Active expiration may contribute to the reduction in end-expiratory volume during emergence from anesthesia and in the immediate post-operative period.

SummaryBackgroundThe role of prone position in preterm infants has not been completely clarified. We investigated prone versus supine posture‐related changes in respiratory system resistance (Rrs) and reactance (Xrs) measured by the Forced Oscillation Technique (FOT) in mechanically ventilated preterm newborns.MethodsPatients were studied in the supine versus prone positions in random order. Oxygen saturation, transcutaneous partial pressure of oxygen (ptcO2), carbon dioxide (ptcCO2), Rrs and Xrs were measured in each position.ResultsNine patients with respiratory distress syndrome (RDS) and nine with evolving broncho‐pulmonary dysplasia (BPD) were studied. Rrs was, on average, 9.8 (1.3, 18.3 as 95%CI) cmH2O*s/l lower in the prone compared to the supine position (P = 0.02), while no differences in Xrs, ptcO2, ptcCO2, and breathing pattern were observed between postures. Only patients with evolving BPD showed a significant reduction of Rrs from 69.0 ± 27.4 to 53.0 ± 16.7 cmH2O*s/l, P = 0.01. No significant correlations were found between changes in lung mechanics and ptcO2, ptcCO2, or breathing pattern.ConclusionsOn short‐term basis, prone positioning does not offer significant advantages in lung mechanics in mechanically ventilated infants with RDS, while it is associated with lower Rrs values in patients with evolving BPD. Pediatr Pulmonol. 2015; 50:798–804. © 2014 Wiley Periodicals, Inc.

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.

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 exponentα. 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.

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.

To evaluate the feasibility of forced oscillation technique (FOT) measurements at the bedside and to describe the relationship between positive end-expiration pressure (PEEP) and lung mechanics in different groups of ventilated infants.

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 (r2 = 0.95 ± 0.04) but not for Rrs (r2 = 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.

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.

In the respiratory management of DMD patients it is still under debate what parameter should indicate the correct timing for institution of nocturnal non-invasive ventilation (NIV), in addition to forced vital capacity, which is generally considered as a prognostic marker of disease progression. The aim of this study was to determine if volume variations of rib cage and abdominal compartments measured by Opto-Electronic Plethysmography can be helpful to distinguish between those patients who are in the early stages of nocturnal oxygen desaturation development and those who do not yet. Pulmonary function, abdominal contribution to tidal volume and to inspiratory capacity (%Abd IC) and a set of breathing pattern indexes were assessed in 40 DMD patients older than 14 years and not yet under nocturnal NIV. ROC analysis revealed that among all the considered parameters, %Abd IC in supine position was the best discriminator between DeSat (at least 10% of the night time with SpO(2) < 95%) and NonDeSat patients, providing an area under the curve with 95%CI equal to 0.752. In conclusion, in adolescents and adults DMD patients who present either no sign or only mild nocturnal oxygen desaturation, a reduced abdominal contribution to inspiratory capacity is a marker of the onset of diaphragm weakness and should be considered to identify the correct timing for the institution of nocturnal NIV.

Background: An increased variability of inspiratory resistance, measured by forced oscillations (FOT) and quantified by the coefficient of variation measured over 4 consecutive days (CV Rinsp ), is a typical feature of asthma and predicts acute deterioration of airway function within a week. Aim: To investigate whether air pollution increases CV Rinsp and the risk of future deterioration in asthma. Methods: Between Jan and Jul 2009, CV Rinsp was measured daily by a portable FOT device in 10 mild asthmatics. CV Rinsp was then compared with the daily concentration of PM10. Results: In 7 subjects PM10 was linearly correlated with CV Rinsp (r=0.27, p Rinsp time-series were then averaged to reduce intra-individual variability (Figure) and used to estimate a linear ARMAX model, with the PM10 as input and a white noise modelling unknown effects on the variability. According to the Akaike criterion, the CV Rinsp at a given day was best modelled by a weighted average of the PM10 over the past 4 days. Conclusions: The concentration of PM10 is associated with an increase in airway resistance variability in asthma, leading to a greater likelihood of future functional deterioration.

BACKGROUND: It has been reported that anesthesia may be associated to variation in chest wall (CW) mechanics. We have developed a CW scanning system (CWSS) based on self-mixing laser interferometers that allows the measure of relative displacement. If this approach is combined with Forced Oscillation Technique (FOT) it allows to infer CW mechanics. METHODS: Five patients were studied during anesthesia induction at different stages, while they were submitted to a sinusoidal pressure forcing at the mouth with components at 5, 11 and 19 Hz. At each step FRC (GE; Engstrom CareStation) and CW mechanics (phase displacement among these points and the pressure stimulus) were estimated by spectral technique. RESULTS: figure 1 shows results at 11 Hz. At all steps rib cage and abdomen the pressure stimulus travels faster in the rib cage than in the abdomen, likely because of the high inertia of the latter. FRC presents a minimum during sedation, then it increased during pressure support and it reaches physiological values after the recruitment maneuver. The marked variation in φ induced by sedation on the lower rib cage may be related to the reduction in FRC.