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.     

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.     

Working ability between air and trimix breathing gas under 8 ATA air condition

Pneumatic caisson work in Japan has come into operation since 1924. Afterward, this technique of compressed air work has been widely utilized in the construction of foundation basements, shafts of the bottom tunnel shields for subway and so forth. While using this technique of compressed air work means that workers have to be exposed to hyperbaric environment, this technique has risks of not only decompression sickness (DCS) but also toxicity of poisonous gas and/or oxygen deficiency. However, this technique is independent of city construction work and the operation of compressed air work higher than 5ATA (4.0 kg/cm2G) is actually been planning recently. Accordingly unmanned caisson work is considered as a better technique for such higher pressurized work, even though workers must enter into hyperbaric working fields for maintenance or repair of unmanned operated machinery and materials. This research is to establish the safe work under hyperbaric air environment at 8ATA.     

Influence of breathing pattern on oxygen exchange during hypoxia and exercise.

During hypoxia, arterial oxygen saturation (SaO2) measured by ear oximeter shows cyclic fluctuations which are related to the pattern and rate of breathing. Continuous recordings of SaO2 may be corrected for distortion, due to circulatory transport, to yield approximate values for pulmonary end-capillary saturation (Sc'O2). This permits calculation of the corresponding end-capillary PO2 (Pc'O2). We have used this technique to study the effect of spontaneous and imposed breathing patterns on mean Pc'O2, amplitude of Pc'O2 (delta Pc'O2) and minute ventilation (VE). The studies were conducted during mild hypoxia, at rest and exercise. The amplitude of delta Pc'O2 is inversely related to breathing frequency. When frequency is constant, patterns with with prolonged expiration or end-expiratory pauses produce large delta Pc'O2 and greater VE. This effect is reversed with prolonged inspiration or end-inspiratory pauses. Spontaneous breathing patterns produced smaller delta Pc'O2, with lower VE than imposed patterns. These findings are compatible with animal studies which suggest the magnitude of PaO2 fluctuations produced by the breathing pattern may act as a feedback stimulus to ventilation. The breathing patterns, which are spontaneously chosen, produce the minimum delta Pc'O2 and VE.     

Gas exchange during separate diaphragm and intercostal muscle breathing.

In patients with diaphragm paralysis, ventilation to the basal lung zones is reduced, whereas in patients with paralysis of the rib cage muscles, ventilation to the upper lung zones in reduced. Inspiration produced by either rib cage muscle or diaphragm contraction alone, therefore, may result in mismatching of ventilation and perfusion and in gas-exchange impairment. To test this hypothesis, we assessed gas exchange in 11 anesthetized dogs during ventilation produced by either diaphragm or intercostal muscle contraction alone. Diaphragm activation was achieved by phrenic nerve stimulation. Intercostal muscle activation was accomplished by electrical stimulation by using electrodes positioned epidurally at the T(2) spinal cord level. Stimulation parameters were adjusted to provide a constant tidal volume and inspiratory flow rate. During diaphragm (D) and intercostal muscle breathing (IC), mean arterial Po(2) was 97.1 +/- 2.1 and 88.1 +/- 2.7 Torr, respectively (P < 0.01). Arterial Pco(2) was lower during D than during IC (32.6 +/- 1.4 and 36.6 +/- 1.8 Torr, respectively; P < 0.05). During IC, oxygen consumption was also higher than that during D (0.13 +/- 0.01 and 0.09 +/- 0.01 l/min, respectively; P < 0.05). The alveolar-arterial oxygen difference was 11.3 +/- 1.9 and 7.7 +/- 1.0 Torr (P < 0.01) during IC and D, respectively. These results indicate that diaphragm breathing is significantly more efficient than intercostal muscle breathing. However, despite marked differences in the pattern of inspiratory muscle contraction, the distribution of ventilation remains well matched to pulmonary perfusion resulting in preservation of normal gas exchange.     

The influence of elevated C02 on growth and age-related changes in leaf gas exchange

Rumex obtusifolius plants were grown for several months in daylitenvironment chambers (Solardomes) force-ventilated with aircontaining 350 or 600 µ;mol mol^–1 C0₂. ElevatedCO₂ was found to accelerate the natural ontogenic decline inphotosynthesis, but did not reduce leaf duration. In both CO₂treatments photosynthetic rates declined progressively withincreasing leaf age, the decline being greater for plants grownin elevated C0₂ such that rates became lower than in ambientCO₂. The degree of CO₂-induced photosynthetic down-regulationas determined by A/C₁ analysis was found to be dependent onleaf age. The major contribution to the decline in photosynthesiswas likely to be a reduction in Rubisco activity as changesin stomataland mesophyll limitations were small. Instantaneouswater use efficiency (WUE₁) was greater for plants in elevatedCO₂, but these values declined rapidly with leaf age, whereasin ambient CO₂ values were always lower, but were maintainedfor longer. Growth analysis indicated an increased root:-shootratio for plants grown in elevated CO₂, this occurring almostentirely as a result of increased root growth. Greater rootproliferation and increased WUE₁, are characteristics whichshould give this persistent and troublesome weed an increasedcompetitive advantage under projected conditions of climatechange Key words: tusifoliu, elevated CO₂, gas exchange, leaf age, senescence     

Breath-by-breath gas exchange kinetics during constant-load work

In order to study respiratory transients during exercise, we examined breath-by-breath gas exchange kinetics during constant-load work. Five male subjects performed cycle ergometer tests which 6 min of constant-load work (150, 200, 250W) followed 50W base-line work. VCO2 and VO2 measured at the mouth ((VCO2)E, (VO2)E) and estimated at the alveolar level ((VCO2)A, (VO2)A) were computed breath-by-breath. The kinetic parameter (time constant) of first- and second-order exponential model was estimated using non-linear least-squares method. Our results demonstrated that a relative stability of PETO2, PETCO2, and R at their control values in the first phase. Independent of work intensities, breath-by-breath variation in gas exchange measured at the mouth was larger than those in gas exchange estimated at the alveolar level both at a non-steady state and a steady state. The time constants of (VO2)A and (VO2)E were varied with increase of work load intensity.     

Measurement of respiratory gas exchange during artificial respiration

This paper reports a new system for the continuous measurements of respiratory gas exchange in ventilated subjects. It involves mixing some of the inspired gas with all of the expired gas and withdrawing the mixture at a constant rate through a dry gas meter that measures the flow. The inspired gas and expired gas mixtures are sampled and O2 and CO2 concentrations measured with a paramagnetic gas analyzer and a capnograph, respectively, to an accuracy of 0.01%. Evidence is presented to confirm the necessary stability and sensitivity of these instruments. It is possible to use the system with high inspired O2 concentrations, with ventilators where there is incomplete separation of inspired and expired gas, and in the presence of intermittent mandatory ventilation, positive end-expiratory pressure, and continuous airway pressure. The system was compared with the N2-dilution method and with the collection of expired gas in a Douglas bag in dog experiments and with patients in the intensive therapy unit. Excellent correlation between these methods was found in all circumstances.     

Periodic breathing in the crocodile, Crocodylus niloticus: consequences for the gas exchange ratio and control of breathing.

The ventilatory pattern in the Nile crocodile consists of episodes of breathing, interrupted by periods of breath-holding, the latter occupying 80% of total time during normal breathing at 25 degrees C. End-tidal gas composition varied with the periodic breathing but PO2 was always high (PO2 less than 110 torr) and PCO2 low (PCO2 less than 25 torr). The alveolar gas exchange ratio, RE, was very low during the non-ventilatory periods (RE congruent to 0.5), but increased markedly during ventilation. Breathing of hypoxic and hpercapnic gases caused a pronounced decrease in the duration of breath-holds. Hypercapnia decreased breathing frequency during ventilatory periods, but increased tidal volume. The results are discussed in relation to the practice of prolonged breath-holding associated with diving in crocodiles.     

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     

The incidence of increased pollen concentrations during rainfall in the air of London

Summary Data from a Burkard volumetric sampler in a densely built-up area of North-central London, England are used to investigate the effects of rainfall on pollen concentrtions over four years. Pollen counts generally decreased with rainfall, although several episodes of increased pollen concentration have been recorded in London following the onset of precipitation.Pollen concentration is recorded as two-hourly pollen counts, while hourly records of nine meteorological variables, including rainfall amount and intensity, are obtained from the London site of the Meteorological Office. The two-hourly changes in concentration that take place during both «normal» rainfall events and during those displaying marked increases in pollen concentration are examined in relation to the patterns of rainfall, the wind regimes, synoptic situation and general characteristics of urban areas.The influence of rainfall in removing pollen from the air is also examined in relation to the rainfall intensity and size of pollen grains for selected taxa.