The influence of gas exchange on lung gas concentrations during air breathing

A model study is made of the contribution that continuing respiratory gas exchange makes to the alveolar plateau slope for O₂ during air breathing. Calculations in the model of the O₂ concentration appearing at the mouth during expiration, are performed for single breaths of air at constant flow rates 18 litres/min and 120 litres/min. At 18 litres/min the breathing period is 5 sec, the initial lung volume is 2300 ml, and the O₂ uptake rate is 300 ml STPD/min; whereas at 120 litres/min these parameters are 4 sec, 1200 ml, and 1800 ml STPD/min respectively. In each case the initial lung O₂ tension is taken to be 98 mm Hg. It is found that at 18 litres/min, the O₂ concentration difference on the alveolar plateau over the last second of expiration is 0.4 mm Hg when gas exchange is omitted and 1.2 mm Hg when gas exchange is included in the model. At 120 litres/min, this difference is zero and 5.0 mm Hg respectively. The gas exchange component predicted from a corresponding well-mixed compartment model is the same at 18 litres/min (0.8 mm Hg) but is 6.0 mm Hg at 120 litres/min.     

Central and peripheral causes of hyperreflexia in humans breathing 5% trimix at 650 m

To clarify the mechanism of increased stretch reflex responsiveness in deep divers (hyperbaric hyperreflexia), comparative studies of stretch (T) and Hoffmann (H) reflexes were done on three men breathing 5% N2-0.5 bar O2-balance He at pressures up to 650 m of seawater (msw) (Atlantis IV simulated dive, F.G. Hall Laboratory, Duke Medical Center). Electromyography revealed increases at depth of up to 160% in the T reflex recruitment ratio (T reflex/Mmax) compared with surface controls. The H reflex recruitment ratio (Hmax/Mmax) did not change significantly. It is concluded that hyperbaric hyperreflexia is mainly due to increased muscle spindle sensitivity, presumably arising as a central effect on gamma-motoneuron activity. However, a purely peripheral effect of pressure on the spindle end-organ itself is not ruled out. Increases of 100-200% in muscle twitch peak force are reported and provide evidence that pressure can act directly on peripheral physiology. Postreflex clonic potentials (rebounds) during voluntary plantar flexion were significantly increased both in amplitude and number, leading to sustained clonus in one subject. In this respect, 5% N2 was less effective than 10% N2 of Atlantis III in controlling underdamping of the reflex loop. Conversely, the twitch contraction rate and clonic frequency in this study were only half as slowed compared with results from the earlier dive.     

Ventilatory and gas exchange responses under spontaneous and fixed breathing modes during arm exercise

To evaluate the difference of ventilatory and gas exchange response differences between arm and leg exercise, six healthy young men underwent ramp exercise testing at a rate of 15 W.min-1 on a cycle ergometer separately under either spontaneous (SPNT) or fixed (FIX) breathing modes, respectively. Controlled breathing was defined as a breathing frequency (fb; 30 breaths.min-1) which was neither equal to, nor a multiple of, cranking frequency (50 rev.min-1) to prevent coupling of locomotion and respiratory movement, i.e., so-called locomotor-respiratory coupling (LRC). Breath-by-breath oxygen uptake (VO2), ventilation (VE), CO2 output (VCO2), tidal volume (VT), fb and end-tidal PCO2 (PETCO2) were determined using a computerized metabolic cart. Arm exercise engendered a higher level of VO2 at each work rate than leg exercise under both FIX and SPNT conditions. However, FIX did not notably affect the VO2 response during either arm or leg exercise at each work rate compared to SPNT. During SPNT a significantly higher fb and lower PETCO2 during arm exercise was found compared with leg exercise up to a fb of 30 breaths.min-1 while VE and VT were nearly the same. During fixed breathing when fb was fixed at a higher rate than during SPNT, a significantly lower PETCO2 was observed during both exercise modes. These results suggest that: 1) FIX breathing does not affect the VO2 response during either arm or leg exercise even when non-synchronization between limb locomotion movement and breathing rate was adopted; 2) at a fb of 30 breaths.min-1 FIX breathing induced a hyperventilation resulting in a lower PETCO2 which was not associated with the metabolic rate during either arm or leg exercise, showing that VE during only leg exercise under the FIX condition was significantly higher than under the SPNT condition.     

Alpha-adrenoreceptor blockade with phenoxybenzamine does not affect the ability of the nose to condition air.

The primary function of the nose is to warm and humidify air. We have previously shown that raising nasal mucosal temperature by immersing feet in warm water increases the amount of water evaporated by the nose as air passes through it (nasal conditioning capacity; Abbott D, Baroody F, Naureckas E, and Naclerio R. Am J Rhinol 15: 41-45, 2001). To investigate further the effect of nasal mucosal temperature on nasal conditioning capacity, we raised the temperature through alpha-adrenoreceptor blockade by intranasally administering phenoxybenzamine. We hypothesized that blocking alpha-adrenoreceptors during inhalation of cold, dry air would lead to an increase in nasal blood flow, surface temperature, and nasal conditioning capacity, as measured by the water gradient. After appropriate pilot studies, we performed a double-blind, placebo-controlled, two-way crossover study in nine nonatopic, healthy subjects by studying the effect of treatment with intranasal phenoxybenzamine. Nasal mucosal temperature increased significantly after administration of phenoxybenzamine and was associated with a significantly smaller net decrease in nasal mucosal temperature after exposure to cold, dry air (P < 0.05). However, there were no significant differences in nasal conditioning capacity between treatments (P > 0.05). Phenoxybenzamine decreased the symptom of rhinorrhea after exposure to cold, dry air (P < 0.05), but congestion was not different between individuals given phenoxybenzamine and placebo (P > 0.05). Our data demonstrate that phenoxybenzamine, despite raising mucosal temperature and not affecting nasal volume, did not affect the ability of the nose to warm and humidify air.     

Beach-spawning fishes, terrestrial eggs, and air breathing

Many fishes have independently evolved beach spawning with oviposition at the water's edge. These include intertidal, subtidal, and estuarine, as well as a few freshwater, species. Their spectacular reproductive behavior at the boundary of water and land has focused attention on adults, but they emerge either briefly or not at all. The need for air breathing is more apparent in the eggs, and the reasons for emergence are more applicable to eggs than to the adults of most beach-spawning fishes. There is little evidence of air breathing in the adults, unless they are regularly emerged at other times as well. Conversely, eggs metabolize in air and show substantial emergence tolerance. We consider beach spawning a form of parental care in fishes. The adults place eggs so they will be emerged into air during part or all of incubation, providing increased temperatures, oxygen availability, and protection. Beach spawning provides habitat segregation at different points in the life history, with air emergence early in the life cycle and a return to water at hatching. The parents take great risks to spawn at the water's edge to give their offspring the most advantageous beginning in life.     

Regenerative ability of gastrocnemius muscle under diabetic condition with special reference to SDH & m-ATPase

The present study analyzes the regeneration of skeletal muscle in streptozotocin (STZ) induced diabetic rats. Two weeks later the gastrocnemius muscle from diabetic rats were transplanted into diabetic and normal host to initiate regeneration and the normal gastrocnemius muscle was transplanted in normal and diabetic hosts for comparison. The regenerates were analyzed after 15 and 30 days of transplantation for histochemical (with respect to SDH and m-ATPase) and 7, 14, 21 and 28 days after transplantation for biochemical studies (with respect to SDH and m-ATPase). Least enzymatic activity and the poorest regenerative ability in case of normal muscle in diabetic host (NM-DbH) and comparatively higher enzymatic activity and better regenerative ability in diabetic muscle in normal host (DbM-NH) was observed. The result of this study strongly supports that the normal host environment is crucial for the muscle recovery.     

Effect of breathing dry air on structure and function of airways

We compared the effect of breathing dry air (0.70 mg H2O/l) with that of breathing room air (8.62 mg H2O/l) in guinea pigs anesthetized with urethane. The data showed that breathing dry air caused a reduction of extravascular water (EVW) in the trachea (P less than 0.01) but not the lung. Structural analysis showed that this water loss occurred from the loose connective tissue of the submucosa. Histamine dose response curves performed on the animals showed that breathing dry air caused an increase in the maximum response (delta max RL) (P less than 0.01) without changing either the dose required to produce 50% of the delta max RL or the ratio of delta max RL to this dose. We conclude that breathing dry air produces an acute reduction of EVW of the loose connective tissue of the airways and an increase in the maximum response to histamine.     

Cardiovascular dynamics inCrocodylus porosus breathing air and during voluntary aerobic dives

Summary Pressure records from the heart and out-flow vessels of the heart ofCrocodylus porosus resolve previously conflicting results, showing that left aortic filling via the foramen of Panizza may occur during both cardiac diastole and systole. Filling of the left aorta during diastole, identified by the asynchrony and comparative shape of pressure events in the left and right aortae, is reconciled more easily with the anatomy, which suggests that the foramen would be occluded by opening of the pocket valves at the base of the right aorta during systole. Filling during systole, indicated when pressure traces in the left and right aortae could be superimposed, was associated with lower systemic pressures, which may occur at the end of a voluntary aerobic dive or can be induced by lowering water temperature or during a long forced dive. To explain this flexibility, we propose that the foramen of Panizza is of variable calibre. The presence of a right-left shunt, in which increased right ventricular pressure leads to blood being diverted from the lungs and exiting the right ventricle via the left aorta, was found to be a frequent though not obligate correlate of voluntary aerobic dives. This contrasts with the previous concept of the shunt as a correlate of diving bradycardia. The magnitude of the shunt is difficult to assess but is likely to be relatively small. This information has allowed some new insights into the functional significance of the complex anatomy of the crocodilian heart and major blood vessels.Abbreviations bpm beats per minute - LAo left aorta (aortic) - LV left ventricle (ventricular) - PA pulmonary artery - RAo right aorta (aortic) - RV right ventricle (ventricular) - SC subclavian artery Deceased     

Ventilation-perfusion lines and gas exchange in liquid breathing: theory

Alveolar exchange of a gas is governed by the ventilation-perfusion ratio (VA/Q) and the Ostwald partition coefficient for that species. We altered the Ostwald coefficients for O2 and CO2 by considering an animal breathing water or a fluorocarbon (FC-80) and studied the effects on gas exchange. Among our conclusions are the following. 1) When the ratio of the CO2 to O2 solubility in the inspirate exceeds the ratio of the O2 to the CO2 slope of the blood dissociation curve, as in water breathing, the VA/Q line becomes concave upward, and elements having a low VA/Q differ from each other more in terms of CO2 than of O2. 2) As the ratio of the CO2 to O2 solubility in the inspired medium increases, CO2 elimination becomes more dependent on perfusion. 3) At times, the same R will prevail in areas having different VA/Q values. 4) The alveolar-to-arterial O2 and CO2 differences resulting from a given VA/Q distribution do not depend on the O2 and CO2 solubility coefficients of the inspired medium, but on the inspired and mixed venous concentrations necessary to maintain adequate arterial gas levels in the presence of different inspired media.     

2'-O,4'-C-ethylene bridged nucleic acid modification enhances pyrimidine motif triplex-forming ability under physiological condition

Since pyrimidine motif triplex DNA is unstable at physiological neutral pH, triplex stabilization at physiological neutral pH is important for improvement of its potential to be applied to various methods in vivo, such as repression of gene expression, mapping of genomic DNA and gene-targeted mutagenesis. For this purpose, we studied the thermodynamic and kinetic effects of a chemical modification, 2'-O,4'-C-ethylene bridged nucleic acid (ENA) modification of triplex-forming oligonucleotide (TFO), on pyrimidine motif triplex formation at physiological neutral pH. Thermodynamic investigations indicated that the modification achieved more than 10-fold increase in the binding constant of the triplex formation. The increased number of the modification in TFO enhanced the increased magnitude of the binding constant. On the basis of the obtained thermodynamic parameters, we suggested that the remarkably increased binding constant by the modification may result from the increased stiffness of TFO in the unbound state. Kinetic studies showed that the considerably decreased dissociation rate constant resulted in the observed increased binding constant by the modification. We conclude that ENA modification of TFO could be a useful chemical modification to promote the triplex formation under physiological neutral condition, and may advance various triplex formation-based methods in vivo.     

无水分胁迫下行作物蒸发散与双涌源能量分配和交换关系

以内蒙古浑善达克沙地人工草地种植的行作物——青贮玉米为研究对象,将FAO-56的双作物系数法与双涌源能量平衡模型相结合,计算了太阳入射能量按叶面积指数（LAI）分配到两个涌源（冠层、土壤表面）的有效能量A_c和A_s、潜热通量λE_c和λE_s以及显热通量H_c和H_s.分析两个涌源在有效能量驱使下的潜热和显热通量相互作用.结果表明,1）在无水分胁迫条件下,冠层H_c与λE_c相互作用使冠层吸收微热平流,强化蒸腾作用,加大蒸腾量.蒸腾（以潜热通量表示）超过冠层有效能量的增量(λE_cⁱ-A_cⁱ).最大值出现在生长发育阶段LAI为0.6的7月15日到LAI为2.4 的8月9日之间,其平均值为4.32 MJ·m^-2·d^-1.2）无水分胁迫情况下,λE_s和H_s相互作用,除强湿润过程后的1~2 d外,其他各天土壤均以低于土壤表面有效能量的速率蒸发.蒸发强度取决于土壤表面有效能量消散为土壤潜热通量的百分比,这个百分比最小值出现在生长中期阶段,其平均值为11.5%;最大值出现在生长初始阶段,其平均值为51.9%.3）两个涌源潜热通量是蒸散过程中能量交换的主要成分,在生长发育、中期、后期阶段转换为两个涌源潜热通量的有效能量均占总能量的83%以上.     

Interaction between PGPR and PGR for water conservation and plant growth attributes under drought condition

Drought is one of the key restraints to agricultural productivity worldwide and is expected to increase further. Drought stress accompanied by reduction in precipitation pose major challenges to future food safety. Strategies should be develop to enhance drought tolerance in crops like chickpea and wheat, in order to enhance their growth and yield. Drought tolerance strategies are costly and time consuming however, recent studies specify that plant growth promoting rhizobacteria (PGPR) and plant growth regulators (PGRs) can help plants to withstand under harsh environmental condition and enable plants to cope with drought stress. PGPR can act as biofertilizer and bioenhancer for different legumes and non-legumes. The use of PGPR and symbiotic microorganisms, may be valuable in developing strategies to assist water conservation in plants. The use of PGPR has been confirmed to be an ecologically sound way of enhancing crop yields by facilitating plant growth through direct or indirect mechanism. The mechanisms of PGPR for water conservation include secretion of exopolysaccharides, biofilm formation, alternation in phytohormone content, improvement in sugar concentration, enhancing availability of micro- and macronutrients and changes in plant functional traits. Similarly, plant growth regulators (PGRs) are specially noticed in actively growing tissues under stress conditions and have been associated in the control of cell division, embryogenesis, root formation, fruit development and ripening, and reactions to biotic and abiotic stresses and upholding water conservation status in plants. Previous studies also suggest that plant metabolites interact with plant physiology under stress condition and impart drought tolerance. Metabolites like, sugars, amino acids, organic acid and polyols play a key role in drought tolerance of crop plants grown under stress condition. It is concluded from the present study that PGRs in combination with PGPR consortium can be an effective formulation to promote plant growth and maintenance of plant turgidity under drought stress. This review is a compilation of the effect of drought stress on crop plants and described interactions between PGPR/PGRs and plant development, knowledge of water conservation and stress release strategies of PGPR and PGRs and the role of plant metabolites in drought tolerance of crop plants. This review also bridges the gaps that summarizes the mechanism of action of PGPR for drought tolerance of crop plants and sustainability of agriculture and applicability of these beneficial rhizobacteria in different agro-ecosystems under drought stress.     

The probable metabolic relation between phosphate uptake and energy storages formations under single-stage oxic condition

To investigate the possible biochemical metabolisms for excess phosphate uptake in a sequencing batch reactor (SBR) with single-stage oxic process, which was reported using glucose as the sole carbon source previously, glucose and acetate were fed to two SBRs as the sole carbon source, respectively. The changes of polyhydroxyalkanoates (PHAs), glycogen and the removal of phosphorus were compared between two SBRs. It was observed that the phosphorus removal efficiency was 91.8–94.4% with glucose, and 23.3–28.5% with acetate, although the former showed much lower accumulations/transformations of PHAs. Instead, the former showed a much higher transformation of glycogen. The facts suggested that glycogen could replace PHAs to supply energy for phosphate uptake under the single-stage oxic condition. Furthermore, the possible biochemical metabolisms were proposed to describe the relation between phosphate uptake and energy storages formations under such a single-stage oxic process. Such a process may serve as a prototype for the development of alternative biological and chemical options for phosphate removal from wastewaters.