Drone-based imaging to assess the microbial water quality in an irrigation pond: A pilot study

Microbial water quality datasets are essential in irrigated agricultural practices to detect and inform measures to prevent the contamination of produce. Escherichia coli (E. coli) concentrations are commonly used to evaluate microbial water quality. Remote sensing imagery has been successfully used to retrieve several water quality parameters that can be determinants of E. coli habitats in waterbodies. This pilot study was conducted to test the possibility of using imagery from a small unmanned aerial vehicle (sUAV or drone) to improve the estimation of microbial water quality in small irrigation ponds. In situ measurements of pH, turbidity, specific conductance, and concentrations of dissolved oxygen, chlorophyll-a, phycocyanin, and fluorescent dissolved organic matter were taken at depths of 0-15 cm in 23 locations across a pond in Central Maryland, USA. The pond surface was concurrently imaged using a drone with three modified GoPro cameras, and a multispectral MicaSense RedEdge camera with five spectral bands. The GoPro imagery was decomposed into red, blue, and green components. Mean digital numbers for 1-m radius areas in the images were combined with the water quality data to provide input for a regression tree-based analysis. The accuracy of the regression-tree data description with "only imagery" inputs was the same or better than that of trees constructed with "only water-quality parameters" as inputs. From multiple cross-validation runs with "only imagery" inputs for the regression trees, the average (±SD) determination coefficient and root-mean-squared error of the decimal logarithm of E. coli concentrations were 0.793 ± 0.035 and 0.131 ± 0.011, respectively. The results of this study demonstrate the opportunities for using sUAV imagery for obtaining a more accurate delineation of the spatial variation of E. coli concentrations in irrigation ponds.

Habitat differentiation among three Nigeria-Cameroon chimpanzee (Pan troglodytes ellioti) populations

Ecological niche models (ENMs) are often used to predict species distribution patterns from datasets that describe abiotic and biotic factors at coarse spatial scales. Ground-truthing ENMs provide important information about how these factors relate to species-specific requirements at a scale that is biologically relevant for the species. Chimpanzees are territorial and have a predominantly frugivorous diet. The spatial and temporal variation in fruit availability for different chimpanzee populations is thus crucial, but rarely depicted in ENMs. The genetic and geographic distinction within Nigeria-Cameroon chimpanzee (Pan troglodytes ellioti) populations represents a unique opportunity to understand fine scale species-relevant ecological variation in relation to ENMs. In Cameroon, P. t. ellioti is composed of two genetically distinct populations that occupy different niches: rainforests in western Cameroon and forest-woodland-savanna mosaic (ecotone) in central Cameroon. We investigated habitat variation at three representative sites using chimpanzee-relevant environmental variables, including fruit availability, to assess how these variables distinguish these niches from one another. Contrary to the assumption of most ENM studies that intact forest is essential for the survival of chimpanzees, we hypothesized that the ecotone and human-modified habitats in Cameroon have sufficient resources to sustain large chimpanzee populations. Rainfall, and the diversity, density, and size of trees were higher at the rainforest. The ecotone had a higher density of terrestrial herbs and lianas. Fruit availability was higher at Ganga (ecotone) than at Bekob and Njuma. Seasonal variation in fruit availability was highest at Ganga, and periods of fruit scarcity were longer than at the rainforest sites. Introduced and secondary forest species linked with anthropogenic modification were common at Bekob, which reduced seasonality in fruit availability. Our findings highlight the value of incorporating fine scale species-relevant ecological data to create more realistic models, which have implications for local conservation planning efforts.

Chimpanzee population structure in Cameroon and Nigeria is associated with habitat variation that may be lost under climate change

Background

The Nigeria-Cameroon chimpanzee (Pan troglodytes ellioti) is found in the Gulf of Guinea biodiversity hotspot located in western equatorial Africa. This subspecies is threatened by habitat fragmentation due to logging and agricultural development, hunting for the bushmeat trade, and possibly climate change. Although P. t. ellioti appears to be geographically separated from the neighboring central chimpanzee (P. t. troglodytes) by the Sanaga River, recent population genetics studies of chimpanzees from across this region suggest that additional factors may also be important in their separation. The main aims of this study were: 1) to model the distribution of suitable habitat for P. t. ellioti across Cameroon and Nigeria, and P. t. troglodytes in southern Cameroon, 2) to determine which environmental factors best predict their optimal habitats, and 3) to compare modeled niches and test for their levels of divergence from one another. A final aim of this study was to examine the ways that climate change might impact suitable chimpanzee habitat across the region under various scenarios.

Results

Ecological niche models (ENMs) were created using the software package Maxent for the three populations of chimpanzees that have been inferred to exist in Cameroon and eastern Nigeria: (i) P. t. troglodytes in southern Cameroon, (ii) P. t. ellioti in northwestern Cameroon, and (iii) P. t. ellioti in central Cameroon. ENMs for each population were compared using the niche comparison test in ENMtools, which revealed complete niche divergence with very little geographic overlap of suitable habitat between populations.

Conclusions

These findings suggest that a positive relationship may exist between environmental variation and the partitioning of genetic variation found in chimpanzees across this region. ENMs for each population were also projected under three different climate change scenarios for years 2020, 2050, and 2080. Suitable habitat of P. t. ellioti in northwest Cameroon / eastern Nigeria is expected to remain largely unchanged through 2080 in all considered scenarios. In contrast, P. t. ellioti in central Cameroon, which represents half of the population of this subspecies, is expected to experience drastic reductions in its ecotone habitat over the coming century.

Electronic supplementary material

The online version of this article (doi:10.1186/s12862-014-0275-z) contains supplementary material, which is available to authorized users.

Understanding the electronic structure of IrO2 using hard-X-ray photoelectron spectroscopy and density-functional theory

The electronic structure of IrO2 has been investigated using hard x-ray photoelectron spectroscopy and density-functional theory. Excellent agreement is observed between theory and experiment. We show that the electronic structure of IrO2 involves crystal field splitting of the iridium 5d orbitals in a distorted octahedral field. The behavior of IrO2 closely follows the theoretical predictions of Goodenough for conductive rutile-structured oxides [J. B. Goodenough, J. Solid State Chem. 3, 490 (1971).

Devastating decline of forest elephants in central Africa

African forest elephants- taxonomically and functionally unique-are being poached at accelerating rates, but we lack range-wide information on the repercussions. Analysis of the largest survey dataset ever assembled for forest elephants (80 foot-surveys; covering 13,000 km; 91,600 person-days of fieldwork) revealed that population size declined by ca. 62% between 2002-2011, and the taxon lost 30% of its geographical range. The population is now less than 10% of its potential size, occupying less than 25% of its potential range. High human population density, hunting intensity, absence of law enforcement, poor governance, and proximity to expanding infrastructure are the strongest predictors of decline. To save the remaining African forest elephants, illegal poaching for ivory and encroachment into core elephant habitat must be stopped. In addition, the international demand for ivory, which fuels illegal trade, must be dramatically reduced.

Attempted predation by Nigeria-Cameroon chimpanzees (Pan troglodytes ellioti) on Preuss's red colobus (Procolobus preussi) in the Ebo forest, Cameroon

We describe the first observation of a predation attempt by Nigerian-Cameroon chimpanzees (Pan troglodytes ellioti) on Preuss's red colobus (Procolobus preussi) in the Ebo forest, Cameroon. The activity, which was observed for 15 min, primarily involved 1 chimpanzee and 1 red colobus individual, with a further 2 chimpanzees observing the event. Although the behaviour was interrupted when we were detected by the chimpanzees, we believe that this is the first recorded observation of hunting behaviour in Nigeria-Cameroon chimpanzees.

Genetic signatures of a demographic collapse in a large-bodied forest dwelling primate (Mandrillus leucophaeus)

It is difficult to predict how current climate change will affect wildlife species adapted to a tropical rainforest environment. Understanding how population dynamics fluctuated in such species throughout periods of past climatic change can provide insight into this issue. The drill (Mandrillus leucophaeus) is a large-bodied rainforest adapted mammal found in West Central Africa. In the middle of this endangered monkey's geographic range is Lake Barombi Mbo, which has a well-documented palynological record of environmental change that dates to the Late Pleistocene. We used a Bayesian coalescent-based framework to analyze 2,076 base pairs of mitochondrial DNA across wild drill populations to infer past changes in female effective population size since the Late Pleistocene. Our results suggest that the drill underwent a nearly 15-fold demographic collapse in female effective population size that was most prominent during the Mid Holocene (approximately 3-5 Ka). This time period coincides with a period of increased dryness and seasonality across Africa and a dramatic reduction in forest coverage at Lake Barombi Mbo. We believe that these changes in climate and forest coverage were the driving forces behind the drill population decline. Furthermore, the warm temperatures and increased aridity of the Mid Holocene are potentially analogous to current and future conditions faced by many tropical rainforest communities. In order to prevent future declines in population size in rainforest-adapted species such as the drill, large tracts of forest should be protected to both preserve habitat and prevent forest loss through aridification.

Absence of a space-charge-derived enhancement of ionic conductivity in β|γ- heterostructured 7H- and 9R-AgI

Extreme room temperature conductivity enhancements have been reported for nanocrystalline AgI of up to  × 10(4) relative to bulk β-AgI (Guo et al 2005 Adv. Mater. 17 2815-9). These samples were identified as possessing 7H and 9R polytype structures, which can be considered as heterostructures composed of thin, commensurate layers in the β (wurtzite) and γ (zincblende) phases. It has been proposed that space-charge layer formation at β|γ-interfaces causes near complete disordering of the Ag(+) sublattice in these polytypes, resulting in a massive intrinsic enhancement of ionic conductivity. We have performed molecular dynamics simulations of β- and γ-AgI and mixed β|γ superlattices, to study the effect of heterostructuring on intrinsic defect populations and Ag(+) transport. The ionic conductivities and Ag(+) diffusion coefficients vary as β > 7H ≈ 9R ≈ 10L > γ. The β|γ-heterostructured polytypes show no enhancement in defect populations or Ag(+) mobilities relative to the β-AgI phase, and instead behave as simple composites of β- and γ-AgI. This contradicts the proposal that the extreme conductivity enhancement observed for 7H and 9R polytypes is explained by extensive space-charge formation.

Chemical bonding in copper-based transparent conducting oxides: CuMO2 (M = In, Ga, Sc)

The geometry and electronic structure of copper-based p-type delafossite transparent conducting oxides, CuMO(2) (M = In, Ga, Sc), are studied using the generalized gradient approximation (GGA) corrected for on-site Coulomb interactions (GGA + U). The bonding and valence band compositions of these materials are investigated, and the origins of changes in the valence band features between group 3 and group 13 cations are discussed. Analysis of the effective masses at the valence and conduction band edge explains the experimentally reported conductivity trends.

Muzzle size, paranasal swelling size and body mass in Mandrillus leucophaeus

The drill (Mandrillus leucophaeus), a forest-living Old World monkey, is highly sexually dimorphic, with males exhibiting extreme secondary sexual characteristics, including growth of paranasal swellings on the muzzle. In this study, the size of the secondary bone that forms the paranasal swellings on the muzzles of drills was assessed in relation to body mass proxies. The relationship between the overall size of the muzzle and surrogate measures of body mass was also examined. In female drills, muzzle breadth was positively correlated with two proxies of overall body mass, greatest skull length and upper M1 area. However, there was no such correlation in males. Paranasal swellings in males also appeared to have no significant relationship to body mass proxies. This suggests that secondary bone growth on the muzzles of male drills is independent of overall body size. Furthermore, this secondary bone appears to be vermiculate, probably developing rapidly and in an irregular manner, with no correlation in the sizes of paranasal swelling height and breadth. However, various paranasal swelling dimensions were related to the size of the muzzle. It is suggested that the growth of the paranasal swellings and possibly the muzzle could be influenced by androgen production and reflect testes size and sperm motility. The size and appearance of the paranasal swellings may thus be an indicator of reproductive quality both to potential mates and male competitors. Further work is required to investigate the importance of the paranasal swellings as secondary sexual characteristics in Mandrillus and the relationship between body size and secondary sexual characteristics. Attention should also be paid to the mechanisms and trajectories of facial growth in Mandrillus.

Evaluation of an educational intervention for military tobacco users

This study evaluated the short-term effect of a one-time tobacco hazard education intervention on tobacco use and intention to quit among military tobacco users. Of the 151 Army infantry soldiers who received the intervention, 60 (40%) participated in a 1-month follow-up survey. Respondents' reported pre-intervention tobacco habits included 51% smoking, 22% smokeless tobacco use, and 27% both. A one-group, posttest-only design demonstrated a decline in tobacco use in more than half of tobacco users: 14% quit, and 37% decreased use. However, 46% stayed the same, and 3% increased use. A statistically significant difference in tobacco use existed among the three subgroups of tobacco users (p = 0.004). Smokeless-tobacco-only users were more likely to quit than smoking-only or combined users. Eighty percent had positive thoughts or actions toward quitting tobacco use after the intervention. Results suggest that a one-time tobacco education intervention can positively influence tobacco use in the short term and motivate tobacco users toward quitting.

Fatiguing inspiratory muscle work causes reflex reduction in resting leg blood flow in humans

1. We recently showed that fatigue of the inspiratory muscles via voluntary efforts caused a time-dependent increase in limb muscle sympathetic nerve activity (MSNA) (St Croix et al. 2000). We now asked whether limb muscle vasoconstriction and reduction in limb blood flow also accompany inspiratory muscle fatigue. 2. In six healthy human subjects at rest, we measured leg blood flow (.Q(L)) in the femoral artery with Doppler ultrasound techniques and calculated limb vascular resistance (LVR) while subjects performed two types of fatiguing inspiratory work to the point of task failure (3-10 min). Subjects inspired primarily with their diaphragm through a resistor, generating (i) 60 % maximal inspiratory mouth pressure (P(M)) and a prolonged duty cycle (T(I)/T(TOT) = 0.7); and (ii) 60 % maximal P(M) and a T(I)/T(TOT) of 0.4. The first type of exercise caused prolonged ischaemia of the diaphragm during each inspiration. The second type fatigued the diaphragm with briefer periods of ischaemia using a shorter duty cycle and a higher frequency of contraction. End-tidal P(CO2) was maintained by increasing the inspired CO(2) fraction (F(I,CO2)) as needed. Both trials caused a 25-40 % reduction in diaphragm force production in response to bilateral phrenic nerve stimulation. 3. .Q(L) and LVR were unchanged during the first minute of the fatigue trials in most subjects; however, .Q(L) subsequently decreased (-30 %) and LVR increased (50-60 %) relative to control in a time-dependent manner. This effect was present by 2 min in all subjects. During recovery, the observed changes dissipated quickly (< 30 s). Mean arterial pressure (MAP; +4-13 mmHg) and heart rate (+16-20 beats min(-1)) increased during fatiguing diaphragm contractions. 4. When central inspiratory motor output was increased for 2 min without diaphragm fatigue by increasing either inspiratory force output (95 % of maximal inspiratory pressure (MIP)) or inspiratory flow rate (5 x eupnoea), .Q(L), MAP and LVR were unchanged; although continuing the high force output trials for 3 min did cause a relatively small but significant increase in LVR and a reduction in .Q(L). 5. When the breathing pattern of the fatiguing trials was mimicked with no added resistance, LVR was reduced and .Q(L) increased significantly; these changes were attributed to the negative feedback effects on MSNA from augmented tidal volume. 6. Voluntary increases in inspiratory effort, in the absence of diaphragm fatigue, had no effect on .Q(L) and LVR, whereas the two types of diaphragm-fatiguing trials elicited decreases in .Q(L) and increases in LVR. We attribute these changes to a metaboreflex originating in the diaphragm. Diaphragm and forearm muscle fatigue showed very similar time-dependent effects on LVR and .Q(L).

Exposure to hypoxia produces long-lasting sympathetic activation in humans

The relative contributions of hypoxia and hypercapnia in causing persistent sympathoexcitation after exposure to the combined stimuli were assessed in nine healthy human subjects during wakefulness. Subjects were exposed to 20 min of isocapnic hypoxia (arterial O(2) saturation, 77-87%) and 20 min of normoxic hypercapnia (end-tidal P(CO)(2), +5.3-8.6 Torr above eupnea) in random order on 2 separate days. The intensities of the chemical stimuli were manipulated in such a way that the two exposures increased sympathetic burst frequency by the same amount (hypoxia: 167 +/- 29% of baseline; hypercapnia: 171 +/- 23% of baseline). Minute ventilation increased to the same extent during the first 5 min of the exposures (hypoxia: +4.4 +/- 1.5 l/min; hypercapnia: +5.8 +/- 1.7 l/min) but declined with continued exposure to hypoxia and increased progressively during exposure to hypercapnia. Sympathetic activity returned to baseline soon after cessation of the hypercapnic stimulus. In contrast, sympathetic activity remained above baseline after withdrawal of the hypoxic stimulus, even though blood gases had normalized and ventilation returned to baseline levels. Consequently, during the recovery period, sympathetic burst frequency was higher in the hypoxia vs. the hypercapnia trial (166 +/- 21 vs. 104 +/- 15% of baseline in the last 5 min of a 20-min recovery period). We conclude that both hypoxia and hypercapnia cause substantial increases in sympathetic outflow to skeletal muscle. Hypercapnia-evoked sympathetic activation is short-lived, whereas hypoxia-induced sympathetic activation outlasts the chemical stimulus.

On the near-singularity of models for animal recovery data

Certain probability models sometimes provide poor descriptions when fitted to data by maximum likelihood. We examine one such model for the survival of wild animals, which is fitted to two sets of data. When the model behaves poorly, its expected information matrix, evaluated at the maximum likelihood estimate of parameters, has a 'small' smallest eigenvalue. This is due to the fitted model being similar to a parameter-redundant submodel. In this case, model parameters that are precisely estimated have small coefficients in the eigenvector corresponding to the smallest eigenvalue. Approximate algebraic expressions are provided for the smallest eigenvalue. We discuss the general applicability of these results.

Age, sex, density, winter weather, and population crashes in Soay sheep

Quantifying the impact of density, extrinsic climatic fluctuations, and demography on population fluctuations is a persistent challenge in ecology. We analyzed the effect of these processes on the irregular pattern of population crashes of Soay sheep on the St. Kilda archipelago, United Kingdom. Because the age and sex structure of the population fluctuates independently of population size, and because animals of different age and sex respond in different ways to density and weather, identical weather conditions can result in different dynamics in populations of equal size. In addition, the strength of density-dependent processes is a function of the distribution of weather events. Incorporating demographic heterogeneities into population models can influence dynamics and their response to climate change.

Effect of burst-mode transcutaneous electrical nerve stimulation on peripheral vascular resistance

BACKGROUND AND PURPOSE

Based on changes in skin temperature alone, some authors have proposed that postganglionic sympathetic vasoconstrictor fibers can be stimulated transcutaneously. Our goal was to determine the effects of low-frequency (2 bursts per second), burst-mode transcutaneous electrical nerve stimulation (TENS) on calf vascular resistance, a more direct marker of sympathetic vasoconstrictor outflow than skin temperature, in subjects with no known pathology.

SUBJECTS

Fourteen women and 6 men (mean age=31 years, SD=13, range=18-58) participated in this study.

METHODS

Calf blood flow, arterial pressure, and skin temperature were measured while TENS was applied over the common peroneal and tibial nerves.

RESULTS

Blood flow immediately following stimulation was not affected by TENS applied just under or just above the threshold for muscle contraction. Transcutaneous electrical nerve stimulation applied at 25% above the motor threshold caused a transient increase in calf blood flow. Regardless of stimulation intensity, TENS had no effect on arterial pressure; therefore, calf vascular resistance decreased only during the trial that was 25% above the motor threshold. Regardless of stimulation intensity, TENS failed to alter dorsal or plantar skin temperature.

DISCUSSION AND CONCLUSION

These results demonstrate that the effects of TENS on circulation depend on stimulation intensity. When the intensity was sufficient to cause a moderate muscle contraction, a transient, local increase in blood flow occurred. Cooling of the dorsal and plantar skin occurred in both the stimulated and control legs, most likely because skin temperature acclimatized to ambient room temperature, rather than because of any effect of TENS on circulation. The data, therefore, call into question the idea that postganglionic sympathetic efferent fibers are stimulated when TENS is applied at clinically relevant intensities to people without symptoms of cardiovascular or neuromuscular pathology.

Abalone I: analyzing mark-recapture-recovery data incorporating growth and delayed recovery

Abalone are semimobile marine gastropods that form the basis of Australia's second most valuable fishery. A site off the coast of Port Arthur, Tasmania, was visited on six occasions. On each occasion, any unmarked live abalone found were marked with a unique identification number and were recorded. Any previously marked abalone found had its identification number and whether or not it was still alive recorded. This results in integrated mark-recapture-recovery data, as in Catchpole et al. (1998, Biometrics 54, 33-46). During the study period, abalone grew in size, and we model the survival of individuals as a function of their size, estimated from a fitted growth curve. The shells of dead animals are long lasting, and we extend existing methodology to allow for the possibility that an animal found dead may have been dead but overlooked for several visits.

Fatiguing inspiratory muscle work causes reflex sympathetic activation in humans

We tested the hypothesis that reflexes arising from working respiratory muscle can elicit increases in sympathetic vasoconstrictor outflow to limb skeletal muscle, in seven healthy human subjects at rest. We measured muscle sympathetic nerve activity (MSNA) with intraneural electrodes in the peroneal nerve while the subject inspired (primarily with the diaphragm) against resistance, with mouth pressure (PM) equal to 60 % of maximal, a prolonged duty cycle (TI/TTot) of 0.70, breathing frequency (fb) of 15 breaths min-1 and tidal volume (VT) equivalent to twice eupnoea. This protocol was known to reduce diaphragm blood flow and cause fatigue. MSNA was unchanged during the first 1-2 min but then increased over time, to 77 +/- 51 % (s.d.) greater than control at exhaustion (mean time, 7 +/- 3 min). Mean arterial blood pressure (+12 mmHg) and heart rate (+27 beats min-1) also increased. When the VT, fb and TI/TTot of these trials were mimicked with no added resistance, neither MSNA nor arterial blood pressure increased. MSNA and arterial blood pressure also did not change in response to two types of increased central respiratory motor output that did not produce fatigue: (a) high inspiratory flow rate and fb without added resistance; or (b) high inspiratory effort against resistance with PM of 95 % maximal, TI/TTot of 0.35 and fb of 12 breaths min-1. The heart rate increased by 5-16 beats min-1 during these trials. Thus, in the absence of any effect of increased central respiratory motor output per se on limb MSNA, we attributed the time-dependent increase in MSNA during high resistance, prolonged duty cycle breathing to a reflex arising from a diaphragm that was accumulating metabolic end products in the face of high force output plus compromised blood flow.

Neurocirculatory consequences of intermittent asphyxia in humans

We examined the neurocirculatory and ventilatory responses to intermittent asphyxia (arterial O(2) saturation = 79-85%, end-tidal PCO(2) =3-5 Torr above eupnea) in seven healthy humans during wakefulness. The intermittent asphyxia intervention consisted of 20-s asphyxic exposures alternating with 40-s periods of room-air breathing for a total of 20 min. Minute ventilation increased during the intermittent asphyxia period (14.2 +/- 2.0 l/min in the final 5 min of asphyxia vs. 7.5 +/- 0.4 l/min in baseline) but returned to the baseline level within 2 min after completion of the series of asphyxic exposures. Muscle sympathetic nerve activity increased progressively, reaching 175 +/- 12% of baseline in the final 5 min of the intervention. Unlike ventilation, sympathetic activity remained elevated for at least 20 min after removal of the chemical stimuli (150 +/- 10% of baseline in the last 5 min of the recovery period). Intermittent asphyxia caused a small, but statistically significant, increase in heart rate (64 +/- 4 beats/min in the final 5 min of asphyxia vs. 61 +/- 4 beats/min in baseline); however, this increase was not sustained after the return to room-air breathing. These data demonstrate that relatively short-term exposure to intermittent asphyxia causes sympathetic activation that persists after removal of the chemical stimuli. This carryover effect provides a potential mechanism whereby intermittent asphyxia during sleep could lead to chronic sympathetic activation in patients with sleep apnea syndrome.

On the Bayesian analysis of ring-recovery data

Vounatsou and Smith (1995, Biometrics 51, 687-708) describe the modern Bayesian analysis of ring-recovery data. Here we discuss and extend their work. We draw different conclusions from two major data analyses. We emphasize the extreme sensitivity of certain parameter estimates to the choice of prior distribution and conclude that naive use of Bayesian methods in this area can be misleading. Additionally, we explain the discrepancy between the Bayesian and classical analyses when the likelihood surface has a flat ridge. In this case, when there is no unique maximum likelihood estimate, the Bayesian estimators are remarkably precise.

Circulatory responses to voluntary and electrically induced muscle contractions in humans

BACKGROUND AND PURPOSE

Transcutaneous electrical nerve stimulation (TENS) increases regional blood flow when applied at intensities sufficient to cause skeletal muscle contraction. It is not known whether increases in blood flow elicited by TENS differ from those caused by voluntary muscle contraction. The purpose of this study, therefore, was to compare the hemodynamic effects of these 2 types of muscle contraction.

SUBJECTS AND METHODS

Fourteen people with no known pathology, aged 18 to 49 years (mean=28, SD=8), served as subjects. Calf blood flow (venous occlusion plethysmography), heart rate (electrocardiogram), blood pressure (automated sphygmomanometry), and force (footplate transducer) were measured during electrically induced and voluntary contractions.

RESULTS

Both modes of exercise caused rapid, but short-lived vasodilation (calf vascular resistance [mean(SEM]: (53%(3% for voluntary contractions versus (57%(4% for electrically induced contractions). The vasodilation caused by electrically induced contractions persisted for at least 15 seconds in the postexercise period, whereas the vasodilation elicited by voluntary contractions had resolved by this time point.

CONCLUSION AND DISCUSSION

The hemodynamic changes elicited by voluntary and electrically induced muscle contractions are similar in magnitude but different in duration.

Role of respiratory motor output in within-breath modulation of muscle sympathetic nerve activity in humans

We measured muscle sympathetic nerve activity (MSNA, peroneal microneurography) in 5 healthy humans under conditions of matched tidal volume, breathing frequency, and end-tidal CO(2), but varying respiratory motor output as follows: (1) passive positive pressure mechanical ventilation, (2) voluntary hyperventilation, (3) assisted mechanical ventilation that required the subject to generate -2.5 cm H(2)O to trigger each positive pressure breath, and (4) added inspiratory resistance. Spectral analyses showed marked respiratory periodicities in MSNA; however, the amplitude of the peak power was not changed with changing inspiratory effort. Time domain analyses showed that maximum MSNA always occurred at end expiration (25% to 30% of total activity) and minimum activity at end inspiration (2% to 3% of total activity), and the amplitude of the variation was not different among conditions despite marked changes in respiratory motor output. Furthermore, qualitative changes in intrathoracic pressure were without influence on the respiratory modulation of MSNA. In all conditions, within-breath changes in MSNA were inversely related to small changes in diastolic pressure (1 to 3 mm Hg), suggesting that respiratory rhythmicity in MSNA was secondary to loading/unloading of carotid sinus baroreceptors. Furthermore, at any given diastolic pressure, within-breath MSNA varied inversely with lung volume, demonstrating an additional influence of lung inflation feedback on sympathetic discharge. Our data provide evidence against a significant effect of respiratory motor output on the within-breath modulation of MSNA and suggest that feedback from baroreceptors and pulmonary stretch receptors are the dominant determinants of the respiratory modulation of MSNA in the intact human.

Daytime blood pressure elevation after nocturnal hypoxia

The purpose of this study was to investigate whether nocturnal hypoxia causes daytime blood pressure (BP) elevation. We hypothesized that overnight exposure to hypoxia leads the next morning to elevation in BP that outlasts the hypoxia stimulus. We studied the effect on BP of two consecutive night exposures to hypobaric hypoxia in 10 healthy normotensive subjects. During the hypoxia nights, subjects slept for 8 h in a hypobaric chamber at a simulated altitude of 4,000 m (barometric pressure = 462 mmHg). Arterial O(2) saturation and electrocardiogram were monitored throughout the night. For 30 min before the nocturnal simulated ascent and for 4 h after return to baseline altitude the next morning, BP was measured every 5 min while the subject was awake. The same measurements were made before and after 2 normoxic nights of sleep in the hypobaric chamber at ambient barometric pressure (745 mmHg). Principal components analysis was applied to evaluate patterns of BP response after the second night of hypoxia and normoxia. A distinct pattern of diastolic BP (DBP) elevation was observed after the hypoxia night in 9 of the 10 subjects but in none after the normoxia night. This pattern showed a mean increase of 4 mmHg in DBP compared with the presleep-awake baseline in the first 60 min and a return to baseline by 90 min. We conclude that nocturnal hypoxia leads to a carryover elevation of daytime DBP.

Arousal from sleep shortens sympathetic burst latency in humans

1. Bursts of sympathetic activity in muscle nerves are phase-locked to the cardiac cycle by the sinoaortic baroreflexes. Acoustic arousal from non-rapid eye movement (NREM) sleep reduces the normally invariant interval between the R-wave of the electrocardiogram (ECG) and the peak of the corresponding sympathetic burst; however, the effects of other forms of sleep disruption (i.e. spontaneous arousals and apnoea-induced arousals) on this temporal relationship are unknown. 2. We simultaneously recorded muscle sympathetic nerve activity in the peroneal nerve (intraneural electrodes) and the ECG (surface electrodes) in seven healthy humans and three patients with sleep apnoea syndrome during NREM sleep. 3. In seven subjects, burst latencies were shortened subsequent to spontaneous K complexes (1.297 +/- 0.024 s, mean +/- s. e.m.) and spontaneous arousals (1.268 +/- 0.044 s) compared with latencies during periods of stable NREM sleep (1.369 +/- 0.023 s). In six subjects who demonstrated spontaneous apnoeas during sleep, apnoea per se did not alter burst latency relative to sleep with stable electroencephalogram (EEG) and breathing (1.313 +/- 0.038 vs. 1.342 +/- 0.026 s); however, following apnoea-induced EEG perturbations, burst latencies were reduced (1.214 +/- 0.034 s). 4. Arousal-induced reduction in sympathetic burst latency may reflect a temporary diminution of baroreflex buffering of sympathetic outflow. If so, the magnitude of arterial pressure perturbations during sleep (e.g. those caused by sleep disordered breathing and periodic leg movements) may be augmented by arousal.

Blood pressure perturbations caused by subclinical sleep-disordered breathing

We studied the acute effects of apneas and hypopneas on blood pressure in a nonclinic population of middle-aged adults. Arterial pressure was measured noninvasively (photoelectric plethysmography) during an overnight, in-laboratory polysomnographic study in 72 men and 23 women enrolled in the Wisconsin Sleep Cohort Study, a population-based study of sleep-disordered breathing. Sleep-disordered breathing events (272 apneas and 1469 hypopneas) were observed in 92% of subjects. The across-subject mean decreases in arterial O2 saturation were 9+/-8% (SD) for apneas (17+/-8 seconds duration) and 4+/-3% for hypopneas (21+/-6 seconds duration; 41+/-17% of baseline ventilation). In both apneas and hypopneas, even those with only 1% to 3% O2 desaturations, blood pressure decreased during the event, followed by an abrupt increase in the postevent recovery period. Mean values for peak changes in blood pressure (difference between the maximum during the recovery period and the minimum during the event) were 23+/-10 mm Hg for systolic and 13+/-6 mm Hg for diastolic pressure. The strongest predictors of the pressor responses to apneas and hypopneas were (in order of importance): magnitude of the ventilatory overshoot, length of the event, magnitude of changes in heart rate and arterial O2 saturation, and presence or absence of electroencephalographic arousal. We speculate that these fluctuations may play a role in the pathogenesis of hypertension in individuals with subclinical sleep-disordered breathing.

Neural mechanism of the pressor response to obstructive and nonobstructive apnea

Obstructive and nonobstructive apneas elicit substantial increases in muscle sympathetic nerve activity and arterial pressure. The time course of change in these variables suggests a causal relationship; however, mechanical influences, such as release of negative intrathoracic pressure and reinflation of the lungs, are potential contributors to the arterial pressure rise. To test the hypothesis that apnea-induced pressor responses are neurally mediated, we measured arterial pressure (photoelectric plethysmography), muscle sympathetic nerve activity (peroneal microneurography), arterial O2 saturation (pulse oximeter), and end-tidal CO2 tension (gas analyzer) during sustained Mueller maneuvers, intermittent Mueller maneuvers, and simple breath holds in six healthy humans before, during, and after ganglionic blockade with trimethaphan (3-4 mg/min, titrated to produce complete disappearance of sympathetic bursts from the neurogram). Ganglionic blockade abolished the pressor responses to sustained and intermittent Mueller maneuvers (-4 +/- 1 vs. +15 +/- 3 and 0 +/- 2 vs. +15 +/- 5 mmHg) and breath holds (0 +/- 3 vs. +11 +/- 3, all P < 0.05). We conclude that the acute pressor response to obstructive and nonobstructive voluntary apnea is sympathetically mediated.

Ventilatory response to induced auditory arousals during NREM sleep

Sleep state instability is a potential mechanism of central apnea/hypopnea during non-rapid eye movement (NREM) sleep. To investigate this postulate, we induced brief arousals by delivering transient (0.5 second) auditory stimuli during stable NREM sleep in eight normal subjects. Arousal was determined according to American Sleep Disorders Association (ASDA) criteria. A total of 96 trials were conducted; 59 resulted in cortical arousal and 37 did not result in arousal. In trials associated with arousal, minute ventilation (VE) increased from 5.1 +/- 1.24 minutes to 7.5 +/- 2.24 minutes on the first posttone breath (p = 0.001). However, no subsequent hypopnea or apnea occurred as VE decreased gradually to 4.8 +/- 1.5 l/minute (p > 0.05) on the fifth posttone breath. Trials without arousal did not result in hyperpnea on the first breath nor subsequent hypopnea. We conclude that 1) auditory stimulation resulted in transient hyperpnea only if associated with cortical arousal; 2) hypopnea or apnea did not occur following arousal-induced hyperpnea in normal subjects; 3) interaction with fluctuating chemical stimuli or upper airway resistance may be required for arousals to cause sleep-disordered breathing.

Finite mixture models for proportions

Six data sets recording fetal control mortality in mouse litters are presented. The data are clearly overdispersed, and a standard approach would be to describe the data by means of a beta-binomial model or to use quasi-likelihood methods. For five of the examples, we show that beta-binomial model provides a reasonable description but that the fit can be significantly improved by using a mixture of a beta-binomial model with a binomial distribution. This mixture provides two alternative solutions, in one of which the binomial component indicates a high probability of death but is selected infrequently; this accounts for outlying litters with high mortality. The influence of the outliers on the beta-binomial fits is also demonstrated. The location and nature of the two main maxima to the likelihood are investigated through profile log-likelihoods. Comparisons are made with the performance of finite mixtures of binomial distributions.

Effect of transcutaneous electrical nerve stimulation on the pressor response to static handgrip exercise

BACKGROUND AND PURPOSE

A proposed mechanism for the pain-relieving properties of transcutaneous electrical nerve stimulation (TENS) is gating of impulses carried by group III and IV afferent nerve fibers. The purpose of this study was to determine the effects of TENS on the pressor response to static exercise, a response mediated by group III and IV muscle afferents.

SUBJECTS

Sixteen subjects (9 men, 7 women) with no known history of cardiovascular, neurologic, or musculoskeletal disease participated.

METHODS

We measured arterial pressure, heart rate, and sympathetic activity during sustained, 25% maximal handgrip exercise. Each subject performed the handgrip exercise with and without conventional TENS applied to the ipsilateral forearm and, in a separate trial, to the contralateral leg.

RESULTS

The sympathetically mediated pressor response to handgrip exercise was blunted when TENS was applied to the ipsilateral forearm, but not when TENS was applied to the contralateral leg.

CONCLUSION AND DISCUSSION

These data support the concept that central transmission of neural impulses traveling in group III and IV fibers can be modulated by other afferent inputs converging on the same spinal level.

Acute and chronic cardiovascular responses to sleep disordered breathing

Episodes of sleep disordered breathing are surprisingly common in asymptomatic, middle-aged individuals. The majority of these events are hypopneas, rather than apneas. Even though these events cause rather modest decreases in arterial oxygen saturation, they evoke substantial increases in arterial pressure. In this population, mild to moderate sleep disordered breathing is associated with elevated daytime blood pressure. The mechanisms responsible for the acute and chronic cardiovascular effects of sleep disordered breathing are incompletely understood. Chemoreflex mechanisms appear to be more important than intrathoracic pressure changes in causing the acute elevation in arterial pressure that occurs after obstructive sleep apnea. Arousal from sleep may contribute to this pressor response, either in an additive or synergistic manner. Relatively brief exposure to combined hypoxia and hypercapnia during wakefulness can produce an increase in sympathetic outflow to skeletal muscle that persists after return to room air breathing. This lingering post-asphyxic effect on sympathetic outflow may be the basis of chronically elevated sympathetic nervous system activity which accompanies sleep apnea syndrome and may contribute to sustained hypertension in these individuals.

Neurocirculatory consequences of abrupt change in sleep state in humans

The arterial pressure elevations that accompany sleep apneas may be caused by chemoreflex stimulation, negative intrathoracic pressure, and/or arousal. To assess the neurocirculatory effects of arousal alone, we applied graded auditory stimuli during non-rapid-eye-movement (NREM) sleep in eight healthy humans. We measured muscle sympathetic nerve activity (intraneural microelectrodes), electroencephalogram (EEG; C4/A1 and O1/A2), arterial pressure (photoelectric plethysmography), heart rate (electrocardiogram), and stroke volume (impedance cardiography). Auditory stimuli caused abrupt increases in systolic and diastolic pressures (21 +/- 2 and 15 +/- 1 mmHg) and heart rate (11 +/- 2 beats/min). Cardiac output decreased (-10%). Stimuli that produced EEG evidence of arousal evoked one to two large bursts of sympathetic activity (316 +/- 46% of baseline amplitude). Stimuli that did not alter EEG frequency produced smaller but consistent pressor responses even though no sympathetic activation was observed. We conclude that arousal from NREM sleep evokes a pressor response caused by increased peripheral vascular resistance. Increased sympathetic outflow to skeletal muscle may contribute to, but is not required for, this vasoconstriction. The neurocirculatory effects of arousal may augment those caused by asphyxia during episodes of sleep-disordered breathing.

Combined hypoxia and hypercapnia evokes long-lasting sympathetic activation in humans

We studied ventilatory and neurocirculatory responses to combined hypoxia (arterial O2 saturation 80%) and hypercapnia (end-tidal CO2 + 5 Torr) in awake humans. This asphyxic stimulus produced a substantial increase in minute ventilation (6.9 +/- 0.4 to 20.0 +/- 1.5 l/min) that promptly subsided on return to room air breathing. During asphyxia, muscle sympathetic nerve activity (intraneural microelectrodes) increased to 220 +/- 28% of the room air baseline. Approximately two-thirds of this sympathetic activation persisted after return to room air breathing for the duration of our measurements (20 min in 8 subjects, 1 h in 2 subjects). In contrast, neither ventilation nor sympathetic outflow changed during time control experiments. A 20-min exposure to hyperoxic hypercapnia also caused a sustained increase in sympathetic activity, but, unlike the aftereffect of asphyxia, this effect was short lived and coincident with continued hyperpnea. In summary, relatively brief periods of asphyxic stimulation cause substantial increases in sympathetic vasomotor outflow that outlast the chemical stimuli. These findings provide a potential explanation for the chronically elevated sympathetic nervous system activity that accompanies sleep apnea syndrome.

Effect of interference current on forearm vascular resistance in asymptomatic humans

BACKGROUND AND PURPOSE

Several case reports suggest that transcutaneous application of interference current (IC) produces physical blockade of sympathetic vasoconstrictor fibers in peripheral nerves. To test this theory, we studied the effects of IC on forearm vascular resistance in asymptomatic humans.

SUBJECTS

One man and four women, aged 21 to 44 years (mean = 33, SD = 12), served as subjects.

METHODS

We measured forearm blood flow during IC applications over the left stellate ganglion. Forearm vascular resistance was calculated by dividing mean arterial pressure by forearm blood flow.

RESULTS

Interference current did not alter flow (mean = 5.6 [SD = 1.0] versus 6.2 [SD = 1.1] mL/100 mL/min) or resistance (mean = 15.4 [SD = 3.1] versus 13.8 [SD = 2.4] units). When sympathetic outflow was augmented using lower-body suction, IC again failed to alter flow or resistance.

CONCLUSION AND DISCUSSION

Interference current applied over the stellate ganglion does not alter forearm hemodynamics in asymptomatic individuals. These findings challenge the concept that IC can block sympathetic vasoconstrictor impulses in peripheral nerves.

Mechanism of cyclosporine-induced sympathetic activation and acute hypertension in rats

Although intravenous cyclosporine A (CsA) previously has been shown to cause a robust sympathetically mediated increase in blood pressure in the rat, the underlying mechanism by which CsA increases the activity of the sympathetic nervous system is unknown. To determine the relative contributions of central neural versus peripheral reflex mechanisms in causing this sympathetic activation, we recorded efferent renal sympathetic nerve activity and blood pressure during intracerebroventricular or intravenous infusion of CsA, the latter performed in intact rats and in those with sinoaortic denervation, cervical or subdiaphragmatic vagotomy, or dorsal rhizotomy (T10 through L1). In intact rats, intravenous CsA (5 mg/kg), as expected, tripled renal sympathetic nerve activity and increased mean arterial pressure by 27 +/- 4 mm Hg (P < .05). The new findings are that this sympathoexcitatory effect of intravenous CsA (1) was not duplicated by central administration (either into the cerebroventricular system or directly onto the ventrolateral surface of the medulla), (2) was unaffected by sinoaortic denervation, but (3) was greatly attenuated by either cervical or subdiaphragmatic vagotomy or by dorsal rhizotomy. In additional experiments, we found that intravenous cyclosporine increased the multiunit activity of subdiaphragmatic but not cardiopulmonary vagal afferents. From these data, we conclude that in the rat CsA-induced increases in sympathetic activity and blood pressure are caused mainly by activation of excitatory neural reflexes arising in the subdiaphragmatic region. These reflex mechanisms use at least two different afferent neural pathways: one involving the subdiaphragmatic vagi and the other involving the low thoracic dorsal spinal roots.

Effects of high-frequency transcutaneous electrical nerve stimulation on limb blood flow in healthy humans

BACKGROUND AND PURPOSE

Although transcutaneous electrical nerve stimulation (TENS) has been used clinically for more than 20 years, the hemodynamic effects of this intervention remain controversial. Our goal was to determine the effects of high-frequency TENS on calf blood flow in healthy subjects.

SUBJECTS

Four men and seven women ranging in age from 20 to 44 years (mean = 30, SD = 9) served as subjects.

METHODS

We measured calf blood flow during 20-minute TENS applications over the common peroneal and tibial nerves at intensities above and below the motor threshold.

RESULTS

Calf blood flow was not changed by sensory-level TENS (3.2 +/- 1.0 versus 2.9 +/- 1.0 mL/100 mL/min) or by motor-level TENS (3.1 +/- 1.2 versus 2.8 +/- 1.0 mL/100 mL/min).

CONCLUSION AND DISCUSSION

Neither sensory-level nor low-intensity motor-level TENS applied over peripheral nerves at clinically relevant pulse durations and frequencies altered limb blood flow in asymptomatic individuals. The applicability of these findings in conditions of abnormally elevated or diminished vascular resistance has not been determined.