Biomedical subjects

V M Ranieri

Publications and source records attributed to V M Ranieri.

46 records · Page 3Linked to original sources

PubMed1993

Physiologic effects of positive end-expiratory pressure in patients with chronic obstructive pulmonary disease during acute ventilatory failure and controlled mechanical ventilation.

Dynamic hyperinflation and intrinsic positive end-expiratory pressure (PEEPi) are observed in patients with chronic obstructive pulmonary disease (COPD) and flow limitation. Several reports suggest that PEEP levels approaching PEEPi reduce inspiratory load due to PEEPi, without further hyperinflation. Hence PEEP should not increase intrathoracic pressure or affect hemodynamics and gas exchange. To verify this hypothesis, the effects of PEEP (0 to 15 cm H2O) on respiratory mechanics, hemodynamics, and gas exchange were studied in nine COPD patients during controlled mechanical ventilation. PEEP levels approaching PEEPi (9.8 +/- 0.5 cm H2O) did not affect the expiratory flow/volume relationship, confirming the presence of flow limitation. PEEP levels of 5 and 10 cm H2O did not change lung volume and PEEPi in the respiratory system (PEEPtot,rs) and chest wall (PEEPtot,cw) or affect hemodynamics and gas exchange. When applied PEEP overcame PEEPi, changes in lung volume and the expiratory flow/volume relationship were observed. PEEPtot,rs and PEEPtot,cw also increased. Under these circumstances, PEEP increased static elastance in both the respiratory system and the chest wall, reducing cardiac index and affecting hemodynamics and gas exchange. Our data show that in mechanically ventilated COPD patients with PEEPi due to flow limitation, PEEP levels exceeding the 85% of PEEPi (Pcrit) caused further hyperinflation and compromised hemodynamics and gas exchange.

Aged↗

PubMed1992

A simple method for the measurement of intrinsic positive end-expiratory pressure during controlled and assisted modes of mechanical ventilation.

OBJECTIVE: To evaluate a new and simple method for the measurement of intrinsic positive end-expiratory pressure during controlled and assisted modes of mechanical ventilation. DESIGN: Prospective study. SETTING: Three university hospital medical ICUs. PATIENTS: A total of 13 intubated, mechanically ventilated patients with severe airway obstruction. INTERVENTIONS: Airway occlusions reproducibly timed to occur coincidently with end-expiration were obtained by: a) manipulation of a three-way manual valve placed in the inspiratory limb of the external ventilator circuit (manual valve method) and b) activation of the expiratory pause hold function of the mechanical ventilator (Siemens 900C). MEASUREMENTS AND MAIN RESULTS: Airway pressure, flow, and volume were recorded during controlled and assisted modes of mechanical ventilation. Intrinsic positive end-expiratory pressure was determined from the plateau in airway pressure, which was developed during end-expiratory occlusions. For controlled mechanical ventilation, intrinsic positive end-expiratory pressure averaged 11.42 +/- 0.77 (SEM) cm H2O with the manual valve method, compared with 11.38 +/- 0.70 cm H2O, using the ventilator expiratory pause hold function. There was close correlation between results over the wide range of intrinsic positive end-expiratory pressure observed, which varied from approximately 5 to 22 cm H2O (y = 1.08x - 0.92; r2 = .99). Values of intrinsic positive end-expiratory pressure were comparable for the two methods during assist-control ventilation, pressure support ventilation, and spontaneous breathing through the ventilator circuit. The manual valve method was also effective when tested with different mechanical ventilators using a mechanical lung model. CONCLUSIONS: The manual valve method can be used to determine intrinsic positive end-expiratory pressure during controlled and assisted modes of ventilatory support with current ventilators. The availability of such an approach should facilitate the routine monitoring of intrinsic positive end-expiratory pressure in mechanically ventilated patients, thereby aiding clinical decision-making and management in these critically ill individuals.

Adult↗

PubMed1992

Effect of PEEP on the mechanics of the respiratory system in ARDS patients.

In patients with adult respiratory distress syndrome (ARDS) we studied the effect of positive end-expiratory pressure (PEEP) on respiratory mechanics. We used the technique of rapid airway occlusion during constant flow (V) inflation to partition the total respiratory system resistance (Rrs) into the interrupter resistance (Rint,rs) and the additional resistance (delta Rrs) due to viscoelastic pressure dissipations and time constant inequalities. We also measured static (Est,rs) and dynamic (Edyn,rs) elastance of the respiratory system. The procedure was carried out in nine ARDS patients at different inspiratory V and inflation volumes (delta V) at PEEP of 0, 5, 10, and 15 cmH2O. We found that during baseline ventilation (delta V = 0.7 liter and V = 1 l/s), Est,rs, Edyn,rs, and Rint,rs did not change significantly with PEEP, whereas delta Rrs and Rrs increased significantly only with PEEP of 15 cmH2O. The increase of delta Rrs and Rrs with PEEP was positively correlated with the concomitant changes in end-expiratory lung volume (P < 0.001). At all levels of PEEP, under iso-delta V conditions, delta Rrs decreased with increasing V, whereas at a fixed V, delta Rrs increased with increasing delta V. A four-parameter model of the respiratory system failed to fully describe respiratory dynamics in the ARDS patients, probably due to nonlinearities.

Airway Resistance↗

PubMed1991

Analysis of behavior of the respiratory system in ARDS patients: effects of flow, volume, and time.

The effects of inspiratory flow (V) and inflation volume (delta V) on the mechanical properties of the respiratory system in eight ARDS patients were investigated using the technique of rapid airway occlusion during constant-flow inflation. We measured interrupter resistance (Rint,rs), which in humans represents airway resistance, the additional resistance (delta Rrs) due to viscoelastic pressure dissipations and time constant inequalities, and static (Est,rs) and dynamic (Edyn,rs) elastance. The results were compared with a previous study on 16 normal anesthetized paralyzed humans (D'Angelo et al. J. Appl. Physiol. 67: 2556-2564, 1989). We observed that 1) resistance and elastance were higher in ARDS patients; 2) with increasing V, Rint,rs and Est,rs did not change, delta Rrs decreased progressively, and Edyn,rs increased progressively; 3) with increasing delta V, Rint,rs decreased slightly, delta Rrs increased progressively, and Est,rs and Edyn,rs showed an initial decrease followed by a secondary increase noted only in the ARDS patients. The above findings could be explained in terms of a model incorporating a standard resistance in parallel with a standard elastance and a series spring-and-dashpot body that represents the stress adaptation units within the tissues of the respiratory system.

Aged↗

PubMed1991

Effects of positive end-expiratory pressure, lung volume, and inspiratory flow on interrupter resistance in patients with adult respiratory distress syndrome.

Although it has been shown in normal subjects that airway resistance changes significantly with changes in lung volume and inspiratory flow, no studies have as yet examined these phenomena in patients with adult respiratory distress syndrome (ARDS). The effect of positive end-expiratory pressure (PEEP) on airway resistance in ARDS also is unknown. We have used the technique of rapid airway occlusion during constant-flow inflation to measure the interrupter resistance (Rint,rs), which in humans is thought to correspond to airway resistance, in nine patients with ARDS under different inflation flows and volumes. This procedure was carried out at four levels of PEEP (0, 5, 10, and 15 cm H2O). We found that (1) at constant inflation volume, Rint,rs did not change significantly with increasing flow; (2) at constant inflation flow, Rint,rs showed an initial decrease followed by a distinct rise with increasing lung volume; (3) on average, PEEP did not significantly change Rint,rs measured during baseline ventilation; and (4) this latter finding occurred because patients behaved differently with application of PEEP, depending on their degree of lung inflation: Rint,rs measured close to full inflation almost invariably exhibited a rise, but values obtained at lower volumes exhibited the characteristic decrease of Rint,rs with increasing inflation volume.

Airway Resistance↗

PubMed1991

Effects of positive end-expiratory pressure on alveolar recruitment and gas exchange in patients with the adult respiratory distress syndrome.

The effects of different levels of positive end-expiratory pressure (PEEP) (zero to 15 cm H2O) on the static inflation volume-pressure (V-P) curve of the respiratory system and on gas exchange were studied in eight patients with the adult respiratory distress syndrome (ARDS). Alveolar recruitment with PEEP was quantified in terms of recruited volume, i.e., as difference in lung volume between PEEP and zero end-expiratory pressure (ZEEP) for the same static inflation pressure (20 cm H2O) from the V-P curves obtained at the different PEEP levels. In addition, static compliance of the respiratory system at fixed tidal volume (0.7 L) was determined at the different PEEP levels. The results suggest that: (1) in some patients with ARDS the V-P curves determined on ZEEP exhibit an upward concavity reflecting progressive alveolar recruitment with increasing inflation volume, and PEEP results in alveolar recruitment (range of recruited volume at 15 cm H2O of PEEP: 0.11 to 0.36 L); (2) in other patients with ARDS the V-P curves on ZEEP are characterized by an upward convexity, and PEEP results in a volume displacement along this curve without alveolar recruitment and with enhanced risk of barotrauma; (3) the PEEP-induced increase in arterial oxygenation is significantly correlated to the recruited volume but not to the changes in static compliance. The shape of the static inflation V-P curves on ZEEP allows the prediction of alveolar recruitment with PEEP.

Aged↗

PubMed1991