Gas exchange pattern in the two‐spot ladybird beetle,Adalia bipunctata,differs in dry vs. moist air

Gas exchange patterns in the ladybird beetle, Adalia bipunctata (L.) (Coleoptera: Coccinellidae), were investigated using an infrared gaseous analyser (IRGA) and a coulometric O₂ respirometer (manometric–volumetric system). Before testing, the beetles were kept either in dry (dehydrated) or moist (hydrated) conditions for 1 day. Their subsequent gas exchange patterns did not depend on their state of humidity but rather were controlled by the humidity of the insect chamber during gas exchange measurement. If this chamber contained dry air, the beetles exhibited CO₂ release by burst, which we interpreted as cyclic gas exchange (CGE) with inter‐burst periods, but if the chamber was switched to contain moist air, then cyclic CO₂ release was soon abandoned and a pattern of continuous gas exchange appeared. Measurements with the coulometric respirometer in moist air showed that continuous gas exchange was often associated with weak abdominal pulsations, which we interpreted as active ventilation. Their metabolic rate was lower during gas exchange cycles than during continuous gas exchange. We revealed that in the ladybird beetle metabolic rate increased in moist air when the gas exchange pattern transitioned from cyclic to continuous.     

Ventilatory responses to temperature variation in the fresh water turtle,Mauremys caspica leprosa

A study of lung gas exchange in the fresh water turtle Mauremys caspica leprosa at normal physiological body temperatures (15, 25 and 35 °C) was extended to extreme temperatures (5 and 40 °C) to determine whether the direct relationship between body temperature and ventilatory response found in many lung-breathing ectotherms including other chelonian species was maintained. From 5 to 35 °C the lung ventilation per unit of O₂ uptake and CO₂ removed declined with temperature. Consequently, lung CO₂ partial pressure increased with temperature. Its value was maintained within narrow limits at each thermal constant, suggesting a suitable control throughout the complete ventilatory cycle. At 40 °C the ventilatory response showed the opposite trend. The ratios of ventilation to lung gas exchange increased compared to their values at 35 °C. The impact of this increased breathing-lowering the estimated mean alveolar CO₂ partial pressure-was nevertheless less than expected due to an increase in calculated physiological dead space. This suggests that the relative hyperventilation in response to hyperthermia found in Mauremys caspica leprosa is related to evaporative heat loss.Abbreviations BTPS body temperature, ambient pressure, saturated with water vapour - CTM critical thermal maximum - F_N2 fractional concentration of nitrogen - PA _CO2or PL _CO2 alveolar or lung CO₂ pressure - PA_O2or PL_O2 alveolar or lung O₂ pressure - PI_O2 inspired O₂ pressure - R respiratory exchange ratio - STPD standard temperature, standard pressure, dry - T _a ambient temperature - T _b body temperature - VA alveolar ventilation - VA/VCO₂ relative alveolar ventilation (alveolar ventilation per unit of CO₂ removed) - VO₂ O₂ uptake - VCO₂ CO₂ output - V _D anatomical dead space volume - V _D physiological dead space volume - VE/VO₂ ventilatory equivalent for O₂ - VE pulmonary ventilation or expiratory minute volume - VE/VCO₂ ventilatory equivalent for CO₂ - V _T tidal volume     

A method of reconstruction of clinical gas-analyzer signals corrupted by positive-pressure ventilation.

The use of sidestream infrared and paramagnetic clinical gas analyzers is widespread in anesthesiology and respiratory medicine. For most clinical applications, these instruments are entirely satisfactory. However, their ability to measure breath-by-breath volumetric gas fluxes, as required for measurement of airway dead space, oxygen uptake, and so on, is usually inferior to that of the mass spectrometer, and this is thought to be due, in part, to their slower response times. We describe how volumetric gas analysis with the Datex Ultima analyzer, although reasonably accurate for spontaneous ventilation, gives very inaccurate results in conditions of positive-pressure ventilation. We show that this problem is a property of the gas sampling system rather than the technique of gas analysis itself. We examine the source of this error and describe how cyclic changes in airway pressure result in variations in the flow rate of the gas within the sampling catheter. This results in the phenomenon of "time distortion," and the resultant gas concentration signal becomes a nonlinear time series. This corrupted signal cannot be aligned or integrated with the measured flow signal. We describe a method to correct for this effect. With the use of this method, measurements required for breath-by-breath gas-exchange models can be made easily and reliably in the clinical setting.     

A Non Invasive Estimate of Dead Space Ventilation from Exercise Measurements

Rationale

During exercise, heart failure patients (HF) show an out-of-proportion ventilation increase, which in patients with COPD is blunted. When HF and COPD coexist, the ventilatory response to exercise is unpredictable.

Objectives

We evaluated a human model of respiratory impairment in 10 COPD-free HF patients and in 10 healthy subjects, tested with a progressive workload exercise with different added dead space. We hypothesized that increased serial dead space upshifts the VE vs. VCO₂ relationship and that the VE-axis intercept might be an index of dead space ventilation.

Measurements

All participants performed a cardiopulmonary exercise test with 0, 250 and 500 mL of additional dead space. Since DS does not contribute to gas exchange, ventilation relative to dead space is ventilation at VCO₂ = 0, i.e. VE-axis intercept. We compared dead space volume, estimated dividing VE-axis intercept by the intercept on respiratory rate axis of the respiratory rate vs. VCO₂ relationship with standard method measured DS.

Main results

In HF, adding dead space increased VE-axis intercept (+0 mL = 4.98±1.63 L; +250 mL = 9.69±2.91 L; +500 mL = 13.26±3.18 L; p<0.001) and upshifted the VE vs.VCO₂ relationship, with a minor slope rise (+0 mL = 27±4 L; +250 = 28±5; +500 = 29±4; p<0.05). In healthy, adding dead space increased VE-axis intercept (+0 mL = 4.9±1.4 L; +250 = 9.3±2.4; +500 = 13.1±3.04; p<0.001) without slope changes. Measured and estimated dead space volumes were similar both in HF and healthy subjects.

Conclusions

VE-axis intercept is related to dead space ventilation and dead space volume can be non-invasively estimated.     

Temporal trends in N2O flux dynamics in a Danish wetland – effects of plant‐mediated gas transport of N2O and O2 following changes in water level and soil mineral‐N availability

Temporal trends of N₂O fluxes across the soil–atmosphere interface were determined using continuous flux chamber measurements over an entire growing season of a subsurface aerating macrophyte (Phalaris arundinacea) in a nonmanaged Danish wetland. Observed N₂O fluxes were linked to changes in subsurface N₂O and O₂ concentrations, water level (WL), light intensity as well as mineral‐N availability. Weekly concentration profiles showed that seasonal variations in N₂O concentrations were directly linked to the position of the WL and O₂ availability at the capillary fringe above the WL. N₂O flux measurements showed surprisingly high temporal variability with marked changes in fluxes and shifts in flux directions from net source to net sink within hours associated with changing light conditions. Systematic diurnal shifts between net N₂O emission during day time and deposition during night time were observed when max subsurface N₂O concentrations were located below the root zone. Correlation (P < 0.001) between diurnal variations in O₂ concentrations and incoming photosynthetically active radiation highlighted the importance of plant‐driven subsoil aeration of the root zone and the associated controls on coupled nitrification/denitrification. Therefore, P. arundinacea played an important role in facilitating N₂O transport from the root zone to the atmosphere, and exclusion of the aboveground biomass in flux chamber measurements may lead to significant underestimations on net ecosystem N₂O emissions. Complex interactions between seasonal changes in O₂ and mineral‐N availability following near‐surface WL fluctuations in combination with plant‐mediated gas transport by P. arundinacea controlled the subsurface N₂O concentrations and gas transport mechanisms responsible for N₂O fluxes across the soil–atmosphere interface. Results demonstrate the necessity for addressing this high temporal variability and potential plant transport of N₂O in future studies of net N₂O exchange across the soil–atmosphere interface.     

DenNit – Experimental analysis and modelling of soil N2O efflux in response on changes of soil water content, soil temperature, soil pH, nutrient availability and the time after rain event

To quantify the effects of soil temperature (T_soil), and relative soil water content (RSWC) on soil N₂O emission we measured N₂O soil efflux with a closed dynamic chamber in situ in the field and from soil cores in a controlled climate chamber experiment. Additionally we analysed the effect of soil acidity, ammonium, and nitrate concentration in the field. The analysis was performed on three meadows, two bare soils and in one forest. We identified soil water content, soil temperature, soil nitrogen content, and pH as the main parameters influencing soil N₂O emission. The response of N₂O emission to soil temperature and relative soil water content was analysed for the field and climate chamber measurements. A non-linear regression model (DenNit) was developed for the field data to describe soil N₂O efflux as a function of soil temperature, soil moisture, pH value, and ammonium and nitrate concentration. The model could explain 81% of the variability in soil N₂O emission of all individual field measurements, except for data with short-term soil water changes, namely during and up to 2 h after rain stopped. We validated the model with an independent dataset. For this additional meadow site 73% of the flux variation could be explained with the model.     

The leucine operon carrying theleu-500 promoter mutation is expressed under anaerobic conditions

TheSalmonella typhimurium leu-500 auxotrophic mutant grew when cultivated in minimal medium anaerobically, but not aerobically. This mutant carries an AT CG mutation in the Pribnow box of the promoter region of the leucine operon and was found to be suppressible by anaerobic conditions. Analysis of the anaerobic gases revealed that hydrogen in the anaerobic gas mixture (85% N₂, 10% CO₂, 5% H₂) is essential for the suppression of theleu-500 mutation. Whenleu-500 mutant cells were incubated in the presence of the hydrogen gas, the synthetic rates for the first and last gene products of theleu-500 operon were similar to those of the wild-type cells. It was concluded that the entire leucine operon was efficiently expressed inleu-500 when the cells were grown under the hydrogen gas-containing anaerobic environment. Thus, theleu-500 promoter mutant is a model system for regulation of gene expression by a specific atmospheric environment, i.e., hydrogen gas found in the anaerobic environment.     

The variability of pulmonary gas exchange and respiratory pattern

Very-low-frequency (VLF) fluctuations, whose nature is probably determined by rhythms of energy processes, are known to determine the variability of respiratory and heart rates. It is still unclear to which type of wave processes (chaotic or regular) these rhythm patterns belong. The goal of this study was to investigate the rhythms of pulmonary gas exchange and the variability of the respiratory pattern, as well as to find their possible relation. To analyze the variability of ventilation indices in the VLF band, pneumograms were recorded for 30 min and then the pulmonary gas exchange indices (Ve, pulmonary ventilation; V_O2 V_{O_2 }, oxygen consumption; V_CO2 V_{CO_2 }, carbon dioxide release) were recorded for 30 min using the breath-by-breath method in ten healthy subjects. Spectral analysis carried out using the fast Fourier transform revealed two groups of major peaks: the first one was in the range from 0.2 to 0.3 Hz (the time interval of 3–5 s), which was in good agreement with the respiratory rate varied from 12 to 20 per min in tested subjects; the second was from 0.002 to 0.0075 Hz, which corresponded to the VLF band. The data make it possible to draw a conclusion about the stability of the wave processes found. Apparently, the slow-wave pattern of the pulmonary gas exchange indices belongs to the quasi-periodic oscillation type, reflecting synchronization of oscillators with incommensurable frequencies when the two-frequency pattern dominates. The first oscillator is the chemoreceptor mechanism of the regulation of ventilation, the nature of the second one is still unclear. Taking into consideration that V_O2 V_{O_2 } and V_CO2 V_{CO_2 } depend on energy demand, one can suppose that energy processes form (an)other oscillator(s) of periodic processes.     

Continuous, automated acetylene reduction assays using intact plants

An automated method was developed for continuous, in situ determination of acetylene reduction (N₂ fixation) by intact soybean plants (Glycine max [L.]). The culture vessel containing the roots of intact plants grown in sand culture is sealed at the surface and an air-acetylene mixture continuously injected into the root chamber. The effluent gas is automatically sampled and injected into a gas chromatograph. Continuous acetylene assay at intervals as short as 3.5 min may be made over a period of several days, without attention, except for plant watering. Adverse effects of prolonged exposure of the root system to acetylene were mitigated by pulse injection of acetylene for 20 min followed by 40 min of acetylene-free air. Bare root systems can be suspended in a reaction chamber and sprayed with water or nutrient solution; this permits periodic removal of the root system for sampling nodules.     

Diamide model for the optical activity of collagen and polyproline I and II

A diamide, N-acetyl-L -proline-N,N-dimethylamide (AcProDMA), in water solution has optical rotatory dispersion (ORD) and circular dichroism (CD) spectra very similar to those of poly-L -proline II and the fibrous protein collagen. In contrast, AcProDMA in cyclohexane solution has optical activity resembling that of poly-L -proline I. Conformational analysis shows that AcProDMA is confined by steric constraints to either of two narrow regions of conformational space. The trans isomer of AcProDMA assumes conformations near those of polyproline II and collagen nearest neighbors, while cis-AcProDMA assumes conformations near that of polyproline I nearest neighbors. Nuclear magnetic resonance (NMR) experiments show that an equilibrium mixture of the cis and trans isomers of AcProDMA is present in solution. The trans isomer predominates in aqueous solution, but the equilibrium shifts to favor the cis isomer in nonpolar organic solvents such as cyclohexane. Analysis of the ORD spectra in terms of two basic spectra reveals a solvent dependent isomerization which parallels that observed by NMR. The optical activity of the pure isomers of AcProDMA can be derived from the ORD, CD and NMR data. A comparison of component cotton effects confirms the similarity in optical activity of trans-AcProDMA, polyproline II, and collagen on the one hand, and of cis-AcProDMA and Polyproline I on the other.     

A system to simulate gas exchange in humans to control quality of metabolic measurements

We have developed a gas exchange simulation system (GESS) to assess the quality control in measurements of metabolic gas exchange. The GESS simulates human breathing from rest to maximal exercise. It approximates breath-by-breath waveforms, ventilatory output, gas concentrations, temperature and humidity during inspiration and expiration. A programmable motion control driving two syringes allows the ventilation to be set at any tidal volume (V _T), respiratory frequency (f), flow waveform and period of inspiration and expiration. The GESS was tested at various combinations of V _T (0.5–2.5 l) and f (10–60 stroke · min⁻¹) and at various fractional concentrations of expired oxygen (0.1294–0.1795); and carbon dioxide (0.0210–0.0690) for a pre-set flow waveform and for expired gases at the same temperature and humidity as room air. Expired gases were collected in a polyethylene bag for measurement of volume and gas concentrations. Accuracy was assessed by calculating the absolute and relative errors on parameters (error = measured−predicted). The overall error in the gas exchange values averaged less than 2% for oxygen uptake and carbon dioxide output, which is within the accuracy of the Douglas bag method. Accepted: 4 June 1998     

Physiological dead space and effective parabronchial ventilation in ducks

Gas exchange in avian lungs is described by a cross-current model that has several differences from the alevolar model of mammalian gas exchange [e.g., end-expired PCO2 greater than arterial PCO2 (PaCO2)]. Consequently the methods available for estimating effective ventilation and physiological dead space (VDphys) in alveolar lungs are not suitable for an analysis of gas exchange in birds. We tested a method for measuring VDphys in birds that is functionally equivalent to the conventional alveolar VDphys. A cross-current O2-CO2 diagram was used to define the ideal expired point (PEi) and VDphys was calculated as from the equation, VDphys = [(PEiCO2--PECO2)/PEiCO2]. VT, where VT is tidal volume. In seven Pekin ducks VDphys was 13.8 ml greater than anatomic dead space and measured changes in the instrument dead space volume. VDphys also reflected changes in ventilation-perfusion inequality induced by temporary unilateral pulmonary arterial occlusion. Bohr dead space, calculated by substituting end-expired PCO2 for PEiCO2, was insensitive to such inhomogeneity. Enghoff dead space, calculated by substituting PaCO2 for PEiCO2, is theoretically incorrect for cross-current gas exchange and was often less than anatomic dead space. We conclude that VDphys is a useful index of avian gas exchange and propose a standard definition for effective parabronchial ventilation (VP) analogous to alveolar ventilation (i.e., VP = VE--VDphys, where VE is total ventilation).     

Effects of temperature on respiration and acid-base balance in a monitor lizard

Summary Ventilation, gas exchange, blood gas tensions and arterial pH were measured simultaneously in monitor lizards,Varanus exanthematicus. In contrast to previously studied poikilotherms, the arterial pH is independent of body temperature within the normally encountered temperature range (Fig. 1). This exception to the relative alkalinity concept (Rahn, 1966) is correlated with the finding thatV. exanthematicus maintains a constant ratio of ventilation to oxygen uptake (and CO₂ production) at different temperatures (Fig. 3). The increase in arterial (Fig. 1) is related to an increase in physiological dead space; i.e., alveolar ventilation increases less with temperature than total ventilation (Fig. 4). This may result from the increased frequency of breathing which results in a reduced breath holding time (Fig. 2). Varanid lizards have a higher oxygen requirement than other reptiles. This is reflected in the control of ventilation, the specialized lung morphology, the high arterial saturation due to low intracardiac shunting, pH regulation and other mammal-like features ofVaranus.     

Lung clearance index in adults with non-cystic fibrosis bronchiectasis

Background

Lung clearance index (LCI) is a measure of abnormal ventilation distribution derived from the multiple breath inert gas washout (MBW) technique. We aimed to determine the clinical utility of LCI in non-CF bronchiectasis, and to assess two novel MBW parameters that distinguish between increases in LCI due to specific ventilation inequality (LCI_vent) and increased respiratory dead space (LCI_ds).

Methods

Forty-three patients with non-CF bronchiectasis and 18 healthy control subjects underwent MBW using the sulphur hexafluoride wash-in technique, and data from 40 adults with CF were re-analysed. LCI_vent and LCI_ds were calculated using a theoretical two-compartment lung model, and represent the proportional increase in LCI above its ideal value due to specific ventilation inequality and increased respiratory dead space, respectively.

Results

LCI was significantly raised in patients with non-CF bronchiectasis compared to healthy controls (9.99 versus 7.28, p < 0.01), and discriminated well between these two groups (area under receiver operating curve = 0.90, versus 0.83 for forced expiratory volume in one second [% predicted]). LCI, LCI_vent and LCI_ds were repeatable (intraclass correlation coefficient > 0.75), and correlated significantly with measures of spirometric airflow obstruction.

Conclusion

LCI is repeatable, discriminatory, and is associated with spirometric airflow obstruction in patients with non-CF bronchiectasis. LCI_vent and LCI_ds are a practical and repeatable alternative to phase III slope analysis and may allow a further level of mechanistic information to be extracted from the MBW test in patients with severe ventilation heterogeneity.     

Denitrification of nitrate to nitrogen gas by washed cells ofRhizobium japonicum and by bacteroids fromGlycine max

Nitrate, nitrite and nitrous oxide were denitrified to N₂ gas by washed cells ofRhizobium japonicum CC706 as well as by bacteroids prepared from root nodules ofGlycine max (L.) Merr. (CV. Clark 63). Radiolabelled N₂ was produced from either K¹⁵NO₃ or Na¹⁵NO₂ by washed cells ofRh. japonicum CC705 grown with either nitrate only (5 mM) or nitrate (5 mM) plus glutamate (10 mM). Nitrogen gas was also produced from N₂O. Similar results were obtained with bacteroids ofG. max. The stoichiometry for the utilization of¹⁵NO ₃ ^- or¹⁵NO ₂ ^- and the produciton of¹⁵N₂ was 2:1 and for N₂O utilization and N₂ production it was 1:1. Some of the¹⁵N₂ gas produced by denitrification of¹⁵NO ₃ ^- in bacteroids was recycled via nitrogenase into cell nitrogen.     

Measurement of breath-by-breath gas exchange during general anaesthesia using a single pneumotachograph

A breath-by-breath gas exchange measurement system using a single pneumotachograph suitable for use during general anaesthesia is described. The system's accuracy has been assessed by a combination of error sensitivity analysis, laboratory testing of the component measurements used to calculate gas exchange and measurements on volunteers and patients. The system is shown to have a mean accuracy of ± 2.6 ml breath⁻¹ for V_CO2 measurements, ± 7.12 ml breath⁻¹ for V_O2 and ± 5.55 ml breath⁻¹ for V_N2O measurement. The application of a lung gas stores correction using argon improved between breath variability by 50%.     

The physiological factors which govern inert gas exchange

The decay constants (k _j ) of the equation of inert gas exchanges are the roots of an algebraic equation of degreen+1, wheren is the number of distinct absorbing tissues. The coefficients of this equation can be obtained numerically by certain independent experiments to measure the tissue parameters. Graphical solution of this equation yields theoretical values of thek _j . Combining these constants with the numerical values for the partial derivatives of thek _j then gives the per cent rate of change of thek _j as any one tissue parameter varies by a given fraction of its normal range. A numerical example of these calculations shows good conformity with experiment, and permits a quantitative estimate of variations in the speed of gas exchange from a knowledge of changes in the physiological state. The opinions expressed in this article are the private ones of the writers, and are not to be construed as reflecting the policies of the Navy Department or the Naval Service at large.     

华南地区尾巨桉和马占相思人工林地表温室气体通量

为探索华南地区尾巨桉人工林和马占相思人工林地表温室气体的季节排放规律、排放通量和主控因子,采用静态箱-气相色谱法,对两种林型地表3种温室气体(CO_2、CH_4、N_2O)通量进行为期1年的逐月测定。结果表明:(1)尾巨桉人工林和马占相思人工林均为CO_2和N_2O的排放源,CH_4的吸收汇。马占相思林地表N_2O通量显著(P0.01)高于尾巨桉林,CO_2通量和CH_4通量无明显差异。(2)两种林型3种温室气体通量有着相似季节变化规律,地表CO_2通量均呈现雨季高旱季低的单峰规律;地表CH_4吸收通量表现为旱季高雨季低的单峰趋势;地表N_2O通量呈现雨季高旱季低且雨季内有两个峰值的排放规律。(3)地表CO_2、N_2O通量和土壤5 cm温度呈极显著(P0.01)正相关,3种温室气体地表通量同土壤含水量呈极显著(P0.01)或显著相关(P0.05)。(4)尾巨桉林和马占相思林温室气体年温室气体排放总量为31.014 t/hm~2和28.782 t/hm~2,均以CO_2排放占绝对优势(98.46%—99.15%),CH_4和N_2O处于次要地位。