Resting two dimensional (2-D)- and M-mode echocardiography is an accurate and reproducible technique for assessing left ventricular and atrial size and performance in normal-sized hearts without segmental myocardial disease. Echocardiograms can be successfully recorded in selected subjects during various types of exercise (2). However, in various studies, exercise echocardiographic evaluations of the selected parameters was carried out from 0 to 30 s after the end of maximal power output (3,5,11,12,14) or at submaximal exercise levels (2,6,20,23,24,26), but not during exhaustion. Rowland et al. (18) used the Doppler technique to compare cardiac response (estimation of stroke volume) with maximal cycle exercise in prepubertal boys and young men, but they did not measure changes immediately post exercise. To characterize cardiovascular response to maximal cycle exercise using echocardiographic dimension measurement, Rowland et al. (19) investigated a group of young patients with myocardial dysfunction and healthy children. But there was again no information about changes immediately post exercise and changes in respect to gender.
Therefore, the aim of this study was to evaluate differences in the left atrial (LAD), total ventricular end-diastolic (TEDD), end-systolic diameters (TESD), and left ventricular shortening fraction (SF) compared with heart rate (HR) and systolic blood pressure (SBP) at rest, at the end of each of the three phases of energy supply, and during recovery in young male and female subjects.
A group of healthy young male (N = 15, mean age 26 ± 4 yr, mean height 180 ± 4 cm, mean body mass 78 ± 6 kg) and female (N = 16, mean age 24 ± 2 yr, mean height 168 ± 4 cm, mean body mass 62 ± 6 kg) subjects was investigated. Resting echocardiography (2-D-mode, color Doppler) revealed that no subject had valvular disease, hypertensive heart disease, or dilated cardiomyopathy. All subjects were in sinus rhythm without bundle-branch block. No subject received cardioactive medication. Informed consent was obtained from all subjects, and the institutional ethics committee for protection of human subjects from research risks of the University of Vienna, Austria, approved the study.
Each subject performed an incremental exercise test on a cycle ergometer (Excalibur-Sport, Lode, Groningen, The Netherlands) in an upright position to the limit of tolerance. Subjects were required to rest their arms on a steering bar and to lean their upper body forward. The initial level was 20 W, and increments of 20 W for male subjects and 15 W for female subjects were added every 60 s until the intensity limit of each individual was obtained. HR was recorded continuously for 5-s increments with a Sporttester Polar VANTAGE NV (Polar Electro, Finland). SBP was measured by auscultation at rest, at the end of each exercise and during recovery. Capillary blood sample for determination of lactic acid concentration (LA) measurement was collected from the hyperemic ear lobe (13) at rest, during the last 10 s of each increment, and at the end of the exercise test. Whole blood LA was measured by an enzymatic-amperometric method (EBIO 6666, Eppendorf-Nethler-Hinz GmbH, Hamburg, Germany). Respiratory gas exchange measures, specifically, pulmonary ventilation (V̇E), carbon dioxide production (V̇CO2), and oxygen uptake (V̇O2) were measured continuously by an open air spirometry via metabolic cart (Oxycon Alpha, Jäger, Germany).
A computer-aided iterative calculation of the point of intersection of two regression lines with minimal standard deviation of the two straight lines was used to determine turn points in the time course of measured variables (PA7000, Leitner, Austria). According to Skinner and McLellan (22), LA performance curves were used to determine three phases of energy supply. Two lactate turn points (LTP1 and LTP2) were defined. LTP1 was defined as the point where the LA level began to increase systematically above resting values, which is comparable to the “lactate threshold” (1) and shows a relationship to the “anaerobic threshold” according to Wassermann and McIlroy (25). LTP2 was defined as the second abrupt increase of LA, the “so-called” lactate turn point according to Davis et al. (4). Both LTP1 and LTP2 were analyzed as previously described (8–10,15–17). LTP1 was determined exclusively between the first LA value and 75% of the maximal performance (Pmax); LTP2 was determined exclusively between predetermined LTP1 and the LA value at Pmax. By using respiratory gas exchange variables likewise, two turn points were defined (1): 1) turn point of the V̇E/V̇O2 ratio (V̇E/V̇O2TP) and 2) turn point of the V̇E/V̇CO2 ratio (V̇E/V̇CO2TP) (16,21). According to our previous studies, LA performance curves and respiratory gas exchange variables were used to define three phases of energy supply (16,21,22).
Two-dimensional echocardiograms were performed in all subjects using a commercially available instrument (GE Ving Med ULTRASOUND AS CVFM 800 and 3.5- MHz transducer, Horten, Norway) at rest (R) for each intensity, immediately within 15 s post, and 6 min after exercise by means of 2-D images in the parasternal long-axis. We used VINGMED’s “Anatomical M-Mode,” equipped with a special mode feature that makes it possible to extract M-Mode Sweeps from stored 2-D-Loops and perform the M-Mode measurements just distal to the tips of the mitral valve leaflets and to the tips of the aortic valve leaflets. Echocardiographic calculations were conducted for the loops from rest to the last intensity of each phase of energy supply and, immediately within 15 s post, and 6 min after exercise. For each measurement interval at rest, during exercise, and recovery, three consecutive heart beats were measured, and a single most representative and regular heart beat dimensions for a given condition were used for calculation and data inclusion. In our calculations, we found that averaging three consecutive heart beats measured during echocardiography did not produce better results than utilizing a single heart beat measured during any of the above described conditions. For the evaluation of the exercise-dependent heart dimensions, total left ventricular end-diastolic dimension (TEDD), total left ventricular end-systolic dimension (TESD), and left atrial dimension (LAD) as well as left ventricular-shortening fraction (SF) were determined. The greatest distance from the anterior edge of the ventricular septum to the left ventricular epicardial echo was recorded TEDD. The TESD was determined as the shortest distance from the post wall epicardial echo in systole to the anterior edge of the ventricular septum. EDD and ESD were calculated from TEDD and TESD deducting posterior wall thickness and ventricular septum thickness. SF was calculated as the quotient as follows: ([EDD − ESD]/ESD × 100).
The results are expressed as means ± standard deviation (SD). Analysis of variance (ANOVA) with repeated measures was used to evaluate differences in the time course of P, HR, SBP, LA, V̇O2, TEDD, TESD, LAD, and SF. Post hoc comparisons were made employing the least-significant differences test. Correlational analysis for the group was also conducted for values measured during maximal performance and values obtained during 15-s post maximal exercise.
Tables 1 and 2 show the values of P, HR, LA, and V̇O2 at rest, V̇E/V̇O2TP, LTP1, V̇E/V̇CO2TP, LTP2, and Pmax. No significant differences were found for P, HR, LA, and V̇O2 and between V̇E/V̇O2TP, and LTP1 as well as between V̇E/V̇CO2TP and LTP2.
A significant (P < 0.001) decrease in TEDD for both male and female subjects was found only between III and 15 s, and a significant increase (P < 0.001) between 15 s and 6 min (Fig. 1). In male subjects, TESD decreased significantly between rest and I, and between I and II (P < 0.05). There was also a significant decrease for TESD during exercise in female subjects between rest and I (P < 0.05). No significant changes were found for TESD between II and III for both sexes. Similar to TEDD, TESD in both sexes significantly decreased from III to 15 s and increased from 15 s to 6 min (Fig. 2) (P < 0.001). SF significantly increased from rest to I in both sexes, but this change was only significant from I to II in male subjects (P < 0.01). No significant changes were found for SF between II and III for both sexes. A significant increase in SF was observed in both sexes from I to 15 s, whereas SF significantly decreased from 15 s to 6 min (P < 0.01) (Fig. 3). In Figure 4, a significant dilatation (P < 0.001) of the LAD from rest to I is shown in both sexes and also in male subjects from I to II. During recovery, this dilatation disappeared from III to 15 s and 6 min (Fig. 4). HR presented the typical behavior shown in the literature (10). In contrast to the changes in heart dimensions from III to 15 s, the decrease in HR was not significant (P > 0.05) (Fig. 5). Significant change in SBP was found for both sexes between rest, all exercise levels, and during recovery (Fig. 6). Correlation between maximal performance in III and values obtained within 15 s immediately after maximal performance were all significant (P < 0.0001) and yielded an r2 = 0.87 for TEDD, an r2 = 0.85 for TESD, an r2 = 0.72 for LAD, an r2 = 0.62 for EF, and for SF an r2 = 0.51.
In a group of young, healthy male and female subjects, this study intended to demonstrate changes in left atrial and ventricular heart dimensions during incremental cycle ergometer exercise and immediately after exercise.
To optimize echocardiographic imaging, numerous clinical settings have the subject perform maximal upright exercise followed by a quick supine positioning after exercise to allow imaging in the conventional position. This approach optimizes imaging but compromises exercise imagery in favor of recovery (7). Our results indicate that post exercise measurements of left ventricular and atrial dimensions or SF were not valid to describe heart function at maximal exercise, although, immediately post exercise, HR and SBP were near maximal level. Left ventricular dimensions changed rapidly during first 15 s of recovery. In our investigation, we found that there was a rapid decrease in left ventricular dimensions; however, the values measured within the 15 s after maximal performance were well correlated with left ventricular dimensions, reflecting near maximal performance. This change in left ventricular dimensions occurred in all subjects without exception.
An exercise-dependent reversible dilatation of the left atrium was found in both genders. The reduction in the dimension of the left atrium (in contrast to the decrease in the dimensions of the left ventricle immediately post exercise) was comparable with the reduction of HR and SBP during recovery. These continuous reductions of dimensions of the left atrium lasting several minutes have to be addressed in the context of the decrease in cardiac load that can be observed also in the rate pressure product. The immediate shortening of the left ventricle to lower than resting values occurs within the first seconds after termination of maximal exercise. This reaction of the left ventricle is related to the changes in hemodynamic conditions. Obviously, preload is markedly reduced due to a reduced venous return.
Peters and Silberstein (14) reported in a pulse wave Doppler transmitral flow velocity study the attainment of images within seconds of stopping exercise while still at or very close to the true peak heart rate. The suggestion of these authors that the patterns seen in their study are primarily the effect of exercise are not supported by our data. Near maximal heart rate and minimally reduced SBP immediately after termination of maximal exercise may not lead to the assumption that measures of cardiac function immediately post exercise are representative of cardiac function during maximal or submaximal exercise. Di Bello et al. (5) investigated end-diastolic and end-systolic left ventricular volumes by means of 2-D echo in a four-chamber view using an area × length formula. Compared with our results, these authors found similar dimensional changes of the left ventricle during exercise. A comparison between their measures and our results during early recovery was not possible, as they measured echo only 4 min post exercise.
Measured dimensions were lower in female subjects, mostly due to the lower body mass. But no sex-specific differences of the relative changes of dimensions during exercise and recovery were found for the left ventricle and the left atrium, respectively.
We did not use invasive methods to measure ventricular and atrial dimensions and the myocardial function, as these were deemed inappropriate in a healthy asymptomatic population. Echocardiographic studies during exercise are more difficult to interpret than radionuclide studies because the greater expansion of the lungs and the higher respiratory frequency during exercise reduce the acoustic window (7). The best echocardiographic approach is usually in the supine left decubitus position. Acquiring images during maximal upright exercise is usually quite difficult. Our subjects in this investigation were required to rest theirs arms on a steering bar and to lean their upper body forward. This technique seems to be optimal to obtain quality echocardiographic images during maximal exercise in upright position. Additionally, our subjects were young, healthy, and slender and therefore well suited for the echocardiographic study. In cases where subjects exhibited a poor quality of their echocardiographic images obtained during exercise, subjects were excluded from the analysis. In contrast to usually used radionuclide angiographic images with a acquisition time between 90 and 180 s (15), this technique allowed the evaluation of single heart actions immediately after termination of maximal exercise. By using VINGMED’s “Anatomical M-Mode,” it was possible to extract M-Mode Sweeps from stored 2-D-Loops. The measures of the dimensions and the calculation of SF were determined after the exercise test, which allowed us to choose only images of good echocardiographic quality for further analysis. This was especially important for the analysis of images during maximal exercise and during early recovery (15 s).
Our study presented no changes in the end-diastolic dimension during exercise; therefore, end-diastolic dimension seems to be a less useful parameter for evaluating left ventricular function during physical stress in healthy subjects. In healthy subjects, the end-systolic dimension during exercise only decreased from rest up to phase II of the energy supply but did not significantly change during phase III. The greatest changes in left ventricular dimensions were observed immediately post exercise.
A reversible dilatation of the left atrium was found during exercise in healthy subjects. Therefore, post exercise measurements of left ventricular and atrial dimensions or SF are not valid to describe heart function during exercise, although HR and SBP were still near maximal level.
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Keywords:© 2000 Lippincott Williams & Wilkins, Inc.
ECHOCARDIOGRAPHY; HEART DIMENSIONS; EXERCISE; LACTATE; RESPIRATORY GAS EXCHANGE VARIABLES