Pulmonary transit of agitated contrast is associated with enhanced pulmonary vascular reserve and right ventricular function during exercise

Acute and Chronic Response to Exercise in Athletes: The "Supernormal Heart"

During last decades, most studies have examined the exercise-induced remodeling defined as "athlete's heart". During exercise, there is an increased cardiac output that causes morphological, functional, and electrical modification of the cardiac chambers. The cardiac remodeling depends also on the type of training, age, sex, ethnicity, genetic factors, and body size. The two main categories of exercise, endurance and strength, determine different effects on the cardiac remodeling. Even if most sport comprise both strength and endurance exercise, determining different scenarios of cardiac adaptation to the exercise. The aim of this paper is to assemble the current knowledge about physiologic and pathophysiologic response of both the left and the right heart in highly trained athletes.

The blood transfer conductance for nitric oxide: Infinite vs. finite θNO

Whether the specific blood transfer conductance for nitric oxide (NO) with hemoglobin (θ_NO) is finite or infinite is controversial but important in the calculation of alveolar capillary membrane conductance (Dm_CO) and pulmonary capillary blood volume (V_C) from values of lung diffusing capacity for carbon monoxide (DLCO) and nitric oxide (DLNO). In this review, we discuss the background associated with θ_NO, explore the resulting values of Dm_CO and V_C when applying either assumption, and investigate the mathematical underpinnings of Dm_CO and V_C calculations. In general, both assumptions yield reasonable rest and exercise Dm_CO and V_C values. However, the finite θ_NO assumption demonstrates increasing V_C, but not Dm_CO, with submaximal exercise. At relatively high, but physiologic, DLNO/DLCO ratios both assumptions can result in asymptotic behavior for V_C values, and under the finite θ_NO assumption, Dm_CO values. In conclusion, we feel that the assumptions associated with a finite θ_NO require further in vivo validation against an established method before widespread research and clinical use.

Effect of aerobic fitness on capillary blood volume and diffusing membrane capacity responses to exercise

KEY POINTS

Endurance trained athletes exhibit enhanced cardiovascular function compared to non-athletes, although it is considered that exercise training does not enhance lung structure and function. An increased pulmonary capillary blood volume at rest is associated with a higher V̇O2 max . In the present study, we compared the diffusion capacity, pulmonary capillary blood volume and diffusing membrane capacity responses to exercise in endurance-trained males compared to non-trained males. Exercise diffusion capacity was greater in athletes, secondary to an increased membrane diffusing capacity, and not pulmonary capillary blood volume. Endurance-trained athletes appear to have differences within the pulmonary membrane that facilitate the increased O2 demand needed for high-level exercise.

ABSTRACT

Endurance-trained athletes exhibit enhanced cardiovascular function compared to non-athletes, allthough it is generally accepted that exercise training does not enhance lung structure and function. Recent work has shown that an increased resting pulmonary capillary blood volume (VC ) is associated with a higher maximum oxygen consumption (V̇O2 max ), although there have been no studies to date examining how aerobic fitness affects the VC response to exercise. Based on previous work, we hypothesized that endurance-trained athletes will have greater VC compared to non-athletes during cycling exercise. Fifteen endurance-trained athletes (HI: V̇O2 max 64.6 ± 1.8 ml kg(-1)  min(-1) ) and 14 non-endurance trained males (LO: V̇O2 max 45.0 ± 1.2 ml kg(-1)  min(-1) ) were matched for age and height. Haemoglobin-corrected diffusion capacity (DLCO), VC and diffusing membrane capacity (DM ) were determined using the Roughton and Forster () multiple fraction of inspired O2 (FI O2 )-DLCO method at baseline and during incremental cycle exercise up to 90% of peak O2 consumption. During exercise, both groups exhibited increases in DLCO, DM and VC with exercise intensity. Athletes had a greater DLCO and greater DM at 80 and 90% of V̇O2 max compared to non-athletes. However, VC was not different between groups during exercise. In contrast to our hypothesis, exercise VC was not greater in endurance-trained subjects compared to controls; rather, the increased DLCO in athletes at peak exercise was secondary to an enhanced DM . These findings suggest that endurance-trained athletes appear to have differences within the pulmonary membrane that facilitate the increased O2 demand needed for high-level exercise.

Right ventricular and pulmonary vascular reserve in asymptomatic BMPR2 mutation carriers

BACKGROUND

Non-invasive estimates have suggested that asymptomatic BMPR2 mutation carriers may have an abnormal pulmonary vascular response to exercise and hypoxia. However, this has not been assessed with "gold standard" invasive measures.

METHODS

Eight controls and 8 asymptomatic BMPR2 mutation carriers underwent cardiac magnetic resonance imaging with simultaneous invasive pressure recording during bicycle exercise in normoxia, hypoxia and after sildenafil administration. Abnormal pulmonary vascular reserve was defined as an increase in mean pulmonary artery pressure relative to cardiac output (P/Q slope) >3 mm Hg/liter/min.

RESULTS

During normoxic exercise, BMPR2 mutation carriers had a similar P/Q slope when compared with healthy subjects. Only 1 of 8 BMPR2 mutation carriers had a P/Q slope >3 mm Hg/liter/min. During exercise in hypoxia, 3 of 8 BMPR2 mutation carriers had P/Q slopes >3 mm Hg/liter/min compared with none of the controls. Sildenafil decreased the P/Q slope both in controls and BMPR2 mutation carriers. The exercise-induced increase in right ventricular ejection fraction was similar between groups. None of the BMPR2 mutation carriers developed pulmonary arterial hypertension within 2 (range 1.3 to 2.8) years.

CONCLUSIONS

The presence of a BMPR2 mutation, per se, is not associated with an abnormal pulmonary vascular and right ventricular functional response to exercise in asymptomatic individuals. Longer follow-up will be required to determine whether a P/Q slope of >3 mm Hg/liter/min during exercise in normoxia or hypoxia is a sign of pre-clinical disease expression.

Influence of exercise intensity and duration on functional and biochemical perturbations in the human heart

KEY POINTS

Strenuous endurance exercise induces transient functional and biochemical cardiac perturbations that persist for 24-48 h. The magnitude and time-course of exercise-induced reductions in ventricular function and increases in cardiac injury markers are influenced by the intensity and duration of exercise. In a human experimental model, exercise-induced reductions in ventricular strain and increases in cardiac troponin are greater, and persist for longer, when exercise is performed within the heavy- compared to moderate-intensity exercise domain, despite matching for total mechanical work. The results of the present study help us better understand the dose-response relationship between endurance exercise and acute cardiac stress/injury, a finding that has implications for the prescription of day-to-day endurance exercise regimes.

ABSTRACT

Strenuous endurance exercise induces transient cardiac perturbations with ambiguous health outcomes. The present study investigated the magnitude and time-course of exercise-induced functional and biochemical cardiac perturbations by manipulating the exercise intensity-duration matrix. Echocardiograph-derived left (LV) and right (RV) ventricular global longitudinal strain (GLS), and serum high-sensitivity cardiac troponin (hs-cTnI) concentration, were examined in 10 males (age: 27 ± 4 years; V̇O2, peak : 4.0 ± 0.8 l min(-1) ) before, throughout (50%, 75% and 100%), and during recovery (1, 3, 6 and 24 h) from two exercise trials. The two exercise trials consisted of 90 and 120 min of heavy- and moderate-intensity cycling, respectively, with total mechanical work matched. LVGLS decreased (P < 0.01) during the 90 min trial only, with reductions peaking at 1 h post (pre: -19.9 ± 0.6%; 1 h post: -18.5 ± 0.7%) and persisting for >24 h into recovery. RVGLS decreased (P < 0.05) during both exercise trials with reductions in the 90 min trial peaking at 1 h post (pre: -27.5 ± 0.7%; 1 h post: -25.1 ± 0.8%) and persisting for >24 h into recovery. Serum hs-cTnI increased (P < 0.01) during both exercise trials, with concentrations peaking at 3 h post but only exceeding cardio-healthy reference limits (14 ng l(-1) ) in the 90 min trial (pre: 4.2 ± 2.4 ng l(-1) ; 3 h post: 25.1 ± 7.9 ng l(-1) ). Exercise-induced reductions in ventricular strain and increases in cardiac injury markers persist for 24 h following exercise that is typical of day-to-day endurance exercise training; however, the magnitude and time-course of this response can be altered by manipulating the intensity-duration matrix.

Physiologic and pathophysiologic changes in the right heart in highly trained athletes

Exercise causes changes in the heart in response to the hemodynamic demands of increased systemic and pulmonary requirements during exercise. Understanding these adaptations is of great importance, since they may overlap with those caused by pathological conditions. Initial descriptions of athlete's heart focused mainly on chronic adaptation of the left heart to training. In recent years, the substantial structural and functional adaptations of the right heart have been documented, highlighting the complex interplay with left heart. Moreover, there is evolving evidence of acute and chronic cardiac damage, mainly involving the right heart, which may predispose subjects to atrial and ventricular arrhythmias, configuring an exercise-induced cardiomyopathy. The aim of this article is to review the current knowledge on the physiologic and pathophysiologic changes in the right heart in highly trained athletes.

Are There Deleterious Cardiac Effects of Acute and Chronic Endurance Exercise?

Multiple epidemiological studies document that habitual physical activity reduces the risk of atherosclerotic cardiovascular disease (ASCVD), and most demonstrate progressively lower rates of ASCVD with progressively more physical activity. Few studies have included individuals performing high-intensity, lifelong endurance exercise, however, and recent reports suggest that prodigious amounts of exercise may increase markers for, and even the incidence of, cardiovascular disease. This review examines the evidence that extremes of endurance exercise may increase cardiovascular disease risk by reviewing the causes and incidence of exercise-related cardiac events, and the acute effects of exercise on cardiovascular function, the effect of exercise on cardiac biomarkers, including "myocardial" creatine kinase, cardiac troponins, and cardiac natriuretic peptides. This review also examines the effect of exercise on coronary atherosclerosis and calcification, the frequency of atrial fibrillation in aging athletes, and the possibility that exercise may be deleterious in individuals genetically predisposed to such cardiac abnormalities as long QT syndrome, right ventricular cardiomyopathy, and hypertrophic cardiomyopathy. This review is to our knowledge unique because it addresses all known potentially adverse cardiovascular effects of endurance exercise. The best evidence remains that physical activity and exercise training benefit the population, but it is possible that prolonged exercise and exercise training can adversely affect cardiac function in some individuals. This hypothesis warrants further examination.

Pulmonary capillary reserve and exercise capacity at high altitude in healthy humans

Purpose

We determined whether well-acclimatized humans have a reserve to recruit pulmonary capillaries in response to exercise at high altitude.

Methods

At sea level, lung diffusing capacity for carbon monoxide (DLCO), alveolar-capillary membrane conductance (Dm_CO), and pulmonary capillary blood volume (V_c) were measured at rest before maximal oxygen consumption (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\dot{V}{\text{O}}_{2\hbox{max} }$$\end{document}V˙O2max) was determined in seven adults. Then, DLCO, Dm_CO and V_c were measured pre- and post-exhaustive incremental exercise at 5150 m after ~40 days of acclimatization.

Results

Immediately after exercise at high altitude, there was an increase in group mean Dm_CO (14 ± 10 %, P = 0.040) with no pre- to post-exercise change in group mean DLCO (46.9 ± 5.8 vs. 50.6 ± 9.6 ml/min/mmHg, P = 0.213) or V_c (151 ± 28 vs. 158 ± 37 ml, P = 0.693). There was, however, a ~20 % increase in DLCO from pre- to post-exercise at high altitude (51.2 ± 0.2 vs. 61.1 ± 0.2 ml/min/mmHg) with a concomitant increase in Dm_CO (123 ± 2 vs. 156 ± 4 ml/min/mmHg) and V_c (157 ± 3 vs. 180 ± 8 ml) in 2 of the 7 participants. There was a significant positive relationship between the decrease in \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\dot{V}{\text{O}}_{2\hbox{max} }$$\end{document}V˙O2max from sea level to high altitude and the change in DLCO and lung diffusing capacity for nitric oxide (DLNO) from rest to end-exercise at high altitude.

Conclusion

These data suggest that recruitment of the pulmonary capillaries in response to exercise at high altitude is limited in most well-acclimatized humans but that any such a reserve may be associated with better exercise capacity.

Clinical consideration for techniques to detect and quantify blood flow through intrapulmonary arteriovenous anastomoses: lessons from physiological studies

Intrapulmonary arteriovenous anastomoses (IPAVA) are large diameter (>50 μm) vascular conduits, present in >95% of healthy humans. Because IPAVA are large diameter pathways that allow blood flow to bypass the pulmonary capillary network, blood flow through IPAVA (QIPAVA) can permit the transpulmonary passage of particles larger than pulmonary capillaries. IPAVA have been known to exist for over 50 years, but their physiological and clinical significance are still being established; although, currently suggested roles for QIPAVA include allowing emboli to reach the systemic circulation and providing a source of shunt. Studying QIPAVA is an important area of research and as the suggested roles become better established, detecting and quantifying QIPAVA may become significantly more important in the clinic. Several techniques that can be used to quantify and/or detect QIPAVA in animals, ex vivo human/animal lungs, and intact healthy humans; microspheres, radiolabeled macroaggregated albumin particles, and saline contrast echocardiography, are reviewed with limitations and advantages to each. The current body of literature using these techniques to study QIPAVA in animals, ex vivo lungs, and healthy humans has established conditions when QIPAVA is present, such as during exercise or with arterial hypoxemia and conditions when QIPAVA is absent, such as at rest or during exercise breathing 100% O2 . Many of these physiological studies have direct application to patient populations and we discuss each of these findings in the context of their potential to influence the clinical utility, and interpretation, of the results from these techniques highlighted in this review.

Pulmonary vascular function and exercise capacity in black sub-Saharan Africans

Sex and age affect the pulmonary circulation. Whether there may be racial differences in pulmonary vascular function is unknown. Thirty white European Caucasian subjects (15 women) and age and body-size matched 30 black sub-Saharan African subjects (15 women) underwent a cardiopulmonary exercise test and exercise stress echocardiography with measurements of pulmonary artery pressure (PAP) and cardiac output (CO). A pulmonary vascular distensibility coefficient α was mathematically determined from the natural curvilinearity of multipoint mean PAP (mPAP)-CO plots. Maximum oxygen uptake (V̇o2max) and workload were higher in the whites, while maximum respiratory exchange ratio and ventilatory equivalents for CO2 were the same. Pulmonary hemodynamics were not different at rest. Exercise was associated with a higher maximum total pulmonary vascular resistance, steeper mPAP-CO relationships, and lower α-coefficients in the blacks. These differences were entirely driven by higher slopes of mPAP-CO relationships (2.5 ± 0.7 vs. 1.4 ± 0.7 mmHg·l−1·min; P < 0.001) and lower α-coefficients (0.85 ± 0.33 vs. 1.35 ± 0.51%/mmHg; P < 0.01) in black men compared with white men. There were no differences in any of the hemodynamic variables between black and white women. In men only, the slopes of mPAP-CO relationships were inversely correlated to V̇o2max ( P < 0.01). Thus the pulmonary circulation is intrinsically less distensible in black sub-Saharan African men compared with white Caucasian Europeans men, and this is associated with a lower exercise capacity. This study did not identify racial differences in pulmonary vascular function in women.

Humans In Hypoxia: A Conspiracy Of Maladaptation?!

We address adaptive vs. maladaptive responses to hypoxemia in healthy humans and hypoxic-tolerant species during wakefulness, sleep, and exercise. Types of hypoxemia discussed include short-term and life-long residence at high altitudes, the intermittent hypoxemia attending sleep apnea, or training regimens prescribed for endurance athletes. We propose that hypoxia presents an insult to O2 transport, which is poorly tolerated in most humans because of the physiological cost.

Dopamine receptor blockade improves pulmonary gas exchange but decreases exercise performance in healthy humans

Pulmonary gas exchange, as evaluated by the alveolar-arterial oxygen difference (A-aDO2), is impaired during intense exercise, and has been correlated with recruitment of intrapulmonary arteriovenous anastomoses (IPAVA) as measured by agitated saline contrast echocardiography. Previous work has shown that dopamine (DA) recruits IPAVA and increases venous admixture (Q̇s/Q̇t) at rest. As circulating DA increases during exercise, we hypothesized that A-aDO2 and IPAVA recruitment would be decreased with DA receptor blockade. Twelve healthy males (age: 25 ± 6 years, V̇O2 max : 58.6 ± 6.5 ml kg(-1) min(-1) ) performed two incremental staged cycling exercise sessions after ingestion of either placebo or a DA receptor blocker (metoclopramide 20 mg). Arterial blood gas, cardiorespiratory and IPAVA recruitment (evaluated by agitated saline contrast echocardiography) data were obtained at rest and during exercise up to 85% of V̇O2 max . On different days, participants also completed incremental exercise tests and exercise tolerance (time-to-exhaustion (TTE) at 85% of V̇O2 max ) with or without dopamine blockade. Compared to placebo, DA blockade did not change O2 consumption, CO2 production, or respiratory exchange ratio at any intensity. At 85% V̇O2 max , DA blockade decreased A-aDO2, increased arterial O2 saturation and minute ventilation, but did not reduce IPAVA recruitment, suggesting that positive saline contrast is unrelated to A-aDO2. Compared to placebo, DA blockade decreased maximal cardiac output, V̇O2 max and TTE. Despite improving pulmonary gas exchange, blocking dopamine receptors appears to be detrimental to exercise performance. These findings suggest that endogenous dopamine is important to the normal cardiopulmonary response to exercise and is necessary for optimal high-intensity exercise performance.

Altered ventricular mechanics after 60 min of high-intensity endurance exercise: insights from exercise speckle-tracking echocardiography

Transient reductions in myocardial strain coupled with cardiac-specific biomarker release have been reported after prolonged exercise (>180 min). However, it is unknown if 1) shorter-duration exercise (60 min) can perturb cardiac function or 2) if exercise-induced reductions in strain are masked by hemodynamic changes that are associated with passive recovery from exercise. Left ventricular (LV) and right ventricular global longitudinal strain (GLS), LV torsion, and high-sensitivity cardiac troponin T were measured in 15 competitive cyclists (age: 28 ± 3 yr, peak O2 uptake: 4.8 ± 0.6 l/min) before and after a 60-min high-intensity cycling race intervention (CRIT60). At both time points (pre- and post-CRIT60), strain and torsion were assessed at rest and during a standardized low-intensity exercise challenge (power output: 96 ± 8 W) in a semirecumbent position using echocardiography. During rest, hemodynamic conditions were different from pre- to post-CRIT60 (mean arterial pressure: 96 ± 1 vs. 86 ± 2 mmHg, P < 0.001), and there were no changes in strain or torsion. In contrast, during the standardized low-intensity exercise challenge, hemodynamic conditions were unchanged from pre- to post-CRIT60 (mean arterial pressure: 98 ± 1 vs. 97 ± 1 mmHg, not significant), but strain decreased (left ventricular GLS: −20.3 ± 0.5% vs. −18.5 ± 0.4%, P < 0.01; right ventricular GLS: −26.4 ± 1.6% vs. −22.4 ± 1.5%, P < 0.05), whereas LV torsion remained unchanged. Serum high-sensitivity cardiac troponin T increased by 345% after the CRIT60 (6.0 ± 0.6 vs. 20.7 ± 6.9 ng/l, P < 0.05). This study demonstrates that exercise-induced functional and biochemical cardiac perturbations are not confined to ultraendurance sporting events and transpire during exercise that is typical of day-to-day training undertaken by endurance athletes. The clinical significance of cumulative exposure to endurance exercise warrants further study.

Pulmonary vascular and right ventricular reserve in patients with normalized resting hemodynamics after pulmonary endarterectomy

Background

Patients with normalized mean pulmonary artery pressure (mPAP) after pulmonary endarterectomy (PEA) for chronic thromboembolic pulmonary hypertension (CTEPH) do not always regain normal exercise capacity. We evaluated right ventricular function, its interaction with both pulsatile and resistive afterload, and the effect of sildenafil during exercise in these patients.

Methods and Results

Fourteen healthy controls, 15 CTEPH patients, and 7 patients with normalized resting mPAP (≤25 mm Hg) post‐PEA underwent cardiopulmonary exercise testing, followed by cardiac magnetic resonance imaging with simultaneous invasive mPAP measurement during incremental supine cycling exercise. Peak oxygen consumption and peak heart rate were significantly reduced in post‐PEA and CTEPH patients compared to controls. The mPAP–cardiac output slope was steeper in post‐PEA patients than in controls and similar to CTEPH. Relative to controls, resting right ventricular ejection fraction was reduced in CTEPH, but not in post‐PEA patients. In contrast, peak exercise right ventricular ejection fraction was reduced both in post‐PEA and CTEPH patients. Exercise led to reduction of pulmonary arterial compliance in all groups. Nevertheless, resting pulmonary arterial compliance values in CTEPH and post‐PEA patients were even lower than those in controls at peak exercise. In post‐PEA patients, sildenafil did not affect resting hemodynamics nor right ventricular function, but decreased the mPAP/cardiac output slope and increased peak exercise right ventricular ejection fraction.

Conclusions

Exercise intolerance in post‐PEA patients is explained by abnormal pulmonary vascular reserve and chronotropic incompetence. The mPAP/cardiac output slope and pulmonary arterial compliance are sensitive measures demonstrating abnormal resistive and pulsatile pulmonary vascular function in post‐PEA patients. These abnormalities are partially attenuated with sildenafil.

Exercise pathophysiology and sildenafil effects in chronic thromboembolic pulmonary hypertension

OBJECTIVES

Symptoms in patients with chronic thromboembolic pulmonary hypertension (CTEPH) predominantly occur during exercise, while haemodynamic assessment is generally performed at rest. We hypothesised that exercise imaging of RV function would better explain exercise limitation and the acute effects of pulmonary vasodilator administration than resting measurements.

METHODS

Fourteen patients with CTEPH and seven healthy control subjects underwent cardiopulmonary testing to determine peak exercise oxygen consumption (VO2peak) and ventilatory equivalent for carbon dioxide (VE/VCO2) at the anaerobic threshold. Subsequently, cardiac MRI was performed at rest and during supine bicycle exercise with simultaneous invasive measurement of mean pulmonary arterial pressure (mPAP) before and after sildenafil.

RESULTS

During exercise, patients with CTEPH had a greater increase in the ratio of mPAP relative to cardiac output (CO) than controls (6.7 (5.1-8.7) vs 0.94 (0.86-1.8) mm Hg/L/min; p < 0.001). Stroke volume index (SVi) and RVEF increased during exercise in controls, but not in patients with CTEPH (interaction p < 0.001). Sildenafil decreased the mPAP/CO slope and increased SVi and RVEF in patients with CTEPH (p < 0.05) but not in controls. In patients with CTEPH, RVEF reserve correlated moderately with VO2peak (r = 0.60; p = 0.030) and VE/VCO2 (r = -0.67; p = 0.012). By contrast, neither VO2peak nor VE/VCO2 correlated with resting RVEF.

CONCLUSIONS

Exercise measures of RV function explain much of the variance in the exercise capacity of patients with CTEPH while resting measures do not. Sildenafil increases SVi during exercise in patients with CTEPH, but not in healthy subjects.

The response of the pulmonary circulation and right ventricle to exercise: exercise-induced right ventricular dysfunction and structural remodeling in endurance athletes (2013 Grover Conference series)

There is unequivocal evidence that exercise results in considerable health benefits. These are the result of positive hormonal, metabolic, neuronal, and structural changes brought about by the intermittent physiological challenge of exercise. However, there is evolving evidence that intense exercise may place disproportionate physiological stress on the right ventricle (RV) and the pulmonary circulation. Both echocardiographic and invasive studies are consistent in demonstrating that pulmonary arterial pressures increase progressively with exercise intensity, such that the harder one exercises, the greater the load on the RV. This disproportionate load can result in fatigue or damage of the RV if the intensity and duration of exercise is sufficiently prolonged. This is distinctly different from the load imposed by exercise on the left ventricle (LV), which is moderated by a greater capacity for reductions in systemic afterload. Finally, given the increasing RV demand during exercise, it may be hypothesized that chronic exercise-induced cardiac remodeling (the so-called athlete's heart) may also disproportionately affect the RV. Indeed, there is evidence, although somewhat inconsistent, that RV volume increases may be relatively greater than those for the LV. Perhaps more importantly, there is a suggestion that chronic endurance exercise may cause electrical remodeling, predisposing some athletes to serious arrhythmias originating from the RV. Thus, a relatively consistent picture is emerging of acute stress, prolonged fatigue, and long-term remodeling, which all disproportionately affect the RV. Thus, we contend that the RV should be considered a potential Achilles' heel of the exercising heart.

Intrapulmonary arteriovenous anastomoses in humans--response to exercise and the environment

Intrapulmonary arteriovenous anastomoses (IPAVA) have been known to exist in human lungs for over 60 years. The majority of the work in this area has largely focused on characterizing the conditions in which IPAVA blood flow (Q̇IPAVA ) is either increased, e.g. during exercise, acute normobaric hypoxia, and the intravenous infusion of catecholamines, or absent/decreased, e.g. at rest and in all conditions with alveolar hyperoxia (FIO2 = 1.0). Additionally, Q̇IPAVA is present in utero and shortly after birth, but is reduced in older (>50 years) adults during exercise and with alveolar hypoxia, suggesting potential developmental origins and an effect of age. The physiological and pathophysiological roles of Q̇IPAVA are only beginning to be understood and therefore these data remain controversial. Although evidence is accumulating in support of important roles in both health and disease, including associations with pulmonary arterial pressure, and adverse neurological sequelae, there is much work that remains to be done to fully understand the physiological and pathophysiological roles of IPAVA. The development of novel approaches to studying these pathways that can overcome the limitations of the currently employed techniques will greatly help to better quantify Q̇IPAVA and identify the consequences of Q̇IPAVA on physiological and pathophysiological processes. Nevertheless, based on currently published data, our proposed working model is that Q̇IPAVA occurs due to passive recruitment under conditions of exercise and supine body posture, but can be further modified by active redistribution of pulmonary blood flow under hypoxic and hyperoxic conditions.

Right Ventricular Changes in Highly Trained Athletes: Between Physiology and Pathophysiology

Several studies have described the adaptive remodeling of the heart during exercise. In some more practiced endurance athletes, there is a disproportionate load on the right ventricle (RV), at least during exercise, and this might be the basis for a chronic pro-arrhythmic RV remodeling. Especially, in these kinds of athletes the recovery after detraining might be incomplete, in particular for RV changes. The observation of acute myocardial injury based on transient elevation of biomarkers and chronic myocardial scar, not completely reversible changes of the RV and an increased prevalence of some arrhythmias support the existence of an “exercise-induced cardiomyopathy.” The aim of this paper is to review current knowledge about changes in the right heart in highly trained athletes and how these change influence cardiac function.

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.

Increased cardiac output, not pulmonary artery systolic pressure, increases intrapulmonary shunt in healthy humans breathing room air and 40% O2

Blood flow through intrapulmonary arteriovenous anastomoses (IPAVAs) has been demonstrated to increase in healthy humans during a variety of conditions; however, whether or not this blood flow represents a source of venous admixture (Q̇ VA /Q̇T) that impairs pulmonary gas exchange efficiency (i.e. increases the alveolar-to-arterial PO2 difference (A-aDO2)) remains controversial and unknown. We hypothesized that blood flow through IPAVAs does provide a source of Q̇ VA /Q̇T. To test this, blood flow through IPAVAs was increased in healthy humans at rest breathing room air and 40% O2: (1) during intravenous adrenaline (epinephrine) infusion at 320 ng kg(-1) min(-1) (320 ADR), and (2) with vagal blockade (2 mg atropine), before and during intravenous adrenaline infusion at 80 ng kg(-1) min(-1) (ATR + 80 ADR). When breathing room air the A-aDO2 increased by 6 ± 2 mmHg during 320 ADR and by 5 ± 2 mmHg during ATR + 80 ADR, and the change in calculated Q̇ VA /Q̇T was +2% in both conditions. When breathing 40% O2, which minimizes contributions from diffusion limitation and alveolar ventilation-to-perfusion inequality, the A-aDO2 increased by 12 ± 7 mmHg during 320 ADR, and by 9 ± 6 mmHg during ATR + 80 ADR, and the change in calculated Q̇ VA /Q̇T was +2% in both conditions. During 320 ADR cardiac output (Q̇T) and pulmonary artery systolic pressure (PASP) were significantly increased; however, during ATR + 80 ADR only Q̇T was significantly increased, yet blood flow through IPAVAs as detected with saline contrast echocardiography was not different between conditions. Accordingly, we suggest that blood flow through IPAVAs provides a source of intrapulmonary shunt, and is mediated primarily by increases in Q̇T rather than PASP.

Hypoxia and exercise increase the transpulmonary passage of 99mTc-labeled albumin particles in humans

Intrapulmonary arteriovenous anastomoses (IPAVs) are large diameter connections that allow blood to bypass the lung capillaries and may provide a route for right-to-left embolus transmission. These anastomoses are recruited by exercise and catecholamines and hypoxia. Yet, whether IPAVs are recruited via direct, oxygen sensitive regulatory mechanisms or indirect effects secondary to redistribution pulmonary blood flow is unknown. Here, we hypothesized that the addition of exercise to hypoxic gas breathing, which increases cardiac output, would augment IPAVs recruitment in healthy humans. To test this hypothesis, we measured the transpulmonary passage of 99mTc-macroaggregated albumin particles (99mTc-MAA) in seven healthy volunteers, at rest and with exercise at 85% of volitional max, with normoxic (FIO2 = 0.21) and hypoxic (FIO2 = 0.10) gas breathing. We found increased 99mTc-MAA passage in both exercise conditions and resting hypoxia. However, contrary to our hypothesis, we found the greatest 99mTc-MAA passage with resting hypoxia. As an additional, secondary endpoint, we also noted that the transpulmonary passage of 99mTc-MAA was well-correlated with the alveolar-arterial oxygen difference (A-aDO2) during exercise. While increased cardiac output has been proposed as an important modulator of IPAVs recruitment, we provide evidence that the modulation of blood flow through these pathways is more complex and that increasing cardiac output does not necessarily increase IPAVs recruitment. As we discuss, our data suggest that the resistance downstream of IPAVs is an important determinant of their perfusion.

Exercise- and hypoxia-induced blood flow through intrapulmonary arteriovenous anastomoses is reduced in older adults

Mean pulmonary arterial pressure (Ppa) during exercise is significantly higher in individuals aged ≥50 yr compared with their younger counterparts, but the reasons for this are unknown. Blood flow through intrapulmonary arteriovenous anastomoses (IPAVA) can be detected during exercise or while breathing hypoxic gas mixtures using saline contrast echocardiography in almost all healthy young individuals. It has been previously hypothesized that a lower degree of exercise-induced blood flow through IPAVA is associated with high Ppa during exercise. This association may suggest that individuals who are known to have high Ppa during exercise, such as those ≥50 yr of age, may have lower blood flow through IPAVA, but the presence and degree of exercise-induced blood flow through IPAVA has not been specifically studied in older populations. Using transthoracic saline contrast echocardiography, we investigated the potential effects of age on exercise-induced blood flow through IPAVA in a cross-section of subjects aged 19–72 yr. To verify our findings, we assessed the effects of age on hypoxia-induced blood flow through IPAVA. Age groups were ≤41 yr (younger, n = 16) and ≥50 yr (older, n = 14). Qualitatively measured exercise- and hypoxia-induced blood flow through IPAVA was significantly lower in older individuals compared with younger controls. Older individuals also had significantly higher pulmonary arterial systolic pressure and total pulmonary resistance (TPR) during exercise. Low blood flow through IPAVA was independently associated with high TPR. The reasons for the age-related decrease in blood flow through IPAVA are unknown.

Pulmonary circulation and gas exchange at exercise in Sherpas at high altitude

Tibetans have been reported to present with a unique phenotypic adaptation to high altitude characterized by higher resting ventilation and arterial oxygen saturation, no excessive polycythemia, and lower pulmonary arterial pressures (Ppa) compared with other high-altitude populations. How this affects exercise capacity is not exactly known. We measured aerobic exercise capacity during an incremental cardiopulmonary exercise test, lung diffusing capacity for carbon monoxide (DlCO) and nitric oxide (DlNO) at rest, and mean Ppa (mPpa) and cardiac output by echocardiography at rest and at exercise in 13 Sherpas and in 13 acclimatized lowlander controls at the altitude of 5,050 m in Nepal. In Sherpas vs. lowlanders, arterial oxygen saturation was 86 ± 1 vs. 83 ± 2% (mean ± SE; P = nonsignificant), mPpa at rest 19 ± 1 vs. 23 ± 1 mmHg ( P < 0.05), DlCO corrected for hemoglobin 61 ± 4 vs. 37 ± 2 ml·min−1·mmHg−1 ( P < 0.001), DlNO 226 ± 18 vs. 153 ± 9 ml·min−1·mmHg−1 ( P < 0.001), maximum oxygen uptake 32 ± 3 vs. 28 ± 1 ml·kg−1·min−1 ( P = nonsignificant), and ventilatory equivalent for carbon dioxide at anaerobic threshold 40 ± 2 vs. 48 ± 2 ( P < 0.001). Maximum oxygen uptake was correlated directly to DlCO and inversely to the slope of mPpa-cardiac index relationships in both Sherpas and acclimatized lowlanders. We conclude that Sherpas compared with acclimatized lowlanders have an unremarkable aerobic exercise capacity, but with less pronounced pulmonary hypertension, lower ventilatory responses, and higher lung diffusing capacity.

Transient intrapulmonary shunting in a patient treated with β₂-adrenergic agonists for status asthmaticus

Intrapulmonary arteriovenous anastomoses (IPAVs) are large-diameter pathways that directly connect the arterial and venous networks, bypassing the pulmonary capillaries. Ubiquitously present in healthy humans, these pathways are recruited in experimental conditions by exercise, hypoxia, and catecholamines and have been previously shown to be closed by hyperoxia. Whether they play a role in pulmonary pathophysiology is unknown. Here, we describe IPAV recruitment associated with hypoxemia and right-to-left shunt in a patient with status asthmaticus, treated with agonists of the B2-adrenergic pathway. Our observation of IPAVs in a pediatric patient, mechanically ventilated with 100% O₂, suggests that these pathways are recruited in clinically important circumstances and challenges the notion that IPAVs are always closed by alveolar hyperoxia.

Pulmonary vascular reserve and exercise capacity at sea level and at high altitude

It has been suggested that increased pulmonary vascular reserve, as defined by reduced pulmonary vascular resistance (PVR) and increased pulmonary transit of agitated contrast measured by echocardiography, might be associated with increased exercise capacity. Thus, at altitude, where PVR is increased because of hypoxic vasoconstriction, a reduced pulmonary vascular reserve could contribute to reduced exercise capacity. Furthermore, a lower PVR could be associated with higher capillary blood volume and an increased lung diffusing capacity. We reviewed echocardiographic estimates of PVR and measurements of lung diffusing capacity for nitric oxide (DL(NO)) and for carbon monoxide (DL(CO)) at rest, and incremental cardiopulmonary exercise tests in 64 healthy subjects at sea level and during 4 different medical expeditions at altitudes around 5000 m. Altitude exposure was associated with a decrease in maximum oxygen uptake (VO2max), from 42±10 to 32±8 mL/min/kg and increases in PVR, ventilatory equivalents for CO2 (V(E)/VCO2), DL(NO), and DL(CO). By univariate linear regression VO2max at sea level and at altitude was associated with V(E)/VCO2 (p<0.001), mean pulmonary artery pressure (mPpa, p<0.05), stroke volume index (SVI, p<0.05), DL(NO) (p<0.02), and DL(CO) (p=0.05). By multivariable analysis, VO2max at sea level and at altitude was associated with V(E)/VCO2, mPpa, SVI, and DL(NO). The multivariable analysis also showed that the altitude-related decrease in VO2max was associated with increased PVR and V(E)/VCO2. These results suggest that pulmonary vascular reserve, defined by a combination of decreased PVR and increased DL(NO), allows for superior aerobic exercise capacity at a lower ventilatory cost, at sea level and at high altitude.

Prevalence of left heart contrast in healthy, young, asymptomatic humans at rest breathing room air

Our purpose was to report the prevalence of healthy, young, asymptomatic humans who demonstrate left heart contrast at rest, breathing room air. We evaluated 176 subjects (18-41 years old) using transthoracic saline contrast echocardiography. Left heart contrast appearing ≤3 cardiac cycles, consistent with a patent foramen ovale (PFO), was detected in 67 (38%) subjects. Left heart contrast appearing >3 cardiac cycles, consistent with the transpulmonary passage of contrast, was detected in 49 (28%) subjects. Of these 49 subjects, 31 were re-evaluated after breathing 100% O2 for 10-15min and 6 (19%) continued to demonstrate the transpulmonary passage of contrast. Additionally, 18 of these 49 subjects were re-evaluated in the upright position and 1 (5%) continued to demonstrate the transpulmonary passage of contrast. These data suggest that ~30% of healthy, young, asymptomatic subjects demonstrate the transpulmonary passage of contrast at rest which is reduced by breathing 100% O2 and assuming an upright body position.

Pulmonary gas exchange and acid-base balance during exercise

As the first step in the oxygen-transport chain, the lung has a critical task: optimizing the exchange of respiratory gases to maintain delivery of oxygen and the elimination of carbon dioxide. In healthy subjects, gas exchange, as evaluated by the alveolar-to-arterial PO2 difference (A-aDO2), worsens with incremental exercise, and typically reaches an A-aDO2 of approximately 25 mmHg at peak exercise. While there is great individual variability, A-aDO2 is generally largest at peak exercise in subjects with the highest peak oxygen consumption. Inert gas data has shown that the increase in A-aDO2 is explained by decreased ventilation-perfusion matching, and the development of a diffusion limitation for oxygen. Gas exchange data does not indicate the presence of right-to-left intrapulmonary shunt developing with exercise, despite recent data suggesting that large-diameter arteriovenous shunt vessels may be recruited with exercise. At the same time, multisystem mechanisms regulate systemic acid-base balance in integrative processes that involve gas exchange between tissues and the environment and simultaneous net changes in the concentrations of strong and weak ions within, and transfer between, extracellular and intracellular fluids. The physicochemical approach to acid-base balance is used to understand the contributions from independent acid-base variables to measured acid-base disturbances within contracting skeletal muscle, erythrocytes and noncontracting tissues. In muscle, the magnitude of the disturbance is proportional to the concentrations of dissociated weak acids, the rate at which acid equivalents (strong acid) accumulate and the rate at which strong base cations are added to or removed from muscle.