An allometric study of pulmonary morphometric parameters in birds, with mammalian comparisons

Comprehensive pulmonary morphometric data from 42 species of birds representing ten orders were compared with those of other vertebrates, especially mammals, relating the comparisons to the varying biological needs of these avian taxa. The total lung volume was strongly correlated with body mass. The volume density of the exchange tissue was lowest in the charadriiform and anseriform species and highest in the piciform, cuculiform and passeriform species. The surface area of the blood-gas (tissue) barrier, the volume of the pulmonary capillary blood and the total morphometric pulmonary diffusing capacity were all strongly correlated with body mass. The harmonic mean thickness of both the blood-gas (tissue) barrier and the plasma layer were weakly correlated with body mass. The mass-specific surface area of the blood-gas (tissue) barrier (surface area per gram body mass) and the surface density of the blood-gas (tissue) barrier (i.e. its surface area per unit volume of exchange tissue) were inversely correlated (though weakly) with body mass. The passeriform species exhibited outstanding pulmonary morphometric adaptations leading to a high specific total diffusing capacity per gram body mass, consistent with the comparatively small size and energetic mode of life which typify passeriform birds. The relatively inactive, ground-dwelling domestic fowl (Gallus gallus) had the lowest pulmonary diffusing capacity per gram body mass. The specific total lung volume is about 27% smaller in birds than in mammals but the specific surface area of the blood-gas (tissue) barrier is about 15% greater in birds. The ratio of the surface area of the tissue barrier to the volume of the exchange tissue was also much greater in the birds (170-305%). The harmonic mean thickness of the tissue barrier was 56-67% less in the birds, but that of the plasma layer was about 66% greater in the birds. The pulmonary capillary blood volume was also greater (22%) in the birds. Except for the thickness of the plasma layer, these morphometric parameters all favour the gas exchange capacity of birds. Consequently, the total specific mean morphometric pulmonary diffusing capacity for oxygen was estimated to be about 22% greater in birds than in mammals of similar body mass. This estimate was obtained by employing oxygen permeation constants for mammalian tissue, plasma and erythrocytes, as avian constants were not then available.(ABSTRACT TRUNCATED AT 400 WORDS)     

Red cell distortion and conceptual basis of diffusing capacity estimates: finite element analysis

Hsia, C. C. W., C. J. C. Chuong, and R. L. Johnson, Jr.Red cell distortion and conceptual basis of diffusing capacity estimates: finite element analysis. J. Appl.Physiol. 83(4): 1397-1404, 1997.To understandthe effects of dynamic shape distortion of red blood cells (RBCs) as itdevelops under high-flow conditions on the standard physiological andmorphometric methods of estimating pulmonary diffusing capacity, wecomputed the uptake of CO across a two-dimensional geometric capillarymodel containing a variable number of equally spaced RBCs. RBCs arecircular or parachute shaped, with the same perimeter length. Total COdiffusing capacity (DL_CO)and membrane diffusing capacity(DM_CO)were calculated by a finite element method.DL_COcalculated at two levels of alveolar PO₂ were used to estimateDM_CO by theRoughton-Forster (RF) technique. The same capillary model was subjectedto morphometric analysis by the random linear intercept method toobtain morphometric estimates ofDM_CO. Results show thatshape distortion of RBCs significantly reduces capillary diffusive gasuptake. Shape distortion exaggerates the conceptual errors inherent inthe RF technique (J. Appl. Physiol.79: 1039-1047, 1995); errors are exaggerated at a high capillaryhematocrit. Shape distortion also introduces additional error inmorphometric estimates ofDM_CO causedby a biased sampling distribution of random linear intercepts; errors are exaggerated at a low capillary hematocrit.

     

Role of nitrogen in transmucosal gas exchange rate in the rat middle ear.

This study investigates the role of nitrogen (N2) in transmucosal gas exchange of the middle ear (ME). We used an experimental rat model to measure gas volume variations in the ME cavity at constant pressure. We disturbed the steady-state gas composition with either air or N2 to measure resulting changes in volume at ambient pressure. Changes in gas volume over time could be characterized by three phases: a primary transient increase with time (phase I), followed by a linear decrease (phase II), and then a gradual decrease (phase III). The mean slope of phase II was -0.128 microl/min (SD 0.023) in the air group (n = 10) and -0.105 microl/min (SD 0.032) in the N2 group (n = 10), but the difference was not significant (P = 0.13), which suggests that the rate of gas loss can be attributed mainly to the same steady-state partial pressure gradient of N2 reached in this phase. Furthermore, a mathematical model was developed analyzing the transmucosal N2 exchange in phase II. The model takes gas diffusion into account, predicting that, in the absence of change in mucosal blood flow rate, gas volume in the ME should show a linear decrease with time after steady-state conditions and gas composition are established. In accordance with the experimental results, the mathematical model also suggested that transmucosal gas absorption of the rat ME during steady-state conditions is governed mainly by diffusive N2 exchange between the ME gas and its mucosal blood circulation.     

Capillary volume fraction is the principal determinant of villous membrane thickness in the normal human placenta at term.

The thickness of the villous membrane is known to be an important factor in determining the morphometric diffusing capacity of the placenta at term. As yet it is not certain how areas of the villous membrane specialised for gaseous exchange, the vasculo-syncytial membranes, differentiate. One mechanism suggested is that they arise through obtrusion of the fetal capillaries contained within the stromal core. As a result the bulk of the overlying trophoblast is displaced laterally, reducing the thickness of the villous membrane to as little as 1-2 microns at these points. To test this hypothesis the relationship between the vascularity of the villi, as determined by the villous capillary volume fraction, and the mean thickness of the villous membrane was investigated. Data were taken from a recent study in which placental villi were biopsied from normal term placentae within 1 min of caesarean delivery and at 5, 10, 15 and 20 min thereafter. Since intuitively the membrane has both a maximum and a minimum thickness a sigmoid relationship was fitted to the data using least squares regression analysis. Estimates of arithmetic and harmonic mean thicknesses were then predicted from the capillary volume fraction for a large number of placentae using data from previous studies. These all employed similar stereological techniques but were performed over a number of years by several workers in this laboratory. The predicted values were tested against the measured values using paired 't' tests, but no significant differences (P greater than 0.05) were detected.(ABSTRACT TRUNCATED AT 250 WORDS)     

Allometric analysis of the morphometric pulmonary diffusing capacity in dogs

The lung volume, the morphometrically determined alveolar and capillary surface area, and the capillary volume of 27 dogs (weight 2.65–57 kg) all were linearly correlated with body weight. The thickness of the air-blood barrier increased only slightly with increasing body size. The structural diffusing capacity, containing these parameters, was used to estimate the gas exchange capabilities of the lung and was also found to scale in direct proportion to body size. This coincides with reports on physiologically estimated diffusing capacity but is obviously different from the interspecies slope for metabolism which scales to the 3/4 power of body weight.     

A morphometric study of the lungs of different sized bats: correlations between structure and function of the chiropteran lung.

1. The lungs of four species of bats, Phyllostomus hastatus (PH, mean body mass, 98 g), Pteropus lylei (PL, 456 g), Pteropus alecto (PA, 667 g), and Pteropus poliocephalus (PP, 928 g) were analysed by morphometric methods. These data increase fivefold the range of body masses for which bat lung data are available, and allow more representative allometric equations to be formulated for bats. 2. Lung volume ranged from 4.9 cm3 for PH to 39 cm3 for PP. The volume density of the lung parenchyma (i.e. the volume proportion of the parenchyma in the lung) ranged from 94% in PP to 89% in PH. Of the components of the parenchyma, the alveoli composed 89% and the blood capillaries about 5%. 3. The surface area of the alveoli exceeded that of the blood-gas (tissue) barrier and that of the capillary endothelium whereas the surface area of the red blood cells as well as that of the capillary endothelium was greater than that of the tissue barrier. PH had the thinnest tissue barrier (0.1204 microns) and PP had the thickest (0.3033 microns). 4. The body mass specific volume of the lung, that of the volume of pulmonary capillary blood, the surface area of the blood-gas (tissue) barrier, the diffusing capacity of the tissue barrier, and the total morphometric pulmonary diffusing capacity in PH all substantially exceeded the corresponding values of the pteropid species (i.e. PL, PA and PP). This conforms with the smaller body mass and hence higher unit mass oxygen consumption of PH, a feature reflected in the functionally superior gas exchange performance of its lungs. 5. Morphometrically, the lungs of different species of bats exhibit remarkable differences which cannot always be correlated with body mass, mode of flight and phylogeny. Conclusive explanations of these pulmonary structural disparities in different species of bats must await additional physiological and flight biomechanical studies. 6. While the slope, the scaling factor (b), of the allometric equation fitted to bat lung volume data (b = 0.82) exceeds the value for flight VO2max (b = 0.70), those for the surface area of the blood-gas (tissue) barrier (b = 0.74), the pulmonary capillary blood volume (b = 0.74), and the total morphometric lung diffusing capacity for oxygen (b = 0.69) all correspond closely to the VO2max value. 7. Allometric comparisons of the morphometric pulmonary parameters of bats, birds and non-flying mammals reveal that superiority of the bat lung over that of the non-flying mammal.(ABSTRACT TRUNCATED AT 400 WORDS)     

Oxygen transport during exercise in large mammals. II. Oxygen uptake by the pulmonary gas exchanger

Because the maximal rate of O2 consumption (VO2max) of the horse is 2.6 times larger than that of steers of equal size, we wondered whether their pulmonary gas exchanger is proportionately larger. Three Standardbred racehorses [body mass (Mb) = 447 kg] and three domestic steers (Mb = 474 kg) whose cardiovascular function at VO2max had been thoroughly studied (Jones et al. J. Appl. Physiol. 67: 862-870, 1989) were used to study their lungs by morphometry. The basic morphometric parameters were similar in both species. The nearly 2 times larger lung volumes of the horses caused the gas exchange surfaces and capillary blood volume to be 1.6 to 1.8 times larger. Morphometric pulmonary diffusing capacity was 2 times larger in the horse than in the steer; the 2.6-fold greater rate of O2 uptake thus required the alveolar-capillary PO2 difference to be 1.3 times larger in the horse than in the steer. Combining physiological and morphometric data, we calculated capillary transit time at VO2max to be 0.4-0.5 s. Bohr integration showed capillary blood to be equilibrated with alveolar air after 75 and 58% of transit time in horses and steers, respectively; horses maintain a smaller degree of redundancy in their pulmonary gas exchanger.     

Quantitative observations on the pulmonary anatomy of the domestic Muscovy duck (Cairina moschata)

The lungs of five female domestic Muscovy ducks, mean body weight 1.627 kg, total lung volume 48.07 cm³, were analysed by standard morphometric methods. Principal results obtained are: lung volume per unit body weight, 30.17 cm³/g; volume densities of exchange tissue relative to lung volume, 49.24%, blood capillaries relative to exchange tissue, 29.63%, tissue of the blood gas (tissue) barrier relative to exchange tissue, 5.88%; surface area of the blood-gas (tissue) barrier per unit body weight, 30.04 cm²/g; ratios of the surface area of the blood-gas (tissue) barrier per unit volume of the lung and per unit volume of exchange area, 979 cm²/cm³ and 200.06 mm²/mm³, respectively; harmonic and arithmetic mean thicknesses of the tissue barrier, 0.199 μm and 0.303 μm, respectively. The anatomical diffusing capacity of the tissue barrier for oxygen ( DtO₂ ) and the total pulmonary diffusing capacity ( DLO₂ ), 49.58 ml O₂/min/mmHg/kg and 4.55 ml O₂/min/mm Hg/kg, respectively. The lungs of the domestic Muscovy duck appear to be about as well adapted anatomically for gas exchange as the lungs of wild anatid species, and there is no clear evidence that domestication has been associated with any deterioration in the anatomical capacity for oxygen uptake. The weight-specific anatomical diffusing capacity of the lung for oxygen ( DLO₂/W ) was about 3.6 times greater than the weight-specific physiological value, a factor which falls within the expected range.     

Red cell distribution and the recruitment of pulmonary diffusing capacity.

The distribution of red blood cells in alveolar capillaries is typically nonuniform, as shown by intravital microscopy and in alveolar tissue fixed in situ. To determine the effects of red cell distribution on pulmonary diffusive gas transport, we computed the uptake of CO across a two-dimensional geometric capillary model containing a variable number of red blood cells. Red blood cells are spaced uniformly, randomly, or clustered without overlap within the capillary. Total CO diffusing capacity (DLCO) and membrane diffusing capacity (DmCO) are calculated by a finite-element method. Results show that distribution of red blood cells at a fixed hematocrit greatly affects capillary CO uptake. At any given average capillary red cell density, the uniform distribution of red blood cells yields the highest DmCO and DLCO, whereas the clustered distribution yields the lowest values. Random nonuniform distribution of red blood cells within a single capillary segment reduces diffusive CO uptake by up to 30%. Nonuniform distribution of red blood cells among separate capillary segments can reduce diffusive CO uptake by >50%. This analysis demonstrates that pulmonary microvascular recruitment for gas exchange does not depend solely on the number of patent capillaries or the hematocrit; simple redistribution of red blood cells within capillaries can potentially account for 50% of the observed physiological recruitment of DLCO from rest to exercise.     

Morphometric analysis of the tracheal walls of the harvestmen Nemastoma lugubre (Arachnida, Opiliones, Nemastomatidae)

The tracheal system of harvestmen consists of two stem tracheae, which give rise to higher order tracheae that supply the extremities and internal organs. In this study, we used stereological morphometric methods to investigate diffusing capacities of the walls ('lateral diffusing capacity') of the tracheae of adult males and females of Nemastoma lugubre. Diffusing barriers of the tracheal walls tend to be thinnest (0.17-0.19 microm) for the smallest tracheae (inner diameter 0.5-2 microm). In other tracheal classes the diffusing barriers increase with increasing diameters. Calculation of the mass-specific diffusing capacity for oxygen (D(O2)) of the walls of all higher order tracheae revealed 10.57 microl min(-1)g(-1)kPa(-1) for the females (mean body mass 3.8 mg) and 25.23 microl min(-1)g(-1)kPa(-1) for the males (mean body mass 1.4 mg). In both animal groups, the main D(O2) (58-67%) lies in the tracheae with an inner diameter of 0.5-2 microm, but also tracheae up to an inner diameter of 20 microm allow gas exchange via the tracheal walls. Stem tracheae are of no importance for lateral diffusion. Our results are consistent with the hypothesis that the functional morphology of the tracheal system of harvestmen represents an 'intermediate state' between the tracheal system of insects in which gas exchange is focused on the distal portions and that of spiders, in which the walls of all tracheae serve in gas exchange.     

Morphology and morphometry of the normal lung of the adult vervet monkey (Cercopithecus aethiops)

The lungs of four adult specimens of the vervet monkey (Cercopithecus aethiops) have been examined by transmission and scanning electron microscopy. A morphometric evaluation of the structural components directly involved in gas exchange has been carried out and the data have been modelled to estimate the anatomical diffusing capacity of the lung. The upper air-conducting airways of the lung were lined by an epithelium characterized by ciliated cells among which were dispersed goblet cells. The alveolar surface was lined by squamous type I pneumocytes and cuboidal type II granular pneumocytes. The blood-gas (tissue) barrier consisted of an epithelial cell, a common basal lamina, and an endothelial cell in the thin parts of the interalveolar septum. In the thicker parts of the septum, an interstitial space interposed between the basal laminae of the epithelial and endothelial cells contained supportive elements such as collagen, elastic tissue, and fibrocytes. The alveoli, the blood capillaries, and septal tissue composed 73%, 16%, and 11%, respectively, of the parenchyma. The harmonic and arithmetic mean thicknesses of the blood-gas (tissue) barrier were 0.311 micron and 1.048 microns; the surface area of the blood-gas (tissue) barrier per unit body weight was 50 cm2g-1, and the surface density was 117 mm2.mm3-1. The weight-specific total morphometric diffusing capacity was 0.11 mlO2 (sec.mbar.kg)-1. In comparison, the pulmonary morphometric characteristics of vervet monkey lung were superior to those of the other primates (Macaca irus, M. mulatta, and Homo sapiens) for which equivalent data are available. The gas-exchange potential of the lungs of the nonhuman primates as revealed by morphometric studies surpasses that of man, a feature that can be attributed to the relatively less energetic human lifestyle.     

Microvascular Regulation of Cutaneous Gas Exchange in Amphibians

SYNOPSIS. Gas exchange across amphibian skin is regulated bythe cutaneous microcirculation. Parameters involved in regulatinggas exchange are capillary density, radius and blood flow. Changesin capillary density and radius should affect gas exchange byaltering the cutaneous diffusing capacity (D₂) while changesin capillary blood flow affect the perfusive conductance ofthe skin. A simple model predicts that the effect of capillary densitychanges on D₂ will become more pronounced as capillary densityand epidermal thickness decrease. Changes in capillary radiusshould have only a minor effect on D₂ Previous analyses havesuggested that cutaneous gas exchange is not significantly affectedby the perfusive conductance of the skin. Consequently, it hasbeen thought that changes in total capillary blood flow havelittle impact on cutaneous gas exchange. Earlier analyses, however,may have underestimated the importance of perfusive conductancein amphibian skin, primarily because functional heterogeneitiesin the microcirculation were not considered. The density of perfused capillaries is regulated in the footweb of Rana esculenta by environmental Po₂ and PCO₂, and alsoby lung ventilation. In Rana catesbeiana, capillary densityin the web decreases during air exposure. Chronic exposure toenvironmental hypoxia increases total capillary density in bullfrogtadpole skin. In Rana pipiens, regulation of cutaneous gas exchangeby environmental and pulmonary O₂ probably involves changesin total capillary blood flow.     

Evaluation of lung diffusing capacity by physiological and morphometric techniques

Determinations of pulmonary diffusing capacity for CO (DLCO) by physiological and morphometric techniques have resulted in substantially different values for both DLCO and its major components. To evaluate the differences in these methods of measurement of DLCO, measurements were made under controlled conditions on isolated perfused dog lungs. Multiple gas-rebreathing techniques were used to measure DLCO, the membrane component of the diffusing capacity for CO (DmCO), and pulmonary capillary blood volume (Vc) in both anesthetized dogs and after isolation and perfusion of their lungs. The isolated perfused lungs were than perfusion fixed for morphometric analysis of the components of DLCO. The values obtained morphometrically for Vc were similar to those measured by physiological techniques. Perfusion fixation did not substantially alter the morphometric estimate of DmCO when compared with previous values obtained on inflation fixed lungs. However, the morphometric estimate of DmCO was over 10 times higher than that estimated physiologically. Analysis of the potential errors in the techniques suggests that the correct value for DmCO is substantially higher than that commonly estimated by use of physiological techniques and that the explanation for the difference is due to a number of factors that can influence the binding of CO to hemoglobin under in vivo conditions. The net effect of these factors can be represented by an unknown in each component of the Roughton-Forster relationship so that 1/DL = 1/(U1.Dm) + 1/(U2.theta Vc), where theta is the binding rate for CO to hemoglobin. Because the magnitudes of the unknown terms (U1 and U2) in the Roughton-Forster relationship are likely to be large, this relationship cannot be reliably used to determine Dm and Vc.     

Three-dimensional,unsteady simulation of alveolar respiration

A novel macroscopic gas transport model, derived from fundamental engineering principles, is used to simulate the three-dimensional, unsteady respiration process within the alveolar region of the lungs. The simulations, mimicking the single-breath technique for measuring the lung diffusing capacity for carbon-monoxide (CO), allow the prediction of the red blood cell (RBC) distribution effects on the lung diffusing capacity. Results, obtained through numerical simulations, unveil a strong relationship between the type of distribution and the lung diffusing capacity. Several RBC distributions are considered, namely: normal (random), uniform, center-cluster, and corner-cluster red cell distributions. A nondimensional correlation is obtained in terms of a geometric parameter characterizing the RBC distribution, and presented as a useful tool for predicting the RBC distribution effect on the lung diffusing capacity. The effect of red cell movement is not considered in the present study because CO does not equilibrate with capillary blood within the time spent by blood in the capillary. Hence, blood flow effect on CO diffusion is expected to be only marginal.     

Stereological determination of tracheal volume and diffusing capacity of the tracheal walls in the stick insect Carausius morosus (Phasmatodea, Lonchodidae)

First instars of Carausius morosus provide a good model for morphometric evaluation of the diffusing capacity between the tracheal system and hemolymph: air sacs are lacking, tracheoles do not penetrate the organs and muscles, and entire animals can be evaluated electron microscopically without subsampling. The tracheal volume makes up 1.3% of the volume of the whole insect excluding appendages. We calculated the lateral diffusing capacity for oxygen and carbon dioxide for five classes of tracheae according to their diameters, from 0.2 microm to 35 microm. The harmonic mean thickness of the tracheal epithelium is lowest in smallest tracheae and increases with increasing tracheal diameter. Although the smallest tracheae make up 70% (O2) and 60% (CO2) of the total diffusing capacity, the proximal four classes may also be significant in diffusion of oxygen and particularly of carbon dioxide. The suppression of the development of respiratory pigments in the evolution of terrestrial insects may have increased the relative importance of small tracheal elements for local oxygen consumption.     

Pulmonary gas transfer related to markers of angiogenesis during the menstrual cycle.

Gas transfer in the female lung varies over the menstrual cycle in parallel with the cyclic angiogenesis that occurs in the uterine endometrium. Given that vessels form and regress in the uterus under the control of hormones, angiogenic factors, and proangiogenic circulating bone marrow-derived progenitor cells, we tested the possibility that variation in pulmonary gas transfer over the menstrual cycle is related to a systemic cyclic proangiogenic state that influences lung vascularity. Women were evaluated over the menstrual cycle with weekly measures of lung diffusing capacity and its components, the pulmonary vascular capillary bed and membrane diffusing capacity, and their relation to circulating CD34(+)CD133(+) progenitor cells, hemoglobin, factors affecting hemoglobin binding affinity, and proangiogenic factors. Lung diffusing capacity varied over the menstrual cycle, reaching a nadir during the follicular phase following menses. The decline in lung diffusing capacity was accounted for by approximately 25% decrease in pulmonary capillary blood volume. In parallel, circulating CD34(+)CD133(+) progenitor cells decreased by approximately 24% and were directly related to angiogenic factors and to lung diffusing capacity and pulmonary capillary blood volume. The finding of a greater number of lung microvessels in ovariectomized female mice receiving estrogen compared with placebo verified that pulmonary vascularity is influenced by hormonal changes. These findings suggest that angiogenesis in the lungs may participate in the cyclic changes in gas transfer that occur over the menstrual cycle.     

Estimation of oxygen-diffusing capacity in the gills of different sizes of a tilapia, Oreochromis niloticus

Measurements on gills of features that affect gas exchange have been studied in relation to body weight in specimens (0.0112–812.3 g) of a tilapia, Oreochromis niloticus . The data were analysed with respect to body weight by means of logarithmic transformations (log Y = log a+b log W ). The slopes ( b ) of the log/log regression lines for the gill area, harmonic mean diffusion distance and oxygen diffusing capacity were 0.777, 0.077 and 0.700, respectively. The gill respiratory area of O. niloticus (Trewavas) increases as the fish develops because the number and bilateral area of secondary lamellae increase. The scaling value for oxygen-diffusing capacity is less than the value for gill area because of the slight increase in harmonic mean diffusion distance with development.     

Estimating body size of fossil sirenians

Estimates of fossil sirenian body size are important for understanding niche partitioning among possibly sympatric species. Because of the paucity of complete fossil skeletons, we explored the utility of three morphometric predictors of body size: (condylobasal skull length [BSL]; occipital condyle width [OCW]; and foramen magnum width [FMW]) in extant sirenians—Florida manatees (Trichechus manatus latirostris) and dugongs (Dugong dugon)—and then applied these to obtain estimates of body size in extinct sirenian taxa. Condylobasal length of the skull is a more accurate predictor of body size in extant Florida manatees and dugongs than are width of the occipital condyles or width of the foramen magnum. Body length (BL) is predicted more accurately than is body weight (BW) for all three morphometric predictors. For our sample of fossil sirenians, BSL, OCW, and FMW were used to generate predicted BLs and BWs. Preliminary assessments of fossil sirenian faunas from Florida and India suggest that body mass could have been one of several possible important morphological parameters accounting for feeding niche separation.     

Pulmonary Hypertension in Patients with Idiopathic Pulmonary Fibrosis – The Predictive Value of Exercise Capacity and Gas Exchange Efficiency

Exercise capacity and survival of patients with IPF is potentially impaired by pulmonary hypertension. This study aims to investigate diagnostic and prognostic properties of gas exchange during exercise and lung function in IPF patients with or without pulmonary hypertension.In a multicentre setting, patients with IPF underwent right heart catheterization, cardiopulmonary exercise and lung function testing during their initial evaluation. Mortality follow up was evaluated.Seventy-three of 135 patients [82 males; median age of 64 (56; 72 years)] with IPF had pulmonary hypertension as assessed by right heart catheterization [median mean pulmonary arterial pressure 34 (27; 43) mmHg]. The presence of pulmonary hypertension was best predicted by gas exchange efficiency for carbon dioxide (cut off ≥152% predicted; area under the curve 0.94) and peak oxygen uptake (≤56% predicted; 0.83), followed by diffusing capacity. Resting lung volumes did not predict pulmonary hypertension. Survival was best predicted by the presence of pulmonary hypertension, followed by peak oxygen uptake [HR 0.96 (0.93; 0.98)].Pulmonary hypertension in IPF patients is best predicted by gas exchange efficiency during exercise and peak oxygen uptake. In addition to invasively measured pulmonary arterial pressure, oxygen uptake at peak exercise predicts survival in this patient population.     

Morphometric estimation of oxygen diffusing capacity for the air-sac in the catfish Heteropneustes fossilis

A detailed morphometric study has been made of the air-sacs of this air-breathing catfish using whole mounts, light and electron microscopy, of six specimens, body weight 40±2 g. Measurements of surface areas of the gas exchange and non-respiratory surfaces have taken into account foldings of the surface at macro and ultramicroscopic levels. Area of the gas exchange surface was estimated as 23.915cm² (=0.598cm²/g) which is 67%of the total surface area of the two air-sacs. Significant differences were found in some morphometric parameters which were related to the three antero-posterior regions into which air-sacs were divided. Harmonic mean thickness of the tissue component of the air/blood barrier was estimated for the whole air-sac as 0.342 μ m. These and other measurements enabled the diffusing capacity for the air-sacs to be calculated as 0.0638 m1O₂/min/mmHg/kg.
These results show that Heteropneustes has an air-breathing organ which is superior to that of Amphipnous cuchia , similar to that of Lepidosiren , but less well developed than that of Protopterus . In addition, Heteropneustes is well adapted to obtain oxygen directly from water by means of its gills and skin as indicated by both morphometric and physiological measurements which also correlate with its life in ponds and streams which are Iiable to dry up.