scholarly journals Discontinuous gas exchange in Madagascan hissing cockroaches is not a consequence of hysteresis around a fixed PCO2 threshold

Author(s):  
Tormod T. C. Rowe ◽  
Martin S. Gutbrod ◽  
Philip G. D. Matthews

It has been hypothesised that insects display discontinuous gas-exchange cycles (DGCs) due to hysteresis in their ventilatory control, where CO2-sensitive respiratory chemoreceptors respond to changes in hemolymph PCO2 only after some delay. If correct, DGCs would be a manifestation of an unstable feedback loop between chemoreceptors and ventilation causing PCO2 to oscillate around some fixed threshold value: PCO2 above this ventilatory threshold would stimulate excessive hyperventilation, driving PCO2 below the threshold and causing a subsequent apnoea. This hypothesis was tested by implanting micro-optodes into the hemocoel of Madagascar hissing cockroaches and measuring hemolymph PO2 and PCO2 simultaneously during continuous and discontinuous gas exchange. The mean hemolymph PCO2 of 1.9 kPa measured during continuous gas exchange was assumed to represent the threshold level stimulating ventilation, and this was compared with PCO2 levels recorded during DGCs elicited by decapitation. Cockroaches were also exposed to hypoxic (PO2 10 kPa) and hypercapnic (PCO2 2 kPa) gas mixtures to manipulate hemolymph PO2 and PCO2. Decapitated cockroaches maintained DGCs even when their hemolymph PCO2 was forced above or below the putative ∼2 kPa ventilation threshold, demonstrating that the characteristic oscillation between apnoea and gas exchange is not driven by a lag between changing hemolymph PCO2 and a PCO2 chemoreceptor with a fixed ventilatory threshold. However, it was observed that the gas exchange periods within the DGC were altered to enhance O2 uptake and CO2 release during hypoxia and hypercapnia exposure. This indicates that while respiratory chemoreceptors do modulate ventilatory activity in response to hemolymph gas levels, their role in initiating or terminating the gas exchange periods within the DGC remains unclear.

Author(s):  
S.B. Egorov ◽  
R.I. Gorbachev

Предложена вероятностная модель работы автономного обнаружителя на этапе ожидания сигнала, когда момент появления сигнала неизвестен и по этой причине решающая статистика, сравниваемая с порогом, формируется непрерывно во времени в режиме скользящего окна . Ложная тревога в этом случае эквивалентна появлению хотя бы одного выброса помехового индикаторного процесса выше порога на максимально возможном интервале ожидания сигнала. Высота порога такова, что ложные выбросы являются редкими событиями, подчиняющимися закону Пуассона. На основе такой вероятностной модели показано, что вероятность ложной тревоги равна среднему числу ложных выбросов на максимально возможном интервале ожидания сигнала. Для обнаружителей с нормализованным индикаторным процессом получены соотношения, определяющие порог селекции сигнала по заданной вероятности ложной тревоги на заданном максимально возможном интервале ожидания сигнала. Показано, что в определении порога важную роль играет средняя квадратичная частота флюктуаций помехового индикаторного процесса. Дана численная оценка увеличения порога по сравнению с его значением, определенным по вероятности ложной тревоги в точке . Показано, что определение порога по предложенной методике особенно актуально для обнаружителей, работающих в длительном автономном режиме.This article proposes a probabilistic model of the autonomous detector in standby mode, when the moment of the signal appearance is unknown and for this reason the decisive statistics is generated continuously in time in the sliding window mode and compared with the threshold value. In this case, false alarm is equivalent to the appearance of at least one outlier of the jamming indicator process above the threshold at the maximum possible signal waiting interval. The threshold level match case when the false alarm are rare events and obey the Poisson law of distribution. Based on such a probabilistic model, we show that the probability of a false alarm is equal to the average number of false emissions at the maximum possible interval for a signal waiting. For detectors with a normalized indicator process, are obtained relations that determine the threshold for signal selection by a given probability of false alarm at a given maximum possible signal waiting interval. It is shown that in determining the threshold, the mean square frequency of fluctuations of the interference indicator process plays an important role. Also, a numerical estimate of the increase in the threshold is given compared with its value determined by the probability of false alarm at a point . It is shown that the determination of the threshold by the proposed method is especially relevant for detectors operating in a long autonomous mode.


1987 ◽  
Vol 26 (03) ◽  
pp. 143-146 ◽  
Author(s):  
H. Fill ◽  
M. Oberladstätter ◽  
J. W. Krzesniak

The mean activity concentration of1311 during inhalation by the nuclear medicine personnel was measured at therapeutic activity applications of 22 GBq (600 mCi) per week. The activity concentration reached its maximum in the exhaled air of the patients 2.5 to 4 hours after oral application. The normalized maximum was between 2 • 10−5 and 2 • 10−3 Bq-m−3 per administered Bq. The mean activity concentration of1311 inhaled by the personnel was 28 to 1300 Bq-m−3 (0.8 to 35 nCi-rrf−3). From this the1311 uptake per year was estimated to be 30 to 400 kBq/a (x̄ = 250, SD = 50%). The maximum permitted uptake from air per year is, according to the German and Austrian radiation protection ordinances 22/21 µiCi/a (= 8 • 105 Bq/a). At maximum 50% and, on the average, 30% of this threshold value are reached. The length of stay of the personnel in the patient rooms is already now limited to such an extent that 10% of the maximum permissible whole-body dose for external radiation is not exceeded. Therefore, increased attention should be paid also to radiation exposure by inhalation.


2020 ◽  
Vol 2020 (1) ◽  
Author(s):  
Xiangjun Dai ◽  
Suli Wang ◽  
Weizhi Xiong ◽  
Ni Li

Abstract We propose and study a stochastic delay single-species population system in polluted environment with psychological effect and pulse toxicant input. We establish sufficient conditions for the extinction, nonpersistence in the mean, weak persistence, and strong persistence of the single-species population and obtain the threshold value between extinction and weak persistence. Finally, we confirm the efficiency of the main results by numerical simulations.


2006 ◽  
Vol 31 (5) ◽  
pp. 612-620 ◽  
Author(s):  
Lixin Wang ◽  
Takahiro Yoshikawa ◽  
Taketaka Hara ◽  
Hayato Nakao ◽  
Takashi Suzuki ◽  
...  

Various near-infrared spectroscopy (NIRS) variables have been used to estimate muscle lactate threshold (LT), but no study has determined which common NIRS variable best reflects muscle estimated LT. Establishing the inflection point of 2 regression lines for deoxyhaemoglobin (ΔHHbi.p.), oxyhaemoglobin (ΔO2Hbi.p.), and tissue oxygenation index (TOIi.p.), as well as for blood lactate concentration, we then investigated the relationships between NIRS variables and ventilatory threshold (VT), LT, or maximal tissue hemoglobin index (nTHImax) during incremental cycling exercise. ΔHHbi.p. and TOIi.p. could be determined for all 15 subjects, but ΔO2Hbi.p. was determined for only 11 subjects. The mean absolute values for the 2 measurable slopes of the 2 continuous linear regression lines exhibited increased changes in 3 NIRS variables. The workload and VO2 at ΔO2Hbi.p. and nTHImax were greater than those at VT, LT, ΔHHbi.p., and TOIi.p.. For workload and VO2, ΔHHbi.p. was correlated with VT and LT, whereas ΔO2Hbi.p. was correlated with nTHImax, and TOIi.p. with VT and nTHImax. These findings indicate that ΔO2Hb strongly corresponds with local perfusion, and TOI corresponds with both local perfusion and deoxygenation, but that ΔHHb can exactly determine deoxygenation changes and reflect O2 metabolic dynamics. The finding of strongest correlations between ΔHHb and VT or LT indicates that ΔHHb is the best variable for muscle LT estimation.


1986 ◽  
Vol 60 (5) ◽  
pp. 1590-1598 ◽  
Author(s):  
M. D. Hammond ◽  
G. E. Gale ◽  
K. S. Kapitan ◽  
A. Ries ◽  
P. D. Wagner

Previous studies have shown both worsening ventilation-perfusion (VA/Q) relationships and the development of diffusion limitation during exercise at simulated altitude and suggested that similar changes could occur even at sea level. We used the multiple-inert gas-elimination technique to further study gas exchange during exercise in healthy subjects at sea level. Mixed expired and arterial respiratory and inert gas tensions, cardiac output, heart rate, minute ventilation, respiratory rate, and blood temperature were recorded at rest and during steady-state exercise in the following order: rest, minimal exercise (75 W), heavy exercise (300 W), heavy exercise breathing 100% O2, repeat rest, moderate exercise (225 W), and light exercise (150 W). Alveolar-to-arterial O2 tension difference increased linearly with O2 uptake (VO2) (6.1 Torr X min-1 X 1(-1) VO2). This could be fully explained by measured VA/Q inequality at mean VO2 less than 2.5 l X min-1. At higher VO2, the increase in alveolar-to-arterial O2 tension difference could not be explained by VA/Q inequality alone, suggesting the development of diffusion limitation. VA/Q inequality increased significantly during exercise (mean log SD of perfusion increased from 0.28 +/- 0.13 at rest to 0.58 +/- 0.30 at VO2 = 4.0 l X min-1, P less than 0.01). This increase was not reversed by 100% O2 breathing and appeared to persist at least transiently following exercise. These results confirm and extend the earlier suggestions (8, 21) of increasing VA/Q inequality and O2 diffusion limitation during heavy exercise at sea level in normal subjects and demonstrate that these changes are independent of the order of performance of exercise.


1978 ◽  
Vol 45 (5) ◽  
pp. 666-673 ◽  
Author(s):  
A. Bidani ◽  
E. D. Crandall

A quantitative analysis of the reaction and transport processes that occur in blood during and after gas exchange has been used to investigate mechanisms that might account for positive alveolar-mixed venous (A-V) and alveolar-arterial (Aa) PCO2 differences during rebreathing. The analysis was used to determine PCO2 changes that take place in blood as it travels from veins to arteries under conditions in which no CO2 is exchanged in the lung. The predicted A-V and Aa PCO2 differences are all positive and lie within the range of reported measured values. The differences are due to disequilibrium of [H+] between plasma and red blood cells, and to disequilibrium of the reactions CO2 in equilibrium HCO3- + H+ in plasma, as blood leaves the tissue and/or lung capillaries. The differences are increased with exercise and with continued O2 uptake in the lung, the latter due to the Haldane shift. We conclude that the two disequilibria and the Haldane shift contribute to the reported PCO2 differences in rebreathing animals but may not fully account for them. These mechanisms cannot explain any PCO2 differences that might exist during net CO2 elimination from blood in the lung.


1981 ◽  
Vol 51 (5) ◽  
pp. 1261-1267 ◽  
Author(s):  
J. W. Shepard ◽  
V. D. Minh ◽  
G. F. Dolan

Gas exchange was studied under conditions of zero perfusion both in situ and in vitro. Six dogs, anesthetized with pentobarbital sodium, underwent surgical interruption of both pulmonary and bronchial circulations to the left lung. Despite the absence of perfusion, O2 uptake for the left lung ranged from 0.76 to 0.98 ml/min, whereas CO2 elimination greatly exceeded O2 uptake ranging from 1.68 to 4.34 ml/min. In addition, CO2 output was observed to vary directly with the level of minute ventilation (VE) and inversely with end-tidal CO2 concentration. To investigate the mechanisms responsible for these findings we studied 20 excised, ventilated, but nonperfused dog lungs to evaluate the relative roles of tissue metabolism and transpleural diffusion to gas exchange. The results obtained with these excised lungs under conditions of varying VE and extrapleural gas concentrations indicate that the high respiratory exchange ratios observed in situ can be explained by the greater rate with which CO2 diffuses through the pleura, and that reduced ventilation decreases total gas transfer by decreasing the transpleural partial pressure driving gradient. Our data further document that the concentration of CO2 in alveolar gas may differ significantly from that present in inspired gas under conditions of ventilation-perfusion ratio equal to infinity, and that tissue metabolism as well as transpleural diffusion contribute to gas exchange in nonperfused lung.


1994 ◽  
Vol 76 (3) ◽  
pp. 1144-1149 ◽  
Author(s):  
A. Weltman ◽  
C. M. Wood ◽  
C. J. Womack ◽  
S. E. Davis ◽  
J. L. Blumer ◽  
...  

Ten collegiate rowers performed discontinuous incremental exercise to their tolerable limit on two occasions: once on a rowing ergometer and once on a treadmill. Ventilation and pulmonary gas exchange were monitored continuously, and blood was sampled from a venous catheter located in the back of the hand or forearm for determination of blood lactate ([La]) and plasma epinephrine ([Epi]) and norepinephrine ([NE]) concentrations. Thresholds for lactate (LT), epinephrine (Epi-T), and norepinephrine (NE-T) were determined for each subject under each condition and defined as breakpoints when plotted as a function of O2 uptake (VO2). For running, LT (3.76 +/- 0.18 l/min) was lower (P < 0.05) than Epi-T (4.35 +/- 0.14 l/min) and NE-T (4.04 +/- 0.19 l/min). For rowing, LT (3.35 +/- 0.16 l/min) was lower (P < 0.05) than Epi-T (3.72 +/- 0.22 l/min) and NE-T (3.70 +/- 0.18 l/min) and was lower (P < 0.05) than LT for running. Within each mode of exercise, Epi-T and NE-T did not differ. Because LT occurred at a significantly lower VO2 than either Epi-T or NE-T, we conclude that catecholamine thresholds, per se, were not the cause of LT. However, for both modes of exercise LT occurred at a plasma [Epi] of approximately 200–250 pg/ml (rowing, 221 +/- 48 pg/ml; running, 245 +/- 45 pg/ml); these concentrations are consistent with the plasma [Epi] reported necessary for eliciting increments in blood [La] during Epi infusion at rest. Plasma [NE] at LT differed significantly between modes (rowing, 820 +/- 127 pg/ml; running, 1,712 +/- 217 pg/ml).(ABSTRACT TRUNCATED AT 250 WORDS)


2016 ◽  
Vol 15 (1) ◽  
pp. 97-102 ◽  
Author(s):  
Janet A. Ademola ◽  
Oluwaferanmi R. Ojeniran

Water samples collected from different sources were analysed for radon concentrations in order to evaluate the health effect associated with radon in water. The radon concentrations were in the range of 3.56–98.57, 0.88–25.49, 0.73–1.35 and 0.24–1.03 Bq.L−1 for borehole, well, packaged and utility water, respectively. Samples from boreholes had the highest radon concentrations with about 67% being higher than the threshold value of 11.1 Bq.L−1 recommended by the USEPA. The mean annual effective dose (AED) due to ingestion for adult, child and infant ranged from 8.71 × 10−3 to 0.831 mSv.y−1 for the different sources. The mean AED calculated for consuming water from boreholes and wells for the three age groups were higher than the recommended reference dose level of 0.1 mSv.y−1. The mean AED due to inhalation of radon in drinking water was negligible, ranging from 0.13 to 6.20 μSv.y−1. The health burden associated with radon in water in the study is through ingestion of water directly from boreholes.


Author(s):  
M Pranay Kumar ◽  
Shaik Arshad Rajmohammad

Background: Placenta is an important connecting organ between the mother and fetus. It provides nutrition, gas exchange, waste removal, immune support, and endocrine functions. Since variations of the placenta result in effects on fetal development and neonatal survival it is the area of interest to be studied by anatomists, pathologists, and obstetricians. We in the current studied the placental morphology, variations, and abnormalities of the human placenta. Methods: The samples comprised of a collection of placentae in the Department of Anatomy of Prathima Institute of Medical Sciences, Karimnagar. Samples were collected after delivery, placentae were mopped to remove any clotted blood, and then weighed with 10 cm of the umbilical cord. The specimen is fixed in 10% formalin immediately over 24-48 hours and then subjected to thorough gross examination. Results: Out of n=60 placentae studied the mean weight of the placenta was found to be highest at 38 weeks of gestation with a mean surface area of 964.46 cm2 and mean weight of 463.75 Kgs. N=49(81.67%) were normal maternal conditions and history of abortions and pre-eclampsia was in n=2 cases each and oligohydramnios in n=3 cases. Among the fetal abnormalities Anencephaly, Macrostomia, MS/TS/Cerebellar hypoplasia, and holoprosencephaly with single nostril was found in n=1(1.67%) cases each. Conclusion: Examination of the placenta performed in the delivery room provides information that may be important to the care of both mother and infant. The findings of this assessment should be documented in the delivery records. The placenta should be submitted for pathologic evaluation if an abnormality is detected. Keywords: Placenta, Morphological Variations, Anencephaly, oligohydramnios, Macrostomia.


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