COMPARATIVE STUDIES ON RESPIRATION : XI. THE EFFECT OF HYDROGEN ION CONCENTRATION ON THE RESPIRATION OF PENICILLIUM CHRYSOGENUM.

1. Variations in pH value between 4 and 8 produce practically no effect on the normal rate of respiration (the rate at neutrality is called normal). 2. Increasing the pH value to 8.80 causes respiration to fall to 60 per cent of the normal, after which it remains stationary for the duration of the experiment. 3. Decreasing the pH value to 2.65 causes a gradual rise and a gradual return to normal; at pH 1.10 to 1.95 the preliminary rise amounts to 20 per cent and is followed by a fall to below the normal. 4. The decrease in respiration brought about by solutions of a pH value of 1.95 or less are irreversible, while a similar decrease which occurs at pH 8.80 is reversible, the rate coming back to practically normal after the material is replaced in a neutral solution. 5. Determinations by means of Winkler''s method showed an increase in the consumption of oxygen in acid solutions and a decrease in alkaline solutions.     

Growth of Sclerotiumrolfsiiat Different Concentration of Oxygen and Carbon Dioxide

Sclerotium rolfsii was grown in various atmospheres, the compositionsof which were controlled by the diffusion column technique.Growth-rate of mycelium was constant within a range of oxygenconcentrations from 3 to 21 per cent, but dirminished steadilyas carbon dioxide concentration increased from about 0.03 percent. The rate of sclerotial germination was reduced by oxygenconcentrations less than 6 per cent and by carbon dioxide concentrationsgreater than about 10 per cent. No sclerotia were formed ifthe concentration of oxygen fell below 15 per cent or if thatof carbon dioxide exceeded 4 per cent. The effects of inverserationof gases, from 0 per cent oxygen: 20 per cent carbon dioxideto 21 per cent oxygen: 0 per cent carbon dioxide, were in eachcase similar to the effect of the corresponding carbon dioxideconcentration when combined with 21 per cent oxygen.     

The Influence of Gaseous Environment on the Storage Life of Araucaria hunsteinii Seed

The effect of various gas mixtures on the longevity of hydratedseeds of Araucaria hunsteinii K. Schum. was assessed under controlledconditions. The length of storage life decreased as oxygen concentrationwas reduced from 21 to zero per cent. No effect of carbon dioxideon seed longevity was detected within the range 1–50 percent when combined with 10 or 21 per cent oxygen. Ethylene at0.01 per cent, and sealed foil or polyethylene bag storage reducedthe period of seed germinability compared with that for 21 percent oxygen. Ethanol accumulation took place in stored seedswhen the environmental oxygen concentration was below a thresholdvalue which lay between 1 and 5 per cent. It is proposed that the observed effects of gases on longevityof hydrated seeds may be mediated through an influence on aerobicrespiration rate. Practical implications of the results areconsidered. Araucaria hunsteinii, Klinkii pine, seed longevity, seed storage, gas environments, oxygen, carbon dioxide, ethanol accumulation     

Effects of azide and choretone on the sodium and potassium contents and the respiration of frog sciatic nerves

Azide (0.2 to 5.0 mM) and chloretone (2.0 to 15.0 mM) reversibly inhibited 20 to 90 per cent of the resting respiration of frog sciatic nerves, and caused a loss of potassium and a gain of sodium in this tissue. The changes in ionic contents that developed after 5 or 10 hours were roughly correlated with the degree of respiratory depression, but the time courses of these changes were different with the two reagents. In azide these changes appeared to begin immediately, while in chloretone, at concentrations between 3.0 and 5.0 mM, the ionic shifts developed after a delay of several hours. Fifteen millimolar chloretone produced immediate changes in ionic contents several times greater than those produced by anoxia. The changes in ionic distribution produced in 5 hours by anoxia, 5.0 mM azide, or 5.0 mM chloretone were at least partially reversible; those produced by 15.0 mM chloretone were irreversible. With the exception of 15.0 mM chloretone the ionic shifts produced by these reagents may be due primarily to the depression of the respiration, although there are indications that azide acts, in addition, by another pathway. Concentrations of azide or chloretone that depressed the resting rate of oxygen consumption more than 50 per cent produced a slow conduction block, while 15.0 mM chloretone blocked conduction within 15 minutes.     

Impact of Low Filter Resistances on Subjective and Physiological Responses to Filtering Facepiece Respirators

Ten subjects underwent treadmill exercise at 5.6 km/h over one hour while wearing each of three identical appearing, cup-shaped, prototype filtering facepiece respirators that differed only in their filter resistances (3 mm, 6 mm, and 9 mm H₂O pressure drop). There were no statistically significant differences between filtering facepiece respirators with respect to impact on physiological parameters (i.e., heart rate, respiratory rate, oxygen saturation, transcutaneous carbon dioxide levels, tympanic membrane temperature), pulmonary function variables (i.e., tidal volume, respiratory rate, volume of carbon dioxide production, oxygen consumption, or ventilation), and subjective ratings (i.e., exertion, thermal comfort, inspiratory effort, expiratory effort and overall breathing comfort). The nominal filter resistances of the prototype filtering facepiece respirators correspond to airflow resistances ranging from 2.1 - 6.6 mm H₂O/L/s which are less than, or minimally equivalent to, previously reported values for the normal threshold for detection of inspiratory breathing resistance (6 - 7.6 mm H₂O/L/sec). Therefore, filtering facepiece respirators with filter resistances at, or below, this level may not impact the wearer differently physiologically or subjectively from those with filter resistances only slightly above this threshold at low-moderate work rates over one hour.     

Negative arterial-mixed expired PC02 gradient during acute and chronic hypercapnia.

In resting conscious dogs physiological dead space was calculated using the Bohr equation and measurements of arterial and mixed expired carbon dioxide tension. Whenever dogs inhaled carbon dioxide mixtures (5-10%) that had normal or low oxygen concentrations, the calculated dead space became negative. This paradox was based on the fact that the mixed expired carbon dioxide tension in resting hypercapnic dogs. Under these circumstances carbon dioxide was produced from the lung as measured by gas analyses and blood analyses. By the lung as measured by gas analyses and blood analyses. By reasoning this implies that "alveolar" carbon dioxide tension was higher than pulmonary venous carbon dioxide tension. The negative carbon dioxide gradient persisted at 14 days of chronic hypercapnia and reverted to normal within 10 min of breathing air after chronic hypercapnia. These findings suggest that the exchange of carbon dioxide in the lung cannot be explained solely on the basis of passive diffusion.     

The mechanisms which affect the periodic cycle of Pacific Wuchereria bancrofti microfilariae

1. Investigations were made of the effect of various procedures in raising or lowering the microfilaria count of Pacific type Wuchereria bancrofti in the peripheral blood. 2. Raising the body temperature in the early morning was followed by a moderate fall in the counts. Breathing increased oxygen, or reduced oxygen (hypoxia) or increased carbon dioxide, or the ingestion of sodium bicarbonate produced no consistent and significant change in the count. Ingestion of glucose (in one volunteer) was followed by a small rise in the count. Muscular exercise was followed by a fall in the count, which is interpreted as probably being a response to a lower concentration of oxygen in the venous blood returning to the lung. 3. It has not been possible to identify the physiological components on the circadian rhythm of the human body which entrain the cycle of these microfilariae. Attempts to obtain evidence incriminating the stimuli described above have been unsuccessful.     

Carbon Dioxide Effects on Auxin Responses of Coleoptile Sections

In the wheat cylinder bioassay technique as previously usedhere 5 sections have been enclosed in a 2 x 38 in, assay tubetogether with 0.5 ml. of the test solution. A method developedfor estimating the amount of carbon dioxide which accumulatesin these tubes through the respiration of the enclosed sectionshas shown that the level can rise to 20 per cent. after 24 hrs.at 25°C. In the presence of a 100 p.p.m. IAA(6x10^-4M.) testsolution, growth of 5 enclosed sections is depressed from 8hrs. onwardas and they eventually shrink, releasing their accumulatedIAA back into the solution. The growth of sections under various gas mixtures of carbondioxide in air has also been followed and these experimentsshow that section length is reduced approximately lineraly withrespect to increasing carbon dioxide concentration up to 20per cent. in air, both in the presence and absence of a 100p.p.m. IAA solution. The slope of the fitted regression line,however, is much steeper when the test solution contains IAA—i.e.there is a large interaction. In the presence of IAA, growth-time data show that a reductionin the growth rate, as compared with that in normal air, canbe detected after only 4 hrs, at the highest carbon dioxideconcentration. In the absence of IAA, high concentrations ofcarbon dioxide accelerate growth during the first 8 hrs. ofthe assay but depress it later. The mechanism of action of this interaction is unknown but itis not shown at very high concentrations of IAA, e.g. 1,000p.p.m. (6x10^-3M.).     

Arterial Blood Gas Tensions and pH in Acute Asthma in Childhood

Studies of the arterial blood gas tensions and pH in 21 children during 24 acute attacks of asthma showed that all were hypoxic on admission to hospital, and in 10 there was evidence of carbon dioxide retention. Cyanosis, invariably present when the So₂ was below 85%, and restlessness in patients breathing air were the most reliable indices of the severity of hypoxia. There were no reliable clinical guides to the Pco₂ level. Conventional oxygen therapy in tents (25–40%) did not always relieve hypoxia, and in three cases the administration of oxygen at a concentration of 40% or over failed to produce a normal arterial oxygen tension. Uncontrolled oxygen therapy may aggravate respiratory acidosis, and three of our patients developed carbon dioxide narcosis while breathing oxygen. The necessity for blood gas measurements in the management of severe acute asthma in childhood is emphasized.     

COMPARATIVE STUDIES ON RESPIRATION : XIX. A PRELIMINARY STAGE IN THE PROGRESS OF ETHER ANESTHESIA.

Using these concentrations of ether (1 per cent, 3.65 per cent, 7.3 per cent), the following conclusions may be drawn. 1. The first effect of ether is to cause a depression in the rate of respiration. This is followed by a rapid rise above normal, which in turn is succeeded by a fall. 2. With all these concentrations the respiration is ultimately reduced to approximately the same level; the stronger the ether, the less time required to produce this result. 3. Even when the respiration has been reduced below normal, recovery is possible on removal from the ether, and appears to be complete, if sufficient time is allowed. If, however, the rate has been too far depressed, no recovery is possible. 4. These results extend those of Irwin on frog eggs and Fundulus embryos.     

Metabolic consequences of reduced frequency breathing during submaximal exercise at moderate altitude

The intention of this study was to determine the metabolic consequences of reduced frequency breathing (RFB) at total lung capacity (TLC) in competitive cyclists during submaximal exercise at moderate altitude (1520 m; barometric pressure, PB = 84.6 kPa; 635 mm Hg). Nine trained males performed an RFB exercise test (10 breaths.min-1) and a normal breathing exercise test at 75-85% of the ventilatory threshold intensity for 6 min on separate days. RFB exercise induced significant (P less than 0.05) decreases in ventilation (VE), carbon dioxide production (VCO2), respiratory exchange ratio (RER), ventilatory equivalent for O2 consumption (VE/VO2), arterial O2 saturation and increases in heart rate and venous lactate concentration, while maintaining a similar O2 consumption (VO2). During recovery from RFB exercise (spontaneous breathing) a significant (P less than 0.05) decreases in blood pH was detected along with increases in VE, VO2, VCO2, RER, and venous partial pressure of carbon dioxide. The results indicate that voluntary hypoventilation at TLC, during submaximal cycling exercise at moderate altitude, elicits systemic hypercapnia, arterial hypoxemia, tissue hypoxia and acidosis. These data suggest that RFB exercise at moderate altitude causes an increase in energy production from glycolytic pathways above that which occurs with normal breathing.     

THE EFFECT OF CARBON DIOXIDE TENSION ON THE METABOLISM OF CEREBRAL CORTEX AND MEDULLA OBLONGATA

Manometric measurements were made of oxygen uptake (Q _OO2) and aerobic lactic acid output (Q_G) by slices of cerebral cortex and medulla oblongata of the cat in the presence of mixtures of 1, 5, and 20 volumes per cent of carbon dioxide in oxygen. The concentrations of NaHCO₃ and NaCl in the medium were varied to maintain constant pH and sodium ion concentrations. The calcium ion concentration was 0.0002 M. At pH 7.5 under these conditions, an increase in carbon dioxide from 1 per cent to 5 per cent doubled the Q_G of both tissues but did not alter Q _OO2; an increase from 5 per cent to 20 per cent carbon dioxide had no further effect on Q_G in either tissue or Q _OO2 of cortex, but did depress the Q _OO2 of medulla. At pH 8.1, an increase in carbon dioxide from 1 per cent to 5 per cent raised the Q _OO2 and Q_G of cortex by about 60 per cent. Measurements at low oxygen tension carried out previously in phosphate medium were repeated in bicarbonate medium to obtain data for the combined output of lactic acid and carbon dioxide (Q_A). When the oxygen in the gas phase was decreased from 95 to 3 volumes per cent, the lactic acid output as measured colorimetrically increased by 114 mg./gm. in cortex and by 8 mg./gm. in medulla; Q_A increased from 12.3 to 13.5 in cortex and decreased from 5.1 to 3.8 in medulla.     

Effects of hypoxia, anoxia, and endogenous ethanol on thermoregulation in goldfish, Carassius auratus

Effects of hypoxia, anoxia, and endogenous ethanol (EtOH) on selected temperature (T(sel)) and activity in goldfish were evaluated. Blood and brain EtOH concentrations ([EtOH]) and brain oxygen partial pressure (PO(2)) were quantified at crucial ambient oxygen pressures. Below a threshold value near 31 Torr, T(sel) decreased as a function of environmental PO(2). T(sel) of 15 degrees C-acclimated fish was approximately 10 degrees C at the onset of anoxia and changed little over 2 h. Activity showed a similar response pattern. Brain [EtOH] was significantly elevated above control levels after 1 h anoxia. In normoxic water, T(sel) remained different in previously anoxic and normoxic control fish for approximately 20 min. Blood [EtOH] of previously anoxic fish remained significantly elevated ([EtOH] >4.0 micromol/g blood), and activity was significantly depressed at 20 min. Brain PO(2) reached normal levels in <3 min. We conclude that [EtOH] (brain or blood) and brain PO(2) are not proximal causes of either behavioral anapyrexia (hypothermia) or inactivity in goldfish exposed to oxygen-depleted environments.     

Carbon monoxide-induced localized toxic anoxia in the rat brain cortex.

A new method has been developed for the determination of maximal reduction of NAD in the rat cerebral cortex. NADH fluorescence (450 nm) induced by 366-nm light and UV reflectance were measured by a time-sharing light pipe fluorometer. The redox state of the cortical surface was altered by perfusion of oxygen or carbon monoxide through a Teflon chamber adjacent to the dura. This study examines changes caused by local perfusion with the two gases in normoxia, hypoxia, and anoxia. Alternation of topical carbon monoxide and oxygen becomes effective in altering the intracellular redox state at 15% inspired oxygen and caused 20% changes at zero inspired oxygen. Conversely, topical application of oxygen to the systemically anoxic tissue causes oxidation of reduced NAPH in the cells within the field of fluorometric observation equivalent to that caused by breathing approximately 8% oxygen systemically.     

THE EFFECTS OF VARIATIONS IN THE CONCENTRATION OF OXYGEN AND OF GLUCOSE ON DARK ADAPTATION

In this study we have analyzed the effects of variations in the concentrations of oxygen and of blood sugar on light sensitivity; i.e. dark adaptation. The experiments were carried out in an air-conditioned light-proof chamber where the concentrations of oxygen could be changed by dilution with nitrogen or by inhaling oxygen from a cylinder. The blood sugar was lowered by the injection of insulin and raised by the ingestion of glucose. The dark adaptation curves were plotted from data secured with an apparatus built according to specifications outlined by Hecht and Shlaer. During each experiment, observations were first made in normal air with the subject under basal conditions followed by one, and in most instances two, periods under the desired experimental conditions involving either anoxia or hyper- or hypoglycemia or variations in both the oxygen tension and blood sugar at the same time. 1. Dark adaptation curves were plotted (threshold against time) in normal air and compared with those obtained while inhaling lowered concentrations of oxygen. A decrease in sensitivity was observed with lowered oxygen tensions. Both the rod and cone portions of the curves were influenced in a similar way. These effects were counteracted by inhaling oxygen, the final rod thresholds returning to about the level of the normal base line in air or even below it within 2 to 3 minutes. The impairment was greatest for those with a poorer tolerance for low O₂. Both the inter- and intra-individual variability in thresholds increased significantly at the highest altitude. 2. In a second series of tests control curves were obtained in normal air. Then while each subject remained dark adapted, the concentrations of oxygen were gradually decreased. The regeneration of visual purple was apparently complete during the 40 minutes of dark adaptation, yet in each case the thresholds continued to rise in direct proportion to the degree of anoxia. The inhalation of oxygen from a cylinder quickly counteracted the effects for the thresholds returned to the original control level within 2 to 3 minutes. 3. In experiments where the blood sugar was raised by the ingestion of glucose in normal air, no significant changes in the thresholds were observed except when the blood sugar was rapidly falling toward the end of the glucose tolerance tests. However, when glucose was ingested at the end of an experiment in low oxygen, while the subject remained dark adapted, the effects of the anoxia were largely counteracted within 6 to 8 minutes. 4. The influence of low blood sugar on light sensitivity was then studied by injecting insulin. The thresholds were raised as soon as the effects of the insulin produced a fall in the blood sugar. When the subjects inhaled oxygen the thresholds were lowered. Then when the oxygen was withdrawn so that the subject was breathing normal air, the thresholds rose again within 1 to 2 minutes. Finally, if the blood sugar was raised by ingesting glucose, the average threshold fell to the original control level or even below it. 5. The combined effects of low oxygen and low blood sugar on light sensitivity were studied in one subject (W. F.). These effects appeared to be greater than when a similar degree of anoxia or hypoglycemia was brought about separately. 6. In a series of experiments on ten subjects the dark adaptation curves were obtained both in the basal state and after a normal breakfast. In nine of the ten subjects, the food increased the sensitivity of the subjects to light. 7. The experiments reported above lend support to the hypothesis that both anoxia and hypoglycemia produce their effects on light sensitivity in essentially the same way; namely, by slowing the oxidative processes. Consequently the effects of anoxia may be ameliorated by giving glucose and the effects of hypoglycemia by inhaling oxygen. In our opinion, the changes may be attributed directly to the effects on the nervous tissue of the visual mechanism and the brain rather than on the photochemical processes of the retina.     

THE EFFECT OF MODERATE AND MARKED HYPERCAPNIA UPON THE ENERGY STATE AND UPON THE CYTOPLASMIC NADH/NAD+ RATIO OF THE RAT BRAIN

Abstract— The energy state of brain tissue was evaluated from the tissue concentrations of ATP, ADP and AMP and the cytoplasmic NADH/NAD⁺ ratio from the tissue, CSF and blood concentrations of lactate and pyruvate, and from the intracellular pH', in rats exposed to carbon dioxide concentrations of 640 per cent. The hypercapnia had no significant effect on the energy state of the tissue. Hypercapnia of increasing severity gave rise to a progressive decrease in the pyruvate concentration; the lactate concentration fell at low CO₂ concentrations, but no further decrease was observed at CO₂ concentrations greater than 20 per cent. There was a progressive rise in the intracellular lactate/pyruvate ratio at increasing CO₂ concentrations, corresponding to the fall in intracellular pH, i.e. the calculated NADH/NAD⁺ ratios remained normal. It is therefore concluded that hypercapnia does not affect the cytoplasmic redox state.     

THE EFFECT OF BREATHING OXYGEN ON THE METABOLISM OF THE RAT BRAIN UNDER NORMAL AND ISCHAEMIC CONDITIONS

Abstract—

• 1 Breathing oxygen (1 atm.) for 2 hr increased the glycogen content of the rat brain from 3·38 to 4·35 μmoles glucosyl residues/g wet wt. At the same time the glucose and lactate concentrations were significantly decreased.
• 2 Both under normal conditions and when breathing oxygen, the sum (glycogen + glucose) × 2 + lactate, with which the balance of carbohydrate breakdown and lactate formation was assessed, was 13·5 μmoles/g wet wt.
• 2 Oxygen breathing effected a significant decrease in this sum after an ischaemic period of 1–15 min. In the control group breathing normal air, the sum, after all periods of ischaemia, ranged from 98 to 106 per cent of the starting value.
• 3 An increased partial pressure of oxygen did not change the breakdown rate of the high-energy phosphate compounds. This result was not consistent with an oxidation of the carbohydrates which were missing in the balance. It is probable that other metabolites, which were not tested for, accumulated.
• 5 0 We failed to find any indication of storage of oxygen which the ischaemic brain could use for oxidative energy production.

     

Supradian and infradian cycles in oxygen uptake of diapausing pupae of Pieris brassicae

The general characteristics of diapause respiration in P. brassicae are described, together with an examination of short-term (supradian) and long-term (infradian) variation in oxygen uptake. Supradian cycles occur approximately every 3 hr at 10°C and are shown by closed box analyses to be initiated by carbon dioxide bursts. Maximal rates of oxygen uptake occur shortly after the burst in carbon dioxide release, not at the start of the burst as recorded in other diapausing species. The frequency of supradian cycles is directly related to temperature and metabolism in accordance with the characteristics of discontinuous carbon dioxide release.Infradian cycles of between 3 and 7 days duration are recorded for both oxygen uptake and net exchange rates. Peaks in oxygen demand occur on average every 4 days at 10°C, and are related in frequency to the level of metabolism of individual pupae. Just before post-diapause development, oxygen demands fall to about half their normal levels; these changes are associated with appropriate changes in the frequency of supradian and infradian cycles.     

The Germination of Avena fatua under Different Gaseous Environments

The atmosphere in which seeds germinate can profoundly affect the level of germination and dormancy. Seeds were germinated in atmospheres containing various concentrations of carbon dioxide and oxygen. At the same time the effect of light on these systems was examined. The germination of partially dormant populations of wild oat seed is inhibited by white light. This response to light is most apparent when the curyopsis is enclosed in the pales. Investigations into the effect of the ambient atmosphere on germination have indicated that, while oxygen is a necessary factor in the germination of tliis species, carbon dioxide also has an effect. A lack of carbon dioxide increases the degree of light inhibition of germination; 3 per cent carbon dioxide (by volume) allows germination in light; 20 per cent carbon dioxide inhibits germination in light and darkness at all tested oxygen concentrations.     

Studies in Stomatal Behaviour: V. THE ROLE OF CARBON DIOXIDE IN THE LIGHT RESPONSE OF STOMATA

Experiments are described in which the responses of wheat stomatato carbon dioxide concentration (0·00, 0·01, 0·02,0·03 per cent.), light intensity (275, 625, 975 f.c.),and rate of air flow (2, 5, 12·5 l./hr.) were studied. Reduction of carbon dioxide concentration from 0·03 to0·01 per cent. resulted in marked stomatal opening; furtherreduction to 0·00 per cent, was accompanied by a slightbut not significant closure. These effects were found at alllight intensities and rates of flow, except at 975 f.c. with2 l./hr. air flow, where no effect of carbon dioxide concentrationwas detected. This last is attributed to excessive depletionof the carbon dioxide supply by assimilation. The apparent lowerlimit of 0·01 per cent, carbon dioxide causing maximalstomatal opening is discussed in relation to recent assimilationexperiments. Increase of light intensity caused considerable stomatal opening,this effect being as great with air of 0·00 and 0·01per cent. as with higher concentrations of carbon dioxide. Thissuggests an effect of light on stomatal movement other thanthat exerted indirectly through photosynthesis by the mesophylcells. Increased rate of flow of dry air caused closure of the stomata;this was shown to be a drying effect and was absent when moistair was used.