Exercise-Induced Pulmonary Hemorrhage (EIPH)

Exercise-induced pulmonary hemorrhage (EIPH) represents a common condition affecting performance horses in which strenuous exercise causes bleeding into the airways from damaged blood vessels within the lungs. The condition occurs when the extreme cardiovascular demands of high-intensity exercise rupture fragile pulmonary capillaries, releasing blood into the airways and alveoli. While only a small percentage of affected horses show visible bleeding from the nostrils (epistaxis), endoscopic studies reveal that the vast majority of horses engaged in intense athletic pursuits experience some degree of pulmonary hemorrhage. Understanding EIPH is essential for owners, trainers, and veterinarians involved with performance horses across multiple disciplines.

EIPH affects horses worldwide and is remarkably prevalent in athletic horse populations. Studies using endoscopic examination after exercise have demonstrated that 75 to 95 percent of Thoroughbred and Standardbred racehorses experience EIPH at some point during their racing careers, with similar high rates documented in barrel racing horses, eventers, and polo ponies. The condition appears to be inherent to equine athletic performance rather than representing an abnormal disease state, though severity varies considerably among individuals. While most commonly recognized in racing breeds, any horse subjected to maximal or near-maximal exercise intensity can develop EIPH, making it relevant across the full spectrum of competitive equine pursuits.

The impact of EIPH on horse performance ranges from subclinical effects detectable only by endoscopy to severe bleeding that visibly compromises racing ability. Even mild EIPH not visible externally can reduce gas exchange efficiency in the lungs, potentially limiting peak performance. Moderate to severe episodes may cause post-exercise coughing, increased recovery time, and measurable decrements in race times and competitive results. Repeated episodes lead to cumulative lung damage including fibrosis and vascular changes that worsen over time. The economic significance of EIPH to the racing industry is substantial, influencing medication policies, training decisions, and career longevity of affected horses.

While EIPH cannot be cured or completely prevented, effective management strategies significantly reduce severity and frequency of bleeding episodes. The diuretic furosemide (Lasix) remains the most widely used treatment and is permitted race-day in many jurisdictions, though regulations vary. Environmental modifications, training adjustments, and supportive treatments provide additional benefit. Early recognition and proactive management help protect lung health and extend athletic careers. Working with a licensed equine veterinarian experienced in performance horse medicine enables development of individualized management protocols optimizing outcomes for affected horses.

The primary cause of EIPH is the rupture of pulmonary capillaries due to extreme pressure differentials generated during strenuous exercise. During high-intensity exercise, horses experience dramatic increases in pulmonary arterial pressure, with pressures potentially exceeding 120 mmHg during maximal exertion. Simultaneously, the highly negative pressures generated during forceful inspiration create additional stress on the delicate capillary walls. This combination of high vascular pressure and low airway pressure creates transmural pressure gradients that exceed the structural capacity of pulmonary capillaries, causing them to rupture and release blood into the alveoli and airways.

Genetic and breed predisposition to EIPH appears significant, though specific causative genes have not been definitively identified. Thoroughbreds and Standardbreds show particularly high prevalence rates, likely reflecting both genetic factors and the extreme intensity of racing. Studies have demonstrated familial patterns of EIPH severity, suggesting heritable components to capillary fragility or hemodynamic responses during exercise. Within racing populations, some family lines are recognized as producing more bleeders than others. Research continues into genetic markers that might identify horses at higher risk before they enter training.

Environmental and management factors significantly influence EIPH occurrence and severity. Airborne irritants including dust, mold spores, and ammonia from bedding can cause lower airway inflammation that predisposes to bleeding. Poor air quality in training facilities and during exercise exacerbates risk. Cold, dry air may increase bleeding tendency compared to warmer, humid conditions. Track or arena surface characteristics affect the intensity of concussive forces transmitted through the limbs to the thorax during exercise. Training patterns that include frequent maximal exertion without adequate recovery between sessions may increase cumulative lung damage.

Risk factors for EIPH include racing discipline, exercise intensity, age, and pre-existing respiratory conditions. Racing at distances requiring sustained maximal effort produces more severe bleeding than shorter sprints. Horses in active racing careers experience more frequent and severe episodes than those in lighter training. Older horses with longer competitive careers typically show more severe changes, suggesting cumulative damage over time. Underlying inflammatory airway disease (IAD) or equine asthma significantly increases EIPH risk by compromising lung health and potentially affecting vascular integrity. Recent respiratory infections may temporarily increase susceptibility.

The pathophysiology of EIPH involves complex interactions between cardiovascular dynamics, respiratory mechanics, and pulmonary vascular structure. Exercise dramatically increases cardiac output and pulmonary blood flow to meet oxygen demands, elevating pulmonary vascular pressures. Simultaneously, the respiratory muscles generate highly negative inspiratory pressures to move large volumes of air rapidly. The pulmonary capillaries, designed for gas exchange with walls only one cell thick, lack structural resilience to withstand these extreme pressure gradients. Capillary rupture occurs predominantly in the dorsocaudal lung regions where hemodynamic stress is greatest. Released blood damages adjacent alveoli and triggers inflammatory responses that, over time, lead to fibrosis, vascular remodeling, and increased susceptibility to future bleeding episodes.

Early warning signs of EIPH are often absent or extremely subtle because most bleeding occurs within the lungs without visible external evidence. Owners and trainers may notice subtle performance decrements before recognizing any physical signs of bleeding. Horses may show slightly prolonged recovery times after exercise or require more effort than expected during workouts. Occasional swallowing during or after exercise may indicate blood entering the pharynx from the trachea. Because horses are prey animals that instinctively hide signs of weakness, they do not display obvious distress during all but the most severe bleeding episodes. Awareness that EIPH is common allows proactive monitoring.

Common symptoms of EIPH vary dramatically with severity. The majority of affected horses show no externally visible signs despite endoscopic evidence of pulmonary hemorrhage. When bleeding is more severe, blood may be visible in the nostrils (epistaxis), though this occurs in only 1 to 5 percent of EIPH episodes. Post-exercise coughing, sometimes productive of blood-tinged mucus, indicates blood has reached the major airways. Swallowing repeatedly during exercise or immediately after may signal blood trickling down the trachea. Reduced performance not explained by other factors, particularly unexpected fading late in races, suggests EIPH even without visible bleeding.

Behavioral changes associated with EIPH episodes may be subtle or absent in most cases. Horses experiencing significant bleeding may appear distressed during or immediately after exercise, though many show no obvious behavioral changes. Reluctance to extend fully during exercise might indicate horses are self-limiting to avoid triggering more severe bleeding. Some horses become head-shy or resistant to having their nostrils examined if they associate this area with bleeding experiences. Post-exercise attitude may be subdued compared to normal. Horses with chronic severe EIPH may show exercise intolerance and reluctance to work at high intensity.

Physical signs on examination depend on bleeding severity and timing of evaluation relative to exercise. In most cases, physical examination findings are normal because bleeding remains confined to the lungs. When epistaxis occurs, blood is typically bright red and frothy, appearing during or within minutes after high-intensity exercise. Auscultation of the lungs may reveal crackles or abnormal breath sounds in severe cases, though findings are often normal. Heart rate and respiratory rate recovery may be prolonged compared to normal. Endoscopic examination of the trachea within hours of exercise reveals blood in the vast majority of horses that have engaged in strenuous work.

Symptom progression in individual horses and across careers demonstrates the cumulative nature of EIPH. Early in racing careers, horses may show minimal or no evidence of bleeding. With continued high-intensity work, episodes typically become more frequent and severe. Endoscopic findings may progress from minimal blood flecks to substantial tracheal blood pooling over successive examinations. Some horses eventually develop severe bleeding leading to visible epistaxis regularly or continuously declining performance. The natural history involves progressive lung damage from repeated hemorrhage, inflammation, and fibrosis, making management increasingly challenging over time.

Emergency symptoms requiring immediate veterinary care include profuse bleeding from the nostrils, signs of severe respiratory distress, or collapse associated with exercise. While most EIPH episodes are self-limiting, horses occasionally experience catastrophic pulmonary hemorrhage that can be fatal within minutes. Any horse showing continuous heavy bleeding, labored breathing, extreme distress, or weakness following exercise requires emergency assessment. Blue or pale mucous membrane color indicates inadequate oxygenation requiring urgent intervention. Fortunately, such severe events are rare, but their possibility underscores the importance of monitoring horses during and after high-intensity work.

Physical examination alone is insufficient for EIPH diagnosis because most affected horses show no externally visible abnormalities. Post-exercise evaluation may reveal prolonged heart rate or respiratory rate recovery in affected horses. Auscultation of the chest occasionally identifies abnormal breath sounds, though findings are usually unremarkable. Examination of the nostrils and nasal passages may show blood if epistaxis has occurred, though this is present in only a small minority of cases. Physical examination is most valuable for ruling out other causes of exercise intolerance or visible bleeding and assessing overall health status.

Diagnostic tests for EIPH center on tracheobronchial endoscopy performed within one to two hours following strenuous exercise. Direct visualization of the trachea allows observation and grading of any blood present. Standardized grading systems rate severity from Grade 0 (no blood) through Grade 4 (large amounts of blood with pooling), enabling consistent documentation and comparison over time. Endoscopy also evaluates for inflammatory airway disease, anatomical abnormalities, or other conditions that might contribute to or mimic EIPH. Bronchoalveolar lavage (BAL) performed during endoscopy can detect hemosiderophages (iron-laden macrophages indicating prior bleeding) even when no fresh blood is visible, confirming history of EIPH.

Advanced diagnostics may be employed for comprehensive evaluation or when standard testing is inconclusive. Thoracic radiography can reveal changes consistent with chronic EIPH including increased interstitial density in the dorsocaudal lung fields. Thoracic ultrasound evaluates pleural surfaces and superficial lung regions for abnormalities. Nuclear scintigraphy has been used in research settings to evaluate pulmonary blood flow patterns. Cardiac evaluation including echocardiography rules out cardiac conditions that might contribute to pulmonary hypertension or hemorrhage. Blood work including coagulation profiles may be performed to exclude bleeding disorders, though these rarely contribute to true EIPH.

Differential diagnosis for bleeding observed from the respiratory tract includes conditions other than EIPH. Guttural pouch mycosis causes epistaxis from fungal erosion of vessels in the guttural pouches and represents a serious differential requiring urgent diagnosis. Ethmoid hematoma, a progressive vascular mass in the nasal passages, causes recurrent epistaxis not necessarily related to exercise. Pharyngeal or laryngeal trauma during exercise can produce bleeding. Upper airway abnormalities including subepiglottic cysts may bleed. Coagulation disorders causing generalized bleeding tendency require consideration. Exercise intolerance without visible bleeding has numerous potential causes requiring systematic evaluation. Proper diagnosis guides appropriate treatment selection.

Emergency treatment for severe EIPH episodes focuses on stabilization and supportive care. Horses showing profuse bleeding should be kept calm and quiet to minimize further cardiovascular stress. Light sedation may be helpful in anxious horses if not contraindicated. The head should be allowed to hang naturally rather than being elevated, enabling blood to drain from airways rather than accumulating. Oxygen supplementation may be provided if available and the horse tolerates application. Intravenous fluids support cardiovascular function if significant blood loss occurs. Severe cases potentially require hospitalization for monitoring and intensive support. Fortunately, most EIPH episodes resolve spontaneously within minutes to hours without emergency intervention.

Medical management of EIPH predominantly involves furosemide (Lasix), a loop diuretic that reduces EIPH severity through mechanisms not fully understood but likely related to decreased pulmonary vascular pressures. Administered intravenously four hours before exercise, furosemide significantly reduces EIPH incidence and severity in controlled studies. Regulations regarding furosemide use vary by jurisdiction and governing body, with some allowing race-day administration and others prohibiting it. Other medications with variable evidence include aminocaproic acid (an antifibrinolytic), conjugated estrogens, and various supplements purported to support capillary integrity. Bronchodilators and corticosteroids may benefit horses with concurrent inflammatory airway disease.

Surgical options for EIPH are not available, as the condition involves diffuse changes throughout the pulmonary vasculature rather than a discrete lesion amenable to surgical correction. No surgical procedure can address the fundamental hemodynamic stresses causing capillary rupture during exercise. Treatment therefore remains medical and management-based rather than surgical.

Supportive care for EIPH management extends beyond medication to comprehensive environmental and management strategies. Minimizing airborne irritants through improved barn ventilation, dust-free bedding, and hay soaking or alternatives reduces inflammatory airway disease that exacerbates EIPH. Treating any concurrent respiratory conditions optimizes baseline lung health. Allowing adequate recovery time between high-intensity exercise sessions reduces cumulative stress. Training modifications may include reducing the frequency or intensity of maximal efforts. Some trainers and veterinarians employ nasal strips during exercise, believing they may reduce negative inspiratory pressures, though evidence for efficacy is limited.

Rehabilitation and return to work following significant EIPH episodes requires balancing continued fitness maintenance with lung recovery. Complete rest following severe bleeding allows healing before resuming training. Gradual return to exercise intensity monitors for recurrence at each level. Some horses require permanent reduction in exercise intensity to prevent severe bleeding. Others can return to full competition with appropriate prophylactic treatment. Ongoing monitoring through periodic endoscopy helps assess lung status and guides management decisions. Career decisions consider whether the horse can be managed successfully at the required competition level.

Treatment decision factors include severity and frequency of EIPH episodes, regulatory environment, intended use, and individual response to management strategies. Horses with mild, infrequent bleeding detected only endoscopically may require minimal intervention. Those with moderate bleeding may benefit from furosemide prophylaxis where permitted, along with environmental management. Severe or frequent bleeders require comprehensive approaches and may ultimately need career modifications. Jurisdictional regulations constraining medication use affect available options. Owner goals, financial considerations, and horse welfare collectively inform appropriate management decisions. Close collaboration with an experienced equine veterinarian optimizes outcomes.

Recovery timeline following individual EIPH episodes is generally rapid, with acute bleeding typically resolving within hours. Blood visible in the trachea after exercise usually clears within 24 to 48 hours. Horses can often return to training within days of an episode, though the optimal rest period before resuming high-intensity work is debated. Some clinicians recommend at least one week of reduced work following visible epistaxis before returning to racing or other maximal exercise. The microscopic inflammatory and healing processes triggered by bleeding continue for longer than gross blood clearance, potentially spanning one to two weeks. Chronic lung changes from cumulative damage, however, are permanent and progressive.

Post-treatment care and monitoring involve ongoing assessment of EIPH status throughout the horse's athletic career. Regular endoscopic examinations following exercise establish baseline and track progression or response to management changes. The frequency of monitoring depends on EIPH severity and competitive level, with racehorses in active campaigns potentially scoped multiple times per season. Documentation of EIPH grades over time reveals patterns and trends guiding management adjustments. Response to treatments is assessed through comparative endoscopic findings. Overall respiratory health monitoring includes attention to concurrent conditions like inflammatory airway disease that influence EIPH.

Prognosis factors affecting EIPH outcomes include baseline severity, age, duration of racing career, response to treatment, and presence of concurrent respiratory disease. Horses with mild EIPH responding well to management can often maintain successful athletic careers. Those with severe or refractory bleeding may face career limitations or early retirement. Younger horses earlier in their careers typically have less cumulative damage than veterans with extensive racing histories. Horses with concurrent inflammatory airway disease or equine asthma face more challenging management. Individual variation in treatment response affects prognosis, with some horses achieving excellent control while others remain problematic despite comprehensive management.

Long-term outlook for horses with EIPH varies from continued successful competition to career-ending lung damage. Many racehorses complete full careers while managing EIPH, particularly with furosemide use in permissive jurisdictions. Others experience progressive worsening requiring reduced training intensity or retirement from racing. The cumulative nature of EIPH means that longer careers typically involve more significant lung changes. Post-racing careers in lower-intensity disciplines are often possible for horses retired from racing due to EIPH. Some horses transition successfully to breeding, pleasure riding, or companion roles. Quality of life in retirement is generally good, as EIPH symptoms only manifest during intense exercise.

Management practices to reduce EIPH focus on minimizing risk factors and optimizing respiratory health. Maintaining excellent air quality in barns and training facilities reduces lower airway inflammation that predisposes to bleeding. Regular stall cleaning, appropriate ventilation, and dust control in indoor arenas protect respiratory health. Training programs should incorporate adequate recovery between high-intensity sessions to allow lung healing. Avoiding excessive frequency of maximal efforts may reduce cumulative damage. Monitoring horses for early signs of respiratory issues enables prompt treatment before EIPH is exacerbated. Some trainers believe warming up thoroughly before high-intensity work reduces bleeding risk, though evidence is limited.

Nutritional approaches to EIPH prevention lack strong scientific evidence but remain popular among horsemen. Omega-3 fatty acid supplementation is theorized to support vascular health and reduce inflammation. Vitamin C and bioflavonoids are sometimes supplemented for purported effects on capillary integrity. Vitamin K supplementation aims to support coagulation, though clotting ability is not typically deficient in EIPH horses. Ensuring adequate overall nutrition supports general health and immune function. While nutritional interventions remain largely unproven for EIPH specifically, maintaining optimal nutritional status contributes to overall respiratory health.

Exercise and conditioning strategies influence EIPH through effects on cardiovascular and respiratory fitness. Appropriate conditioning programs develop cardiovascular capacity gradually, potentially allowing the pulmonary system to adapt to increasing demands. Interval training approaches may be less stressful to the pulmonary vasculature than continuous high-intensity work. Adequate fitness before asking for maximal efforts reduces the relative stress of competition. Training at altitude has been explored for potential cardiovascular adaptations, though results are mixed. Exercise in cold weather may require additional warm-up due to potential effects of cold air on bleeding tendency.

Environmental factors significantly influence EIPH risk and should be optimized where possible. Barn air quality directly affects lower airway health, making ventilation a priority. Ammonia levels from urine decomposition in bedding irritate airways and should be minimized through frequent stall cleaning. Hay storage away from horse housing reduces mold spore exposure. Alternatives to dusty hay including soaked hay, steamed hay, or hay cubes benefit respiratory health. Arena and track surfaces should be maintained to minimize dust. Racing or competing in humid conditions may be preferable to dry, dusty environments when options exist.

Prophylactic medication protocols center on furosemide administration before exercise where regulations permit. Pre-exercise furosemide has demonstrated efficacy in reducing EIPH severity in controlled studies and remains the mainstay of pharmacological prevention. Timing of administration (typically four hours pre-exercise for intravenous dosing) is important for optimal effect. Other medications used preventively have less robust evidence supporting their efficacy. Regulatory constraints on medication use vary by jurisdiction and discipline, affecting available prevention options. Compliance with applicable rules while optimizing horse welfare requires understanding specific regulatory requirements.

Daily management adjustments for horses with EIPH focus on respiratory health optimization and monitoring. Stall environment should prioritize air quality through excellent ventilation, low-dust bedding (shavings, paper, or dust-extracted products over straw), and minimal ammonia accumulation. Hay should be soaked for 10 to 30 minutes before feeding or replaced with alternatives such as hay cubes, pellets, or steamed hay to reduce respirable particles. Water availability should ensure adequate hydration supporting respiratory secretion management. Daily observation for coughing, nasal discharge, or other respiratory signs enables early intervention for developing problems. Documentation of exercise performance and any symptoms provides valuable longitudinal information.

Housing and turnout considerations balance respiratory health with other management needs. Turnout maximizes fresh air exposure and is generally beneficial for respiratory health. Pasture conditions should avoid dusty paddocks during dry weather. When stabling is necessary, positioning in well-ventilated areas of the barn provides incremental benefit. Stalls with outdoor exposure or excellent cross-ventilation are preferable to interior locations with limited airflow. During weather extremes, protecting respiratory health may require balancing temperature concerns with ventilation needs, generally prioritizing air quality over warmth. Companion horses without EIPH concerns can share airspace without transmission risk, as the condition is not contagious.

Exercise modifications for EIPH-affected horses balance maintaining fitness with managing bleeding risk. The intensity and frequency of maximal efforts should be carefully controlled based on individual bleeding severity and response to management. Some horses tolerate regular racing with appropriate prophylaxis while others require reduced competitive schedules. Training patterns may incorporate more lower-intensity work and fewer all-out efforts. Warm-up protocols should be thorough before high-intensity exercise. Post-exercise monitoring for visible bleeding, coughing, or prolonged recovery guides subsequent training decisions. Career paths may ultimately be modified if EIPH proves unmanageable at elite competitive levels.

Monitoring and ongoing care involve regular assessment of EIPH status throughout the horse's athletic career. Periodic endoscopic examination following exercise provides objective documentation of bleeding severity and response to management strategies. Frequency of endoscopy depends on severity and competitive level, ranging from occasional checks in mild cases to regular monitoring in actively racing horses with significant EIPH. Overall respiratory health should be evaluated, with concurrent conditions like inflammatory airway disease aggressively managed. Communication between owners, trainers, and veterinarians ensures coordinated care. Documentation creates longitudinal records supporting management decisions.

Quality of life and use considerations for horses with EIPH recognize that the condition primarily affects intense athletic performance. Horses retired from racing due to EIPH typically enjoy excellent quality of life in less demanding pursuits. Pleasure riding, light showing, breeding, and companion roles rarely trigger bleeding episodes because they do not involve the extreme exercise intensity that causes EIPH. Career transitions should be planned proactively when EIPH becomes unmanageable at competitive levels, rather than waiting for severe episodes or lung damage to force retirement. Post-racing life can be long and comfortable for EIPH horses with appropriate expectations. The welfare of the horse should guide decisions about continued competition versus retirement.

High-risk breeds for EIPH include Thoroughbreds, Standardbreds, Quarter Horses used in racing, and other breeds subjected to maximal exercise intensity. The extremely high prevalence in racing Thoroughbreds (75 to 95 percent by endoscopic detection) reflects both genetic predisposition and the extreme nature of the sport. Standardbred trotters and pacers show similar rates related to racing intensity. Quarter Horses in racing and barrel racing disciplines demonstrate significant EIPH prevalence. Arabians and other breeds competing in high-intensity disciplines including endurance racing and polo experience EIPH. The condition correlates more strongly with exercise intensity than breed per se, meaning any horse performing maximal exertion faces risk regardless of breed.

Use and discipline considerations strongly influence EIPH occurrence. Racing disciplines across breed types show highest prevalence due to the sustained maximal effort required. Flat racing, harness racing, barrel racing, and similar sprinting sports produce the most severe cardiovascular stress triggering bleeding. Three-day eventing, particularly the cross-country phase, subjects horses to intense sustained effort and associated EIPH risk. Polo ponies experience repeated intense sprints throughout matches. Show jumping at upper levels involves considerable cardiovascular demand. Dressage and pleasure disciplines rarely trigger EIPH due to lower exercise intensity. Understanding discipline-specific risk helps guide monitoring and management priorities.

Genetic testing and breeding recommendations for EIPH remain areas of ongoing research rather than established practice. No commercially available genetic test identifies EIPH susceptibility, though research continues exploring genetic markers. The high prevalence in racing populations makes complete avoidance through breeding selection impractical without genetic tools. Anecdotal recognition that certain family lines produce more severe bleeders than others suggests heritable components, and some breeders consider EIPH history in breeding decisions. Documentation of EIPH severity in racing records could theoretically inform breeding choices. Future identification of genetic markers would enable more targeted selection, though the complex multifactorial nature of EIPH makes this challenging.

Commonly co-occurring conditions with EIPH include inflammatory airway disease (IAD) and other lower respiratory conditions that share risk factors and potentially exacerbate each other. IAD, characterized by lower airway inflammation without severe systemic signs, frequently accompanies EIPH in performance horses and worsens bleeding tendency. Equine asthma in its various forms affects airway health and may increase EIPH severity. Pharyngeal abnormalities including dorsal displacement of the soft palate (DDSP) may co-occur in performance horses. Upper airway obstructions can increase negative inspiratory pressures potentially affecting EIPH. Systemic inflammation or illness may temporarily worsen EIPH. Management of co-occurring respiratory conditions improves EIPH outcomes.

Conditions with similar symptoms that must be differentiated from EIPH include other causes of respiratory tract bleeding and exercise intolerance. Guttural pouch mycosis causes epistaxis from fungal erosion of vessels in the guttural pouches and represents a serious condition requiring distinct treatment. Ethmoid hematomas are progressive vascular masses in the nasal passages causing recurrent bleeding. Upper airway trauma during exercise can produce bleeding not originating from the lungs. Coagulopathies (bleeding disorders) cause generalized bleeding tendency. Non-bleeding causes of exercise intolerance including cardiac conditions, musculoskeletal problems, and metabolic disorders present diagnostic differentials. Accurate diagnosis guides appropriate treatment.

Potential complications of EIPH include progressive lung damage from cumulative bleeding episodes and associated inflammation. Chronic changes include fibrosis (scarring), vascular remodeling, and hemosiderin deposition in lung tissue. These changes may reduce gas exchange efficiency, limiting performance even between acute bleeding episodes. Severely affected horses may develop exercise intolerance preventing continued athletic use. Rarely, catastrophic pulmonary hemorrhage can cause acute death during exercise, though this is uncommon. Secondary bacterial infection of blood in the airways is theoretically possible but rarely documented. The main complication remains career limitation or termination due to uncontrollable bleeding affecting performance and welfare.