Ecological and socioeconomic factors associated with the human burden of environmentally mediated pathogens: a global analysis

BACKGROUND

Billions of people living in poverty are at risk of environmentally mediated infectious diseases-that is, pathogens with environmental reservoirs that affect disease persistence and control and where environmental control of pathogens can reduce human risk. The complex ecology of these diseases creates a global health problem not easily solved with medical treatment alone.

METHODS

We quantified the current global disease burden caused by environmentally mediated infectious diseases and used a structural equation model to explore environmental and socioeconomic factors associated with the human burden of environmentally mediated pathogens across all countries.

FINDINGS

We found that around 80% (455 of 560) of WHO-tracked pathogen species known to infect humans are environmentally mediated, causing about 40% (129 488 of 359 341 disability-adjusted life years) of contemporary infectious disease burden (global loss of 130 million years of healthy life annually). The majority of this environmentally mediated disease burden occurs in tropical countries, and the poorest countries carry the highest burdens across all latitudes. We found weak associations between disease burden and biodiversity or agricultural land use at the global scale. In contrast, the proportion of people with rural poor livelihoods in a country was a strong proximate indicator of environmentally mediated infectious disease burden. Political stability and wealth were associated with improved sanitation, better health care, and lower proportions of rural poverty, indirectly resulting in lower burdens of environmentally mediated infections. Rarely, environmentally mediated pathogens can evolve into global pandemics (eg, HIV, COVID-19) affecting even the wealthiest communities.

INTERPRETATION

The high and uneven burden of environmentally mediated infections highlights the need for innovative social and ecological interventions to complement biomedical advances in the pursuit of global health and sustainability goals.

FUNDING

Bill & Melinda Gates Foundation, National Institutes of Health, National Science Foundation, Alfred P. Sloan Foundation, National Institute for Mathematical and Biological Synthesis, Stanford University, and the US Defense Advanced Research Projects Agency.

Evidence gaps and diversity among potential win-win solutions for conservation and human infectious disease control

As sustainable development practitioners have worked to "ensure healthy lives and promote well-being for all" and "conserve life on land and below water", what progress has been made with win-win interventions that reduce human infectious disease burdens while advancing conservation goals? Using a systematic literature review, we identified 46 proposed solutions, which we then investigated individually using targeted literature reviews. The proposed solutions addressed diverse conservation threats and human infectious diseases, and thus, the proposed interventions varied in scale, costs, and impacts. Some potential solutions had medium-quality to high-quality evidence for previous success in achieving proposed impacts in one or both sectors. However, there were notable evidence gaps within and among solutions, highlighting opportunities for further research and adaptive implementation. Stakeholders seeking win-win interventions can explore this Review and an online database to find and tailor a relevant solution or brainstorm new solutions.

Environmental Persistence of the World's Most Burdensome Infectious and Parasitic Diseases

Humans live in complex socio-ecological systems where we interact with parasites and pathogens that spend time in abiotic and biotic environmental reservoirs (e.g., water, air, soil, other vertebrate hosts, vectors, intermediate hosts). Through a synthesis of published literature, we reviewed the life cycles and environmental persistence of 150 parasites and pathogens tracked by the World Health Organization's Global Burden of Disease study. We used those data to derive the time spent in each component of a pathogen's life cycle, including total time spent in humans versus all environmental stages. We found that nearly all infectious organisms were “environmentally mediated” to some degree, meaning that they spend time in reservoirs and can be transmitted from those reservoirs to human hosts. Correspondingly, many infectious diseases were primarily controlled through environmental interventions (e.g., vector control, water sanitation), whereas few (14%) were primarily controlled by integrated methods (i.e., combining medical and environmental interventions). Data on critical life history attributes for most of the 150 parasites and pathogens were difficult to find and often uncertain, potentially hampering efforts to predict disease dynamics and model interactions between life cycle time scales and infection control strategies. We hope that this synthetic review and associated database serve as a resource for understanding both common patterns among parasites and pathogens and important variability and uncertainty regarding particular infectious diseases. These insights can be used to improve systems-based approaches for controlling environmentally mediated diseases of humans in an era where the environment is rapidly changing.

Host preferences inhibit transmission from potential superspreader host species

Host species that are particularly abundant, infectious and/or infected tend to contribute disproportionately to symbiont (parasite or mutualist) maintenance in multi-host systems. Therefore, in a facultative multi-host system where two host species had high densities, high symbiont infestation intensities and high infestation prevalence, we expected interspecific transmission rates to be high. Instead, we found that interspecific symbiont transmission rates to caged sentinel hosts were an order of magnitude lower than intraspecific transmission rates in the wild. Using laboratory experiments to decompose transmission rates, we found that opportunities for interspecific transmission were frequent, where interspecific and intraspecific contact rate functions were statistically indistinguishable. However, most interspecific contacts did not lead to transmission events owing to a previously unrecognized transmission barrier: strong host preferences. During laboratory choice experiments, the symbiont preferred staying on or dispersing to its current host species, even though the oligochaete symbiont is a globally distributed host generalist that can survive and reproduce on many snail host species. These surprising results suggest that when managing symbiont transmission, identifying key host species is still important, but it may be equally important to identify and manage transmission barriers that keep potential superspreader host species in check.

Schistosome infection in Senegal is associated with different spatial extents of risk and ecological drivers for Schistosoma haematobium and S. mansoni

Schistosome parasites infect more than 200 million people annually, mostly in sub-Saharan Africa, where people may be co-infected with more than one species of the parasite. Infection risk for any single species is determined, in part, by the distribution of its obligate intermediate host snail. As the World Health Organization reprioritizes snail control to reduce the global burden of schistosomiasis, there is renewed importance in knowing when and where to target those efforts, which could vary by schistosome species. This study estimates factors associated with schistosomiasis risk in 16 villages located in the Senegal River Basin, a region hyperendemic for Schistosoma haematobium and S. mansoni. We first analyzed the spatial distributions of the two schistosomes’ intermediate host snails (Bulinus spp. and Biomphalaria pfeifferi, respectively) at village water access sites. Then, we separately evaluated the relationships between human S. haematobium and S. mansoni infections and (i) the area of remotely-sensed snail habitat across spatial extents ranging from 1 to 120 m from shorelines, and (ii) water access site size and shape characteristics. We compared the influence of snail habitat across spatial extents because, while snail sampling is traditionally done near shorelines, we hypothesized that snails further from shore also contribute to infection risk. We found that, controlling for demographic variables, human risk for S. haematobium infection was positively correlated with snail habitat when snail habitat was measured over a much greater radius from shore (45 m to 120 m) than usual. S. haematobium risk was also associated with large, open water access sites. However, S. mansoni infection risk was associated with small, sheltered water access sites, and was not positively correlated with snail habitat at any spatial sampling radius. Our findings highlight the need to consider different ecological and environmental factors driving the transmission of each schistosome species in co-endemic landscapes.

Schistosome parasites infect more than 200 million people worldwide, mainly in sub-Saharan Africa, where many people are at-risk for infection by multiple schistosome species simultaneously. To reduce the global burden of schistosomiasis, control of the parasites’ intermediate host–specific species of freshwater snails–has been elevated in priority to complement mass drug administration campaigns in endemic areas. To maximize the efficacy and efficiency of snail control efforts, a better understanding of where to target intermediate host snails is badly needed. This includes a better understanding of the spatial scale at which snails in the environment contribute to human infection risk, and, in co-endemic settings, how ecological determinants of infection risk vary by schistosome species. We used quantitative snail sampling and remotely-sensed data at 16 villages in the Senegal River Basin to compare and contrast ecological correlates and spatial scales of infection risk from freshwater snails that transmit Schistosoma haematobium versus S. mansoni. We found that infection risk for S. haematobium was associated with snail habitat at a larger spatial radius than is typically considered for schistosomiasis monitoring and control, whereas infection risk for S. mansoni was not positively correlated with snail habitat at any spatial sampling radius, but was associated with small water access sites enclosed by emergent vegetation. Our findings highlight the need to consider the different ecological and environmental factors driving the transmission of each schistosome species in co-endemic landscapes.

Improving rural health care reduces illegal logging and conserves carbon in a tropical forest

Tropical forest loss currently exceeds forest gain, leading to a net greenhouse gas emission that exacerbates global climate change. This has sparked scientific debate on how to achieve natural climate solutions. Central to this debate is whether sustainably managing forests and protected areas will deliver global climate mitigation benefits, while ensuring local peoples' health and well-being. Here, we evaluate the 10-y impact of a human-centered solution to achieve natural climate mitigation through reductions in illegal logging in rural Borneo: an intervention aimed at expanding health care access and use for communities living near a national park, with clinic discounts offsetting costs historically met through illegal logging. Conservation, education, and alternative livelihood programs were also offered. We hypothesized that this would lead to improved health and well-being, while also alleviating illegal logging activity within the protected forest. We estimated that 27.4 km2 of deforestation was averted in the national park over a decade (∼70% reduction in deforestation compared to a synthetic control, permuted P = 0.038). Concurrently, the intervention provided health care access to more than 28,400 unique patients, with clinic usage and patient visitation frequency highest in communities participating in the intervention. Finally, we observed a dose-response in forest change rate to intervention engagement (person-contacts with intervention activities) across communities bordering the park: The greatest logging reductions were adjacent to the most highly engaged villages. Results suggest that this community-derived solution simultaneously improved health care access for local and indigenous communities and sustainably conserved carbon stocks in a protected tropical forest.

Handling times and saturating transmission functions in a snail-worm symbiosis

All dynamic species interaction models contain an assumption that describes how contact rates scale with population density. Choosing an appropriate contact-density function is important, because different functions have different implications for population dynamics and stability. However, this choice can be challenging, because there are many possible functions, and most are phenomenological and thus difficult to relate to underlying ecological processes. Using one such phenomenological function, we described a nonlinear relationship between field transmission rates and host density in a common snail-oligochaete symbiosis. We then used a well-known contact function from predator-prey models, the Holling Type II functional response, to describe and predict host snail contact rates in the laboratory. The Holling Type II functional response accurately described both the nonlinear contact-density relationship and the average contact duration that we observed. Therefore, we suggest that contact rates saturate with host density in this system because each snail contact requires a non-instantaneous handling time, and additional possible contacts do not occur during that handling time. Handling times and nonlinear contact rates might also explain the nonlinear relationship between symbiont transmission and snail density that we observed in the field, which could be confirmed by future work that controls for other potential sources of seasonal variation in transmission rates. Because most animal contacts are not instantaneous, the Holling Type II functional response might be broadly relevant to diverse host-symbiont systems.

Dispersal of a defensive symbiont depends on contact between hosts, host health, and host size

Symbiont dispersal is necessary for the maintenance of defense mutualisms in space and time, and the distribution of symbionts among hosts should be intricately tied to symbiont dispersal behaviors. However, we know surprisingly little about how most defensive symbionts find and choose advantageous hosts or what cues trigger symbionts to disperse from their current hosts. In a series of six experiments, we explored the dispersal ecology of an oligochaete worm (Chaetogaster limnaei) that protects snail hosts from infection by larval trematode parasites. Specifically, we determined the factors that affected net symbiont dispersal from a current "donor" host to a new "receiver" host. Symbionts rarely dispersed unless hosts directly came in contact with one another. However, symbionts overcame their reluctance to disperse across the open environment if the donor host died. When hosts came in direct contact, net symbiont dispersal varied with both host size and trematode infection status, whereas symbiont density did not influence the probability of symbiont dispersal. Together, these experiments show that symbiont dispersal is not a constant, random process, as is often assumed in symbiont dispersal models, but rather the probability of dispersal varies with ecological conditions and among individual hosts. The observed heterogeneity in dispersal rates among hosts may help to explain symbiont aggregation among snail hosts in nature.

The effect of supine exercise on the distribution of regional pulmonary blood flow measured using proton MRI

The Zone model of pulmonary perfusion predicts that exercise reduces perfusion heterogeneity because increased vascular pressure redistributes flow to gravitationally nondependent lung, and causes dilation and recruitment of blood vessels. However, during exercise in animals, perfusion heterogeneity as measured by the relative dispersion (RD, SD/mean) is not significantly decreased. We evaluated the effect of exercise on pulmonary perfusion in six healthy supine humans using magnetic resonance imaging (MRI). Data were acquired at rest, while exercising (∼27% of maximal oxygen consumption) using a MRI-compatible ergometer, and in recovery. Images were acquired in most of the right lung in the sagittal plane at functional residual capacity, using a 1.5-T MR scanner equipped with a torso coil. Perfusion was measured using arterial spin labeling (ASL-FAIRER) and regional proton density using a fast multiecho gradient-echo sequence. Perfusion images were corrected for coil-based signal heterogeneity, large conduit vessels removed and quantified (in ml·min(-1)·ml(-1)) (perfusion), and also normalized for density and quantified (in ml·min(-1)·g(-1)) (density-normalized perfusion, DNP) accounting for tissue redistribution. DNP increased during exercise (11.1 ± 3.5 rest, 18.8 ± 2.3 exercise, 13.2 ± 2.2 recovery, ml·min(-1)·g(-1), P < 0.0001), and the increase was largest in nondependent lung (110 ± 61% increase in nondependent, 63 ± 35% in mid, 70 ± 33% in dependent, P < 0.005). The RD of perfusion decreased with exercise (0.93 ± 0.21 rest, 0.73 ± 0.13 exercise, 0.94 ± 0.18 recovery, P < 0.005). The RD of DNP showed a similar trend (0.82 ± 0.14 rest, 0.75 ± 0.09 exercise, 0.81 ± 0.10 recovery, P = 0.13). In conclusion, in contrast to animal studies, in supine humans, mild exercise decreased perfusion heterogeneity, consistent with Zone model predictions.

Parasite predators exhibit a rapid numerical response to increased parasite abundance and reduce transmission to hosts

Predators of parasites have recently gained attention as important parts of food webs and ecosystems. In aquatic systems, many taxa consume free-living stages of parasites, and can thus reduce parasite transmission to hosts. However, the importance of the functional and numerical responses of parasite predators to disease dynamics is not well understood. We collected host–parasite–predator cooccurrence data from the field, and then experimentally manipulated predator abundance, parasite abundance, and the presence of alternative prey to determine the consequences for parasite transmission. The parasite predator of interest was a ubiquitous symbiotic oligochaete of mollusks, Chaetogaster limnaei limnaei, which inhabits host shells and consumes larval trematode parasites. Predators exhibited a rapid numerical response, where predator populations increased or decreased by as much as 60% in just 5 days, depending on the parasite:predator ratio. Furthermore, snail infection decreased substantially with increasing parasite predator densities, where the highest predator densities reduced infection by up to 89%. Predators of parasites can play an important role in regulating parasite transmission, even when infection risk is high, and especially when predators can rapidly respond numerically to resource pulses. We suggest that these types of interactions might have cascading effects on entire disease systems, and emphasize the importance of considering disease dynamics at the community level.

Rapid intravenous infusion of 20 mL/kg saline alters the distribution of perfusion in healthy supine humans

Rapid intravenous saline infusion, a model meant to replicate the initial changes leading to pulmonary interstitial edema, increases pulmonary arterial pressure in humans. We hypothesized that this would alter lung perfusion distribution. Six healthy subjects (29 ± 6 years) underwent magnetic resonance imaging to quantify perfusion using arterial spin labeling. Regional proton density was measured using a fast-gradient echo sequence, allowing blood delivered to the slice to be normalized for density and quantified in mL/min/g. Contributions from flow in large conduit vessels were minimized using a flow cutoff value (blood delivered > 35% maximum in mL/min/cm(3)) in order to obtain an estimate of blood delivered to the capillary bed (perfusion). Images were acquired supine at baseline, after infusion of 20 mL/kg saline, and after a short upright recovery period for a single sagittal slice in the right lung during breath-holds at functional residual capacity. Thoracic fluid content measured by impedance cardiography was elevated post-infusion by up to 13% (p<0.0001). Forced expiratory volume in 1s was reduced by 5.1% post-20 mL/kg (p=0.007). Infusion increased perfusion in nondependent lung by up to 16% (6.4 ± 1.6 mL/min/g baseline, 7.3 ± 1.8 post, 7.4 ± 1.7 recovery, p=0.03). Including conduit vessels, blood delivered in dependent lung was unchanged post-infusion; however, was increased at recovery (9.4 ± 2.7 mL/min/g baseline, 9.7 ± 2.0 post, 11.3 ± 2.2 recovery, p=0.01). After accounting for changes in conduit vessels, there were no significant changes in perfusion in dependent lung following infusion (7.8 ± 1.9 mL/min/g baseline, 7.9 ± 2.0 post, 8.5 ± 2.1 recovery, p=0.36). There were no significant changes in lung density. These data suggest that saline infusion increased perfusion to nondependent lung, consistent with an increase in intravascular pressures. Dependent lung may have been "protected" from increases in perfusion following infusion due to gravitational compression of the pulmonary vasculature.

Pulmonary perfusion heterogeneity is increased by sustained, heavy exercise in humans

Exercise presents a considerable stress to the pulmonary system and ventilation-perfusion (Va/Q) heterogeneity increases with exercise, affecting the efficiency of gas exchange. In particular, prolonged heavy exercise and maximal exercise are known to increase Va/Q heterogeneity and these changes persist into recovery. We hypothesized that the spatial heterogeneity of pulmonary perfusion would be similarly elevated after prolonged exercise. To test this, athletic subjects (n = 6, Vo(2max) = 61 ml. kg(-1).min(-1)) with exercising Va/Q heterogeneity previously characterized by the multiple inert gas elimination technique (MIGET), performed 45 min of cycle exercise at approximately 70% Vo(2max). MRI arterial spin labeling measures of pulmonary perfusion were acquired pre- and postexercise (at 20, 40, 60 min post) to quantify the spatial distribution in isogravitational (coronal) and gravitationally dependent (sagittal) planes. Regional proton density measurements allowed perfusion to be normalized for density and quantified in milliliters per minute per gram. Mean lung density did not change significantly in either plane after exercise (P = 0.19). Density-normalized perfusion increased in the sagittal plane postexercise (P =or <0.01) but heterogeneity did not (all P >or= 0.18), likely because of perfusion redistribution and vascular recruitment. Density-normalized perfusion was unchanged in the coronal plane postexercise (P = 0.66), however, perfusion heterogeneity was significantly increased as measured by the relative dispersion [RD, pre 0.62(0.07), post 0.82(0.21), P < 0.0001] and geometric standard deviation [GSD, pre 1.74(0.14), post 2.30(0.56), P < 0.005]. These changes in heterogeneity were related to the exercise-induced changes of the log standard deviation of the ventilation distribution, an MIGET index of Va/Q heterogeneity (RD R(2) = 0.68, P < 0.05, GSD, R(2) = 0.55, P = 0.09). These data are consistent with but not proof of interstitial pulmonary edema as the mechanism underlying exercise-induced increases in both spatial perfusion heterogeneity and Va/Q heterogeneity.

Hypoxic pulmonary vasoconstriction does not contribute to pulmonary blood flow heterogeneity in normoxia in normal supine humans

We hypothesized that some of the heterogeneity of pulmonary blood flow present in the normal human lung in normoxia is due to hypoxic pulmonary vasoconstriction (HPV). If so, mild hyperoxia would decrease the heterogeneity of pulmonary perfusion, whereas it would be increased by mild hypoxia. To test this, six healthy nonsmoking subjects underwent magnetic resonance imaging (MRI) during 20 min of breathing different oxygen concentrations through a face mask [normoxia, inspired O(2) fraction (Fi(O(2))) = 0.21; hypoxia, Fi(O(2)) = 0.125; hyperoxia, Fi(O(2)) = 0.30] in balanced order. Data were acquired on a 1.5-T MRI scanner during a breath hold at functional residual capacity from both coronal and sagittal slices in the right lung. Arterial spin labeling was used to quantify the spatial distribution of pulmonary blood flow in milliliters per minute per cubic centimeter and fast low-angle shot to quantify the regional proton density, allowing perfusion to be expressed as density-normalized perfusion in milliliters per minute per gram. Neither mean proton density [hypoxia, 0.46(0.18) g water/cm(3); normoxia, 0.47(0.18) g water/cm(3); hyperoxia, 0.48(0.17) g water/cm(3); P = 0.28] nor mean density-normalized perfusion [hypoxia, 4.89(2.13) ml x min(-1) x g(-1); normoxia, 4.94(1.88) ml x min(-1) x g(-1); hyperoxia, 5.32(1.83) ml x min(-1) x g(-1); P = 0.72] were significantly different between conditions in either imaging plane. Similarly, perfusion heterogeneity as measured by relative dispersion [hypoxia, 0.74(0.16); normoxia, 0.74(0.10); hyperoxia, 0.76(0.18); P = 0.97], fractal dimension [hypoxia, 1.21(0.04); normoxia, 1.19(0.03); hyperoxia, 1.20(0.04); P = 0.07], log normal shape parameter [hypoxia, 0.62(0.11); normoxia, 0.72(0.11); hyperoxia, 0.70(0.13); P = 0.07], and geometric standard deviation [hypoxia, 1.88(0.20); normoxia, 2.07(0.24); hyperoxia, 2.02(0.28); P = 0.11] was also not different. We conclude that HPV does not affect pulmonary perfusion heterogeneity in normoxia in the normal supine human lung.

Quantification of regional pulmonary blood flow using ASL-FAIRER

Pulsed arterial spin labeling (ASL) techniques have been theoretically and experimentally validated for cerebral blood flow (CBF) quantification. In this study ASL-FAIRER was used to measure regional pulmonary blood flow (rPBF) in seven healthy subjects. Two general ASL strategies were investigated: 1) a single-subtraction approach using one tag-control pair acquisition at an inversion time (TI) matched to the RR-interval, and 2) a multiple-subtraction approach using tag-control pairs acquired at various TIs. The mean rPBF averaged 1.70 +/- 0.38 ml/min/ml when measured with the multiple-subtraction approach, and was approximately 2% less when measured with the single-subtraction method (1.66 +/- 0.24 ml/min/ml). Assuming an average lung density of 0.33 g/ml, this translates into a regional perfusion of approximately 5.5 ml/g/min, which is comparable to other measures of pulmonary perfusion. As with other ASL applications, a key problem with quantitative interpretation of the results is the physical gap between the tagging region and imaged slice. Because of the high pulsatility of PBF, ASL acquisition and data analysis differ significantly between the lung and the brain. The advantages and drawbacks of the single- vs. multiple-subtraction approaches are considered within a theoretical framework tailored to PBF.

Ventilation-perfusion inequality during normoxic and hypoxic exercise in the emu

Many avian species exhibit an extraordinary ability to exercise under hypoxic condition compared with mammals, and more efficient pulmonary O(2) transport has been hypothesized to contribute to this avian advantage. We studied six emus (Dromaius novaehollandaie, 4-6 mo old, 25-40 kg) at rest and during treadmill exercise in normoxia and hypoxia (inspired O(2) fraction approximately 0.13). The multiple inert gas elimination technique was used to measure ventilation-perfusion (V/Q) distribution of the lung and calculate cardiac output and parabronchial ventilation. In both normoxia and hypoxia, exercise increased arterial Po(2) and decreased arterial Pco(2), reflecting hyperventilation, whereas pH remained unchanged. The V/Q distribution was unimodal, with a log standard deviation of perfusion distribution = 0.60 +/- 0.06 at rest; this did not change significantly with either exercise or hypoxia. Intrapulmonary shunt was <1% of the cardiac output in all conditions. CO(2) elimination was enhanced by hypoxia and exercise, but O(2) exchange was not affected by exercise in normoxia or hypoxia. The stability of V/Q matching under conditions of hypoxia and exercise may be advantageous for birds flying at altitude.

Common themes of adaptation to hypoxia. Insights from comparative physiology

Many vertebrate animals have superior tolerance to environmental hypoxia compared to humans. For example, turtles tolerate an environment of 100% N2 for several hours, without apparent ill effect. This hypoxia tolerance is not limited to heterotherms, as some species of marine mammals, such as the northern elephant seal, may voluntarily dive for periods of up to 2 hours. Torpid bats exhibit prolonged periods of apnea and passive diffusion of oxygen down their trachea through an open glottis supplies a significant amount of the oxygen uptake. The Ruppell's griffon holds the known avian record of flight at 11,278 m, and other birds regularly migrate at altitudes over 8000m. These animals exhibit diverse adaptations for tolerating their hypoxic environment, many of which are poorly understood. Some of theses strategies include 1) the ability to lower metabolic rate when exposed to hypoxia 2) the ability to recruit alternate biochemical pathways for energy production 3) a left shifted oxy-hemoglobin dissociation curve 4) more efficient pulmonary gas exchange 5) the ability to alter blood flow distribution under hypoxic stress. Although there are common themes of animal adaptation to hypoxic stress, many animal solutions are unique.

Ventilatory response to 2-h sustained hypoxia in humans

We used two protocols to determine if hypoxic ventilatory decline (HVD) involves changes in slope and/or intercept of the isocapnic HVR (hypoxic ventilatory response, expressed as the increase in VI per percentage decrease in SaO2). Isocapnia was defined as 1.5 mmHg above hyperoxic PET(CO2). HVD was recorded in protocol I during two sequential 25 min exposures to isocapnic hypoxia (85 and 75% SaO2, n=7) and in protocol II during 14 min of isocapnic hypoxia (90% SaO2, FIO2=0.13, n=15), extended to 2 h of hypoxia with CO2-uncontrolled in eight subjects. HVR was measured by the step reduction to sequentially lower levels of SaO2 in protocol I and by 3 min steps to 80% SaO2 at 8, 14 and 120 min in protocol II. The intercept of the HVR (VI predicted at SaO2=100%) decreased after 14 and 25 min in both protocols (P<0.05). Changes in slope were observed only in protocol I at SaO2=75%, suggesting that the slope of the HVR is more sensitive to depth than duration of hypoxic exposure. After 2 h of hypoxia the HVR intercept returned toward control value (P<0.05) with still no significant changes in the HVR slope. We conclude that HVD in humans involves a decrease in hyperoxic ventilatory drive that can occur without significant change in slope of the HVR. The partial reversal of the HVD after 2 h of hypoxia may reflect some components of ventilatory acclimatization to hypoxia.

Intermittent vs continuous hypoxia: effects on ventilation and erythropoiesis in humans

OBJECTIVE

Recently, we showed that 5 days of normobaric intermittent hypoxia at rest (IH; 2 hours daily at 3,800 m simulated altitude; partial pressure of inspired oxygen 90 torr) can induce an increase in the isocapnic hypoxic ventilatory response (HVR) and blood reticulocyte count. The purpose of the present study was to compare these data with continuous exposure to the same hypoxic level.

METHODS

Four of the same subjects were exposed, a year later, to 2 days of continuous hypoxia (CH), and 4 different subjects were exposed to 8 weeks of CH, both at the White Mountain Research Station (3,800 m altitude, barometric pressure approximately 489 torr). Inspired minute ventilation (VI), end-tidal partial pressure of carbon dioxide, arterial oxygen saturation (SaO2[sat]), hematocrit, and hemoglobin concentration were measured at different times during the continuous exposures. The HVR was expressed as the increase in V1 per 1% decrease in SaO2.

RESULTS

The HVR showed no significant difference in the control values 1 year apart (IH, 0.06 +/- 0.03; CH2d (2 days' continuous hypoxia), 0.19 +/- 0.07 L x min(-1) x %sat(-1); means +/- SE), and the HVR values were similar after 2 days of IH compared to CH (0.42 +/- 0.26 and 0.51 +/- 0.22 L x min(-1) x %sat(-1), respectively). On the new subjects after 2 weeks of CH, the HVR showed a maximum increase, similar to the increase observed after only 5 days of IH, hemoglobin concentrations and hematocrit were significantly increased (45.0 +/- 2.7% vs 51.5 +/- 3.0% and 14.5 +/- 0.7 vs 17.2 +/- 1.0 g x dL(-1), respectively). The HVR did not change significantly from week 2 to 8 of CH, whereas hematological data were still increasing at the end of the 8 weeks.

CONCLUSION

Changes in ventilatory oxygen sensitivity induced by IH and CH are similar in magnitude but occur with different time courses. The effects of IH on erythropoiesis are significant but fewer than on CH.

Time domains of the hypoxic ventilatory response in awake ducks: episodic and continuous hypoxia

Time-dependent ventilatory responses to episodic and continuous isocapnic hypoxia were measured in unidirectionally ventilated, awake ducks. Three protocols were used: (1) ten 3-min episodes of moderate hypoxia (10% O(2)) with 5-min normoxic intervals; (2) three 3-min episodes of severe hypoxia (8% O(2)) with 5-min normoxic intervals; and (3) 30-min of continuous moderate hypoxia. Ventilation (V(I)) increased immediately within a hypoxic episode (acute response), followed by a further slow rise in V(I) (short-term potentiation). The peak V(T) response increased from the first to second moderate hypoxic episode (progressive augmentation), but was unchanged thereafter. During normoxic intervals, V(I) increased progressively (56% following the tenth episode; long term facilitation). Time-dependent changes were not observed during or following 30-min of continuous hypoxia. Although several time-dependent ventilatory responses to episodic hypoxia are observed in awake ducks, they are relatively small and biased towards facilitation versus inhibitory mechanisms.

Effects of intermittent hypoxia on the isocapnic hypoxic ventilatory response and erythropoiesis in humans

Isocapnic hypoxic ventilatory response (HVR) and hematological variables were measured in nine adult males (age: 29.3+/-3.4) exposed to normobaric intermittent hypoxia (IH, 2 h daily at FI(O(2))=0.13, equivalent to 3800 m altitude) for 12 days. Mean HVR significantly increased during IH, however, after reaching a peak on Day 5 (0.79+/-0.12 vs. 0.27+/-0.11 L.min(-1).%(-1) on Day 1, P<0.05), it progressively decreased toward a lower value (0.46+/-0.16 L min(-1) x %(-1) on Day 12). In contrast, the subjects showed no changes in the ventilatory data and arterial O(2)-saturation in normoxia or poikilocapnic hypoxia (PET(CO(2)) uncontrolled). Hematocrit and hemoglobin concentration did not change, but the reticulocyte count increased by Day 5 (P<0.01). Our results suggest that moderate intermittent hypoxia induces changes in ventilatory O(2)-sensitivity and triggers the hematological acclimatization by increasing the percentage of reticulocytes in the blood. Normal ventilatory acclimatization to hypoxia was, however, not observed and the mechanisms involved in the biphasic changes in HVR we observed remain to be determined.

Pulmonary gas exchange during exercise in women: effects of exercise type and work increment

Exercise-induced arterial hypoxemia (EIAH) has been reported in male athletes, particularly during fast-increment treadmill exercise protocols. Recent reports suggest a higher incidence in women. We hypothesized that 1-min incremental (fast) running (R) protocols would result in a lower arterial PO(2) (Pa(O(2))) than 5-min increment protocols (slow) or cycling exercise (C) and that women would experience greater EIAH than previously reported for men. Arterial blood gases, cardiac output, and metabolic data were obtained in 17 active women [mean maximal O(2) uptake (VO(2 max)) = 51 ml. kg(-1). min(-1)]. They were studied in random order (C or R), with a fast VO(2 max) protocol. After recovery, the women performed 5 min of exercise at 30, 60, and 90% of VO(2 max) (slow). One week later, the other exercise mode (R or C) was similarly studied. There were no significant differences in VO(2 max) between R and C. Pulmonary gas exchange was similar at rest, 30%, and 60% of VO(2 max). At 90% of VO(2 max), Pa(O(2)) was lower during R (mean +/- SE = 94 +/- 2 Torr) than during C (105 +/- 2 Torr, P < 0.0001), as was ventilation (85.2 +/- 3.8 vs. 98.2 +/- 4.4 l/min BTPS, P < 0.0001) and cardiac output (19.1 +/- 0.6 vs. 21.1 +/- 1.0 l/min, P < 0.001). Arterial PCO(2) (32.0 +/- 0.5 vs. 30.0 +/- 0.6 Torr, P < 0.001) and alveolar-arterial O(2) difference (A-aDO(2); 22 +/- 2 vs. 16 +/- 2 Torr, P < 0.0001) were greater during R. Pa(O(2)) and A-aDO(2) were similar between slow and fast. Nadir Pa(O(2)) was </=80 Torr in four women (24%) but only during fast-R. In all subjects, Pa(O(2)) at VO(2 max) was greater than the lower 95% prediction limit calculated from available data in men (n = 72 C and 38 R) for both R and C. These data suggest intrinsic differences in gas exchange between R and C, due to differences in ventilation and also efficiency of gas exchange. The Pa(O(2)) responses to R and C exercise in our 17 subjects do not differ significantly from those previously observed in men.

Pulmonary gas exchange during exercise in highly trained cyclists with arterial hypoxemia

The causes of exercise-induced hypoxemia (EIH) remain unclear. We studied the mechanisms of EIH in highly trained cyclists. Five subjects had no significant change from resting arterial PO(2) (Pa(O(2)); 92.1 +/- 2.6 Torr) during maximal exercise (C), and seven subjects (E) had a >10-Torr reduction in Pa(O(2)) (81.7 +/- 4.5 Torr). Later, they were studied at rest and during various exercise intensities by using the multiple inert gas elimination technique in normoxia and hypoxia (13.2% O(2)). During normoxia at 90% peak O(2) consumption, Pa(O(2)) was lower in E compared with C (87 +/- 4 vs. 97 +/- 6 Torr, P < 0.001) and alveolar-to-arterial O(2) tension difference (A-aDO(2)) was greater (33 +/- 4 vs. 23 +/- 1 Torr, P < 0. 001). Diffusion limitation accounted for 23 (E) and 13 Torr (C) of the A-aDO(2) (P < 0.01). There were no significant differences between groups in arterial PCO(2) (Pa(CO(2))) or ventilation-perfusion (VA/Q) inequality as measured by the log SD of the perfusion distribution (logSD(Q)). Stepwise multiple linear regression revealed that lung O(2) diffusing capacity (DL(O(2))), logSD(Q), and Pa(CO(2)) each accounted for approximately 30% of the variance in Pa(O(2)) (r = 0.95, P < 0.001). These data suggest that EIH has a multifactorial etiology related to DL(O(2)), VA/Q inequality, and ventilation.

Measurement of cardiac output during exercise by open-circuit acetylene uptake

Noninvasive measurement of cardiac output (QT) is problematic during heavy exercise. We report a new approach that avoids unpleasant rebreathing and resultant changes in alveolar PO(2) or PCO(2) by measuring short-term acetylene (C(2)H(2)) uptake by an open-circuit technique, with application of mass balance for the calculation of QT. The method assumes that alveolar and arterial C(2)H(2) pressures are the same, and we account for C(2)H(2) recirculation by extrapolating end-tidal C(2)H(2) back to breath 1 of the maneuver. We correct for incomplete gas mixing by using He in the inspired mixture. The maneuver involves switching the subject to air containing trace amounts of C(2)H(2) and He; ventilation and pressures of He, C(2)H(2), and CO(2) are measured continuously (the latter by mass spectrometer) for 20-25 breaths. Data from three subjects for whom multiple Fick O(2) measurements of QT were available showed that measurement of QT by the Fick method and by the C(2)H(2) technique was statistically similar from rest to 90% of maximal O(2) consumption (VO(2 max)). Data from 12 active women and 12 elite male athletes at rest and 90% of VO(2 max) fell on a single linear relationship, with O(2) consumption (VO(2)) predicting QT values of 9.13, 15.9, 22.6, and 29.4 l/min at VO(2) of 1, 2, 3, and 4 l/min. Mixed venous PO(2) predicted from C(2)H(2)-determined QT, measured VO(2), and arterial O(2) concentration was approximately 20-25 Torr at 90% of VO(2 max) during air breathing and 10-15 Torr during 13% O(2) breathing. This modification of previous gas uptake methods, to avoid rebreathing, produces reasonable data from rest to heavy exercise in normal subjects.

Evidence of skeletal muscle metabolic reserve during whole body exercise in patients with chronic obstructive pulmonary disease

When freed from central cardiorespiratory limitations, healthy human skeletal muscle has exhibited a significant metabolic reserve. We studied the existence of this reserve in 10 severely compromised (FEV1 = 0.97 +/- SE 0.01) patients with chronic obstructive pulmonary disease (COPD). To manipulate O2 supply and O2 demand in locomotor and respiratory muscles, subjects performed both maximal conventional two-legged cycle ergometry (large muscle mass) and single-leg knee extensor exercise (KE, small muscle mass) while breathing room air (RA), 100% O2, and 79% helium + 21% O2 (HeO2). With each gas mixture, peak ventilation, peak heart rate, and perceived breathlessness were lower in KE than cycle exercise (p < 0. 05). Arterial O2 saturation and maximal work capacity increased in both exercise modalities while subjects breathed 100% O2 (work: +10% bike, +25% KE, p < 0.05). HeO2 increased maximal work capacity on the cycle (+14%, p < 0.05) but had no effect on KE. HeO2 resulted in the greatest maximum minute ventilation in both bike and KE (p < 0. 05) but had no effect on arterial O2 saturation. Thus, a skeletal muscle metabolic reserve in these patients with COPD is evidenced by: (1) greater muscle mass specific work in KE; (2) greater work rates with higher fraction of inspired oxygen (FIO2); (3) an even greater effect of FIO2 during KE (i.e., when the lungs are less challenged); and (4) the positive effect of HeO2 on bicycle work rate. This skeletal muscle metabolic reserve suggests that reduced whole body exercise capacity in COPD is the result of central restraints rather than peripheral skeletal muscle dysfunction, while the beneficial effect of 100% O2 (with no change in maximum ventilation) suggests that the respiratory system is not the sole constraint to oxygen consumption.

Pulmonary gas exchange during exercise in pigs

Increased ventilation-perfusion (VA/Q) inequality is observed in approximately 50% of humans during heavy exercise and contributes to the widening of the alveolar-arterial O2 difference (A-aDO2). Despite extensive investigation, the cause remains unknown. As a first step to more direct examination of this problem, we developed an animal model. Eight Yucatan miniswine were studied at rest and during treadmill exercise at approximately 30, 50, and 85% of maximal O2 consumption (VO2 max). Multiple inert-gas, blood-gas, and metabolic data were obtained. The A-aDO2 increased from 0 +/- 3 (SE) Torr at rest to 14 +/- 2 Torr during the heaviest exercise level, but arterial PO2 (PaO2) remained at resting levels during exercise. There was normal VA/Q inequality [log SD of the perfusion distribution (log) = 0.42 +/- 0.04] at rest, and moderate increases (log = 0.68 +/- 0.04, P < 0.0001) were observed with exercise. This result was reproducible on a separate day. The VA/Q inequality changes are similar to those reported in highly trained humans. However, in swine, unlike in humans, there was no inert gas evidence for pulmonary end-capillary diffusion limitation during heavy exercise; there was no systematic difference in the measured PaO2 and the PaO2 as predicted from the inert gases. These data suggest that the pig animal model is well suited for studying the mechanism of exercise-induced VA/Q inequality.

Effect of prolonged, heavy exercise on pulmonary gas exchange in athletes

During maximal exercise, ventilation-perfusion inequality increases, especially in athletes. The mechanism remains speculative. We hypothesized that, if interstitial pulmonary edema is involved, prolonged exercise would result in increasing ventilation-perfusion inequality over time by exposing the pulmonary vascular bed to high pressures for a long duration. The response to short-term exercise was first characterized in six male athletes [maximal O2 uptake (V(O2)max) = 63 ml x kg-1 x min-1] by using 5 min of cycling exercise at 30, 65, and 90% V(O2) max. Multiple inert-gas, blood-gas, hemodynamic, metabolic rate, and ventilatory data were obtained. Resting log SD of the perfusion distribution (log SDQ) was normal [0.50 +/- 0.03 (SE)] and increased with exercise (log SDQ = 0.65 +/- 0.04, P < 0.005), alveolar-arterial O2 difference increased (to 24 +/- 3 Torr), and end-capillary pulmonary diffusion limitation occurred at 90% V(O2)max. The subjects recovered for 30 min, then, after resting measurements were taken, exercised for 60 min at approximately 65% V(O2)max. O2 uptake, ventilation, cardiac output, and alveolar-arterial O2 difference were unchanged after the first 5 min of this test, but log SDQ increased from 0.59 +/- 0.03 at 5 min to 0. 66 +/- 0.05 at 60 min (P < 0.05), without pulmonary diffusion limitation. Log SDQ was negatively related to total lung capacity normalized for body surface area (r = -0.97, P < 0.005 at 60 min). These data are compatible with interstitial edema as a mechanism and suggest that lung size is an important determinant of the efficiency of gas exchange during exercise.

Effect of prolonged heavy exercise on pulmonary gas exchange in horses

During short-term maximal exercise, horses have impaired pulmonary gas exchange, manifested by diffusion limitation and arterial hypoxemia, without marked ventilation-perfusion (VA/Q) inequality. Whether gas exchange deteriorates progressively during prolonged submaximal exercise has not been investigated. Six thoroughbred horses performed treadmill exercise at approximately 60% of maximal oxygen uptake until exhaustion (28-39 min). Multiple inert gas, blood-gas, hemodynamic, metabolic rate, and ventilatory data were obtained at rest and 5-min intervals during exercise. Oxygen uptake, cardiac output, and alveolar-arterial PO2 gradient were unchanged after the first 5 min of exercise. Alveolar ventilation increased progressively during exercise, from increased tidal volume and respiratory frequency, resulting in an increase in arterial PO2 and decrease in arterial PCO2. At rest there was minimal VA/Q inequality, log SD of the perfusion distribution (log SDQ) = 0.20. This doubled by 5 min of exercise (log SDQ = 0.40) but did not increase further. There was no evidence of alveolar-end-capillary diffusion limitation during exercise. However, there was evidence for gas-phase diffusion limitation at all time points, and enflurane was preferentially overretained. Horses maintain excellent pulmonary gas exchange during exhaustive, submaximal exercise. Although VA/Q inequality is greater than at rest, it is less than observed in most mammals and the effect on gas exchange is minimal.

Sustained submaximal exercise does not alter the integrity of the lung blood-gas barrier in elite athletes

The extreme thinness of the pulmonary blood-gas barrier results in high mechanical stresses in the capillary wall when the capillary pressure rises during exercise. We have previously shown that, in elite cyclists, 6-8 min of maximal exercise increase blood-gas barrier permeability and result in higher concentrations of red blood cells, total protein, and leukotriene B4 in bronchoalveolar lavage (BAL) fluid compared with results in sedentary controls. To test the hypothesis that stress failure of the barrier only occurs at the highest level of exercise, we performed BAL in six healthy athletes after 1 h of exercise at 77% of maximal O2 consumption. Controls were eight normal nonathletes who did not exercise before BAL. In contrast with our previous study, we did not find higher concentrations of red blood cells, total protein, and leukotriene B4 in the exercising athletes compared with control subjects. However, higher concentrations of surfactant apoprotein A and a higher surfactant apoprotein A-to-phospholipid ratio were observed in the athletes performing prolonged exercise, compared with both the controls and the athletes from our previous study. These results suggest that, in elite athletes, the integrity of the blood-gas barrier is altered only at extreme levels of exercise.

Effects of inhaled nitric oxide on gas exchange in lungs with shunt or poorly ventilated areas

Inhaled nitric oxide (NO) is a selective pulmonary vasodilator with beneficial effects on some lung diseases, yet conflicting results, particularly in chronic obstructive pulmonary disease, have been reported. We hypothesized that although inhaled NO would improve gas exchange in the presence of shunt (by increasing blood flow to normal areas), it could worsen gas exchange when areas of low ventilation-perfusion (VA/Q) ratio were present since these areas could be preferentially vasodilated by NO. We examined how approximately 80 ppm inhaled NO altered pulmonary gas exchange in anesthetized ventilated dogs with the following: (1) normal lungs (n = 8), (2) shunt (n = 9, 24.7% shunt) produced by complete obstruction of one lobar bronchus, and (3) VA/Q inequality (n = 8) created by partial obstruction of one lobar bronchus resulting in a bimodal VA/Q distribution with 13% perfusion of low VA/Q areas (0.005 < VA/Q < 0.1) without shunt. Inhaled No significantly reduced pulmonary arterial (p < 0.001) and wedge pressures (p < 0.01) and pulmonary vascular resistance (p < 0.01) without changing cardiac output in each group. In normal lungs, NO did not alter PaO2 or VA/Q inequality. However, with complete obstruction, shunt fell slightly (p < 0.001) with NO. In lungs with VA/Q inequality, NO variably affected VA/Q matching, which was improved in some dogs and worsened in others. In these lungs, changes in pulmonary vascular resistance of the abnormal area of the lung were negatively correlated with changes in VA/Q dispersion (logSDQ) (R = -0.85, p < 0.01) and positively correlated with PaO2 (R = 0.79, p < 0.05). We conclude that NO has net effects on pulmonary gas exchange, depending on the underlying lung pathology consistent with competing vasodilatory effects on the normal and abnormal areas that receive the gas.

Intense exercise impairs the integrity of the pulmonary blood-gas barrier in elite athletes

The blood-gas barrier must be very thin to allow gas exchange and it is therefore subjected to high mechanical stresses when the capillary pressure rises. In some animals, such as the thoroughbred race-horse during intense exercise, the stresses are so large that the capillaries fail and bleeding occurs. We tested the hypothesis that, in elite human athletes, the high capillary pressure that occurs during severe exercise alters the structure and function of the blood-gas barrier. We performed bronchoalveolar lavage (BAL) in six healthy athletes, who had a history suggestive of lung bleeding, 1 h after a 7-min cycling race simulation and four normal sedentary control subjects who did not exercise before BAL. The athletes had higher (p < 0.05) concentrations of red blood cells (0.51 x 10(5) versus 0.01 x 10(5).ml-1), total protein (128.0 versus 94.1 micrograms/ml), albumin (65.6 versus 53.0 micrograms/ml), and leukotriene B4 (LTB4) (243 versus 0 pg/ml) in BAL fluid than control subjects. The proportion of neutrophils was similar in athletes and control subjects but the proportion of lymphocytes in BAL fluid was reduced (p < 0.05). There were no differences in levels of surfactant apoprotein A, tumor necrosis factor bioactivity, lipopolysaccharide, or interleukin-8 (IL-8) between groups. These results show that brief intense exercise in athletes with a history suggestive of lung bleeding alters blood-gas barrier function resulting in higher concentrations of red cells and protein in BAL fluid. The lack of activation of proinflammatory pathways (except LTB4) in the airspaces supports the hypothesis that the mechanism for altered blood-gas barrier function is mechanical stress.

Effects of dietary cholesterol and triglycerides on lipid concentrations in liver, plasma, and bile

Dietary cholesterol (CHL) and triglycerides (TG) can influence plasma, hepatic, and biliary lipid composition, but effects on lipids in these three compartments during the early stages of CHL gallstone formation have not been studied in parallel. We fed prairie dogs diets containing one of four test oils (safflower, coconut, olive, or menhaden) at either 5 or 40% of calories, in the presence of 0 or 0.34% CHL, for 3 wk. In the absence of dietary CHL, increases in dietary TG produced 50-200% increases in the concentrations of biliary CHL and hepatic cholesteryl ester (CE), while the concentrations of hepatic free CHL (FC) as well as plasma FC and CE remained relatively unchanged. Increasing dietary CHL to 0.34% resulted in increases in hepatic FC of approximately 50% for all four fats regardless of whether they were supplied at 5 or 40% of calories. CHL supplementation caused more pronounced increases in biliary CHL (200-400%), hepatic CE (50-200%), plasma FC (up to 100%), and plasma CE (up to 150%), and these increases were exacerbated by concurrent supplementation of dietary fat and CHL (biliary CHL: 300-700%; hepatic CE: 100-250%; plasma FC: up to 165%; plasma CE: 100-350%). These results indicate that enhanced secretion of biliary CHL and, to a lesser extent, increased synthesis of hepatic CE, may be primary mechanisms for maintaining the hepatic FC pool. Furthermore, dietary CHL and high levels of fat intake are independent risk factors for increasing biliary CHL concentrations, and adverse effects on lipid concentrations in plasma and bile tend to be exacerbated by ingestion of diets rich in both fat and CHL.

The effect of altering pulmonary blood flow on pulmonary gas exchange in the turtle Trachemys (Pseudemys) scripta

In resting reptiles, the PO2 of pulmonary venous return (PLAO2; left atrial blood) may be 20 mmHg (1 mmHg = 0.1333 kPa) lower than the PO2 of gas in the lung. This level of PO2 is considerably higher than that observed in resting mammals and birds and results from ventilation-perfusion (V/Q) heterogeneity, pulmonary diffusion limitation and intrapulmonary shunting. However, the relative contribution of each of these factors is unknown. Many reptiles, particularly chelonians, exhibit an intermittent ventilation pattern where pulmonary blood flow (QL) increases during the ventilatory periods and, therefore, we hypothesized that V/Q matching would improve with increasing QL. We applied the multiple inert gas elimination technique in anaesthetized turtles at 22 degrees C. Turtles were continuously ventilated at a rate of 140 ml kg-1 min-1, equivalent to the rate of ventilation within a ventilatory period. Trace amounts of six inert gases were infused through the jugular vein. Blood samples from the pulmonary artery and the left atrium and mixed expired gases were collected for analysis. QL was reduced by a factor of six (low flow) using a vascular occluder placed around the common pulmonary artery or increased by a factor of two (high flow) through bolus injection of adrenaline. V/Q heterogeneity was significantly reduced with increasing pulmonary blood flow (P &lt; 0.05). Consistent with these changes, the effective lung-pulmonary artery PO2 difference (PLO2-PLAO2) was reduced (P &lt; 0.05) from 58 +/- 16 mmHg to 29 +/- 5 mmHg (means +/- S.E.M.) and PLAO2 increased significantly (P &lt; 0.05) from 88 +/- 17 mmHg (low flow) to 120 +/- 14 mmHg (high flow). There was evidence of pulmonary diffusion limitation under all conditions, which was unchanged with increasing blood flow. These findings suggest that increased pulmonary blood flow during a ventilatory period results in both temporal and spatial matching of ventilation and perfusion, without altering pulmonary diffusion limitation.

Pulmonary hemodynamic response to exercise in subjects with prior high-altitude pulmonary edema

Individuals with a prior history of (susceptible to high altitude pulmonary edema (HAPE-S) have high resting pulmonary arterial pressures, but little data are available on their vascular response to exercise. We studied the pulmonary vascular response to exercise in seven HAPE-S and nine control subjects at sea level and at 3,810 m altitude. At each location, both normoxic (inspired PO2 = 148 Torr) and hypoxic (inspired PO2 = 91 Torr) studies were conducted. Pulmonary hemodynamic measurements included pulmonary arterial and pulmonary arterial occlusion pressures. A multiple regression analysis demonstrated that the pulmonary arterial pressure reactivity to exercise was significantly greater in the HAPE-S group. This reactivity was not influenced by altitude or oxygenation, implying that the response was intrinsic to the pulmonary circulation. Pulmonary arterial occlusion pressure reactivity to exercise was also greater in the HAPE-S group, increasing with altitude but independent of oxygenation. These findings suggest an augmented flow-dependent pulmonary vasoconstriction and/or a reduced vascular cross-sectional area in HAPE-S subjects.

Exercise-induced VA/Q inequality in subjects with prior high-altitude pulmonary edema

Ventilation-perfusion (VA/Q) mismatch has been shown to increase during exercise, especially in hypoxia. A possible explanation is subclinical interstitial edema due to high pulmonary capillary pressures. We hypothesized that this may be pathogenetically similar to high-altitude pulmonary edema (HAPE) so that HAPE-susceptible people with higher vascular pressures would develop more exercise-induced VA/Q mismatch. To examine this, seven healthy people with a history of HAPE and nine with similar altitude exposure but no HAPE history (control) were studied at rest and during exercise at 35, 65, and 85% of maximum 1) at sea level and then 2) after 2 days at altitude (3,810 m) breathing both normoxic (inspired Po2 = 148 Torr) and hypoxic (inspired Po2 = 91 Torr) gas at both locations. We measured cardiac output and respiratory and inert gas exchange. In both groups, VA/Q mismatch (assessed by log standard deviation of the perfusion distribution) increased with exercise. At sea level, log standard deviation of the perfusion distribution was slightly higher in the HAPE-susceptible group than in the control group during heavy exercise. At altitude, these differences disappeared. Because a history of HAPE was associated with greater exercise-induced VA/Q mismatch and higher pulmonary capillary pressures, our findings are consistent with the hypothesis that exercise-induced mismatch is due to a temporary extravascular fluid accumulation.

Pulmonary transit time and diffusion limitation during heavy exercise in athletes

To investigate relationships between pulmonary transit times (PTT) and pulmonary diffusion limitation during exercise, 10 high aerobic capacity athletes (VO2max = 5.15 +/- 0.52 l.min-1) who had multiple inert gas elimination analysis evidence suggestive of diffusion disequilibrium were studied at rest and maximal exercise. Diffusing capacity for oxygen (DLO2) was calculated from the inert gas data. First pass radionuclide angiography was performed using 99mTechnecium labeled erythrocytes and whole lung PTT and pulmonary blood volume (PBV) were calculated. PTT decreased from 9.32 +/- 1.41 sec at rest, to 2.91 +/- 0.30 sec during exercise and was correlated with diffusion limitation suggested by the inert gases (r = -0.58, P < 0.05). PBV increased during exercise to over 25% of whole blood volume and correlated with DLO2 (r = 0.82, P < 0.01). These data suggest that diffusion limitation is related to shortened PTT in athletes and that maximal recruitment of PBV may defend against diffusion limitation.

Ventilation and pulmonary gas exchange during exercise in the savannah monitor lizard (Varanus exanthematicus)

During exercise, pulmonary gas exchange in reptiles was predicted to differ from that in mammals because of their less complex lung structure, which might reduce ventilation-perfusion heterogeneity (V/QL) at the expense of pulmonary diffusion limitation. To investigate this, the multiple inert gas elimination technique was used in six Varanus exanthematicus at rest and during maximal exercise. Trace amounts of six inert gases were infused into the external jugular vein and blood samples were collected from the pulmonary artery and the left atrium. Mixed expired gas samples and ventilatory and metabolic data were acquired. Indices of V/QL heterogeneity, calculated using a 50-compartment model, were low at rest (log standard deviation of perfusion distribution, logSDQ = 0.39) and increased significantly with exercise (logSDQ = 0.78). Oxygen diffusion limitation was apparent during exercise and was comparable to reported mammalian values. A molecular-mass-dependent limitation, suggesting limited intrapulmonary gas mixing, was evident only at rest. An increase in left atrial PO2 from 82mmHg at rest to 96 mmHg during exercise was associated with a corresponding decrease in PCO2. These data indicate adequacy of pulmonary ventilation and gas exchange for metabolic demands in exercising varanid lizards and suggest that less complex lung structures are not necessarily linked to increased pulmonary diffusion limitation.

The laboratory assessment of endurance performance in cyclists

Performance in endurance activities depends on maximal aerobic capacity (VO2max) and the ability to sustain a high percentage of VO2max over time. This study examined whether noninvasive laboratory measures would be valid predictors of endurance performance in an individual-start bicycle race (TT). Eight experienced male cyclists (age = 25.1 +/- 3.3 years, weight = 75.0 +/- 5.7 kg, VO2max = 5.05 +/- 0.4 L.min-1) performed a progressive incremental exercise test to exhaustion on a cycle ergometer. VO2max, maximum power output, and ventilatory threshold were determined. Later the subjects completed a 40-km TT. Power output at the ventilatory threshold (VT watts) was correlated with race performance time and calculated power output during the competition (r = -0.81; r = 0.82). VT watts and VO2max accounted for 75% of the variance between subjects (r = 0.91) in performance time. These data indicate that simple laboratory measures can predict TT performance in trained cyclists. Individual differences may be accounted for by motivation, aerodynamic position, and efficiency.

Pulmonary gas exchange during exercise in athletes. I. Ventilation-perfusion mismatch and diffusion limitation

To investigate pulmonary gas exchange during exercise in athletes, 10 high aerobic capacity athletes (maximal aerobic capacity = 5.15 +/- 0.52 l/min) underwent testing on a cycle ergometer at rest, 150 W, 300 W, and maximal exercise (372 +/- 22 W) while trace amounts of six inert gases were infused intravenously. Arterial blood samples, mixed expired gas samples, and metabolic data were obtained. Indexes of ventilation-perfusion (VA/Q) mismatch were calculated by the multiple inert gas elimination technique. The alveolar-arterial difference for O2 (AaDO2) was predicted from the inert gas model on the basis of the calculated VA/Q mismatch. VA/Q heterogeneity increased significantly with exercise and was predicted to increase the AaDO2 by > 17 Torr during heavy and maximal exercise. The observed AaDO2 increased significantly more than that predicted by the inert gas technique during maximal exercise (10 +/- 10 Torr). These data suggest that this population develops diffusion limitation during maximal exercise, but VA/Q mismatch is the most important contributor (> 60%) to the wide AaDO2 observed.

Changes in hepatocyte NADH fluorescence during prolonged hypoxia

Deprivation of oxygen reduces oxidative phosphorylation and rapidly causes an increase in cellular NADH which can be monitored by fluorimetry. Previous studies have established that increases in NADH fluorescence accurately reflect the impairment in oxidative phosphorylation which occurs during brief periods of acute hypoxia. However, the potential usefulness of fluorimetry for following longer, clinically relevant periods of ischemia has not been explored. We studied changes in NADH fluorescence in rat hepatocyte suspensions and in isolated-buffer-perfused rat livers during hypoxia (pO2 < 50 mm Hg) for periods as long as 180 min. NADH fluorescence of hepatocyte suspensions consistently increased by about 15% after 13 to 15 min of hypoxia and coincided with a marked decrease in tissue ATP levels. Reoxygenation after 15 or 30 min of hypoxia resulted in recovery of ATP and NADH with minimal loss of viability, as measured by trypan blue exclusion. After 60 to 180 min hypoxia, the initial increase in NADH fluorescence was followed by a progressive, irreversible decline which correlated with decreased cell viability. Similar changes in NADH fluorescence were observed in isolated-perfused rat livers in which NADH fluorescence was monitored at the liver surface with a fiberoptic probe. Hypoxia for 30 min had no effect on NADH fluorescence, but hypoxia for longer periods caused a steady increase in fluorescence after 45-60 min. When hypoxia was prolonged (120 or 180 min), fluorescence peaked after 60-75 min and then declined progressively to levels below baseline. The greatest decrease in fluorescence was seen after 180 min of hypoxia.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of salbutamol on performance in elite nonasthmatic athletes

The effect of salbutamol on performance was studied in seven male nonasthmatic highly trained (VO2max > or = 60 ml.kg-1 x min-1) cyclists. Salbutamol (S = 2 puffs = 200 micrograms) or placebo (P) was administered by metered-dose inhaler, through a spacer device, 20 min prior to testing in a double-blind, randomized cross-over design. Testing sessions on a cycle ergometer included the measurement of maximal oxygen uptake (VO2max), peak power, maximal heart rate, and pulmonary function. A timed sprint to exhaustion was performed after 45 min of exercise at 70% of VO2max, and a Wingate anaerobic test was used to measure total work and peak power. There was a nonsignificant decrease in VO2max (P = 63.5 +/- 3.2; S = 62.6 +/- 3.3 ml.kg-1 x min-1). No difference was found in peak power, maximum heart rate, endurance sprint time, Wingate peak power, or total work. After an anticipated baseline increase was taken into account, the pattern of change in FEV1 over time did not differ between salbutamol and placebo. It was concluded that a therapeutic dose of aerosol salbutamol does not have an ergogenic effect in elite nonasthmatic athletes, and it is therefore recommended that inhaled salbutamol continue to be permitted in international competition for individuals with exercise induced bronchospasm.

Liver viability after ischemia-reperfusion

Lack of a reproducible model to quantitatively assess hepatocellular injury following ischemia has made it difficult to assess new strategies for minimizing hepatic injury. We studied the progression of hepatocellular injury after ischemia and ischemia with reperfusion in rats. Irreversible injury was quantitated using a triphenyltetrazolium chloride assay that was shown to correlate with ultrastructural changes. Adenosine triphosphate decreased to 36% of basal values after 30 minutes, but returned to normal with reperfusion with no decrease in viability. In contrast, viability fell by 30% after 60 minutes of ischemia, and by 64% when 60 minutes of ischemia was followed by reperfusion. We conclude that reperfusion of ischemic liver increases the degree of irreversible damage. The model employed here seems to be useful for studying ischemic and reperfusion injury in the liver.

Isolated fractures of the capitate: use of nuclear medicine as an aid to diagnosis

Fractures of the capitate are considered to be uncommon injuries of the wrist, however, delay in diagnosis may result in prolonged disability and avascular necrosis. Two cases are reported in which an isolated fracture of the capitate was diagnosed with a 99mTc-MDP nuclear medicine bone scan and confirmed with CT scan or repeated conventional x-rays. These two cases illustrate that an isolated fracture of the capitate should be considered in an individual presenting with persistent wrist pain of traumatic origin, even when conventional x-ray views are negative. The nuclear medicine bone scan can be a useful investigative tool and serve to guide further radiological investigations.

Hypoxic ventilatory response and arterial desaturation during heavy work

Arterial desaturation in athletes during intense exercise has been reported by several authors, yet the etiology of this phenomenon remains obscure. Inadequate pulmonary ventilation, due to a blunted respiratory drive, has been implicated as a factor. To investigate the relationship between the ventilatory response to hypoxia, exercise ventilation, and arterial desaturation, 12 healthy male subjects [age, 23.8 +/- 3.6 yr; height, 181.6 +/- 5.6 cm; weight, 73.7 +/- 6.2 kg; and maximal O2 uptake (VO2max), 63.0 +/- 2.2 ml.kg-1 min-1] performed a 5-min treadmill test at 100% of VO2max, during which arterial blood samples and ventilatory data were collected every 15 s. Alveolar PO2 (PAO2) was determined using the ideal gas equation. On a separate occasion the ventilatory response to isocapnic hypoxia was measured. Arterial PO2 decreased by an average of 29 Torr during the test, associated with arterial desaturation [arterial O2 saturation (SaO2) 92.0%]. PAO2 was maintained; however, alveolar-arterial gas pressure difference increased progressively to greater than 40 Torr. Minimal hypocapnia was observed, despite marked metabolic acidosis. There was no significant correlation observed between hypoxic drives and ventilation-to-O2 uptake ratio or SaO2 (r = 0.1 and 0.06, respectively, P = NS). These data support the conclusions that hypoxic drives are not related to maximal exercise ventilation or to the development of arterial desaturation during maximal exercise.

Adenine nucleotides and other factors indicative of glycolytic metabolism in murine spermatozoa

Cyclic adenosine 3':5' monophosphate (cAMP) accumulation during one hour's incubation in 10 mM theophylline and 10 mM pyruvate; initial concentrations of adenosine triphosphate (ATP) and their rate of depletion during one hour's incubation; concentrations of adenosine diphosphate (ADP), adenosine monophosphate (AMP), fructose 2,6 diphosphate (FDP), and glyceraldehyde 3-phosphate (GAP), were assayed in spermatozoa of various genotypes. No effects of transmission ratio distorting t-haplotypes (in heterozygous males) on these variables were found.

Reversion to virulence of chicken-passaged infectious bronchitis vaccine virus

Serial passage of two infectious bronchitis virus (IBV) vaccine strains in chickens enhanced their capacity to increase the incidence and severity of Mycoplasma synoviae (MS) airsacculitis. Included in this report were the mild Massachusetts-type Connaught strain and the Arkansas 99 vaccine strain of IBV. The Connaught strain and one of two Ark 99 vaccine strains passaged in chickens increased the incidence of airsacculitis markedly compared with nonpassaged virus. The other Ark 99 vaccine virus already exacerbated MS airsacculitis, before passage in chickens, and its influence did not increase on passage. All IBV strains studied to date have either possessed this trait or reacquired it on passage in the natural host.

Efficacy of experimental inactivated mycoplasma gallisepticum oil-emulsion bacterin in egg-layer chickens

Six groups of white leghorn pullets were studied to determine the ability of beta-propiolactone-inactivated Mycoplasma gallisepticum (MG) oil-emulsion bacterins to counteract reductions in egg production caused by MG infection. The pullets were inoculated with 0.5 ml of MG bacterin subcutaneously in the neck at about 20 weeks of age and were challenged with MG near 28 weeks of age, when they were in peak egg production. Various challenge schemes with infectious bronchitis virus were used at the time of MG challenge to increase the reduction in egg production. MG bacterins afforded protection against moderate drops in egg production in at least three of the studies, where the unvaccinated challenged control hens exhibited reduced egg production.