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Biomedical subjects

A P Mackenzie

Publications and source records attributed to A P Mackenzie.

25 records · Page 2Linked to original sources
PubMed1993

A simple method of rapid freezing adequately preserves brain tissue for immunocytochemistry, light and electron microscopic examination.

A simple and reproducible method for cryopreservation of brain tissue from patients with Alzheimer's disease is described. Fresh brain slices (1 cm thick) obtained less than 6 h postmortem are placed in sealed plastic bags, sandwiched between 0.3-cm-thick aluminium sheets, and frozen by placing the entire "sandwich" between layers of dry ice pellets. The frozen brain slices are stored at -85 degrees C. Specific anatomic areas can be retrieved at any time for light and electron microscopic, immunocytochemical, autoradiographic and neurochemical studies.

Aged↗
PubMed1993

The effects of freeze-drying and rehydration on cancellous bone.

Processing technique significantly affects the strength and stiffness of bone for use as a structural alloimplant in reconstructive surgery. The effects of the rehydration of freeze-dried human cancellous bone were studied using 14-mm-diameter cancellous dowels taken from matched cadaveric sites. Three different methods of rehydration were evaluated and compared with unrehydrated freeze-dried and frozen grafts. All samples were biomechanically tested in anatomically matched pair groups to determine compressive strength and stiffness. The strength of each tested graft was expressed as a percentage of its matched pair control. Freeze-dried grafts rehydrated for 24 hours compared with frozen grafts showed no significant difference in mean compressive strength (92.6% +/- 13.3% of control). Analysis of in vacuo versus ex vacuo rehydration at one hour showed a 38% greater mean compressive strength and a 42% greater mean stiffness for the ex vacuo group. Unrehydrated grafts appeared to be both stronger and stiffer than their rehydrated counterparts. These results suggest that the rehydration of freeze-dried grafts may adversely affect graft strength and stiffness. Rehydration under a negative pressure may proceed more rapidly than the process at atmospheric pressures. These findings limit the acceptability of freeze-dried grafts as structural implants.

Adolescent↗
PubMed1991

Effect of high-frequency ventilation on the development of alveolar edema in premature monkeys at risk for hyaline membrane disease.

High-frequency oscillatory ventilation (HFOV) permits adequate gas exchange but avoids the large phasic pressure-volume excursions of conventional mechanical ventilation (CMV); such avoidance may reduce the lung injury associated with hyaline membrane disease (HMD). We hypothesized that premature monkeys ventilated from birth with HFOV would have reduced lung injury compared to those assigned to CMV. Macaca nemestrina were delivered at 134 days (80% of term gestation) and ventilated from the first breath with either HFOV (n = 10) or CMV (n = 10). The mean airway pressure (Paw) was kept at 15 cm H2O pressure in HFOV animals; in CMV animals Paw was increased from 8 cm H2O at 2 h to 13 cm H2O at 6 h to prevent hypoxemia. At the conclusion of the 6-h experiment the HFOV animals had better oxygenation (p less than 0.05) and less evidence of HMD by chest radiograph (p less than 0.05). At 6 h of age a piece of the right middle lung lobe was removed, divided, and placed in fixatives for light and transmission electron microscopy. The lungs were subsequently inflated to 30 cm H2O pressure, and the right lower lobe was rapidly frozen in situ for morphometric studies. The proportion of peripheral lung tissue occupied by clear alveoli was greater in HFOV animals (66.3 +/- 14.8%) than in those assigned to CMV (44.2 +/- 16.9%, p less than 0.01); less alveolar debris and fluid was present in the HFOV animals (12.7 +/- 9.9%) compared with CMV animals (27.1 +/- 12.5%, p less than 0.02).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMedDate not supplied

Dielectric characterization of thermodynamic first order events in model frozen systems intended for lyophilization.

The degree and ease with which permanent dipoles in a frozen sample orient in an applied electric field is affected during thermal transitions. This motion can be monitored with dielectric analysis (DEA) at low AC frequencies (< approximately 300,000 Hz). The systems characterized with respect to their behavior in the frozen state consisted of common lyophile excipients in aqueous solutions known to exhibit typical thermodynamic first order transitions. Prior to freezing, solution samples were placed on an interdigitated electrodes and served as the dielectric component of the resulting capacitor. Plots of derivative of dielectric permittivity with respect to time (or temperature) showed the presence of frequency independent peaks (signifying a first order event) at temperatures that coincided with eutectic temperatures (ca. -22 degrees C for sodium chloride-water and ca. -5 degrees C for mannitol-water), amorphous to crystalline transition temperatures (ca. -25 degrees C for mannitol-water), and/or freezing point depression values in water. The values obtained by DEA correlated well with differential scanning calorimetry (DSC) and literature values. DEA appears to offer added insight over established techniques by not only determining the temperature at which these events occur, but also by defining the thermodynamic order of the event.

Electrochemistry↗
PubMedDate not supplied

Prediction of lyophile collapse temperature by dielectric analysis.

A new method for predicting lyophile collapse temperatures based upon dielectric analysis (DEA) of frozen two component systems is presented. The method, called the take off frequency model (TOF), relies both on the inherent ability of DEA to detect molecular motion and on the abrupt change in viscosity experienced by a frozen sample undergoing a glass-liquid transition. Collapse temperatures for binary glass forming systems (an antibiotic, sucrose, trehalose, or sorbitol, with water) were in good agreement with the values reported in the literature. DEA was easily able to detect glass transitions poorly defined by differential scanning calorimetry (DSC). Conservative lyophilization cycles for simple systems can be quickly determined on the basis of the TOF model.

Calorimetry, Differential Scanning↗