Kinetic energy loss and convective acceleration in respiratory resistance measurements

Loring, S. H.; Elliott, E. A.; Drazen, Jeffrey M.

doi:10.1007/bf02713989

Cited by 55 publications

(24 citation statements)

References 6 publications

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“…The RETT may have masked any change in Rrs with a change in lung volume, inasmuch as ET tubes do not change in diameter during respiration, and errors are undoubtedly present in the calculation of RETT. Loring et al (27) demonstrated that the RETT is influenced by the kinetic energy losses due to flow separation, which is dependent on the geometry at the junction of the ET tube and the trachea in vivo and the geometry at the end of the ET tube in isolation. Any errors in the calculation of RETT arise from kinetic energy dissipation at the end of the ET tube and are dependent on the magnitude of the kinetic term ' /2 P(V/A)~, where p is the gas density, V is the gas flow, and A is the area at a given cross section.…”

Section: Discussionmentioning

confidence: 99%

“…The ET tubes used in this study had an internal diameter of 3.0 mm, and therefore the RETT calculated in vitro may significantly overestimate the in vivo RETT. The in vitro RETT may have more accurately estimated the in vivo RETT if the distal tip had been inserted into another tube with an internal diameter equal to the internal diameter of the trachea of the rabbits studied, as this would have reduced the cross-sectional area at the distal end of the ET tube and therefore flow separation and kinetic energy loss (27). However, flow separation in vivo depends on many factors, including the geometry of the ET tube-tracheal connection, the exact area of the trachea, the distance the ET tube is inserted into the trachea and the position or angulation of the distal ET tube.…”

Section: Discussionmentioning

confidence: 99%

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Effect of Volume History on Measurements of Respiratory Mechanics Using the Interrupter Technique

Freezer

Nicolaï

Sly³

1993

Pediatr Res

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ABSTRACT. The importance of the viscoelastic properties of the tissues of the respiratory system has recently been recognized, and lung models have been produced to describe the resistive and viscoelastic properties of the lung. The pulmonary mechanics of 10 rabbits were studied using the interrupter technique to assess the effect of volume history on the resistive and viscoelastic elements of the respiratory system. The influence of the tone of the muscles of respiration was also studied. In healthy lungs, the resistive and viscoelastic elements of the lung are dependent on the volume history of the respiratory system and are significantly lower if these elements do not reach a resting position before expiration. The chest wall made a significant contribution to the resistive and viscoelastic elements of the respiratory system, which was also dependent on the lung volume history. The tone of the muscles of respiration had no effect on the resistive or viscoelastic elements of the respiratory system. (Pediatr Res 33: 261-266, 1993) Abbreviations R1, resistance of respiratory system RZ, dissipative properties of lung or chest wall El, static elastance of respiratory system E2, elastic properties ET, endotracheal FRC, functional residual capacity Pao, airway opening pressure Pes, esophageal pressure Pdiff, static recoil pressure of respiratory system Pinit, resistance pressure drop across airways and chest wall Rinit, Newtonian flow resistance of airways and chest wall Rrs, flow resistance of the respiratory system ANOVA, analysis of variance RE=, endotracheal tube resistance Recently, the importance of the viscoelastic properties of the tissues of the respiratory system has been recognized (1-10). The two-compartment model for the lung that best represents experimental data consists of a single alveolar compartment surrounded by a viscoelastic tissue compartment (1 1), and models have been produced to describe the resistive and viscoelastic properties of the lung. This model can be represented by springs 26and dashpots as shown in Figure 1, where R1 represents the airway resistance and any Newtonian component of tissue resistance that is in parallel with another three elements (El, E2, and R2) in the form of the Kelvin body, an elastic element in parallel with a series elastance-resistance. El represents the static elastance of the respiratory system and E2 and R2 the dissipative and elastic properties of the tissues of the lung and chest wall (12). If the two bars at either end of the model are moved relative to each other to represent the changes in volume during respiration, the properties of R1, El, R2, and E2 determine the behavior of the model. If the bars are stopped abruptly, simulating a flow interruption, the "energy dissipation" in R I and El will stop immediately; however, some time will be required for R2 and E2 to reach their resting position. This model allows a better description of the changes in Pao observed after rapid airway occlusions during passive expiration than the traditional one-com...

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Effect of Volume History on Measurements of Respiratory Mechanics Using the Interrupter Technique

Freezer

Nicolaï

Sly³

1993

Pediatr Res

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“…Req was subtracted, wherever appropriate, so that the results reported represent intrinsic resistance values. Because abrupt changes of diameter were not present in our circuit, errors of measurement of flow resistance were avoided [14,15]. The equipment dead space was 0.4 ml.…”

Section: Methodsmentioning

confidence: 99%

Mechanical and morphometrical changes in progressive bilateral pneumothorax and pleural effusion in normal rats

Sousa¹,

Moll²,

Pontes³

et al. 1995

Eur Respir J

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M Me ec ch ha an ni ic ca al l a an nd d m mo or rp ph ho om me et tr ri ic ca al l c ch ha an ng ge es s i in n p pr ro og gr re es ss si iv ve e b bi il la at te er ra al l p pn ne eu um mo ot th ho or ra ax x a an nd d p pl le eu ur ra al l e ef ff fu us si io on n i in n n no or rm ma al l r ra at ts s Respiratory system, lung, and chest wall resistances and elastances (static and dynamic) were determined in 14 animals. For this purpose, the end-inflation occlusion during constant inspiratory flow method was used. Chest wall configuration at both functional residual capacity (FRC) and end-inspiration tidal volume (i.e. FRC+(VT)) was also evaluated in: 1) 15 rats by measurements of lateral and anteroposterior diameters, and circumferences at the 3rd intercostal space and xiphoid levels; and 2) in 16 rats by measurements of thoracic cephalocaudal diameter. In addition, changes in functional residual capacity were measured.Both in pneumothorax and pleural effusion, resistances were not altered, but static and dynamic respiratory system and lung elastances increased progressively. Morphometric changes were similar at both functional residual capacity and endinspiration; however, whereas pleural effusion increased all diameters, pneumothorax did not modify lateral diameter. Functional residual capacity was decreased in both conditions.In conclusion, pneumothorax and pleural effusion induced similar mechanical changes, but thoracic configuration was differently affected, since lateral diameters were increased in pleural effusion only.

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“…However, it is still uncertain whether test bench measurements may be safely applied in a clinical setting. Loring et al (9) noted that changes in the position or angulation of the distal ETT could cause several-fold changes in effective resistance and concluded: "These factors make it difficult, if not impossible, to estimate ETT resistance reliably." Also, Sly et al (10) seriously cautioned against the use of constants derived from in vitro experiments.…”

mentioning

confidence: 99%

Direct Measurement of Intratracheal Pressure in Pediatric Respiratory Monitoring

et al. 2002

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We describe a method based on a Fabry-Perot interferometer at the tip of an optic fiber with a diameter of 0.25 mm for direct measurement of tracheal pressure in pediatric respiratory monitoring. The response time of the pressure transducer and its influence on the resistance of pediatric endotracheal tubes (internal diameter, 2.5 to 5 mm) during constant and dynamic flow at different ventilator settings in a lung model were measured. The transducer was positioned at Ϫ1.5 (inside), 0, and ϩ1.5 cm (outside) relative to the tip of the endotracheal tube and compared with a reference pressure inside the trachea. The clinical application of the transducer was tested in five pediatric patients. The response time of the transducer was 1.3 ms. The influence of the fiberoptic transducer on tube resistance was negligible during constant flow in inspiratory and expiratory directions for all endotracheal tubes tested. There was no difference in pressure measurements with the transducer positioned at or 1.5 cm below or above the tip of the endotracheal tube during dynamic measurements. During clinical circumstances insertion of the fiberoptic transducer was easy, recordings were stable, and the safety of the patient was not jeopardized. The fiberoptic transducer provided a reliable and promising way of monitoring tracheal pressure in intubated pediatric patients. The presence of the probe did not interfere with either pressure-flow relationship or patient care and safety. The technique is proposed for monitoring of respiratory mechanics and calculation of changes in tube resistance caused by kinking and secretions. Respiratory monitoring in pediatric intensive care is currently represented by proximal P/V loops obtained in ventilator software or intensive care monitors using flowmeters placed near the connection between the ventilator system and ETT. This is obviously insufficient as information gained from such P/V loops mainly stems from ETT resistance and performance of ventilator valves. We have previously demonstrated that monitoring respiratory mechanics by direct measurement of tracheal pressure offers considerable advantages compared with monitoring based on either measurements obtained proximal to the tube or tracheal pressures calculated by subtracting pressure needed to overcome flow-dependent tube resistance. In the adult setting tracheal pressure measurement is accomplished by introducing an air-or liquid-filled catheter into the ETT and connecting it to a conventional pressure transducer (1). In the pediatric setting it has generally been held to be impossible to use endotracheal catheters for continuous pressure measurement owing to the encroachment on cross-sectional area of the narrow pediatric tubes (2). Instead hydrodynamic models of varying complexity have been proposed for the calculation of tracheal pressure, i.e. the pressure fall across the ETT because of its resistance, based on measurements above the tube. Guttmann et al. (2)

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Kinetic energy loss and convective acceleration in respiratory resistance measurements

Cited by 55 publications

References 6 publications

Effect of Volume History on Measurements of Respiratory Mechanics Using the Interrupter Technique

Effect of Volume History on Measurements of Respiratory Mechanics Using the Interrupter Technique

Mechanical and morphometrical changes in progressive bilateral pneumothorax and pleural effusion in normal rats

Direct Measurement of Intratracheal Pressure in Pediatric Respiratory Monitoring

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