Tomoaki Takasugi

Distribution of ventilation and of diffusing capacity to perfusion in the lung

We developed a method for estimating the distribution of ventilation (VA) and of diffusing capacity (G) to perfusion (Q) in the lungs. We used O2, CO2 and CO together with six inert gases of widely differing solubility and assumed that mass transfer efficiency of each gas in a gas exchange unit is limited by both VA/Q and G/Q ratios. The underlying lung model comprised 20 units along both the VA/Q and G/Q axes. Using numerical analysis, we transformed the data into a virtually continuous distribution of Q in the VA/Q-G/Q field. We tested the precision of the numerical procedure by examining the recovery of various artificial distributions, and found that distributions with up to two modes could be recovered with reasonable accuracy. Analytical results from 15 patients with interstitial pneumonia of unknown etiology (IPF) revealed the following features. (1) In an early disease stage, most of the lung was operating in the range of normal VA/Q, without a significant contribution of diffusion limitation. (2) An advanced stage of the disease exhibited a widening of VA/Q distribution and either broad unimodal or bimodal distribution of G/Q, extending to G/Q below 10(-3) ml (STPD)/(ml.Torr) with diffusion-limited O2 exchange. (3) Severe diffusion limitation causing disequilibrium of inert gas across the blood-gas barrier was observed in three (far advanced fibrosis; active interstitial inflammation) out of 15 patients. These findings suggest that inhomogeneity of G/Q does exist and may play an appreciable role in causing impairment of gas exchange in patients with interstitial pneumonia.

Constriction and dilatation of pulmonary arterial ring by hydrogen peroxide - Importance of prostanoids

Reactive oxygen species (ROS) have been considered as one of the important factors causing acute lung injury associated with alveolar flooding, especially in the case of sepsis, fat embolism, hyperoxic lung damage as well as reperfusion injury (Hefner and Repine, 1989). Among them, hydrogen peroxide (H2O2) and its derivatives are relatively stable as compared to other ROS and are taken notice as the substance altering pulmonary hemodynamics accompanied by alveolar flooding (Archer et al., 1989; Gurtner and Burke-Wolin, 1991; Barnard et al., 1992). Effects of H2O2 on pulmonary circulation is much complicated, namely vasoactive action of H2O2 is dependent on the vascular tone. In other words, H2O2 relaxes the pulmonary vessel when the tone is high but constricts it when the tone is low (Burke-Wolin et al., 1991). Gurtner and Burke-Wolin (1991) reported that vasoconstrictive effect of H2O2 would be mainly mediated through thromboxane A2 (TXA2) generated in the endothelial cells of pulmonary vasculature. However, several authors (Madden et al., 1986; Smith, 1986; Takayasu et al., 1990) showed that arachidonate metabolism might exist not only in endothelial cells but also in smooth muscle cells and fibroblasts in vascular walls, indicating that the conclusion derived by Gurtner and Burke-Wolin (1991) should be reassessed.

Temporal alterations of endothelial-vasodilator functions in lung injury induced by monocrotaline

To assess the time course of alterations in pulmonary endothelial vasodilator functions during pathological development of pulmonary hypertension (PH) and right ventricular hypertrophy (RVH), we examined changes in serotonin (5-HT) removal rates and the production of prostacyclin (PGI2) and nitric oxide (NO) in isolated rat lungs harvested at various times after single exposure to monocrotaline (MCT). We assessed the generation of vasodilator substances under conditions of both the absence and the presence of 5-HT in lungs perfused with blood-free solution. Major findings included: (i) remodeling of the pulmonary vasculature associated with RVH evident 14 days after MCT injection; (ii) the capacity for 5-HT removal was suppressed at day 1 and 7 but had been restored by day 14 after MCT exposure; (iii) basal PGI2 production in the absence of 5-HT was augmented at day 1 but had returned to control levels in lungs harvested 7 or 14 days postinjection of MCT; (iv) PGI2 production evoked by 5-HT was suppressed in MCT lungs obtained at all time points examined; (v) basal NO production was suppressed at day 1 but enhanced at day 7 and 14 in MCT lungs; (vi) NO production elicited by 5-HT stimulation in 1-day-MCT lungs was obviously suppressed while that in 7- and 14-day-MCT lungs had been restored to the control level. These findings suggest that transitional changes in endothelial functions including 5-HT removal and production of vasodilators in MCT lungs do not follow the same time course.

Regulation of Blood Flow in Pulmonary Microcirculation by Vasoactive Arachidonic Acid Metabolites – Analysis in Acute Lung Injury

In order to assess the physiological abnormalities and the pathogenesis of adult respiratory distress syndrome (ARDS), especially that associated with pulmonary fat embolism, acute lung injury caused by monounsaturated nonsterified fat oleic acid (cis-9-octadecenoic acid) has been widely used in animal experiments. This lung injury results in an extensive, multifocal, and heterogeneously distributed lung damage with alveolar flooding, interstitial edema and microatelectasis. The ability to reduce the perfusion entering into damaged and edematous areas is essentially important in preserving blood oxygenation in ARDS.

Ventilation-perfusion inequality and diffusion impairment in acutely injured lungs

To assess the significant role of diffusion impairment and its unequal distribution in acutely injured lungs with alveolar flooding, oleic acid was intravenously injected into twenty-five mongrel dogs. The animals were divided into two groups, A and B. 0.1% CO in air was delivered, as an inspired gas, to the animals of group A. Simultaneously, saline containing a trace amount of six foreign inert gases was infused through a peripheral vein. While allowing the animals in group B to breathe air, saline containing ethylene, acetylene and freon 22 was infused. After injection of oleic acid, group A revealed increase in intrapulmonary shunt accompanied by a marked broadening of ventilation-perfusion (VA/Q) and diffusing capacity-perfusion (G/Q) distributions. A considerable amount of total cardiac output was received by the lung areas with low G/Q ratios where significant diffusion limitation was predicted to occur. Group B showed that excretion of freon 22 (gas with lower diffusivity) in injured lungs was considerably distorted as compared to those of ethylene and acetylene (gases with higher diffusivities), again ascertaining the importance of diffusion limitation in lungs with exudate in alveolar regions.

Behavior of Stimulated Leukocytes in the Pulmonary Microcirculation of Perfused Rat Lungs

To investigate the dynamics of activated leukocytes and the roles of CD18-ICAM-1 pathway, we examined the effects of rat IL-8 and monoclonal antibodies (mAbs) against CD18 and ICAM-1 on the behavior of leukocytes in microvessels of perfused rat lungs. Specific pathogen free male Sprague-Dawley rats were used. Perfused rat lungs were prepared so as to obtain stable physiological shear rates. We used a confocal laser scanning microscope equipped with a high speed video analysis system to visualize pulmonary microcirculation. Rat leukocytes were activated with rat IL-8. No rolling leukocytes were observed in either pulmonary arterioles or venules, and leukocytes were sequestered in capillaries. The majority of unstimulated capillary leukocytes moved smoothly. About 50% of stimulated leukocytes, however, showed a transient cessation of movement in pulmonary capillaries. Rat IL-8 decreased the relative leukocyte velocities against mean blood velocities in capillaries (45%) and venules (65%), and increased intracapillary neutrophils. Anti-CD18 and anti-ICAM-1 mAbs attenuated these changes. These results suggest that unique features exist in the interaction between activated leukocytes and pulmonary microvessels, and that CD18-ICAM-1-dependent capillary sequestration is one of the major mechanisms by which activated leukocytes accumulate in lungs.

Effects of 5-Hydroxytryptamine Inhibition on Gas Exchange and Pulmonary Hemodynamics in Acute Canine Pulmonary Embolism

5-Hydroxytryptamine (Serotonin; 5-HT), a potent vasoconstrictor of pulmonary arteries, has been reported to play an important role in cardiopulmonary dysfunction that accompanies pulmonary embolization (Huval et al.,1983). The quantitative effects of 5-HT on gas exchange efficiency, however, have not been systematically investigated in pulmonary embolism. Using a new type of selective serotonin receptor antagonist, we examined the distribution of ventilation-perfusion (VA/Q) ratios and pulmonary hemodynamics to clarify the effects of serotonin on gas exchange in acute canine pulmonary embolism.

Attenuation of Hypoxic Pulmonary Vasoconstriction in Acute Oleic Acid Lung Injury — Significance of Vasodilator Prostanoids

To assess a significant role of hypoxic pulmonary vasoconstriction, HPV, on maintaining the gas exchange efficiency in acute lung injury, 24 mongrel dogs were treated with intravenously injecting 0.07 ml/kg of oleic acid. Hemodynamic and gas-exchange parameters were investigated at varied inspired O2 concentration, FIO2. To know a possible contribution of vasoactive prostanoids in regulating vascular reactivity under these circumstances, observations were repeated after infusion of indomethacin. The impairment of gas exchange in injured lungs was examined by measuring the fractional retention, R, of the gas in arterial blood. For this evaluation, a normal saline containing five foreign inert gases such as sulfur hexafluoride, SF6, ethane, cyclopropane, halothane and diethyl ether was infused at a constant rate through a peripheral vein. After a steady state was established, the expired gas was collected and the samples of both arterial and mixed venous blood were simultaneously taken for the inert-gas analysis. The concentrations of the indicator gases in the samples were measured in terms of a gas chromatograph equipped with an electron capture detector for SF6 and a flame ionization detector for the other four gases. Although pulmonary vascular resistance, PVR, after injecting oleic acid at FIO2 0.60 was significantly smaller than that obtained at FIO2 0.21, cardiac output, QT as well as extravascular lung water were not different between the two conditions. R value for the indicator gas was consistently lower at FIO2 0.60 irrespective of the gas species. As increasing FIO2, R estimate concerning SF6, RSF6, rational index of the fractional blood flow perfusing shunt area, decreased significantly. Administration of indomethacin caused the rise in PVR without an appreciable change in either QT or extravascular lung water but a considerable diminution in R value for the inert gas. RSF6 after infusion of indomethacin decreased from 0.35 to 0.27, accompanied by a significant rise in arterial PO2 from 84 to 99 Torr. The findings are highly compatible with the idea that HPV is distinctly attenuated in diseases areas induced by oleic acid probably due to a local accumulation of vasodilator prostanoids. Inhibiting prostanoid biosynthesis may selectively enhance the vascular reactivity to O2 in shunt vessels and may redistribute the perfusion from shunt to relatively normal areas, thereby improving gas exchange at alveolar region without altering the total amount of extravascular lung water.

Continuous Distributions of Ventilation and Gas Conductance to Perfusion in the Lungs

Theoretical analysis and experimental observations were conducted to establish a method allowing to demonstrate the characteristics of distribution of ventilation (VA) as well as of diffusive conductance (G) to perfusion (Q) in the lungs. O2, CO2 and CO binding to hemoglobin molecules within the erythrocyte together with six inert gases including SF6, ethane, cyclopropane, halothane, diethyl ether and acetone, of varied solubility in blood and different diffusivity in lung tissue, were used as indicator gases. 15 patients with interstitial pneumonia of unknown etiology, placed in the supine position, were given a mixture of 21% O2 and 0.1% CO in N2 as the inspired gas and saline containing appropriate amount of the six inert gases was infused via an antecubital vein. After a steady state was established, the expired gas was collected and the samples of both arterial and mixed venous blood were simultaneously taken through catheters inserted into the femoral and pulmonary artery. The concentrations of the indicator gases in the samples were measured by gas chromatography, with electrodes or with the Scholander gas analyzer. Assuming that the mass transfer efficiency of a given indicator gas at each gas exchange unit would be limited by VA/Q and G/Q ratios, the data obtained from the human subjects were analyzed in terms of a lung model having 20 units along the VA/Q and G/Q axes, respectively. The numerical analysis including the procedure of simultaneous Bohr integration for O2, CO2 and CO in a pulmonary capillary and the method of weighted least-squares combined with constrained optimization permitted the data to be transformed into a virtually continuous distribution of Q against VA/Q and G/Q axes. The numerical procedure was strictly tested using various artificial distributions of VA/Q and G/Q ratios, showing that it could characterize the distributions containing up to at least two modes on VA/Q-G/Q field with a substantial accuracy. Analytical results estimated from the patients with interstitial lung disease revealed the following features. (1) There appears to be bimodal distribution of Q along G/Q axis extending to relatively low G/Q less than 10(-3) ml(STPD)/(ml.Torr), which may limit O2 exchange between alveolar gas and capillary blood. This area of low G/Q receives 10% of total Q. (2) Severe diffusion limitation causing disequilibrium of the inert gas across the blood-gas barrier is solely observed in 2 out of 15 patients and an amount of Q associated with this phenomenon is very small (below 1%).(ABSTRACT TRUNCATED AT 400 WORDS)

Displacement of gold marker in immunoelectron microscopy of human respiratory cilia

Preembedding immunogold electron microscopy was performed to evaluate the position of outer arm dynein heavy chains in normal human respiratory cilia. Anti‐dynein antibody (AD2), which is specific for sea urchin sperm flagellar dynein heavy chains, was used as primary antibody. Direct cross‐sections of cilia were selected, and the distance between the center of a cilium and the center of a colloidal gold particle attached to the cilium (X) was measured. The distance between the center of a cilium and the farthest edge of an outer dynein arm of the cilium was measured by ordinary electron microscopy (Yo) and by immunoelectron microscopy (Yi). X was significantly longer than Yo and Yi. If it is assumed that the structure of respiratory cilia is dense and that antibodies are located at the outer side of the actual position of the heavy chains, then the average distance difference of approximately 90–120 Å may represent the length of two conjugated antibodies. This length should be kept in mind when performing immunoelectron microscopy. The data suggest that AD2 recognizes the outer arm dynein heavy chains of normal human respiratory cilia. Micros. Res. Tech. 38:500–504, 1997.