Comparison of 3 modes of automated weaning from mechanical ventilation: A bench study

Purpose: Automated weaning modes are available in some mechanical ventilators, but no studies compared them hitherto. We compared the performance of 3 automated modes under standard and challenging situations. Methods: We used a lung simulator to compare 3 automated modes, adaptive support ventilation (ASV), mandatory rate ventilation (MRV), and Smartcare, in 6 situations, weaning success, weaning failure, weaning success with extreme anxiety, weaning success with Cheyne-Stokes, weaning success with irregular breathing, and weaning failure with ineffective efforts. Results: The 3 modes correctly recognized the situations of weaning success and failure, even when anxiety or irregular breathing were present but incorrectly recognized weaning success with Cheyne-Stokes. MRV incorrectly recognized weaning failure with ineffective efforts. Time to pressure support (PS) stabilization was shorter for ASV (1-2 minutes for all situations) and MRV (1-7 minutes) than for Smartcare (8-78 minutes). ASV had higher rates of PS oscillations per 5 minutes (4-15), compared with Smartcare (0-1) and MRV (0-12), except when extreme anxiety was present. Conclusions: Smartcare, ASV, and MRV were equally able to recognize weaning success and failure, despite the presence of anxiety or irregular breathing but performed incorrectly in the presence of Cheyne-Stokes. PS behavior over the time differs among modes, with ASV showing larger and more frequent PS oscillations over the time. Clinical studies are needed to confirm our results. (C) 2012 Elsevier Inc. All rights reserved.

Efeitos de diferentes padrões respiratórios no desempenho e na organização temporal das braçadas do nado "Crawl"

O objetivo deste estudo foi investigar os efeitos de diferentes padrões respiratórios no desempenho e na organização temporal das braçadas do nado "Crawl" de atletas de elite. Vinte e um jovens atletas do gênero masculino participaram de forma voluntária do estudo. Eles foram filmados nadando 25 m do nado "Crawl", em velocidade máxima, em quatro condições de respiração: inspiração para o lado preferido (LP); para o lado não preferido (LNP); bilateral (B); e, sem respiração (S). Duas filmadoras digitais (60 fps) captaram as imagens que foram analisadas através do "software" Kinovea 0.8.7 nos 10 metros centrais do percurso. Para análise foram consideradas medidas de desempenho e de organização temporal das braçadas. Os resultados permitiram concluir que o padrão respiratório afeta o desempenho de atletas jovens de elite. Mostraram que, em termos de velocidade, tempo, frequência e comprimento de braçada, é mais vantajosa a condição de nadar "Crawl" em apneia (S) que em qualquer das condições com inspiração (B, LP e LNP). Portanto, o padrão preferido de respiração, não necessariamente, corresponde ao mais eficiente em termos do desempenho. Assim, professores e técnicos de Natação deveriam incentivar a prática e o emprego do padrão em apneia como estratégia tática para nadadores velocistas. Em relação à braçada, os resultados mostraram que diante da modificação do padrão respiratório, nadadores peritos jovens mantêm a estrutura temporal das braçadas direita e esquerda (aspectos invariantes da braçada) bem como a coordenação entre os braços inalterada enquanto efetuam ajustes na fase aérea da braçada (aspectos variantes). Assim sendo, atletas jovens de elite apresentam braçada com relativa autonomia frente ao componente respiração e nadam efetuando ajustes considerando a economia de recursos.

Respiratory muscle activity related to flow and lung volume in preterm infants compared with term infants

Infants with chronic lung disease (CLD) have a capacity to maintain functional lung volume despite alterations to their lung mechanics. We hypothesize that they achieve this by altering breathing patterns and dynamic elevation of lung volume, leading to differences in the relationship between respiratory muscle activity, flow and lung volume. Lung function and transcutaneous electromyography of the respiratory muscles (rEMG) were measured in 20 infants with CLD and in 39 healthy age-matched controls during quiet sleep. We compared coefficient of variations (CVs) of rEMG and the temporal relationship of rEMG variables, to flow and lung volume [functional residual capacity (FRC)] between these groups. The time between the start of inspiratory muscle activity and the resulting flow (tria)--in relation to respiratory cycle time--was significantly longer in infants with CLD. Although FRC had similar associations with tria and postinspiratory activity (corrected for respiratory cycle time), the CV of the diaphragmatic rEMG was lower in CLD infants (22.6 versus 31.0%, p = 0.030). The temporal relationship of rEMG to flow and FRC and the loss of adaptive variability provide additional information on coping mechanisms in infants with CLD. This technique could be used for noninvasive bedside monitoring of CLD.

A realistic validation study of a new nitrogen multiple-breath washout system

Background For reliable assessment of ventilation inhomogeneity, multiple-breath washout (MBW) systems should be realistically validated. We describe a new lung model for in vitro validation under physiological conditions and the assessment of a new nitrogen (N2)MBW system. Methods The N2MBW setup indirectly measures the N2 fraction (FN2) from main-stream carbon dioxide (CO2) and side-stream oxygen (O2) signals: FN2 = 1−FO2−FCO2−FArgon. For in vitro N2MBW, a double chamber plastic lung model was filled with water, heated to 37°C, and ventilated at various lung volumes, respiratory rates, and FCO2. In vivo N2MBW was undertaken in triplets on two occasions in 30 healthy adults. Primary N2MBW outcome was functional residual capacity (FRC). We assessed in vitro error (√[difference]2) between measured and model FRC (100–4174 mL), and error between tests of in vivo FRC, lung clearance index (LCI), and normalized phase III slope indices (Sacin and Scond). Results The model generated 145 FRCs under BTPS conditions and various breathing patterns. Mean (SD) error was 2.3 (1.7)%. In 500 to 4174 mL FRCs, 121 (98%) of FRCs were within 5%. In 100 to 400 mL FRCs, the error was better than 7%. In vivo FRC error between tests was 10.1 (8.2)%. LCI was the most reproducible ventilation inhomogeneity index. Conclusion The lung model generates lung volumes under the conditions encountered during clinical MBW testing and enables realistic validation of MBW systems. The new N2MBW system reliably measures lung volumes and delivers reproducible LCI values.

Ventilatory response to nitrogen multiple-breath washout in infants

BACKGROUND Nitrogen multiple-breath washout (N2 MBW) using 100% oxygen (O2 ) has regained interest to assess efficiency of tracer gas clearance in, for example, children with Cystic Fibrosis (CF). However, the influence of hyperoxia on the infants' respiratory control is unclear. We assessed safety and impact on breathing pattern from hyperoxia, and if exposure to 40% O2 first induces tolerance to subsequent 100% O2 for N2 MBW. METHODS We prospectively enrolled 39 infants aged 3-57 weeks: 15 infants with CF (8 sedated for testing) and 24 healthy controls. Infants were consecutively allocated to the protocols comprising of 100% O2 or 40/100% O2 administered for 30 breaths. Lung function was measured using an ultrasonic flowmeter setup. Primary outcome was tidal volume (VT ). RESULTS None of the infants experienced apnea, desaturation, or bradycardia. Both protocols initially induced hypoventilation. VT temporarily declined in 33/39 infants across 10-25 breaths. Hypoventilation occurred independent of age, disease, and sedation. In the new 40/100% O2 protocol, VT returned to baseline during 40% O2 and remained stable during 100% O2 exposure. End-tidal carbon dioxide monitored online did not change. CONCLUSION The classical N2 MBW protocol with 100% O2 may change breathing patterns of the infants. The new protocol with 40% O2 induces hyperoxia-tolerance and does not lead to changes in breathing patterns during later N2 washout using 100% O2 . Both protocols are safe, the new protocol seems an attractive option for N2 MBW in infants. Pediatr Pulmonol. © 2013 Wiley Periodicals, Inc.

Improving 4D plan quality for PBS-based liver tumour treatments by combining online image guided beam gating with rescanning.

Pencil beam scanned (PBS) proton therapy has many advantages over conventional radiotherapy, but its effectiveness for treating mobile tumours remains questionable. Gating dose delivery to the breathing pattern is a well-developed method in conventional radiotherapy for mitigating tumour-motion, but its clinical efficiency for PBS proton therapy is not yet well documented. In this study, the dosimetric benefits and the treatment efficiency of beam gating for PBS proton therapy has been comprehensively evaluated. A series of dedicated 4D dose calculations (4DDC) have been performed on 9 different 4DCT(MRI) liver data sets, which give realistic 4DCT extracting motion information from 4DMRI. The value of 4DCT(MRI) is its capability of providing not only patient geometries and deformable breathing characteristics, but also includes variations in the breathing patterns between breathing cycles. In order to monitor target motion and derive a gating signal, we simulate time-resolved beams' eye view (BEV) x-ray images as an online motion surrogate. 4DDCs have been performed using three amplitude-based gating window sizes (10/5/3 mm) with motion surrogates derived from either pre-implanted fiducial markers or the diaphragm. In addition, gating has also been simulated in combination with up to 19 times rescanning using either volumetric or layered approaches. The quality of the resulting 4DDC plans has been quantified in terms of the plan homogeneity index (HI), total treatment time and duty cycle. Results show that neither beam gating nor rescanning alone can fully retrieve the plan homogeneity of the static reference plan. Especially for variable breathing patterns, reductions of the effective duty cycle to as low as 10% have been observed with the smallest gating rescanning window (3 mm), implying that gating on its own for such cases would result in much longer treatment times. In addition, when rescanning is applied on its own, large differences between volumetric and layered rescanning have been observed as a function of increasing number of re-scans. However, once gating and rescanning is combined, HI to within 2% of the static plan could be achieved in the clinical target volume, with only moderately prolonged treatment times, irrespective of the rescanning strategy used. Moreover, these results are independent of the motion surrogate used. In conclusion, our results suggest image guided beam gating, combined with rescanning, is a feasible, effective and efficient motion mitigation approach for PBS-based liver tumour treatments.

ANÁLISE CEFALOMÉTRICA COMPARATIVA ENTRE CRIANÇAS RESPIRADORAS BUCAIS E NASAIS

Existem muitas controvérsias sobre a real interferência da respiração no crescimento craniofacial. Este estudo avaliou a possível relação da influência do padrão respiratório com as variáveis cefalométricas: 1) variáveis esqueléticas sagitais: convexidade do ponto A, profundidade facial, profundidade da maxila e comprimento do corpo mandibular; 2) variáveis esqueléticas verticais: altura facial inferior, eixo facial, cone facial, plano palatal, plano mandibular, altura facial posterior e arco mandibular; 3) variáveis dentárias: protrusão do incisivo inferior e protrusão do incisivo superior. A amostra constituiu-se de 120 crianças do sexo masculino e do sexo feminino com más-oclusões dentárias de Classe I e II-1, respiradores bucais e nasais na fase da dentadura mista e permanente, com indicação para tratamento ortodôntico. Após as avaliações ortodôntica, otorrinolaringológica e fonoaudiológica a amostra foi dividida em 2 grupos: 60 crianças portadoras de más-oclusões Classe I e Classe II-1 respiradoras bucais e 60 crianças portadoras de más-oclusões Classe I e Classe II-1 respiradoras nasais, sendo cada grupo divididos em 3 subgrupos nas faixas etárias: 7 a 8 anos, 9 a 10 anos e 11 a 12 anos. Após a obtenção dos resultados e a interpretação da análise estatística, foi possível concluir que: 1) das relações entre os padrões respiratórios (bucal e nasal) e as variáveis esqueléticas sagitais: constatou-se que houve diferença estatisticamente significante, apresentando-se as variáveis cefalométricas: Convexidade pto. A: aumentada no grupo de respiração bucal, idade de 7 a 8 anos com má-oclusão Classe I. Profundidade facial : aumentada no grupo de respiração bucal, idade de 9 a 10 anos com má-oclusão Classe II-1. Profundidade maxila: aumentada no grupo de respiração bucal, idade de 9 a 10 anos com má-oclusão Classe II-1; 2) das relações entre os padrões respiratórios (bucal e nasal) e as variáveis esqueléticas verticais: constatou-se que houve diferença estatisticamente significante, apresentando-se as variáveis cefalométricas: Cone facial: diminuída no grupo de respiração bucal, idade 9 a 10 anos com má-oclusão Classe I. Arco mandibular : diminuída no grupo de respiração bucal, idade 7 a 8 anos com má-oclusão Classe II-1.; 3) das relações entre os padrões respiratórios (bucal e nasal) e as variáveis dentárias: constatou-se que não houve diferença estatisticamente significante para nenhuma das variáveis dentárias analisadas: protrusão do incisivo inferior e superior , não se relacionando com os padrões respiratórios (bucal e nasal).

ANÁLISE CEFALOMÉTRICA COMPARATIVA ENTRE CRIANÇAS RESPIRADORAS BUCAIS E NASAIS

Existem muitas controvérsias sobre a real interferência da respiração no crescimento craniofacial. Este estudo avaliou a possível relação da influência do padrão respiratório com as variáveis cefalométricas: 1) variáveis esqueléticas sagitais: convexidade do ponto A, profundidade facial, profundidade da maxila e comprimento do corpo mandibular; 2) variáveis esqueléticas verticais: altura facial inferior, eixo facial, cone facial, plano palatal, plano mandibular, altura facial posterior e arco mandibular; 3) variáveis dentárias: protrusão do incisivo inferior e protrusão do incisivo superior. A amostra constituiu-se de 120 crianças do sexo masculino e do sexo feminino com más-oclusões dentárias de Classe I e II-1, respiradores bucais e nasais na fase da dentadura mista e permanente, com indicação para tratamento ortodôntico. Após as avaliações ortodôntica, otorrinolaringológica e fonoaudiológica a amostra foi dividida em 2 grupos: 60 crianças portadoras de más-oclusões Classe I e Classe II-1 respiradoras bucais e 60 crianças portadoras de más-oclusões Classe I e Classe II-1 respiradoras nasais, sendo cada grupo divididos em 3 subgrupos nas faixas etárias: 7 a 8 anos, 9 a 10 anos e 11 a 12 anos. Após a obtenção dos resultados e a interpretação da análise estatística, foi possível concluir que: 1) das relações entre os padrões respiratórios (bucal e nasal) e as variáveis esqueléticas sagitais: constatou-se que houve diferença estatisticamente significante, apresentando-se as variáveis cefalométricas: Convexidade pto. A: aumentada no grupo de respiração bucal, idade de 7 a 8 anos com má-oclusão Classe I. Profundidade facial : aumentada no grupo de respiração bucal, idade de 9 a 10 anos com má-oclusão Classe II-1. Profundidade maxila: aumentada no grupo de respiração bucal, idade de 9 a 10 anos com má-oclusão Classe II-1; 2) das relações entre os padrões respiratórios (bucal e nasal) e as variáveis esqueléticas verticais: constatou-se que houve diferença estatisticamente significante, apresentando-se as variáveis cefalométricas: Cone facial: diminuída no grupo de respiração bucal, idade 9 a 10 anos com má-oclusão Classe I. Arco mandibular : diminuída no grupo de respiração bucal, idade 7 a 8 anos com má-oclusão Classe II-1.; 3) das relações entre os padrões respiratórios (bucal e nasal) e as variáveis dentárias: constatou-se que não houve diferença estatisticamente significante para nenhuma das variáveis dentárias analisadas: protrusão do incisivo inferior e superior , não se relacionando com os padrões respiratórios (bucal e nasal).

ANÁLISE CEFALOMÉTRICA COMPARATIVA ENTRE CRIANÇAS RESPIRADORAS BUCAIS E NASAIS

Existem muitas controvérsias sobre a real interferência da respiração no crescimento craniofacial. Este estudo avaliou a possível relação da influência do padrão respiratório com as variáveis cefalométricas: 1) variáveis esqueléticas sagitais: convexidade do ponto A, profundidade facial, profundidade da maxila e comprimento do corpo mandibular; 2) variáveis esqueléticas verticais: altura facial inferior, eixo facial, cone facial, plano palatal, plano mandibular, altura facial posterior e arco mandibular; 3) variáveis dentárias: protrusão do incisivo inferior e protrusão do incisivo superior. A amostra constituiu-se de 120 crianças do sexo masculino e do sexo feminino com más-oclusões dentárias de Classe I e II-1, respiradores bucais e nasais na fase da dentadura mista e permanente, com indicação para tratamento ortodôntico. Após as avaliações ortodôntica, otorrinolaringológica e fonoaudiológica a amostra foi dividida em 2 grupos: 60 crianças portadoras de más-oclusões Classe I e Classe II-1 respiradoras bucais e 60 crianças portadoras de más-oclusões Classe I e Classe II-1 respiradoras nasais, sendo cada grupo divididos em 3 subgrupos nas faixas etárias: 7 a 8 anos, 9 a 10 anos e 11 a 12 anos. Após a obtenção dos resultados e a interpretação da análise estatística, foi possível concluir que: 1) das relações entre os padrões respiratórios (bucal e nasal) e as variáveis esqueléticas sagitais: constatou-se que houve diferença estatisticamente significante, apresentando-se as variáveis cefalométricas: Convexidade pto. A: aumentada no grupo de respiração bucal, idade de 7 a 8 anos com má-oclusão Classe I. Profundidade facial : aumentada no grupo de respiração bucal, idade de 9 a 10 anos com má-oclusão Classe II-1. Profundidade maxila: aumentada no grupo de respiração bucal, idade de 9 a 10 anos com má-oclusão Classe II-1; 2) das relações entre os padrões respiratórios (bucal e nasal) e as variáveis esqueléticas verticais: constatou-se que houve diferença estatisticamente significante, apresentando-se as variáveis cefalométricas: Cone facial: diminuída no grupo de respiração bucal, idade 9 a 10 anos com má-oclusão Classe I. Arco mandibular : diminuída no grupo de respiração bucal, idade 7 a 8 anos com má-oclusão Classe II-1.; 3) das relações entre os padrões respiratórios (bucal e nasal) e as variáveis dentárias: constatou-se que não houve diferença estatisticamente significante para nenhuma das variáveis dentárias analisadas: protrusão do incisivo inferior e superior , não se relacionando com os padrões respiratórios (bucal e nasal).

Influence of respiratory biofeedback associated to re-expansive ventilation patterns in individuals with functional mouth breathing

Objectives: Assess the effect of re-expansive respiratory patterns associated to respiratory biofeedback (RBF) on pulmonary function, respiratory muscle strength and habits in individuals with functional mouth breathing (FMB).Methods: Sixty children with FMB were divided into experimental and control groups. The experimental group was submitted to 15 sessions of re-expansive respiratory patterns associated to RBF (biofeedback pletsmovent; MICROHARD (R) V1.0), which provided biofeedback of the thoracic and abdominal movements. The control group was submitted to 15 sessions using biofeedback alone. Spirometry, maximum static respiratory pressure measurements and questions regarding habits (answered by parents/guardians) were carried out before and after therapy. The Student's t-test for paired data and non-parametric tests were employed for statistical analysis at a 5% Level of significance.Results: Significant changes were found in forced vital. capacity, Tiffeneau index scores, maximum expiratory pressure, maximum inspiratory pressure and habits assessed in FMB with the use of RBF associated to the re-expansive patterns. No significant differences were found comparing the experimental and control groups.Conclusions: The results allow the conclusion that RBF associated to re-expansive patterns improves forced vital capacity, Tiffeneau index scores, respiratory muscle strength and habits in FMB and can therefore be used as a form of therapy for such individuals. (C) 2008 Elsevier B.V. All rights reserved.

Determination of particle concentration in the breathing zone for four different types of office ventilation systems

Many factors affect the airflow patterns, thermal comfort, contaminant removal efficiency and indoor air quality at individual workstations in office buildings. In this study, four ventilation systems were used in a test chamber designed to represent an area of a typical office building floor and reproduce the real characteristics of a modern office space. Measurements of particle concentration and thermal parameters (temperature and velocity) were carried out for each of the following types of ventilation systems: a) conventional air distribution system with ceiling supply and return; b) conventional air distribution system with ceiling supply and return near the floor; c) underfloor air distribution system; and d) split system. The measurements aimed to analyse the particle removal efficiency in the breathing zone and the impact of particle concentration on an individual at the workstation. The efficiency of the ventilation system was analysed by measuring particle size and concentration, ventilation effectiveness and the Indoor/Outdoor ratio. Each ventilation system showed different airflow patterns and the efficiency of each ventilation system in the removal of the particles in the breathing zone showed no correlation with particle size and the various methods of analyses used.

Influence of historical landscapes, drainage evolution and ecological traits on patterns of genetic diversity in Southeast Asian freshwater snakehead fishes

Snakehead fishes in the family Channidae are obligate freshwater fishes represented by two extant genera, the African Parachannna and the Asian Channa. These species prefer still or slow flowing water bodies, where they are top predators that exercise high levels of parental care, have the ability to breathe air, can tolerate poor water quality, and interestingly, can aestivate or traverse terrestrial habitat in response to seasonal changes in freshwater habitat availability. These attributes suggest that snakehead fishes may possess high dispersal potential, irrespective of the terrestrial barriers that would otherwise constrain the distribution of most freshwater fishes. A number of biogeographical hypotheses have been developed to account for the modern distributions of snakehead fishes across two continents, including ancient vicariance during Gondwanan break-up, or recent colonisation tracking the formation of suitable climatic conditions. Taxonomic uncertainty also surrounds some members of the Channa genus, as geographical distributions for some taxa across southern and Southeast (SE) Asia are very large, and in one case is highly disjunct. The current study adopted a molecular genetics approach to gain an understanding of the evolution of this group of fishes, and in particular how the phylogeography of two Asian species may have been influenced by contemporary versus historical levels of dispersal and vicariance. First, a molecular phylogeny was constructed based on multiple DNA loci and calibrated with fossil evidence to provide a dated chronology of divergence events among extant species, and also within species with widespread geographical distributions. The data provide strong evidence that trans-continental distribution of the Channidae arose as a result of dispersal out of Asia and into Africa in the mid–Eocene. Among Asian Channa, deep divergence among lineages indicates that the Oligocene-Miocene boundary was a time of significant species radiation, potentially associated with historical changes in climate and drainage geomorphology. Mid-Miocene divergence among lineages suggests that a taxonomic revision is warranted for two taxa. Deep intra-specific divergence (~8Mya) was also detected between C. striata lineages that occur sympatrically in the Mekong River Basin. The study then examined the phylogeography and population structure of two major taxa, Channa striata (the chevron snakehead) and the C. micropeltes (the giant snakehead), across SE Asia. Species specific microsatellite loci were developed and used in addition to a mitochondrial DNA marker (Cyt b) to screen neutral genetic variation within and among wild populations. C. striata individuals were sampled across SE Asia (n=988), with the major focus being the Mekong Basin, which is the largest drainage basin in the region. The distributions of two divergent lineages were identified and admixture analysis showed that where they co-occur they are interbreeding, indicating that after long periods of evolution in isolation, divergence has not resulted in reproductive isolation. One lineage is predominantly confined to upland areas of northern Lao PDR to the north of the Khorat Plateau, while the other, which is more closely related to individuals from southern India, has a widespread distribution across mainland SE Asian and Sumatra. The phylogeographical pattern recovered is associated with past river networks, and high diversity and divergence among all populations sampled reveal that contemporary dispersal is very low for this taxon, even where populations occur in contiguous freshwater habitats. C. micropeltes (n=280) were also sampled from across the Mekong River Basin, focusing on the lower basin where it constitutes an important wild fishery resource. In comparison with C. striata, allelic diversity and genetic divergence among populations were extremely low, suggesting very recent colonisation of the greater Mekong region. Populations were significantly structured into at least three discrete populations in the lower Mekong. Results of this study have implications for establishing effective conservation plans for managing both species, that represent economically important wild fishery resources for the region. For C. micropeltes, it is likely that a single fisheries stock in the Tonle Sap Great Lake is being exploited by multiple fisheries operations, and future management initiatives for this species in this region will need to account for this. For C. striata, conservation of natural levels of genetic variation will require management initiatives designed to promote population persistence at very localised spatial scales, as the high level of population structuring uncovered for this species indicates that significant unique diversity is present at this fine spatial scale.

The autonomic control and functional significance of the changes in heart rate associated with air breathing in the jeju, Hoplerythrinus unitaeniatus

The jeju is a teleost fish with bimodal respiration that utilizes a modified swim bladder as an air-breathing organ (ABO). Like all air-breathing fish studied to date, jeju exhibit pronounced changes in heart rate (f(H)) during air-breathing events, and it is believed that these may facilitate oxygen uptake (M-O2) from the ABO. The current study employed power spectral analysis (PSA) of f(H) patterns, coupled with instantaneous respirometry, to investigate the autonomic control of these phenomena and their functional significance for the efficacy of air breathing. The jeju obtained less than 5% of total M-O2 (M-tO2) from air breathing in normoxia at 26 degrees C, and PSA of beat-to-beat variability in fH revealed a pattern similar to that of unimodal water-breathing fish. In deep aquatic hypoxia (water P-O2=1 kPa) the jeju increased the frequency of air breathing (f(AB)) tenfold and maintained M-tO2 unchanged from normoxia. This was associated with a significant increase in heart rate variability (HRV), each air breath (AB) being preceded by a brief bradycardia and then followed by a brief tachycardia. These f(H) changes are qualitatively similar to those associated with breathing in unimodal air-breathing vertebrates. Within 20 heartbeats after the AB, however, a beat-to-beat variability in f(H) typical of water-breathing fish was re-established. Pharmacological blockade revealed that both adrenergic and cholinergic tone increased simultaneously prior to each AB, and then decreased after it. However, modulation of inhibitory cholinergic tone was responsible for the major proportion of HRV, including the precise beat-to-beat modulation of f(H) around each AB. Pharmacological blockade of all variations in f(H) associated with air breathing in deep hypoxia did not, however, have a significant effect upon f(AB) or the regulation of M-tO2. Thus, the functional significance of the profound HRV during air breathing remains a mystery.

Regulation of breathing and body temperature of a burrowing rodent during hypoxic-hypercapnia

Burrowing mammals usually have low respiratory sensitivity to hypoxia and hypercapnia. However, the interaction between ventilation (V), metabolism and body temperature (Tb) during hypoxic-hypercapnia has never been addressed. We tested the hypothesis that Clyomys bishopi, a burrowing rodent of the Brazilian cerrado, shows a small ventilatory response to hypoxic-hypercapnia, accompanied by a marked drop in Tb and metabolism. V, Tb and O-2 consumption (VO2) of C. bishopi were measured during exposure to air, hypoxia (10% and 7% O-2), hypercapnia (3% and 5% CO2) and hypoxic-hypercapnia (10% O-2 + 3% CO2). Hypoxia of 7% but not 10%, caused a significant increase in V, and a significant drop in Tb. Both hypoxic levels decreased VO2 and 7% O-2 significantly increased V/VO2. Hypercapnia of 5%, but not 3%, elicited a significant increase in V, although no significant change in Tb, VO2 or V/VO2 was detected. A combination of 10% O-2 and 3% CO2 had minor effects on V and Tb, while VO2 decreased and V/VO2 tended to increase. We conclude that C. bishopi has a low sensitivity not only to hypoxia and hypercapnia, but also to hypoxic-hypercapnia, manifested by a biphasic ventilatory response, a drop in metabolism and a tendency to increase V/VO2. The effect of hypoxic-hypercapnia was the summation of the hypoxia and hypercapnia effects, with respiratory responses tending to have hypercapnic patterns while metabolic responses, hypoxic patterns. (C) 2004 Elsevier B.V. All rights reserved.

Pulmonary receptors in reptiles: discharge patterns of receptor populations in snakes versus turtles

This study examines the effects of lung inflation/deflation with and without CO2 on the entire population of pulmonary receptors in the vagus nerve in two species of snakes and two species of turtles. We asked the question, how does the response of the entire mixed population of pulmonary stretch receptors (PSR) and intrapulmonary chemoreceptors (IPC) in species possessing both differ from that in species with only PSR? This was studied under conditions of artificial ventilation with the secondary goal of extending observations on the presence/absence of IPC to a further three species. Our results indirectly illustrate the presence of IPC in the Burmese python and South American rattlesnake but not the side necked turtle, adding support to the hypothesis that IPC first arose in diapsid reptiles. In both species of snake, CO2-sensitive discharge (presumably from IPC) predominated almost to the exclusion of CO2-insensitive discharge (presumably arising from PSR) while the opposite was true for both species of turtle. The data suggest that for animals breathing air under conditions of normal metabolism there is little to distinguish between the discharge profiles of the total population of receptors arising from the lungs in the different groups. Interestingly, however, under conditions of elevated environmental CO2 most volume-related feedback from the lungs is abolished in the two species of snakes, while under conditions of elevated metabolic CO2, it is estimated that volume feedback from the lungs would be enhanced in these same species.