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Biomedical subjects

E E Davies

Publications and source records attributed to E E Davies.

At least 19 recordsLinked to original sources
PubMed1986

A rapid rebreathing method for measurement of pulmonary gas volume in humans.

We have developed a rapid gas-dilution technique, with which pulmonary gas volume can be measured in only 20 s, even in the presence of maldistribution of ventilation. The subject rebreathes from a 0.75-liter anesthetic bag filled with 10% He and 30% O2 in argon. Breath-by-breath flow-weighted inspired concentrations of all gases present are calculated from continuous measurement by mass spectrometry. Insoluble gas concentrations are corrected continuously for shrinkage of the system volume. By use of these corrected values a mathematical extrapolation predicts the equilibrium concentration for He in the absence of complete mixing. Validation of the technique was carried out by comparing volumes calculated from the predicted equilibrium value with those obtained by whole-body plethysmography in 7 normal subjects and 12 patients with lung disease. In normal subjects equilibrium was usually attained within the 20 breaths and no extrapolation was required. In most of the patients, however, equilibrium was not reached and the use of the extrapolation technique increased the proportion of the lung volume measured by gas dilution from 0.82 +/- 0.16 (SD) to 0.95 +/- 0.12 of that measured by plethysmography.

Adult↗
PubMed1986

Modification of pulmonary gas mixing by postural changes.

Mixing for two gases of markedly different gaseous diffusivity, helium (He) (mol wt = 4) and sulfur hexafluoride (SF6) (mol wt = 146) has been studied by a rebreathing method in different postures. In nine normal subjects duplicate measurements were made in the erect (seated), supine, and lateral decubitus posture, at a constant tidal volume (700 ml) and frequency (1 Hz) starting from functional residual capacity (FRC). Additional measurements were made on four of the subjects, rebreathing seated erect at a volume similar to the relaxed FRC supine and supine at a volume similar to the relaxed FRC seated. In the supine posture the mean breath number to reach 99% equilibrium (n99), was not significantly different for the two gases, 8.9 for He and 9.8 for SF6. There was a difference (P less than 0.01) when erect; n99 (He) = 8.2 and n99 (SF6) = 10.9. The greatest He-SF6 difference (P less than 0.001) was in the lateral decubitus position n99 (He) = 10.1 and n99 (SF6) = 15.9. The mean relaxed FRC as percent of seated was 71% supine and 75% in lateral decubitus posture. Rebreathing seated at a lower volume did not abolish the He-SF6 mixing difference nor did rebreathing at a higher volume when supine induce a He-SF6 mixing difference. Thus the effect of posture on gas mixing cannot be due solely to lung volume and must represent a convective and diffusive dependent change in the distribution of ventilation per unit lung volume.

Adult↗
PubMed1984

Effect of posture on ventilatory response to steady-state hypoxia and hypercapnia.

The ventilatory response to steady-state normocapnic hypoxia and hypercapnia was measured in eight normal subjects after 15 min inhalation of 10.5% oxygen (with added CO2) or 4.2% CO2 in air through a loose-fitting high-flow Venturi mask. The erect (sitting) and the supine postures were studied. Ventilation was measured with inductance coils around the chest and the abdomen (Respitrace). Oxygen saturation was measured with an ear oximeter and PCO2 was measured transcutaneously on forearm skin using a modified pH electrode (Radiometer). In the erect posture (without stimulation), compared to supine, VE(21%) and VT/TI(32%) were greater but TI(19%) and TE(8%), abdominal contribution to tidal volume (24%) and 'arterial' PCO2 (0.6 mm Hg) were less. The mean ventilatory response to hypoxia at an 'arterial' PCO2 of 41 +/- 4 mm Hg (SD) was 0.61 +/- 0.34 L X min-1 X Sa-1O2 erect and 0.84 +/- 0.58 supine and to hypercapnia 2.89 +/- 1.4 L X min-1 X mm Hg-1 erect and 3.73 +/- 2.35 supine. The postural differences did not reach statistical significance. The pattern of response to both stimuli was similar, with doubling of VT, constant TI and slight shortening of TE. The abdominal contribution to tidal volume decreased by 9% with both forms of stimulation. In the steady state, the response to peripheral and central chemoreceptor stimuli was identical and essentially independent of position.

Adult↗
PubMed1984

The effects of oral almitrine on pattern of breathing and gas exchange in patients with chronic obstructive pulmonary disease.

Almitrine at a low dose of 100 mg orally significantly raises PaO2 and lowers PaCO2 in patients with chronic obstructive pulmonary disease, compared with placebo, when they were breathing air or 28% oxygen. The estimated ideal alveolar-arterial PO2 difference was less after almitrine compared with placebo, when patients were breathing either air or 28% oxygen. After almitrine overall ventilation breathing air increased by 10% but this did not reach statistical significance. During 28% oxygen breathing almitrine hardly altered overall ventilation but the inspiratory duty cycle (Ti/Ttot.) decreased and mean inspiratory flow rate (VT/Ti) increased compared with placebo. These changes were significant on a paired t-test (P less than 0.05). Changes in both volume and pattern of breathing may explain the improved gas exchange in the lung after almitrine.

Administration, Oral↗
PubMed1983

Quantitative measurement of intrapulmonary and extrapulmonary right-to-left shunt.

We have developed a new technique that enables the shunting of blood from the right to the left side of the circulation to be partitioned into a cardiac and a lung component. The effects of recirculation are minimal, and the method does not require on-line data analysis. Quantitative estimates of these components have been made in two normal dogs and in five patients with raised pulmonary arterial pressures, some of whom were known to have a patent foramen ovale. The results were compared with oxygen shunt measured during air breathing. A poorly soluble gas, nitrogen, radiolabelled with 13N in solution is injected first into a central vein while matched samples of blood are drawn from the pulmonary artery and the aorta. A second solution containing 13N is injected into the right ventricle and sampled from the aorta only. Standardized gamma-counting techniques were used to analyze both the injected radioactivity and the radioactivity in the samples. These two measurements enable us to calculate the total right-to-left shunt, the pulmonary shunt, and by subtraction the extrapulmonary cardiac shunt.

Animals↗
PubMed1983

Pattern of breathing and gas exchange following oral almitrine bismesylate in patients with chronic obstructive pulmonary disease.

Almitrine bismesylate (100 mg orally) significantly raised PaO2 and lowered PaCO2 in six patients with chronic obstructive pulmonary disease, compared to placebo, when they were breathing air or 28% oxygen. The estimated ideal alveolar arterial PO2 difference (AaDO2) was less after almitrine bismesylate compared to placebo, when patients were breathing either air or 28% oxygen. After almitrine bismesylate overall ventilation breathing air increased by 10% but this did not reach statistical significance. During 28% oxygen breathing, almitrine bismesylate hardly altered overall ventilation but the inspiratory duty cycle (TI/TTOT) decreased and mean inspiratory flow rate (VT/TI) increased compared to placebo. These changes were significant on a paired T test (P less than 0.05). The improvement in AaDO2 correlated with the rise in VT/TI (r = 0.67, P = 0.02) and thus we suggest that changes in both volume and pattern of breathing might explain the improved gas exchange in the lung after almitrine bismesylate .

Administration, Oral↗
PubMed1982

The contribution of heart beat to gas mixing in the lungs of dogs.

The mixing efficiency for two gases of different gaseous diffusivity, helium (He) and sulphur hexafluoride (SF6) have been studied in anaesthetised dogs, closed and open chested, with and without the heart beating. Equilibration of He and SF6 was studied during rebreathing at frequency of 0.5 Hz and a tidal volume of either 0.3 or 0.5 L. Circulation and gas exchange were taken over by a complete heart and lung bypass circuit during the periods when the heart was stopped. The number of breaths required to reach 99% equilibration (n99) ranged from 4 to 14 for He and from 6 to 17 for SF6. There was no significant change in mixing efficiency in any situation. Stopping the heart increased the n99 for He by only 0.4 +/- 11% (1 SD) (n = 21). Opening the chest increased n99 by 1.4 +/- 13% with the heart beating and 2.5 +/- 19% with the heart stopped. The n99 for SF6 was 30 +/- 22% higher than that for He with the chest closed with or without the heart beating. This increased to 37% with the chest opened but was not altered by stopping the heart. The findings for the final phase equilibration rate constant were similar. We conclude that the beating action of the heart does not affect gas mixing in the lungs in the tidal breathing range.

Animals↗
PubMed1982

Rate of uptake of carbon monoxide at different inspired concentrations in humans.

The rate of uptake of carbon monoxide (CO) in the lungs of normal subjects were measured at inspired concentrations of less than 1, 300, and 3,000 ppm (less than 0.0001-0.3%) using radioactive CO (11CO). In nine subjects the rate of uptake was monitored at the mouth during rebreathing. At inspired CO concentrations of approximately 1, 300, and 3,000 ppm and a mean alveolar O2 fraction of 0.15, the mean lung diffusing capacity was 25.8, 26.4, and 25.3 ml . min-1. Torr-1, respectively. In seven subjects the measurements were repeated after a period of O2 breathing, giving a mean alveolar O2 fraction of 0.78. The calculated membrane diffusing capacity was 31.9, 33.7, and 32.0 ml . min-1. Torr-1 at less than 1, 300, and 3,000 ppm inspired CO. We conclude that there is no difference in the rate of uptake of CO over the range of concentrations studied in these experiments. No evidence for the presence of a facilitated transport system for CO in the normal human lung was found.

Adult↗
PubMed1979

Endodontic perforations which resulted in alveolar bone loss. Report of five cases.

Five cases in which perforations of mandibular molars into the furca occurred during endodontic instrumentation of the canal are presented. This resulted in alveolar bone loss. All were relatively asymptomatic, which could present a problem in diagnosis of the periodontal defect. The prognosis is questionable. The only tooth retained was treated surgically by an apically positioned flap and opening of the furca area to make it accessible to cleansing. The best treatment is the avoidance of the perforation. This is accomplished by considering the configuration of the canals and the size of the reamer than can follow it. Overinstrumentation with an endodontic instrument that is too large in diameter should be avoided.

Adult↗
PubMed1978

Alveolar bone loss associated with vertical root fractures. Report of six cases.

Six cases of vertical root fractures accompanied by vertical bone loss are presented. Possible causes for these fractures are suggested. Four vertical fractures probably resulted from the use of excessive pressure at the time of obturation of the canals. One vertical root fracture may have been caused by the cementation of a post, and another may have been caused by the cementation of an inlay in an endodontically treated tooth. All of the fractures resulted in alveolar bone loss to the apical extent of the fracture lines. The definitive treatment in each case was extraction of the tooth or root amputation. In one case successful treatment was accomplished by apically positioning the flap.

Adult↗