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Biomedical subjects

J Braidy

Publications and source records attributed to J Braidy.

16 recordsLinked to original sources
PubMed1996

Mean airway pressure as an index of mean alveolar pressure.

Mean airway pressure (Pao) has been advocated as a useful index for monitoring hemodynamic performance and risk for barotrauma during mechanical ventilation. This is based on the assumption that Pao closely reflects mean alveolar pressure (Palv). In the present study we have compared Pao with Palv in 12 sedated, paralyzed, mechanically ventilated patients. External PEEP ranged from 0.3 to 8.9 cm H2O. Palv was estimated by measuring Pao after rapid flow interruptions made at different points in time of the breathing cycle, using a modification of the method of Fuhrman and coworkers (4). All subjects exhibited intrinsic PEEP (PEEPi), which ranged from 0.5 to 9.4 cm H2O. A significant negative correlation (p < 0.001) was found between Pao/Palv and PEEPi. On average, at PEEPi of 10 cm H2O, Pao underestimated Palv by about 50%. We conclude that Pao cannot be taken as an index of Palv in patients who exhibit dynamic hyperinflation and PEEPi caused by expiratory flow limitation.

Adult↗
PubMed1995

Clinical usefulness of intravenous human immunoglobulins in invasive group A Streptococcal infections: case report and review.

The spectrum of invasive Streptococcus pyogenes (group A streptococcus) infections includes bacteremia, toxic shock syndrome, and necrotizing fasciitis or myositis. We report the successful use of intravenous immunoglobulins in conjunction with antibiotics and surgery in a case of necrotizing myositis, toxic shock, and bacteremia. A literature review revealed that three other patients with invasive group A streptococcal infections had been treated with immunoglobulins: one adult patient had toxic shock syndrome, one had necrotizing fasciitis, and one child had septic arthritis. On the basis of this report and the review, we suggest that intravenous immunoglobulins may be useful in the treatment of all forms of invasive group A streptococcal infections associated with toxic shock syndrome.

Humans↗
PubMed1995

A simple method to detect expiratory flow limitation during spontaneous breathing.

Patients with severe chronic obstructive pulmonary disease (COPD) often exhale along the same flow-volume curve during quiet breathing as during a forced expiratory vital capacity manoeuvre, and this has been taken as indicating flow limitation at rest. To obtain such curves, a body plethysmograph and the patient's co-operation are required. We propose a simple technique which does not entail these requirements. It consists in applying negative pressure at the mouth during a tidal expiration (NEP). Patients in whom NEP elicits an increase in flow throughout the expiration are not flow-limited. In contrast, patients in whom application of NEP does not elicit an increase in flow during most or part of the tidal expiration are considered as flow-limited. Using this technique, 26 stable COPD patients were studied sitting and supine. Eleven patients were flow-limited both seated and supine, eight were flow-limited only when supine, and seven were not flow-limited either seated or supine. Only 5 of 19 patients who were flow-limited seated and/or supine had severe ventilatory impairment (forced expiratory volume in one second (FEV1) < 40% predicted). We conclude that the NEP technique provides a simple, rapid, and reliable method for detection of expiratory flow limitation in spontaneously breathing subjects, which does not require the patient's co-operation, and can be applied in different body positions both at rest and during muscular exercise. Our results also indicate a high prevalence of flow limitation in COPD patients at rest, particularly when supine.

Aged↗
PubMed1994

Detection of expiratory flow limitation during mechanical ventilation.

Two new methods, application of negative pressure at the airway opening during expiration (NEP) and reduction of flow resistance by bypassing the expiratory line of the ventilator by exhaling into the atmosphere (ATM), were used to detect expiratory flow limitation in 12 semirecumbent (45 degree) mechanically ventilated patients, seven with chronic airway obstruction (CAO). An increase of expiratory flow with NEP or ATM, relative to the preceding control breath, was taken as indicating absence of expiratory flow limitation. By contrast, the portion of the tidal expiration over which there was no change in flow with NEP or ATM was considered as flow-limited. With NEP, nine patients exhibited flow limitation, six (all with CAO) were flow-limited over most of the tidal expiration (> 70% VT), and three at < 60% VT. Although the results with NEP and ATM were in general in good agreement, in the three non-flow-limited patients the ATM method gave erroneous results. Six patients were also studied supine, including two who were not flow-limited when semirecumbent: both became flow-limited when supine. We conclude that NEP provides a simple method to detect flow limitation in mechanically ventilated patients. The supine position enhances flow limitation.

Aged↗
PubMed1993

Flow resistance in mechanically ventilated patients with severe neurological injury.

In 5 mechanically ventilated patients with severe neurological injury (SNI), we measured the respiratory system's flow resistance (Rrs) over a range of inspiratory flows between 0.2 to 2 L/s, at inflation volumes (delta V) ranging from 0.1 to 1 L. Under baseline ventilatory conditions (V = 1 L/s; delta V = 0.95 L), we also partitioned Rrs into airway resistance (Raw) and the additional resistance offered by the tissues of the lung and chest wall (delta Rrs). At all inflation volumes, Rrs decreased hyperbolically with increasing flow but was higher than in normal anesthetized paralyzed subjects (N). At V of 1 L/s and delta V of 0.5 L, Rrs was significantly greater in SNI than in N (7.7 +/- 1.5 v 4.2 +/- 0.5 cm H2O/L/s; P < .01). This discrepancy was due to higher Raw in SNI. Indeed, at V of 1 L/s, Raw (mean +/- SEM) was significantly higher in SNI than in N (4.0 +/- 0.9 v 2.4 +/- 0.2 cm H2O/L/s; P < .001), whereas delta Rrs did not differ significantly. The increased Raw in SNI was due to the fact that these patients were therapeutically hyperventilated (PaCO2 = 30.4 +/- 4.2 mm Hg) and as a result their airways were bronchoconstricted. We conclude that in the intensive care unit setting, hyperventilated patients with severe neurological injury can not be considered to be adequate controls in terms of Rrs and Raw, because hypocapnia induces an increase of Raw and consequently also in Rrs (= Raw+delta Rrs).

Adult↗
PubMed1993

Lung and chest wall mechanics in mechanically ventilated COPD patients.

By use of the technique of rapid airway occlusion, the effects of inspiratory flow, volume, and time on lung and chest wall mechanics were investigated in 10 chronic obstructive pulmonary disease (COPD) patients mechanically ventilated for acute respiratory failure. We measured the interrupter resistance (Rint), which in humans reflects airway resistance; the additional resistances due to time constant inequality and viscoelastic pressure dissipations within the lungs (delta RL) and the chest wall; and the static and dynamic elastances of lung and chest wall. We observed that 1) static elastances of lung and chest wall in COPD patients were similar to those of normal subjects; 2) Rint of the lung was markedly increased and flow dependent in COPD patients, whereas Rint of the chest wall was negligible as in normal subjects; and 3) in COPD patients, delta RL was markedly increased at all inflation flows and volumes, reflecting increased time constant inequalities within the lungs and/or altered viscoelastic behavior. The results imply increased dynamic work due to Rint and delta RL and marked time dependency of pulmonary resistance and elastance in COPD patients.

Aged↗
PubMed1993

Partitioning of work of breathing in mechanically ventilated COPD patients.

In 10 sedated paralyzed mechanically ventilated chronic obstructive pulmonary disease (COPD) patients, we measured the inspiratory mechanical work done per breath on the respiratory system (WI,rs). We measured the tracheal and esophageal pressures to assess the lung (L) and chest wall (W) components of WI and used the technique of rapid airway occlusion during constant-flow inflation to partition WI into static work [Wst, including work due to intrinsic positive end-expiratory pressure (WPEEPi)], dynamic work due to airway resistance, and the additional resistance offered by the respiratory tissues. Although the patients were hyperinflated, the slope of the static volume-pressure relationships of the lung did not decrease with inflation volume up to 0.8 liter. WI,W was similar in COPD patients and normal subjects. All components of WI,L were higher in COPD patients. The increase in Wst,rs was due entirely to WPEEPi. Our data suggest that, during spontaneous breathing, COPD patients would probably develop inspiratory muscle fatigue, unless continuous positive airway pressure were applied to reduce WPEEPi.

Acute Disease↗
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↗
PubMed1992

Flow and volume dependence of respiratory system flow resistance in patients with adult respiratory distress syndrome.

Using a simple and rapid technique, we studied the flow and volume dependence of the total resistance of the respiratory system (Rrs) in six patients with ARDS. At any given inflation volume, Rrs decreased progressively with increasing flow (V) according to the following hyperbolic function: Rrs = a/V + b, where a and b are constants. At any fixed inflation flow, Rrs increased progressively with increasing inflation volume. The observed flow and volume dependence of Rrs is probably mainly due to the viscoelastic properties of the pulmonary and chest wall tissues. The flow and volume dependence of Rrs found in the patients with ARDS is qualitatively similar to that previously observed in normal anesthetized paralyzed subjects. In ARDS, however, Rrs was considerably greater than in the normal subjects, indicating that besides a low respiratory compliance ARDS is characterized by a high flow resistance. This mainly reflects increased effective flow resistance of the pulmonary and chest wall tissues, although airway resistance is also higher than normal.

Adult↗
PubMed1992

Bilateral pneumothoraces hasten mortality in AIDS patients receiving secondary prophylaxis with aerosolized pentamidine. Association with a lower Dco prior to receiving aerosolized pentamidine.

We have administered aerosolized pentamidine (AP) to 48 AIDS patients for secondary prophylaxis of Pneumocystis carinii pneumonia (PCP). Pentamidine 60 mg was administered by ultrasonic nebulization (Fisoneb) five times during the first two weeks and then every two weeks. The mean follow-up was 343 +/- 22 days. PCP recurred in ten patients, 297 +/- 33 days after starting AP therapy. All responded to anti-Pneumocystis therapy but two patients died of unrelated reasons (20 percent mortality). Five patients developed bilateral pneumothoraces 260 +/- 35 days after starting AP therapy. Recurrence of PCP could be documented in only one patient. All died 66 +/- 27 days after the onset of the first pneumothorax. Only 5 of 33 patients without recurrence of pneumonia or pneumothorax died during the study period (15 percent mortality). No association was found between the development of pneumothorax and age, smoking, previous respiratory or infectious problems, time from last PCP and the initiation of AP therapy, and treatment duration of last PCP. Patients with pneumothoraces had a significantly lower Dco (58.6 +/- 2.6 percent predicted) prior to AP therapy than patients with recurrence of PCP without pneumothoraces (81.1 +/- 2.1 percent predicted) or patients with no recurrence of PCP (67 +/- 2.5 percent predicted) (p less than 0.05, ANOVA). In conclusion, bilateral pneumothoraces are associated with a hastened mortality in patients receiving AP for secondary prophylaxis of PCP. Low Dco before AP therapy is associated with an increased risk of bilateral pneumothoraces in patients treated with AP for secondary prophylaxis of PCP.

Acquired Immunodeficiency Syndrome↗
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

Flow resistance in patients with chronic obstructive pulmonary disease in acute respiratory failure. Effects of flow and volume.

The flow and volume dependence of the total resistance of the respiratory system (Rrs) was investigated in six mechanically ventilated patients with chronic obstructive pulmonary disease (COPD) using a simple, rapid method. Isovolume Rrs-flow (V) relationships obtained at different inflation volumes (range 0.1 to 1 L) fitted (p less than 0.001) the following function: Rrs = a/V + b + cV, where a, b, and c are constants. The term "a/V" in this equation represents the hyperbolic decrease in thoracic tissue resistance with increasing flow; the term "cV" represents the linear increase in airway resistance with increasing flow. Rrs initially decreased with increasing V because at low flow the weight of the a/V was greater than that of the cV. At higher flow, however, cV became predominant and hence Rrs tended to increase. At an inflation volume of 0.5 L, minimum Rrs occurred at average inflation flow of 1.28 L/s. At low flow, Rrs increased progressively with increasing inflation volume; at inflation V greater than 1 L/s, the highest values of Rrs were obtained at low inflation volumes. The flow and volume dependence of Rrs implies that, for comparative purposes, measurements of Rrs should be standardized to a fixed inflation flow and volume.

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↗
PubMed1989

Effect of corticosteroids on post-intubation tracheal stenosis.

A 57 year old patient presented with progressive tracheal stenosis two months after intubation. An intraluminal polypoid lesion was found at the site of the cuff of the endotracheal tube. It disappeared within five days of treatment with inhaled beclomethasone. Further improvement of forced expiratory and inspiratory flow occurred after systemic corticosteroid treatment, with resolution of peritracheal oedema. Topical and systemic corticosteroids may be useful in the management of early post-intubation tracheal stenosis.

Adrenal Cortex Hormones↗