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Biomedical subjects

G C Man

Publications and source records attributed to G C Man.

29 records · Page 2Linked to original sources
PubMed1986

Altered pulmonary epithelial permeability in canine radiation lung injury.

A radioaerosol scanning technique measuring regional clearance of sodium pertechnetate (99mTcO-4) and 99mTc-labeled diethylenetriaminepentaacetate (99mTc-DTPA) was used to assess changes in canine pulmonary epithelial permeability following lung irradiation. Doses of 2,000 cGy (11 dogs), 1,000 cGy (2 dogs), and 500 cGy (2 dogs) were given in one fraction to either the entire right hemithorax (500 cGy) or the right lower lung (1,000 and 2,000 cGy). Radioaerosol scans, chest roentgenograms, and computerized tomograms (CT) were obtained before and serially after irradiation. A dose of 2,000 cGy resulted in a decrease in regional pulmonary epithelial permeability to both 99mTcO4- and 99mTc-DTPA; both showed significant decreases from the 2nd wk postirradiation onward. In comparison, CT and chest roentgenogram did not become abnormal until 7.1 +/- 2.8 (SD) and 8.2 +/- 2.6 wk, respectively. Doses of 1,000 and 500 cGy produced reversible decreases in 99mTcO4- clearance. Lung morphology showed definite changes of radiation pneumonitis after 2,000 and 1,000 cGy but not after 500 cGy at approximately 9, 17, and 12 wk postirradiation, respectively. These results suggest that dose-dependent changes in pulmonary physiology may precede obvious structural alterations in radiation lung injury.

Aerosols↗
PubMed1986

Effect of alprazolam on exercise and dyspnea in patients with chronic obstructive pulmonary disease.

To evaluate the efficacy of a mild anxiolytic, alprazolam, in relieving dyspnea, we conducted a randomized, placebo-controlled double-blind study on patients with chronic obstructive lung disease. Twenty-four patients had alprazolam (0.5 mg bid) or placebo administered for one week, followed by placebo for one week, then either placebo or alprazolam for the third week. Assessment tests were performed at the outset, end of the first and second weeks, and finally end of the third week. The parameters measured were: pulmonary function, exercise testing on a bicycle ergometer, and the distance covered in a 12 minute walk. Subjective sensations of dyspnea at rest and during guarded exercise, as well as subjective feelings of calmness or anxiety were also recorded. There was no difference in mechanical lung function, but the PO2 tended to decrease and PCO2 to increase after alprazolam administration. The maximum exercise level attained and the distance covered in the 12 minute walk was unchanged. The subjective perception of dyspnea was the same before and after alprazolam, at rest and during exercise. We conclude that alprazolam is not effective in relieving exercise dyspnea in patients with obstructive lung disease.

Aged↗
PubMed1986

The effect of high frequency oscillatory ventilation on pulmonary stretch receptors in the dog.

High frequency oscillatory ventilation is a form of artificial ventilation where the tidal volume is less than the anatomical dead space. The efficacy of gas exchange depends upon the oscillatory frequency, volume, bias flow and the airway pressure. The present study was undertaken to determine the influence of oscillatory frequency, oscillatory volume and mean airway pressure upon the activity of pulmonary stretch receptors and rapidly adapting receptors during high frequency oscillatory ventilation. The experiments were conducted on dogs anaesthetized with either chloralose or nembutal. In Series I (16 slowly adapting stretch receptors) the effects of changing in turn, the oscillatory frequency, oscillatory volume and mean airway pressure were examined. The bias flow was held constant. Significant changes in the frequency of discharge of slowly adapting stretch receptors occurred only with alterations in oscillatory frequency (8,16,28 Hz) and mean airway pressure (3, 6 & 9 cm H2O). No significant changes in the activity of slowly adapting stretch receptors were observed when the oscillatory volume was altered (2.5, 5.0 & 7.5 ml/kg). With each manoeuvre there were significant small increments in intrathoracic gas volume. In Series II (16 slowly adapting stretch receptors) the interaction between oscillatory frequency and mean airway pressure was studied. The effect of each was greatest at the lowest value of the other variable. In Series III the effect of changing oscillatory frequency on the discharge from rapidly adapting receptors were examined. It was found that changes in frequency at a fixed airway pressure (3 cm H2O) and oscillatory volume failed to alter the activity significantly.(ABSTRACT TRUNCATED AT 250 WORDS)

Action Potentials↗
PubMed1985

Interaction of left atrial receptors and carotid sinus baroreceptors on heart rate in the dog.

This study was undertaken to determine the influence of 1) the left atrial receptors (LA) on the ability of the carotid sinus baroreceptors (CS) to regulate heart rate and 2) the CS on the reflex increase in heart rate mediated by the LA. The LA were stimulated by stretching the pulmonary vein-atrial junctions in dogs anesthetized with alpha-chloralose. Aortic pressure was controlled, and the pressure in the CS was regulated. Stimulus-response curves were obtained relating heart rate to pressures in the CS, in the control state, and during stimulation of LA (6 dogs). Factorial analysis revealed that LA exerted a significant influence on heart rate (P less than 0.01). Next the CS pressure was set at mid, low, and high levels and the LA stimulated. It was found that the effect on heart rate was greatest at the mid setting (+19.3 +/- 2.9 beats/min) and least at the low setting of the pressure in the CS (+0.9 +/- 0.5, 11 dogs). Sympathetic blockade attenuated significantly the response in the mid setting of the CS pressure and left intact the response at the high setting of the pressure in the CS. It is concluded that there is a significant interaction between these two reflexes.

Animals↗
PubMed1985

Characteristics of pertechnetate movement across the canine tracheal epithelium.

Several 99mTechnetium-labeled markers have been used to study the barrier properties of the pulmonary epithelium; among these compounds is sodium pertechnetate (TcO4-). As TcO4- has pseudohalide properties, and as the characteristics of the movement of this ion across the airway epithelium are unknown, we examined its bidirectional permeability coefficients, and compared them with those of radiolabeled Cl- and mannitol in canine tracheal epithelium in vitro. We found that this ion behaves similarly to Cl- in its translocation across the airway epithelium.

Animals↗
PubMed1983

Effects of high-frequency oscillatory ventilation on vagal and phrenic nerve activities.

This study was undertaken to define the mechanism for the respiratory inhibition observed during high-frequency oscillatory ventilation (HFOV). The effects of HFOV on the activities of single units in the vagus (Vna) and phrenic nerves (Pna) were examined in pentobarbital-anesthetized dogs. The animals were either ventilated by intermittent positive-pressure ventilation (IPPV) with and without positive end-expiratory pressure (PEEP), or by HFOV at a frequency of 25 Hz and pump displacement volume of 3 ml/kg. In 13 vagal units the Vna was much higher during HFOV than during IPPV or airway occlusion at a matched airway pressure. Ten units in the phrenic nerves were examined, and Pna (expressed as bursts/min) was attenuated by HFOV in all of them. In four of them, the effect of cooling the vagi to 8-10 degrees C on Pna was examined, and it was found that HFOV failed to alter the Pna. We conclude that 1) HFOV stimulates the pulmonary vagal afferent fibers continuously and to a degree greater than that due to static lung inflation and increased airway pressure and 2) the increased vagal activity during HFOV probably causes phrenic nerve activity inhibition.

Action Potentials↗
PubMed1981

Effects of the respiratory cycle on cardiac output measurements: reproducibility of data enhanced by timing the thermodilution injections in dogs.

Cardiac output (Q) was measured with the thermodilution technique at 4 points during the respiratory cycle in dogs. Boluses of an ice-cold solution were injected at mid- and end-inspiration while the animals were on intermittent positive-pressure ventilation (IPPV) or after induction of positive end-expiratory pressure (PEEP), with and without induction of experimental respiratory failure. Values were mot constant at end-inspiration. During IPPV without respiratory failure, the standard error of 74 measurements at end-inspiration was 5.1% and of 74 measurements randomly selected was 9.8%. Continuous infusion resulted in similar fluctuations in Q (r = 0.92). Values obtained during experimental respiratory failure were not significantly different. The authors conclude that timing the bolus injections with the respiratory cycle enhances the reproducibility of Q values obtained with the thermodilution technique.

Animals↗
PubMed1981

Aspiration biopsy in the diagnosis of pulmonary disease.

We reviewed the results of 146 aspiration lung biopsies (ALB) performed on 140 patients over a five-year period. A negative fiberoptic bronchoscopy in patients with a pulmonary mass lesion or infiltrate was the major indication for ALB in this group. Seventy-two patients had various malignant chest lesions, 63 had benign or inflammatory pulmonary disease. A definite diagnosis was not obtained in the remaining five patients. The diagnostic accuracy of ALB was 73.6 percent in malignant disease and 17.5 percent in benign disease with no false positive results. Of 50 patients ultimately proven to have unresectable cancer, 46 (92.6 percent) were spared the necessity of exploratory thoracotomy for diagnosis by prior ALB. Complications included pneumothorax in 30 percent necessitating chest tube drainage in 14.3 percent. Minor hemoptysis occurred in 3.4 percent, hemothorax in 0.68 percent and subcutaneous emphysema in 1.36 percent. There were no deaths directly attributable to the procedure. We conclude that ALB is a valuable procedure in the diagnosis of malignant chest lesions, sparing exploratory thoracotomy for histologic diagnosis in many patients.

Adenocarcinoma↗
PubMed1979

Diphenylhydantoin and pulmonary function.

Thirty-nine epileptic patients underwent pulmonary function testing. Twenty-one of these patients, ranging in age from 16 to 44 years, had taken diphenylhydantoin (DPH) for 2 to 17 years. Eighteen patients, who had taken other anticonvulsants for similar time periods served as controls. Five patients in the DPH group had lung volume abnormalities, four had abnormal airway function, and five had abnormalities of alveolar gas mixing. One patient in the control group had lung volume abnormalities, two had abnormal airway function, and five had abnormalities of alveolar gas mixing. Statistical analysis revealed no significant differences between the groups, or between either group and predicted values.

Adolescent↗