Johannes Piiper

Oncepts and basic quantities in gas exchange physiology

Abstract 1. 1) The amount of a gas species is dimensionally considered not as a volume, but as a quantity of substance M, expressed in moles, but also, less appropriately, in volumes stpd. The transfer rate of a gas species (), with dimension (quantity of substance)·(time)−1, may thereby be clearly distinguished from the volume flow rate () which has the dimension (volume).(time)−1. 2. 2) The concentration (C), defined as quantity of substance per volume, is used for all media (blood, water and gas). For the gas phase, C is proportional to the fractional concentration, F, and is dependent on temperature, pressure and water vapor pressure. 3. 3) For the increment of concentration in liquid or gas phase of a gas species per increment of its partial pressure, solΔC ΔP , the term “capacitance coefficient” is proposed. In respect to gas transfer, it is a measure of the carrying capacity of a medium for a given gas species. It is usefully applied not only to water and to blood (slope of CO2 and O2 dissociation curves), but also to the gas phase, for which it is identical for all ideal gases at a given temperature. Some basic equations of gas transfer by blood, air and water convection and by diffusion have been rewritten according to these concepts.

Model for capillary-alveolar equilibration with special reference to O2 uptake in hypoxia

Abstract This paper presents a simple model for the study of diffusion limitation effects in capillary-alveolar gas transfer. The decisive parameter to determine the extent of diffusion limitation is shown to be the dimensionless ratio D/(Qβ) (D, diffusing capacity, Q, blood flow; β, capacitance coefficient or effective solubility in blood). The model predicts a considerable extent of diffusion limitation for pulmonary O 2 uptake in hypoxia, which sets an upper limit to the level of exercise at high altitude.

Gas transport efficacy of gills, lungs and skin: Theory and experimental data

The general functional principles encountered in respiratory organs of vertebrates are investigated. Generally three steps are involved in external gas exchange in vertebrates: (1) convective transport by flow of external respiratory medium, air or water (=ventilation); (2) transfer of gas between external respiratory medium and blood by diffusion (=medium/blood transfer); (3) convective transport by blood flow (=perfusion). According to the arrangement of external medium flow relative to capillary blood flow four construction principles may be distinguished: (a) counter-current system (fish gills), (b) cross-current system (avian lungs), (c) ventilated pool system (mammalian lungs), and (d) infinite pool system (amphibian skin). The gas transfer performance of these systems is analyzed in terms of conductances, relative partial pressure differences and limitations attributable to ventilation. to medium/blood transfer and to perfusion. The theory is applied to analysis of gas exchange data obtained in an elasmobranch fish, domestic fowl, dog and a lungless salamander. The analysis shows that, despite distinct differences in maximum efficiencies of these systems, the differences in efficiency values actually attained are much less pronounced, and may be even less marked when taking functional inhomogeneities into account which are neglected in this study.

Analysis of gas exchange in the avian lung: theory and experiments in the domestic fowl.

Abstract Gas exchange in the parabronchial lung of birds is analysed in theory using a model suggested by Zeuthen (1942), consisting of a continuously ventilated tube, representing the parabronchi, surrounded by blood-perfused capillaries. Equations describing how partial pressures of CO2 and O2 in pulmonary gas and blood depend upon ventilation, perfusion and diffusing capacity are derived. The theory was applied to measurements of gas exchange in unanesthetized White Leghorn hens, of 1.6 kg average weight. In order to confine the pulmonary gas exchange to a PCO2 and PO2 range in which the blood dissociation curves were relatively straight, a combination of inspiratory hypoxia and hypercapnia was used ( F i CO 2 = 0.03 , F i O 2 = 0.13 ). Arterial PCO2 was lower and arterial PO2 was higher than the corresponding values in end-expired gas. This finding is explainable by the theory. From the experimental data the pulmonary diffusing capacity for O2 (DLO2) was estimated at 1.1 to 1.5 ml·min−1·mm Hg−1. As the calculations were based on a homogeneous lung model, these values represent a lower limit for dLO2.

Analysis of chorioallantoic gas exchange in the chick embryo

To analyze the gas exchange mechanisms in the chorioallantois, PO2 and PCO2 were measured in air cell gas, in the allantoic artery and in the allantoic vein in chicken embryos on the 16th day of incubation. In addition, the O2 dissociation curve of blood, and O2 uptake and CO2 output of the embryo were determined. From O2 measurements performed in hypoxia (FIO2=0.14), normoxia and hyperoxia (FIO2=0.67), it was concluded that there was a sizable functional arterio-venous shunt amounting to 10-15% of the total chorioallantoic blood flow and that the diffusing capacity of the air cell-blood barrier for O2 was about 7 microliter . min-1. Torr-1. The CO2 measurements are in agreement with the model. In hypoxia, the air cell-blood transfer of O2 was markedly diffusion limited. The diffusion limitation effect was slight in normoxia, and not detectable in hyperoxia. At all oxygenation levels the effect of the shunt on blood arterialization was marked, particularly so in hyperoxia where the air cell-arterialized blood PO2 difference averaged 180 Torr.

Cross-current gas exchange in avian lungs: Effects of reversed parabronchial air flow in ducks☆

Abstract Experiments have been performed in ducks in order to determine which of both previously proposed physical models, the counter-current or the cross-current system, is best suited for analysis of gas exchange in parabronchial lungs of birds. Mesobronchi of both sides of the body were blocked between the origins of ventrobronchi and dorsobronchi using inflatable catheters, and both postthoracic air sacs were opened by introduction of large bore tubing through the body wall into their lumen. In this preparation a continuous parabronchial air flow could be achieved in either of both directions, from ventrobronchi to dorsobronchi by blowing air into the trachea, or in the opposite direction, from dorsobronchi to ventrobronchi, by blowing air from the air sacs into the bronchial system. During steady state, the pulmonary gas flow and PCO2 and PO2 in air as well as in arterial and mixed venous blood were measured. The results showed no dependence of partial pressures on the direction of parabronchial air flow. In particular, arterial PCO2 was found to be lower than expired (=end-parabronchial) PCO2 with both directions of parabronchial air flow. These findings cannot be easily explained on the basis of a counter-current gas exchange system, which has been proposed by Schmidt-Nielsen (1971), but are in good agreement with the assumption of a cross-current gas exchange system operative in the avian lung.

Gas exchange in the domestic fowl during spontaneous breathing and artificial ventilation

In unanesthetized White Leghorn hens, mean weight 1.6 kg, gas exchange was studied during spontaneous breathing and artificial ventilation delivered by a Starling pump. The trachea was cannulated and connected to an open spirometric system. Arterial and mixed venous blood samples were obtained by catheters introduced into a brachial artery and into the right ventricle, respectively. Air sac gas was sampled. During spontaneous breathing the following mean values were measured: total ventilation, 760 ml BTPS·min−1 respiratory frequency, 23 min−1; O2 uptake 24 ml STPD·min−1; arterial PO2, 87 mm Hg; arterial PCO2, 29 mm Hg; cardiac output (Pick Principle), 430 ml·min−1. When the unanesthetized hens were relaxed with succinylcholine and artificially ventilated, using the same tidal volume and frequency as observed during spontaneous respiration, the same values for O2 uptake and for CO2 and O2 partial pressures in arterial blood were measured, indicating unchanged gas exchange efficiency of the respiratory system. However, the gas composition of the air sacs in respect to expired CO2 and O2 was changed, suggesting alterations in the pattern of gas flow through the respiratory system.

Direct measurement of the pathway of respired gas in duck lungs

Abstract For measurement of gas flow, a flowmeter consisting of a heated wire anemometer combined with a thermocouple was implanted into a dorsobronchus of the lungs in unanesthetized ducks. The direction of gas flow recorded in the dorsobronchus during spontaneous breathing and during artificial ventilation was from the mesobronchus to the parabronchi both in inspiration and expiration. This result is in accordance with the unidirectional flow hypothesis propounded by Bethe and by Hazelhoff, and is incompatible with the alternating respiratory flow hypothesis of Zeuthen.

Respiration and circulation during swimming activity in the dogfish Scyliorhinus stellaris.

A number of respiratory and circulatory parameters was measured in the Larger Spotted Dogfish Scyliorhinus stellaris before, during and after periods of spontaneous swimming. During swimming the gill ventilation was increased, mainly due to increased ventilatory stroke volume, the respiratory frequency showing a small rise only, and the cardiac output was increased at only slightly elevated cardiac frequency. Coordination between cardiac, ventilatory or locomotor (tail-beat) rhythms was not observed. The decrease in utilization of inspired water O2 during swimming was attributable to diffusion limitation in branchial O2 transfer. A considerable fraction of the total net amount of O2 required for swimming was taken up during the recovery phase. From the observations that (1) the decrease in gill ventilatory flow after cessation of swimming revealed a very rapid component (followed by a slow component), and that (2) changes in swimming speed were reflected by immediate changes in momentary ventilatory flow, it is concluded that the increased ventilation during swimming was in part mechanical-passive and/or due to nervous coupling between respiratory and locomotor centers.

Mechanisms of unidirectional flow in parabronchi of avian lungs: Measurements in duck lung preparations☆

Abstract To investigate the pathway of respired air in birds, lungs of ducks, fixed by means of glutaraldehyde, were separated from the air sacs and from all other organs. When this isolated lung was ventilated by applying pressure or suction to the main bronchus, the dorsobronchial flow was shown to be unidirectional in both respiratory phases, leading from the mesobronchus through the dorsobronchi to the parabronchi, as has previously been shown for the living duck. Flow direction could also be measured in other parts of the bronchial tree including ventrobronchi where the measurements were not in agreement with the hypothesis of Hazelhoff (1943). To analyze the mechanisms of this rectification of flow, the aerodynamical properties of some structures of the bronchial tree, especially the openings of the secondary bronchi into the mesobronchus, were investigated. These openings offered a direction-dependent resistance to air flow, presumably due to detachment of flow at sites of sharp edges. These results lend support to the hypothesis that the particular pathway of respired air in duck lungs is effected by “aerodynamical valving”.