Flow and volume dependence of pulmonary mechanics in anesthetized cats

In mechanically ventilated patients the flow pattern during bronchodilator delivery by metered-dose inhaler (MDI) could be a factor that might influence the effectiveness of this therapy. In order to test this the effect of two different inspiratory flow patterns on the bronchodilation induced by b 2 -agonists administered via MDI and spacer in a group of mechanically ventilated patients with chronic obstructive pulmonary disease (COPD) was examined.Eighteen mechanically ventilated patients with COPD, were prospectively randomized to receive two (n=8, protocol A) or six (n=10 protocol B) puffs salbutamol (100 mg . puff -1 ) either under pressure control (decelerating flow pattern) or under volume control (square wave flow pattern). With both modes, tidal volume and inspiratory time were identical. Salbutamol was administered via an MDI adapted to the inspiratory limb of the ventilator circuit using an aerosol cloud-enhancer spacer. After a 6-h washout, patients were crossed over to receive the same dose of salbutamol (200 or 600 mg, respectively in protocols A and B) by the alternative mode of administration. Static and dynamic airway pressures, minimum (Rint) and maximum (Rrs) inspiratory resistance and the difference between Rrs and Rint (DR) were measured before and at 15, 30 and 60 min after salbutamol.Independent of the dose, salbutamol caused a significant decrease in dynamic and static airway pressures, Rint and Rrs. These changes were not influenced by the inspiratory flow pattern and were evident at 15, 30 and 60 min after salbutamol.It is concluded that salbutamol delivered via metered dose inhaler and spacer device, induces significant bronchodilation in mechanically ventilated patients with chronic obstructive pulmonary disease, the magnitude of which is not affected by the inspiratory flow/time profile. Eur Respir J 2000; 16: 263±268. The delivery of bronchodilators via metered-dose inhalers (MDIs) in mechanically ventilated patients has received considerable interest in recent years [1±5]. It has been shown that MDIs adapted to the inspiratory line of the ventilator using a spacer device are as effective as nebulizers, despite the significantly lower dose of bronchodilator given by MDI [1±5]. A spacer device is thought to be fundamental to demonstrating the efficacy of the bronchodilatory therapy given by MDI [1±5]. Studies that delivered bronchodilators via MDI directly to the endotracheal tube failed to demonstrate any beneficial effect even after administration of high doses of bronchodilators [6]. The use of MDIs has several advantages over use of nebulizers, such as reduced cost, ease of administration, less personnel time, reliability of dosing and lower risk of contamination [7±10].The technique of administration of bronchodilators in mechanically ventilated patients using an MDI and a spacer is an important factor determining the efficacy of this therapy. The timing of drug delivery and ventilator parameters during the administration of bronchodilators, such as the tidal volume (V...

Section: Methodsmentioning

confidence: 99%

Bronchodilator delivery by metered-dose inhaler in mechanically ventilated COPD patients: influence of flow pattern

Mouloudi¹,

Prinianakis²,

Kondili³

et al. 2000

“…Respiratory mechanics were measured from end-inspiratory occlusions after constant flow inflations [14]. Although this method has been used for a long time, the significance of the variables measured has only recently been clarified [13,[15][16][17][18]. After end-inspiratory occlusion, there is an initial fast drop in tracheal pressure (∆P1,rs) from the preocclusion value down to an inflection point (Pi,rs), followed by a slow pressure decay (∆P2,rs), until a plateau is reached.…”

Section: Methodsmentioning

confidence: 99%

Respiratory mechanics and morphometric changes during pneumoperitoneum in normal rats

Moreira

Gobbi²,

Feijoo³

et al. 1997

Pneumoperitoneum may give rise to several respiratory changes; nevertheless, no comprehensive analysis of respiratory mechanics has been performed under this condition.Respiratory mechanics and thoracoabdominal morphometry were evaluated in six sedated, anaesthetized, paralysed, and mechanically-ventilated rats before (control) and during pneumoperitoneum. After airway occlusion at end-inspiration, respiratory system, pulmonary, and chest wall resistive pressures (∆P1,rs, ∆P1,L and ∆P1,cw, respectively) and viscoelastic/inhomogeneous pressures (∆P2,rs, ∆P2,L and ∆P2,cw, respectively) were determined. Total pressure changes (∆Ptot) were calculated as the sum of ∆P1 and ∆P2, yielding the values of ∆Ptot,rs, ∆Ptot,L and ∆Ptot,cw, respectively. Respiratory system, lung, and chest wall static (Est,rs, Est,L and Est,cw, respectively), and dynamic elastances (Edyn,rs, Edyn,L and Edyn,cw, respectively), and the corresponding changes in elastance (∆E) (calculated as Edyn-Est) were also obtained. Chest wall configuration both at functional residual capacity (FRC) and end-inspiration (FRC + tidal volume (VT)) was also evaluated in another four rats.Pneumoperitoneum significantly increased ∆Ptot,rs, ∆Ptot,cw, ∆P2,rs, AP2,cw, ∆Ers, ∆Ecw, Est,rs, Est,L and Est,cw. Lateral and anteroposterior diameters increased significantly, with the exception of lateral diameters at the level of crista iliaca. Cephalocaudal diameter and FRC decreased.In conclusion, pneumoperitoneum augments elastances and increases the pressure dissipated against viscoelasticity/inhomogeneity of the respiratory system and chest wall. These changes are related to a cephalad displacement of the diaphragm plus changes in thoracoabdominal configuration.

“…During the test breaths, a 5-s end-inspiratory pause could be generated by adjusting the ventilator settings, whereas during baseline ventilation no pause was used. In order to avoid the effects of different V ' and VT [16], and thence inspiratory duration [17], on the measured variables, special care was taken to keep VT (2 mL) and V ' (10 mL . s -1 ) constant in all animals.…”

Section: Experimental Protocolmentioning

confidence: 99%

“…Pulmonary mechanics were measured using end-inspiratory occlusions after constant flow inflations [16,18,19]. In an open chest preparation, Ptr reflects transpulmonary pressure (PL).…”

Section: Pulmonary Mechanicsmentioning

confidence: 99%

“…Values are presented as mean SD of eight±10 determinations on each occasion in all groups, and were corrected for BW. The experiments did not last >3 h. The delay between the beginning and end of valve closure (10 ms) was allowed for by back extrapolation of the pressure records to the time of occlusion, and the corrections in pressure, although very minute, were performed as previously described [16].…”

Section: Pulmonary Mechanicsmentioning

confidence: 99%

See 1 more Smart Citation

Pulmonary morphofunctional effects of acute myocardial infarction

Faffe¹,

Chagas²,

Medeiros³

et al. 1999

Acute myocardial infarction (AMI) may yield several respiratory changes. Nevertheless, no comprehensive pulmonary morphological/physiological correlation has been performed under this condition. The aims of the present investigation were: 1) to determine the respiratory parameters in an experimental model of coronary artery occlusion, 2) to relate these results to findings from lung histopathology, and 3) to evaluate the effects of propranolol used prior to AMI.Twenty-eight rats were anaesthetized and mechanically ventilated. In the control group (C), a suture line was passed around the left anterior descending coronary artery (LADCA). The infarct group (I) was similarly prepared but the LADCA was ligated and infarct resulted. In the control/propranolol (CP) and infarct/propranolol (IP) groups, propranolol was intravenously injected 5 min before surgery as performed in groups C and I, respectively. Lung static (EL,st) and dynamic (EL,dyn) elastances, airway resistance (RL,int), and viscoelastic/inhomogeneous pressure (DP2L) were determined before and 30, 60 and 120 min after surgery.In group I, EL,st, EL,dyn, RL,int and DP2L increased progressively throughout the experiment, and were higher than those found in groups C, CP and IP. All respiratory parameters but EL,st remained unaltered in group IP. Lung histopathological examination demonstrated alveolar, interstitial and intrabronchial oedema in group I. Group IP showed only interstitial oedema.Acute myocardial infarction yields lung resistive, elastic and viscoelastic changes. The last two results from alveolar and interstitial oedema, respectively. The previous use of propranolol diminishes respiratory changes.