Circulatory Studies in Well Trained Athletes at Rest and During Heavy Exercise, with Special Reference to Stroke Volume and the Influence of Body Position

Interactive effects of exercise intensity and recovery posture on postexercise hypotension

Postexercise reduction in blood pressure, termed postexercise hypotension (PEH), is relevant for both acute and chronic health reasons and potentially for peripheral cardiovascular adaptations. We investigated the interactive effects of exercise intensity and recovery postures (seated, supine, and standing) on PEH. Thirteen normotensive men underwent a V̇o2max test on a cycle ergometer and five exhaustive constant load trials to determine critical power (CP) and the gas exchange threshold (GET). Subsequently, work-matched exercise trials were performed at two discrete exercise intensities (10% > CP and 10% < GET), with 1 h of recovery in each of the three postures. For both exercise intensities, standing posture resulted in a more substantial PEH (all P < 0.01). For both standing and seated recovery postures, the higher exercise intensity led to larger reductions in systolic [standing: -33 (11) vs. -21 (8) mmHg; seated: -34 (32) vs. -17 (37) mmHg, P < 0.01], diastolic [standing: -18 (7) vs. -8 (5) mmHg; seated: -10 (10) vs. -1 (4) mmHg, P < 0.01], and mean arterial pressures [-13 (8) vs. -2 (4) mmHg, P < 0.01], whereas in the supine recovery posture, the reduction in diastolic [-9 (9) vs. -4 (3) mmHg, P = 0.08) and mean arterial pressures [-7 (5) vs. -3 (4) mmHg, P = 0.06] was not consistently affected by prior exercise intensity. PEH is more pronounced during recovery from exercise performed above CP versus below GET. However, the effect of exercise intensity on PEH is largely abolished when recovery is performed in the supine posture.NEW & NOTEWORTHY The magnitude of postexercise hypotension is greater following the intensity above the critical power in a standing position.

Impact of body position on hemodynamic measurements during exercise: A tale of two bikes

The addition of exercise testing during right heart catheterization (RHC) is often required to accurately diagnose causes of exercise intolerance like early pulmonary vascular disease, occult left heart disease, and preload insufficiency. We tested the influence of body position (supine vs. seated) on hemodynamic classification both at rest and during exercise. We enrolled patients with exercise intolerance due to dyspnea who were referred for exercise RHC at the Cleveland Clinic. Patients were randomized (1:1) to exercise in seated or supine position to a goal of 60 W followed by maximal exercise in the alternate position. We analyzed 17 patients aged 60.3 ± 10.9 years, including 13 females. At rest in the sitting position, patients had significantly lower right atrial pressure (RAP), mean pulmonary artery pressure (mPAP), pulmonary artery wedge pressure (PAWP) and cardiac index (CI). In every stage of exercise (20, 40, and 60 W), the RAP, mPAP, and PAWP were lower in the sitting position. Exercise in the sitting position allowed the identification of preload insufficiency in nine patients. Exercise in either position increased the identification of postcapillary pulmonary hypertension (PH). Body position significantly influences hemodynamics at rest and with exercise; however, mPAP/CO and PAWP/CO were not positionally affected. Hemodynamic measurements in the seated position allowed the detection of preload insufficiency, a condition that was predominantly identified as no PH during supine exercise.

Cardiopulmonary parameters and organ blood flows for workers expressed in terms of VO2 for use in physiologically based toxicokinetic modeling

Minute ventilation rates (VE), alveolar ventilation rates (VA), cardiac outputs (Q), liver blood flow (LBF) and kidneys blood flows (KBF) for physiologically based toxicokinetic modeling and occupational health risk assessment in active workers have apparently not been determined. Minute energy expenditure rates (E) and oxygen consumption rates (VO₂) in workers during exertions and their aggregate daytime activities are obtained by using open-circuit wearable devices for indirect calorimetry measurements and the doubly labeled water method respectively. Hundreds of E (in kcal/min) and VO₂ (in L of O₂/min) were previously reported for workers. The oxygen uptake factors of 0.2059 ± 0.0019 and 0.2057 ± 0.0018 L of O₂/kcal during postprandial and fasting phases respectively enabled conversion of E into VO₂. Equations determined in this study based upon more than 25 000 published measurements enable the calculation of 15 parameters in the same worker only by using the VO₂ reflecting workload. These parameters, notably VE, VA, VE/VO₂ VA/Q, Q, LBF and KBF were found to be interrelated. Altering one of these changes the order of magnitude of the others. Q, LBF and KBF decrease when supine adults at rest switch to an upright position. This effect of gravity diminished when VO₂ increased. The fall in LBF and KBF during exertion might enhance muscle blood flow as reported previously. Taken together these equations and data may improve the accuracy of physiologically based toxicokinetic modeling as well as occupational health assessment studies in active workers exposed to xenobiotics.List of main abbreviations: AVOD: arterioveinous oxygen content difference.BMI: body mass index (in kg/m²).BSA: body surface area (in m²).BTPS: body temperature and saturated with water vapor.Bw: body weight (in kg).E: minute energy expenditure rate (in kcal/min).F_GE: organ blood flow factor for the gravitational effect on blood circulation.H: oxygen uptake factor, volume of oxygen (at STPD) consumed to produce 1 kcal of energy expended.KBF: kidneys blood flow (in ml/min).LBF: liver blood flow (in ml/min).P_BF: liver or kidneys blood flows expressed in terms of percentages (in %) of Q_{sup C} values: namely P_BF = (LBF or KBF/Q_{sup C}) x 100.Q: cardiac output (in L/min or ml/min).Q_{sup C:} cardiac output for the cohort of males or females in supination (in ml/min).STPD: standard temperature and pressure, dry air.sup: values measured when adults are in the supine position.up: values measured when adults are in the upright position.VDphys: physiological dead space at BTPS (in L).VT: tidal volume at BTPS (in L).VA: alveolar ventilation rate at BTPS (in L/min).VA/Q: ventilation-perfusion ratio (unitless).VE: minute ventilation rate at BTPS (in L/min).VO₂: oxygen consumption rate (i.e. the oxygen uptake) at STPD (in L/min).VQ: ventilatory equivalent for VO₂ (VE at BTPS /VO₂ at STPD).

Influence of Upright Versus Supine Position on Resting and Exercise Hemodynamics in Patients Assessed for Pulmonary Hypertension

Background

The aim of the present work was to study the influence of body position on resting and exercise pulmonary hemodynamics in patients assessed for pulmonary hypertension (PH).

Methods and Results

Data from 483 patients with suspected PH undergoing right heart catheterization for clinical indications (62% women, age 61±15 years, 246 precapillary PH, 48 postcapillary PH, 106 exercise PH, 83 no PH) were analyzed; 213 patients (main cohort, years 2016–2018) were examined at rest in upright (45°) and supine position, such as under upright exercise. Upright exercise hemodynamics were compared with 270 patients (historical cohort) undergoing supine exercise with the same protocol. Upright versus supine resting data revealed a lower mean pulmonary artery pressure 31±14 versus 32±13 mm Hg, pulmonary artery wedge pressure 11±4 versus 12±5 mm Hg, and cardiac index 2.9±0.7 versus 3.1±0.8 L/min per m 2 , and higher pulmonary vascular resistance 4.1±3.1 versus 3.9±2.8 Wood P <0.001. Exercise data upright versus supine revealed higher work rates (53±26 versus 33±22 watt), and adjusting for differences in work rate and baseline values, higher end‐exercise mean pulmonary artery pressure (52±19 versus 45±16 mm Hg, P =0.001), similar pulmonary artery wedge pressure and cardiac index, higher pulmonary vascular resistance (5.4±3.7 versus 4.5±3.4 Wood units, P =0.002), and higher mean pulmonary artery pressure/cardiac output (7.9±4.7 versus 7.1±4.1 Wood units, P =0.001).

Conclusions

Body position significantly affects resting and exercise pulmonary hemodynamics with a higher pulmonary vascular resistance of about 10% in upright versus supine position at rest and end‐exercise, and should be considered and reported when assessing PH.

Utility of the oxygen pulse in the diagnosis of obstructive coronary artery disease in physically fit patients

Cardiopulmonary exercise testing (CPET) guidelines recommend analysis of the oxygen (O₂ ) pulse for a late exercise plateau in evaluation for obstructive coronary artery disease (OCAD). However, whether this O₂ pulse trajectory is within the range of normal has been debated, and the diagnostic performance of the O₂ pulse for OCAD in physically fit individuals, in whom V ˙ O 2 may be more likely to plateau, has not been evaluated. Using prospectively collected data from a sports cardiology program, patients were identified who were free of other cardiac disease and underwent clinically-indicated CPET within 90 days of invasive or computed tomography coronary angiography. The diagnostic performance of quantitative O₂ pulse metrics (late exercise slope, proportional change in slope during late exercise) and qualitative assessment for O₂ pulse plateau to predict OCAD was assessed. Among 104 patients (age:56 ± 12 years, 30% female, peak V ˙ O 2 119 ± 34% predicted), the diagnostic performance for OCAD (n = 24,23%) was poor for both quantitative and qualitative metrics reflecting an O₂ pulse plateau (late exercise slope: AUC = 0.55, sensitivity = 68%, specificity = 41%; proportional change in slope: AUC = 0.55, sensitivity = 91%, specificity = 18%; visual plateau/decline: AUC = 0.51, sensitivity = 33%, specificity = 67%). When O₂ pulse parameters were added to the electrocardiogram, the change in AUC was minimal (-0.01 to +0.02, p ≥ 0.05). Those patients without OCAD with a plateau or decline in O₂ pulse were fitter than those with linear augmentation (peak V ˙ O 2 133 ± 31% vs. 114 ± 36% predicted, p < 0.05) and had a longer exercise ramp time (9.5 ± 3.2 vs. 8.0 ± 2.5 min, p < 0.05). Overall, a plateau in O₂ pulse was not a useful predictor of OCAD in a physically fit population, indicating that the O₂ pulse should be integrated with other CPET parameters and may reflect a physiologic limitation of stroke volume and/or O₂ extraction during intense exercise.

Development of in-airway laser absorption spectroscopy for respiratory based measurements of cardiac output

Respiratory approaches to determining cardiac output in humans are securely rooted in mass balance and therefore potentially highly accurate. To address existing limitations in the gas analysis, we developed an in-airway analyser based on laser absorption spectroscopy to provide analyses every 10 ms. The technique for estimating cardiac output requires both a relatively soluble and insoluble tracer gas, and we employed acetylene and methane for these, respectively. A multipass cell was used to provide sufficient measurement sensitivity to enable analysis directly within the main gas stream, thus avoiding errors introduced by sidestream gas analysis. To assess performance, measurements of cardiac output were made during both rest and exercise on five successive days in each of six volunteers. The measurements were extremely repeatable (coefficient of variation ~ 7%). This new measurement technology provides a stable foundation against which the algorithm to calculate cardiac output can be further developed.

Gradual reduction in exercise capacity in chronic kidney disease is associated with systemic oxygen delivery factors

Background

The cause of reduced exercise capacity (ExCap) in chronic kidney disease (CKD) is multifactorial. The aim of this study was to investigate determinants of aerobic ExCap in patients with mild to severe CKD not undergoing dialysis.

Methods

We included 52 individuals with CKD stage 2–3, 47 with stage 4–5, and 54 healthy controls. Peak workload and peak heart rate (HR) were assessed by a maximal cycle exercise test. Cardiac function including stroke volume (SV) and vascular stiffness were evaluated by ultrasound at rest. Handgrip strength, body composition, haemoglobin level and self-reported physical activity were assessed.

Results

Peak workload (221±60, 185±59, 150±54 W for controls, CKD 2–3 and CKD 4–5 respectively), peak HR (177±11, 161±24, 144±31 beats/min) and haemoglobin level (14.2±1.2, 13.5±1.4, 12.2±1.3 g/dL) were all three significantly lower in CKD 2–3 than in controls, (p = 0.001, 0.001 and 0.03 respectively) and were even lower in stages 4–5 CKD than in CKD 2–3 (p = 0.01, 0.001 and <0.001 respectively). Resting SV and lean body mass did not differ between groups and handgrip strength was significantly lower only in CKD 4–5 compared to controls (p = 0.02). Peak workload was strongly associated with the systemic oxygen delivery factors: SV, peak HR and haemoglobin level. These three factors along with age, sex and height² explained 82% of variation in peak workload. Peak HR contributed most to the variation; the peripheral variables handgrip strength and vascular stiffness did not improve the explanatory value in regression analysis.

Conclusions

In this cross-sectional study of CKD patients not on dialysis, aerobic ExCap decreased gradually with disease severity. ExCap was associated mainly with systemic oxygen delivery factors, in particular peak HR. Neither muscle function and mass, nor vascular stiffness were independent determinants of aerobic ExCap in this group of CKD patients.

An official European Respiratory Society statement: pulmonary haemodynamics during exercise

There is growing recognition of the clinical importance of pulmonary haemodynamics during exercise, but several questions remain to be elucidated. The goal of this statement is to assess the scientific evidence in this field in order to provide a basis for future recommendations.

Right heart catheterisation is the gold standard method to assess pulmonary haemodynamics at rest and during exercise. Exercise echocardiography and cardiopulmonary exercise testing represent non-invasive tools with evolving clinical applications. The term “exercise pulmonary hypertension” may be the most adequate to describe an abnormal pulmonary haemodynamic response characterised by an excessive pulmonary arterial pressure (PAP) increase in relation to flow during exercise. Exercise pulmonary hypertension may be defined as the presence of resting mean PAP <25 mmHg and mean PAP >30 mmHg during exercise with total pulmonary resistance >3 Wood units. Exercise pulmonary hypertension represents the haemodynamic appearance of early pulmonary vascular disease, left heart disease, lung disease or a combination of these conditions. Exercise pulmonary hypertension is associated with the presence of a modest elevation of resting mean PAP and requires clinical follow-up, particularly if risk factors for pulmonary hypertension are present. There is a lack of robust clinical evidence on targeted medical therapy for exercise pulmonary hypertension.

Readdressing the entity of exercise pulmonary arterial hypertension

Exercise pulmonary hypertension (EPH) indicates an abnormally elevated pulmonary artery pressure (PAP) during exercise. The physiological range of PAP during exercise remains poorly defined and, therefore, a universally accepted definition of EPH remains elusive. Nevertheless, previous data concerning the distribution of PAP in normal populations and more recent retrospective clinical data enhanced our ability to define EPH. EPH can impair exercise capacity and cause dyspnea. The underlying pathophysiology of the arterial form of EPH (EPAH) appears to be similar to that seen in resting pulmonary arterial hypertension (PAH), and EPAH individuals are at risk of developing resting PAH. Patients with collagen vascular disease, especially scleroderma, are at risk for EPAH and its presence indicates a relatively poor prognosis. The prevalence of EPAH in scleroderma may be as high as 50%. The utility of pulmonary vasodilator therapy for EPAH is not well defined; however, a sizable subgroup of EPAH patients will achieve an improvement in symptoms.

The Evolving Landscape of Exercise-Induced Pulmonary Hypertension

OPINION STATEMENT

Normal pulmonary artery pressures at rest, with an exaggerated rise during exercise, characterize exercise-induced pulmonary hypertension. Exercise itself as it relates to this condition is not deleterious, nor does it cause or induce disease. However much like any classical stress test, it is a physiologic probe that aids in disease unmasking. Although more work is required to establish criteria for defining this clinical entity, the phenomenon is real. It remains unknown whether it represents a nascent form of cardiopulmonary disease and whether its genesis predicts fulminant cardiopulmonary disease. Incremental cardiopulmonary exercise testing and the construction of pressure-flow plots to describe the pulmonary vascular response to exercise will be essential in defining this disease. The critical first step remains a consensus definition that will allow for further prospective study focused by a common language.

Acute aerobic exercise increases exogenously infused bone marrow cell retention in the heart

Stem cell therapy for myocardial infarction (MI) has been shown to improve cardiac function and reduce infarct size. Exercise training, in the form of cardiac rehabilitation, is an essential part of patient care post-MI. Hence, we tested the effects of acute and chronic aerobic exercise on stem cell retention and cardiac remodeling post-MI. Small epicardial MI's were induced in 12-month-old C57BL/6 mice via cryoinjury. Two weeks post-MI, vehicle infusion (N = 4) or GFP(+) bone marrow-derived cells (BMC) were injected (tail vein I.V.) immediately after acute exercise (N = 14) or sedentary conditions (N = 14). A subset of mice continued a 5-week intervention of chronic treadmill exercise (10-13 m/min; 45 min/day; 4 days/week; N = 7) or remained sedentary (N = 6). Exercise tolerance was assessed using a graded exercise test, and cardiac function was assessed with echocardiography. Acute exercise increased GFP(+) BMC retention in the infarcted zone of the heart by 30% versus sedentary (P < 0.05). This was not associated with alterations in myocardial function or gene expression of key cell adhesion molecules. Animals treated with chronic exercise increased exercise capacity (P < 0.05) and cardiac mass (P < 0.05) without change in left ventricular ejection fraction (LVEF), infarct size, or regional wall thickness (P = NS) compared with sedentary. While BMC's alone did not affect exercise capacity, they increased LVEF (P < 0.05) and Ki67(+) nuclei number in the border zone of the heart (P < 0.05), which was potentiated with chronic exercise training (P < 0.05). We conclude that acute exercise increases BMC retention in infarcted hearts and chronic training increases exogenous BMC-mediated effects on stimulating the cardiomyocyte cell cycle. These preclinical results suggest that exercise may help to optimize stem cell therapeutics following MI.

Criteria for diagnosis of exercise pulmonary hypertension

The previous definition of exercise pulmonary hypertension (PH) with a mean pulmonary artery pressure (mPAP) >30 mmHg was abandoned because healthy individuals can exceed this threshold at high cardiac output (CO). We hypothesised that incorporating assessment of the pressure–flow relationship using the mPAP/CO ratio, i.e. total pulmonary resistance (TPR), might enhance the accuracy of diagnosing an abnormal exercise haemodynamic response.

Exercise haemodynamics were evaluated in 169 consecutive subjects with normal resting mPAP ≤20 mmHg. Subjects were classified into controls without heart or lung disease (n=68) versus patients with pulmonary vascular disease (PVD) (n=49) and left heart disease (LHD) (n=52).

TPR and mPAP at maximal exercise produced diagnostic accuracy with area under the receiver operating curve of 0.99 and 0.95, respectively, for discriminating controls versus patients with PVD and LHD. The old criterion of mPAP >30 mmHg had sensitivity of 0.98 but specificity of 0.77. Combining maximal mPAP >30 mmHg and TPR >3 mmHg·min·L−1 retained sensitivity at 0.93 but improved specificity to 1.0. The accuracy of the combined criteria was high across different age groups, sex, body mass index and diagnosis (PVD or LHD).

Combining mPAP >30 mmHg and TPR >3 mmHg·min·L−1 is superior to mPAP >30 mmHg alone for defining a pathological haemodynamic response of the pulmonary circulation during exercise.

Cardiopulmonary responses at various angles of cycle backrest inclination

The purpose of this study was to evaluate cardiopulmonary responses during submaximal cycle exercise at various angles of backrest inclination. Ten healthy Japanese men of mean age 25.9 yrs, height 170.6 cm, and body mass 66.1 kg, performed cycle exercises at a constant workload which reached the anaerobic threshold, at 20 degrees, 40 degrees, and 60 degrees of backrest inclination from the vertical plane, but the angle between the seat and back rest was kept at 110 degrees. The results were as follows: 1) Both cardiac output and stroke volume showed a higher value at the resting control state and during exercise as the backrest angle increased. 2) Oxygen consumption, carbon dioxide output, heart rate, gas exchange ratio, and oxygen pulse were not affected by the angle of backrest inclination. 3) Tidal volume at 20 degrees of backrest inclination was higher than at 60 degrees. 4) No significant differences were found in minute ventilation between each backrest angle. These findings suggest that changes in the backrest angle significantly alter cardiopulmonary parameters at rest and during exercise; in particular, an angle difference of 40 degrees may be enough to alter tidal volume, cardiac output and stroke volume, but not the minute ventilation.

Definitions and diagnosis of pulmonary hypertension

Pulmonary hypertension (PH) is defined by a mean pulmonary artery pressure ≥ 25 mm Hg at rest, measured during right heart catheterization. There is still insufficient evidence to add an exercise criterion to this definition. The term pulmonary arterial hypertension (PAH) describes a subpopulation of patients with PH characterized hemodynamically by the presence of pre-capillary PH including an end-expiratory pulmonary artery wedge pressure (PAWP) ≤ 15 mm Hg and a pulmonary vascular resistance >3 Wood units. Right heart catheterization remains essential for a diagnosis of PH or PAH. This procedure requires further standardization, including uniformity of the pressure transducer zero level at the midthoracic line, which is at the level of the left atrium. One of the most common problems in the diagnostic workup of patients with PH is the distinction between PAH and PH due to left heart failure with preserved ejection fraction (HFpEF). A normal PAWP does not rule out the presence of HFpEF. Volume or exercise challenge during right heart catheterization may be useful to unmask the presence of left heart disease, but both tools require further evaluation before their use in general practice can be recommended. Early diagnosis of PAH remains difficult, and screening programs in asymptomatic patients are feasible only in high-risk populations, particularly in patients with systemic sclerosis, for whom recent data suggest that a combination of clinical assessment and pulmonary function testing including diffusion capacity for carbon monoxide, biomarkers, and echocardiography has a higher predictive value than echocardiography alone.

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.

Exercise-induced pulmonary hypertension: physiological basis and methodological concerns

Exercise stresses the pulmonary circulation through increases in cardiac output (.Q) and left atrial pressure. Invasive as well as noninvasive studies in healthy volunteers show that the slope of mean pulmonary artery pressure (mPAP)-flow relationships ranges from 0.5 to 3 mm Hg.min.L(-1). The upper limit of normal mPAP at exercise thus approximates 30 mm Hg at a .Q of less than 10 L.min(-1) or a total pulmonary vascular resistance at exercise of less than 3 Wood units. Left atrial pressure increases at exercise with an average upstream transmission to PAP in a close to one-for-one mm Hg fashion. Multipoint PAP-flow relationships are usually described by a linear approximation, but present with a slight curvilinearity, which is explained by resistive vessel distensibility. When mPAP is expressed as a function of oxygen uptake or workload, plateau patterns may be observed in patients with systolic heart failure who cannot further increase .Q at the highest levels of exercise. Exercise has to be dynamic to avoid the increase in systemic vascular resistance and abrupt changes in intrathoracic pressure that occur with resistive exercise and can lead to unpredictable effects on the pulmonary circulation. Postexercise measurements are unreliable because of the rapid return of pulmonary vascular pressures and flows to the baseline resting state. Recent studies suggest that exercise-induced increase in PAP to a mean higher than 30 mm Hg may be associated with dyspnea-fatigue symptomatology.

Attenuated relationship between cardiac output and oxygen uptake during high-intensity exercise

AIM

Recent findings have challenged the belief that the cardiac output (CO) and oxygen consumption (VO(2) ) relationship is linear from rest to maximal exercise. The purpose of this study was to determine the CO and stroke volume (SV) response to a range of exercise intensities, 40-100% of VO(2max), during cycling.

METHODS

Ten well-trained cyclists performed a series of discontinuous exercise bouts to determine the CO and SV vs. VO(2) responses.

RESULTS

The rate of increase in CO, relative to VO(2) , during exercise from 40 to 70% of VO(2max) was 4.4 ± 1.4 L L(-1). During exercise at 70-100% of VO(2max) , the rate of increase in CO was reduced to 2.1 ± 0.9 L L(-1) (P = 0.01). Stroke volume during exercise at 80-100% of VO(2max) was reduced by 7% when compared to exercise at 50-70% of VO(2max) (134 ± 5 vs. 143 ± 5 mL per beat, P = 0.02). Whole body arterial-venous O(2) difference increased significantly as intensity increased.

CONCLUSION

The observation that the rate of increase in CO is reduced as exercise intensity increases suggests that cardiovascular performance displays signs of compromised function before maximal VO(2) is reached.

Pulmonary circulation at exercise

The pulmonary circulation is a high-flow and low-pressure circuit, with an average resistance of 1 mmHg/min/L in young adults, increasing to 2.5 mmHg/min/L over four to six decades of life. Pulmonary vascular mechanics at exercise are best described by distensible models. Exercise does not appear to affect the time constant of the pulmonary circulation or the longitudinal distribution of resistances. Very high flows are associated with high capillary pressures, up to a 20 to 25 mmHg threshold associated with interstitial lung edema and altered ventilation/perfusion relationships. Pulmonary artery pressures of 40 to 50 mmHg, which can be achieved at maximal exercise, may correspond to the extreme of tolerable right ventricular afterload. Distension of capillaries that decrease resistance may be of adaptative value during exercise, but this is limited by hypoxemia from altered diffusion/perfusion relationships. Exercise in hypoxia is associated with higher pulmonary vascular pressures and lower maximal cardiac output, with increased likelihood of right ventricular function limitation and altered gas exchange by interstitial lung edema. Pharmacological interventions aimed at the reduction of pulmonary vascular tone have little effect on pulmonary vascular pressure-flow relationships in normoxia, but may decrease resistance in hypoxia, unloading the right ventricle and thereby improving exercise capacity. Exercise in patients with pulmonary hypertension is associated with sharp increases in pulmonary artery pressure and a right ventricular limitation of aerobic capacity. Exercise stress testing to determine multipoint pulmonary vascular pressures-flow relationships may uncover early stage pulmonary vascular disease.

Cardiac remodeling and function following exercise and angiotensin II receptor antagonism

The purpose of this study was to test the impact of chronic exercise training combined with selective angiotensin II receptor (AT1) antagonism on systolic blood pressure (SBP) and the left-ventricular pressure-volume relationship in normotensive, non-infarcted rat hearts. Wistar rats (N = 19) were randomly assigned to either a sedentary control group (N = 8) or an exercise-trained group (N = 11). Losartan was administered to individually caged rats via the drinking water (10 mg/kg/d). Exercise training consisted of running on a motorized driven treadmill for 6 weeks at 30 m/min, 60 min/day, 5 days/week. Tail cuff SBP was measured weekly. Left ventricular performance was assessed in an ex vivo Langendorff isovolumic mode. One week of losartan treatment significantly reduced SBP in both groups by 13% relative to baseline (P < 0.05). SBP was lower in exercise-trained animals versus sedentary animals in the later weeks of the protocol (P < 0.05) Body weight was significantly lower in exercise-trained animals versus sedentary animals, but heart weight, heart to body weight ratio, atrial weight, and absolute left ventricular mass and length were similar between groups. The LV systolic pressure-volume relationship (PV) and systolic elastance were significantly greater in exercise-trained animals versus sedentary controls (P < 0.05). The left ventricular end-diastolic PV and diastolic stiffness were similar between exercise-trained and sedentary animals. These data suggest that chronic aerobic exercise training can improve the Starling response in the presence of AT1 receptor blockade without altering absolute cardiac size.

Diagnosis and assessment of pulmonary arterial hypertension

The diagnosis and assessment of pulmonary arterial hypertension is a rapidly evolving area, with changes occurring in the definition of the disease, screening and diagnostic techniques, and staging and follow-up assessment. The definition of pulmonary hypertension has been simplified, and is now based on currently available evidence. There has been substantial progress in advancing the imaging techniques and biomarkers used to screen patients for the disease and to follow up their response to therapy. The importance of accurate assessment of right ventricular function in following up the clinical course and response to therapy is more fully appreciated. As new therapies are developed for pulmonary arterial hypertension, screening, prompt diagnosis, and accurate assessment of disease severity become increasingly important. A clear definition of pulmonary hypertension and the development of a rational approach to diagnostic assessment and follow-up using both conventional and new tools will be essential to deriving maximal benefit from our expanding therapeutic armamentarium.

Diastolic dysfunction in exercise and its role for exercise capacity

Diastolic dysfunction is frequent in elderly subjects and in patients with left ventricular hypertrophy, vascular disease and diabetes mellitus. Patients with diastolic dysfunction demonstrate a reduced exercise capacity and might suffer from congestive heart failure (CHF). Presence of symptoms of CHF in the setting of a normal systolic function is referred to as heart failure with normal ejection fraction (HFNEF) or, if evidence of an impaired diastolic function is observed, as diastolic heart failure (DHF). Reduced exercise capacity in diastolic dysfunction results from a number of pathophysiological alterations such as slowed myocardial relaxation, reduced myocardial distensibility, elevated filling pressures, and reduced ventricular suction forces. These alterations limit the increase of ventricular diastolic filling and cardiac output during exercise and lead to pulmonary congestion. In healthy subjects, exercise training can enhance diastolic function and exercise capacity and prevent deterioration of diastolic function in the course of aging. In patients with diastolic dysfunction, exercise capacity can be enhanced by exercise training and pharmacological treatment, whereas improvement of diastolic function can only be observed in few patients.

Reduced leg blood flow during submaximal exercise in type 2 diabetes

It is unclear whether impaired cardiac and/or vascular function contribute to exercise intolerance in patients with type 2 diabetes.

PURPOSE

Magnetic resonance imaging (MRI) was used to determine whether reductions in cardiac output and/or femoral arterial blood flow contribute to reduced aerobic capacity in patients with type 2 diabetes.

METHODS

Cardiac and femoral arterial blood flow MRI scans were performed at rest and during low-intensity leg exercise in eight patients with type 2 diabetes and 11 healthy individuals. Maximal aerobic capacity VO(2 max) and maximal oxygen pulse were also determined in all participants.

RESULTS

V O(2 max) was 20% lower and maximal oxygen pulse was 16% lower in patients with type 2 diabetes (P < 0.05), whereas maximal heart rate was the same between groups. Low-intensity exercise induced a 20% increase in heart rate and cardiac output as well as a 60-70% increase in femoral blood flow in both groups (P < 0.05). Femoral arterial blood flow indexed to thigh lean mass was reduced during exercise in patients with type 2 diabetes compared with healthy individuals. Stroke volume indexed to fat-free mass was lower in patients with type 2 diabetes, but greater heart rate allowed cardiac output to be maintained during submaximal exercise.

CONCLUSIONS

These findings suggest that impaired femoral arterial blood flow, an indirect marker of muscle perfusion, affects low-intensity exercise performance in patients with type 2 diabetes. However, because of lower exercising stroke volume, we propose that femoral arterial blood flow and, possibly, cardiac output, limit V O(2 max) in patients with type 2 diabetes.

The contribution of intrapulmonary shunts to the alveolar-to-arterial oxygen difference during exercise is very small

Exercise is well known to cause arterial PO2 to fall and the alveolar-arterial PO2 difference(Aa PO2 ) to increase. Until recently, the physiological basis for this was considered to be mostly ventilation/perfusion ((.)VA/(.)Q) inequality and alveolar-capillary diffusion limitation. Recently, arterio-venous shunting through dilated pulmonary blood vessels has been proposed to explain a significant part of the Aa PO2 during exercise. To test this hypothesis we determined venous admixture during 5 min of near-maximal, constant-load, exercise in hypoxia (in inspired O2 fraction, FIO2 , 0.13), normoxia (FIO2 , 0.21) and hyperoxia (FIO2 , 1.0) undertaken in balanced order on the same day in seven fit cyclists ((.)VO2max, 61.3 +/- 2.4 ml kg(-1) min(-1); mean +/- S.E.M.). Venous admixture reflects three causes of hypoxaemia combined: true shunt, diffusion limitation and ((.)VA/(.)Q) inequality. In hypoxia, venous admixture was 22.8 +/- 2.5% of the cardiac output; in normoxia it was 3.5 +/- 0.5%; in hyperoxia it was 0.5 +/- 0.2%. Since only true shunt accounts for venous admixture while breathing 100% O2, the present study suggests that shunt accounts for only a very small portion of the observed venous admixture, Aa PO2 and hypoxaemia during heavy exercise.

Oxygen delivery by blood determines the maximal VO2 and work rate during whole body exercise in humans: in silico studies

It has been proposed by Saltin (J Exp Biol 115: 345-354, 1985) that oxygen delivery by blood is limiting for maximal work and oxygen consumption in humans during whole body exercise but not during single-muscle exercise. To test this prediction quantitatively, we developed a static (steady-state) computer model of oxygen transport to and within human skeletal muscle during single-muscle (quadriceps) exercise and whole body (cycling) exercise. The main system fluxes, namely cardiac output and oxygen consumption by muscle, are described as a function of the "primary" parameter: work rate. The model is broadly validated by comparison of computer simulations with various experimental data. In silico studies show that, when all other parameters and system properties are kept constant, an increase in the working muscle mass from 2.5 kg (single quadriceps) to 15 kg (two legs) causes, at some critical work intensity, a drop in oxygen concentration in muscle cells to (very near) zero, and therefore oxygen supply by blood limits maximal oxygen consumption and oxidative ATP production. Therefore, the maximal oxygen consumption per muscle mass is significantly higher during single-muscle exercise than during whole body exercise. The effect is brought about by a distribution of a limited amount of oxygen transported by blood in a greater working muscle mass during whole body exercise.

Relationship between cardiac output and oxygen consumption during upright cycle exercise in healthy humans

The relationship between cardiac output (CardOut) and oxygen consumption (VO2) during exercise has generally been assumed to be linear. To test this assumption, we studied 72 healthy subjects using a graded, 2-min cycle-ergometry exercise test to maximum while measuring gas exchange continuously and CardOut at the end of each stage, the latter using an open-circuit gas technique. Data for VO2 and CardOut at each stage were fit to a quadratic expression y = a + (b.VO2) + (c.VO2(2)), and statistical significance of the quadratic c term was determined in each subject. Subjects were then divided into two groups: those with statistically significant negative quadratic term ("negative curvature group," n = 25) and those with either nonsignificant quadratic term or c significantly > 0 ("non-negative curvature group," n = 47, 2 with c significantly > 0). We found the negative curvature group had significantly higher maximal VO2/kg (median 37.9 vs. 32.4 ml x min(-1) x kg(-1); P = 0.03) higher resting stroke volume (SV; median 77 vs. 60 ml; P = 0.04), lower resting heart rate (HR; median 72 vs. 82 beats/min, P = 0.04), and higher tissue oxygen extraction at maximal exercise (17.1 +/- 2.2 vs 15.5 +/- 2.1 ml/100 ml; P < 0.01), with tendencies for higher maximal CardOut and SV. We also found the HR vs. VO2 relationship to be negatively curved, with negative curvature in HR associated with the negative curvature in CardOut (P < 0.05), suggesting the curvature in the CardOut vs. VO2 relationship was secondary to curvature in HR vs. VO2. We conclude that the CardOut vs. VO2 relationship is not always linear, and negative curvature in the relationship is associated with higher fitness levels in normal, non-elite-athletic subjects.

Reduced Exercise Capacity and Stress-Induced Pulmonary Hypertension in Patients With Scleroderma

OBJECTIVES

We sought to determine the incidence of stress-induced pulmonary artery (PA) systolic hypertension in a referral population of patients with scleroderma, and to examine the relation between stress-induced pulmonary systolic hypertension and exercise capacity in this population.

BACKGROUND

Early detection of patients with scleroderma at risk for pulmonary hypertension (PHTN) could lead to more timely intervention and thus reduce morbidity and improve mortality. The change in PA systolic pressure (PASP) with exercise provides a possible tool for such detection.

METHODS

Sixty-five patients with scleroderma (9 men and 56 women; mean age 51 +/- 12 years [SD]), normal resting PASP, and normal resting left ventricular function underwent exercise Doppler echocardiography using a standard Bruce protocol. Tricuspid regurgitation velocity was measured before and after exercise. Exercise variables including workload achieved in metabolic equivalents (METS), total exercise time, percentage of target heart rate achieved, and PASP at rest and within 60 s after exercise were recorded.

RESULTS

Thirty patients (46%) demonstrated an increase in PASP to > 35 mm Hg plus an estimated right atrial pressure of 5 mm Hg. Postexercise PASP inversely correlated to both the maximum workload achieved (r = - 0.34, p = 0.006) and exercise time (r = - 0.31, p = 0.01). In women, the correlation was more significant (r = - 0.38, p = 0.003). Patients in the lowest quartile of exercise time, with the least cardiac workload achieved, produced the highest postexercise PASP.

CONCLUSION

Stress-induced PHTN is common in patients with scleroderma, even when resting PASP is normal. Stress Doppler echocardiography identifies scleroderma patients with an abnormal rise in PASP during exertion. Peak PASP is linearly related to exercise time and maximum workload achieved. Measurement of PASP during exercise may prove to be a useful tool for the identification of future resting PHTN.

Does fitness level modulate the cardiovascular hemodynamic response to exercise?

Subjects with greater aerobic fitness demonstrate better diastolic compliance at rest, but whether fitness modulates exercise cardiac compliance and cardiac filling pressures remains to be determined. On the basis of maximal oxygen consumption (VO2max), healthy male subjects were categorized into either low (LO: VO2max=43+/-6 ml.kg-1.min-1; n=3) or high (HI: VO2max=60+/-3 ml.kg-1.min-1; n=5) aerobic power. Subjects performed incremental cycle exercise to 90% Vo(2max). Right atrial (RAP) and pulmonary artery wedge (PAWP) pressures were measured, and left ventricular (LV) transmural filling pressure (TMFP=PAWP-RAP) was calculated. Cardiac output (CO) and stroke volume (SV) were determined by direct Fick, and LV end-diastolic volume (EDV) was estimated from echocardiographic fractional area change and Fick SV. There were no between-group differences for any measure at rest. At a submaximal workload of 150 W, PAWP and TMFP were higher (P<0.05) in LO compared with HI (12 vs. 8 mmHg, and 9 vs. 4 mmHg, respectively). At peak exercise, CO, SV, and EDV were lower in LO (P<0.05). RAP was not different at peak exercise, but PAWP (23 vs. 15 mmHg) and TMFP (12 vs. 6 mmHg) were higher in LO (P<0.05). Compared with less fit subjects, subjects with greater aerobic fitness demonstrated lower LV filling pressures during exercise, whereas SV and EDV were either similar (submaximal exercise) or higher (peak exercise), suggesting superior diastolic function and compliance.

Time components of circulatory transport from the lungs to a peripheral artery in humans

Blood gas changes occurring in the lung undergo delay and damping on their way to a peripheral artery sampling site. Knowledge of the time components of circulatory transfer is important for the understanding of respiratory control and cardiovascular reflexes in response to blood gas transients. Providing steady state with regard to VA/Q distribution, cardiac output and peripheral blood flow, the relationship between the time courses of small end-tidal and peripheral PO2 changes is determined by the transfer function of the interposed vascular segment. This transfer function, expressed as delay time TD and mean transit time (MTT), was measured in six well-trained subjects, allowing the calculation of arterial time-courses from end-tidal to the reverse. They were studied at rest and during four different dynamic leg exercise intensities in the supine posture. TD and MTT amounted to 15.8 +/- 1.7 (mean +/- SEM) and 18.3 +/- 2.1 s at rest and were shortened to 7.7 +/- 0.6 and 11.5 +/- 1.8 s during exercise at 170 W. The shortening of TD and MTT did not appear to be simply an inverse function of cardiac output, suggesting that the shortening occurs in the central circulatory segment but not in the arm segment.

Peak oxygen uptake. Myth and truth about an internationally accepted reference value

This article critically examines the execution of VO(2)-peak testing in cardiac patients and questions their appropriate interpretation. In the first part, the most common clinical implications of VO(2)peak measurements are discussed: assessment of (changes in) functional capacity, evaluation of the necessity of invasive diagnostic/therapeutic measures, reference for exercise prescriptions, determination of prognosis. In the second part, important methodological problems and constraints are addressed and illustrated by references to scientific studies. Finally, recommendations are given for meaningful VO(2)peak testing. It is evident that failure to strictly follow such recommendations might result in misleading ergometric findings and, thus, in over- or underestimation of endurance capacity and/ or training effects.

A review of the stroke volume response to upright exercise in healthy subjects

Traditionally, it has been accepted that, during incremental exercise, stroke volume plateaus at 40% of Vo(2)max. However, recent research has documented that stroke volume progressively increases to Vo(2)max in both trained and untrained subjects. The stroke volume response to incremental exercise to Vo(2)max may be influenced by training status, age, and sex. For endurance trained subjects, the proposed mechanisms for the progressive increase in stroke volume to Vo(2)max are enhanced diastolic filling, enhanced contractility, larger blood volume, and decreased cardiac afterload. For untrained subjects, it has been proposed that continued increases in stroke volume may result from a naturally occurring high blood volume. However, additional research is needed to evaluate the importance of blood volume, or other mechanisms, that influence the stroke volume response to exercise in untrained subjects.

Limitations to systemic and locomotor limb muscle oxygen delivery and uptake during maximal exercise in humans

Reductions in systemic and locomotor limb muscle blood flow and O2 delivery limit aerobic capacity in humans. To examine whether O2 delivery limits both aerobic power and capacity, we first measured systemic haemodynamics, O2 transport and O2 uptake during incremental and constant (372 +/- 11 W; 85% of peak power; mean +/- S.E.M.) cycling exercise to exhaustion (n = 8) and then measured systemic and leg haemodynamics and during incremental cycling and knee-extensor exercise in male subjects (n = 10). During incremental cycling, cardiac output and systemic O2 delivery increased linearly to 80% of peak power (r2 = 0.998, P < 0.001) and then plateaued in parallel to a decline in stroke volume (SV) and an increase in central venous and mean arterial pressures (P < 0.05). In contrast, heart rate and increased linearly until exhaustion (r2 = 0.993; P < 0.001) accompanying a rise in systemic O2 extraction to 84 +/- 2%. In the exercising legs, blood flow and O2 delivery levelled off at 73-88% of peak power, blunting leg per unit of work despite increasing O2 extraction. When blood flow increased linearly during one-legged knee-extensor exercise, per unit of work was unaltered on fatigue. During constant cycling, , SV, systemic O2 delivery and reached maximal values within approximately 5 min, but dropped before exhaustion (P < 0.05) despite increasing or stable central venous and mean arterial pressures. In both types of maximal cycling, the impaired systemic O2 delivery was due to the decline or plateau in because arterial O2 content continued to increase. These results indicate that an inability of the circulatory system to sustain a linear increase in O2 delivery to the locomotor muscles restrains aerobic power. The similar impairment in SV and O2 delivery during incremental and constant load cycling provides evidence for a central limitation to aerobic power and capacity in humans.

Distensibility of the normal human lung circulation during exercise

Increasing pulmonary arterial (Ppa) and wedge (Pw) pressures at high flow (Q) during exercise could distend the thin-walled vessels. A mechanical descriptor of vascular distension, the distensibility (α, fractional diameter change/mmHg pressure), has been reported to be ∼0.02 for isolated large and small arteries, i.e., a 2% change in diameter per millimeter mercury pressure. In this review we used a pulmonary hemodynamic model to estimate α for data from exercising humans to determine whether interpretable results might be obtained. In 59 normal sea level subjects having published measurements of Ppa and Pw over a range of Q, we found values of α (0.02 ± 0.002) giving calculated Ppa, which matched measured Ppa to within 1.3 ± 0.1 (SE) mmHg. When subjects were exposed to chronic hypoxia ( n = 6, in Operation Everest II), α decreased (0.022 ± 0.002 vs. 0.008 ± 0.001, P < 0.05), but when subjects were exposed to acute hypoxia (Duke chamber study, n = 8), α did not decrease (0.014 ± 0.002 vs. 0.012 ± 0.002, P = not significant). Values of α tended to decrease with age in men >60 yr. Thus at rest and during exercise, normal values of α in young persons were similar to those measured in vitro, and the values decreased in chronic hypoxia and with aging where vascular remodeling or vascular wall stiffening was expected. We propose that the estimation of pulmonary vascular distensibility in humans may be a useful descriptor of pulmonary hemodynamics.

The physiology behind exercise testing

Despite significant advances in related technologies, the exercise test remains a useful clinical tool. It can define the limits of performance in an athlete or the functional capabilities of the patient with heart disease. Although virtually all of the body's physiologic and metabolic systems interact in a coordinated fashion to perform a single bout of exhaustive exercise, a major burden falls on the cardiopulmonary system. A good understanding of the basic physiologic responses to acute exercise can assist the clinician in applying the information gained from the test. These responses are influenced by state of health and fitness, age, gender, type of exercise, exercise position, and the environment. This article provides an overview of the physiologic responses to acute exercise, and discusses the many factors that influence these responses.

Myocardial diastolic function and exercise

There are several important links between aerobic exercise performance and the diastolic phase of the cardiac cycle. During acute exercise, diastolic function must be augmented in order for left ventricular filling to match increased left ventricular output, i.e., cardiac output. This challenges the myocardium because the shortened duration of diastole during exercise may compromise left ventricular filling, thereby limiting the stroke volume. Additionally, left ventricular filling must be accomplished at relatively low filling pressures, otherwise pulmonary vascular congestion may occur. Left ventricular diastolic function may be impaired in the elderly and/or in individuals with ischemic coronary syndromes. Regular aerobic exercise training appears to enhance left ventricular diastolic function and may benefit patients with clinically relevant "diastolic dysfunction." The purpose of this paper is to discuss the relative importance between diastole and exercise and to review some of the involved putative mechanisms.

Supine exercise restores arterial blood pressure and skin blood flow despite dehydration and hyperthermia

We determined whether the deleterious effects of dehydration and hyperthermia on cardiovascular function during upright exercise were attenuated by elevating central blood volume with supine exercise. Seven trained men [maximal oxygen consumption (VO(2 max)) 4.7 +/- 0. 4 l/min (mean +/- SE)] cycled for 30 min in the heat (35 degrees C) in the upright and in the supine positions (VO(2) 2.93 +/- 0.27 l/min) while maintaining euhydration by fluid ingestion or while being dehydrated by 5% of body weight after 2 h of upright exercise. When subjects were euhydrated, esophageal temperature (T(es)) was 37. 8-38.0 degrees C in both body postures. Dehydration caused equal hyperthermia during both upright and supine exercise (T(es) = 38. 7-38.8 degrees C). During upright exercise, dehydration lowered stroke volume (SV), cardiac output, mean arterial pressure (MAP), and cutaneous vascular conductance and increased heart rate and plasma catecholamines [30 +/- 6 ml, 3.0 +/- 0.7 l/min, 6 +/- 2 mmHg, 22 +/- 8%, 14 +/- 2 beats/min, and 50-96%, respectively; all P < 0. 05]. In contrast, during supine exercise, dehydration did not cause significant alterations in MAP, cutaneous vascular conductance, or plasma catecholamines. Furthermore, supine versus upright exercise attenuated the increases in heart rate (7 +/- 2 vs. 9 +/- 1%) and the reductions in SV (13 +/- 4 vs. 21 +/- 3%) and cardiac output (8 +/- 3 vs. 14 +/- 3%) (all P < 0.05). These results suggest that the decline in cutaneous vascular conductance and the increase in plasma norepinephrine concentration, independent of hyperthermia, are associated with a reduction in central blood volume and a lower arterial blood pressure.