Acoustical estimation of impact of single dive in closed-type breathing apparatus on human ventilatory lung function

Diving renders negative influence on human respiratory system especially when oxygen breathing apparatus is used. Spirometry indexes, traditionally used to estimate ventilator lung function, have poor sensitivity to toxic effect of hyperbaric hyperoxia. The objective is to study possibility of revealing minimum impairments of lung ventilator function in oxygen divers by analysis of forced expiratory tracheal noise duration. 48 divers were studied before and after single shallow water dive in oxygen closed-type breathing apparatus. A significant drop of FVC, FEV1 over the group as a whole was found after dive however being in the limits of norm. The significant increase of individual forced expiratory tracheal noise duration, exceeding the natural variability limit (19.6%, p < 0.05), was found in 10 subjects (20.8%). Three of them during dive had respiratory symptoms characteristic for initial manifestations of pulmonary oxygen poisoning. The asymptomatic reversible increase of forced expiratory tracheal noise duration in the rest 7 divers was interpreted as a sign of hidden phase of hyperbaric hyperoxia effect.     

The effects of breathing pattern training on ventilatory function in patients with COPD

The purpose of this study was to assess the effects of a particular breathing pattern training (BPT) on forced expiratory volume during the first second (FEV₁) and forced vital capacity (FVC) in patients with chronic obstructive pulmonary disease (COPD). The subjects adjusted each breath to a target breath displayed on a video screen, by using visual feedback. This target was chosen in an individual sample recorded at rest. We used a randomized, controlled group design. Twenty patients with stable COPD, FEV₁ less than 1.5 liters, undergoing a traditional rehabilitation program were randomly assigned to the BPT group or to the control group. Each BPT subject underwent 30–35 training sessions spread out over four weeks, in addition to the traditional program. FEV₁ and FVC were performed before and after this program. ANOVAs showed that FEV₁ and FVC significantly improved in BPT subjects, with a mean percent increase of 22% and 19%, respectively. Corresponding changes in controls were not significant. This study showed short-term increases in FEV₁ and FVC in COPD patients practicing BPT in addition to respiratory rehabilitation, in comparison with controls. Further studies should incorporate outcome data to clarify the mechanisms and the duration of this effect.The authors express their gratitude to Philippe Carrias, Elizabeth Maclet, Françoise Tulane, and Bernard Cossalter for their contribution to this study, as well as to Michèle Delaire for her technical assistance.     

Effect of paced breathing on ventilatory and cardiovascular variability parameters during short-term investigations of autonomic function

Paced breathing (PB) around 0.25 Hz has been advocated as a means to avoid confounding and to standardize measurements in short-term investigations of autonomic cardiovascular regulation. Controversy remains, however, as to whether it causes any alteration in autonomic control. We addressed this issue in 40 supine, middle-aged, healthy volunteers by assessing the changes induced by PB (0.25 Hz for 8 min) on 1) ventilatory parameters, 2) the indexes of autonomic control of cardiovascular function, and 3) the spectral indexes of cardiovascular variability. Subjects were grouped into group 1 (n = 31), if spontaneous breathing was regular and within the high-frequency (HF) band (0.15-0.45 Hz), or group 2 (n = 9), if it was irregular or slow (< 0.15 Hz). In both groups, PB was accompanied by an increase in minute ventilation (both groups, P < 0.01), whereas tidal volume increased only in group 1 (P = 0.0003). End-tidal CO2 decreased by [median (lower quartile, upper quartile)] -0.2 (-0.5, -0.1)% (group 1, P < 0.0001) and -0.6 (-0.8, -0.5)% (group 2, P = 0.008). Mean R-R interval and systolic and diastolic pressure remained remarkably stable (all P > or = 0.13, both groups). No significant changes were observed in spectral indexes of R-R and pressure variability (all P > or = 0.12, measured only in group 1 to avoid confounding), except in the HF power of pressure signals, which significantly increased (all P < 0.05) in association with increased tidal volume. In conclusion, PB at 0.25 Hz causes a slight hyperventilation and does not affect traditional indexes of autonomic control or, in subjects with spontaneous breathing in the HF band, most relevant spectral indexes of cardiovascular variability. These findings support the notion that PB does not alter cardiovascular autonomic regulation compared with spontaneous breathing.     

Effects of human pregnancy on cardiac autonomic function above and below the ventilatory threshold

This study examined the effectsof human pregnancy on heart rate variability (HRV), spontaneousbaroreflex (SBR) sensitivity, and plasma catecholamines at rest andduring exercise. Subjects were 14 healthy, physically active pregnantwomen (PG; mean gestational age = 33.9 ± 1.0 wk). Resultswere compared with an age-matched nonpregnant control group (NPG;n = 14) with similar characteristics. Theelectrocardiographic R-wave-R-wave interval and systolic blood pressure (via finger plethysmograph) were measured on a beat-to-beat basis at rest and during upright cycling at 60 and 110% of the ventilatory threshold (T_vent). Parasympathetic nervoussystem (PNS) modulation (as reflected by HRV high-frequency/total power and SBR slope) was significantly reduced at rest in the PG vs. the NPG.During exercise, PNS modulation decreased significantly in both groups,but the magnitude of PNS withdrawal from rest to 110%T_vent was smaller in the PG vs. NPG. Sympathetic nervous system (SNS) modulation (reflected by the low-frequencypower-to-high-frequency power ratio) increased above resting values at60 and 110% T_vent in the NPG. SNS modulation at 110%T_vent was significantly lower in the PG compared with theNPG. Plasma norepinephrine and epinephrine levels were also lower at110% T_vent in the PG. It was concluded that healthypregnant women exhibit lower PNS modulation at rest and blunted SNSmodulation during exercise above T_vent in late gestation.

     

The pattern of breathing and the ventilatory response to breathing through a tube and to physical exercise in sport divers

Well-trained divers can be expected to differ from healthy controls in their ventilatory response to breathing through a tube and to physical exercise. Therefore, we measured their minute ventilation (VE) at rest and during breathing through a tube combined with two levels of physical exercise (1 or 2 W.kg body weight-1). For breathing through a tube an additional dead space of 600 ml was used. All divers were trained in the breath-hold technique and in the use of the breathing apparatus. Their mean period of training as divers was 9 +/- 6 years. The approximate age of the subjects was 25 years. The pattern of breathing and the oxygen uptake were measured by spirometer, the end-tidal concentration of CO2 was measured and all experiments were carried out above sea level. The ventilation of the divers at rest was comparable to that of the controls. During physical exercise it was smaller whether during breathing through a tube or not. The inadequate increase of VE during exercise in divers was associated with hypercapnia only at a higher physical work intensity (of 2 W.kg-1). This finding is interpreted as a lower chemoregulatory response to the combined stimuli of hypercapnia, hypoxia and physical exercise. In some situations significant bradypnoea and higher tidal volumes were found in the divers.     

Evaluation of a semi-closed underwater breathing apparatus, the "eOBA"

Semi-closed underwater breathing apparatus has commonly been used among military and commercial divers, but never available for recreational divers because of complicated operations, difficulties of maintenance, and expensiveness. Nippon Sanso K.K. has newly deployed a semi-closed circuit underwater breathing apparatus called the "eOBA". It is especially designed for divers to enjoy shallow (max. 5 m) and short (10 min.) dives. This eOBA was evaluated from manned testing based on physiological requirements for the apparatus. Four male and four female subjects participated in the three test trials. Subjects maintained their position at the depths of 2 m and 4 m for 10 min. and e exercised on the underwater ergometer at the depth of 2.4 m. The pressure at the mouthpiece, tidal volume, breathing rate, the inspired O2 level, CO2 level were monitored on breath-by-breath basis. The inspired O2 level ranged from 45% (at exercise) to 60% (at rest) and the inspired CO2 level were kept less than 1.0% in the most cases. The P-V loop indicated relatively little external work of breathing (less than 0.1 kg.m/l) and allowable peak pressures (less than 25cmH2O). Results show that the eOBA meets the standards sufficiently under the test conditions and is a safe apparatus for recreational divers if it is properly used.     

Development of a semi-closed underwater breathing apparatus, the "eOBA"

Nippon Sanso K.K developed a compact semi-closed underwater breathing apparatus, the eOBA. It consists of a mouthpiece, manifold with a purge valve, two spring-loaded flexible tubes, a small CO2 absorbent canister (net wt. = 190g), and two compact high pressure bottles (50ccx2: 190kg/cm2: 80%O2, 20%N2) with a regulator which supplies the gas at the constant flow rate of 1.5 l/min and lasts for 10 min. Thus, a counterlung is not incorporated. However, spring-loaded tubes act as a counterlung since its volume increases to 3.5 l when fully inflated. Dives to a depth of 5m are also recommended because of no bypass valve. This new eOBA was tested using the mechanical breathing machine and CO2 supply system to the circuit. For the various combinations of tidal volumes (0.5-2.5 l) and respiratory rates (10-20 breaths/min), the pressure at the mouthpiece, respiratory volume and the CO2 level were continuously monitored. The CO2 absorption rates were then calculated. The thin sloping P-V loops demonstrate that the eOBA is a flow dependent type of apparatus. It was found that the external work of breathing (0.1 kg.m/l at 30 l/min) were allowable. The CO2 absorption rates were sufficient when minute ventilation increased to 30 l/min. Thus, results show that the eOBA must be suitable for shallow and short dives.     

Mitogenome phylogenetics: the impact of using single regions and partitioning schemes on topology, substitution rate and divergence time estimation

The availability of mitochondrial genome sequences is growing as a result of recent technological advances in molecular biology. In phylogenetic analyses, the complete mitogenome is increasingly becoming the marker of choice, usually providing better phylogenetic resolution and precision relative to traditional markers such as cytochrome b (CYTB) and the control region (CR). In some cases, the differences in phylogenetic estimates between mitogenomic and single-gene markers have yielded incongruent conclusions. By comparing phylogenetic estimates made from different genes, we identified the most informative mitochondrial regions and evaluated the minimum amount of data necessary to reproduce the same results as the mitogenome. We compared results among individual genes and the mitogenome for recently published complete mitogenome datasets of selected delphinids (Delphinidae) and killer whales (genus Orcinus). Using Bayesian phylogenetic methods, we investigated differences in estimation of topologies, divergence dates, and clock-like behavior among genes for both datasets. Although the most informative regions were not the same for each taxonomic group (COX1, CYTB, ND3 and ATP6 for Orcinus, and ND1, COX1 and ND4 for Delphinidae), in both cases they were equivalent to less than a quarter of the complete mitogenome. This suggests that gene information content can vary among groups, but can be adequately represented by a portion of the complete sequence. Although our results indicate that complete mitogenomes provide the highest phylogenetic resolution and most precise date estimates, a minimum amount of data can be selected using our approach when the complete sequence is unavailable. Studies based on single genes can benefit from the addition of a few more mitochondrial markers, producing topologies and date estimates similar to those obtained using the entire mitogenome.     

Impact responses of the flexed human knee using a deformable impact interface

Blunt impact trauma to the patellofemoral joint during car accidents, sporting activities, and falls can produce a range of injuries to the knee joint, including gross bone fracture, soft tissue injury, and/or microinjuries to bone and soft tissue. Currently, the only well-established knee injury criterion applies to knee impacts suffered during car accidents. This criterion is based solely on the peak impact load delivered to seated cadavers having a single knee flexion angle. More recent studies, however, suggest that the injury potential, its location, and the characteristics of the damage are also a function of knee flexion angle and the stiffness of the impacting structure. For example, at low flexion angles, fractures of the distal patella are common with a rigid impact interface, while at high flexion angles splitting of the femoral condyles is more evident. Low stiffness impact surfaces have been previously shown to distribute impact loads over the anterior surface of the patella to help mitigate gross and microscopic injuries in the 90 deg flexed knee. The objective of the current study was to determine if a deformable impact interface would just as effectively mitigate gross and microscopic injuries to the knee at various flexion angles. Paired experiments were conducted on contralateral knees of 18 human cadavers at three flexion angles (60, 90, 120 deg). One knee was subjected to a fracture level impact experiment with a rigid impactor, and the opposite knee was impacted with a deformable interface (3.3 MPa crush strength honeycomb material) to the same load. This (deformable) impact interface was effective at mitigating gross bone fractures at approximately 5 kN at all flexion angles, but the frequency of split fracture of the femoral condyles may not have been significantly reduced at 120 deg flexion. On the other hand, this deformable interface was not effective in mitigating microscopic injuries observed for all knee flexion angles. These new data, in concert with the existing literature, suggest the chosen impact interface was not optimal for knee injury protection in that fracture and other minor injuries were still produced. For example, in 18 cadavers a total of 20 gross fractures and 20 subfracture injuries were produced with a rigid interface and 5 gross fractures and 21 subfracture injuries with the deformable interface selected for the current study. Additional studies will be needed to optimize the knee impact interface for protection against gross and microscopic injuries to the knee.     

Assay of centromere function using a human artificial chromosome

In order to define a functional human centromere sequence, an artificial chromosome was constructed as a reproducible DNA molecule. Mammalian telomere repeats and a selectable marker were introduced into yeast artificial chromosomes (YACs) containing alphoid DNA from the centromere region of human chromosome 21 in a recombination-deficient yeast host. When these modified YACs were introduced into cultured human cells, a YAC with the alphoid DNA from the α21-I locus, containing CENP-B boxes at a high frequency and a regular repeat array, efficiently formed minichromosomes that were maintained stably in the absence of selection and bound CENP-A, CENP-B, CENP-C and CENP-E. The minichromosomes, 1–5 Mb in size and composed of multimers of the introduced YAC DNA, aligned at metaphase plates and segregated to opposite poles correctly in anaphase. Extensive cytological analyses strongly suggested that the minichromosomes had not acquired host sequences and were formed in all cases by a de novo mechanism. In contrast, minichromosomes were never produced with a modified YAC containing alphoid DNA from the α21-II locus, which contains no CENP-B boxes and has a less regular sequence arrangement. We conclude that α21-I alphoid DNA can induce de novo assembly of active centromere/kinetochore structures on minichromosomes. Received: 22 August 1998 / Accepted: 28 August 1998     

The impact of high CO2 concentrations on the structure and function of the photosynthetic apparatus and the role of polyamines

Here we examined the influence of high CO2 concentrations on the structure and functioning of the photosynthetic apparatus in the unicellular green alga Scenedesmus obliquus. Presented in this work are: chlorophyll (Chl) a fluorescence induction kinetics, measurements of photosynthetic and respiration rates, estimation of Chl a/Chl b ratios, isolation and quantitative assessment of the photosynthetic subcomplexes, quantitative analyses of thylakoid bound polyamines, and experiments with exogenously supplied polyamines with cultures grown in low- and high-CO2 concentrations. Together, they indicated that high-CO2 concentrations affect polyamines and, more specifically, increase the thylakoid bound putrescine (PUT) level that leads to an increase of the active reaction center density combined with a decrease in the LHCII-size and the ratio of LHCII-oligomeres/LHCII-monomeres. This reorganization of the photosynthetic apparatus leads to enhanced photosynthetic rates, which in combination with the high-CO2 concentrations, leads to an immense increase of biomass (800%). Further incubation for longer time periods under the same conditions produces, due to an increase in cell density, a self-shading effect and photoadaptation of the photosynthetic apparatus to low light conditions and therefore also results in reduction of the high-CO2 effect. The photoadaptation of the photosynthetic apparatus to high-light conditions (Kotzabasis et al. 1999) and the acclimation to high-CO2 concentrations (present work) lead to the same changes in the structure and function of the photosynthetic apparatus. These changes could be induced or inhibited through the manipulation of intracellular polyamines, especially through the putrescine/spermine ratio. The possibility that polyamines influence the photoadaptation of the photosynthetic apparatus and its acclimation to high-CO2 concentrations through a common mechanism is discussed.