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Biomedical subjects

L P Lee

Publications and source records attributed to L P Lee.

At least 19 recordsLinked to original sources
PubMed1992

A density method for determining plasma and red blood cell volume.

We employed a highly sensitive density measuring system to measure the decrease in blood density and plasma density due to the infusion of a saline bolus into the rabbit's circulation. Based on a vasculature model with the Fahraeus effect, we deduced a set of equations to calculate from the density decreases the red-blood-cell volume and plasma volume of the rabbit. A value of 0.82 +/- 0.02 was obtained for Fcell, the ratio of the hematocrit calculated from the two volumes and the arterial hematocrit.

Animals↗
PubMed1992

Fluid restitution and shift of blood volume in anesthetized rabbits subject to cyclic hemorrhage.

We investigated the effect of a 10% cyclic blood volume change with a period of 2 or 4 min to study the short-term control of blood volume. In experiments with pentobarbital-anesthetized rabbits, the blood density variation over a 2-min cycle is 0.94 +/- 0.04 (SE) g/l, and the plasma density variation is 0.17 +/- 0.04 g/l. The plasma density variation could result from a fluid restitution from the extravascular space (with a density 1,005 g/l), with a volume equal to 14% of the withdrawn blood volume. This restitution cannot account, however, for the entire observed density change in arterial blood. Because of the Fahraeus effect in microvascular flow, a shift in blood volume from the microvasculature is another mechanism that could lead to a decrease in the density of arterial blood. An analysis of the blood and plasma density variations indicates that a blood volume (49% of the shed volume) is shifted from the micro- to macrocirculation. This volume compensation by fluid restitution and volume shift acts to minimize the effect of hemorrhage on the filling of the venous system. We found that the blood density waveform parallels the change in blood volume. When the blood volume change reverses its direction, the density change also reverses direction with a time delay less than 8 s. The blood density variations are not altered by bilateral vagotomy or its combination with hexamethonium (a sympathetic ganglionic blocker). These observations of anesthetized rabbits indicate that the short-term compensation is primarily due to the volume shift from the microcirculation and is not regulated by humoral or neural mechanisms but by local mechanisms such as autoregulation and the passive response due to changes in microvascular pressure.

Anesthesia↗
PubMed1988

Respiratory effect on the blood volume of pulmonary capillaries.

We measured the density variations of aortic blood from rabbits ventilated by a positive end inspiratory pressure of 6 mmHg or a negative box pressure of the same magnitude. When calculated from the density variations, the fluctuations in blood volume of the pulmonary capillaries within one cycle as induced by an intermittent positive pressure ventilation were found to be similar to the ones induced by an intermittent negative pressure ventilation. Using these volumetric fluctuations as a means to assess the transpulmonary pressure and the transmural pressure across the pulmonary capillaries, we conclude that the switching of the ventilation method did not alter the cyclic fluctuations of these pressures.

Animals↗
PubMed1988

Effect of hemodilution on ventilatory fluctuations of pulmonary capillary blood volume.

By diluting the hematocrit (Ha) in the rabbit's circulation without changing its blood volume, we found that the ventilatory-induced fluctuation (delta rho) in the density of aortic blood and Ha (which was in the range of 8-39%) are related by this linear regression: delta rho = 0.63 g/l (-0.009 + Ha). In this hemodilution experiment, the rabbits were ventilated by an intermittent positive pressure of 6 mmHg at a frequency of 30-35 cycles/min. Based on the Fahraeus effect for capillary blood flows and the dispersion of the density indicator in the rabbit's central circulation, we computed from the fluctuation of the measured density within a ventilation cycle the fluctuation of pulmonary capillary blood volume and found it to be 4.1 +/- 0.4% of the capillary blood volume for all hematocrits. Since the same fluctuation in the airway pressure was used to induce the volumetric fluctuation, its independence of Ha indicates that the hemodilution has no effect on the viscoelasticity of pulmonary capillaries.

Animals↗
PubMed1987

Time shift in ventilation-induced density fluctuation of arterial blood.

In an artificially ventilated dog, the varying tracheal pressure causes a density fluctuation in the blood sampled from the aorta. We cross-correlated the tracheal pressure with the density to determine the time shift or delay of the latter from the former waveform for a ventilation frequency in the range of 6-30 CPM. The delay time was found to be 29% of the mean transit time (MTT) of the pulmonary vasculature and independent of the ventilation frequency. A comparison of this percentage with the reported arterial-to-capillary-to-venous fractional volumes of the lung suggested that the delay time may be the MTT time for blood flowing through the venous network of the lung and the cross-correlation may serve as an in vivo means to partition the MTT of the pulmonary vasculature at its capillaries. These results and an analysis on the deformation of the viscoelastic, pulmonary capillaries indicated that the tracheal pressure, acting primarily through the viscous part of the viscoelasticity, deforms the capillaries to produce the density fluctuation in blood outflowing from the lung.

Animals↗
PubMed1986

Ventilatory changes of pulmonary capillary blood volume assessed by arterial density.

By use of an improved density measuring system, we found that the gravimetric density of arterial blood of dogs fluctuates at the same frequency as the spontaneous or mechanical ventilation. Similar density fluctuations were observed in the blood leaving isolated, perfused lobes of dogs that were ventilated cyclicly. Employing an analysis that balanced the erythrocyte and plasma flows through distensible capillaries containing blood with a tube hematocrit lower than the hematocrit in large blood vessels, we derived a relationship to estimate from the density fluctuation the change in pulmonary capillary blood volume (Vc). For mechanical ventilation, the maximum change in density over one ventilation cycle increased from 0.084 +/- 0.01 to 0.47 +/- 0.05 (SE) g/l as the frequency decreased from 29 to 6 cycles/min. These density changes were estimated to be the result of an 1-16% change in Vc. A larger tidal volume for the mechanical ventilation led to a larger density fluctuation. The maximum density change of spontaneous respiration of 6 cycles/min was one-sixth of the mechanical case, indicating a much smaller change in Vc during spontaneous respiration. When the airway flow resistance was increased for spontaneous respiration, larger density fluctuations were observed.

Airway Resistance↗
PubMed1985

A density method to quantify pulmonary microvascular hematocrit.

We perfused the left lower lobe of a dog with autologous blood having a hematocrit Ha. When the vascular pressure perfusing the lobe was elevated, we observed a transient increase in the density of venous blood. Converting the density increase to a rise in hematocrit, we could calculate a volume (Vr) of red blood cells (RBC) over their normal outflow that was released by the lobe as a result of the elevation. We measured the weight gain of the lobe to determine the increase in pulmonary vascular volume, V' - V. We found that the ratio, Vr/Ha/(V' - V), is 0.11 +/- 0.02. To determine the implication of this ratio, we divided the lobular vasculature into an arterial, microvascular, and venous compartment. Due to the Fahraeus effect, the tube hematocrit in the microvascular compartment (Hc) is lower than that of two macrovascular compartments, Ha. An analysis on the balance of RBC and plasma flows through the lobe identified the volume Vr as (Vc' - Vc) (Ha - Hc) with Vc' - Vc being the volumetric increase of the lobular microvascular compartment. Based on the reported volumetric fractional change of microvascular compartment, we estimated that the microvascular (tube) hematocrit in pulmonary capillaries is 80% (ranging from 78 to 82%) of the hematocrit perfusing the lobe. Since the additional RBC volume (Vr) being released from the lobe cannot be accounted for by transcapillary filtration or capillary recruitment, we conclude from this analysis that the measurement of the transient density change in pulmonary outflow can be used to quantify the microvascular hematocrit of the lung.

Animals↗
PubMed1984

Serum enzymes in the BB rat before and after onset of the overt diabetic syndrome.

As part of a six-month prospective study of the effects of neonatal thymectomy in the spontaneously diabetic BB Wistar rat, activities of the following enzymes were determined: alkaline phosphatase (AP), lactate dehydrogenase (LDH), creatine phosphokinase (CPK), glutamic-oxaloacetic transaminase (GOT), glutamic-pyruvic transaminase (GPT) and UDP-galactosyltransferase (UDPG). In prediabetics, AP and LDH levels were higher than in sham-operated, non-diabetic controls; however, this increase was seen in nearly all diabetes-prone BB rats, diminishing the usefulness of these changes in discerning potential diabetics from asymptomatic, diabetes-prone rats. After onset of the syndrome, there was a striking elevation of AP values in all diabetics with no similar alteration in asymptomatic, diabetes-prone rats suggesting this was a diabetes-related phenomenon. By contrast, UDPG was the only enzyme to decrease immediately following the onset of the syndrome. Both UDPG and AP levels correlated with blood glucose, the former negatively and the latter positively, suggesting a close relationship with changes occurring after onset of the syndrome. The remaining enzymes increased only in a portion of diabetics alone (GOT, GPT) or in a portion of both diabetics and asymptomatic, diabetes-prone BB rats (LDH, CPK).

Alanine Transaminase↗
PubMed1982

Comparison of four commercial methods for the determination of fast hemoglobins.

The performance of three commercial kits, based on microchromatographic techniques for the determination of glycosylated hemoglobins (fast hemoglobins) has been evaluated. All three kits showed good precision, provided the laboratory temperature remained constant. Temperature variations of even one degree C had a profound effect on the kits from Helena Laboratories and Isolab Inc., while the one from BIO-RAD Laboratories was less influenced. The use of the temperature correction tables provided by Helena Laboratories and Isolab Inc., improved the reproducibility of their results significantly. Since there is no designated reference method, an evaluation of accuracy was not possible. The absolute values for fast hemoglobins, as measured by the three microchromatographic kits, differed from each other. Also, when a series of specimens from diabetic patients and from healthy control subjects were compared, the relative ratios of the results obtained from the three kits differed from specimen to specimen. However, there was no overlap between results from diabetic and control specimens. The performance of the electrophoretic method of Corning Medical Co. was also evaluated.

Diabetes Mellitus↗
PubMed1978

Transferred pulmonary surfactant film: chemical analysis and contact angle study.

The Langmuir dip plate transfer technique was adapted to isolate the interfacial film formed at the surface of lung wash. The chemical analysis of the film showed that the weight ratio of lipid to protein of this surfactant film and its content of surface active substances were higher than those of lung wash. It was found that the wettability of the surfactant film could be simulated by a Dipalmitoyl lecithin and albumin film. When the surfactant film was transferred at condensed state (one of low air-lung-wash surface tension), we found the film exhibited a low critical surface tension which indicates the dominance of the lipid in the outer most layer of the film. On the other hand, insignificant amount of lipid was found in the film transferred at expanded state (one of high surface tension) and its surface behavior was shown to be similar to that of a protein film.

Animals↗
PubMed1977

Serum UDP-galactose: glycoprotein galactosyltransferase in diabetics with microangiopathy.

1. Levels of serum UDP-galactose:glycoprotein galactosyltransferase in 117 unselected diabetics were compared with those in 60 non-diabetic healthy controls. 2. Enzyme activity (mean +/- 2 S.D.) of control sera was found to be 90.2 +/- 21.5 etamoles/ml/hr at 37 degrees. In 30 of the 117 diabetic sera (26%) enzyme activity was elevated (greater than mean + 2 S.D. of the controls). Sixteen of 19 (84%) patients with retinopathy, 16 of 26 (62%) patients with peripheral vasculopathy and 13 of 26 (50%) patients with neuropathy had higher levels of serum enzyme. When serum enzyme levels of groups of diabetics with retinopathy, peripheral vasculopathy and neuropathy were compared with the enzyme level in all diabetics, there was a significant difference with p values of 0.001, 0.05 and 0.05 respectively.

Adolescent↗