Concentric and Eccentric Remodelling of the Left Ventricle and Its Association to Function in the Male Athletes Heart: An Exploratory Study

AIMS

To compare (1) conventional left ventricular (LV) functional parameters, (2) LV peak strain and strain rate and (3) LV temporal strain and strain rate curves in age, ethnicity and sport-matched athletes with concentric, eccentric and normal LV geometry.

METHODS

Forty-five male athletes were categorised according to LV geometry including concentric remodelling/hypertrophy (CON), eccentric hypertrophy (ECC) or normal (NORM). Athletes were evaluated using conventional echocardiography and myocardial speck tracking, allowing the assessment of myocardial strain and strain rate; as well as twist mechanics.

RESULTS

Concentric remodelling was associated with an increased ejection fraction (EF) compared to normal geometry athletes (64% (48-78%) and 56% (50-65%), respectively; p < 0.04). No differences in peak myocardial strain or strain rate were present between LV geometry groups including global longitudinal strain (GLS; CON -16.9% (-14.9-20.6%); ECC -17.9% (-13.0-22.1%); NORM -16.9% (-12.8-19.4%)), global circumferential strain (GCS; CON -18.1% (-13.5-24.5%); ECC -18.7% (-15.6-22.4%); NORM -18.0% (-13.5-19.7%)), global radial strain (GRS; CON 42.2% (30.3-70.5%); ECC 50.0% (39.2-60.0%); NORM 40.6 (29.9-57.0%)) and twist (CON 14.9° (3.7-25.3°); ECC 12.5° (6.3-20.8°); NORM 13.2° (8.8-24.2°)). Concentric and eccentric remodelling was associated with alterations in temporal myocardial strain and strain rate as compared to normal geometry athletes.

CONCLUSION

Physiological concentric and eccentric remodelling in the athletes heart is generally associated with normal LV function; with concentric remodelling associated with an increased EF. Physiological concentric and eccentric remodelling in the athletes heart has no effect on peak myocardial strain but superior deformation and untwisting is unmasked when assessing the temporal distribution.

Intensity-dependent cardiopulmonary response during and after strength training

Whereas cardiopulmonary responses are well understood in endurance training, they are rarely described in strength training. This cross-over study examined acute cardiopulmonary responses in strength training. Fourteen healthy male strength training-experienced participants (age 24.5 ± 2.9 years; BMI 24.1 ± 2.0 kg/m²) were randomly assigned into three strength training sessions (three sets of ten repetitions) with different intensities (50%, 62,5%, and 75% of the 3-Repetition Maximum) of squats in a smith machine. Cardiopulmonary (impedance cardiography, ergo-spirometry) responses were continuously monitored. During exercise period, heart rate (HR 143 ± 16 vs. 132 ± 15 vs. 129 ± 18 bpm, respectively; p < 0.01; η²_p 0.54) and cardiac output (CO: 16.7 ± 3.7 vs. 14.3 ± 2.5 vs. 13.6 ± 2.4 l/min, respectively; p < 0.01; η²_p 0.56) were higher at 75% of 3-RM compared to those at the other intensities. We noted similar stroke volume (SV: p = 0.08; η²_p 0.18) and end-diastolic volume (EDV: p = 0.49). Ventilation (V_E) was higher at 75% compared to 62.5% and 50% (44.0 ± 8.0 vs. 39.6 ± 10.4 vs. 37.6 ± 7.7 l/min, respectively; p < 0.01; η²_p 0.56). Respiration rate (RR; p = .16; η²_p 0.13), tidal volume (VT: p = 0.41; η²_p 0.07) and oxygen uptake (VO₂: p = 0.11; η²_p 0.16) did not differ between intensities. High systolic and diastolic blood pressure were evident (62.5% 3-RM 197 ± 22.4/108.8 ± 13.4 mmHG). During the post-exercise period (60 s), SV, CO, V_E, VO_2, and VCO₂ were higher (p < 0.01) than during the exercise period, and the pulmonary parameters differed markedly between intensities (V_E p < 0.01; RR p < 0.01; VT p = 0.02; VO₂ p < 0.01; VCO₂ p < 0.01). Despite the differences in strength training intensity, the cardiopulmonary response reveals significant differences predominantly during the post-exercise period. Intensity-induced breath holding induces high blood pressure peaks and cardiopulmonary recovery effects after exercise.

Physical Exercise and Cardiac Repair: The Potential Role of Nitric Oxide in Boosting Stem Cell Regenerative Biology

Over the years strong evidence has been accumulated showing that aerobic physical exercise exerts beneficial effects on the prevention and reduction of cardiovascular risk. Exercise in healthy subjects fosters physiological remodeling of the adult heart. Concurrently, physical training can significantly slow-down or even reverse the maladaptive pathologic cardiac remodeling in cardiac diseases, improving heart function. The underlying cellular and molecular mechanisms of the beneficial effects of physical exercise on the heart are still a subject of intensive study. Aerobic activity increases cardiovascular nitric oxide (NO) released mainly through nitric oxidase synthase 3 activity, promoting endothelium-dependent vasodilation, reducing vascular resistance, and lowering blood pressure. On the reverse, an imbalance between increasing free radical production and decreased NO generation characterizes pathologic remodeling, which has been termed the "nitroso-redox imbalance". Besides these classical evidence on the role of NO in cardiac physiology and pathology, accumulating data show that NO regulate different aspects of stem cell biology, including survival, proliferation, migration, differentiation, and secretion of pro-regenerative factors. Concurrently, it has been shown that physical exercise generates physiological remodeling while antagonizes pathologic remodeling also by fostering cardiac regeneration, including new cardiomyocyte formation. This review is therefore focused on the possible link between physical exercise, NO, and stem cell biology in the cardiac regenerative/reparative response to physiological or pathological load. Cellular and molecular mechanisms that generate an exercise-induced cardioprotective phenotype are discussed in regards with myocardial repair and regeneration. Aerobic training can benefit cells implicated in cardiovascular homeostasis and response to damage by NO-mediated pathways that protect stem cells in the hostile environment, enhance their activation and differentiation and, in turn, translate to more efficient myocardial tissue regeneration. Moreover, stem cell preconditioning by and/or local potentiation of NO signaling can be envisioned as promising approaches to improve the post-transplantation stem cell survival and the efficacy of cardiac stem cell therapy.

Faster Heart Rate Recovery Correlates With High-Intensity Match Activity in Female Field Hockey Players-Training Implications

Harry, K and Booysen, MJ. Faster heart rate recovery correlates with high-intensity match activity in female field hockey players-training implications. J Strength Cond Res 34(4): 1150-1157, 2020-The physical match demands of female field hockey are intense and may differ according to playing positions. In addition, conducting sports-specific field tests can assist coaches in determining their players' preparedness for competition. There is limited research regarding the match demands and relevance of field testing at premier league levels. Therefore, the aims were to describe the physical match demands of female premier league (amateur) field hockey, and to determine the relationships between match activity patterns and physical performance tests. Match activity and heart rate data were collected from 32 female participants using the Zephyr BioHarness 3 system. Participants also performed the Yo-Yo intermittent recovery (level 1) (n = 22), repeated sprint ability (n = 21), and the heart rate recovery (n = 16) tests. Moderate to large effect sizes were observed when defenders were compared with midfielders and forwards for time spent (%) in standing/walking and jogging (d = 0.64-1.30) in addition to the playing time (%) spent in the low-to-moderate and very high heart rate zones (d = 0.69-0.85). Heart rate recovery (10 s) correlated with the playing time (%) spent in sprinting (r = 0.73, p = 0.002). Heart rate recovery (60 s) and the Yo-Yo intermittent recovery test both correlated with the playing time (%) spent in running (r = 0.77, p = 0.0006 and r = 0.54, p = 0.01). The differences in physical match demands between positions emphasize the importance of training specificity at premier league levels. The heart rate recovery test can be used to assess a female field hockey player's capability to perform high-intensity match activity.

Effect of sympathetic autonomic stress from the cold pressor test on left ventricular function in young healthy adults

There is a dearth of studies investigating the effect of sympathetic activation on left ventricular function. This study aimed to investigate the effect of sympathetic autonomic stress on left ventricular function in young healthy adults. Fifty‐six normotensive healthy participants (age 23.55 ± 3.82 years) took part in the study after giving informed consent. After obtaining baseline measurements, heart rate (HR), blood pressure (BP), peripheral saturation of oxygen (SpO2) and left ventricular function (assessed by means of ejection fraction (EF) obtained by transthoracic 2‐D echocardiography) were determined before and following sympathetic activation using cold pressor test (CPT). Exposure to CPT led to significant increase (P < 0.0001) in HR (70.4 ± 10.7 bpm to 91.6 ± 14.8 bpm), SBP (118 ± 8 mmHg to 138 ± 14 mmHg) and DBP (71 ± 7 mmHg to 91 ± 11 mmHg). Participants’ EDV (101.1 ± 15.8 ml to 104.2 ± 19.3 mL), ESV (38.7 ± 9.1 mL to 40.3 ± 11.6 mL), SpO2 (99.5 ± 0.79% to 99.5 ± 0.77%) and EF (61.9 ± 5.9% to 60.9 ± 6.4%) were only slightly changed (P > 0.05). However, cardiac output (4.3 ± 0.9 L/min to 5.4 ± 1.4 L/min) and cardiac index (3.7 ± 0.8 L/min per m² to 4.5 ± 1.4 L/min per m²) increased significantly (P < 0.0001). We conclude that sympathetic stress induced by cold pressor test has marginal effect on ejection fraction and fractional shortening while increasing cardiac output and cardiac index in young healthy adults.

Metabolic Mechanisms of Exercise-Induced Cardiac Remodeling

Exercise has a myriad of physiological benefits that derive in part from its ability to improve cardiometabolic health. The periodic metabolic stress imposed by regular exercise appears fundamental in driving cardiovascular tissue adaptation. However, different types, intensities, or durations of exercise elicit different levels of metabolic stress and may promote distinct types of tissue remodeling. In this review, we discuss how exercise affects cardiac structure and function and how exercise-induced changes in metabolism regulate cardiac adaptation. Current evidence suggests that exercise typically elicits an adaptive, beneficial form of cardiac remodeling that involves cardiomyocyte growth and proliferation; however, chronic levels of extreme exercise may increase the risk for pathological cardiac remodeling or sudden cardiac death. An emerging theme underpinning acute as well as chronic cardiac adaptations to exercise is metabolic periodicity, which appears important for regulating mitochondrial quality and function, for stimulating metabolism-mediated exercise gene programs and hypertrophic kinase activity, and for coordinating biosynthetic pathway activity. In addition, circulating metabolites liberated during exercise trigger physiological cardiac growth. Further understanding of how exercise-mediated changes in metabolism orchestrate cell signaling and gene expression could facilitate therapeutic strategies to maximize the benefits of exercise and improve cardiac health.

Case Study: Physical Capacity and Nutritional Status Before and After a Single-Handed Yacht Race

During solitary sailing, the sailor is exposed to sleep deprivation and difficulties in consuming regular meals. Sailor weight loss is often reported. In the present case study, we describe changes in the physical capacity and nutritional status of an athlete attempting a single-handed yacht race around the globe. An Italian male ocean racer (Gaetano Mura) asked for our help to reach an optimum level of physical and nutritional preparation. We planned his diet after assessing his anthropometric parameters and body composition, as well as his usual energy intake and nutritional expenditure. The diet consisted of 120 meals stored in sealed plastic bags. Before his departure, GM performed two incremental exercise tests (cycle ergometry and arm crank ergometry) to assess his physical capacity. Cardiac functions were also estimated by Doppler echocardiography. All measures and exercise tests were repeated 10 days after GM finished the race, which lasted 64 days. Anthropometric measures did not change significantly, with the exception of arm fat area and thigh muscle area, which decreased. There were evident increments in maximum oxygen intake and maximum workload during arm cranking after the race. On the contrary, maximum oxygen uptake and maximum workload decreased during cycling. Finally, end-diastolic and stroke volume decreased after the race. It was concluded that nutritional counseling was useful to avoid excessive changes in nutritional status and body composition due to 64 days of solitary navigation. However, a reduction in physical leg capacity and cardiovascular functions secondary to leg disuse were present.

A Doppler Echocardiographic Study of the Myocardial Inotropic Response to Peak Semisupine Exercise in Healthy Children: Development of a Simplified Index of Myocardial Reserve

BACKGROUND

Stress echocardiography has been advocated for the detection of abnormal myocardial function and unmasking diminished myocardial reserve in pediatric patients. The aim of this study was to create a simplified index of myocardial reserve, derived from the myocardial inotropic response to peak semisupine exercise in healthy children, and illustrate its applicability in a sample of pediatric oncology patients.

METHODS

In this prospective analysis, children (7-18 years of age) with normal cardiac structure and function performed semisupine stress echocardiography to volitional fatigue. The quotient of wall stress at peak systole and heart rate-corrected velocity of circumferential fiber shortening were calculated at baseline and at peak exercise, the difference of which was termed the index of myocardial reserve (IMR). The IMR was also calculated in a retrospective sample of pediatric oncology patients with normal resting left ventricular function who had received anthracycline treatment and had performed the same exercise protocol to illustrate utility.

RESULTS

Fifty healthy subjects (mean age, 13.2 ± 2.6 years) and 33 oncology patients (mean age, 12.7 ± 4.0 years) were assessed. In the healthy children at peak exercise, heart rate-corrected velocity of circumferential fiber shortening significantly increased (from 1.17 ± 0.17 to 1.58 ± 0.24 circ · sec^-1, P < .001), while the quotient of wall stress at peak systole significantly decreased (from 75.3 ± 17.1 to 55.3 ± 13.8 g · cm^-2, P < .001), shifting the plot of the relationship between the two parameters upward and to the left. The mean IMR was -30.8 ± 17.8, and the normal distribution ranged from -4.7 (fifth percentile) to -67.3 (95th percentile). The IMR was abnormal in 10 oncology patients who were treated with anthracyclines.

CONCLUSIONS

The authors have developed a novel IMR. Relative to the normal distribution of this IMR in healthy subjects, it is possible to identify patients with abnormal myocardial reserve. Thus, this study demonstrates the application of the IMR to aid in clinical decision making in individual patients.

Cardiac Autonomic Responses during Exercise and Post-exercise Recovery Using Heart Rate Variability and Systolic Time Intervals-A Review

Cardiac parasympathetic activity may be non-invasively investigated using heart rate variability (HRV), although HRV is not widely accepted to reflect sympathetic activity. Instead, cardiac sympathetic activity may be investigated using systolic time intervals (STI), such as the pre-ejection period. Although these autonomic indices are typically measured during rest, the “reactivity hypothesis” suggests that investigating responses to a stressor (e.g., exercise) may be a valuable monitoring approach in clinical and high-performance settings. However, when interpreting these indices it is important to consider how the exercise dose itself (i.e., intensity, duration, and modality) may influence the response. Therefore, the purpose of this investigation was to review the literature regarding how the exercise dosage influences these autonomic indices during exercise and acute post-exercise recovery. There are substantial methodological variations throughout the literature regarding HRV responses to exercise, in terms of exercise protocols and HRV analysis techniques. Exercise intensity is the primary factor influencing HRV, with a greater intensity eliciting a lower HRV during exercise up to moderate-high intensity, with minimal change observed as intensity is increased further. Post-exercise, a greater preceding intensity is associated with a slower HRV recovery, although the dose-response remains unclear. A longer exercise duration has been reported to elicit a lower HRV only during low-moderate intensity and when accompanied by cardiovascular drift, while a small number of studies have reported conflicting results regarding whether a longer duration delays HRV recovery. “Modality” has been defined multiple ways, with limited evidence suggesting exercise of a greater muscle mass and/or energy expenditure may delay HRV recovery. STI responses during exercise and recovery have seldom been reported, although limited data suggests that intensity is a key determining factor. Concurrent monitoring of HRV and STI may be a valuable non-invasive approach to investigate autonomic stress reactivity; however, this integrative approach has not yet been applied with regards to exercise stressors.

Assessing exercise cardiac reserve using real-time cardiovascular magnetic resonance

BACKGROUND

Exercise cardiovascular magnetic resonance (ExCMR) has great potential for clinical use but its development has been limited by a lack of compatible equipment and robust real-time imaging techniques. We developed an exCMR protocol using an in-scanner cycle ergometer and assessed its performance in differentiating athletes from non-athletes.

METHODS

Free-breathing real-time CMR (1.5T Aera, Siemens) was performed in 11 athletes (5 males; median age 29 [IQR: 28-39] years) and 16 age- and sex-matched healthy volunteers (7 males; median age 26 [interquartile range (IQR): 25-33] years). All participants underwent an in-scanner exercise protocol on a CMR compatible cycle ergometer (Lode BV, the Netherlands), with an initial workload of 25W followed by 25W-increment every minute. In 20 individuals, exercise capacity was also evaluated by cardiopulmonary exercise test (CPET). Scan-rescan reproducibility was assessed in 10 individuals, at least 7 days apart.

RESULTS

The exCMR protocol demonstrated excellent scan-rescan (cardiac index (CI): 0.2 ± 0.5L/min/m²) and inter-observer (ventricular volumes: 1.2 ± 5.3mL) reproducibility. CI derived from exCMR and CPET had excellent correlation (r = 0.83, p < 0.001) and agreement (1.7 ± 1.8L/min/m²). Despite similar values at rest (P = 0.87), athletes had increased exercise CI compared to healthy individuals (at peak exercise: 12.2 [IQR: 10.2-13.5] L/min/m² versus 8.9 [IQR: 7.5-10.1] L/min/m², respectively; P < 0.001). Peak exercise CI, where image acquisition lasted 13-17 s, outperformed that at rest (c-statistics = 0.95 [95% confidence interval: 0.87-1.00] versus 0.48 [95% confidence interval: 0.23-0.72], respectively; P < 0.0001 for comparison) in differentiating athletes from healthy volunteers; and had similar performance as VO_2max (c-statistics = 0.84 [95% confidence interval = 0.62-1.00]; P = 0.29 for comparison).

CONCLUSIONS

We have developed a novel in-scanner exCMR protocol using real-time CMR that is highly reproducible. It may now be developed for clinical use for physiological studies of the heart and circulation.

Assessing exercise cardiac reserve using real-time cardiovascular magnetic resonance

BACKGROUND

Exercise cardiovascular magnetic resonance (ExCMR) has great potential for clinical use but its development has been limited by a lack of compatible equipment and robust real-time imaging techniques. We developed an exCMR protocol using an in-scanner cycle ergometer and assessed its performance in differentiating athletes from non-athletes.

METHODS

Free-breathing real-time CMR (1.5T Aera, Siemens) was performed in 11 athletes (5 males; median age 29 [IQR: 28-39] years) and 16 age- and sex-matched healthy volunteers (7 males; median age 26 [interquartile range (IQR): 25-33] years). All participants underwent an in-scanner exercise protocol on a CMR compatible cycle ergometer (Lode BV, the Netherlands), with an initial workload of 25W followed by 25W-increment every minute. In 20 individuals, exercise capacity was also evaluated by cardiopulmonary exercise test (CPET). Scan-rescan reproducibility was assessed in 10 individuals, at least 7 days apart.

RESULTS

The exCMR protocol demonstrated excellent scan-rescan (cardiac index (CI): 0.2 ± 0.5L/min/m2) and inter-observer (ventricular volumes: 1.2 ± 5.3mL) reproducibility. CI derived from exCMR and CPET had excellent correlation (r = 0.83, p < 0.001) and agreement (1.7 ± 1.8L/min/m2). Despite similar values at rest (P = 0.87), athletes had increased exercise CI compared to healthy individuals (at peak exercise: 12.2 [IQR: 10.2-13.5] L/min/m2 versus 8.9 [IQR: 7.5-10.1] L/min/m2, respectively; P < 0.001). Peak exercise CI, where image acquisition lasted 13-17 s, outperformed that at rest (c-statistics = 0.95 [95% confidence interval: 0.87-1.00] versus 0.48 [95% confidence interval: 0.23-0.72], respectively; P < 0.0001 for comparison) in differentiating athletes from healthy volunteers; and had similar performance as VO2max (c-statistics = 0.84 [95% confidence interval = 0.62-1.00]; P = 0.29 for comparison).

CONCLUSIONS

We have developed a novel in-scanner exCMR protocol using real-time CMR that is highly reproducible. It may now be developed for clinical use for physiological studies of the heart and circulation.

The relationship between biventricular myocardial performance and metabolic parameters during incremental exercise and recovery in healthy adolescents

Background left ventricular (LV) and right ventricular (RV) myocardial reserve during exercise in adolescents has not been directly characterized. The aim of this study was to quantify myocardial performance response to exercise by using two-dimensional (2-D) speckle tracking echocardiography and describe the relationship between myocardial reserve, respiratory, and metabolic exercise parameters. A total of 23 healthy boys and girls (mean age 13.2 ± 2.7 yr; stature 159.1 ± 16.4 cm; body mass 49.5 ± 16.6 kg; BSA 1.47 ± 0.33 m(2)) completed an incremental cardiopulmonary exercise test (25 W · 3 min increments) with simultaneous acquisition of 2-D transthoracic echocardiography at rest, each exercise stage up to 100 W, and in recovery at 2 min and 10 min. Two-dimensional LV (LV Sl) and RV (RV Sl) longitudinal strain and LV circumferential strain (LV Sc) were analyzed to define the relationship between myocardial performance reserve and metabolic exercise parameters. Participants achieved a peak oxygen uptake (V̇o 2peak) of 40.6 ± 8.9 ml · kg(-1) · min(-1) and a work rate of 154 ± 42 W. LV Sl and LV Sc and RV Sl increased significantly across work rates (P < 0.05). LV Sl during exercise was significantly correlated to resting strain, V̇o 2peak, oxygen pulse, and work rate (0.530 ≤ r ≤ 0.784, P < 0.05). This study identifies a positive and moderate relationship between LV and RV myocardial performance and metabolic parameters during exercise by using a novel methodology. Relationships detected present novel data directly describing myocardial adaptation at different stages of exercise and recovery that in the future can help directly assess cardiac reserve in patients with cardiac pathology.

Metabolic Effects of Exercise Training Among Fitness-Nonresponsive Patients With Type 2 Diabetes: The HART-D Study

OBJECTIVE

To evaluate the impact of exercise training (ET) on metabolic parameters among participants with type 2 diabetes mellitus (T2DM) who do not improve their cardiorespiratory fitness (CRF) with training.

RESEARCH DESIGN AND METHODS

We studied participants with T2DM participating in the Health Benefits of Aerobic and Resistance Training in Individuals With Type 2 Diabetes (HART-D) trial who were randomized to a control group or one of three supervised ET groups for 9 months. Fitness response to ET was defined as a change in measured peak absolute oxygen uptake (ΔVO(2peak), in liters per minute) from baseline to follow-up. ET participants were classified based on ΔVO(2peak) into fitness responders (ΔVO(2peak) ≥5%) and nonresponders (ΔVO(2peak) <5%), and changes in metabolic profiles were compared across control, fitness responder, and fitness nonresponder groups.

RESULTS

A total of 202 participants (mean age 57.1 ± 7.9 years, 63% women) were included. Among the exercise groups (n = 161), there was substantial heterogeneity in ΔVO(2peak); 57% had some improvement in CRF (ΔVO(2peak) >0), with only 36.6% having a ≥5% increase in VO(2peak). Both fitness responders and nonresponders (respectively) had significant improvements in hemoglobin A1c and measures of adiposity (ΔHbA(1c): -0.26% [95% CI -0.5 to -0.01] and -0.26% [-0.45 to -0.08]; Δwaist circumference: -2.6 cm [-3.7 to -1.5] and -1.8 cm [-2.6 to -1.0]; Δbody fat: -1.07% [-1.5 to -0.62] and -0.75% [-1.09 to -0.41]). No significant differences were observed in the degree of change of these metabolic parameters between fitness responders and nonresponders. Control group participants had no significant changes in any of these metabolic parameters.

CONCLUSIONS

ET is associated with significant improvements in metabolic parameters irrespective of improvement in cardiorespiratory fitness.

The Effect of Habitual Physical Training on Left Ventricular Function During Exercise Assessed by Three-Dimensional Echocardiography

BACKGROUND

Stroke volume (SV) in trained athletes continuously increases with progressive exercise intensity. We studied whether physical training affected left ventricle (LV) function response to exercise using 3D echocardiography and tissue Doppler imaging (TDI).

METHODS

Eleven male university athletes and 12 male university nonathletes were enrolled in this study. After baseline data were collected, subjects performed a symptom-limited supine bicycle ergometer exercise test. Initial workload was 25 Watts (W) and increased 25 W every 3 minutes. At rest and every exercise stage, LV end-systolic and diastolic volume index (LVEDVI and LVESVI), SV index (SVI), cardiac index (CI), LV ejection fraction (LVEF), and early lateral mitral flow velocity (Ea) were evaluated. Heart rate (HR), and systolic and diastolic blood pressure (SBP and DBP) were continuously recorded.

RESULTS

Nonathletes showed a slow increase in CI, and SVI reached a plateau value at a HR of 90 beats per minute (bpm). In contrast, CI and SVI increased progressively and continuously in athletes. Both CI and SVI were significantly higher in athletes than in nonathletes at HRs of 100, 110, and 120 bpm. LVEDVI kept increasing in athletes while it plateaued in nonathletes. In contrast, LVESV decreased continuously during exercise in both groups. There was no significant difference in LVEF, Ea, SBP, or DBP at rest and during exercise between the two groups.

CONCLUSION

LV responses to exercise in athletes were different from those of in nonathletes; thus, habitual physical training may play an important role in the increase in both SVI and CI in young individuals.

Changes in systemic and pulmonary blood flow distribution in normal adult volunteers in response to posture and exercise: a phase contrast magnetic resonance imaging study

Hemodynamics are usually evaluated in the supine position at rest. This is only a snapshot of an individual's daily activities. This study describes circulatory adaptation, as assessed by magnetic resonance imaging, to changes in position and exercise. Phase contrast magnetic resonance imaging of blood flow within systemic and pulmonary arteries and veins was performed in 24 healthy volunteers at rest in the prone and supine position and with bicycle exercise in the supine position. No change was seen in systemic blood flow when moving from prone to supine. Exercise resulted in an increased percentage of cardiac output towards the lower body. Changes in position resulted in a redistribution of blood flow within the left lung--supine positioning resulted in decreased blood flow to the left lower pulmonary vein. With exercise, both the right and left lower lobes received increased blood flow, while the upper lobes received less.

Orthostatic effects on echocardiographic measures of ventricular function

Orthostatic-induced alterations in Doppler echocardiographic measures of ventricular function have not been well-defined. Identifying such changes may provide useful insights regarding the responses of these measures to variations in ventricular loading conditions. Standard assessment of mitral inflow velocity and tissue Doppler imaging (TDI) of left ventricular longitudinal myocardial velocities was performed on 14 young males (mean age 17.9 ± 0.7 years) in the supine position and then 5 minutes after assuming a sitting position with legs dependent. Upon sitting, average values of stroke volume and cardiac output fell by 28% and 18%, respectively, while heart rate increased from 64 ± 10 to 73 ± 12 beats/min (+14%) and calculated systemic vascular resistance rose from 12.9 ± 2.2 to 16.4 ± 3.1 units (+27%). Mitral E peak velocity declined from 87 ± 16 to 64 ± 16 cm/sec, and average TDI-E' and TDI-S both decreased (by -44% and -20%, respectively). When adjusted for orthostatic decreases in left ventricular end-diastolic volume, the mean decrease in TDI-E' was reduced to -29 (P < 0.01), but no significant decline was observed in adjusted TDI-S. Average E/E' rose with sitting by 40% (P = 0.02). These findings suggest that (a) decreases in TDI measures when assuming the upright position reflect the reduction of left ventricular size; (b) orthostatic fall in TDI-E' is also related to smaller ventricular size but, in addition, to a nonspecified reduction in ventricular relaxation; and (c) values of E/E' do not reflect alterations in ventricular preload, which occur during an orthostatic challenge.

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.

Time-of-day effect on cardiac responses to progressive exercise

This study was designed to examine time-of-day effects on markers of cardiac functional capacity during a standard progressive cycle exercise test. Fourteen healthy, untrained young males (mean ± SD: 17.9 ± 0.7 yrs of age) performed identical maximal cycle tests in the morning (08:00-11:00 h) and late afternoon (16:00-19:00 h) in random order. Cardiac variables were measured at rest, submaximal exercise, and maximal exercise by standard echocardiographic techniques. No differences in morning and afternoon testing values at rest or during exercise were observed for oxygen uptake, heart rate, cardiac output, or markers of systolic and diastolic myocardial function. Values at peak exercise for Vo(2) at morning and afternoon testing were 3.20 ± 0.49 and 3.24 ± 0.55 L min(-1), respectively, for heart rate 190 ± 11 and 188 ± 15 bpm, and for cardiac output 19.5 ± 2.8 and 19.8 ± 3.5 L min(-1). Coefficients of variation for morning and afternoon values for these variables were similar to those previously published for test-retest reproducibility. This study failed to demonstrate evidence for significant time-of-day variation in Vo(2)max or cardiac function during standard progressive exercise testing in adolescent males.

Lymph flow in instrumented dogs varies with exercise intensity

BACKGROUND

Although it is generally accepted that exercise accelerates lymph flow, no study has directly measured lymph flow as a function of exercise intensity. In this study, we have measured flow in the thoracic lymph duct of five instrumented dogs while they ran on a treadmill.

METHODS AND RESULTS

Dogs were surgically instrumented with an ultrasonic flow transducer on the thoracic lymph duct and a catheter in the descending thoracic aorta. After recovery from surgery, the dogs ran on a treadmill at speeds which varied stepwise from 0 to 10 mph and from 10 to 0 mph. Dogs ran for 1 min at each speed with 15 min rest between each exercise. Heart rate increased significantly during exercise, whereas mean aortic pressure did not change. Resting lymph flow was 1.7+/-0.2 ml/min. Exercise at 1.5 mph significantly increased lymph flow to 3.9 +/- 0.6 ml/min (P < 0.01), 121% higher than resting flow. Lymph flow was further elevated at higher treadmill speeds, reaching 9.0 +/-1.6 ml/min (P < 0.01) at 10 mph, 419% higher than resting flow. Regression analysis demonstrated a linear relationship between treadmill speed and the percent increase in lymph flow. Lymph flow returned to the resting rate 1-2 min post-exercise.

CONCLUSION

Lymph flow in the thoracic duct is positively correlated with exercise intensity.

Myocardial function and aerobic fitness in adolescent females

A recent report indicated that variations in myocardial functional (systolic and diastolic) responses to exercise do not contribute to inter-individual differences in aerobic fitness (peak VO(2)) among young males. This study was designed to investigate the same question among adolescent females. Thirteen highly fit adolescent football (soccer) players (peak VO(2) 43.5 ± 3.4 ml kg(-1) min(-1)) and nine untrained girls (peak VO(2) 36.0 ± 5.1 ml kg(-1) min(-1)) matched for age underwent a progressive cycle exercise test to exhaustion. Cardiac variables were measured by standard echocardiographic techniques. Maximal stroke index was greater in the high-fit group (50 ± 5 vs. 41 ± 4 ml m(-2)), but no significant group differences were observed in maximal heart rate or arterial venous oxygen difference. Increases in markers of both systolic (ejection rate, tissue Doppler S') and diastolic (tissue Doppler E', mitral E velocity) myocardial functions at rest and during the acute bout of exercise were similar in the two groups. This study suggests that among healthy adolescent females, like young males, myocardial systolic and diastolic functional capacities do not contribute to inter-individual variability in physiologic aerobic fitness.

Sex influence on myocardial function with exercise in adolescents

OBJECTIVES

Ventricular systolic functional response to exercise has been reported to be superior in adult men compared to women. This study explored myocardial responses to maximal upright progressive exercise in late pubertal males and females.

METHODS

Doppler echocardiographic techniques were utilized to estimate myocardial function response to a bout of progressive cycle exercise.

RESULTS

Systolic functional capacity, as indicated by ejection rate (12.5 +/- 2.8 and 13.1 +/- 1.0 [x10(-2)] ml s(-1) cm(-2) for boys and girls, respectively) and peak aortic velocity (208 +/- 45 and 196 +/- 12 cm s(-1), respectively) at maximal exercise, did not differ between the two groups. Similarly, peak values as well as increases in transmitral pressure gradient (mitral E flow velocity), ventricular relaxation (tissue Doppler imaging E'), and left ventricular filling pressure (E/E' ratio) as estimates of diastolic function were similar in males and females.

CONCLUSIONS

This study failed to reveal qualitative or quantitative differences between adolescent boys and girls in ventricular systolic or diastolic functional responses to maximal cycle exercise.

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

Pulmonary transit of agitated contrast (PTAC) occurs to variable extents during exercise. We tested the hypothesis that the onset of PTAC signifies flow through larger-caliber vessels, resulting in improved pulmonary vascular reserve during exercise. Forty athletes and fifteen nonathletes performed maximal exercise with continuous echocardiographic Doppler measures [cardiac output (CO), pulmonary artery systolic pressure (PASP), and myocardial velocities] and invasive blood pressure (BP). Arterial gases and B-type natriuretic peptide (BNP) were measured at baseline and peak exercise. Pulmonary vascular resistance (PVR) was determined as the regression of PASP/CO and was compared according to athletic and PTAC status. At peak exercise, athletes had greater CO (16.0 ± 2.9 vs. 12.4 ± 3.2 l/min, P < 0.001) and higher PASP (60.8 ± 12.6 vs. 47.0 ± 6.5 mmHg, P < 0.001), but PVR was similar to nonathletes ( P = 0.71). High PTAC (defined by contrast filling of the left ventricle) occurred in a similar proportion of athletes and nonathletes (18/40 vs. 10/15, P = 0.35) and was associated with higher peak-exercise CO (16.1 ± 3.4 vs. 13.9 ± 2.9 l/min, P = 0.010), lower PASP (52.3 ± 9.8 vs. 62.6 ± 13.7 mmHg, P = 0.003), and 37% lower PVR ( P < 0.0001) relative to low PTAC. Right ventricular (RV) myocardial velocities increased more and BNP increased less in high vs. low PTAC subjects. On multivariate analysis, maximal oxygen consumption (V̇o2max) ( P = 0.009) and maximal exercise output ( P = 0.049) were greater in high PTAC subjects. An exercise-induced decrease in arterial oxygen saturation (98.0 ± 0.4 vs. 96.7 ± 1.4%, P < 0.0001) was not influenced by PTAC status ( P = 0.96). Increased PTAC during exercise is a marker of pulmonary vascular reserve reflected by greater flow, reduced PVR, and enhanced RV function.

What Limits Cardiac Performance during Exercise in Normal Subjects and in Healthy Fontan Patients?

Exercise is an important determinant of health but is significantly reduced in the patient with a univentricular circulation. Normal exercise physiology mandates an increase in pulmonary artery pressures which places an increased work demand on the right ventricle (RV). In a biventricular circulation with pathological increases in pulmonary vascular resistance and/or reductions in RV function, exercise-induced augmentation of cardiac output is limited. Left ventricular preload reserve is dependent upon flow through the pulmonary circulation and this requires adequate RV performance. In the Fontan patient, the reasons for exercise intolerance are complex. In those patients with myocardial dysfunction or other pathologies of the circulatory components, it is likely that these abnormalities serve as a limitation to cardiac performance during exercise. However, in the healthy Fontan patient, it may be the absence of a sub-pulmonary pump which limits normal increases in pulmonary pressures, trans-pulmonary flow requirements and cardiac output. If so, performance will be exquisitely dependent on pulmonary vascular resistance. This provides a potential explanation as to why pulmonary vasodilators may improve exercise tolerance. As has recently been demonstrated, these agents may offer an important new treatment strategy which directly addresses the physiological limitations in the Fontan patient.