Effect of venous (gut) CO2 loading on intrapulmonary gas fractions and ventilation in the tegu lizard

Summary Studies were conducted to determine regional pulmonary gas concentrations in the tegu lizard lung. Additionally, changes in pulmonary gas concentrations and ventilatory patterns caused by elevating venous levels of CO₂ by gut infusion were measured.It was found that significant stratification of lung gases was present in the tegu and that dynamic fluctuations of CO₂ concentration varied throughout the length of the lung. Mean was greater and less in the posterior regions of the lung. In the posterior regions gas concentrations remained nearly constant, whereas in the anterior regions large swings were observed with each breath. In the most anterior sections of the lung near the bronchi, CO₂ and O₂ concentrations approached atmospheric levels during inspiration and posterior lung levels during expiration.During gut loading of CO₂, the rate of rise of CO₂ during the breathing pause increased. The mean level of CO₂ also increased. Breathing rate and tidal volume increased to produce a doubling ofV _E.These results indicate that the method of introduction of CO₂ into the tegu respiratory system determines the ventilatory response. If the CO₂ is introduced into the venous blood a dramatic increase in ventilation is observed. If the CO₂ is introduced into the inspired air a significant decrease in ventilation is produced. The changes in pulmonary CO₂ environment caused by inspiratory CO₂ loading are different from those caused by venous CO₂ loading. We hypothesize that the differences in pulmonary CO₂ environment caused by either inspiratory CO₂ loading or fluctuations in venous CO₂ concentration act differently on the IPC. The differing response of the IPC to the two methods of CO₂ loading is the cause of the opposite ventilatory response seen during either venous or inspiratory loading.Abbreviations IPC intrapulmonary chemoreceptors - UAC upper airway chemoreceptors - V _T inspiratory tidal volume - CO₂ gas fraction - O₂ gas fraction - V _E minute ventilation     

Pre-and post-branchial blood respiratory status during acute hypercapnia or hypoxia in rainbow trout,Oncorhynchus mykiss

Simultaneous venous (pre-branchial) and arterial (post-branchial) extracorporeal blood circulations were utilized to monitor continuously the rapid and progressive effects of acute environmental hypercapnia (water partial pressure of CO₂ 4.8±0.2 torr) or hypoxia (water partial pressure of O₂ 25±2 torr) on oxygen and carbon dioxide tensions and pH in the blood of rainbow trout (Oncorhynchus mykiss). During hypercapnia, the CO₂ tension in the arterial blood increased from 1.7±0.1 to 6.2±0.2 torr within 20 min and this was associated with a decrease of arterial extracellular pH from 7.95±0.03 to 7.38±0.03; the acid-base status of the mixed venous blood changed in a similar fashion. The decrease in blood pH in vivo was greater than in blood equilibrated in vitro with a similar CO₂ tension indicating a significant metabolic component to the acidosis in vivo. Under normocapnic conditions, venous blood CO₂ tension was slightly higher than arterial blood CO₂ tension difference was abolished or reversed during the initial 25 min of hypercapnia indicating that CO₂ was absorbed from the water during this period. Arterial O₂ tension remained constant during hypercapnia; however, venous blood O₂ tension decreased significantly (from 22.0±2.6 to 9.0±1.0 torr) during the initial 10 min. Hypercapnia elicited the release of catecholamines (adrenaline and noradrenaline) into the blood. The adrenaline concentration increased from 6±3 to 418±141 nmol · l^-1 within 25 min; noradrenaline concentration increased from 3±0.5 to 50±21 nmol · l^-1 within 15 min. During hypoxia arterial blood O₂ tension declined progressively from 108.4±9.9 to 12.8±1.7 torr within 30 min. Venous blood O₂ tension initially was stable but then decreased abruptly as catecholamines were released into the circulation. The release of catecholamines occurred concomitantly with a sudden metabolic acidosis in both blood compartments and a rise in CO₂ tension in the mixed venous blood only.Abbreviations CCO₂ plasmatotal carbondioxide - CtO₂ blood oxygen content - PO₂ partial pressure of oxygen - PCO₂ partial pressure of carbon dioxide - PaO₂ arterial bloodPO₂ - PaCO₂ arterial bloodPCO₂ - PvCO₂ venous bloodPCO₂ - PwO₂ waterPO₂ - PwCO₂ waterPCO₂ - Hb haemoglobin - SHbO₂ haemoglobin oxygen saturation - HPLC high-performance liquid chromatography - rbc red blood cell(s) - Hct haematocrit     

A Mathematical Model of the Controlled Plant of the Réspiratory System

Ability to predict the dynamic response of oxygen, carbon dioxide tensions, and pH in blood and tissues to abrupt changes in ventilation is important in the mathematical modeling of the respiratory system. In this study, the controlled plant (the amount and distribution of O₂ and CO₂) of the respiratory system is modeled. Although the body tissues are divided into a finite number of “compartments” (three tissue groups), in contrast to earlier models, the blood and tissue gas tensions within each compartment are considered to be continuously distributed in time and in one spatial coordinate. The mass conservation equations for oxygen and carbon dioxide involved in the blood-tissue gas exchange are described by a set of partial differential equations which take into account convection of O₂ and CO₂ caused by the flow of blood as well as diffusion due to local tension gradients. Nonlinear algebraic equations for the dissociation curves, which take into account the Haldane and Bohr effects in blood, are used to obtain the relationships between concentrations and partial pressures. Time-variable delays caused by the arterial and venous transport of the respiratory gases are also included. The model so constructed successfully reproduced actual O₂ and CO₂ tensions in arterial blood, and in muscle venous and mixed venous blood when ventilation was abruptly changed.     

Inspiratory and expiratory muscle perfusion in maximally exercised ponies

The present study was carried out on seven healthy ponies to examine the extent of blood flow in various inspiratory and expiratory muscles at rest and during maximal exertion as well as to determine the proportion of cardiac output needed to perfuse respiratory muscles during these conditions. Tissue blood flow was studied with 15 micron-diameter radionuclide-labeled microspheres injected into the left ventricle during steady conditions. The inspiratory and expiratory muscles comprised 2.41 and 3.05% of body weight, respectively, and received 6.17 and 3.75% of the cardiac output at rest. With maximal exercise, heart rate (from 55 +/- 3 to 218 +/- 4 beats/min), mean aortic pressure (from 125 +/- 5 to 170 +/- 6 mmHg), and cardiac output (from 96 +/- 11 to 730 +/- 78 ml.min-1.kg-1) increased markedly. During exercise blood flow increased significantly in all respiratory muscles (P less than 0.0001) as vascular resistance decreased precipitously. Marked heterogeneity of perfusion existed among various inspiratory as well as expiratory muscles during exercise. Among the inspiratory muscles, the highest perfusion occurred in the diaphragm followed by serratus ventralis, and among the expiratory muscles, the highest perfusion occurred in the internal oblique abdominis and the transverse thoracis (triangularis sterni). Collectively, the inspiratory (8.44%) and expiratory (6.35%) muscle blood flow comprised 14.8 +/- 1.2% of the cardiac output during maximal exercise, a significant increase above resting value, whereas renal fraction of cardiac output decreased from 21% (at rest) to 0.72%.     

Mechanical constraints on exercise hyperpnea in endurance athletes.

We determined how close highly trained athletes [n = 8; maximal oxygen consumption (VO2max) = 73 +/- 1 ml.kg-1.min-1] came to their mechanical limits for generating expiratory airflow and inspiratory pleural pressure during maximal short-term exercise. Mechanical limits to expiratory flow were assessed at rest by measuring, over a range of lung volumes, the pleural pressures beyond which no further increases in flow rate are observed (Pmaxe). The capacity to generate inspiratory pressure (Pcapi) was also measured at rest over a range of lung volumes and flow rates. During progressive exercise, tidal pleural pressure-volume loops were measured and plotted relative to Pmaxe and Pcapi at the measured end-expiratory lung volume. During maximal exercise, expiratory flow limitation was reached over 27-76% of tidal volume, peak tidal inspiratory pressure reached an average of 89% of Pcapi, and end-inspiratory lung volume averaged 86% of total lung capacity. Mechanical limits to ventilation (VE) were generally reached coincident with the achievement of VO2max; the greater the ventilatory response, the greater was the degree of mechanical limitation. Mean arterial blood gases measured during maximal exercise showed a moderate hyperventilation (arterial PCO2 = 35.8 Torr, alveolar PO2 = 110 Torr), a widened alveolar-to-arterial gas pressure difference (32 Torr), and variable degrees of hypoxemia (arterial PO2 = 78 Torr, range 65-83 Torr). Increasing the stimulus to breathe during maximal exercise by inducing either hypercapnia (end-tidal PCO2 = 65 Torr) or hypoxemia (saturation = 75%) failed to increase VE, inspiratory pressure, or expiratory pressure. We conclude that during maximal exercise, highly trained individuals often reach the mechanical limits of the lung and respiratory muscle for producing alveolar ventilation. This level of ventilation is achieved at a considerable metabolic cost but with a mechanically optimal pattern of breathing and respiratory muscle recruitment and without sacrifice of a significant alveolar hyperventilation.     

A comparative meta-analysis of maximal aerobic metabolism of vertebrates: implications for respiratory and cardiovascular limits to gas exchange

Maximal aerobic metabolic rates (MMR) in vertebrates are supported by increased conductive and diffusive fluxes of O₂ from the environment to the mitochondria necessitating concomitant increases in CO₂ efflux. A question that has received much attention has been which step, respiratory or cardiovascular, provides the principal rate limitation to gas flux at MMR? Limitation analyses have principally focused on O₂ fluxes, though the excess capacity of the lung for O₂ ventilation and diffusion remains unexplained except as a safety factor. Analyses of MMR normally rely upon allometry and temperature to define these factors, but cannot account for much of the variation and often have narrow phylogenetic breadth. The unique aspect of our comparative approach was to use an interclass meta-analysis to examine cardio-respiratory variables during the increase from resting metabolic rate to MMR among vertebrates from fish to mammals, independent of allometry and phylogeny. Common patterns at MMR indicate universal principles governing O₂ and CO₂ transport in vertebrate cardiovascular and respiratory systems, despite the varied modes of activities (swimming, running, flying), different cardio-respiratory architecture, and vastly different rates of metabolism (endothermy vs. ectothermy). Our meta-analysis supports previous studies indicating a cardiovascular limit to maximal O₂ transport and also implicates a respiratory system limit to maximal CO₂ efflux, especially in ectotherms. Thus, natural selection would operate on the respiratory system to enhance maximal CO₂ excretion and the cardiovascular system to enhance maximal O₂ uptake. This provides a possible evolutionary explanation for the conundrum of why the respiratory system appears functionally over-designed from an O₂ perspective, a unique insight from previous work focused solely on O₂ fluxes. The results suggest a common gas transport blueprint, or Bauplan, in the vertebrate clade.     

d-serine regulation of the timing and architecture of the inspiratory burst in neonatal mice

d-serine, released from mouse medullary astrocytes in response to increased CO₂ levels, boosts the respiratory frequency to adapt breathing to physiological demands. We analyzed in mouse neonates, the influence of d-serine upon inspiratory/expiratory durations and the architecture of the inspiratory burst, assessed by pwelch's power spectrum density (PSD) and continuous wavelet transform (CWT) analyses. Suction electrode recordings were performed in slices from the ventral respiratory column (VRC), site of generation of the respiratory rhythm, and in brainstem-spinal cord (en bloc) preparations, from the C5 ventral roots, containing phrenic fibers that in vivo innervate and drive the diaphragm, the main inspiratory muscle.In en bloc and slice preparations, d-serine (100 μM) reduced the expiratory, but not the inspiratory duration, and increased the frequency and the regularity of the respiratory rhythm. In en bloc preparations, d-serine (100 μM) also increased slightly the amplitude of the integrated inspiratory burst and the area under the curve of the integrated inspiratory burst, suggesting a change in the recruitment or the firing pattern of neurons within the burst. Time-frequency analyses revealed that d-serine changed the burst architecture of phrenic roots, widening their frequency spectrum and shifting the position of the core of firing frequencies towards the onset of the inspiratory burst. At the VRC, no clear d-serine induced changes in the frequency-time domain could be established. Our results show that d-serine not only regulates the timing of the respiratory cycle, but also the recruitment strategy of phrenic motoneurons within the inspiratory burst.     

Effects of augmented respiratory muscle pressure production on locomotor limb venous return during calf contraction exercise.

We determined effects of augmented inspiratory and expiratory intrathoracic pressure or abdominal pressure (Pab) excursions on within-breath changes in steady-state femoral venous blood flow (Qfv) and net Qfv during tightly controlled (total breath time = 4 s, duty cycle = 0.5) accessory muscle/"rib cage" (DeltaPab <2 cmH2O) or diaphragmatic (DeltaPab >5 cmH2O) breathing. Selectively augmenting inspiratory intrathoracic pressure excursion during rib cage breathing augmented inspiratory facilitation of Qfv from the resting limb (69% and 89% of all flow occurred during nonloaded and loaded inspiration, respectively); however, net Qfv in the steady state was not altered because of slight reductions in femoral venous return during the ensuing expiratory phase of the breath. Selectively augmenting inspiratory esophageal pressure excursion during a predominantly diaphragmatic breath at rest did not alter within-breath changes in Qfv relative to nonloaded conditions (net retrograde flow = -9 +/- 12% and -4 +/- 9% during nonloaded and loaded inspiration, respectively), supporting the notion that the inferior vena cava is completely collapsed by relatively small increases in gastric pressure. Addition of inspiratory + expiratory loading to diaphragmatic breathing at rest resulted in reversal of within-breath changes in Qfv, such that >90% of all anterograde Qfv occurred during inspiration. Inspiratory + expiratory loading also reduced steady-state Qfv during mild- and moderate-intensity calf contractions compared with inspiratory loading alone. We conclude that 1) exaggerated inspiratory pressure excursions may augment within-breath changes in femoral venous return but do not increase net Qfv in the steady state and 2) active expiration during diaphragmatic breathing reduces the steady-state hyperemic response to dynamic exercise by mechanically impeding venous return from the locomotor limb, which may contribute to exercise limitation in health and disease.     

Recurrent ventricular fibrillation treated by multiple countershocks.

Dichlorphenamide was administered to 13 patients with chronic respiratory failure, and the effects on gas exchange at rest and during exercise and on the acid-base state of CSF were observed. The ventilation for a given level of CO₂ production was increased both at rest and during exercise, resulting in an increased arterial Po₂ and decreased Pco₂.The ventilatory stimulation paralleled the development of a metabolic acidosis but was not associated with tissue CO₂ accumulation. Indeed, CSF Pco₂ and the oxygenated mixed venous (rebreathing) Pco₂ fell by the same amount as arterial Pco₂. The level of CO₂ elimination after two minutes of exercise was as great for a given work load after dichlorphenamide as before. These findings do not support the view that the drug impairs CO₂ transport from tissues either at rest or during exercise. They are most consistent with the view that the primary locus of action of dichlorphenamide in therapeutic doses is the kidney. The metabolic acidosis which results is likely the basis of the respiratory stimulatin, perhaps by its effects on the CSF H₂CO₃-HCO₃ - system. Inhibition of carbonic anhydrase in the red cell and choroid plexus are probably unimportant effects.     

Initial expiratory activity as one of the criteria of the respiratory center function

In 13 healthy men at rest and dosed muscular loads the authors studied maximal rates of the mouth pressure at the onset of inhalation and expiration (dP/dtI, dP/dtE) as well as the respiratory pattern. The parameter dP/dtE positively correlated with that of dP/dtI which reflects, as is known, an inspiratory activity of the respiratory center. The authors think that dP/dtE parameter can be used for noninvasive determination of expiratory activity.     

Effects of Glucose Feeding on Respiration and Photosynthesis in Photoautotrophic Dianthus caryophyllus Cells: Mass Spectrometric Determination of Gas Exchange

When glucose (20 millimolar) was added to photoautotrophic cell suspension cultures of Dianthus caryophyllus, there was during the first 10 hours an accumulation of carbohydrates and phosphorylated compounds. These biochemical changes were accompanied by a progressive decrease of net photosynthesis and a twofold increase of the dark respiratory rate. The rise of respiration was associated with a rise of fumarase and cytochrome c oxidase activities, two mitochondrial markers. Gas exchange of illuminated cells were performed with a mass spectrometry technique and clearly established that during the first hours of glucose feeding, the decrease of net photosynthesis was essentially due to an increase of respiration in light, whereas the photosynthetic processes (gross O₂ evolution and gross CO₂ fixation) were almost not affected. However, after 24 hours of experiment, O₂ evolution and CO₂ fixation started to decline in turn. While ribulose-1,5-bisphosphate carboxylase activity was little affected during the first 48 hours of the experiment, the maximal light-induced phosphoribulokinase activity dramatically decreased with time and represented after 48 hours only 30% of its initial activity. It is postulated that the decrease in phosphoribulokinase activity was at least partially responsible for the decrease of CO₂ fixation and the metabolic events involved in this regulation are discussed.     

Respiration during exercise in conscious laryngectomized humans

We compared respiratory patterning at rest and during steady cycle exercise at work rates of 30, 60, and 90 W in 7 male chronically laryngectomized subjects and 13 normal controls. Breathing was measured with a pneumotachograph and end-tidal PCO2 by mass spectrometer. Inspired air was humidified and enriched to 35% O2. Peak flow, volume, and times for the inspiratory and expiratory half cycles, time for expiratory flow, minute ventilation, and mean inspiratory flow were computer averaged over at least 40 breaths at rest and during the last 2 min of 5-min periods at each work rate. During the transition from rest to exercise and with increasing work rate in both groups, there was an increase in respiratory rate and depth with selective and progressive shortening of expiratory time; these responses were not significantly different between the two groups, but there was a suggestion that respiratory "drive" as quantitated by mean inspiratory flow may limit in the laryngectomized subjects at high work rates. Time for expiratory flow increased on transition from rest to exercise and then decreased in both groups as the work rate increased; it was shorter in the laryngectomy than control group at all levels. In the laryngectomized subjects there was significantly more breath-by-breath scatter in some variables at rest, but there was no difference during exercise. It is concluded that chronic removal of the larynx and upper airways in mildly hyperoxic conscious humans has only subtle and, therefore, functionally insignificant effects on breathing during moderate exercise. Evidence is provided that the upper airways can modulate expiratory flow but not expiratory time during exercise.     

Mobilization of respiratory metabolism in potato tubers by carbon dioxide

Applying high concentrations of CO₂ to whole potato tubers stimulated a rapid and pronounced respiratory gas exchange, which persisted for a prolonged time. The upsurge in respiration was proportional to the applied CO₂ concentrations and was further augmented by high O₂ levels. Tests using whole potatoes, or potato tissue slices from tubers previously treated with CO₂, indicated that the rapid CO₂-induced respiration is sensitive to cyanide during the first 24 hours of CO₂ application. The respiratory rise cannot be attributed to the emergence of a cyanide-resistant alternative electron transport pathway, although prolonged applications of CO₂, up to 72 hours, led to a gradual development of the pathway. CO₂-stimulated respiration was accompanied by a pronounced decline in the content of starch and glucose 6-phosphate, suggesting an active utilization of respiratory substrates. The ATP content in the CO₂-treated potatoes increased markedly, resembling similar increases in tissues undergoing respiratory upsurge.     

Large-scale activity in neural nets II: A model for the brainstem respiratory oscillator

The formalism developed in a previous paper (Feldman and Cowan, 1974) for the analysis of large scale activity in neural nets is applied to the problem of accounting for the generation and maintenance of respiratory related rhythms in the brain stem. It is shown that coupled nets of excitatory and inhibitory cells can generate slowly augmenting respiratory related activity, and that rapid switching from inspiratory related to expiratory related activity can take place. The effects of lung inflation, CO₂ inhalation, and brain stem lesions are deduced from the model, and certain predictions are made concerning inhibition in the brain stem.     

Nitrogen Fixation and Hydrogen Metabolism in Relation to the Dissolved Oxygen Tension in Chemostat Cultures of the Wild Type and a Hydrogenase-Negative Mutant of Azorhizobium caulinodans

Both the wild type and an isogenic hydrogenase-negative mutant of Azorhizobium caulinodans growing ex planta on N₂ as the N source were studied in succinate-limited steady-state chemostat cultures under 0.2 to 3.0% dissolved O₂ tension. Production or consumption of O₂, H₂, and CO₂ was measured with an on-line-connected mass spectrometer. In the range of 0.2 to 3.0%, growth of both the wild type and the mutant was equally dependent on the dissolved O₂ tension: the growth yield decreased, and the specific O₂ consumption and CO₂ production increased. A similar dependency on the dissolved O₂ tension was found for the mutant with 2.5% H₂ in the influent gas. The H₂/N₂ ratio (moles of H₂ evolved per mole of N₂ consumed via nitrogenase) of the mutant, growing with or without 2.5% H₂, increased with increasing dissolved O₂ tensions. This increase in the H₂/N₂ ratio was small but significant. The dependencies of the ATP/N₂ ratio (moles of ATP consumed per mole of N₂ fixed) and the ATP/2e^- ratio [moles of ATP consumed per mole of electron pairs transferred from NAD(P)H to nitrogenase] on the dissolved O₂ tension were estimated. These dependencies were interpreted in terms of the physiological concepts of respiratory protection and autoprotection.     

High-density surface EMG study on the time course of central nervous and peripheral neuromuscular changes during 8 weeks of bed rest with or without resistive vibration exercise

The aim of the present study was to assess the time course and the origin of adaptations in neuromuscular function as a consequence of prolonged bed rest with or without countermeasure. Twenty healthy males volunteered to participate in the present study and were randomly assigned to either an inactive control group (Ctrl) or to a resistive vibration exercise (RVE) group. Prior to, and seven times during bed rest, we recorded high-density surface electromyogram (sEMG) signals from the vastus lateralis muscle during isometric knee extension exercise at a range of contraction intensities (5–100% of maximal voluntary isometric torque). The high-density sEMG signals were analyzed for amplitude (root mean square, RMS), frequency content (median frequency, F_med) and muscle fiber conduction velocity (MFCV) in an attempt to describe bed rest-induced changes in neural activation properties at the levels of the motor control and muscle fibers. Without countermeasures, bed rest resulted in a significant progressive decline in maximal isometric knee extension strength, whereas RMS remained unaltered throughout the bed rest period. In line with observed muscle atrophy, both F_med and MFCV declined during bed rest. RVE training during bed rest resulted in maintained maximal isometric knee extension strength, and a strong increase (～30%) in maximal EMG amplitude, from 10 days of bed rest on. Exclusion of other factors led to the conclusion that the RVE training increased motor unit firing rates as a consequence of an increased excitability of motor neurons. An increased firing rate might have been essential under training sessions, but it did not affect isometric voluntary torque capacity.     

Respiratory muscle blood flow in exercising dogs after pneumonectomy.

In three foxhounds after left pneumonectomy, the relationships of ventilatory work and respiratory muscle (RM) blood flow to ventilation (VE) during steady-state exercise were examined. VE was measured using a specially constructed respiratory mask and a pneumotach; work of breathing was measured by the esophageal balloon technique. Blood flow to RM was measured by the radionuclide-labeled microsphere technique. Lung compliance after pneumonectomy was 55% of that before pneumonectomy; compliance of the thorax was unchanged. O2 uptake (VO2) of RM comprised only 5% of total body VO2 at exercise. At rest, inspiratory muscles received 62% and expiratory muscles 38% of the total O2 delivered to the RM (QO2RM). During exercise, inspiratory muscles received 59% and expiratory muscles 41% of total QO2RM. Blood flow per gram of muscle to the costal diaphragm was significantly higher than that to the crural diaphragm. The diaphragm, parasternals, and posterior cricoarytenoids were the most important inspiratory muscles, and internal intercostals and external obliques were the most important expiratory muscles for exercise. Up to a VE of 120 l/min through one lung, QO2RM constituted only a small fraction of total body VO2 during exercise and maximal vasodilation in the diaphragm was never approached.     

Interactions between Glucose and Inorganic Carbon Metabolism in Chlorella vulgaris Strain UAM 101

Chlorella vulgaris strain UAM 101 has been isolated from the effluent of a sugar refinery. This alga requires glucose to achieve maximal growth rate even under light saturating conditions. The growth rate of cultures grown on light + CO₂ + glucose (3.16 per day) reaches the sum of those grown on light + CO₂ (1.95 per day) and on dark + glucose (1.20 per day). Unlike other Chlorella strains, uptake of glucose (about 2 micromoles per milligram dry weight per hour) was induced to the same extent in the light and dark and was not photosensitive. The rate of dark respiration was not affected by light and was strongly stimulated by the presence of glucose (up to about 40% in 4 hours). The rate of photosynthetic O₂ evolution was measured as a function of the CO₂ concentration. These experiments were conducted with cells which experienced different concentrations of CO₂ or glucose during growth. The maximal photosynthetic rate was inhibited severely by growing the cells in the presence of glucose. A rather small difference in the apparent photosynthetic affinity for extracellular inorganic carbon (from 10-30 micromolar) was found between cells grown under low and high CO₂. Growth with glucose induced a reduction in the apparent affinity (45 micromolar) even though cells had not been provided with CO₂. Experiments performed at different pH values indicate CO₂ as the major carbon species taken from the medium by Chlorella vulgaris UAM 101.     

Mechanism of action of ozone on the human lung

Fourteen healthy normal volunteers were randomly exposed to air and 0.5 ppm of ozone (O3) in a controlled exposure chamber for a 2-h period during which 15 min of treadmill exercise sufficient to produce a ventilation of approximately 40 l/min was alternated with 15-min rest periods. Before testing an esophageal balloon was inserted, and lung volumes, flow rates, maximal inspiratory (at residual volume and functional residual capacity) and expiratory (at total lung capacity and functional residual capacity) mouth pressures, and pulmonary mechanics (static and dynamic compliance and airway resistance) were measured before and immediately after the exposure period. After the postexposure measurements had been completed, the subjects inhaled an aerosol of 20% lidocaine until response to citric acid aerosol inhalation was abolished. All of the measurements were immediately repeated. We found that the O3 exposure 1) induced a significant mean decrement of 17.8% in vital capacity (this change was the result of a marked fall in inspiratory capacity without significant increase in residual volume), 2) significantly increased mean airway resistance and specific airway resistance but did not change dynamic or static pulmonary compliance or viscous or elastic work, 3) significantly reduced maximal transpulmonary pressure (by 19%) but produced no changes in inspiratory or expiratory maximal mouth pressures, and 4) significantly increased respiratory rate (in 5 subjects by more than 6 breaths/min) and decreased tidal volume.(ABSTRACT TRUNCATED AT 250 WORDS)     

Gas exchange and air flow in the lung of the snake,Pituophis melanoleucus

Summary Gas samples from various regions of the lung were obtained throughout the breathing cycle inPituophis melanoleucus. Changes in CO₂ concentration during the interbreath period differed markedly along the length of the lung. In general, the largest and most rapid increases in CO₂ tension were measured at the cranial end of the vascular lung. Further caudad in the vascular lung, the increase was slower and did not reach mixed venous CO₂ tension before exhalation. In animals exhibiting the lowest breathing frequencies and presumably larger tidal volumes, the region of gas exchange extended into the cranial portion of the air sac. There was little or no change in gas tensions within the remaining caudal regions of the air sac. Measurement of exhaled CO₂ and O₂ tensions at the nares confirmed the longitudinal gradient in gas exchange and also demonstrated the sequential emptying of the lung. Large regional differences in the ratio of blood flow to alveolar volume are probably responsible for the gradients in lung gases.Interpretation of N₂ clearance curves in terms of two freely communicating compartments demonstrated the presence of a ventilation inequality. Consistent with this was the lack of body wall contractions between breaths while animals were resting. However, just prior to and during activity body wall contractions not associated with breathing often occurred and resulted in pressure excursions in the lung of ca. five mm H₂O. In addition, the heart beat results in a pressure change within the lung of ca. 0.2 mmH₂O which may be significant in gas mixing.