Effects of PEEP on inspiratory and expiratory mechanics in adult respiratory distress syndrome

The purpose of the present study was to assess the mechanical behavior of the respiratory system separately during inspiration and expiration in adult respiratory distress syndrome (ARDS) and the influence of PEEP on any phasic variations of the mechanical respiratory parameters. Airways pressure (P), flow (V), and volume (V) signals were recorded in nine patients with ARDS and 10 patients without known respiratory disorder (control group). All patients were artificially ventilated at three levels of positive end-expiratory pressure (PEEP): 0, 5, and 10 hPa. Data were analyzed separately for inspiratory and expiratory records using multiple linear regression analysis (MLRA) according to the equation: P=Ers V + Rrs V’ + P-0, where Ers and Rrs represent, respectively, the intubated respiratory system elastance and resistance, and P-0 the end-expiratory pressure. In the ARDS group expiratory Ers (Ers(EXP)=45.58 +/- 4.24 hPa/L) was substantially higher (p < 0.01) than inspiratory Ers (Ers(INSP)=36.76 +/- 2.55) with a marked effect of applied PEEP in diminishing the difference between Ers(EXP) and Ers(INSP) (P < 0.01). For the ARDS group inspiratory Rrs (Rrs(INSP)) decreased significantly with increasing PEEP (PEEP=0: Rrs(INSP)=1643, PEEP=10: Rrs(INSP)=13.28, p < 0.01). The found differences between Ers(EXP) and Ers(INSP) could be attributable to an influence of mechanical ventilation by positive airway pressure on pulmonary edema and interstitial fluid during the inspiratory phase of the respiratory cycle. (C) 2002 Elsevier Science Ltd, All rights reserved

The immediate effect of a Boston brace on lung volumes and pulmonary compliance in mild adolescent idiopathic scoliosis

Idiopathic scoliosis (IS) is known to result in lung volume and pulmonary compliance reduction. Boston brace treatment of IS is an additional factor causing restrictive respiratory syndrome due to external chest wall compression. Nevertheless, the immediate effect of Boston bracing on the pulmonary compliance of scoliotic patients has not been studied systematically. Spirometric and plethysmographic lung volumes, static lung compliance (C-ST(L)) and specific lung compliance (C-ST(L)/functional residual capacity) of 15 scoliotic adolescents (14 females and 1 male, of mean age 14. 1 +/- 1.67 years, with mean Cobb angle 24.1 degrees +/- 7.88 degrees) were recorded twice, in a random sequence: once without the Boston brace (nBB) and once immediately after wearing the brace (BB). Our findings showed that bracing reduced vital capacity, residual volume, functional residual capacity (FRC), total lung capacity, and forced expiratory volume in 1 s in a proportional and significant way (P < 0.001). C-ST(L) was also significantly reduced (P < 0.001), but C-ST(L)/FRC remained unaltered. All BE and nBB indices were highly correlated. We concluded that Boston bracing in IS patients results in an immediate, predictable, and uniform reduction of lung volumes and pulmonary compliance. The reduction of C-ST(L), under bracing conditions was I elated to the decrease of lung volume; the C-ST(L)/FRC remained unaltered

Linear and nonlinear analysis of pressure and flow during mechanical ventilation

Objective: Linear modeling as a method of exploring respiratory mechanics during mechanical ventilation, was compared to nonlinear modeling for now dependence of resistance in three distinct groups of patients, those with: (a) normal respiratory function (NRF), (b) chronic obstructive pulmonary disease (COPD), or (c) adult respiratory distress syndrome (ARDS). Design and patients: Airways opening pressure (Pao), flow (V’), and volume (V) signals were recorded in 32 ICU mechanically ventilated patients, under sedation and muscle relaxation (10 NRF, 11 COPD, 11 ARDS). All patients were ventilated with controlled mandatory ventilation mode at three levels of end-expiratory pressure (PEEPe): 0, 5, and 10 hPa. Data were analyzed according to: (a) Pao = PE + Ers V + Rrs V’ and (b) Pao = PE + Ers V + k(1)V’ + k(2)’’: where Ers and Rrs represent the intubated respiratory system (RS) elastance and resistance, k(1) and k(2) the linear and the nonlinear RS resistive coefficients, and PE the end-expiratory pressure. The model’s goodness of fit to the data was evaluated by the root mean square difference of predicted minus measured Pao values. Results: NRF data fit both models well at all PEEPe levels. ARDS and particularly COPD data fit the nonlinear model better. Values of k(2) were often negative in COPD and ARDS groups, and they increased in parallel with PEEPe. A gradual increase in PEEPe resulted in better fit of ARDS and COPD data to both models. Conclusions: The model of V’ dependence of resistance is more suitable for the ARDS and particularly the COPD groups. PEEP tends to diminish the V’ dependence of respiratory resistance during the respiratory cycle, particularly in the COPD group, probably through an indirect effect of the increased lung volume

Evaluation of the end-expiratory pressure by multiple linear regression and Fourier analysis in humans

This study was designed to compare the end-expiratory pressure (EEP) during mechanical ventilation (MV) measured dynamically (EEPdyn), by multiple linear regression (MLR) of the airway pressure (Pao) vs volume (V) and flow (V’) and after Fourier analysis (FA) of the Pao and V’. Pao and V were recorded from 32 ICU patients (II without respiratory disease, 10 COPD, II ARDS) under MV at three levels of PEEPe (0, 5 and 10 hPa). Volume was calculated by numerical integration of V’. Data were analysed by MLR and FA, while the actual value of EEPdyn was recognised on the Pao signal at zero V and V EEPdyn, EEPMLR and EEPFA were compared for all patients, for each group of patients and for every level of applied PEEPe. Despite the different evaluation of respiratory mechanics between MLR and FA, the EEP values were always not significantly different between the three applied methods (P> 0.05). A high degree of correlation was found between them, taken two at a time (r > 0.99, P < 0.001). Two non-invasive analytical methods for the evaluation of respiratory mechanics during MV MLR and FA offer a reliable and clinically useful estimation of EEP during MV (C) 2002 Published by Elsevier Science Ltd