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The factor limiting the tolerance of personal respiratory protection equipment should be considered the frequency of respiratory movements, which reflexively changes when additional respiratory resistance occurs. Unfortunately, there is almost no information in the available literature about changes in the tolerability of personal respiratory protection equipment at different rates of respiratory movements. The purpose of this work was to study the tolerability of personal respiratory protection equipment when changing the frequency of respiratory movements.The study was conducted on practically healthy persons of both sexes (78 people), aged from 20 to 36 years. To simulate the conditions for the use of personal respiratory protection equipment, inspiratory resistive respiratory loads of 20% of the maximum intraoral pressure during the Mueller test were used. The tolerance of personal respiratory protection equipment was assessed using the Borg visual analogue of dyspnea scale, which reflected the level of subjective discomfort that occurs when additional respiratory resistance is turned on. During the action of additional respiratory resistance, the persons were asked to hold the frequency of respiratory movements, which was set using a special setting.An increase in the rate of respiratory movements against the background of additional respiratory resistance leads to a significant deterioration in the objective and subjective indicators of the functional state of the persons; replacing the inhaled air with an oxygen-rich respiratory mixture with carbon dioxide absorption did not lead to a significant improvement in the functional state. A moderate decrease (up to 70% of the initial frequency of respiratory movements) in the rate of respiration leads to an improvement in the indicators of adaptive activity in conditions of additional respiratory resistance. A significant decrease (up to 35% of the initial frequency of respiratory movements) in the rate of respiration under conditions of additional respiratory resistance leads to a deterioration of objective and subjective indicators of the functional state of the subjects.An increase in peak respiratory flow rates caused by an increase in the rate of respiration, in accordance with the well – known Rohrer equation, significantly increases inelastic resistance and, as a result, respiratory needs. These needs can be met at some time due to a significant increase in the work of the respiratory muscles, but due to fatigue of the latter, psychoemotional tension increases quite quickly and the use of personal respiratory protection equipment is abandoned.

Both Respiratory Flow (RF) and Respiratory Motion (RM) are visible in thermal recordings of infants. Monitoring these two signals usually requires landmark detection for the selection of a region of interest. Other approaches combine respiratory signals coming from both RF and RM, obtaining a Mixed Respiratory (MR) signal. The detection and classification of apneas, particularly common in preterm infants with low birth weight, would benefit from monitoring both RF and RM, or MR, signals. Therefore, we propose in this work an automatic RF pixel detector not based on facial/body landmarks. The method is based on the property of RF pixels in thermal videos, which are in areas with a smooth circular gradient. We defined 5 features combined with the use of a bank of Gabor filters that together allow selection of the RF pixels. The algorithm was tested on thermal recordings of 9 infants amounting to a total of 132 min acquired in a neonatal ward. On average the percentage of correctly identified RF pixels was 84%. Obstructive Apneas (OAs) were simulated as a proof of concept to prove the advantage in monitoring the RF signal compared to the MR signal. The sensitivity in the simulated OA detection improved for the RF signal reaching 73% against the 23% of the MR signal. Overall, the method yielded promising results, although the positioning and number of cameras used could be further optimized for optimal RF visibility.

With rapid advances in micro-fabrication processes and the availability of biologically-relevant lung cells, the development of lung-on-chip platforms is offering novel avenues for more realistic inhalation assays in pharmaceutical research, and thereby an opportunity to depart from traditional in vitro lung assays. As advanced models capturing the cellular pulmonary make-up at an air-liquid interface (ALI), lung-on-chips emulate both morphological features and biological functionality of the airway barrier with the ability to integrate respiratory breathing motions and ensuing tissue strains. Such in vitro systems allow importantly to mimic more realistic physiological respiratory flow conditions, with the opportunity to integrate physically-relevant transport determinants of aerosol inhalation therapy, i.e. recapitulating the pathway from airborne flight to deposition on the airway lumen. In this short opinion, we discuss such points and describe how these attributes are paving new avenues for exploring improved drug carrier designs (e.g. shape, size, etc.) and targeting strategies (e.g. conductive vs. respiratory regions) amongst other. We argue that while technical challenges still lie along the way in rendering in vitro lung-on-chip platforms more widespread across the general pharmaceutical research community, significant momentum is steadily underway in accelerating the prospect of establishing these as in vitro "gold standards".

Lung function (breath duration, respiratory flow [], and tidal volume [VT]), and end-expiratory O2 were measured in 19 adult bottlenose dolphins (Tursiops spp.) while at rest in water or beached for up to 10 min. The results show that inspiratory VT, expiratory VT, or inspiratory did not differ on land or in water. The average expiratory for all dolphins on land decreased by 16%, and the expiratory and total breath durations increased by 5% and 4%, respectively, compared with in water. There were temporal changes observed during beaching, where expired and inspired VT and inspired decreased by 13%, 16%, and 9%, respectively, after 10 min on land. These data suggest that dolphins compensate for the effect of gravity by adjusting respiration to maintain alveolar ventilation and gas exchange, but during extended durations, the increased work of breathing may impede ventilation and gas exchange. Continuous monitoring of lung function and gas exchange may help prevent long-term damage during out-of-water medical procedures, optimize animal transport conditions, and improve survival during stranding events.

CFD has emerged as a promising diagnostic tool for clinical trials, with tremendous potential. However, for real clinical applications to be useful, overall statistical findings from large population samples (e.g., multiple cases and models) are needed. Fully resolved solutions are not a priority, but rather rapid solutions with fast turn-around times are desired. This leads to the issue of what are the minimum modelling criteria for achieving adequate accuracy in respiratory flows for large-scale clinical applications, with a view to rapid turnaround times. This study simulated a highly-resolved solution using the large eddy simulation (LES) method as a reference case for comparison with lower resolution models that included larger time steps and no turbulence modelling. Differences in solutions were quantified by pressure loss, flow resistance, unsteadiness, turbulence intensity, and hysteresis effects from multiple cycles. The results demonstrated that sufficient accuracy could be achieved with lower resolution models if the mean flow was considered. Furthermore, to achieve an established transient result unaffected by the initial start-up quiescent effects, the results need to be taken from at least the second respiration cycle. It was also found that the exhalation phase exhibited strong turbulence. The results are expected to provide guidance for future modelling efforts for clinical and engineering applications requiring large numbers of cases using simplified modelling approaches.

Objective: The aim of this research was to develop a swallowing assessment method to help prevent aspiration pneumonia. The method uses simple sensors to monitor swallowing function during an individual's daily life. Methods: The key characteristics of our proposed method are as follows. First, we assess swallowing function by using respiratory flow, laryngeal motion, and swallowing sound signals recorded by simple sensors. Second, we classify whether the recorded signals correspond to healthy subjects or patients with dysphagia. Finally, we analyze the recorded signals using both a feature extraction method (linear predictive coding) and a machine learning method (support vector machine). Results: Based on our experimental results for 140 healthy subjects (54.5 $ \pm $ 32.5 years old) and 52 patients with dysphagia (75.5 $ \pm $ 20.5 years old), our proposed method could achieve 82.4% sensitivity and 86.0% specificity. Conclusion: Although 20% of testing sample sets were erroneously classified, we conclude that our proposed method may facilitate screening examinations of swallowing function. Significance: In combination with the portable sensors, our proposed method is worth utilizing for noninvasive swallowing assessment.

Seismocardiography (SCG) offers a potential non-invasive method for cardiac monitoring. Quantification of the effects of different physiological conditions on SCG can lead to enhanced understanding of SCG genesis, and may explain how some cardiac pathologies may affect SCG morphology. In this study, the effect of the respiration on the SCG signal morphology is investigated. SCG, ECG, and respiratory flow rate signals were measured simultaneously in 7 healthy subjects. Results showed that SCG events tended to have two slightly different morphologies. The respiratory flow rate and lung volume information were used to group the SCG events into inspiratory/expiratory groups or low/high lung-volume groups, respectively. Although respiratory flow information could separate similar SCG events into two different groups, the lung volume information provided better grouping of similar SCGs. This suggests that variations in SCG morphology may be due, at least in part, to changes in the intrathoracic pressure or heart location since those parameters correlates more with lung volume than respiratory flow. Categorizing SCG events into different groups containing similar events allows more accurate estimation of SCG features, and better signal characterization, and classification.

Objective: Swallowing experts often implement techniques that alter the breath and swallowing mechanism. However, there is limited understanding regarding the effect of these techniques on the coordination of swallowing and respiration. Hence, the present study examined the respiratory–swallowing coordination in normal adults using tongue‑hold maneuver. Materials and Methods: The study follows a cross‑sectional study design, wherein 25 healthy individuals(8 males and 17 females) within the age range of 18–25 years performed 10 ml water swallow with and without tongue‑hold maneuver. Nasal respiratory flow was recorded, and the duration of the swallow apnea and the phase of respiratory pattern were analyzed. Results: The results of paired t‑test revealed a significant difference for the duration of swallow apnea with tongue‑hold maneuver (mean = 0.782, standard deviation [SD] =0.329) when compared to swallow without tongue‑hold maneuver (mean = 0.60972,SD = 0.188) at P < 0.05. Moreover, the phase of respiration bracketing the swallowing was predominantly expiration in both the swallows. Conclusion: The outcome of the study suggests that tongue‑hold maneuver improves the duration of swallow apnea.

Quantifying respiratory flow characteristics in the pulmonary acinar depths and how they influence inhaled aerosol transport is critical towards optimizing drug inhalation techniques as well as predicting deposition patterns of potentially toxic airborne particles in the pulmonary alveoli. Here, soft-lithography techniques are used to fabricate complex acinar-like airway structures at the truthful anatomical length-scales that reproduce physiological acinar flow phenomena in an optically accessible system. The microfluidic device features 5 generations of bifurcating alveolated ducts with periodically expanding and contracting walls. Wall actuation is achieved by altering the pressure inside water-filled chambers surrounding the thin PDMS acinar channel walls both from the sides and the top of the device. In contrast to common multilayer microfluidic devices, where the stacking of several PDMS molds is required, a simple method is presented to fabricate the top chamber by embedding the barrel section of a syringe into the PDMS mold. This novel microfluidic setup delivers physiological breathing motions which in turn give rise to characteristic acinar air-flows. In the current study, micro particle image velocimetry (µPIV) with liquid suspended particles was used to quantify such air flows based on hydrodynamic similarity matching. The good agreement between µPIV results and expected acinar flow phenomena suggest that the microfluidic platform may serve in the near future as an attractive in vitro tool to investigate directly airborne representative particle transport and deposition in the acinar regions of the lungs.

Background Nasal obstruction is one of the most frequent symptoms in the ear, nose, and throat (ENT) setting. It can be evaluated either subjectively or objectively. In a subjective way, a visual analog scale (VAS) and the Sino-Nasal Outcome Test 20 (SNOT 20) can rapidly quantify the degree of obstruction, whereas the most commonly used objective methods are nasal endoscopy and active anterior rhinomanometry (AAR). It is still a matter of controversy to what extent the sense of nasal obstruction is associated with objective measures for nasal space and airflow. The aim of the study was to evaluate nasal breathing before and after functional nasal surgery by video-rhino-hygrometer (VRH) comparing the results with widely accepted methods. Methods Twenty patient candidates for septoplasty and inferior turbinate reduction were included in the study. SNOT-20, VAS, nasal endoscopy, and AAR were analyzed and compared with VRH values. Results Before surgery VRH showed variability of nasal respiratory flow between individuals and between nostrils. After surgery we had an increase (p < 0.05) of airflow in both nostrils. VRH data were found to be correlated with VAS and SNOT-20 values (p < 0.05) both pre- and postoperatively. Despite the statistically significant correlation of AAR with SNOT-20 and VAS, no statistically significant correlation between AAR and VRH was found. Conclusion VRH provides an immediate, easy, and noninvasive assessment of nasal respiration. For these reasons it can be used, in association with rhinoscopic data and other instrumental tests, to evaluate nasal breathing in daily ENT practice.

We describe how surface-tension-driven instabilities of the lung's liquid lining may lead to pulmonary airway closure via the formation of liquid bridges that occlude the airway lumen. Using simple theoretical models, we demonstrate that this process may occur via a purely fluid-mechanical "film collapse" or through a coupled, fluid-elastic "compliant collapse" mechanism. Both mechanisms can lead to airway closure in times comparable with the breathing cycle, suggesting that surface tension is the primary mechanical effect responsible for the closure observed in peripheral regions of the human lungs. We conclude by discussing the influence of additional effects not included in the simple models, such as gravity, the presence of pulmonary surfactant, respiratory flow and wall motion, the airways' geometry, and the mechanical structure of the airway walls.

The assessment of swallowing function is important for the prevention of aspiration pneumonia. We developed a new swallowing monitoring system that uses respiratory flow, swallowing sound, and laryngeal motion. We applied this device to 11 healthy volunteers and 10 patients with dysphagia. Videofluoroscopy (VF) was conducted simultaneously with swallowing monitoring using our device. We measured laryngeal rising time (LRT), the time required for the larynx to elevate to the highest position, and laryngeal activation duration (LAD), the duration between the onset of rapid laryngeal elevation and the time when the larynx returned to the lowest position. In addition, we evaluated the coordination between swallowing and breathing. We found that LAD was correlated with a VF-derived parameter, pharyngeal response duration (PRD) in healthy subjects (LAD: 959 ± 259 ms vs. PRD: 1062 ± 149 ms, r = 0.60); however, this correlation was not found in the dysphagia patients. LRT was significantly prolonged in patients (healthy subjects: 320 ± 175 ms vs. patients: 465 ± 295 ms, P

Studying the inspiratory recruitment of the scalenes is clinically relevant, but the interpretation of surface electromyographic (EMG) recordings is difficult. The aim of this study was to optimize an averaging method to analyze the surface EMG activity of the scalenes. Ten healthy subjects were studied. Nasal flow and surface EMG of the right scalene were recorded during 15 min epochs of quiet breathing. In four subjects, needle scalene EMG was also recorded. The flow signal was used to trigger the ensemble averaging of the ventilatory wave forms from 80 consecutive breaths. In eight cases, this evidenced a phasic inspiratory activation of the scalenes and permitted the determination of the electromechanical inspiratory delay (134+/-55 ms) and post-inspiratory activity (811+/-233 ms). When simultaneously available, surface and intramuscular recordings provided identical results. An averaging method triggered from a respiratory flow signal can identify and characterize a low phasic inspiratory activity of the scalenes within a noisy surface signal.

Study Objective: To illustrate the influence of anesthetic gases on respiratory flow measurements and to correct this influence. Design: In vitro evaluation. Setting: Laboratory. Measurements and Main Results: An in vitro method using a 120-L Tissot water-seal spirometer was used along with a Bicore CP-100, designed for use in intensive care units, and a Datex Ultima, designed for use in the operating room. The flow transducer of one of the instruments being tested was placed in the gas inlet of the Tissot so that simultaneous measurements could be made. Timed flows (2 to 60 L/min) of various gases (O 2 and air) and gas mixtures (halothane-O 2 , isoflurane-O 2 , N 2 O-O 2 , and N 2 O-O 2 -isoflurane) were used and the measurements made by the Tissot and the test instrument compared. The Datex Ultima, which includes software corrections for anesthetics, was able to accurately measure gas flows (2 to 60 L/min) of air, 100% oxygen, and anesthetic gas mixtures to within ±10% of measurements made by the Tissot. The Bicore CP-100, intended for use with mechanically ventilated patients, accurately measured air and 100% oxygen flow rate to within ±8% of the measurements made by the Tissot, but there were large errors (up to 40%) when anesthetics were used. Conclusions: This study illustrates the effects of anesthetic gases on measurements of ventilatory flow and the need to ascertain whether corrections are needed to improve the accuracy of flow transducers.

A partial-body plethysmograph was developed for measuring the respiratory flow of anesthetized mice during routine microimaging experiments performed in the close confines of an 89-mm-diameter, vertical-bore magnet. Respiratory flow patterns were used for synchronizing conventional T2-weighted spin-echo imaging with the respiratory cycle, thereby, significantly reducing motion-induced artifacts and increasing observed liver lesion contrast.

One objective of mechanical ventilation is the recovery of spontaneous breathing as soon as possible. Remove the mechanical ventilation is sometimes more difficult that maintain it. This paper proposes the study of respiratory flow signal of patients on weaning trials process by autoregressive moving average model (ARMA), through the location of poles and zeros of the model. A total of 151 patients under extubation process (T-tube test) were analyzed: 91 patients with successful weaning (GS), 39 patients that failed to maintain spontaneous breathing and were reconnected (GF), and 21 patients extubated after the test but before 48 hours were reintubated (GR). The optimal model was obtained with order 8, and statistical significant differences were obtained considering the values of angles of the first four poles and the first zero. The best classification was obtained between GF and GR, with an accuracy of 75.3% on the mean value of the angle of the first pole.

Respiratory drives folow various afferent pathways to the respiratory centres; nevertheless, steady-state breathing patterns described in terms of tidal volumes and phase durations are largely independent of the nature of the respiratory stimulus. Flow has now been recorded during steady states from six subjects in rest and hyperpnoea induced by exercise, and hypercapnia in euoxia and in hypoxia (asphyxia). Flow patterns from different stimuli were compared isopnoeically. Quantitative methods allowed the patterns to be described in terms of several variables. The consistent small differences in isopnoeic flow patterns were: In asphyzia, the initial inspiratory acceleration was greater than in hypercapnia, and the peak flow was reached earlier. In exercise the peak flow occured later in inspiration, and the expiratory flow was maintained high until nearer the end of the phase than with the chemical drives so that the flow pattern was less angular in shape. Stimulus-dependent effects, obvious during transient changes, are greatly attenuated rather than absent in steady states.

The inhalation of micron-sized aerosols into the lung's acinar region may be recognized as a possible health risk or a therapeutic tool. In an effort to develop a deeper understanding of the mechanisms responsible for acinar deposition, we have numerically simulated the transport of nondiffusing fine inhaled particles (1 mum and 3 microm in diameter) in two acinar models of varying complexity: (i) a simple alveolated duct and (ii) a space-filling asymmetrical acinar branching tree following the description of lung structure by Fung (1988, "A Model of the Lung Structure and Its Validation," J. Appl. Physiol., 64, pp. 2132-2141). Detailed particle trajectories and deposition efficiencies, as well as acinar flow structures, were investigated under different orientations of gravity, for tidal breathing motion in an average human adult. Trajectories and deposition efficiencies inside the alveolated duct are strongly related to gravity orientation. While the motion of larger particles (3 microm) is relatively insensitive to convective flows compared with the role of gravitational sedimentation, finer 1 microm aerosols may exhibit, in contrast, complex kinematics influenced by the coupling between (i) flow reversal due to oscillatory breathing, (ii) local alveolar flow structure, and (iii) streamline crossing due to gravity. These combined mechanisms may lead to twisting and undulating trajectories in the alveolus over multiple breathing cycles. The extension of our study to a space-filling acinar tree was well suited to investigate the influence of bulk kinematic interaction on aerosol transport between ductal and alveolar flows. We found the existence of intricate trajectories of fine 1 microm aerosols spanning over the entire acinar airway network, which cannot be captured by simple alveolar models. In contrast, heavier 3 microm aerosols yield trajectories characteristic of gravitational sedimentation, analogous to those observed in the simple alveolated duct. For both particle sizes, however, particle inhalation yields highly nonuniform deposition. While larger particles deposit within a single inhalation phase, finer 1 microm particles exhibit much longer residence times spanning multiple breathing cycles. With the ongoing development of more realistic models of the pulmonary acinus, we aim to capture some of the complex mechanisms leading to deposition of inhaled aerosols. Such models may lead to a better understanding toward the optimization of pulmonary drug delivery to target specific regions of the lung.

Background Maximum pressures developed by the respiratory muscles can indicate the health of the respiratory system, help to determine maximum respiratory flow rates, and contribute to respiratory power development. Past measurements of maximum pressures have been found to be inadequate for inclusion in some exercise models involving respiration. Methods Maximum inspiratory and expiratory airway pressures were measured over a range of lung volumes in 29 female and 19 male adults. A commercial bell spirometry system was programmed to occlude airflow at nine target lung volumes ranging from 10% to 90% of vital capacity. Results In women, maximum expiratory pressure increased with volume from 39 to 61 cmH2O and maximum inspiratory pressure decreased with volume from 66 to 28 cmH2O. In men, maximum expiratory pressure increased with volume from 63 to 97 cmH2O and maximum inspiratory pressure decreased with volume from 97 to 39 cmH2O. Equations describing pressures for both sexes are: Pe/Pmax = 0.1426 Ln( %VC) + 0.3402 R2 = 0.95 Pi/Pmax = 0.234 Ln(100 - %VC) - 0.0828 R2 = 0.96 Conclusion These results were found to be consistent with values and trends obtained by other authors. Regression equations may be suitable for respiratory mechanics models.

The possible mechanism of wheeze generation in tracheostenosis was identified by measuring inspiratory and expiratory flow in a “morphological and distensible” realistic tracheostenosis model. The shape of the model was based on CT (Computed Tomography) images of a patient that had tracheostenosis. A trachea consists of tracheal cartilage rings and smooth muscle. Spatial variation of wall distensibility was achieved in the model by varying the wall thickness based on the elastic modulus measured in pig airways. The spatial variation influenced the flow in the airway and the turbulence production rate decreased faster at smooth muscles. Using the model, we investigated the mechanism of wheeze generation by focusing on the turbulence intensity. The turbulence intensity in expiratory flow was about twice that in inspiratory flow, and larger vortices existed in post-stenosis in expiratory flow, and thus might contribute to wheeze generation.

In order to advance our understanding of the relation between respiration and deglutition, simultaneous videofluoroscopy and respirodeglutometry was performed. Fifteen normal, healthy, young adults (20–29 years of age) were connected to a respirodeglutometer and positioned for simultaneous videofluoroscopic assessment in the lateral plane. Subjects performed three swallows each of a 5-ml and a 10-ml bolus of liquid barium and a 5-ml bolus of paste barium, for a total of nine swallows per subject. Location of the bolus head as identified with videofluoroscopy was associated with eight respirodeglutometric variables. In addition, temporal relations for seven respirodeglutometric variables were calculated as a function of bolus volume and viscosity. Significant temporal differences were found for five of the variables by volume. No significant temporal differences were noted by viscosity. Expiration occurred before 79% and after 96% of the swallows. The number of inspirations preceding a swallow suggested a possible effect resulting from the need to hold a bolus in the mouth before receiving instructions to swallow during videofluoroscopic assessment. This effect may be important during patient evaluation. For a significant number of swallows, respiratory flow ceased before the velum was fully elevated.

Summary The effects of training on ventilation and blood gases during exercise were investigated in 6 clinically normal, detrained Thoroughbred horses. They underwent a 16 week training programme similar to the type frequently used for Thoroughbred racehorses in Great Britain. Standardised treadmill exercise tests (2 min canter at 8 and 10 m/s [C8 and C10] and 2 min gallop at 12 m/s [G12], on a level surface) were performed prior to and after 16 weeks of training. Respiratory flow rates were measured using ultrasound flow transducers. Blood samples were drawn from a transverse facial artery and the right atrium. Minute ventilation, respiratory frequency and tidal volume were not significantly altered by training. Peak inspiratory flow rate was lower following training at 8 and 10 m/s, but not at 12 m/s. Arterial oxygen tension was decreased during trot and canter following training. Blood lactate concentration post G12 decreased following training (10.5 ± 2.2 mmol/l vs. 7.7 ± 2.2 mmol/l; P

To investigate the influence of increased respiratory frequency on respiratory mechanics in the horse, measurements were made in two groups of seven tracheostomised horses before and after the administration of doxapram. The horses in group I had normal base line values for respiratory mechanics, whereas the horses in group II had significantly lower values of dynamic compliance (Cdyn), higher respiratory resistance (R), and a higher total change in pleural pressure (ΔP). The administration of 0·3 mg kg −1 doxapram intravenously resulted in a significant increase in respiratory frequency (f R ), R, ΔP, tidal volume (V T ), and peak to peak respiratory flow (V), and a decrease in Cdyn in both groups of horses. The group II horses had significantly greater increases in R and ΔP than the horses in group I.

Employing a bolus inhalation system, we noninvasively measured the fraction of inhaled ozone (O3) that is absorbed during a single breath (lambda) as a function of bolus penetration volume into the respiratory tract (Vp). During nasal breathing at a constant respiratory flow of 250 ml/s, lambda increased smoothly as Vp increased with 80% of the inhaled O3 absorbed in the upper airways and 90% absorbed at the distal end of the trachea. Oral breathing caused a distal shift of the lambda-Vp distribution to the extent that absorption in the upper airways was reduced to 50% and inhaled O3 was 90% absorbed only after a bolus reached the 13th bronchial generation. Therefore, an exercise-induced change from nasal to oral breathing can render the distal lung more susceptible to O3 damage because of an elevation in O3 dose. We also found that changing the peak inhaled bolus concentration over a 10-fold range of 0.4–4 ppm O3 did not affect the lambda-Vp distribution. This finding implies that the diffusion and chemical reaction dynamics that dictate O3 absorption are linear processes.

The additional work attributable to breathing through five Mapleson A anaesthetic breathing systems (Magill, Lack, Parallel Lack, Humphrey ADE and Enclosed Magill) was studied using a lung model. With all five systems, the additional work was found to be a function of fresh gas flow, respiratory flow as well as system geometry. Within the range of fresh gas flow and respiratory flow studied, the additional work ranged between 80 mJ.l-1 and 182 mJ.l-1. Expiratory work was always greater than the inspiratory workload. Increasing fresh gas inflow into the system increases expiratory work, both resistive and elastic components. The Magill system posed the least work expenditure. The values for the additional work obtained with the lung model were of the same order of magnitude when measurements were taken in volunteers.

This study investigates the effect of helium concentration in inspired gas on resistance to breathing during experimental upper airway obstruction. Obstruction was modeled by use of a series of four polyvinyl endotracheal tubes narrowed progressively in their midportions with C clamps. Percentage ratios of helium-oxygen gas mixtures were 0:100, 40:60, 60:40, and 80:20. Gas flow was provided by two methods: 1) nontidal flow from compressed gas tanks from which resistance was calculated from pressure and flow measurements, and 2) tidal respiratory flow from human volunteers from whom respiratory effort was evaluated by using airway pressure measurements integrated over 90-second trial periods. The results derived from both methods demonstrated that the effect of helium in reducing resistance and pressure in an obstructed airway is linear (p < .016) and inversely proportional to helium concentration. Reductions in resistance and pressure were larger for the tighter obstructions (p < .007). As helium was added to the gas mixture (from 0% to 80%), resistance and airway pressure measurements dropped 42% and 58%, respectively. The major conclusions are that 1) even low concentrations of helium may have therapeutic value and 2) helium is effective only for more severe obstructions.

The regular involuntary inspiratory muscle contractions that occur in normal conscious men during breath holding were quantified by means of the waves of intrathoracic pressure that they produced. A stream of cool air circulated through the nose and mouth reproducibly inhibited the contractions. The degree of inhibition increased with increasing nasal flow in the range of normal resting respiratory flow and with lower temperature of circulating gas. The effect depended on the phase of respiration in which flow occurred and was abolished by local anesthesia of the nose and pharynx. The results demonstrate that the upper airway contains flow-sensitive receptors, the discharge of which can have a marked influence on respiration.

In a lung model the rebreathing effects of different respiratory flow patterns (RFP) were studied in the coaxial Mapleson A (Lack) and D (Bain, Coax-II) systems during spontaneous breathing. In the Mapleson A system RFP was not found to have any impact. In the D systems FACO2 was higher with an RFP typical of halothane-anaesthetized patients than with an RFP with an exponentially decreasing expiratory flow and an end-expiratory flow pause (FTEP). The difference in FACO2 was 26% with a VF corresponding to 100 ml X min-1 X kg-1 body weight. The RFP in a non-anaesthetized volunteer was intermediate between these two patterns. Rebreathing decreased in the D systems with prolongation of FTEP and when a decelerating expiratory flow was used.

The validity of the Stenqvist-Sonander formula for calculating the end-expiratory fraction of carbon dioxide (FACO2) in the coaxial Mapleson D (Bain) systems was evaluated using a lung model for simulated spontaneous breathing with an optional respiratory wave form. Two different respiratory flow patterns were used, one representing relaxed breathing in a volunteer and one resembling the respiration found in halothane anaesthesia. Each pattern was used with five different fresh gas flows and three different respiratory rates. The formula was found to be quite accurate when the flow pattern of an awake volunteer was simulated, but it underestimated the observed FETCO2 value by about 10% in halothane breathing. It is concluded that the formula can be recommended for use in theoretical and educational situations but that it is too complicated for application in clinical practice.

We studied the effects of prostacyclin on pattern of breathing in six anaesthetized pigs with aortic obstruction. PGI 2 causes a rightward displacement of VT/T relationship (Hering-Breuer threshold curve) without a corresponding change I respiratory flow. With airways occluded at the end expiratory level, we analyzed how PGI affects the central respiratory rhythm in the absence of the phasic lung volumi-related vagal loop. Infusion of prostacyclin causes leftward displacement of the T /T relationship and an increase in T o correlated with the hypotensive action The change in the bulbo-pontine pacemaker is caused by a marked increase in T , and this suggests that PGI can modulate the central respiratory rhythm, inde$endently of the blood pressure level.

Vagal influence on inspiratory motor output was assessed in 20 normal subjects and in 12 patients with respiratory disorders under enflurane anethesia using the method of airway occlusion. The change in inspiratory duration during occlusion (delta TI) was measured from mechanical parameters (respiratory flow and tracheal pressure). In eight of the subjects, however, the effect of occlusion and augmentation of tidal volume was further evaluated from diaphragmatic electromyogram. In normal subjects delta TI (mechanical) averaged 0.15 s (range -0.1 to +0.77 s) and correlated with the duration of inspiration during occlusion. Electromyographic observations indicated that the change in neural TI exceeds the change in mechanical TI by approximately 0.2 s and that augmentation of tidal volume shortens TI with no apparent volume threshold. There was a tendency for vagal influence to be higher with restrictive lung disease and lower with obstructive airway disease. These observations indicate that a majority of humans display a significant vagal influence on TI in the spontaneous tidal volume range under anesthesia.

When the whole body is exposed to sinusoidal variations of ambient pressure (delta Pam) at very low frequencies (f), the resulting compression and expansion of alveolar gas is almost entirely achieved by gas flow through the airways (Vaw). As a consequence thoracic gas volume (TGV) may be computed from the imaginary part (Im) of the delta Pam/Vaw relationship: TGV = PB/[2 pi f X Im(delta Pam/Vaw)], where PB is barometric minus alveolar water vapor pressure. The method was tested in 35 normal subjects and compared with body plethysmography. The subjects sat in a chamber connected to a large-stroke-volume reciprocating pump that brought about pressure swings of 40 cmH2O at 0.05 Hz. delta Pam and Vaw were digitally processed by fast Fourier transform to extract the low-frequency component from the much larger respiratory flow. Total lung capacities (TLC) obtained by ambient pressure changes and by plethylsmography were highly correlated (r = 0.959, p less than 0.001) and not significantly different (6.96 +/- 1.38 l vs. 6.99 +/- 1.38). TLC obtained by ambient pressure changes were not influenced by lowering the frequency to 0.03 Hz, adding an external resistance at the mouth, or increasing abdominal gas volume. We conclude that the method is practical and in agreement with body plethysmography in normal subjects.

SUMMARY The effect of the respiratory flow pattern on the fresh gas flow required to prevent rebreathing in a T-piece system was investigated using laboratory models. With a sine wave pattern slighdy less than 2½ times the minute volume was necessary. With the flow patterns produced by the ventilators studied, up to 3 times the minute volume was required. It is suggested that during artificial ventilation with certain flow patterns higher fresh gas flows may be required.

Apparatus and procedures are described for measuring respiratory function in intact and unanesthetized guinea pigs during exposure to clean or contaminated air. Modification of previously reported methods enabled measurements on several animals in a single experiment. With this multi-animal test system, values for total respiratory flow resistances, respiratory rates, and tidal volumes that were obtained during inhalation of air or formaldehyde-contaminated air agreed closely with previously reported values for single-animal test methods. The method is sensitive for detecting early functional alterations during inhalation of irritants at concentrations much below acutely toxic levels, and the multi-animal test system permits rapid screening tests for respiratory effects of contaminated atmospheres.

Measurements of flow resistance of various components of the respiratory system were measured in adult male subjects in the sitting position. Nasal resistance is the largest single component being nearly one-half the total and two-thirds of the airway resistance during nose breathing. It is highly nonlinear, and shows much variability. During mouth breathing upper airway resistance (mouth, pharynx, glottis, larynx and upper trachea) is also markedly nonlinear, and accounts for one-third the total airway resistance. Lower airway resistance is approximately linear up to flows of 2 liters/sec. Pulmonary tissue resistance is low as reported in this study. Chest wall resistance is nearly linear up to flow rates of 2 liters/sec and accounts for slightly less than half the total respiratory resistance during mouth breathing and 10–19% during nasal breathing. larynx; airways; chest wall; nose Submitted on December 16, 1963

For measurement of gas flow, a flowmeter consisting of a heated wire anemometer combined with a thermocouple was implanted into a dorsobronchus of the lungs in unanesthetized ducks. The direction of gas flow recorded in the dorsobronchus during spontaneous breathing and during artificial ventilation was from the mesobronchus to the parabronchi both in inspiration and expiration. This result is in accordance with the unidirectional flow hypothesis propounded by Bethe and by Hazelhoff, and is incompatible with the alternating respiratory flow hypothesis of Zeuthen.

To evaluate the regional ventilation using 133Xe under different conditions, the respiratory flow and the phase with image were measured simultaneously, and sequential frames were made breath by breath. The flow signal and phase signal were converted to pulse signals by a microcomputer and stored with image data in the same file. Thus, the tidal volume and duration of each breath were measured. From sequential frames compiled breath by breath, an activity breath-number curve was made in each pixel, and the half-clearance breath number (B1/2) was calculated. The changes in conventional half-clearance time (T1/2) and B1/2 were compared under different ventilatory conditions in normal subjects and in patients with chronic pulmonary emphysema. Values of B1/2 indicated the change of turnover rate more accurately than T1/2. It is considered that B1/2 is a better parameter than T1/2 for evaluating the change in regional ventilatory function under different conditions.

A previously developed transport analysis was used to simulate two sets of single-breath nitrogen washout data from each of four normal subjects. The analysis treats simultaneous gas flow and longitudinal diffusion and incorporates a modified form of Weibel's anatomical model “A” to describe the airway geometry. For each data set, four geometric parameters of the analysis were varied in a computer simulation until it matched the instantaneous expiratory concentration curve; particular emphasis was placed on matching the data in the concentration transition. Monitored values of functional residual capacity and instantaneous respiratory flow were supplied as inputs to each simulation. For each subject, a reasonable computer simulation could be obtained using a single set of lower airway geometric parameters, even though the average respiratory flow rate varied by as much as 53% from test to test; this result is due to the ability of the transport analysis to directly account for gas mixing during normal respiration. Under the same conditions the anatomic dead space varied by as much as 24%.

To investigate the reflex mechanisms of sighs (spontaneous large breaths)(VT greater than 2 X control VT) in infants, recordings of respiratory flow and tidal volume (VT) were made during sleep. The frequency of sighs was greater at 1 than at 5 days of age, while respiratory frequency and controlVT did not change. Most sighs (93%) had a biphasic pattern of inspiratory flow characterized by an inspiratory duration nearly twice that of control breaths, with an abrupt change in flow rate halfway through inspiration. Interruption of ventilation (3–7 s of airway occlusion) appeared to generate astimulus for biphasic sighs, since sighs occurred during the first breath after termination of airway occlusion more frequently after long thanafter brief occlusions. However, a biphasic inspiratory pattern in airway pressure was rarely observed while the airways were occluded, regardless of occlusion duration. This suggests that increase in lung volume during the initialpart of the biphasic inspiration following occlusion is a stimulus for the second part. Thus the underlying reflex mechanism of sighs in human infantsappears to be the same as occurs in the so-called Head's paradoxical response to lung inflation.

Inspiratory ramp activity, postramp activity (PRA) of diaphragm and respiratory flow were studied in anesthetized rabbits and conscious humans under inspiratory resistive load. Under load with chloralose-urethane anesthesia neural inspiration lasted 124 +/- 12 msec more than under control conditions and end of mechanical inspiration lagged behind that of neural inspiration by 114 +/- 4 msec. With pentobarbital-urethane anesthesia corresponding changes under load were 67 +/- 18 msec and 44 +/- 6 msec; after SO2 block of slowly adapting stretch receptors in bronchi corresponding changes under load were nil and 65 +/- 7 msec. In humans corresponding changes under load were about 192 and 127 msec. Both in rabbits and humans time course of PRA under load was essentially unchanged. Hence, under load a considerable part of PRA (or all of it under pentobarbital-urethane anesthesia without SO2 block) occurred during inspiration and that occurring during expiration was smaller than under control conditions. Consequently, under load braking of expiratory flow was smaller and peak expiratory flow occurred earlier than under control conditions.

The modifications of Ayre's T-piece system can be divided into three types. In the first there is no expiratory limb, in the second the capacity of the expiratory limb is greater than the tidal volume, and in the third the capacity of the expiratory limb is less than the tidal volume. On the basis of previous mathematical and laboratory investigations by other authors, the three types are discussed with reference to the resistance to respiration and minimum fresh gas flow required to prevent rebreathing and air dilution during both spontaneous and controlled ventilation. The resistance and the fresh gas flow requirements are related to the expiratory flow rates and respiratory flow patterns which occur in children. It is suggested that the most convenient system is a T-piece of 10 mm diameter with an expiratory limb greater than the tidal volume and a bag attached to the expiratory limb. A fresh gas flow of up to 2½–3 times the minute volume is required.

National audience; The aim of this study was (i) to characterise the glottal dynamics during human breathing in vivo using laryngofiberscopy and synchronised airflow recordings and (ii) to quantify the effects of a mobile glottis and unsteady flow conditions on laryngeal jet-flow dynamics using CFD modelling. The in vivo study showed that the glottis can be extremely variable during breathing and hence influence airflow characteristics. A glottal area widening was quantified during inspiration, with a typical ratio of 3:1 as compared to expiration. Airflow rate variations differ from harmonic signal during eupnea as well as tachypnea. The correlation between flow-rate and glottal area will be discussed and compared to previous clinical investigations. Preliminary 2D CFD simulations of the glottal jet were carried out based on the measured flow-rate and glottal changes during eupnea. Impact of unsteady flow conditions on the jet development is demonstrated.