401 research outputs found
On the possibility to utilize a PCO Edge 4.2 bi scientific CMOS imager for extended ultra violet and soft X-ray photon detection
No full textA state of the art commercial detector, a PCO Edge 4.2 bi based on a back illuminated sCMOS sensor developed for applications in the visible light/ultra violet regime has been adapted for ultra-high vacuum operations and has been characterized using soft X-ray in the energy range from 30 eV to 1000 eV. The imager features 2048 x 2048 pixel with a pixel size of 6.5 mu m x 6.5 mu m and allows full frame acquisitions at 48 Hz with a dynamic range of 88 dB at a noise level of 1.9 e(-). Spatial resolution and quantum efficiency have been elucidated in the aforementioned energy range at a soft X-ray beam line at Elettra Sincrotrone Trieste. The handiness of the camera as well as its Python library package allows easy and fast integration into the beam line environments of synchrotron sources and free electron lasers
New perspectives in breath-by-breath determination of alveolar gas exchange
No full textAlveolar gas transfer over a given breath (i) was determined in ten subjects at rest and during steady-state cycling at 60, 90 or 120 W as the sum of volume of gas transferred at the mouth plus the changes of the alveolar gas stores. This is given by the gas fraction (F-A) change at constant volume plus the volume change (DeltaV(Ai)) at constant fraction i.e. VAl-1(F-Ai-FAi-1)+F-Ai.(Delta VAi), where VAi-1 is the end-expiratory volume at the beginning of the breath. These quantities, except for VAi-1 can be measured on a single-breath (breath-by-breath) basis and VAi-1 equal to the subject's functional residual capacity (FRC, Auchincloss model). Alternatively, the respiratory cycle can be defined as the interval elapsing between two equal expiratory gas fractions in two successive breaths (Gronlund model G). In this case, F-t1=F-t2 and thus the term VAi-1 (F-Ai-FAi-1) vanishes. In the present study, average alveolar O-2 uptake ((V) over dot O-2,O-A) and CO2 output ((V) over dot CO2,A) were equal in both approaches whereby the mean signal-to-noise ratio (S/N) was 40% larger in G. Other approaches yield steady state S/N values equal to that obtained in G, although they are based on the questionable assumption that the inter-breath variability of alveolar gas transfer is minimal. It is concluded that the only promising approach for assessing "true" single breath alveolar gas transfer is that originally proposed by Gronlund
Energy cost of front-crawl swimming at supra-maximal speeds and underwater torque in young swimmers
No full textThe energy cost of front-crawl swimming (C-s, kJ(.)m(-1)) at maximal voluntary speeds over distances of 50, 100, 200 and 400 m, and the underwater torque (T') were assessed in nine young swimmers (three males and six females; 12-17 years old). C-s was calculated from the ratio of the total metabolic energy (E-s, kJ) spent to the distance covered. E-s was estimated as the sum of the energy derived from alactic (AnAl), lactic (AnL) and aerobic (Aer) processes. In turn, Ant was obtained from the net increase of lactate concentration after exercise, AnAl was assumed to amount to 0.393 kJ(.)kg(-1) of body mass, and Aer was estimated from the maximal aerobic power of the subject. Maximal oxygen consumption was calculated by means of the back-extrapolation technique from the oxygen consumption kinetics recorded during recovery after a 400-m maximal trial. Underwater torque (T', N(.)m), defined as the product of the force with which the feet of a subject lying horizontally in water tends to sink times the distance from the feet to the center of volume of the lungs, was determined by means of an underwater balance. C-s (kJ(.)m(-1)) turned out to be a continuous function of the speed (v, m(.)s(-1)) in both males (C-s = 0.603(.)10(0.228v), r(2) = 0.991, n = 12) and females (C-s = 0.360(.)10(0.339v), r(2) = 0.919; n = 24). A significant relationship was found between T' and C-s at 1.2 m(.)s(-1); C-s = 0.042T' + 0.594, r = 0.839, n = 10, P < 0.05. On the contrary, no significant relationships were found between C-s and T' at faster speeds (1.4 and 1.6 m(.)s(-1)). This suggests that T' is a determinant of C-s only at speeds comparable to that maintained by the subjects over the longest, 400-m distance [mean (SD) 1.20 (0.07) m(.)s(-1)]
Algorithms, modelling and V̇O2kinetics
No full textThis article summarises the pros and cons of different algorithms developed for estimating breath-by-breath (B-by-B) alveolar O(2) transfer (VO 2A) in humans. VO 2A is the difference between O(2) uptake at the mouth and changes in alveolar O(2) stores (∆ VO(2s)), which for any given breath, are equal to the alveolar volume change at constant FAO2/FAiO2 ∆VAi plus the O(2) alveolar fraction change at constant volume [V Ai-1(F Ai - F Ai-1) O2, where V (Ai-1) is the alveolar volume at the beginning of a breath. Therefore, VO 2A can be determined B-by-B provided that V (Ai-1) is: (a) set equal to the subject's functional residual capacity (algorithm of Auchincloss, A) or to zero; (b) measured (optoelectronic plethysmography, OEP); (c) selected according to a procedure that minimises B-by-B variability (algorithm of Busso and Robbins, BR). Alternatively, the respiratory cycle can be redefined as the time between equal FO(2) in two subsequent breaths (algorithm of Grønlund, G), making any assumption of V (Ai-1) unnecessary. All the above methods allow an unbiased estimate of VO2 at steady state, albeit with different precision. Yet the algorithms "per se" affect the parameters describing the B-by-B kinetics during exercise transitions. Among these approaches, BR and G, by increasing the signal-to-noise ratio of the measurements, reduce the number of exercise repetitions necessary to study VO2 kinetics, compared to A approach. OEP and G (though technically challenging and conceptually still debated), thanks to their ability to track ∆VO(2s) changes during the early phase of exercise transitions, appear rather promising for investigating B-by-B gas exchange
Oxygen deficit and oxygen delivery kinetics during submaximal intensity exercise in humans after 14 days of head-down tilt bed rest.
No full textBeat-by-beat Q'aO2 and breath-by-breath V'O2were assessed in ten male subjects (24 ± 3.5 years;78 ± 7.7 kg; 182 ± 5.6 cm) during cycling exercise at50 W before and after a 14-day period of head-down tiltbedrest (HDTBR). O2 deficit (DefO2) was calculated asthe difference between the volume of O2 that would havebeen consumed if a steady state had been immediatelyattained minus that actually taken up during exercise. Q'aO2kinetics was described fitting the data with a non-linearmono-exponential model with time delay. Mean responsetimes (MRT) of V'O2 and Q'aO2 kinetics were then calculated.DefO2 and MRT of V'O2 response did not changeafter HDTBR, whereas MRT of Q'aO2 kinetics increased.The invariance of V'O2 kinetics after HDTBR suggests that,although Q'aO2 response became slower after HDTBR, itdid not affect the kinetics of peripheral gas exchange,which probably remained under the control of local muscularmechanisms
New acquisitions in the assessment of breath-by-breath alveolar gas transfer in humans
No full textWe summarise recent results obtained in testing some of the algorithms utilised for estimating breath-by-breath (BB) alveolar O-2 transfer (VO2A) in humans. VO2A is the difference of the O-2 volume transferred at the mouth minus the alveolar O-2 stores changes. These are given by the alveolar volume change at constant O-2 fraction (FAiO2 DeltaV(Ai)) plus the O-2 alveolar fraction change at constant volume [VAi-1(F-Ai-FAi-1)O-2], where VAi-1 is the alveolar volume at the beginning of the breath i. All these quantities can be measured BB, with the exception of VAi-1, which is usually set equal to the subject's functional residual capacity (FRC) (Auchincloss algorithm, AU). Alternatively, the respiratory cycle can be defined as the time elapsing between two equal O-2 fractions in two subsequent breaths (Gronlund algorithm, GR). In this case, FAiO2=FAi-1O2 and the term VAi-1(F-Ai-FAi-1)O-2 disappears. BB alveolar gas transfer was first determined at rest and during exercise at steady-state. AU and GR showed the same accuracy in estimating alveolar gas transfer; however GR turned out to be significantly more precise than AU. Secondly, the effects of using different VAi-1 values in estimating the time constant of alveolar O-2 uptake ((V)over dotO(2A)) kinetics at the onset of 120 W step exercise were evaluated. (V)over dotO(2A) was calculated by using GR and by using (in AU) VAi-1 values ranging from 0 to FRC +0.5 l. The time constant of the phase II kinetics (tau(2)) of (V)over dotO(2A) increased linearly, with VAi-1 ranging from 36.6 s for VAi-1=0 to 46.8 s for VAi-1=FRC+0.5 l, whereas tau(2) amounted to 34.3 s with GR. We concluded that, when using AU in estimating (V)over dotO(2A) during step exercise transitions, the tau(2) value obtained depends on the assumed value of VAi-1
New perspectives in breath-by- breath determination of alveolar transmembrane gas exchange
No full textMithocondrial coupling in humans: assessment of the P/O2 ratio at the onset of calf exercise
No full textCoupling of oxidation to ATP synthesis (P/O2 ratio) is a critical step in the conversion of carbon substrates to fuel (ATP) for cellular activity. The ability to quantitatively assess mitochondrial coupling in vivo can be a valuable tool for basic research and clinical purposes. At the onset of a square wave moderate exercise, the ratio between absolute amount of phosphocreatine split and O2 deficit (corrected for the amount of O2 released from the body O2 stores and in the absence of lactate production), is the mirror image of the P/O2 ratio. To calculate this value, cardiac output (Q), whole body O2 uptake (VO2), O2 deficit (O2(def)) and high-energy phosphates concentration (by 31P-NMR spectroscopy) in the calf muscles were measured on nine healthy volunteers at rest and during moderate intensity plantar flexion exercise (3.44 +/- 0.73 W per unit active muscle mass). Q and VO2 increased (from 4.68 +/- 1.56 to 5.83 +/- 1.59 l min(-1) and from 0.28 +/- 0.05 to 0.48 +/- 0.09 l min(-1), respectively), while phosphocreatine (PCr) concentration decreased significantly (22 +/- 6%) from rest to steady-state exercise. For each volunteer, "gross" O2(def) was corrected for the individual changes in the venous blood O2 stores (representing 49.9 +/- 9.5% of the gross O2(def)) yielding the "net" O2(def). Resting PCr concentration was estimated from the appropriate spectroscopy data. The so calculated P/O2 ratio amounted on average to 4.24 +/- 0.13 and was, in all nine subjects, very close to the literature values obtained directly on intact skeletal muscle. This unfolds the prospect of a non-invasive tool to quantitatively study mitochondrial coupling in vivo
Assessment of breath – to - breath alveolar gas transfer: a comparison of two procedures
No full textAlveolar oxygen uptake kinetics with step, impulse and ramp exercise in humans
No full textThe breath-by-breath V’O2A of five male subjects (21.2 years ±3.2; 78.8 kg ±5.9; 179.6 cm ±5.8) was measured during a cycling exercise. Starting from a 10 W baseline, the subjects performed (i) ON and OFF step transitions (ST-ON; ST-OFF) to 50, 90, and 130 W; (ii) a ramp (R) exercise with work rate gradually increasing by 20 W/min; (iii) impulse transitions (I) to 250 and 410 W lasting 10 and 5 s, respectively. The V’O2A data was modelled using non-linear weighted least square regressions. The amplitudes of the V’O2A response turned out to be proportional to the input work rate intensities in all the modalities of exercise. Time constants (s) and time delays (td) of ST-ON and R responses were not significantly different, whereas those of ST-OFF were characterised by longer s values. s and td of I responses turned _ out to be identical to those of ST-ON when the V’O2A responses were fitted using a five-component model. These results suggest that: (i) the system controlling alveolar gas exchange behaves linearly when it is forced by ST and R inputs (the ON and OFF phases being considered separate); (ii) the analysis of the I response depends strongly on the models selected to fit the V’O2A data. The asymmetry between the ON and OFF responses mirrors that found between the splitting and resynthesis rates of phosphocreatine, and these results support the notion that phosphocreatine could be the main controller of the skeletal muscle respiratory turnover in human
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