Moving Along: In biomechanics, rehabilitation engineering, and movement analysis, Italian researchers are making great strides.

In Italy, biomechanics research and the analysis of human and animal movement have had a very long history, beginning with the exceptional pioneering work of Leonardo da Vinci. In 1489, da Vinci began investigating human anatomy, including an examination of human tendons, muscles, and the skeletal system. He continued this line of inquiry later in life, identifying what he called "the four powers--movement, weight, force, and percussion"--and how he thought they worked in the human body. His approach, by the way, was very modern--analyzing nature through anatomy, developing models for interpretation, and transferring this knowledge to bio-inspired machines.

Correlated variability in the breathing pattern and end-expiratory lung volumes in conscious humans.

In order to characterize the variability and correlation properties of spontaneous breathing in humans, the breathing pattern of 16 seated healthy subjects was studied during 40 min of quiet breathing using opto-electronic plethysmography, a contactless technology that measures total and compartmental chest wall volumes without interfering with the subjects breathing. From these signals, tidal volume (VT), respiratory time (TTOT) and the other breathing pattern parameters were computed breath-by-breath together with the end-expiratory total and compartmental (pulmonary rib cage and abdomen) chest wall volume changes. The correlation properties of these variables were quantified by detrended fluctuation analysis, computing the scaling exponenta. VT, TTOT and the other breathing pattern variables showed α values between 0.60 (for minute ventilation) to 0.71 (for respiratory rate), all significantly lower than the ones obtained for end-expiratory volumes, that ranged between 1.05 (for rib cage) and 1.13 (for abdomen) with no significant differences between compartments. The much stronger long-range correlations of the end expiratory volumes were interpreted by a neuromechanical network model consisting of five neuron groups in the brain respiratory center coupled with the mechanical properties of the respiratory system modeled as a simple Kelvin body. The model-based α for VT is 0.57, similar to the experimental data. While the α for TTOT was slightly lower than the experimental values, the model correctly predicted α for end-expiratory lung volumes (1.045). In conclusion, we propose that the correlations in the timing and amplitude of the physiological variables originate from the brain with the exception of end-expiratory lung volume, which shows the strongest correlations largely due to the contribution of the viscoelastic properties of the tissues. This cycle-by-cycle variability may have a significant impact on the functioning of adherent cells in the respiratory system.

Assessment of dynamic mechanical properties of the respiratory system during high-frequency oscillatory ventilation*.

OBJECTIVES: 1) To investigate the possibility of estimating respiratory system impedance (Zrs, forced oscillation technique) by using high-amplitude pressure oscillations delivered during high-frequency oscillatory ventilation; 2) to characterize the relationship between Zrs and continuous distending pressure during an increasing/decreasing continuous distending pressure trial; 3) to evaluate how the optimal continuous distending pressure identified by Zrs relates to the point of maximal curvature of the deflation limb of the quasi-static pressure-volume curve. DESIGN: Prospective laboratory animal investigation. SETTING: Experimental medicine laboratory. SUBJECTS: Eight New Zealand rabbits. INTERVENTIONS: The rabbits were ventilated with high-frequency oscillatory ventilation. Zrs was measured while continuous distending pressure was increased and decreased between 2 and 26 cm H2O in 1-minute steps of 4 cm H2O. At each step, a low-amplitude (6 cm H2O) sinusoidal signal was alternated with a high-amplitude (18 cm H2O) asymmetric high-frequency oscillatory ventilation square pressure waveform. Pressure-volume curves were determined at the end of the continuous distending pressure trial. All measurements were repeated after bronchoalveolar lavage. MEASUREMENTS AND MAIN RESULTS: Zrs was estimated from flow and pressure measured at the inlet of the tracheal tube and expressed as resistance (Rrs) and reactance (Xrs). Linear correlation between the values, measured by applying the small-amplitude sinusoidal signal and the ventilator waveform, was good for Xrs (r = 0.95 ± 0.04) but not for Rrs (r = 0.60 ± 0.34). Following lavage, the Xrs-continuous distending pressure curves presented a maximum on the deflation limb, identifying an optimal continuous distending pressure that was, on average, 1.1 ± 1.7 cm H2O below the point of maximal curvature of the deflation limb of the pressure-volume curves. CONCLUSIONS: Xrs can be accurately measured during high-frequency oscillatory ventilation without interrupting ventilation and/or connecting additional devices. An optimal continuous distending pressure close to the point of maximal curvature of the deflation limb of quasi-static pressure-volume curve can be identified by measuring Zrs during a decreasing continuous distending pressure trial. Zrs might constitute a useful bedside tool for monitoring lung mechanics and improving the continuous distending pressure optimization during high-frequency oscillatory ventilation.

Influence of an eccentric load added at the back of the head on head-neck posture.

A biomechanical study of the head-neck complex in seated subjects was conducted to verify whether a slight load, applied at the back of the head, could beneficially affect the head-neck posture, one of the factors of postural neck pain. An eccentric load of 0.5 kg was applied to the subjects' head by means of a special cap. A group of asymptomatic subjects (n=10, 28.9±12.1 yrs), and a group of subjects that had experienced mild, occasional neck pain (n=10, 39.6±18.4 yrs) were compared. They were analyzed while maintaining a still posture that was periodically perturbed to avoid habituation. A 3D motion analyzer and reflective markers placed over the head, the neck and the trunk, were used to compute head inclination and translation and head/neck flexion angle in different conditions: before, during and after having had the load applied for 15 min. Although the moment induced by the load was extensor, a forward-oriented movement of the head was observed in both groups. However, the forward displacement, in relation to the initial position, was smaller in the mild neck pain group than in the asymptomatic group (5.7±4.7 mm vs. 8.9±5.5 mm, P<0.05 and 2.6±5.9 mm vs. 11.0±9.0 mm after 15 min, P<0.05). After removing the load, the mild neck pain subjects assumed a retracted position (-3.8±2.7 mm) while the asymptomatic subjects stayed protracted (+3.5±5.1 mm, P<0.01). These unexpected findings suggest that a slight load added to the head can influence the postural control mechanisms and, in symptomatic subjects, lead to a new strategy aimed at a reduction of the neck extensor muscle contraction.

Optimizing positive end-expiratory pressure by oscillatory mechanics minimizes tidal recruitment and distension: an experimental study in a lavage model of lung injury.

INTRODUCTION: It is well established that during mechanical ventilation of patients with acute respiratory distress syndrome cyclic recruitment/derecruitment and overdistension are potentially injurious for lung tissues. We evaluated whether the forced oscillation technique (FOT) could be used to guide the ventilator settings in order to minimize cyclic lung recruitment/derecruitment and cyclic mechanical stress in an experimental model of acute lung injury. METHODS: We studied six pigs in which lung injury was induced by bronchoalveolar lavage. The animals were ventilated with a tidal volume of 6 ml/kg. Forced oscillations at 5 Hz were superimposed on the ventilation waveform. Pressure and flow were measured at the tip and at the inlet of the endotracheal tube respectively. Respiratory system reactance (Xrs) was computed from the pressure and flow signals and expressed in terms of oscillatory elastance (EX5). Positive end-expiratory pressure (PEEP) was increased from 0 to 24 cm H2O in steps of 4 cm H2O and subsequently decreased from 24 to 0 in steps of 2 cm H2O. At each PEEP step CT scans and EX5 were assessed at end-expiration and end-inspiration. RESULTS: During deflation the relationship between both end-expiratory and end-inspiratory EX5 and PEEP was a U-shaped curve with minimum values at PEEP = 13.4 ± 1.0 cm H2O (mean ± SD) and 13.0 ± 1.0 cm H2O respectively. EX5 was always higher at end-inspiration than at end-expiration, the difference between the average curves being minimal at 12 cm H2O. At this PEEP level, CT did not show any substantial sign of intra-tidal recruitment/derecruitment or expiratory lung collapse. CONCLUSIONS: Using FOT it was possible to measure EX5 both at end-expiration and at end-inspiration. The optimal PEEP strategy based on end-expiratory EX5 minimized intra-tidal recruitment/derecruitment as assessed by CT, and the concurrent attenuation of intra-tidal variations of EX5 suggests that it may also minimize tidal mechanical stress.

Rib cage deformities alter respiratory muscle action and chest wall function in patients with severe osteogenesis imperfecta.

BACKGROUND: Osteogenesis imperfecta (OI) is an inherited connective tissue disorder characterized by bone fragility, multiple fractures and significant chest wall deformities. Cardiopulmonary insufficiency is the leading cause of death in these patients. METHODS: Seven patients with severe OI type III, 15 with moderate OI type IV and 26 healthy subjects were studied. In addition to standard spirometry, rib cage geometry, breathing pattern and regional chest wall volume changes at rest in seated and supine position were assessed by opto-electronic plethysmography to investigate if structural modifications of the rib cage in OI have consequences on ventilatory pattern. One-way or two-way analysis of variance was performed to compare the results between the three groups and the two postures. RESULTS: Both OI type III and IV patients showed reduced FVC and FEV(1) compared to predicted values, on condition that updated reference equations are considered. In both positions, ventilation was lower in OI patients than control because of lower tidal volume (p<0.01). In contrast to OI type IV patients, whose chest wall geometry and function was normal, OI type III patients were characterized by reduced (p<0.01) angle at the sternum (pectus carinatum), paradoxical inspiratory inward motion of the pulmonary rib cage, significant thoraco-abdominal asynchronies and rib cage distortions in supine position (p<0.001). CONCLUSIONS: In conclusion, the restrictive respiratory pattern of Osteogenesis Imperfecta is closely related to the severity of the disease and to the sternal deformities. Pectus carinatum characterizes OI type III patients and alters respiratory muscles coordination, leading to chest wall and rib cage distortions and an inefficient ventilator pattern. OI type IV is characterized by lower alterations in the respiratory function. These findings suggest that functional assessment and treatment of OI should be differentiated in these two forms of the disease.

Actual performance of mechanical ventilators in ICU: a multicentric quality control study.

Even if the performance of a given ventilator has been evaluated in the laboratory under very well controlled conditions, inappropriate maintenance and lack of long-term stability and accuracy of the ventilator sensors may lead to ventilation errors in actual clinical practice. The aim of this study was to evaluate the actual performances of ventilators during clinical routines. A resistance (7.69 cmH(2)O/L/s) - elastance (100 mL/cmH(2)O) test lung equipped with pressure, flow, and oxygen concentration sensors was connected to the Y-piece of all the mechanical ventilators available for patients in four intensive care units (ICUs; n = 66). Ventilators were set to volume-controlled ventilation with tidal volume = 600 mL, respiratory rate = 20 breaths/minute, positive end-expiratory pressure (PEEP) = 8 cmH(2)O, and oxygen fraction = 0.5. The signals from the sensors were recorded to compute the ventilation parameters. The average ± standard deviation and range (min-max) of the ventilatory parameters were the following: inspired tidal volume = 607 ± 36 (530-723) mL, expired tidal volume = 608 ± 36 (530-728) mL, peak pressure = 20.8 ± 2.3 (17.2-25.9) cmH(2)O, respiratory rate = 20.09 ± 0.35 (19.5-21.6) breaths/minute, PEEP = 8.43 ± 0.57 (7.26-10.8) cmH(2)O, oxygen fraction = 0.49 ± 0.014 (0.41-0.53). The more error-prone parameters were the ones related to the measure of flow. In several cases, the actual delivered mechanical ventilation was considerably different from the set one, suggesting the need for improving quality control procedures for these machines.

Positive end-expiratory pressure optimization with forced oscillation technique reduces ventilator induced lung injury: a controlled experimental study in pigs with saline lavage lung injury.

INTRODUCTION: Protocols using high levels of positive end-expiratory pressure (PEEP) in combination with low tidal volumes have been shown to reduce mortality in patients with severe acute respiratory distress syndrome (ARDS). However, the optimal method for setting PEEP is yet to be defined. It has been shown that respiratory system reactance (Xrs), measured by the forced oscillation technique (FOT) at 5 Hz, may be used to identify the minimal PEEP level required to maintain lung recruitment. The aim of the present study was to evaluate if using Xrs for setting PEEP would improve lung mechanics and reduce lung injury compared to an oxygenation-based approach. METHODS: 17 pigs, in which acute lung injury (ALI) was induced by saline lavage, were studied. Animals were randomized into two groups: in the first PEEP was titrated according to Xrs (FOT group), in the control group PEEP was set according to the ARDSNet protocol (ARDSNet group). The duration of the trial was 12 hours. In both groups recruitment maneuvers (RM) were performed every 2 hours, increasing PEEP to 20 cmH2O. In the FOT group PEEP was titrated by monitoring Xrs while PEEP was reduced from 20 cmH2O in steps of 2 cmH2O. PEEP was considered optimal at the step before which Xrs started to decrease. Ventilatory parameters, lung mechanics, blood gases and hemodynamic parameters were recorded hourly. Lung injury was evaluated by histopathological analysis. RESULTS: The PEEP levels set in the FOT group were significantly higher compared to those set in the ARDSNet group during the whole trial. These higher values of PEEP resulted in improved lung mechanics, reduced driving pressure, improved oxygenation, with a trend for higher PaCO2 and lower systemic and pulmonary pressure. After 12 hours of ventilation, histopathological analysis showed a significantly lower score of lung injury in the FOT group compared to the ARDSNet group. CONCLUSIONS: In a lavage model of lung injury a PEEP optimization strategy based on maximizing Xrs attenuated the signs of ventilator induced lung injury. The respiratory system reactance measured by FOT could thus be an important component in a strategy for delivering protective ventilation to patients with ARDS/acute lung injury.

Optimisation of positive end-expiratory pressure by forced oscillation technique in a lavage model of acute lung injury.

PURPOSE: We evaluated whether oscillatory compliance (C(X5)) measured by forced oscillation technique (FOT) at 5 Hz may be useful for positive end-expiratory pressure (PEEP) optimisation. METHODS: We studied seven pigs in which lung injury was induced by broncho-alveolar lavage. The animals were ventilated in volume control mode with a tidal volume of 6 ml/kg. Forced oscillations were superimposed on the ventilation waveform for the assessment of respiratory mechanics. PEEP was increased from 0 to 24 cmH(2)O in steps of 4 cmH(2)O and subsequently decreased from 24 to 0 in steps of 2 cmH(2)O. At each 8-min step, a CT scan was acquired during an end-expiratory hold, and blood gas analysis was performed. C(X5) was monitored continuously, and data relative to the expiratory hold were selected and averaged for comparison with CT and oxygenation. RESULTS: Open lung PEEP (PEEP(ol)) was defined as the level of PEEP corresponding to the maximum value of C(X5) on the decremental limb of the PEEP trial. PEEP(ol) was on average 13.4 (± 1.0) cmH(2)O. For higher levels of PEEP, there were no significant changes in the amount of non-aerated tissue (V(tissNA)%). In contrast, when PEEP was reduced below PEEP(ol), V(tissNA)% dramatically increased. PEEP(ol) was able to prevent a 5% drop in V(tissNA)% with 100% sensitivity and 92% specificity. At PEEP(ol) V(tissNA)% was significantly lower than at the corresponding PEEP level on the incremental limb. CONCLUSIONS: The assessment of C(X5) allowed the definition of PEEP(ol) to be in agreement with CT data. Thus, FOT measurements of C(X5) may provide a non-invasive bedside tool for PEEP titration.

Intra-fraction setup variability: IR optical localization vs. X-ray imaging in a hypofractionated patient population.

BACKGROUND: The purpose of this study is to investigate intra-fraction setup variability in hypo-fractionated cranial and body radiotherapy; this is achieved by means of integrated infrared optical localization and stereoscopic kV X-ray imaging. METHOD AND MATERIALS: We analyzed data coming from 87 patients treated with hypo-fractionated radiotherapy at cranial and extra-cranial sites. Patient setup was realized through the ExacTrac X-ray 6D system (BrainLAB, Germany), consisting of 2 infrared TV cameras for external fiducial localization and X-ray imaging in double projection for image registration. Before irradiation, patients were pre-aligned relying on optical marker localization. Patient position was refined through the automatic matching of X-ray images to digitally reconstructed radiographs, providing 6 corrective parameters that were automatically applied using a robotic couch. Infrared patient localization and X-ray imaging were performed at the end of treatment, thus providing independent measures of intra-fraction motion. RESULTS: According to optical measurements, the size of intra-fraction motion was (median ± quartile) 0.3 ± 0.3 mm, 0.6 ± 0.6 mm, 0.7 ± 0.6 mm for cranial, abdominal and lung patients, respectively. X-ray image registration estimated larger intra-fraction motion, equal to 0.9 ± 0.8 mm, 1.3 ± 1.2 mm, 1.8 ± 2.2 mm, correspondingly. CONCLUSION: Optical tracking highlighted negligible intra-fraction motion at both cranial and extra-cranial sites. The larger motion detected by X-ray image registration showed significant inter-patient variability, in contrast to infrared optical tracking measurement. Infrared localization is put forward as the optimal strategy to monitor intra-fraction motion, featuring robustness, flexibility and less invasivity with respect to X-ray based techniques.

Telemetric CPAP titration at home in patients with sleep apnea-hypopnea syndrome.

BACKGROUND: Home continuous positive airway pressure (CPAP) titration with automatic devices is not possible in a non-negligible percentage of patients with sleep apnea-hypopnea syndrome (SAHS). OBJECTIVES: To test the feasibility of a novel telemetric system for home CPAP titration. METHODS: One-night home CPAP titration was carried out on 20 SAHS patients (56±3 years; BMI=35±2 kg/m²). A telemetric unit, based on the conventional GPRS mobile phone network and connected to a commercial CPAP device, allowed the hospital technician to monitor flow, pressure and air leaks by remote control and titrate CPAP (elimination of apneas, hypopneas, flow limitation and snoring) in real time. After 1 week, a full hospital polysomnography was performed while the patient was subjected to the value of CPAP that was previously titrated at home via telemetry. RESULTS: The home-titrated CPAP systematically improved patients' breathing: the apnea-hypopnea index and percentage of sleep time with arterial oxygen saturation below 90% were reduced from 58.1±5.1 to 3.8±0.6 events/h and from 19.8±1.1% to 4.4±0.7%, respectively. This CPAP value (9.15±0.47 cmH2O) was virtually the same as the pressure that optimized breathing during hospital polysomnography (9.20±0.41 cmH2O; mean difference: 0.02 cmH2O, limits of agreement:±1.00 cmH2O). CONCLUSIONS: This pilot study shows that a simple telemetric system, requiring neither a special telemedicine network nor any infrastructure in the patient's home, made it possible to perform effective remote CPAP titration on SAHS patients.

Concomitant ventilatory and circulatory functions of the diaphragm and abdominal muscles.

Expulsive maneuvers (EMs) caused by simultaneous contraction of diaphragm and abdominal muscles shift substantial quantities of blood from the splanchnic circulation to the extremities. This suggests that the diaphragm assisted by abdominal muscles might accomplish ventilation and circulation simultaneously by repeated EMs. We tested this hypothesis in normal subjects by measuring changes (Δ) in body volume (Vb) by whole body plethysmography simultaneously with changes in trunk volume (Vtr) by optoelectronic plethysmography, which measures the same parameters as whole body plethysmography plus the volume of blood shifts (Vbs) between trunk and extremities: Vbs = ΔVtr-ΔVb. We also measured abdominal pressure, pleural pressure, the arterial pressure wave, and cardiac output (Qc). EMs with abdominal pressure ~100 cmH(2)O for 1 s, followed by 2-s relaxations, repeated over 90 s, produced a "stroke volume" from the splanchnic bed of 0.35 ± 0.07 (SD) liter, an output of 6.84 ± 0.75 l/min compared with a resting Qc of 5.59 ± 1.14 l/min. Refilling during relaxation was complete, and the splanchnic bed did not progressively empty. Diastolic pressure increased by 25 mmHg during each EM. Between EMs, Qc increased to 7.09 ± 1.14 l/min due to increased stroke volume and heart rate. The circulatory function of the diaphragm assisted by simultaneous contractions of abdominal muscles with appropriate pressure and duration at 20 min(-1) can produce a circulatory output as great as resting Qc, as well as ventilation. These combined functions of the diaphragm have potential for cardiopulmonary resuscitation. The abdominal circulatory pump can act as an auxiliary heart.

Home monitoring of within-breath respiratory mechanics by a simple and automatic forced oscillation technique device.

Spirometry is the gold standard to determine the presence of airflow obstruction, but it requires volitional participation and needs qualified supervision. The forced oscillation technique (FOT) measures respiratory input impedance (Zrs) during spontaneous breathing and it could be useful for unsupervised monitoring of airway obstruction. We developed a FOT device for home monitoring of Zrs which transmits the data through the Internet. Its accuracy, stability and reliability were evaluated in a pilot study measuring the Zrs in the unsupervised self-measurements of five healthy subjects. Finally, to explore the applicability of the concept, 36 consecutive daily home measurements were recorded from one healthy subject and one chronic obstructive pulmonary disease (COPD) patient. The accuracy of the device fulfilled FOT guidelines, and the reliability test showed a mean discrepancy of resistance of 0.10 +/- 0.01 cmH(2)O s L(-1). The data from the healthy subjects demonstrated high repeatability in assessing Zrs. The measurements on the healthy subjects and the patient with COPD suggest the feasibility of unsupervised FOT measurements. The healthy subjects showed minimal daily variations in Zrs, whereas the patient with COPD had large differences in mean values and important fluctuations over day-to-day measurements. The results of the pilot study demonstrate that unsupervised home monitoring of Zrs using the FOT yields accurate and reproducible data. It could provide new insights into the dynamics of airway obstruction and improve the understanding and management of obstructive diseases.

On-line monitoring of lung mechanics during spontaneous breathing: a physiological study.

BACKGROUND: Monitoring the mechanics of breathing in patients with advanced chronic obstructive lung diseases prior to lung transplantation is useful to characterize changes in the mechanical properties of the lungs. On-line methods of monitoring immediately process the data for clinical decisions. However, the few available methods are so far limited to monitor respiratory mechanics in ventilator-dependent patients. We investigated whether on-line monitoring of the lung mechanics, including intrinsic PEEP, was feasible in spontaneously breathing patients. METHODS: In 9 stable patients with chronic obstructive pulmonary disease (COPD) and 11 with cystic fibrosis (CF) undergoing the procedure for the lung transplantation waiting list, we applied 2 methods of on-line monitoring (modified recursive least squares, RLS and modified multiple linear regression methods, SLS) of intrinsic PEEP (P(0)), dynamic lung elastance (E(Ldyn)) and inspiratory resistance (R(Linsp)), and compared them with an off-line graphical analysis (GA), our reference technique. RESULTS: In CF patients, there was no difference between methods, while in COPD, the median values of E(Ldyn) and R(Linsp) were significantly different between GA/SLS and GA/RLS, respectively (Dunn's, p<0.05). However, the correlation was very high for all comparisons, particularly for E(Ldyn) (R>0.98) and R(Linsp) (R>0.93). Moreover, Bland-Altman plots showed that the mean differences were consistently low and the intervals of agreement reasonable. CONCLUSIONS: Our study suggests that on-line methods are reliable for monitoring lung mechanics in spontaneous breathing patients with severe lung diseases and could help clinicians in their decision-making process.

Measurement of total and compartmental lung volume changes in newborns by optoelectronic plethysmography.

The study of respiratory mechanics in infants requires a noninvasive accurate measurement of the lung volume changes (DeltaVL). Optoelectronic plethysmography (OEP) allows the assessment of DeltaVL through the measurement of the chest wall surface motion and it has been proved to be accurate in adults. The aim of this study was to apply OEP to newborns and to validate it by comparison to pneumotachography. Twenty term and preterm newborns (GA = 34 +/- 5 wk) in stable condition were studied during 1 to 2 min periods of quiet breathing in supine position. Airway opening flow was measured by applying a facemask connected to a pneumotachograph (PNT) and integrated to provide the DeltaVL. Chest wall volume changes were simultaneously measured by OEP. The tidal volume values measured by pneumotachography and by OEP were compared for each breath. A total of 771 breaths from all patients were considered. Bland-Altmann analysis showed a mean difference of -0.08 mL and a limit of agreement ranging from -2.98 to 2.83 mL. Linear regression analysis demonstrated good correlation between the two techniques (r = 0.95, q = 1.00 mL, m = 0.96). OEP provides accurate measurements of DeltaVL in newborns and may be useful to study respiratory mechanics and breathing patterns during spontaneous breathing and mechanical ventilation.

Lung recruitment assessed by total respiratory system input reactance.

PURPOSE: ALI and ARDS are associated with lung volume derecruitment, usually counteracted by PEEP and recruitment maneuvers (RM), which should be accurately tailored to the patient's needs. The aim of this study was to investigate the possibility of monitoring the amount of derecruited lung by the forced oscillation technique (FOT). METHODS: We studied six piglets (26 +/- 2.5 kg) ventilated by a mechanical ventilator connected to a FOT device that produced sinusoidal pressure forcing at 5 Hz. The percentage of non-aerated lung tissue (V (tiss)NA%) was measured by whole-body CT scans at end-expiration with zero end-expiratory pressure. Respiratory system oscillatory input reactance (X (rs)) was measured simultaneously to CT and used to derive oscillatory compliance (C (X5)), which we used as an index of recruited lung. Measurements were performed at baseline and after several interventions in the following sequence: mono-lateral reabsorption atelectasis, RM, bi-lateral derecruitment induced by broncho-alveolar lavage and a second RM. RESULTS: By pooling data from all experimental conditions and all pigs, C (X5) was linearly correlated to V (tiss)NA% (r (2) = 0.89) regardless of the procedure used to de-recruit the lung (reabsorption atelectasis or pulmonary lavage). Separate correlation analysis on single pigs showed similar regression equations, with an even higher coefficient of determination (r (2) = 0.91 +/- 0.07). CONCLUSION: These results suggest that FOT and the measurement of C (X5) could be a useful tool for the non-invasive measurement of lung volume recruitment/derecruitment.

The abdominal circulatory pump.

Blood in the splanchnic vasculature can be transferred to the extremities. We quantified such blood shifts in normal subjects by measuring trunk volume by optoelectronic plethysmography, simultaneously with changes in body volume by whole body plethysmography during contractions of the diaphragm and abdominal muscles. Trunk volume changes with blood shifts, but body volume does not so that the blood volume shifted between trunk and extremities (Vbs) is the difference between changes in trunk and body volume. This is so because both trunk and body volume change identically with breathing and gas expansion or compression. During tidal breathing Vbs was 50-75 ml with an ejection fraction of 4-6% and an output of 750-1500 ml/min. Step increases in abdominal pressure resulted in rapid emptying presumably from the liver with a time constant of 0.61+/-0.1SE sec. followed by slower flow from non-hepatic viscera. The filling time constant was 0.57+/-0.09SE sec. Splanchnic emptying shifted up to 650 ml blood. With emptying, the increased hepatic vein flow increases the blood pressure at its entry into the inferior vena cava (IVC) and abolishes the pressure gradient producing flow between the femoral vein and the IVC inducing blood pooling in the legs. The findings are important for exercise because the larger the Vbs the greater the perfusion of locomotor muscles. During asystolic cardiac arrest we calculate that appropriate timing of abdominal compression could produce an output of 6 L/min. so that the abdominal circulatory pump might act as an auxiliary heart.

Changes in the mechanical properties of the respiratory system during the development of interstitial lung edema.

BACKGROUND: Pulmonary edema induces changes in airway and lung tissues mechanical properties that can be measured by low-frequency forced oscillation technique (FOT). It is preceded by interstitial edema which is characterized by the accumulation of extravascular fluid in the interstitial space of the air-blood barrier. Our aim was to investigate the impact of the early stages of the development of interstitial edema on the mechanical properties of the respiratory system. METHODS: We studied 17 paralysed and mechanically ventilated closed-chest rats (325-375 g). Total input respiratory system impedance (Zrs) was derived from tracheal flow and pressure signals by applying forced oscillations with frequency components from 0.16 to 18.44 Hz distributed in two forcing signals. In 8 animals interstitial lung edema was induced by intravenous infusion of saline solution (0.75 ml/kg/min) for 4 hours; 9 control animals were studied with the same protocol but without infusion. Zrs was measured at the beginning and every 15 min until the end of the experiment. RESULTS: In the treated group the lung wet-to-dry weight ratio increased from 4.3 +/- 0.72 to 5.23 +/- 0.59, with no histological signs of alveolar flooding. Resistance (Rrs) increased in both groups over time, but to a greater extent in the treated group. Reactance (Xrs) did not change in the control group, while it decreased significantly at all frequencies but one in the treated. Significant changes in Rrs and Xrs were observed starting after ~135 min from the beginning of the infusion. By applying a constant phase model to partition airways and tissue mechanical properties, we observed a mild increase in airways resistance in both groups. A greater and significant increase in tissue damping (from 603.5 +/- 100.3 to 714.5 +/- 81.9 cmH2O/L) and elastance (from 4160.2 +/- 462.6 to 5018.2 +/- 622.5 cmH2O/L) was found only in the treated group. CONCLUSION: These results suggest that interstitial edema has a small but significant impact on the mechanical features of lung tissues and that these changes begin at very early stages, before the beginning of accumulation of extravascular fluid into the alveoli.

Benefits of six degrees of freedom for optically driven patient set-up correction in SBRT.

To quantify the advantages of a 6 degrees of freedom (dof) versus the conventional 3- or 4-dof correction modality for stereotactic body radiation therapy (SBRT) treatments. Eighty-five patients were fitted with 5-7 infra-red passive markers for optical localization. Data, acquired during the treatment, were analyzed retrospectively to simulate and evaluate the best approach for correcting patient misalignments. After the implementation of each correction, the new position of the target (tumor's center of mass) was estimated by means of a dedicated stereotactic algorithm. The Euclidean distance between the corrected and the planned location of target point was calculated and compared to the initial mismatching. Initial and after correction median+/-quartile displacements affecting external control points were 3.74+/-2.55 mm (initial), 2.45+/-0.91 mm (3-dof), 2.37+/-0.95 mm (4-dof), and 2.03+/-1.47 mm (6-dof). The benefit of a six-parameter adjustment was particularly evident when evaluating the results relative to the target position before and after the re-alignment. In this context, the Euclidean distance between the planned and the current target point turned to 0.82+/-1.12 mm (median+/-quartile values) after the roto-translation versus the initial displacement of 2.98+/-2.32 mm. No statistical improvements were found after 3- and 4-dof correction (2.73+/-1.22 mm and 2.60+/-1.31 mm, respectively). Angular errors were 0.09+/-0.93 degrees (mean+/-std). Pitch rotation in abdomen site showed the most relevant deviation, being -0.46+/-1.27 degrees with a peak value of 5.46 degrees . Translational misalignments were -0.68+/-2.60 mm (mean+/-std) with the maximum value of 12 mm along the cranio-caudal direction. We conclude that positioning system platforms featuring 6-dof are preferred for high precision radiation therapy. Data are in line with previous results relative to other sites and represent a relevant record in the framework of SBRT.