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Biomedical subjects

B W Armstrong

Publications and source records attributed to B W Armstrong.

At least 19 recordsLinked to original sources
PubMed1995

Pressure-controlled, inverse ratio ventilation that avoids air trapping in the adult respiratory distress syndrome.

OBJECTIVES: To investigate physiologic and outcome data in patients switched from volume-cycled conventional ratio ventilation to pressure-controlled inverse ratio ventilation that did not produce air trapping and intrinsic positive end-expiratory pressure (PEEP). SETTING: Medical intensive care unit. DESIGN: Retrospective analysis of crossover data and outcome. PATIENTS: Fourteen patients with the adult respiratory distress syndrome who were receiving mechanical ventilation with volume-cycled, conventional ratio ventilation followed by pressure-controlled, inverse ratio ventilation. INTERVENTIONS: Our approach to pressure-controlled, inverse ratio ventilation was to use tidal volumes and applied PEEP values comparable to those volumes and values used on volume-cycled, conventional ratio ventilation, use inspiratory times to increase mean airway pressure instead of additional applied PEEP, and avoid air trapping (intrinsic PEEP). MEASUREMENTS AND MAIN RESULTS: With this approach, there was a reduction in peak airway pressure from 53 +/- 8.5 (SD) to 40 +/- 5.9 cm H2O (p < .01), and an increase in mean airway pressure from 20 +/- 3.9 to 30 +/- 5.2 cm H2O (p < .01). Tidal volume, mean inflation pressure, and compliance did not change. Oxygenation (PaO2) improved from 57 +/- 11.3 torr (7.6 +/- 1.5 kPa) to 94 +/- 40.2 torr (12.5 +/- 5.4 kPa) (p = .01) but the oxygenation index (mean airway pressure x FIO2 x 100/PaO2) did not change significantly (25.9 +/- 10.3 to 27.2 +/- 12.2). There was no significant change in PaCO2 or pH even though delivered minute ventilation decreased from 17.4 +/- 4.3 to 14.8 +/- 5.8 L/min (p = .02). Cardiac index slightly decreased, but hemodynamic values were otherwise stable. Only three of the 14 study patients survived. CONCLUSIONS: These data demonstrate that oxygenation is primarily a function of mean airway pressure, and that longer inspiratory times can be used as an alternative to applied PEEP to increase this oxygenation. If no air trapping develops, lung inflation pressures and delivered volumes remain constant with this approach. Because the technique was used only in patients refractory to conventional techniques, the poor outcome is not surprising.

Adult↗
PubMed1994

Heparin-protamine mismatch. A controllable factor in bleeding after open heart surgery.

OBJECTIVE: To test the effect of a new system designed to reduce heparin-protamine mismatch on bleeding after open heart surgery. DESIGN: Nonrandomized but consecutive retrospective review of patients undergoing open heart surgery during a 9-month period. SETTING: Multispecialty referral center. PATIENTS: A total of 150 patients comparable by age, body surface area, and coagulation status undergoing primary open heart surgery for either coronary bypass or heart valve replacement. INTERVENTION: In the first 75 patients (group 1), heparin sodium was neutralized with protamine sulfate, using a fixed ratio (1 mg of heparin sodium to 1.3 mg of protamine sulfate). An activated clotting time was used to confirm heparin neutralization. For the subsequent 75 patients (group 2), titration of heparin and protamine from defined lots was accomplished using activated clotting times adjusted and matched to drug lots to minimize biologic variability. Groups 1 and 2 had comparable operations, pump times, and cross-clamp times. MAIN OUTCOME MEASURES: Doses of heparin and protamine and their effect on blood product transfusion and postoperative bleeding were evaluated in all patients. RESULTS: The average protamine sulfate dose for group 2 patients (287.56 +/- 8.3 mg) was significantly lower than that for group 1 (346.01 +/- 12.6 mg) (P < .0005). Less protamine was associated with the transfusion of fewer red blood cells (0.92 +/- 0.15 vs 2.57 +/- 0.38 U) (P < .001), platelets (0.72 +/- 0.8 vs 2.96 +/- 0.80 U) (P < .01), and fresh-frozen plasma (0.83 +/- 2.0 vs 2.01 +/- 0.48 U) (P < .03). No patients in group 2 required reexploration for bleeding, compared with eight patients in group 1. CONCLUSIONS: A reduction in protamine dose was associated with significant decreases in blood product use and postoperative bleeding. Excess protamine warrants consideration as both an important and a controllable factor in coagulopathy after open heart surgery.

Aged↗
PubMed1986

Metabolic cost of walking: equation and model.

Twenty years of published experience with the Workman-Armstrong equation for predicting walking VO2 is reviewed. The equation is reexpressed in currently accepted terminology, and it is shown that the equation serves well as a basic model of normal walking. Employing this model to analyze VO2/step leads to the elaboration of a three-compartment model of the metabolic cost of walking. This three-compartment model provides a rational estimate of the fraction of walking's metabolic cost that powers the actual walking movement. Doubt is expressed that "comfortable speed of walking" is definable in energy terms. It is suggested that the requirements of maintaining balance while walking may determine both the comfortable speed of walking and the curvilinearity of the relationship between ground-speed and freely chosen step frequency of walking.

Energy Metabolism↗
PubMed1984

Extracranial presentation of craniocervical chordoma.

Chordomas are rare tumors of notochordal origin which arise in the sacral, vertebral, and craniocervical areas. Most patients with craniocervical chordomas have either neurological or ophthalmological symptoms. A patient presented with a parotid mass which was initially diagnosed as benign mixed tumor. One and one-half years later, this patient was found to have an extensive intracranial tumor which was diagnosed as chordoma. Treatment consisted of subtotal surgical excision and radiotherapy. This case demonstrates an unusual presentation of an unusual tumor and the difficulty that may arise in in diagnosing these tumors.

Chordoma↗
PubMed1979

Tympanostomy tubes, their use, abuse, and cost-benefit ratio.

Tympanostomy tubes are employed when middle ear ventilation is indicated, particularly when other forms of treatment have failed. Few other uses have broad acceptance. Any other insertion of a ventilating tube implies abuse, either through error in diagnosis or deliberate misapplication. Hard statistical data relating to abuse are impossible to obtain, but ample illustrations can be cited. The cost-benefit ratio is difficult to assess. Cost of a myringotomy and tube versus the cost of a tympanomastoidectomy was determined in four geographic areas. These figures, however, do not reveal how many ears were spared and how much hearing was conserved by tympanostomy tubes. Informed, diligently aggressive use of tympanostomy tubes offers greater potential to avoid serious middle ear disorders and complications than any other single modality.

Cost-Benefit Analysis↗
PubMed1976

Triple ossicular fixation.

A technique for overcoming conductive deafness secondary to fixation of all three ossicles is described in detail. This procedure is also applicable to previously fenestrated ears.

Hearing Loss↗
PubMed1976

Epitympanic malleus fixation: correction without disrupting the ossicular chain.

The preoperative diagnosis of malleus fixation can be made consistently with a pneumatic otoscope. Nontympanosclerotic epitympanic malleus fixation, for the most part, has been corrected by disrupting the ossicular chain and then reconstructing the sound-conducting mechanism. Once the diagnosis of malleus fixation is established, the surgical approach should be modified to cope with the fixed malleus. A wide, inferiorly based tympanotomy flap affords ample access to the epitympanum and permits definitive resolution of the associated conductive hearing loss. Atticotomy and discreet osteotomy can free the fixed malleus and preserve continuity of the osscular chain in over 90 percent of the patients with this syndrome. Experience for 46 patients having bony epitympanic malleus fixation, both congenital and acquired, was examined in concluding that the anatomical continuity of the ossicular chain can and should be maintained in most patients. The residual air-bone gap is less with an intact, though modified, ossicular chain than it is with a chain that has been reconstructed.

Aged↗