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

Exercise-Induced Pulmonary Hemorrhage in a Non-Athletic Child: Implications for Military Recruits

Hemoptysis is a rare presenting symptom in pediatric and young adult patients with a highly variable outcome ranging from an isolated mild occurrence to severe illness and death. Exercise-induced pulmonary hemorrhage (EIPH) has several reports in adult literature but has not previously been reported in pediatric patients. A 12-year-old female with a history of trisomy X (47, XXX), obesity, depression, anxiety, and obstructive sleep apnea presented to the pediatric pulmonology clinic after several episodes of hemoptysis. Spirometry, imaging, and laboratory evaluation for autoimmune vasculitides and other causes associated with pediatric hemoptysis did not reveal an etiology for the hemoptysis. A combined bronchoscopy with pediatric and adult providers revealed no airway lesions or sources of bleeding. EIPH is a diagnosis of exclusion. This patient was diagnosed with EIPH and had spontaneous resolution with improved fitness. Many military training and service activities are similar to those reported with EIPH. Trainees with various levels of aerobic fitness are at risk of developing EIPH. The hemoptysis evaluation is important for military providers given the range of severity in presentations, even though it is a rare occurrence. In addition to a novel presentation of EIPH, this case demonstrates the value of collaboration between pediatric and adult specialists in the Military Health System (MHS). Military care providers should be aware of this rare phenomenon in service members and trainees who are at risk during maximal aerobic effort.

The Pulmonary Vasculature

The pulmonary circulation is a low-pressure, low-resistance circuit whose primary function is to deliver deoxygenated blood to, and oxygenated blood from, the pulmonary capillary bed enabling gas exchange. The distribution of pulmonary blood flow is regulated by several factors including effects of vascular branching structure, large-scale forces related to gravity, and finer scale factors related to local control. Hypoxic pulmonary vasoconstriction is one such important regulatory mechanism. In the face of local hypoxia, vascular smooth muscle constriction of precapillary arterioles increases local resistance by up to 250%. This has the effect of diverting blood toward better oxygenated regions of the lung and optimizing ventilation-perfusion matching. However, in the face of global hypoxia, the net effect is an increase in pulmonary arterial pressure and vascular resistance. Pulmonary vascular resistance describes the flow-resistive properties of the pulmonary circulation and arises from both precapillary and postcapillary resistances. The pulmonary circulation is also distensible in response to an increase in transmural pressure and this distention, in addition to recruitment, moderates pulmonary arterial pressure and vascular resistance. This article reviews the physiology of the pulmonary vasculature and briefly discusses how this physiology is altered by common circumstances.

Sessile alveolar macrophage connexin-43 determines mechano-immunity in the lung

Although lung immunity is pathogen induced, the immunity can also be induced by mechanical distortion of the lung. The causal basis of the lung's mechanosensitive immunity remains unclear. Here, through live optical imaging of mouse lungs, we show that alveolar stretch due to hyperinflation induced prolonged cytosolic Ca2+ increases in sessile alveolar macrophages (AMs). Knockout studies revealed that the Ca2+ increases resulted from Ca2+ diffusion from the alveolar epithelium to sessile AMs through connexin 43 (Cx43)-containing gap junctions. Lung inflammation and injury in mice exposed to injurious mechanical ventilation were inhibited by AM-specific Cx43 knockout, or AM-specific delivery of a calcium inhibitor. We conclude, Cx43 gap junctions and calcium mobilization in sessile AMs determine the lung's mechanosensitive immunity, providing a therapeutic strategy against hyperinflation-induced lung injury.

A century of exercise physiology: lung fluid balance during and following exercise

PURPOSE

This review recalls the principles developed over a century to describe trans-capillary fluid exchanges concerning in particular the lung during exercise, a specific condition where dyspnea is a leading symptom, the question being whether this symptom simply relates to fatigue or also implies some degree of lung edema.

METHOD

Data from experimental models of lung edema are recalled aiming to: (1) describe how extravascular lung water is strictly controlled by "safety factors" in physiological conditions, (2) consider how waning of "safety factors" inevitably leads to development of lung edema, (3) correlate data from experimental models with data from exercising humans.

RESULTS

Exercise is a strong edemagenic condition as the increase in cardiac output leads to lung capillary recruitment, increase in capillary surface for fluid exchange and potential increase in capillary pressure. The physiological low microvascular permeability may be impaired by conditions causing damage to the interstitial matrix macromolecular assembly leading to alveolar edema and haemorrhage. These conditions include hypoxia, cyclic alveolar unfolding/folding during hyperventilation putting a tensile stress on septa, intensity and duration of exercise as well as inter-individual proneness to develop lung edema.

CONCLUSION

Data from exercising humans showed inter-individual differences in the dispersion of the lung ventilation/perfusion ratio and increase in oxygen alveolar-capillary gradient. More recent data in humans support the hypothesis that greater vasoconstriction, pulmonary hypertension and slower kinetics of alveolar-capillary O2 equilibration relate with greater proneness to develop lung edema due higher inborn microvascular permeability possibly reflecting the morpho-functional features of the air-blood barrier.

An update on environment-induced pulmonary edema – “When the lungs leak under water and in thin air”

Acute pulmonary edema is a serious condition that may occur as a result of increased hydrostatic forces within the lung microvasculature or increased microvascular permeability. Heart failure or other cardiac or renal disease are common causes of cardiogenic pulmonary edema. However, pulmonary edema may even occur in young and healthy individuals when exposed to extreme environments, such as immersion in water or at high altitude. Immersion pulmonary edema (IPE) and high-altitude pulmonary edema (HAPE) share some morphological and clinical characteristics; however, their underlying mechanisms may be different. An emerging understanding of IPE indicates that an increase in pulmonary artery and capillary pressures caused by substantial redistribution of venous blood from the extremities to the chest, in combination with stimuli aggravating the effects of water immersion, such as exercise and cold temperature, play an important role, distinct from hypoxia-induced vasoconstriction in high altitude pulmonary edema. This review aims at a current perspective on both IPE and HAPE, providing a comparative view of clinical presentation and pathophysiology. A particular emphasis will be on recent advances in understanding of the pathophysiology and occurrence of IPE with a future perspective on remaining research needs.

Rare case of occupational pulmonary hemorrhage in a firefighter

Alveolar hemorrhage associated with physical exertion, known as exercise-induced pulmonary hemorrhage (EIPH), is a rare condition linked to strenuous exertion. This can be an unusual form of respiratory and occupational illness. We present the case of a healthy firefighter who developed fatal pulmonary hemorrhage after participating in a strenuous physical training exercise regimen. This case represents a severe presentation of EIPH, which results from the disruption of the pulmonary blood-gas barrier as a result of strenuous exertion. Clinicians caring for those in vocations and recreation involving extremely vigorous exercise should be aware that such activities can cause EIPH.

Yu-Ping-Feng Formula Ameliorates Alveolar-Capillary Barrier Injury Induced by Exhausted-Exercise via Regulation of Cytoskeleton

Background: Yu-ping-feng powder (YPF) is a compound traditional Chinese medicine extensively used in China for respiratory diseases. However, the role of YPF in alveolar-capillary barrier dysfunction remains unknown. This study aimed to explore the effect and potential mechanism of YPF on alveolar-capillary barrier injury induced by exhausted exercise.

Methods: Male Sprague–Dawley rats were used to establish an exhausted-exercise model by using a motorized rodent treadmill. YPF at doses of 2.18 g/kg was administrated by gavage before exercise training for 10 consecutive days. Food intake-weight/body weight, blood gas analysis, lung water percent content, BALF protein concentration, morphological observation, quantitative proteomics, real-time PCR, and Western blot were performed. A rat pulmonary microvascular endothelial cell line (PMVEC) subjected to hypoxia was applied for assessing the related mechanism.

Results: YPF attenuated the decrease of food intake weight/body weight, improved lung swelling and hemorrhage, alleviated the increase of lung water percent content and BALF protein concentration, and inhibited the impairment of lung morphology. In addition, YPF increased the expression of claudin 3, claudin 18, occludin, VE-cadherin, and β-catenin, attenuated the epithelial and endothelial hyperpermeability in vivo and/or in vitro, and the stress fiber formation in PMVECs after hypoxia. Quantitative proteomics discovered that the effect of YPF implicated the Siah2-ubiquitin-proteasomal pathway, Gng12-PAK1-MLCK, and RhoA/ROCK, which was further confirmed by Western blot. Data are available via ProteomeXchange with identifier PXD032737.

Conclusion: YPF ameliorated alveolar-capillary barrier injury induced by exhausted exercise, which is accounted for at least partly by the regulation of cytoskeleton.

Inter-species cell detection - datasets on pulmonary hemosiderophages in equine, human and feline specimens

Pulmonary hemorrhage (P-Hem) occurs among multiple species and can have various causes. Cytology of bronchoalveolar lavage fluid (BALF) using a 5-tier scoring system of alveolar macrophages based on their hemosiderin content is considered the most sensitive diagnostic method. We introduce a novel, fully annotated multi-species P-Hem dataset, which consists of 74 cytology whole slide images (WSIs) with equine, feline and human samples. To create this high-quality and high-quantity dataset, we developed an annotation pipeline combining human expertise with deep learning and data visualisation techniques. We applied a deep learning-based object detection approach trained on 17 expertly annotated equine WSIs, to the remaining 39 equine, 12 human and 7 feline WSIs. The resulting annotations were semi-automatically screened for errors on multiple types of specialised annotation maps and finally reviewed by a trained pathologist. Our dataset contains a total of 297,383 hemosiderophages classified into five grades. It is one of the largest publicly available WSIs datasets with respect to the number of annotations, the scanned area and the number of species covered.

On the importance of integrating comparative anatomy and One Health perspectives in anatomy education

As a result of many factors, including climate change, unrestricted population growth, widespread deforestation and intensive agriculture, a new pattern of diseases in humans is emerging. With increasing encroachment by human societies into wild domains, the interfaces between human and animal ecosystems are gradually eroding. Such changes have led to zoonoses, vector-borne diseases, infectious diseases and, most importantly, the emergence of antimicrobial-resistant microbial strains as challenges for human health. Now would seem to be an opportune time to revisit old concepts of health and redefine some of these in the light of emerging challenges. The One Health concept addresses some of the demands of modern medical education by providing a holistic approach to explaining diseases that result from a complex set of interactions between humans, environment and animals, rather than just an amalgamation of isolated signs and symptoms. An added advantage is that the scope of One Health concepts has now expanded to include genetic diseases due to advancements in omics technology. Inspired by such ideas, a symposium was organised as part of the 19th International Federation of Associations of Anatomists (IFAA) Congress (August 2019) to investigate the scope of One Health concepts and comparative anatomy in contemporary medical education. Speakers with expertise in both human and veterinary anatomy participated in the symposium and provided examples where these two disciplines, which have so far evolved largely independent of each other, can collaborate for mutual benefit. Finally, the speakers identified some key concepts of One Health that should be prioritised and discussed the diverse opportunities available to integrate these priorities into a broader perspective that would attempt to explain and manage diseases within the scopes of human and veterinary medicine.

Nedocromil sodium and diphenhydramine HCl ameliorate exercise-induced arterial hypoxemia in highly trained athletes

INTRODUCTION

Exercise-induced arterial hypoxemia (EIAH) has been observed in highly trained endurance athletes during near maximal exercise, which may be influenced by a histamine-mediated inflammatory response at the pulmonary capillary-alveolar membrane. In order to test this hypothesis, we examined whether the mast cell stabilizer nedocromil sodium (NS) and H1 -receptor antagonist diphenhydramine HCL (DH) would ameliorate EIAH and mitigate the drop in arterial oxyhemoglobin saturation (Sa O2 ) during intensive exercise.

METHODS

Seven highly trained male cross country runners (age, 21 ± 2 years; V̇O2max , 74.7 ± 3.5 ml·kg-1 ·min-1 ) participated in the study. All subjects completed a maximal exercise treadmill test to exhaustion, followed by three 5-min constant-load exercise bouts at 70%, 80%, and 90% V̇O2max . Prior to testing, subjects received either placebo (PL), NS, or DH.

RESULTS

Compared to PL, there was a significant treatment effect on Sa O2 (p < 0.001) for both NS and DH during both constant-load exercise and at V̇O2max . Post hoc tests revealed Sa O2  values, compared to PL, were significantly higher at V̇O2max and during DH trials and higher with NS at constant-load intensities except at 70% (p = 0.13).

CONCLUSION

The findings provide further evidence that histamine contributes directly or indirectly to the development of EIAH during intense exercise in highly trained athletes.

The Effect of an Olympic Distance Triathlon on Pulmonary Diffusing Capacity and its Recovery 24 Hours Later

The Olympic distance triathlon includes maximal exercise bouts with transitions between the activities. This study investigated the effect of an Olympic distance triathlon (1.5-km swim, 40-km bike, 10-km run) on pulmonary diffusion capacity (DLCO). In nine male triathletes (age: 24 ± 4.7 years), we measured DLCO and calculated the DLCO to alveolar volume ratio (DLCO/VA) and performed spirometry testing before a triathlon (pre-T), 2 hours after the race (post-T), and the day following the race (post-T-24 h). DLCO was measured using the 9-s breath-holding method. We found that (1) DLCO decreased significantly between pre- and post-T values (38.52 ± 5.44 vs. 35.92 ± 6.63 ml∙min^-1∙mmHg^-1) (p < 0.01) and returned to baseline at post-T-24 h (38.52 ± 5.44 vs. 37.24 ± 6.76 ml∙min^-1∙mmHg^-1, p > 0.05); (2) DLCO/VA was similar at the pre-, post- and post-T-24 h DLCO comparisons; and (3) forced expiratory volume in the first second (FEV₁) and mean forced expiratory flow during the middle half of vital capacity (FEF25-75%) significantly decreased between pre- and post-T and between pre- and post-T-24-h (p < 0.02). In conclusion, a significant reduction in DLCO and DLCO/VA 2 hours after the triathlon suggests the presence of pulmonary interstitial oedema. Both values returned to baseline 24 hours after the race, which reflects possible mild and transient pulmonary oedema with minimal physiological significance.

Feasibility and Role of Right Ventricular Stress Echocardiography in Adult Patients

Background:

The great technological advancements in the field of echocardiography have led to applications of stress echocardiography (SE) in almost all diagnostic fields of cardiology, from ischemic heart disease to valvular heart disease and diastolic function. However, the assessment of the right ventricle (RV) in general, and in particular in regard to the contractile reserve of the RV, is an area that has not been previously explored. We, therefore, propose a study to investigate the potential use of SE for the assessment of RV function in adult patients.

Aims and objectives:

The primary aim is to evaluate the feasibility of right ventricular SE. The secondary aim is to assess right ventricular contractile reserve.

Matherials and Methods:

Eighty-one patients undergoing a physical or dobutamine stress echocardiogram for cardiovascular risk stratification or chest pain were the subject of the study. An exercise leg cycle using a standard WHO protocol was used to simultaneously assess the right and left ventricular global and regional function as well as acquiring Doppler data. Whereas the patient had limitations in mobility, a dobutamine SE was be performed. We evaluated the average values of tricuspid annular plane systolic excursion (TAPSE), fractional area change (FAC), S-wave, systolic pulmonary artery pressure (sPAP), and right ventricle global longitudinal (free wall) strain (RVGLS) during baseline and at the peak of the effort. RV contractile reserve was defined as the change in RVGLS from rest to peak exercise. We also assessed the reproducibility of these measurements between two different expert operators (blind analysis).

Results:

At least 3 over 5 RV function parameters were measurable both during baseline and at the peak of the effort in 95% of patients, while all 5 parameters in 65% of our population, demonstrating an excellent feasibility. All RV-studied variables showed a statistically significant increase (P < 0.001) at peak compared to the baseline. The average percentage increases at peak were 31.1% for TAPSE, 24.8% for FAC, 50.6% for S-wave, 55.2% for PAPS, and 39.8% for RV strain. The reproducibility between operators at baseline and peak was excellent. Our study demonstrates that TAPSE, FAC, and S-wave are highly feasible at rest and at peak, while TAPSE, S-wave, and sPAP are the most reliable measurements during RV stress echo.

Conclusion:

RVGLS is useful in the assessment of RV contractile reserve in patients with good acoustic window. Further studies are needed to evaluate the impact of contrast echocardiography in improving RV contractile reserve assessment during SE.

Incidence of Swimming-Induced Pulmonary Edema: A Cohort Study Based on 47,600 Open-Water Swimming Distances

Background

Despite increasing awareness of swimming-induced pulmonary edema (SIPE), large population-based studies are lacking and the incidence is unknown.

Research Question

What is the incidence of SIPE in a mixed group of competitive and recreational swimmers during a large open-water swimming event?

Methods

In four consecutive years (2016-2019), a prospective cohort study was conducted during Sweden’s largest open-water swimming event, Vansbrosimningen. All swimmers seeking medical care with acute respiratory symptoms were eligible for the study. SIPE diagnosis was based on clinical findings in 2016 and 2017 and pulmonary edema assessed by lung ultrasound in 2018 and 2019. Data on patient characteristics, clinical findings, and information about the race were collected.

Results

Based on 47,573 consecutive swimming distances, 322 patients with acute respiratory symptoms (0.68%; CI, 0.61%-0.75%) were treated at the mobile medical unit. Of these, 211 patients (0.44%; CI, 0.39%-0.51%) received a diagnosis of SIPE. The annual incidence of SIPE was 0.34%, 0.47%, 0.41%, and 0.57%, respectively, from 2016 through 2019. Most patients diagnosed with SIPE were women (90%), despite about equal percentages of men and women participating (47% men and 53% women). The incidence of SIPE overall was 0.75% in women and 0.09% in men. The incidence increased with age, from 0.08% in the youngest age group (18-30 years) to 1.1% in the oldest age group (≥ 61 years). Based on multiple logistic regression analysis, the adjusted odds for SIPE occurring was 8.59 times higher for women compared with men and 12.74 times higher for the oldest age group compared with the youngest age group.

Interpretation

The incidence of SIPE over 4 years during a large open-water swimming event in Sweden was 0.44%. The incidence was higher in women than in men and increased with age.

Pulmonary Hypertension in Acute and Chronic High Altitude Maladaptation Disorders

Alveolar hypoxia is the most prominent feature of high altitude environment with well-known consequences for the cardio-pulmonary system, including development of pulmonary hypertension. Pulmonary hypertension due to an exaggerated hypoxic pulmonary vasoconstriction contributes to high altitude pulmonary edema (HAPE), a life-threatening disorder, occurring at high altitudes in non-acclimatized healthy individuals. Despite a strong physiologic rationale for using vasodilators for prevention and treatment of HAPE, no systematic studies of their efficacy have been conducted to date. Calcium-channel blockers are currently recommended for drug prophylaxis in high-risk individuals with a clear history of recurrent HAPE based on the extensive clinical experience with nifedipine in HAPE prevention in susceptible individuals. Chronic exposure to hypoxia induces pulmonary vascular remodeling and development of pulmonary hypertension, which places an increased pressure load on the right ventricle leading to right heart failure. Further, pulmonary hypertension along with excessive erythrocytosis may complicate chronic mountain sickness, another high altitude maladaptation disorder. Importantly, other causes than hypoxia may potentially underlie and/or contribute to pulmonary hypertension at high altitude, such as chronic heart and lung diseases, thrombotic or embolic diseases. Extensive clinical experience with drugs in patients with pulmonary arterial hypertension suggests their potential for treatment of high altitude pulmonary hypertension. Small studies have demonstrated their efficacy in reducing pulmonary artery pressure in high altitude residents. However, no drugs have been approved to date for the therapy of chronic high altitude pulmonary hypertension. This work provides a literature review on the role of pulmonary hypertension in the pathogenesis of acute and chronic high altitude maladaptation disorders and summarizes current knowledge regarding potential treatment options.

Swimming exercise transiently decrease lung diffusing capacity in elite swimmers

BACKGROUND

Swimmers have larger lungs and a higher diffusion capacity than other athletes, but it remains unknown whether swimming exercise changes lung diffusing properties. This study aimed to evaluate modifications in pulmonary alveolar-capillary diffusion after swimming exercise.

METHODS

The participants were 21 elite level swimmers, including 7 females and 14 males, with a training volume of 45-70 kilometers of swimming per week. The single-breath method was used to measure the lung diffusing capacity for carbon monoxide (DLCO and the transfer coefficient of the lungs for carbon monoxide (K<inf>CO</inf>) before and after 10 training sessions over 4 weeks along 207 pre- to postevaluations.

RESULTS

Swimming training consistently decreased lung diffusion capacity during the follow-up period, both DL<inf>CO</inf> (44.4±8.1 to 43.3±8.9 mL·min-1·mmHg-1, P=0.047, ŋ²<inf>p</inf>=0.55) and K<inf>CO</inf> (5.92±0.79 to 5.70±0.81 mL·min-1·mmHg-1·L-1, P=0.003, ŋ²<inf>p</inf>=0.75).

CONCLUSIONS

Elite swimmers experience a subclinical impairment in lung diffusing capacity after swimming exercise, but the stress caused by swimming on the lungs and the acute reduction in DL<inf>CO</inf> does not lead to physiological dysfunction.

Is the healthy respiratory system built just right, overbuilt, or underbuilt to meet the demands imposed by exercise?

In the healthy, untrained young adult, a case is made for a respiratory system (airways, pulmonary vasculature, lung parenchyma, respiratory muscles, and neural ventilatory control system) that is near ideally designed to ensure a highly efficient, homeostatic response to exercise of varying intensities and durations. Our aim was then to consider circumstances in which the intra/extrathoracic airways, pulmonary vasculature, respiratory muscles, and/or blood-gas distribution are underbuilt or inadequately regulated relative to the demands imposed by the cardiovascular system. In these instances, the respiratory system presents a significant limitation to O₂ transport and contributes to the occurrence of locomotor muscle fatigue, inhibition of central locomotor output, and exercise performance. Most prominent in these examples of an "underbuilt" respiratory system are highly trained endurance athletes, with additional influences of sex, aging, hypoxic environments, and the highly inbred equine. We summarize by evaluating the relative influences of these respiratory system limitations on exercise performance and their impact on pathophysiology and provide recommendations for future investigation.

A physiological approach to understand the role of respiratory effort in the progression of lung injury in SARS-CoV-2 infection

Deterioration of lung function during the first week of COVID-19 has been observed when patients remain with insufficient respiratory support. Patient self-inflicted lung injury (P-SILI) is theorized as the responsible, but there is not robust experimental and clinical data to support it. Given the limited understanding of P-SILI, we describe the physiological basis of P-SILI and we show experimental data to comprehend the role of regional strain and heterogeneity in lung injury due to increased work of breathing.

In addition, we discuss the current approach to respiratory support for COVID-19 under this point of view.

Deep Learning-Based Quantification of Pulmonary Hemosiderophages in Cytology Slides

Exercise-induced pulmonary hemorrhage (EIPH) is a common condition in sport horses with negative impact on performance. Cytology of bronchoalveolar lavage fluid by use of a scoring system is considered the most sensitive diagnostic method. Macrophages are classified depending on the degree of cytoplasmic hemosiderin content. The current gold standard is manual grading, which is however monotonous and time-consuming. We evaluated state-of-the-art deep learning-based methods for single cell macrophage classification and compared them against the performance of nine cytology experts and evaluated inter- and intra-observer variability. Additionally, we evaluated object detection methods on a novel data set of 17 completely annotated cytology whole slide images (WSI) containing 78,047 hemosiderophages. Our deep learning-based approach reached a concordance of 0.85, partially exceeding human expert concordance (0.68 to 0.86, mean of 0.73, SD of 0.04). Intra-observer variability was high (0.68 to 0.88) and inter-observer concordance was moderate (Fleiss' kappa = 0.67). Our object detection approach has a mean average precision of 0.66 over the five classes from the whole slide gigapixel image and a computation time of below two minutes. To mitigate the high inter- and intra-rater variability, we propose our automated object detection pipeline, enabling accurate, reproducible and quick EIPH scoring in WSI.

Bioengineering the Blood-gas Barrier

The pulmonary blood-gas barrier represents a remarkable feat of engineering. It achieves the exquisite thinness needed for gas exchange by diffusion, the strength to withstand the stresses and strains of repetitive and changing ventilation, and the ability to actively maintain itself under varied demands. Understanding the design principles of this barrier is essential to understanding a variety of lung diseases, and to successfully regenerating or artificially recapitulating the barrier ex vivo. Many classical studies helped to elucidate the unique structure and morphology of the mammalian blood-gas barrier, and ongoing investigations have helped to refine these descriptions and to understand the biological aspects of blood-gas barrier function and regulation. This article reviews the key features of the blood-gas barrier that enable achievement of the necessary design criteria and describes the mechanical environment to which the barrier is exposed. It then focuses on the biological and mechanical components of the barrier that preserve integrity during homeostasis, but which may be compromised in certain pathophysiological states, leading to disease. Finally, this article summarizes recent key advances in efforts to engineer the blood-gas barrier ex vivo, using the platforms of lung-on-a-chip and tissue-engineered whole lungs. © 2020 American Physiological Society. Compr Physiol 10:415-452, 2020.

Relationship between tracheobronchoscopic score and bronchoalveolar lavage red blood cell numbers in the diagnosis of exercise-induced pulmonary hemorrhage in horses

Background

Exercise‐induced pulmonary hemorrhage (EIPH) is diagnosed and its severity assessed by post‐exercise tracheobronchoscopy, and enumeration of bronchoalveolar lavage fluid red blood cells (BALFRBC). Minimal information is available regarding the relationship of tracheobronchoscopy score to BALFRBC number.

Objective

Evaluate the relationship between BALFRBC number and tracheobronchoscopy scores and determine their diagnostic sensitivities.

Animals

Nine sedentary horses, 21 fit Thoroughbreds, 129 Barrel Racers.

Methods

Normal BALFRBC number and the effect of bronchoalveolar lavage (BAL) on it were evaluated by performing 2 BALs 24 hours apart in sedentary horses. Tracheobronchoscopy followed by BAL was performed 247 times on 150 horses after treadmill, racetrack, or barrel racing exercise. Lastly, a BALFRBC diagnostic threshold number that optimized the geometric mean of the sensitivity and precision (F1‐score) was determined using Bayesian analysis.

Results

No increase in BALFRBC occurred after the second BAL (mean ± SD, 304 ± 173/μL). Tracheobronchoscopy scores ranged from 0 (n = 112) to 4 (n = 4) and BALFRBC ranged from 102 to 4605268/μL. Spearman correlation between tracheobronchoscopy score and BALFRBC was weak (P < .001; rs = 0.42) with large ranges of BALFRBC associated with each tracheobronchoscopy score. The highest F1‐score occurred for a BALFRBC threshold number = 992/μL. Seventy‐five tracheobronchoscopy scores equaled 0 although BALFRBC number was ≥992/μL. Sensitivity of tracheobronchoscopy for diagnosing EIPH was poor (0.59; 95% confidence intervals [CI], 0.49‐0.68), compared to BALFRBC number ≥992/μL (0.93; 95% CI, 0.88‐0.96).

Conclusions and Clinical Importance

False negatives are common with tracheobronchoscopy. Follow‐up determination of BALFRBC may be indicated for tracheobronchoscopy scores = 0 before EIPH can be ruled out.

Lung morphology and surfactant function in cardiogenic pulmonary edema: a narrative review

The conventional analysis of acute cardiogenic pulmonary edema involves the development of high pulmonary capillary pressures resulting in hydrostatic gradients for fluid flux out of capillaries into the interstitial space and alveolar spaces. However, some patients respond poorly to diuretic management. The PubMed database was searched to identify experimental studies on pulmonary edema in animals, experimental studies on surfactant function, including patients with pulmonary edema, and clinical studies reporting barrier dysfunction and/or injury in patients with acute pulmonary edema. Studies with animal models demonstrate that high capillary pressures can cause barrier disruption in alveolar capillary units which increases permeability and the transfer of fluid and protein into lung parenchyma. Fluid in alveolar spaces alters surfactant function which increases fluid flux out of capillaries into the lung parenchyma secondary to larger transcapillary hydrostatic gradients. Patients with acute cardiogenic pulmonary edema have increased levels of surfactant protein B in their plasma which reflect barrier disruption and increased levels of tumor necrosis factor alpha which reflect acute tissue injury. Increased surfactant protein B plasma levels are associated with abnormal gas exchange in patients with chronic heart failure. Patients with exercise-induced left ventricular dysfunction have increased levels of surfactant protein B after short periods of exercise. Pathology studies in patients with chronic heart failure have found increased connective tissue in alveolar capillary units and increased numbers of type II alveolar cells, and these changes represent an adaptive response in these patients. Clinicians need to consider the possibility of barrier dysfunction and disruption in patients with both acute and chronic pulmonary edema and understand that diuresis may have a limited effect on symptoms in some patients.

Respiratory Determinants of Exercise Limitation: Focus on Phrenic Afferents and the Lung Vasculature

We examine 2 means by which the healthy respiratory system contributes to exercise limitation. These include the activation of respiratory and locomotor muscle afferent reflexes, which constrain blood flow and hasten fatigue in both sets of muscles, and the excessive increases in pulmonary vascular pressures at high cardiac outputs, which constrain O₂ transport and precipitate maladaptive right ventricular remodeling in endurance-trained subjects.

Exercise-induced Pulmonary Hemorrhage: Is It Important and Can It Be Prevented?

Exercise-induced pulmonary hemorrhage (EIPH) occurs commonly in horses undergoing strenuous exercise. Reported risk factors include racing in cold temperatures and wearing of bar shoes. In horses with documented moderate to severe EIPH, increasing the interval between races and adopting a negative race pace strategy may reduce the severity of EIPH in subsequent races. EIPH seems to have an impact on performance only when moderate to severe. This occurs in a small number of starters, approximately 6%. EIPH often is erratic in severity from race to race, although across a population it is weakly progressive over increasing race starts.

A literature review of immersion pulmonary edema

IMPORTANCE

Immersion pulmonary edema (IPE) is a rare but important complication associated with surface swimming and underwater diving. It tends to reoccur and can be fatal. It is not very well-known to clinicians involved in the care of individuals participating in aquatic activities. We performed a systematic review of immersion pulmonary edema to describe the condition and provide guidelines for its management.

EVIDENCE REVIEW

We searched PubMed to identify case reports and studies using the MeSH terms "immersion," "pulmonary edema," "cold-induced," "exercise," "hemodynamics," "water immersion,'' "cardiovascular response," alone and in combinations. We identified 121 relevant articles including 54 case reports. We reviewed in detail 24 studies and all 54 case reports.

FINDINGS

The incidence of IPE is estimated to be around 1.1- 1.8%. The risk factors for IPE include age >50 years, female sex, overhydration before exercise, tight wetsuits, cold water exposure and physically trained individuals such as endurance athletes. Individuals with pre-existing heart disease are at increased risk, however, IPE is seen even in healthy individuals. Symptoms such as cough, sputum production, hemoptysis and shortness of breath can occur immediately after immersion. Combination of water immersion, cold exposure, and exercise lead to an increase in pulmonary capillary pressures and eventual pulmonary capillary stress failure that leads to the flooding of alveolar spaces and edema. Conclusion and relevance: Clinicians should be aware of IPE to avoid overestimating the severity of coronary or valvular conditions sometimes coincidentally present in IPE victims. Management is usually supportive. Functional and clinical recovery usually happens spontaneously within 24 h to 2 days, with or without diuretic therapy and a beta-adrenergic agonist. IPE can be recurrent and fatal, hence subjects with a history of IPE should undergo extensive cardiopulmonary investigation and should avoid cold water and physically demanding swimming events or avoid immersion activities.

Pulmonary edema during the Boston Marathon

The Boston Marathon is the most popular marathon in the New England region and attracts some of the most qualified athletes participating from the United States and abroad. The race occurs in April, a month in the northeast characterized by unpredictable weather. While there are a number of well described weather-related medical complications that occur during exercise, less is known about noncardiogenic pulmonary edema (NCPE) in marathon runners, a condition that most physician are unfamiliar with. This phenomenon has been described in the literature as a complication of severe hyponatremia and cerebral edema. Here, we describe the case of a healthy athlete who took part in the Boston Marathon in 2018 and presented afterwards with hypothermia and NCPE. We also review the normal cardiopulmonary physiology along with the physiological changes and external factors impacting the respiratory system during exercise. The combination of significant physical exertion, cold and rainy weather and subsequent hypothermia, perhaps along with other less understood factors may have increased the permeability of his lungs and caused NCPE.

Diffuse alveolar hemorrhage following sugammadex and remifentanil administration: A case report

RATIONALE

Diffuse alveolar hemorrhage (DAH) is a rare life-threatening condition that accompanies general anesthesia. Negative-pressure pulmonary edema (NPPE) is a rare cause of DAH.

PATIENT CONCERNS

A 25-year-old male patient developed hemoptysis following remifentanil administration by bolus injection with sugammadex at the emergence from general anesthesia.

DIAGNOSIS

Chest x-ray and computed tomography showed DAH.

INTERVENTIONS

Conservative care was provided with 4L of oxygen via nasal prong, 20 mg of Lasix and 2500 mg of tranexamic acid.

OUTCOMES

The patient was discharged uneventfully.

LESSONS

Muscle rigidity by remifentanil and the dissociated reversal of neuromuscular blockade by sugammadex was suspected as the cause of NPPE-related DAH. Therefore, the possibility NPPE-related DAH should be considered when using a bolus of remifentanil and sugammadex during emergence from general anesthesia.

Hypothesis: Fever control, a niche for alpha-2 agonists in the setting of septic shock and severe acute respiratory distress syndrome?

During severe septic shock and/or severe acute respiratory distress syndrome (ARDS) patients present with a limited cardio-ventilatory reserve (low cardiac output and blood pressure, low mixed venous saturation, increased lactate, low PaO2/FiO2 ratio, etc.), especially when elderly patients or co-morbidities are considered. Rescue therapies (low dose steroids, adding vasopressin to noradrenaline, proning, almitrine, NO, extracorporeal membrane oxygenation, etc.) are complex. Fever, above 38.5-39.5°C, increases both the ventilatory (high respiratory drive: large tidal volume, high respiratory rate) and the metabolic (increased O2 consumption) demands, further limiting the cardio-ventilatory reserve. Some data (case reports, uncontrolled trial, small randomized prospective trials) suggest that control of elevated body temperature ("fever control") leading to normothermia (35.5-37°C) will lower both the ventilatory and metabolic demands: fever control should simplify critical care management when limited cardio-ventilatory reserve is at stake. Usually fever control is generated by a combination of general anesthesia ("analgo-sedation", light total intravenous anesthesia), antipyretics and cooling. However general anesthesia suppresses spontaneous ventilation, making the management more complex. At variance, alpha-2 agonists (clonidine, dexmedetomidine) administered immediately following tracheal intubation and controlled mandatory ventilation, with prior optimization of volemia and atrio-ventricular conduction, will reduce metabolic demand and facilitate normothermia. Furthermore, after a rigorous control of systemic acidosis, alpha-2 agonists will allow for accelerated emergence without delirium, early spontaneous ventilation, improved cardiac output and micro-circulation, lowered vasopressor requirements and inflammation. Rigorous prospective randomized trials are needed in subsets of patients with a high fever and spiraling toward refractory septic shock and/or presenting with severe ARDS.

Spontaneous breathing during veno-venous extracorporeal membrane oxygenation

Veno-venous extracorporeal membrane oxygenation (VV ECMO) has started to be applied in awake spontaneously breathing patients as an alternative to invasive mechanical ventilation. As the physiologic cardiorespiratory variability is increased in this condition, the dynamic interaction between patient respiratory activity and extracorporeal system function affects the clinical management. The effect of extracorporeal CO₂ removal on patient respiratory drive is variable and not always predictable, with some patients responding to CO₂ removal with a decrease in respiratory rate and effort and other patients demonstrating a persistently high work of breathing independent on CO₂ unload. While the pathophysiological mechanisms of this different interactions are still to be clarified, improved monitoring ability is needed both to titrate the support in responders and to avoid the risk of ventilation injury in non-responders. Acute changes in patient respiratory patterns may also occur during spontaneous breathing, making it difficult to maintain constant levels of extracorporeal respiratory support, also because changes in the distribution of venous blood volume due to lung-heart interactions affect extracorporeal blood flow. Assessment of native lung function and of its evolution over time is challenging while respiratory gas exchanges are provided by the extracorporeal system, since both oxygenation and decarboxylation capabilities can be fully evaluated only when alveolar ventilation is restored reducing extracorporeal CO₂ removal. The rationale for using "awake ECMO" varies across different types of acute respiratory failure: the pathophysiological mechanisms of the underlying disease affect the patient-ECMO interaction and the goal of support. In this review we discuss the pathophysiology, technical challenges and monitoring issues of the use of ECMO in awake spontaneously breathing patients with acute respiratory failure of different etiologies.

Observational study of potential risk factors of immersion pulmonary edema in healthy divers: exercise intensity is the main contributor

BACKGROUND

The risk factors of pulmonary edema induced by diving in healthy subjects are not well known. The aim of the present study was to assess the parameters contributing to the increase in extravascular lung water after diving.

METHODS

This study was carried out in a professional diving institute. All divers participating in the teaching program from June 2012 to June 2014 were included in the study. Extravascular lung water was assessed using the detection of ultrasound lung comets (ULC) by chest ultrasonography. Clinical parameters and dive profiles were recorded using a questionnaire and a dive computer.

RESULTS

One-hundred six divers were investigated after 263 dives. They used an open-circuit umbilical supplying compressed gas diving apparatus in 202 cases and a self-contained underwater breathing apparatus in 61 cases. A generalized linear mixed model analysis was performed which demonstrated that the dive induced a significant increase in ULC score (incidence rate ratio: 3.16). It also identified that the predictive variable of increased extravascular lung water after the dive was the exercise intensity at depth (z = 3.99, p < 0.0001). The other parameters studied such as the water temperature, dive profile, hyperoxic exposure, or anthropometric data were not associated with the increase in extravascular lung water after the dive.

CONCLUSIONS

In this study, the exercise intensity was the main contributor to the increase in extravascular lung water in healthy divers. To improve the prevention of immersion pulmonary edema, the exercise intensity experienced during the dive should thus be adapted to the aerobic fitness level of the divers.

Diagnosis of Swimming Induced Pulmonary Edema-A Review

Swimming induced pulmonary edema (SIPE) is a complication that can occur during exercise with the possibility of misdiagnosis and can quickly become life threatening; however, medical literature infrequently describes SIPE. Therefore, the aim of this review was to analyse all individual cases diagnosed with SIPE as reported in scientific sources, with an emphasis on the diagnostic pathways and the key facts resulting in its diagnosis. Due to a multifactorial and complicated pathophysiology, the diagnosis could be difficult. Based on the actual literature, we try to point out important findings regarding history, conditions, clinical findings, and diagnostic testing helping to confirm the diagnosis of SIPE. Thirty-eight cases from seventeen articles reporting the diagnosis of SIPE were selected. We found remarkable differences in the individual described diagnostic pathways. A total of 100% of the cases suffered from an acute onset of breathing problems, occasionally accompanied by hemoptysis. A total of 73% showed initial hypoxemia. In most of the cases (89%), an initial chest X-Ray or chest CT was available, of which one-third (71%) showed radiological signs of pulmonary edema. The majority of the cases (82%) experienced a rapid resolution of symptoms within 48 h, the diagnostic hallmark of SIPE. Due to a foreseeable increase in participation in swimming competitions and endurance competitions with a swimming component, diagnosis of SIPE will be important, especially for medical teams caring for these athletes.

Spontaneous Breathing during Extracorporeal Membrane Oxygenation in Acute Respiratory Failure

BACKGROUND

We evaluate the clinical feasibility of spontaneous breathing on extracorporeal membrane oxygenation and the interactions between artificial and native lungs in patients bridged to lung transplant or with acute exacerbation of chronic obstructive pulmonary disease (COPD) or acute respiratory distress syndrome.

METHODS

The clinical course of a total of 48 patients was analyzed. Twenty-three of 48 patients were enrolled in the prospective study (nine bridged to lung transplant, six COPD, and eight acute respiratory distress syndrome). The response to the carbon dioxide removal was evaluated in terms of respiratory rate and esophageal pressure swings by increasing ("relief" threshold) and decreasing ("distress" threshold) the extracorporeal membrane oxygenation gas flow, starting from baseline condition.

RESULTS

Considering all 48 patients, spontaneous breathing extracorporeal membrane oxygenation was performed in 100% bridge to lung transplant (9 of 9 extubated), 86% COPD (5 of 6 extubated), but 27% acute respiratory distress syndrome patients (6 of 8 extubated; P < 0.001) and was maintained for 92, 69, and 38% of the extracorporeal membrane oxygenation days (P = 0.021), respectively. In all the 23 patients enrolled in the study, gas flow increase (from 2.3 ± 2.2 to 9.2 ± 3.2 l/min) determined a decrease of both respiratory rate (from 29 ± 6 to 8 ± 9 breaths/min) and esophageal pressure swings (from 20 ± 9 to 4 ± 4 cm H2O; P < 0.001 for all). All COPD and bridge to lung transplant patients were responders (reached the relief threshold), while 50% of acute respiratory distress syndrome patients were nonresponders.

CONCLUSIONS

Carbon dioxide removal through extracorporeal membrane oxygenation relieves work of breathing and permits extubation in many patients, mainly bridge to lung transplant and COPD. Only few patients with acute respiratory distress syndrome were able to perform the spontaneous breathing trial, and in about 50% of these, removal of large amount of patient's carbon dioxide production was not sufficient to prevent potentially harmful spontaneous respiratory effort.

Thoraco-abdominal coordination and performance during uphill running at altitude

INTRODUCTION

Running races on mountain trails at moderate-high altitude with large elevation changes throughout has become increasingly popular. During exercise at altitude, ventilatory demands increase due to the combined effects of exercise and hypoxia.

AIM

To investigate the relationships between thoraco-abdominal coordination, ventilatory pattern, oxygen saturation (SpO2), and endurance performance in runners during high-intensity uphill exercise.

METHODS

Fifteen participants (13 males, mean age 42±9 yrs) ran a "Vertical Kilometer," i.e., an uphill run involving a climb of approximately 1000 m with a slope greater than 30%. The athletes were equipped with a portable respiratory inductive plethysmography system, a finger pulse oximeter and a global positioning unit (GPS). The ventilatory pattern (ventilation (VE), tidal volume (VT), respiratory rate (RR), and VE/VT ratio), thoraco-abdominal coordination, which is represented by the phase angle (PhA), and SpO2 were evaluated at rest and during the run. Before and after the run, we assessed respiratory function, respiratory muscle strength and the occurrence of interstitial pulmonary edema by thoracic ultrasound.

RESULTS

Two subjects were excluded from the respiratory inductive plethysmography analysis due to motion artifacts. A quadratic relationship between the slope and the PhA was observed (r = 0.995, p = 0.036). When the slope increased above 30%, the PhA increased, indicating a reduction in thoraco-abdominal coordination. The reduced thoraco-abdominal coordination was significantly related to reduced breathing efficiency (i.e., an increased VE/VT ratio; r = 0.961, p = 0.038) and SpO2 (r = -0.697, p<0.001). Lower SpO2 values were associated with lower speeds at 20%≥slope≤40% (r = 0.335, p<0.001 for horizontal and r = 0.36, p<0.001 for vertical). The reduced thoraco-abdominal coordination and consequent reduction in SpO2 were associated with interstitial pulmonary edema.

CONCLUSION

Reductions in thoraco-abdominal coordination are associated with a less efficient ventilatory pattern and lower SpO2 during uphill running. This fact could have a negative effect on performance.

Exercise-induced pulmonary hemorrhage: where are we now?

As the Thoroughbreds race for the final stretch, 44 hooves flash and thunder creating a cacophony of tortured air and turf. Orchestrated by selective breeding for physiology and biomechanics, expressed as speed, the millennia-old symphony of man and beast reaches its climax. At nearly 73 kilometers per hour (45 mph) over half a ton of flesh and bone dwarfs its limpet-like jockey as, eyes wild and nostrils flaring, their necks stretch for glory. Beneath each resplendent livery-adorned, latherin-splattered coat hides a monstrous heart trilling at 4 beats per second, and each minute, driving over 400 L (105 gallons) of oxygen-rich blood from lungs to muscles. Matching breath to stride frequency, those lungs will inhale 16 L (4 gallons) of air each stride moving >1,000 L/min in and out of each nostril - and yet failing. Engorged with blood and stretched to breaking point, those lungs can no longer redden the arterial blood but leave it dusky and cyanotic. Their exquisitely thin blood-gas barrier, a mere 10.5 μm thick (1/50,000 of an inch), ruptures, and red cells invade the lungs. After the race is won and lost, long after the frenetic crowd has quieted and gone, that blood will clog and inflame the airways. For a few horses, those who bleed extensively, it will overflow their lungs and spray from their nostrils incarnadining the walls of their stall: a horrifically poignant canvas that strikes at horse racing's very core. That exercise-induced pulmonary hemorrhage (EIPH) occurs is a medical and physiological reality. That every reasonable exigency is not taken to reduce/prevent it would be a travesty. This review is not intended to provide an exhaustive coverage of EIPH for which the reader is referred to recent reviews, rather, after a brief reminder of its physiologic and pathologic bases, focus is brought on the latest developments in EIPH discovery as this informs state-of-the-art knowledge, the implementation of that knowledge and recommendations for future research and treatment.

"Awake" extracorporeal membrane oxygenation (ECMO): pathophysiology, technical considerations, and clinical pioneering

Venovenous extracorporeal membrane oxygenation (vv-ECMO) has been classically employed as a rescue therapy for patients with respiratory failure not treatable with conventional mechanical ventilation alone. In recent years, however, the timing of ECMO initiation has been readdressed and ECMO is often started earlier in the time course of respiratory failure. Furthermore, some centers are starting to use ECMO as a first line of treatment, i.e., as an alternative to invasive mechanical ventilation in awake, non-intubated, spontaneously breathing patients with respiratory failure ("awake" ECMO). There is a strong rationale for this type of respiratory support as it avoids several side effects related to sedation, intubation, and mechanical ventilation. However, the complexity of the patient-ECMO interactions, the difficulties related to respiratory monitoring, and the management of an awake patient on extracorporeal support together pose a major challenge for the intensive care unit staff. Here, we review the use of vv-ECMO in awake, spontaneously breathing patients with respiratory failure, highlighting the pros and cons of this approach, analyzing the pathophysiology of patient-ECMO interactions, detailing some of the technical aspects, and summarizing the initial clinical experience gained over the past years.

Update on the Mechanisms of Pulmonary Inflammation and Oxidative Imbalance Induced by Exercise

The mechanisms involved in the generation of oxidative damage and lung inflammation induced by physical exercise are described. Changes in lung function induced by exercise involve cooling of the airways, fluid evaporation of the epithelial surface, increased contact with polluting substances, and activation of the local and systemic inflammatory response. The present work includes evidence obtained from the different types of exercise in terms of duration and intensity, the effect of both acute performance and chronic performance, and the influence of special conditions such as cold weather, high altitude, and polluted environments. Levels of prooxidants, antioxidants, oxidative damage to biomolecules, and cellularity, as well as levels of soluble mediators of the inflammatory response and its effects on tissues, are described in samples of lung origin. These samples include tissue homogenates, induced sputum, bronchoalveolar lavage fluid, biopsies, and exhaled breath condensate obtained in experimental protocols conducted on animal and human models. Finally, the need to simultaneously explore the oxidative/inflammatory parameters to establish the interrelation between them is highlighted.

Pulmonary arterial hypertension: the key role of echocardiography

Echocardiography is a key screening tool in the diagnostic algorithm of pulmonary arterial hypertension (PAH). It provides an estimate of right ventricular function and pulmonary artery pressure, either at rest or during exercise, and is useful in ruling out secondary causes of pulmonary hypertension (PH) such as left heart disease or congenital heart disease. Several studies have showed that echocardiography is insufficiently precise as single tool for the ultimate diagnosis of PH respect to the right heart catheterization, considered the gold standard technique. Echocardiography is valuable in assessing prognosis and treatment options, monitoring the efficacy of specific therapeutic interventions, and detecting the preclinical stages of disease. The ideal imaging modality for accurate noninvasive assessment of the right heart should be accurate and precise, not influenced by loading conditions, routinely practicable and easily repeatable. For all such reasons and considering that PAH is a rare and severe condition, a complete noninvasive assessment of right heart function requires a deep knowledge of the disease and a multimodality approach.

Extracorporeal gas exchange and spontaneous breathing for the treatment of acute respiratory distress syndrome: an alternative to mechanical ventilation?*

OBJECTIVES

Venovenous extracorporeal gas exchange is increasingly used in awake, spontaneously breathing patients as a bridge to lung transplantation. Limited data are available on a similar use of extracorporeal gas exchange in patients with acute respiratory distress syndrome. The aim of this study was to investigate the use of extracorporeal gas exchange in awake, spontaneously breathing sheep with healthy lungs and with acute respiratory distress syndrome and describe the interactions between the native lung (healthy and diseased) and the artificial lung (extracorporeal gas exchange) in this setting.

DESIGN

Laboratory investigation.

SETTING

Animal ICU of a governmental laboratory.

SUBJECTS

Eleven awake, spontaneously breathing sheep on extracorporeal gas exchange.

INTERVENTIONS

Sheep were studied before (healthy lungs) and after the induction of acute respiratory distress syndrome via IV injection of oleic acid. Six gas flow settings (1-10 L/min), resulting in different amounts of extracorporeal CO2 removal (20-100% of total CO2 production), were tested in each animal before and after the injury.

MEASUREMENTS AND MAIN RESULTS

Respiratory variables and gas exchange were measured for every gas flow setting. Both healthy and injured sheep reduced minute ventilation according to the amount of extracorporeal CO2 removal, up to complete apnea. However, compared with healthy sheep, sheep with acute respiratory distress syndrome presented significantly increased esophageal pressure variations (25 ± 9 vs 6 ± 3 cm H2O; p < 0.001), which could be reduced only with very high amounts of CO2 removal (> 80% of total CO2 production).

CONCLUSIONS

Spontaneous ventilation of both healthy sheep and sheep with acute respiratory distress syndrome can be controlled via extracorporeal gas exchange. If this holds true in humans, extracorporeal gas exchange could be used in awake, spontaneously breathing patients with acute respiratory distress syndrome to support gas exchange. A deeper understanding of the pathophysiology of spontaneous breathing during acute respiratory distress syndrome is however warranted in order to be able to propose extracorporeal gas exchange as a safe and valuable alternative to mechanical ventilation for the treatment of patients with acute respiratory distress syndrome.

Respiratory disorders in endurance athletes - how much do they really have to endure?

Respiratory disorders are often a cause of morbidity in top level endurance athletes, more often compromising their performance and rarely being a cause of death. Pathophysiological events occurring during exercise, such as bronchospasm, are sometimes followed by clear pathological symptoms represented by asthma related to physical exertion or rarely by pulmonary edema induced by a strenuous effort. Both bronchospasm and the onset of interstitial edema induced by exercise cannot be considered pathological per se, but are more likely findings that occur in several healthy subjects once physical exhaustion during exertion has been reached. Consequently, we get a vision of the respiratory system perfectly tailored to meet the body's metabolic demands under normal conditions but which is limited when challenged by strenuous exercise, in particular when it happens in an unfavorable environment. As extreme physical effort may elicit a pathological response in healthy subjects, due to the exceeding demand in a perfectly functional system, an overview of the main tools both enabling the diagnosis of respiratory impairment in endurance athletes in a clinical and preclinical phase has also been described.

Exercise-induced pulmonary hemorrhage in a nonathlete: case report and review of physiology

The integrity of the pulmonary blood-gas barrier is vulnerable to intense exercise in elite athletes, similar to the phenomenon of exercise-induced pulmonary hemorrhage in thoroughbred racehorses. A 50-year-old previously healthy man presented with acute onset shortness of breath, dry cough, and hypoxemia after engaging in an extremely vigorous game of handball. CT scan of the chest showed diffuse patchy air-space disease. Bronchoalveolar lavage revealed diffuse alveolar hemorrhage. Infectious etiologies and bleeding diatheses were excluded by laboratory testing. Serological tests for ANCA-associated vasculitis, lupus, and Goodpasture's disease also were negative. A transthoracic echocardiogram was normal. The patient recovered completely on supportive therapy in less than 72 h. This case demonstrates strenuous exercise as a cause of diffuse alveolar hemorrhage in a previously healthy male with no apparent underlying cardiopulmonary disease.

Lung physiology at play: Hemoptysis due to underwater hockey

Hemoptysis can be a very concerning symptom, and the workup of a patient with hemoptysis may be expensive and invasive. Over the past decade, there has been increasing recognition of hemoptysis that occurs in highly trained athletes under conditions of extreme physical exertion and is explained by “pulmonary capillary stress failure”. This report highlights the physiological mechanisms of pulmonary capillary stress failure in the highly trained athlete, with emphasis on the predisposition to develop this condition in underwater sports. We describe the case of an otherwise healthy 34 year-old competitive underwater hockey player who reported hemoptysis following particularly strenuous games. We postulate that the hemoptysis was a result of the pulmonary capillary stress failure caused by the cumulative hemodynamic effects of a markedly elevated cardiac output, the increased central blood volume caused by the hydrostatic effects of submersion in water, and the negative intrathoracic pressure produced by voluntary diaphragmatic contractions.

Comparative physiology of the pulmonary circulation

Two selective pressures have shaped the evolution of the pulmonary circulation. First, as animals evolved from heterothermic ectotherms to homeothermic endoderms with their corresponding increase in the ability to sustain high oxygen consumptions, the blood-gas barrier had to become successively thinner, and also provide an increasingly large area for diffusive gas exchange. Second, the barrier had to find a way to maintain its mechanical integrity in the face of extreme thinness, and this was assisted by the increasing separation of the pulmonary from the systemic circulation. A remarkable feature throughout the evolution of air-breathing vertebrates has been the tight conservation of the tripartite structure of the blood-gas barrier with its three layers: capillary endothelium, extracellular matrix, and alveolar epithelium. The strength of the barrier can be ascribed to the very thin layer of type IV collagen in the extracellular matrix. In the phylogenic progression from amphibia and reptiles to mammals and birds, the blood-gas barrier became successively thinner. Also, the area increased greatly reflecting the greater oxygen demands of the organism. The gradual separation of the pulmonary from the systemic circulation continued from amphibia through reptiles to mammals and birds. Only in the last two classes are the circulations completely separate with the result that the pulmonary capillary pressures can be maintained low enough to avoid stress failure of the blood-gas barrier. Remarkably, the barrier is generally much thinner in birds than mammals, and it is also much more uniform in thickness. These advantages for gas exchange can be explained by the support of avian pulmonary capillaries by the surrounding air capillaries. This arrangement was made possible by the adoption of the flow-through system of ventilation in birds as opposed to the reciprocating pattern in mammals.

Study of Stress Induced Failure of the Blood-gas Barrier and the Epithelial-epithelial Cells Connections of the Lung of the Domestic Fowl, Gallus gallus Variant Domesticus after Vascular Perfusion

Complete blood-gas barrier breaks (BGBBs) and epithelial-epithelial cells connections breaks (E-ECCBs) were enumerated in the lungs of free range chickens, Gallus gallus variant domesticus after vascular perfusion at different pressures. The E-ECCBs surpassed the BGBBs by a factor of ~2. This showed that the former parts of the gas exchange tissue were structurally weaker or more vulnerable to failure than the latter. The differences in the numbers of BGBBs and E-ECCBs in the different regions of the lung supplied with blood by the 4 main branches of the pulmonary artery (PA) corresponded with the diameters of the blood vessels, the angles at which they bifurcated from the PA, and the positions along the PA where they branched off. Most of the BGBBs and the E-ECCBs occurred in the regions supplied by the accessory- and the caudomedial branches: the former is the narrowest branch and the first blood vessel to separate from the PA while the latter is the most direct extension of the PA and is the widest. The E-ECCBs appeared to separate and fail from tensing of the blood capillary walls, as the perfusion- and intramural pressures increased. Compared to the mammalian lungs on which data are available, i.e., those of the rabbit, the dog, and the horse, the blood-gas barrier of the lung of free range chickens appears to be substantially stronger for its thinness.

High-altitude pulmonary edema

High-altitude pulmonary edema (HAPE), a not uncommon form of acute altitude illness, can occur within days of ascent above 2500 to 3000 m. Although life-threatening, it is avoidable by slow ascent to permit acclimatization or with drug prophylaxis. The critical pathophysiology is an excessive rise in pulmonary vascular resistance or hypoxic pulmonary vasoconstriction (HPV) leading to increased microvascular pressures. The resultant hydrostatic stress causes dynamic changes in the permeability of the alveolar capillary barrier and mechanical injurious damage leading to leakage of large proteins and erythrocytes into the alveolar space in the absence of inflammation. Bronchoalveolar lavage and hemodynamic pressure measurements in humans confirm that elevated capillary pressure induces a high-permeability noninflammatory lung edema. Reduced nitric oxide availability and increased endothelin in hypoxia are the major determinants of excessive HPV in HAPE-susceptible individuals. Other hypoxia-dependent differences in ventilatory control, sympathetic nervous system activation, endothelial function, and alveolar epithelial active fluid reabsorption likely contribute additionally to HAPE susceptibility. Recent studies strongly suggest nonuniform regional hypoxic arteriolar vasoconstriction as an explanation for how HPV occurring predominantly at the arteriolar level causes leakage. In areas of high blood flow due to lesser HPV, edema develops due to pressures that exceed the dynamic and structural capacity of the alveolar capillary barrier to maintain normal fluid balance. This article will review the pathophysiology of the vasculature, alveolar epithelium, innervation, immune response, and genetics of the lung at high altitude, as well as therapeutic and prophylactic strategies to reduce the morbidity and mortality of HAPE.