Biomedical subjects

D L Smith-Wright

Publications and source records attributed to D L Smith-Wright.

5 recordsLinked to original sources

PubMed1989

Pulmonary vascular resistance after cessation of positive end-expiratory pressure.

This report describes the pulmonary vascular response of infant lamb lung to abrupt cessation of positive end-expiratory pressure (PEEP) during volume-regulated continuous positive-pressure breathing (CPPB). In an intact, endobronchially ventilated preparation, the increase in left lung blood flow (QL) after abrupt cessation of 11 Torr left lung PEEP was found to be gradual, although peak airway pressure (Pmax) fell promptly from 36 to 14 Torr; 49% of the increase in QL occurred greater than 10 s after cessation of PEEP. Recruitment of zone I vasculature that had been created by balloon occlusion of the left pulmonary artery was found to occur promptly after balloon deflation. Isolated neonatal lamb lungs, perfused at constant flow rate, showed similar persistent elevation of pulmonary vascular resistance after cessation of 15 Torr PEEP, although Pmax fell abruptly from 39 to 12 Torr. This hysteresis was eliminated by calcium channel blockade with verapamil, and the magnitude of the change in pulmonary arterial pressure after either application or cessation of PEEP was reduced (25 and 26%, respectively). These observations suggest that, during CPPB, lung stretch alters neonatal pulmonary vascular tone or, by causing calcium channel-dependent lung volume hysteresis, modulates pulmonary vascular resistance. This interaction exaggerates the effect of airway pressure changes on pulmonary vascular resistance during mechanical ventilation.

Animals↗

PubMed1989

Proximal mean airway pressure: a good estimator of mean alveolar pressure during continuous positive-pressure breathing.

Although airway and alveolar pressures are not instantly equal during positive-pressure ventilation, proximal mean airway pressure (Paw) is the simplest available indirect gauge of mean alveolar pressure (Palv). To ascertain the relation of Paw to Palv and the limits of agreement between the two measures, real-time curves of proximal airway pressure (at the hub of the endotracheal tube) and alveolar pressure were generated by repeated airway occlusion at numerous PEEP levels in four groups of ventilated lambs or piglets: normal controls, oleic acid-injured and serotonin stimulated lambs, and preparations with mechanically induced air trapping. From these curves, Paw and Palv were determined. In all groups, Paw proved to be a precise estimator of Palv during volume-regulated, time-cycled, continuous positive-pressure breathing.

Airway Resistance↗

PubMed1986

Pleural drainage using modified pigtail catheters.

An 8.3-Fr modified pigtail catheter has been developed for chronic percutaneous drainage of pericardial effusions. Placement of this catheter using a modified Seldinger technique is virtually atraumatic. To test the safety and efficacy of this catheter for pleural drainage, it was used to manage eight collections of pleural fluid and nine pneumothoraces in a total of 12 infants and children. There were no placement complications. Fluid accumulations were satisfactorily drained in every instance. Pneumothoraces were treated definitively with a single catheter, except when a bronchopleural fistula was present. Percutaneous pigtail drainage of pleura fluid or air is simple, safe, effective, and substantially less traumatic than standard chest-tube placement.

Catheters, Indwelling↗

PubMed1986

Effects of static and fluctuating airway pressure on intact pulmonary circulation.

The direct effects on the pulmonary circulation of static and fluctuation airway pressure were compared in intact close-chest infant lambs with reactive pulmonary vasculature under alpha-chloralose anesthesia. A preparation developed to permit independent ventilation of right and left lungs and independent measurement of right and left lung blood flow was employed to separate direct from indirect effects of unilateral airway pressure changes on pulmonary vascular resistance (PVR). Both static and fluctuating unilateral airway pressure interventions directly elevated ipsilateral PVR. For purposes of comparison mean alveolar pressure (PA) was estimated for both static and fluctuating trials. Fluctuating interventions increased PVR more than did static trials at comparable levels of PA. Substantially less PA was needed to double ipsilateral PVR by fluctuating than by static interventions (16 vs. 26 mmHg, respectively). These data indicate that, in the intact animal with reactive pulmonary vasculature, both PA and the waveform of airway pressure applied can influence PVR.

Animals↗

PubMed1984

Complications of vascular catheterization in critically ill children.

Invasive hemodynamic monitoring is widely used in the care of critically ill children. In a prospective study, a total of 330 arterial catheters, 397 central venous catheters, and 47 pulmonary artery catheters were placed in 467 children, between February 1981 and September 1982. Complications observed included: bleeding in seven of 774 vascular catheterizations, arterial obstruction in three of 377 arterial catheterizations, and sepsis in 11 of 774 vascular catheterizations. Of the 21 complications noted, 71% occurred in children less than 5 yr of age. A total of 19 (4.1%) children suffered complications of bleeding, arterial obstruction, and/or sepsis. In contrast, the overall mortality in this group of patients was 16%. The risk of morbidity from vascular catheterization appeared justified in this group of critically ill children.

Adolescent↗