Modelling the mechanical effects of tracheal tubes in normal subjects

Rocco, P.R.M.; Zin, Walter A.

doi:10.1183/09031936.95.08010121

Cited by 18 publications

(12 citation statements)

References 25 publications

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“…After a brief period of apnoea (5-6 s) the subjects were disconnected from the ventilator and the occlusion was rapidly released, thus avoiding any equipment resistance except for the tracheal tube (TT) (Rocco and Zin 1995), and they were then allowed to expire freely into the atmosphere until the relaxation volume was achieved (about 15 s), i.e. until the RIP signal was steady for at least 1.5 s and indistinguishable from baseline.…”

Section: Methodsmentioning

confidence: 99%

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Determination of rate-constants as a method to describe passive expiration

2003

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To describe the relaxed expiration by a two-compartment model, we introduced a gas/energy transfer between the lung compartment ( V(1)) and a second one ( V(2)). If V(2) were a real volume, the rate-constants (i.e. the flow/volume ratios) of the compartments would describe a real gas-exchange. Alternatively, if a viscoelastic behaviour of the lung or an energy-exchange between compartments was simulated, V(2) would become a "pseudo-volume". We studied nine mechanically ventilated subjects. Changes in volume were transduced by respiratory inductive plethysmography. The rate-constants were assumed (together with the initial volumes of the compartments) as parameters to fit the total volume [ V(1)( t)+ V(2)( t)]. Once the best fitting was performed using these "physiological" parameters, the system was directly identified and the compartments were independently analysed. The time profile of the second compartment showed a maximum that depended on the value of the rate-constants. Appropriate tests confirmed the reliability of our procedure. In conclusion, our analysis demonstrated that the energy/volume of the second compartment may increase at the beginning of expiration and then decrease, showing a maximum, even though the total curve can only be a decreasing one. In other words, the slowing down of the curve representing expiratory volume is due not only to the longer emptying of the second compartment, but also to the interaction between the two compartments. As presently proposed, this interaction can be represented by either a gas exchange between two actual volumes, or a mechanical energy transfer between the lung and the tissue compartment.

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Section: Methodsmentioning

confidence: 99%

“…Since the passive expiration occurs through a tracheal tube, the flow can be turbulent and may determine ''nonohmic'' resistances (Rocco and Zin 1995). However, when the flow is relatively small, as in this study (<1 l/ s), the assumption of linearity remains valid (Pedley and Drazen 1986).…”

Section: Experimental Conditionsmentioning

confidence: 95%

Determination of rate-constants as a method to describe passive expiration

2003

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“…In normal subjects, airway resistance values do not exceed 15-20 cmH 2 O/L/s under controlled mechanical ventilation (48). Several factors can modify Ppeak, such as endotracheal tube diameter (49,50), airflow intensity, plugging, or bronchospasm.…”

Section: Peak Pressurementioning

confidence: 99%

The basics of respiratory mechanics: ventilator-derived parameters

Silva¹,

Rocco²

2018

Ann. Transl. Med

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Mechanical ventilation is a life-support system used to maintain adequate lung function in patients who are critically ill or undergoing general anesthesia. The benefits and harms of mechanical ventilation depend not only on the operator's setting of the machine (input), but also on their interpretation of ventilator-derived parameters (outputs), which should guide ventilator strategies. Once the inputs-tidal volume (V T), positive end-expiratory pressure (PEEP), respiratory rate (RR), and inspiratory airflow (V')have been adjusted, the following outputs should be measured: intrinsic PEEP, peak (Ppeak) and plateau (Pplat) pressures, driving pressure (ΔP), transpulmonary pressure (P L), mechanical energy, mechanical power, and intensity. During assisted mechanical ventilation, in addition to these parameters, the pressure generated 100 ms after onset of inspiratory effort (P 0.1) and the pressure-time product per minute (PTP/min) should also be evaluated. The aforementioned parameters should be seen as a set of outputs, all of which need to be strictly monitored at bedside in order to develop a personalized, case-by-case approach to mechanical ventilation. Additionally, more clinical research to evaluate the safe thresholds of each parameter in injured and uninjured lungs is required.

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“…Therefore, we seek in our experiments to minimize possible leaks by working at low pressures during ventilatory maneuvers. As this study aimed to investigate the feasibility of an image acquisition system for the evaluation of tracheae in situ, we avoided any constraint (such as suture) around the trachea that could cause deformation of the tracheal tube, which could lead to overestimation of the impedance . In order to better verify possible air leakage, future works will include static pressure‐volume curves prior to ventilatory perturbations.…”

Section: Limitationsmentioning

confidence: 99%

An in vivo image acquisition system for the evaluation of tracheal mechanics in rats

et al. 2019

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Mechanical evaluation of tracheal grafts is of great relevance for transplant research.Although there are some publications demonstrating different techniques of tracheal mechanical evaluation, there is still no definitive or preferred protocol available. Here, we present a simple image processing acquisition system that can be used for in vivo experiments. Six male Wistar rats were submitted to orotracheal intubation and a longitudinal incision was made to expose the trachea. Images of tracheae were acquired from a video camera in different scenarios of bronchoconstriction using methacholine (MCh) (Basal, PBS, MCh 30 μg/kg, MCh 300 μg/kg, and postmetabolized) during imposed-inspiration and imposed-expiration. The area variation ratio (the ratio between areas during expiration vs. inspiration) was 1.1× for the Basal group, while the ratio for MCh 300 µg/kg was 6.5×. The area variation of imaged tracheae was statistically significant at the dose of MCh 300 µg/kg for imposed-inspiration versus imposed-expiration (P = .002). Likewise, elastance data of respiratory mechanics indicated a statistically significant difference at the dose of MCh 300 µg/kg for imposed-inspiration versus imposed-expiration (P = .026). Our image processing analysis protocol presented corresponding behavior when compared to mechanical parameters of the respiratory system. In addition, our image acquisition system was able to highlight the differences between imposed-inspiration and imposed-expiration. Image analysis of the tracheal area variation seems to be in agreement with the elastance of the respiratory system. Taken together, these observations may help future studies of tracheal transplantation for in situ assessment of graft patency.

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Modelling the mechanical effects of tracheal tubes in normal subjects

Cited by 18 publications

References 25 publications

Determination of rate-constants as a method to describe passive expiration

Determination of rate-constants as a method to describe passive expiration

The basics of respiratory mechanics: ventilator-derived parameters

An in vivo image acquisition system for the evaluation of tracheal mechanics in rats

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