Lung and chest wall mechanics in ventilated patients with end stage idiopathic pulmonary fibrosis. (17/3966)

BACKGROUND: Idiopathic pulmonary fibrosis is an inflammatory disease which leads to chronic ventilatory insufficiency and is characterised by a reduction in pulmonary static and dynamic volumes. It has been suggested that lung elastance may also be abnormally increased, particularly in end stage disease, but this has not been systematically tested. The aim of this study was to assess the respiratory mechanics during mechanical ventilation in patients affected by end stage disease. METHODS: Respiratory mechanics were monitored in seven patients with idiopathic pulmonary fibrosis being ventilated for acute respiratory failure (PaO2/FiO2 5.8 (0.3); pH 7. 28 (0.02); PaCO2 8.44 (0.82) kPa; tidal volume 3.4 (0.2) ml/kg; respiratory rate 35.1 (8.8) breaths/min) using an oesophageal balloon and airway occlusion during constant flow inflation. The total respiratory system mechanics (rs) was partitioned into lung (L) and chest wall (w) mechanics to measure static intrinsic positive end expiratory pressure (PEEPi), static (Est) and dynamic (Edyn) elastances, total respiratory resistance (Rrs), interrupter respiratory resistance (Rint,rs), and additional respiratory resistance (DeltaRrs). RESULTS: PEEPi was negligible in all patients. Edyn,rs and Est,rs were markedly increased (60.9 (7.3) and 51.9 (8. 0) cm H2O/l, respectively), and this was due to abnormal lung elastance (dynamic 53.9 (8.0) cm H2O/l, static 46.1 (8.1) cm H2O/l) while chest wall elastance was only slightly increased. Rrs and Rint, rs were also increased above the normal range (16.7 (4.5) and 13.7 (3.5) cm H2O/l/s, respectively). RL and Rint,L contributed 88% and 89%, on average, to the total. Edyn,rs, Est,rs, Rrs and Rint,rs were significantly correlated with the degree of hypercapnia (r = 0.64 (p<0.01), r = 0.54 (p<0.05), r = 0.84 (p<0.001), and r = 0.72 (p<0. 001), respectively). CONCLUSIONS: The elastances and resistances of the respiratory system are significantly altered in ventilated patients with end stage idiopathic pulmonary fibrosis. These features are almost totally due to abnormalities in lung mechanics. These profound alterations in elastic and resistive mechanical properties at this stage of the disease may be responsible for the onset of hypercapnia.  (+info)

Pulmonary and caval flow dynamics after total cavopulmonary connection. (18/3966)

OBJECTIVE: To assess flow dynamics after total cavopulmonary connection (TCPC). DESIGN: Cross-sectional study. SETTING: Aarhus University Hospital. PATIENTS: Seven patients (mean age 9 (4-18) years) who had previously undergone a lateral tunnel TCPC mean 2 (0. 3-5) years earlier. INTERVENTIONS: Pressure recordings (cardiac catheterisation), flow volume, and temporal changes of flow in the lateral tunnel, superior vena cava, and right and left pulmonary arteries (magnetic resonance velocity mapping). RESULTS: Superior vena cava flow was similar to lateral tunnel flow (1.7 (0.6-1.9) v 1. 3 (0.9-2.4) l/min*m2) (NS), and right pulmonary artery flow was higher than left pulmonary artery flow (1.7 (0.6-4.3) v 1.1 (0.8-2. 5) l/min*m2, p < 0.05). The flow pulsatility index was highest in the lateral tunnel (2.0 (1.1-8.5)), lowest in the superior vena cava (0.8 (0.5-2.4)), and intermediate in the left and right pulmonary arteries (1.6 (0.9-2.0) and 1.2 (0.4-1.9), respectively). Flow and pressure waveforms were biphasic with maxima in atrial systole and late ventricular systole. CONCLUSIONS: Following a standard lateral tunnel TCPC, flow returning via the superior vena cava is not lower than flow returning via the inferior vena cava as otherwise seen in healthy subjects; flow distribution to the pulmonary arteries is optimal; and some pulsatility is preserved primarily in the lateral tunnel and the corresponding pulmonary artery. This study provides in vivo data for future in vitro and computer model studies.  (+info)

Analysis of endotoxin effects on the intact pulmonary circulation. (19/3966)

OBJECTIVE: The mechanism of sustained alterations in pulmonary hemodynamics during endotoxin shock remains unclear. To gain more detailed knowledge we used the four-element windkessel model as a descriptor of the pulmonary circuit. METHODS: Consecutive changes in characteristic resistance (R1), vascular compliance (C), input resistance (R2) and inductance (L) were continuously assessed following injection of endotoxin in 6 anaesthetised pigs, and were compared with the corresponding values measured in a similar group of sham-operated animals. RESULTS: Endotoxin challenge resulted in a biphasic pulmonary artery pressure response. Blood flow decreased progressively from 2.8 +/- 0.2 l/min to 2 +/- 0.2 l/min. Ohmic pulmonary vascular resistance (PVR) increased gradually from 0.2 +/- 0.04 to 0.76 +/- 0.1 mm Hg s ml-1. The early increase in PAP (from 14 +/- 2 to 27 +/- 4 mm Hg) was mediated by changes in both R1 (from 0.04 +/- 0.01 to 0.06 +/- 0.01 mm Hg s ml-1) and R2 (from 0.16 +/- 0.04 to 0.61 +/- 0.2 mm Hg s ml-1). These responses, in turn, altered the proximal vascular compliance. A subsequent increase in PAP (from 27 +/- 2 to 32 +/- 3 mm Hg) paralleled the specific decline in distal pulmonary vasculature compliance from 0.84 +/- 0.1 to 0.65 +/- 0.1 ml/mmHg. Analysis of the time course of PVR did not allow us to distinguish between vasoconstriction and stiffening of the vascular tree as mechanisms accounting for PAP changes. CONCLUSIONS: Endotoxemia leads to pulmonary hypertension, which is a result of constriction of proximal pulmonary arteries during the early phase, whereas the late phase is characterised by a decline in distal pulmonary vasculature compliance.  (+info)

Dissociation between microneurographic and heart rate variability estimates of sympathetic tone in normal subjects and patients with heart failure. (20/3966)

The concept that spectral analysis of heart rate variability (HRV) can estimate cardiac sympathetic nerve traffic in subjects with both normal and impaired left ventricular systolic function has not been validated against muscle sympathetic nerve activity (MSNA). We used coarse-graining spectral analysis to quantify the harmonic and non-harmonic, or fractal, components of HRV and to determine low-frequency (0.0-0.15 Hz; PL) and high-frequency (0.15-0.5Hz; PH) harmonic power. To test the hypothesis that MSNA and HRV representations of sympathetic nerve activity (PL and PL/PH) increase in parallel in heart failure, we recorded heart rate and MSNA during supine rest in 35 patients (age 52.4+/-2 years; mean+/-S. E.M.), with a mean left ventricular ejection fraction of 22+/-2%, and in 34 age-matched normal subjects. Power density was log10 transformed. Mean MSNA was 52.9+/-2.6 bursts/min in heart failure patients and 34.9+/-1.9 bursts/min in normal subjects (P<0.0001). In normal subjects, but not in heart failure patients, total power (PT) (r=-0.41; P=0.02) and fractal power (PF) (r=-0.36; P=0.04) were inversely related to age. In heart failure patients, total and fractal power were reduced (P<0.009 for both), and were inversely related to MSNA burst frequency (r=-0.55, P=0.001 and r=-0.60, P=0. 0003 respectively). In normal subjects, there was no relationship between MSNA and either PL or PH. In heart failure patients, as anticipated, PH was inversely related to MSNA (r=-0.41; P<0.02). However, PL was also inversely rather than directly related to MSNA (r=0.44 for 1/log10 PL; P<0.01). There was no relationship between other sympathetic (PL/PH) or parasympathetic (PH/PT) indices and MSNA in either heart failure patients or normal subjects. The lack of concordance between these direct and indirect estimates of sympathetic nervous system activity indicates that this component of HRV cannot be used for between-subject comparisons of central sympathetic nervous outflow. It is the absence of low-frequency power that relates most closely to sympathetic activation in heart failure.  (+info)

Mapping and ablation of ventricular tachycardia with the aid of a non-contact mapping system. (21/3966)

OBJECTIVE: Treatment of ventricular tachycardia (VT) in coronary heart disease has to date been limited to palliative treatment with drugs or implantable defibrillators. The results of curative treatment with catheter ablation have proved disappointing because the complexity of the VT mechanism makes identification of the substrate using conventional mapping techniques difficult. The use of a mapping technology that may address some of these issues, and thus make possible a cure for VT with catheter ablation, is reported. PATIENTS AND INTERVENTION: The non-contact system, consisting of a multielectrode array catheter (MEA) and a computer mapping system, was used to map VT in 24 patients. Twenty two patients had structural heart disease, the remainder having "normal" left ventricles with either fasicular tachycardia or left ventricular ectopic tachycardia. RESULTS: Exit sites were demonstrated in 80 of 81 VT morphologies by the non-contact system, and complete VT circuits were traced in 17. In another 37 morphologies of VT 36 (30)% (mean (SD)) of the diastolic interval was identified. Thirty eight VT morphologies were ablated using 154 radiofrequency energy applications. Successful ablation was achieved by 77% of radiofrequency within diastolic activation identified by the non-contact system and was significantly more likely to ablate VT than radiofrequency at the VT exit, or remote from diastolic activation. Over a mean follow up of 1.5 years, 14 patients have had no recurrence of VT and only two target VTs have recurred. Five patients have had recurrence of either slower non-sustained, undocumented or fast non-target VT. Five patients have died, one from tamponade from a pre-existing temporary pacing wire, and four from causes unrelated to the procedure. CONCLUSION: The non-contact system can safely be used to map and ablate haemodynamically stable VT with low VT recurrence rates. It is yet to be established whether this system may be applied with equal success to patients with haemodynamically unstable VT.  (+info)

The spatial tuning of color and luminance peripheral vision measured with notch filtered noise masking. (22/3966)

We have measured the spatial bandwidths of the bandpass red-green chromatic and luminance mechanisms at four locations in the nasal visual field (0, 10, 20 and 30 degrees) using a method of notch filtered noise masking which effectively removes the artifact of off-frequency looking for our stimuli. Detection thresholds were measured for luminance or isoluminant red-green Gaussian enveloped test gratings of 0.5 cpd embedded in 1/f noise. Firstly, thresholds were obtained as a function of increasing noise spectral density and were fitted using a standard noise masking model. These results support the existence across the visual field of independent, red-green chromatic and luminance mechanisms with similar sampling efficiencies. Secondly, we measured thresholds in notch filtered noise as a function of notch width and derived the spatial bandwidth of the detection mechanism. We find both color and luminance mechanisms have similar bandwidths which remain virtually constant across eccentricity. These results indicate strong overall similarities between the early processing of color and luminance vision, and lend support to the role of color as an 'intrinsic image' in spatial vision. The results are discussed in the light of the anchored channel and shifting channel models of peripheral contrast sensitivity and pattern detection.  (+info)

A comparison of wavelet and Joint Photographic Experts Group lossy compression methods applied to medical images. (23/3966)

This presentation focuses on the quantitative comparison of three lossy compression methods applied to a variety of 12-bit medical images. One Joint Photographic Exports Group (JPEG) and two wavelet algorithms were used on a population of 60 images. The medical images were obtained in Digital Imaging and Communications in Medicine (DICOM) file format and ranged in matrix size from 256 x 256 (magnetic resonance [MR]) to 2,560 x 2,048 (computed radiography [CR], digital radiography [DR], etc). The algorithms were applied to each image at multiple levels of compression such that comparable compressed file sizes were obtained at each level. Each compressed image was then decompressed and quantitative analysis was performed to compare each compressed-then-decompressed image with its corresponding original image. The statistical measures computed were sum of absolute differences, sum of squared differences, and peak signal-to-noise ratio (PSNR). Our results verify other research studies which show that wavelet compression yields better compression quality at constant compressed file sizes compared with JPEG. The DICOM standard does not yet include wavelet as a recognized lossy compression standard. For implementers and users to adopt wavelet technology as part of their image management and communication installations, there has to be significant differences in quality and compressibility compared with JPEG to justify expensive software licenses and the introduction of proprietary elements in the standard. Our study shows that different wavelet implementations vary in their capacity to differentiate themselves from the old, established lossy JPEG.  (+info)

Alterations of autonomic nervous activity in recurrence of variant angina. (24/3966)

OBJECTIVE: To investigate whether autonomic nervous activity is involved in the recurrence of spontaneous coronary spasm in variant angina. DESIGN: Retrospective analysis. SETTING: Cardiology department of a university hospital. PATIENTS: 18 patients with variant angina were divided into single attack group (SA; nine patients) and multiple attack group (MA; nine patients) according to the frequency of ischaemic episodes with ST segment elevation during 24 hour Holter monitoring. METHODS: Heart rate variability indices were calculated using MemCalc method, which is a combination of the maximum entropy method for spectral analysis and the non-linear least squares method for fitting analysis, at 30 second intervals for 30 second periods, from 40 minutes before the attack to 30 minutes after the attack. High frequency (HF; 0.04-0.15 Hz) was defined as a marker of parasympathetic activity, and the ratio of low frequency (LF; 0.15-0.40 Hz) to high frequency (LF/HF) as an indicator of sympathetic activity. The averaged value during the 40 to 30 minute period before an attack was defined as the baseline. RESULTS: Compared with baseline, the HF component decreased in both groups at two minutes before the attack (p < 0.01), and the LF/HF ratio decreased at three minutes before the attack (p < 0.01). The baseline LF/HF was lower in the MA group than in the SA group (p < 0. 01). CONCLUSIONS: A reduction of sympathetic activity may play a key role in determining the recurrence of transient ischaemic events caused by spontaneous coronary spasm in patients with variant angina.  (+info)