardiogram (ECG) analysis techniques and to present research and clinical applications of these methods for characterization of both the fibrillatory process and the ventricular response during AF. Atrial fibrillatory frequency (or rate) can reliably be assessed from the surface ECG using digital signal processing (extraction of atrial signals and spectral analysis). This measurement shows large inter-individual variability and correlates well with intra-atrial cycle length, a parameter which appears to have primary importance in AF maintenance and response to therapy. AF with a low fibrillatory rate is more likely to terminate spontaneously and responds better to antiarrhythmic drugs or cardioversion, whereas high-rate AF is more often persistent and refractory to therapy. Ventricular responses during AF can be characterized by a variety of methods, which include analysis of heart rate variability, RR-interval histograms, Lorenz plots, and non-linear dynamics. These methods have all shown a certain degree of usefulness, either in scientific explorations of atrioventricular (AV) nodal function or in selected clinical questions such as predicting response to drugs, cardioversion, or AV nodal modification. The role of the autonomic nervous system for AF sustenance and termination, as well as for ventricular rate responses, can be explored by different ECG analysis methods. In conclusion, non-invasive characterization of atrial fibrillatory activity and ventricular response can be performed from the surface ECG in AF patients. Different signal processing techniques have been suggested for identification of underlying AF pathomechanisms and prediction of therapy efficacy.

Atrial Fibrillation↗

PubMed2006

Can a simulator that regenerates physiological waveforms evaluate oscillometric non-invasive blood pressure devices?

INTRODUCTION: A simulator has been developed that enables previously recorded clinical oscillometric waveforms to be regenerated for testing oscillometric non-invasive blood pressure measurement devices. Two non-invasive blood pressure devices were evaluated using the simulator with its database of 243 waveforms, to assess the value of a simulator for such evaluations. METHODS: Two oscillometric non-invasive blood pressure devices, both of which had previously been validated against auscultatory references, were selected. The Omron HEM-907 (Omron, Hoofddorp, The Netherlands) measures the pressure during linear cuff deflation and the GE ProCare 400 (GE Healthcare, Tampa, Florida, USA) measures during step deflation. Each non-invasive blood pressure device was attached to the simulator and pressures were recorded from all 243 waveforms. The differences between the systolic and diastolic pressures measured by each non-invasive blood pressure device and the auscultatory references for each waveform were calculated. These were assessed with the European and American validation standards and with the British Hypertension Society protocol. RESULTS: The paired pressure differences (non-invasive blood pressure device minus auscultatory reference) for each device complied partly, but not fully, with the standards or protocol. The means (+/-standard deviation) of the paired systolic and diastolic pressures differences for the Omron were -2.4 mmHg (+/-5.9 mmHg) and -8.9 mmHg (+/-6.5 mmHg), and for the ProCare were -6.5 mmHg (+/-10.4 mmHg) and -2.9 mmHg (+/-7.0 mmHg), respectively. The pressures recorded by the Omron device met the standards for systolic pressures but failed for diastolic pressures and conversely for the ProCare. CONCLUSION: This represents the first evaluation of non-invasive blood pressure devices with a simulator that generates previously recorded clinical oscillometric waveforms. It allowed data from over 100 study participants to be used. Both devices had been previously clinically validated, but their evaluation using the simulator with its regenerated waveforms only partly met the required criteria. Although the results did not fully match previous clinical validations, these initial results give encouragement that a simulator with sufficient stored waveforms might be able to replace the difficult and expensive clinical evaluation of non-invasive blood pressure devices that has prevented many devices from being fully evaluated.

Adolescent↗

PubMed2006

Humoral and cellular immune responses in sheep immunized with a 22 kilodalton exported protein of Mycobacterium avium subspecies paratuberculosis.

An immunogenic 22 kilodalton exported Mycobacterium avium subspecies paratuberculosis (MAP) lipoprotein (P22) was previously identified, and found to belong to the LppX/LprAFG family of mycobacterial lipoproteins. N-terminal polyhistidine-tagged P22 was produced and purified from Escherichia coli. Antibody recognition of P22, and interferon-gamma (IFN-gamma) responses in vitro using blood from a sheep vaccinated with Neoparasec, confirmed its immunogenicity. To evaluate the immunogenicity of P22 in vivo, five sheep were immunized with a single dose containing 0.8 mg recombinant P22 protein in adjuvant. Blood was collected at 4, 13 and 29 weeks post-immunization (p.i.) and tested for anti-P22 antibodies and P22-specific IFN-gamma production. P22-specific antibodies were detected by Western blot analysis in all five Neoparasec-immunized sheep at the three time points. Three out of five P22-immunized sheep produced P22-specific antibodies for up to 13 weeks p.i., and two gave a response at 29 weeks p.i. Recombinant P22 was able to stimulate significant IFN-gamma production in blood of P22-immunized sheep at 13 and 29 weeks p.i. Recombinant P22 also elicited an IFN-gamma response in blood of sheep immunized with Neoparasec.

Adjuvants, Immunologic↗

PubMed2006

Comparison of atrial signal extraction algorithms in 12-lead ECGs with atrial fibrillation.

Analysis of atrial rhythm is important in the treatment and management of patients with atrial fibrillation. Several algorithms exist for extracting the atrial signal from the electrocardiogram (ECG) in atrial fibrillation, but there are few reports on how well these techniques are able to recover the atrial signal. We assessed and compared three algorithms for extracting the atrial signal from the 12-lead ECG. The 12-lead ECGs of 30 patients in atrial fibrillation were analyzed. Atrial activity was extracted by three algorithms, Spatiotemporal QRST cancellation (STC), principal component analysis (PCA), and independent component analysis (ICA). The amplitude and frequency characteristics of the extracted atrial signals were compared between algorithms and against reference data. Mean (standard deviation) amplitude of QRST segments of V1 was 0.99 (0.54) mV, compared to 0.18 (0.11) mV (STC), 0.19 (0.13) mV (PCA), and 0.29 (0.22) mV (ICA). Hence, for all algorithms there were significant reductions in the amplitude of the ventricular activity compared with that in V1. Reference atrial signal amplitude in V1 was 0.18 (0.11) mV, compared to 0.17 (0.10) mV (STC), 0.12 (0.09) mV (PCA), and 0.18 (0.13) mV (ICA) in the extracted atrial signals. PCA tended to attenuate the atrial signal in these segments. There were no significant differences for any of the algorithms when comparing the amplitude of the reference atrial signal with that of the extracted atrial signals in segments in which ventricular activity had been removed. There were no significant differences between algorithms in the frequency characteristics of the extracted atrial signals. There were discrepancies in amplitude and frequency characteristics of the atrial signal in only a few cases resulting from notable residual ventricular activity for PCA and ICA algorithms. In conclusion, the extracted atrial signals from these algorithms exhibit very similar amplitude and frequency characteristics. Users of these algorithms should be observant of residual ventricular activities which can affect the analysis of the fibrillatory waveform in clinical practice.

Algorithms↗

PubMed2006

A neuromorphic depth-from-motion vision model with STDP adaptation.

We propose a simplified depth-from-motion vision model based on leaky integrate-and-fire (LIF) neurons for edge detection and two-dimensional depth recovery. In the model, every LIF neuron is able to detect the irradiance edges passing through its receptive field in an optical flow field, and respond to the detection by firing a spike when the neuron's firing criterion is satisfied. If a neuron fires a spike, the time-of-travel of the spike-associated edge is transferred as the prediction information to the next synapse-linked neuron to determine its state. Correlations between input spikes and their timing thus encode depth in the visual field. The adaptation of synapses mediated by spike-timing-dependent plasticity is used to improve the algorithm's robustness against inaccuracy caused by spurious edge propagation. The algorithm is characterized on both artificial and real image sequences. The implementation of the algorithm in analog very large scale integrated (aVLSI) circuitry is also discussed.

Animals↗

PubMed2005

Thermography and colour duplex ultrasound assessments of arterio-venous fistula function in renal patients.

Vascular and clinical assessments of arterio-venous fistula (AVF) function and access are important in patients undergoing or preparing to undergo renal dialysis. Objective assessment techniques include colour duplex ultrasound and more recently medical infrared thermography. Ideally, these should help assess problems relating to fistula failure or to vascular steal from the hand which can result from excessive fistula blood flow. The clinical value of thermography, as yet, has not been assessed for this patient group. The aims of this study were therefore to investigate the relationships between thermography skin temperature measurement and (a) quantitative ultrasound measurement of AVF blood flow, and (b) qualitative clinical assessment of vascular steal from the hands. Fifteen adult patients underwent thermal imaging of the upper limbs, colour duplex ultrasound to derive AVF blood flow from brachial artery blood flow measurements, and a clinical evaluation for vascular steal. Temperature measurements were extracted from the thermograms, including bilateral arm and hand (Fistula -- Non-Fistula) differences, for comparison with derived AVF blood flow and steal grading. Derived AVF blood flow ranged from 30 to 1,950 ml min(-1), with a mean rate close to one litre per minute. Thermography detected the warmer superficial veins in proximity to the patent fistulas, with bilateral differences in fistula region skin temperature correlated with derived AVF blood flow (using maximum temperature measurements the correlation was +0.71 [p < 0.01]; and using mean temperature measurements the correlation was +0.56 [p < 0.05]). When thermography measurements were compared with the clinical assessment of steal the mean hand temperature differences separated steal from non-steal patients with an accuracy of greater than 90%. In summary, we have now demonstrated the potential clinical value of medical infrared thermography for assessing AVF function in renal patients.

Adult↗

PubMed2005

Photoplethysmography detection of lower limb peripheral arterial occlusive disease: a comparison of pulse timing, amplitude and shape characteristics.

The assessment and diagnosis of lower limb peripheral arterial occlusive disease (PAOD) is important since it can lead progressively to disabling claudication, ischaemic rest pain and gangrene. Historically, the first assessment has been palpation of the peripheral pulse since it can become damped, delayed and diminished with disease. In this study we investigated the clinical value of objective photoplethysmography (PPG) pulse measurements collected simultaneously from the right and left great toes to diagnose disease in the lower limbs. In total, 63 healthy subjects and 44 patients with suspected lower limb disease were studied. Pulse wave analysis techniques extracted timing, amplitude and shape characteristics for both toes and for right-to-left toe differences. Normative ranges of pulse characteristics were then calculated for the healthy subject group. The relative diagnostic values of the different pulse features for detecting lower limb arterial disease were determined, referenced to the established ankle-brachial pressure index (ABPI) measurement. The ranges of pulse characteristics and degree of bilateral similarity in healthy subjects were established, and the degrees of pulse delay, amplitude reduction, and damping and bilateral asymmetry were quantified for different grades of disease. When pulse timing, amplitude and shape features were ranked in order of diagnostic performance, the shape index (SI) gave substantial agreement with ABPI (>90% accuracy, kappa 0.75). SI also detected higher grade disease, for legs with an ABPI less than 0.5, with a sensitivity of 100%. The simple-to-calculate timing differences between pulse peaks produced a diagnostic accuracy of 88% for all grades of arterial disease (kappa 0.70), and 93% for higher grade disease (kappa 0.77). These contrasted with the limited discriminatory value of PPG pulse amplitude. The low-cost and simplicity of this optical-based technology could offer significant benefits to healthcare, such as in primary care where non-invasive, accurate and simple-to-use (de-skilled) diagnostic techniques are desirable.

Adult↗

PubMed2005

Autonomic function is impaired in elderly stroke survivors.

BACKGROUND AND PURPOSE: Impaired autonomic function is common in the acute poststroke phase but little is known about the longer term effects, particularly in older people. We sought to determine if autonomic function is impaired after stroke recovery in older patients. METHODS: A cross-sectional case-control study comparing autonomic function in 76 nondemented stroke patients with 70 community-living controls aged older than 75 years. RESULTS: Cases were assessed on average 9 months after stroke. From power spectral analysis of heart rate variability, stroke patients had lower total (P=0.032) and low-frequency (P=0.014) spectral densities and impaired baroreflex sensitivity (alpha low-frequency baroreflex sensitivity, P=0.006). From a series of cardiovascular autonomic reflex tests, heart rate variation during forced respiration, Valsalva ratio, and blood pressure overshoot during Valsalva maneuver were significantly lower in stroke patients (P=0.003, <0.001, and 0.027, respectively). Blood pressure response to isometric exercise was significantly exaggerated in stroke patients (P=0.007). CONCLUSIONS: Cardiovascular autonomic function is impaired long after the index event in stroke survivors. Impaired autonomic function may increase the risk of all-cause mortality and cardiovascular mortality in older stroke survivors.

Aged↗

PubMed2005

Recommendations for blood pressure measuring devices for office/clinic use in low resource settings.

This paper, which summarizes the conclusions of a WHO Expert meeting, is aimed at proposing indications to develop technical specifications for an accurate and affordable blood pressure measuring device for office/clinic use in low resource settings. Blood pressure measuring devices to be used in low resource settings should be accurate, affordable, and easily available worldwide. Given the serious inherent inaccuracy of the auscultatory technique, validated and affordable electronic devices, that have the option to select manual readings, seem to be a suitable solution for low resource settings. The agreement on the technical specifications for automated blood pressure measuring devices for office/clinic use in low resource settings included the following features: high accuracy, adoption of electronic transducers and solar batteries for power supply, standard rates of cuff inflation and deflation, adequate cuff size, digital display powered by solar batteries, facilities for adequate calibration, environmental requirements, no need of memory function, resistance to shock and temperature changes, and low cost. Availability of a device with these features should be accompanied by adequate training of health care personnel, who should guarantee implementation of the procedures recommended in recent European and American Guidelines for accurate blood pressure measurement.

Blood Pressure Determination↗

PubMed2005

Automated non-invasive blood pressure devices: are they suitable for use?

OBJECTIVES: Measurement of blood pressure by a trained observer using a mercury sphygmomanometer is accepted as the gold standard, but there has been an increase in the use of automated devices employing the oscillometric technique. Not all such devices have been clinically validated, and some do not carry an appropriate CE mark. This survey aimed to assess the state of the European Union market for automated non-invasive blood pressure devices in terms of information provided by companies relating to compliance, validation and intended use. METHODS: A total of 116 companies were identified as being potentially active (i.e. manufacturer, supplier, agent or distributor). Of these, 110 that could be contacted were asked to provide details of their company and their non-invasive blood pressure products via a questionnaire. RESULTS: Eighty-six companies were found to be actively involved in the supply of 158 different models of automated non-invasive blood pressure device. These included 54 devices for use on the arm and 62 for use on the wrist (total 116 in our main categories), and 42 others (ambulatory monitors, patient monitors, defibrillators or finger devices). We received responses for 61% (71/116) of the main category arm and wrist devices and 80% (57/71) of these provided claims for CE marking. Of the CE marked devices for which we received a response, 41% (12/29) of arm devices and 39% (11/28) of wrist devices claimed some form of clinical validation, or evidence was found subsequent to the survey. Of these claims, 65% (15/23) related to an earlier, or similar, product and 48% (11/23) were based on published studies. Inconsistencies were found between claims for diagnostic suitability and claims for clinical validation. CONCLUSIONS: A majority of models available on the European Union market were not validated by clinical trial to one of the recognized protocols.

Automation↗

PubMed2005

Identification and characterization of an immunogenic 22 kDa exported protein of Mycobacterium avium subspecies paratuberculosis.

An exported 22 kDa putative lipoprotein was identified in an alkaline phosphatase gene fusion library of Mycobacterium avium subsp. paratuberculosis and expressed in Mycobacterium smegmatis. The full nucleic acid sequence of the gene encoding P22 was determined and the ORF was cloned into a mycobacterial expression vector, enabling full-length P22 to be produced as a C-terminal polyhistidine-tagged protein in M. smegmatis. N-terminal sequencing of the recombinant protein confirmed cleavage of a signal sequence. Native P22 was detected in culture supernatants and cell sonicates of M. avium subsp. paratuberculosis strain 316F using rabbit antibody raised to recombinant P22. Investigation of the presence of similar genes in other mycobacterial species revealed that the gene was present in Mycobacterium avium subsp. avium and similar genes existed in Mycobacterium intracellulare and Mycobacterium scrofulaceum. Database searches showed that P22 belonged to the LppX/LprAFG family of mycobacterial lipoproteins also found in Mycobacterium leprae and in members of the Mycobacterium tuberculosis complex. P22 shared less than 75% identity to these proteins. Recombinant P22 was able to elicit interferon-gamma secretion in blood from eight of a group of nine sheep vaccinated with a live attenuated strain of M. avium subsp. paratuberculosis (strain 316F) compared to none from a group of five unvaccinated sheep. Antibody to P22 was detected by Western blot analysis in 10 out of 11 vaccinated sheep, in two out of two clinically affected cows and in 11 out of 13 subclinically infected cows.

Animals↗

PubMed2005

Investigations into the influence of host genetics on the predominant eubacteria in the faecal microflora of children.

The eubacterial population was studied in faecal samples of related and unrelated children. Temporal temperature gradient gel electrophoresis (TTGE) provided a snapshot of the bacterial population and allowed calculation of the degree of similarity in the predominant faecal microflora of identical twin pairs, fraternal twin pairs and unrelated paired controls. The highest levels of similarity were found in genetically identical twins. Significant differences were observed between the identical and fraternal twins (P = 0.037), strongly suggesting a genetic influence over the composition of the faecal microflora. The unrelated control group had the lowest similarity and was significantly different from the twins (P = 0.001). The results of this study indicate that host genetics influence the composition of the dominant eubacterial population in children.

Bacteria↗

PubMed2005

Effects of external pressure on arteries distal to the cuff during sphygmomanometry.

The aim of this study was to examine the effect on distal arteries of external pressure, applied by upper arm sphygmomanometer cuff. Photoplethysmographic (PPG) signals were measured on the index fingers of 44 healthy male subjects, during the slow decrease of cuff air pressure. For each pulse the ratio of PPG amplitude to its baseline (AM/BL) and its time delay (deltaTD) relative to the contralateral hand were determined as a function of cuff pressure. At cuff pressures equal to systolic blood pressure, pulses reappeared with the pulse time delay in the cuffed arm significantly greater than in the noncuffed arm, with (deltaTD) (mean +/- SD) 150 +/- 31 ms (p < 0.001). At cuff pressures equal to diastolic blood pressure (81 +/- 12 mmHg), deltaTD was 42 +/- 19 ms (p < 0.001), and at 50 mmHg, which is below diastolic blood pressure, (deltaTD) was still significantly positive at 6 +/- 9 ms (p < 0.001). AM/BL relative to its initial value rose at cuff pressures between systolic and diastolic blood pressure, then deceased to 0.6 +/- 0.41 (p < 0.001) at diastolic blood pressure and 0.54 +/- 0.24 (p < 0.001) at 50 mmHg. The changes in (deltaTD) and AM/BL can be interpreted as originating from changes in the compliance of conduit arteries and small arteries with cuff inflation and deflation.

Adolescent↗

PubMed2005

Spike timing dependent plasticity (STDP) can ameliorate process variations in neuromorphic VLSI.

A transient-detecting very large scale integration (VLSI) pixel is described, suitable for use in a visual-processing, depth-recovery algorithm based upon spike timing. A small array of pixels is coupled to an adaptive system, based upon spike timing dependent plasticity (STDP), that aims to reduce the effect of VLSI process variations on the algorithm's performance. Results from 0.35 microm CMOS temporal differentiating pixels and STDP circuits show that the system is capable of adapting to substantially reduce the effects of process variations without interrupting the algorithm's natural processes. The concept is generic to all spike timing driven processing algorithms in a VLSI.

Action Potentials↗

PubMed2005

Surface atrial frequency analysis in patients with atrial fibrillation: assessing the effects of linear left atrial ablation.

INTRODUCTION: Our group has shown previously that measurements of atrial frequency can be obtained from surface 12-lead ECG recordings of patients during atrial fibrillation (AF), using a combination of principal component and Fourier transform algorithms. Such measurements are reproducible over time and change with drug manipulation of the arrhythmia. AIMS: To determine whether linear left atrial ablation, using a combination of "roof" and "mitral isthmus" lines results in changes in surface atrial frequency during AF and to assess the contribution of each individual line when sited sequentially. METHODS AND RESULTS: Computerized recordings from 26 patients, who had undergone linear ablation procedures for AF, were reviewed. The atrial signal was extracted from the 12-lead ECG data by principal component analysis and the main frequency component identified using Fourier analysis. Atrial frequency before and after these two standard ablation lines was compared. Atrial frequency decreased significantly after the combination of roof and mitral isthmus lines (5.66 vs 5.15 Hz) and when either roof (5.61 vs 5.13 Hz) or mitral isthmus (5.89 vs 5.75 Hz) lines were sited first. However, only the roof line led to a significant reduction in atrial frequency when sited second (5.64 vs 5.49 Hz). CONCLUSIONS: Measurements of atrial frequency can be obtained from surface 12-lead ECG recordings during AF and change as predicted in response to linear left atrial ablation. This technique may be useful in assessing antiarrhythmic treatments for AF.

Adult↗

PubMed2004

Endoscopic cauterization of fourth branchial cleft sinus tracts.

OBJECTIVE: To evaluate the effectiveness of endoscopic cauterization as definitive treatment for fourth branchial cleft sinuses. DESIGN: Retrospective chart review with follow-up questionnaire. SETTING: Tertiary care children's hospital. PATIENTS: Ten children (age range, 10 months to 10 years) with fourth branchial cleft sinuses treated with endoscopic cauterization between 1995 and 2002. MAIN OUTCOME MEASURE: Recurrence of neck infections after endoscopic cauterization of fourth brachial cleft sinus tracts. RESULTS: Seven of the 10 patients treated with endoscopic cauterization of the fourth branchial cleft sinuses showed no recurrence with an average follow-up of 3 years. Three of the patients were unavailable for follow-up, but medical records of the hospital showed no additional admissions for those patients for neck masses. No morbidity of the procedure was identified. All patients were discharged the day of surgery. CONCLUSIONS: Endoscopic cauterization of fourth branchial cleft sinuses appears to be an effective alternative to open excision.

Branchial Region↗

PubMed2004

Interaction between cardiac beat-to-beat interval changes and systolic blood pressure changes.

This study assessed the interaction between cardiac beat-to-beat interval changes and systolic pressure (SP) changes. Twenty subjects breathed regularly following displayed breathing signals at 4, 6, 8, 10, 12 and 14 breaths per minute, each for 5 minutes. ECG, non-invasive blood pressure (Finapres) and respiration waveforms were recorded. Time offsets between the cyclic patterns of RR-interval and SP changes were calculated. Displayed breathing signals were well followed; the mean correlation between displayed and recorded breathing signals ranged from 0.72 to 0.86. The time offset between RR-interval peaks and subsequent SP troughs decreased with increasing respiration rate, 3.8 +/- 1.7 s, 3.5 +/- 0.7 s, 3.1 +/- 0.6 s, 2.6 +/- 0.4 s, 2.3 +/- 0.4 s and 2.0 +/- 0.4 s mean +/- SD at 4, 6, 8, 10, 12 and 14 breaths per minute respectively. The relationship between mean time offset and frequency was significant (p < 0.001), with a 95% prediction interval of +/- 0.24 s. Published data showed no relationship between time offset and frequency, with a 95% prediction interval of +/- 2.8 s. However, when the offset definition proposed in this research was applied to these data, a significant relationship (p < 0.01) was evident, with a 95% prediction interval of +/- 1.5 s. In conclusion, apparently contradictory previous findings achieve good consensus when a standardized method for presenting results is applied. A delay exists between RR-interval and blood pressure changes, and this delay varies with breathing frequency.

Adult↗