About objective 3-d analysis of airway geometry in computerized tomography.

The technology of multislice X-ray computed tomography (MSCT) provides volume data sets with approximately isotropic resolution, which permits a noninvasive 3-D measurement and quantification of airway geometry. In different diseases, like emphysema, chronic obstructive pulmonary disease (COPD), or cystic fribrosis, changes in lung parenchyma are associated with an increase in airway wall thickness. In this paper, we describe an objective measuring method of the airway geometry in the 3-D space. The limited spatial resolution of clinical CT scanners in comparison to thin structures like airway walls causes difficulties in the measurement of the density and the thickness of these structures. Initially, these difficulties will be addressed and then a new method is introduced to circumvent the problems. Therefore the wall thickness is approximated by an integral based closed-form solution, based on the volume conservation property of convolution. We evaluated the method with a phantom containing 10 silicone tubes and proved the repeatability in datasets of eight pigs scanned twice. Furthermore, a comparison of CT datasets of 16 smokers and 15 nonsmokers was done. Further medical studies are ongoing.

CT-guided vertebroplasty in osteoprotic vertebral fractures: incidence of secondary fractures and impact of intradiscal cement leakages during follow-up.

The purpose of this study was to analyse the number and types of secondary fractures, and to investigate the impact of intradiscal cement leaks for adjacent vertebral fractures. Patients with osteoporotic vertebral fractures were treated with vertebroplasty. Results were documented and prospectively followed by means of computed tomography (CT) and magnetic resonance imaging. The frequency and the types of cement leakages were analysed from multiplanar CT images and secondary fractures were characterised as follows: (1) adjacent fracture in the immediate vicinity of an augmented vertebra; (2) sandwich fracture, fracture of an untreated vertebra between two vertebrae that had been previously augmented, and (3) distant fractures not in the vicinity of augmented vertebrae. A total of 385 osteoporotic vertebral fractures were treated in 191 patients (61 men, 130 women, age 70.7 +/- 9.7 years). The overall rate of cement leaks was 55.6%, including all leaks detectable by CT. Intradiscal leaks through the upper, the lower, and both endplates occurred in 18.2%, 6.8%, and 2.6%, respectively. In 39 patients (20.4%), a total of 72 secondary fractures occurred: 30 adjacent fractures in 23 patients (12.0%) with a time to fracture of 2 months [median; 1.0/4.0 months, first/third quartile (Q1/Q3)]; 11 secondary sandwich fractures in 11 patients (5.8%) after 1.5 months (median; 0.25/7.5 months, Q1/Q3); and 31 distant fractures in 20 patients (10.5%) after 5 months (median; 2.0/8.0 months, Q1/Q3). Ten of 30 adjacent fractures occurred in the presence of pre-existing intradiscal cement leaks and 20 where there was no leakage. Six of 11 sandwich fractures occurred in the presence of intradiscal leaks (five leaks in both adjacent disc spaces, one leak in the lower disc space) and five where there was no leakage. The rate of secondary adjacent and non-adjacent fractures is quite similar and there is no specific impact of intradiscal leakages on the occurrence of adjacent secondary fractures. Adjacent fractures occur sooner than distant secondary fractures. Sandwich fractures are associated with specific biomechanical conditions, with a 37.9% fracture rate in sandwich constellations.

Quantification of atelectatic lung volumes in two different porcine models of ARDS.

BACKGROUND: Cyclic recruitment during mechanical ventilation contributes to ventilator associated lung injury. Two different pathomechanisms in acute respiratory distress syndrome (ARDS) are currently discussed: alveolar collapse vs persistent flooding of small airways and alveoli. We compare two different ARDS animal models by computed tomography (CT) to describe different recruitment and derecruitment mechanisms at different airway pressures: (i) lavage-ARDS, favouring alveolar collapse by surfactant depletion; and (ii) oleic acid ARDS, favouring alveolar flooding by capillary leakage. METHODS: In 12 pigs [25 (1) kg], ARDS was randomly induced, either by saline lung lavage or oleic acid (OA) injection, and 3 animals served as controls. A respiratory breathhold manoeuvre without spontaneous breathing at different continuous positive airway pressure (CPAP) was applied in random order (CPAP levels of 5, 10, 15, 30, 35 and 50 cm H(2)O) and spiral-CT scans of the total lung were acquired at each CPAP level (slice thickness=1 mm). In each spiral-CT the volume of total lung parenchyma, tissue, gas, non-aerated, well-aerated, poorly aerated, and over-aerated lung was calculated. RESULTS: In both ARDS models non-aerated lung volume decreased significantly from CPAP 5 to CPAP 50 [oleic acid lung injury (OAI): 346.9 (80.1) to 96.4 (48.8) ml, P<0.001; lavage-ARDS: 245 17.6) to 42.7 (4.8) ml, P<0.001]. In lavage-ARDS poorly aerated lung volume decreased at higher CPAP levels [232 (45.2) at CPAP 10 to 84 (19.4) ml at CPAP 50, P<0.001] whereas in OAI poorly aerated lung volume did not vary at different airway pressures. CONCLUSIONS: In both ARDS models well-aerated and non-aerated lung volume respond to different CPAP levels in a comparable fashion: Thus, a cyclical alveolar collapse seems to be part of the derecruitment process also in the OA-ARDS. In OA-ARDS, the increase in poorly aerated lung volume reflects the specific initial lesion, that is capillary leakage with interstitial and alveolar oedema.

[Analysis of the static pressure volume curve of the lung in experimentally induced pulmonary damage by CT-densitometry]. / CT-Densitometrie zur Analyse der statischen Druckvolumenkurve der Lunge bei experimentell induziertem Lungenschaden.

PURPOSE: To study quantitative changes of lung density distributions when recording in- and expiratory static pressure-volume curves by single slice computed tomography (CT). MATERIALS AND METHODS: Static in- and expiratory pressure volume curves (0 to 1000 ml, increments of 100 ml) were obtained in random order in 10 pigs after induction of lung damage by saline lavage. Simultaneously, CT acquisitions (slice thickness 1 mm, temporal increment 2 s) were performed in a single slice (3 cm below the carina). In each CT image lung segmentation and planimetry of defined density ranges were achieved. The lung density ranges were defined as: hyperinflated (-1024 to -910 HU), normal aerated (-910 to -600 HU), poorly aerated (-600 to -300 HU), and non aerated (-300 to 200 HU) lung. Fractional areas of defined density ranges in percentage of total lung area were compared to recorded volume increments and airway pressures (atmospheric pressure, lower inflection point (LIP), LIP*0.5, LIP*1.5, peak airway pressure) of in- and expiratory pressure-volume curves. RESULTS: Quantitative analysis of defined density ranges showed no differences between in- and expiratory pressure-volume curves. The amount of poorly aerated lung decreased and normal aerated lung increased constantly when airway pressure and volume were increased during inspiratory pressure-volume curves and vice versa during expiratory pressure-volume loops. CONCLUSION: Recruitment and derecruitment of lung atelectasis during registration of static in- and expiratory pressure-volume loops occurred constantly, but not in a stepwise manner. CT was shown to be an appropriate method to analyse these recruitment process.

[Quantification of atelectases in artificial respiration: spiral-CT versus dynamic single-slice CT]. / Quantifizierung von Atelektasen bei kontrollierter Beatmung: Spiral-CT versus dynamische Einzelschicht-CT.

PURPOSE: Dynamic CT (dCT) allows visualization and quantification of ventilated lung and atelectases with high temporal resolution during continuous ventilation. This study compares a quantitative image analysis in a subcarinal single slice dCT series versus a whole lung spiral-CT, in order to analyze, whether the distribution of atelectasis of a single dCT series is representative for the whole lung. MATERIALS AND METHODS: dCT in sliding windows technique (slice thickness 1 mm, temporal increment 100 ms) was performed in 8 healthy pigs 3 cm caudal to the carina during continuous mechanical ventilation. Subsequently, a spiral-CT of the whole lung (slice thickness 2 mm; pitch 1.5; increment 2 mm) was acquired during inspiratory breath hold (airway pressure 20 mbar). Lung segmentation and planimetry of predefined density ranges were achieved using a dedicated software tool in both data-sets. Thus, the fractions of the following functional lung compartments were averaged over time: hyperinflated lung (- 1024 to - 910 HE), normal ventilated lung -900 to -300 HE) and atelectasis (-300 to +200 HE). RESULTS: Quantitative analysis of dCT-series during continuous respiration correlated with the density analysis in spiral-CT as follows: hyperinflated lung r = 0.56; normal ventilated lung r = 0.83 and atelectases r = 0.84. Analysis of spiral-CT showed the following distribution of functional lung compartments: hyperinflated lung 3.1% normal ventilated lung 77.9% and atelectasis 19.0%. In dCT, hyperinflated lung represented 6.4%, normal ventilated lung 65.2% and atelectasis 28.4% of total the lung area. CONCLUSION: The results of our study demonstrate that dCT allows monitoring of atelectasis formation in response to different ventilatory strategies. However, a deviation between dCT and spiral-CT has to be taken into account. In subcarinal dCT series, hyperinflated lung areas and atelectases were overestimated due to a craniocaudal gradient of atelectases, whereas normal ventilated lung was underestimated.

The calcium sensitizer EMD 53998 antagonizes phosphate-induced increases in energy cost of isometric tension in cardiac skinned fibres.

We have investigated whether a Ca(2+)-sensitizing substance, the thiadiazinone derivative EMD 53998, can alter the ratio of ATPase activity to force, i.e. the tension cost in skinned fibres of swine cardiac trabecula in which the tension cost was increased by inorganic phosphate. In the presence of 10 mM inorganic phosphate (Pi) and thapsigargin 20 microM, EMD 53998 reduced the energy cost of isometric tension over the entire range of activating Ca2+ concentrations, resulting in a consistent change in slope (approximately 20% decrease) of the ATPase/force relation. We confirmed that in the absence of added phosphate and at maximal Ca2+ activation EMD 53998 had little if any effect on tension cost. We had previously reported that the effects of EMD 53998 and Pi on calcium sensitivity and maximum isometric tension are mutually antagonistic and our new energy data now support the proposal that EMD 53998 functionally antagonizes the effects of Pi on crossbridges. The decrease in the slope of the relation between ATPase and force caused by EMD 53998 may be interpreted to reflect either a decrease in the rate of 'detachment' (g(app)) of crossbridges or an increase in average force per crossbridge, as predicted by classical crossbridge models. Since the Pi release step of the crossbridge cycle is associated with the rate of 'attachment' (f(app)) rather than g(app), we conclude that the decrease in tension cost with EMD 53998 most likely reflects an increased force per crossbridge.(ABSTRACT TRUNCATED AT 250 WORDS)

Troponin replacement in permeabilized cardiac muscle. Reversible extraction of troponin I by incubation with vanadate.

Calcium-dependent regulation of tension and ATPase activity in permeabilized porcine ventricular muscle was lost after incubation with 10 mM vanadate. After transfer from vanadate to a vanadate-free, low-Ca2+ solution (pCa greater than 8), the permeabilized muscle produced 84.8% +/- 20.1% (+/- S.D., n = 98) of the isometric force elicited by high Ca2+ (pCa approximately 4.5) prior to incubation with vanadate. Transfer back to a high Ca2+ solution elicited no additional force (83.2% +/- 18.7% of control force). SDS-PAGE and immunoblot analysis of fibers and solutions demonstrated substantial extraction (greater than 90%) of Troponin I (TnI). Calcium dependence was restored after incubation with solutions containing either whole cardiac troponin or a combination of TnI and troponin C subunits. This reversible extraction of troponin directly demonstrates the role of TnI in the regulation of striated muscle contractility and permits specific substitution of the native TnI with exogenously supplied protein.

Modulation of crossbridge kinetics by myosin isoenzymes in skinned human heart fibers.

Skinned fibers from the normal human heart with the beta-myosin heavy chain (ventricular fibers) revealed both a higher force generation per cross section and a higher Ca2+ sensitivity than skinned fibers with the alpha-myosin heavy chain (atrial fibers). The relation between isometric ATPase activity and isometric tension of atrial fibers was higher than that of ventricular fibers. Since the ATPase-tension relation equals the rate constant for the transition from force-generating into non-force-generating crossbridge states (g(app)), myosin heavy chain isoenzymes seem to have different crossbridge turnover kinetics. Modulation of g(app) by myosin heavy chain isoenzymes could explain the different contractile behavior of atrial and ventricular fibers. g(app) was independent of Ca2+.

Inorganic phosphate inhibits contractility and ATPase activity in skinned fibers from human myocardium.

During hypoxic heart failure, inorganic phosphate (Pi) accumulates. We report the effects of Pi on force development and on myofibrillar ATPase-activity of human skinned atrial fibers, both at normal and at reduced levels of Mg-ATP. Pi (10 mM) depressed force production at maximal calcium activation (pCa 4.3) by about 40%. At higher pCa values (pCa 5.6), force inhibition was even more pronounced, but at low concentrations of Mg-ATP (10 microM), Pi was less effective. In contrast to contractile force, myofibrillar ATPase was only inhibited by about 10% at pCa 4.3, whereas it could be inhibited by 40-50% at submaximal calcium activation (pCa 5.6). As Pi inhibited contractile force more than ATPase activity, the ratio of ATPase-activity to force (tension cost) was increased by inorganic phosphate. ATPase-activity and tension cost were significantly reduced by lowering Mg-ATP concentration to 10 microM, whereas contractile force was less affected. Pi did not affect ATPase under these conditions at 10 mM Mg-ATP. Pi also shifted the calcium-force relationship towards higher Ca++ concentrations, that is, it decreased calcium sensitivity. In contrast, the calcium sensitivity of myofibrillar ATPase was less affected. These findings suggest that inorganic phosphate may affect the myocardium by altering crossbridge kinetics rather than the calcium affinity of troponin-C. Because of its inhibitory effect on myofibrillar ATPase, inorganic phosphate may be partly cardioprotective in the hypoxic myocardium. However, this "energy sparing' effect is probably offset by the greater "tension cost' that decreases the "efficiency' of tension maintenance in the presence of inorganic phosphate.

Stretch-induced increase in the Ca2+ sensitivity of myofibrillar ATPase activity in skinned fibres from pig ventricles.

The increase in force development in the heart with increase in end-diastolic pressure (Frank-Starling mechanism) has been ascribed to an increase in contractile responsiveness of the myofibrils to calcium. We now show that this calcium sensitization is also associated with an increase in calcium responsiveness of the myofibrillar ATPase. Thus, at submaximal Ca activation (pCa 6.0), the ATPase activity of skinned fibres from pig right ventricles is increased from 57.9 +/- 4.4% to 70.6 +/- 4.4% of the maximal Ca2+ activation of ATPase by stretching (by 15% lo). At maximal Ca2+ activation, ATPase was barely altered by stretching. The relationship between ATPase activity of skinned trabecula of pig right ventricle and ATPase-Ca2+ concentrations is shifted (by 0.1 pCa unit) to higher pCa values after a stretch-induced increase of the sarcomere length from 2.1 microns to 2.4 microns. The relationship between force and pCa was affected in a similar way by extension. This increased calcium sensitivity is, however, not associated with an alteration in the relationship between ATPase activity and force development (tension cost). In accordance with Brenner's hypothesis, we propose therefore that stretch activation of ATPase is associated with an increase in the apparent rate constant of crossbridge attachment rather than with a decrease in the apparent rate constant of crossbridge detachment.

Calcium sensitivity and unloaded shortening velocity of hypertrophied and non-hypertrophied skinned human atrial fibres.

The mechanical properties of myocardium of different animals are modified by a chronic increase in haemodynamic load. In this study differences in calcium sensitivity and maximum unloaded shortening velocity of hypertrophic and non-hypertrophic chemically skinned human atrial fibres are characterized. Investigating right atria of 34 patients, possible correlations are studied between preoperative atrial pressure, degree of hypertrophy (estimated from the muscle fibre diameter), calcium responsiveness (pCa50 eliciting half-maximum contraction) and Vmax (unloaded shortening velocity). Hypertrophic fibres from atrial appendages of patients having an increased right atrial pressure (RAP 8.5 +/- 1.6 mm Hg) and suffering from mitral valve disease (stenosis and insufficiency combined) had a fibre diameter of 18.0 +/- 0.9 microns. They also had a higher calcium sensitivity (pCa50 5.65 +/- 0.08) and a lower unloaded shortening velocity (1.7 +/- 0.1 muscle lengths/s) than non-hypertrophic fibres from the appendages of patients with normal right atrial pressure (RAP 3.2 +/- 0.5 mm Hg) and coronary heart disease (CHD: pCa50 5.45 +/- 0.04; Vmax = 3.4 +/- 0.2 muscle lengths/s; fibre diameter 12.8 +/- 0.4 microns). Thus non-hypertrophic fibres from control CHD patients differed significantly (p less than 0.01) from hypertrophied atrial fibres of patients with mitral valve disease and with combined valve disease (MAV, pCa50 = 5.58 +/- 0.05, Vmax 2.0 +/- 0.3 muscle lengths/s, fibre diameter 14.6 +/- 0.9 microns) or aortic valve disease (stenosis combined with insufficiency, fibre diameter 14.8 +/- 1.4 microns, pCa50 5.56 +/- 0.03, Vmax 2.0 +/- 0.24 muscle length/s; RAP 11.0 +/- 2.6 mm Hg).(ABSTRACT TRUNCATED AT 250 WORDS)

Perhexiline increases calcium-activated force in skinned psoas fibres by raising calcium affinity of troponin-C.

We investigated the influence of the calcium-/calmodulin antagonist perhexiline on the calcium sensitivity of skinned muscle fibres from rabbit psoas muscle suspended in MgATP salt solution (pH 7.0; 20 degrees C). Perhexiline strongly sensitized the skinned fibres for calcium; thus the relationship between isometric force development and calcium ion concentration was shifted to the left in the presence of perhexiline. Similar results have been achieved with skinned fibres from pig cardiac (ventricular) muscle fibres. In skinned psoas we also determined the binding of Ca2+ to troponin-C by using the method developed by Güth and Potter (1987). Troponin-C labelled with DANZ (5-dimethyl-aminonaphthalene-2-sulfonyl aziridine) was incorporated into skinned fibres after previous extraction of troponin-C. The fluorescence signal (at 460 nm) as well as force increased when the calcium ion concentration rose to pCa 5.7. Addition of perhexiline increased this force and the fluorescence signal indicating that the increase in calcium responsiveness of the contractile apparatus was, at least partly, due to an increase in calcium occupancy of troponin-C.

The effect of MgATP on forming and breaking actin-myosin linkages in contracted skinned insect flight muscle fibres.

At neutral pH, fully Ca2+ -activated glycerinated dorsal longitudinal fibre bundles from Lethocerus indicus contract under isometric conditions and respond to release by deactivation, i.e. quick release causes a delayed tension fall. At slightly alkaline pH, the release-induced deactivation becomes a transient phenomenon, i.e. a delayed tension fall is followed by a slow tension recovery. This enabled us to study the effect of MgATP concentration on the phases of deactivation and slow recovery. Reduction of the MgATP concentration slows down the tension response to a quick length change and increases the time constants of the delayed deactivation phase and of the slow recovery phase. The rate constants depend on the ATP concentration according to the Michaelis-Menten law yielding apparent dissociation constants (Km) of 2 mM and 0.09 mM and maximal rate constants of 700 s-1 and 20 s-1 for the deactivation phase (crossbridge detachment) and slow recovery phase (crossbridge reattachment) respectively. The rate of MgATP hydrolysis is also hyperbolically related to the MgATP concentration (Km = 0.14 mM, maximal MgATP turnover rate 1.2 s-1. It is concluded that the effect of MgATP on the deactivation phase, in which crossbridges dissociate strain dependent from the actin, is controlled by at least two mechanisms: (1) fast equilibrium transitions within attached crossbridge states which augment MgATP dissociation from crossbridges with discharged elastic elements; and (2) a crossbridge strain-dependent isomerization of the ternary actin-myosin-MgATP complex which determines crossbridge detachment from the actin.