SIZE OF GAS EXCHANGE VESSELS IN THE LUNG

Perfusion heterogeneity in rat lungs assessed from the distribution of 4-microm-diameter latex particles

Pulmonary vascular perfusion has been shown to follow a fractal distribution down to a resolution of 0.5 cm(3) (5E11 microm(3)). We wanted to know whether this distribution continued down to tissue volumes equivalent to that of an alveolus (2E5 microm(3)). To investigate this, we used confocal microscopy to analyze the spatial distribution of 4-microm-diameter fluorescent latex particles trapped within rat lung microvessels. Particle distributions were analyzed in tissue volumes that ranged from 1.7E2 to 2.8E8 microm(3). The analysis resulted in fractal plots that consisted of two slopes. The left slope, encompassing tissue volumes less than 7E5 microm(3), had a fractal dimension of 1.50 +/- 0.03 (random distribution). The right slope, encompassing tissue volumes greater than 7E5 microm(3), had a fractal dimension of 1.29 +/- 0.04 (nonrandom distribution). The break point at 7E5 microm(3) corresponds closely to a tissue volume equivalent to that of one alveolus. We conclude that perfusion distribution is random at tissue volumes less than that of an alveolus and nonrandom at tissue volumes greater than that of an alveolus.

Pulmonary arterial dilation by inhaled NO: arterial diameter, NO concentration relationship

The objective of this study was to determine the nitric oxide (NO) concentration and vessel diameter dependence of the pulmonary arterial dilation induced by inhaled NO. Isolated dog lung lobes were situated between a microfocal X-ray source and X-ray detector and perfused with either blood or plasma. Boluses of radiopaque contrast medium were injected into the lobar artery under control conditions, when the pulmonary arteries were constricted by infusion of serotonin and when the serotonin infusion was accompanied by inhalation of from 30 to 960 parts/million NO. Arterial diameter measurements were obtained from X-ray images of vessels having control diameters in the 300- to 3,400-microm range. Serotonin constricted the vessels throughout the size range studied, with an average decrease in diameter of approximately 20%. The fractional reversal of the serotonin-induced constriction by inhaled NO was directly proportional to inhaled NO concentration, inversely proportional to vessel size, and greater with plasma than with blood perfusion in vessels as large as 3 mm in diameter. The latter indicates that intravascular hemoglobin affected the bronchoalveolar-to-arterial luminal NO concentration gradient in fairly large pulmonary arteries. The data provide information regarding pulmonary arterial smooth muscle accessibility to intrapulmonary gas that should be useful as part of the database for modeling the communication between intrapulmonary gas and pulmonary arterial smooth muscle cells in future studies.

Blood flow velocity in pulmonary microvessels of bullfrog

Flow velocity in the pulmonary microvessels of the exposed lung of bullfrogs was measured by means of a laser Doppler microscope of an oblique backward mode, together with a signal-analyzing system having a time sharing circuit triggered by the R-wave of the ECG. By these means, measurements of the changes of flow velocity contour in the cardiac cycle were made. Flow velocity was clearly pulsatile in response to cardiac cycles in all microvessels including capillaries. Flow velocities in the arteriole and venule consistently decreased for a short period after the R-wave (84 +/- 33 msec (mean +/- SD) in the arteriole and 130 +/- 31 msec in the venule, respectively) and rapidly increased up to a maximicronm value. The mean flow velocities in arterioles (diameter 50 +/- 17 micron) and venules (39 +/- 9 micronm) were 2.29 +/- 0.32 and 2.30 +/- 0.27 mm/sec. The amplitudes of pulsatile flow in these vessels were 0.83 +/- 0.31 and 0.63 +/- 0.16 mm/sec, respectively. In the capillary the times from the R-wave to the minimicronm and maximum values were variable. In some cases the velocity gradually increased without first decreasing and the increase sharply accelerated a certain time after the R-wave. The mean velocity in the pulmonary capillary and the amplitude of the pulsatile flow ere 1.78 +/- 0.31 and 0.37 +/- 0.12 mm/sec, resepctively. The ratios of the pulsatile amplitude to the mean velocity in the pulmonary capillary, venule and arteriole averaged 0.21, and 0.36, respectively.

Uneven perfusion and ventilation within lung regions studied with nitrogen-13

The clearance of nitrogen-13 (13N) from the upper, mid and lower zones was measured with a gamma camera during spontaneous breathing in 10 seated subjects. The clearance was monitored after (a) an intravenous injection of 13N dissolved in saline and (b) equilibration with 13N gas in closed circuit. Subjects breathed air first, and then a 30 or 11% oxygen mixture. For any region, the time for 90% elimination (T90) was related to the volume expired by the whole lung during that time (VE90). For the mid and lower zones, the clearance was faster (VE90 smaller) after intravenous 13N than after equilibration with 13N gas. This difference persisted when 30% or 11% oxygen was inspired. For the lung overall, the physiological dead space for a mean tidal volume of 884 ml was 277 ml for intravenous 13N clearance, and 384 ml for 13N clearance after equilibration. The conclusions drawn for this study are (1) ventilation in relation to volume is uneven within lung regions (2) intraregional perfusion in relation to volume is also uneven (3) at a local level the well-ventilated units are better perfused (4) these inhomogeneities are not affected by raising or lowering the inspired oxygen concentration.

Hypoxia and hydrothoraces in a case of liver cirrhosis: correlation of physiological, radiographic, scintigraphic, and pathological findings

Stanley, N. N., Williams, A. J., Dewar, C. A., Blendis, L. M., and Reid, Lynne (1977).Thorax, 32, 457-471. Hypoxia and hydrothoraces in a case of liver cirrhosis: correlation of physiological, radiographic, scintigraphic, and pathological findings. A case is reported of liver cirrhosis complicated by cyanosis and recurrent right hydrothorax. A diagnostic pneumoperitoneum demonstrated that direct movement of ascites through a diaphragmatic defect was responsible for the hydrothoraces. Pulmonary function tests between episodes of hydrothorax showed severe arterial hypoxaemia, a 23% right-to-left shunt, and a reduction in the carbon monoxide transfer factor to less than half of the predicted value. Evidence of abnormal intrapulmonary arteriovenous communications was obtained by perfusion scanning. At necropsy the central tendon of the diaphragm showed numerous areas of thinning which were easily ruptured. Injection of the pulmonary arterial tree demonstrated precapillary arteriovenous anastomoses and pleural spider naevi. A morphometric analysis provided quantitative evidence of pulmonary vasodilatation limited to the intra-acinar arteries, consistent with the effect of a circulating vasodilator. The scintigraphic and pathological findings suggested that shunting had been greater in the right than the left lung. Examination of thin lung sections by light microscopy showed that the walls of small veins were thickened, and electron microscopy showed that this was due to a layer of collagen. The walls of capillaries were similarly thickened, which caused an approximately two-fold increase in the minimum blood-gas distance and contributed to the reduction in transfer factor.

Pulmonary arterial blood volume and tissue volume in man and dog

After the injection of an ethyl ether-alcohol solution above the pulmonic valve, the pulmonary arterial circulation time was determined in conscious man by an established body plethysmographic technique and in anesthetized man by a newly developed pneumotachographic method. In the anesthetized dog, estimates of pulmonary arterial circulation time determined by this new method were compared with those simultaneously determined by the plethysmographic method; agreement was good. The usefulness of applying corrective factors for the right-to-left intrapulmonary shunt and the uptake of ether gas from the alveoli into the blood while the ether gas is being evolved from the initial injection was evaluated from the dog experiments. In five humans with normal pulmonary arterial pressures, pulmonary arterial blood volume estimated by these methods was 172 ± 22 (sd) ml. Estimates of pulmonary tissue volume in both dogs and man were much larger than previously reported values determined from the tritiated water space of the lungs but more in keeping with previously published estimates of the total water content of the lungs determined at postmortem examination.

Rate of disappearance of labeled carbon dioxide from the lungs of humans during breath holding: a method for studying the dynamics of pulmonary CO2 exchange

The dynamics of CO(2) exchange in the lungs of man was studied by observing the rate of disappearance of a stable isotope of CO(2) ((13)CO(2)) from the alveolar gas during breath holding. Over 50% of the inspired isotope disappeared within the first 3 sec followed by a moderately rapid logarithmic decline in which one-half of the remaining (13)CO(2) disappeared every 10 sec. The large initial disappearance of (13)CO(2) indicated that alveolar (13)CO(2) equilibrated in less than 3 sec with the CO(2) stored in the pulmonary tissues and capillary blood. The volume of CO(2) in the pulmonary tissues calculated from this initial disappearance was 200 ml or 0.33 ml of CO(2) per milliliter of pulmonary tissue volume. The alveolar to end-capillary gradient for (13)CO(2) was calculated by comparing the simultaneous disappearance rates of (13)CO(2) and acetylene. At rest and during exercise this gradient for (13)CO(2) was either very small or not discernible, and diffusing capacity for CO(2) (D(LCO2)) exceeded 200 ml/(min x mm Hg). After the administration of a carbonic anhydrase inhibitor the rate of disappearance of (13)CO(2) decreased markedly. D(LCO2) fell to 42 ml/(min x mm Hg) and at least 70% of the exchange of (13)CO(2) with the CO(2) stores in the pulmonary tissues and blood was blocked by the inhibitor. These changes were attributed to impairment of exchange of (13)CO(2) with the bicarbonate in the pulmonary tissues and blood. The pH of the pulmonary tissues (V(tis)) was determined by a method based on the premise that the CO(2) space in the pulmonary tissues blocked by the inhibitor represented total bicarbonate content. At an alveolar P(CO2) of 40 mm Hg pH of V(tis) equalled 6.97 +/- 0.09.

Longitudinal distribution of vascular resistance in the pulmonary arteries, capillaries, and veins

A new method has been described for measuring the pressure and resistance to blood flow in the pulmonary arteries, capillaries, and veins. Studies were performed in dog isolated lung lobes perfused at constant flow with blood from a donor dog. Pulmonary artery and vein volume and total lobar blood volume were measured by the ether plethysmograph and dyedilution techniques. The longitudinal distribution of vascular resistance was determined by analyzing the decrease in perfusion pressure caused by a bolus of low viscosity liquid introduced into the vascular inflow of the lobe. The pulmonary arteries were responsible for 46% of total lobar vascular resistance, whereas the pulmonary capillaries and veins accounted for 34 and 20% of total lobar vascular resistance respectively. Vascular resistance was 322 dynes .sec.cm(-5)/ml of vessel in the lobar pulmonary arteries, 112 dynes.sec.cm(-5)/ml in the pulmonary capillaries, and 115 dynes.sec.cm(-5)/ml in the lobar pulmonary veins. Peak vascular resistivity (resistance per milliliter of volume) was in an area 2 ml proximal to the capillary bed, but resistivity was high throughout the pulmonary arterial tree. The pulmonary arteries accounted for approximately 50% of vascular resistance upstream from the sluice point when alveolar pressure exceeded venous pressure. The method described provides the first measurements of pulmonary capillary pressure. Mid-capillary pressure averaged 13.3 cm H(2)O, pulmonary artery pressure averaged 20.4 cm H(2)O, and pulmonary vein pressure averaged 9.2 cm H(2)O. These techniques also provide a way of analyzing arterial, capillary, and venous responses to various pharmacologic and physiologic stimuli.

Determination of distribution of diffusing capacity in relation to blood flow in the human lung

A method for appraising the distribution of diffusing capacity of the lungs (D(L)) in relationship to pulmonary capillary blood flow ([unk]Q(C)) in normal human subjects was derived from measurements of oxygen diffusing capacity (D(LO2)) and carbon monoxide diffusing capacity (D(LCO)) performed during breath holding. This method utilizes the fact that the observed D(LO2) is considerably reduced in value if uneven distribution of D(L) with respect to [unk]Q(C) (uneven D(L)/[unk]Q(C)) is present. In contrast, D(LCO) is barely affected by uneven D(L)/[unk]Q(C), and from its measured value one can calculate the value D(LO2) would have if no uneven D(L)/[unk]Q(C) were present (true D(LO2)). Once observed D(LO2) and true D(LO2) are known, the degree of uneven D(L)/[unk]Q(C) in the lung can be calculated. In five normal, resting, sitting subjects average values for true D(LO2) were 57 ml per (minute x mm Hg), and the directly measured D(LO2) was 33 ml per (minute x mm Hg). These values could be explained if one-half of total [unk]Q(C) were distributed to approximately 15% of total D(L). These measurements did not permit the determination of the alveolar to end capillary O(2) gradient, but calculations demonstrate that an important factor in determining its size may be the pattern of uneven D(L)/[unk]Q(C) present in the lungs. Estimations of the alveolar-end capillary O(2) gradient from measurements of D(LCO) or D(LO2) that do not take into account uneven D(L)/[unk]Q(C) may underestimate its size.