Left ventricular systolic performance during prolonged strenuous exercise in female triathletes

BACKGROUND: The effect of prolonged strenuous exercise (PSE) on left ventricular (LV) systolic function has not been well studied in younger female triathletes. This study examined LV systolic function prior to, during and immediately following PSE (i.e., 40 km bicycle time trial followed by a 10 km run) in 13 younger (29 PlusMinus; 6 years) female triathletes. METHODS: Two-dimensional echocardiographic images were obtained prior to, at 30-minute intervals during and immediately following PSE. Heart rate, systolic blood pressure, end-diastolic and end-systolic cavity areas were measured at each time point. Echocardiographic and hemodynamic measures were also combined to obtain LV end-systolic wall stress and myocardial contractility (i.e., systolic blood pressure - end-systolic cavity area relation). RESULTS: Subjects exercised at an intensity equivalent to 90 PlusMinus; 3% of maximal heart rate. Heart rate, systolic blood pressure, systolic blood pressure - end-systolic cavity area relation and fractional area change increased while end-diastolic and end-systolic cavity areas decreased during exertion. CONCLUSIONS: PSE is associated with enhanced LV systolic function secondary to an increase in myocardial contractility in younger female triathletes.     

Left ventricular systolic and diastolic function during tilt-table positioning and passive heat stress in humans

The ventricular response to passive heat stress has predominantly been studied in the supine position. It is presently unclear how acute changes in venous return influence ventricular function during heat stress. To address this question, left ventricular (LV) systolic and diastolic function were studied in 17 healthy men (24.3 ± 4.0 yr; mean ± SD), using two-dimensional transthoracic echocardiography with Doppler ultrasound, during tilt-table positioning (supine, 30° head-up tilt, and 30° head-down tilt), under normothermic and passive heat stress (core temperature 0.8 ± 0.1°C above baseline) conditions. The supine heat stress LV volumetric and functional response was consistent with previous reports. Combining head-up tilt with heat stress reduced end-diastolic (25.2 ± 4.1%) and end-systolic (65.4 ± 10.5%) volume from baseline, whereas heart rate (37.7 ± 2.0%), ejection fraction (9.4 ± 2.4%), and LV elastance (37.7 ± 3.6%) increased, and stroke volume (-28.6 ± 9.4%) and early diastolic inflow (-17.5 ± 6.5%) and annular tissue (-35.6 ± 7.0%) velocities were reduced. Combining head-down tilt with heat stress restored end-diastolic volume, whereas LV elastance (16.8 ± 3.2%), ejection fraction (7.2 ± 2.1%), and systolic annular tissue velocities (22.4 ± 5.0%) remained elevated above baseline, and end-systolic volume was reduced (-15.3 ± 3.9%). Stroke volume and the early and late diastolic inflow and annular tissue velocities were unchanged from baseline. This investigation extends previous work by demonstrating increased LV systolic function with heat stress, under varied levels of venous return, and highlights the preload dependency of early diastolic function during passive heat stress.     

Left ventricular systolic torsion correlates global cardiac performance during dyssynchrony and cardiac resynchronization therapy

Left ventricular (LV) systolic torsion is a primary mechanism contributing to stroke volume (SV). We hypothesized that change in LV torsion parallels changes in global systolic performance during dyssynchrony and cardiac resynchronization therapy (CRT). Seven anesthetized open chest dogs had LV pressure-volume relationship. Apical, basal, and mid-LV cross-sectional echocardiographic images were studied by speckle tracking analysis. Right atrial (RA) pacing served as control. Right ventricular (RV) pacing simulated left bundle branch block. Simultaneous RV-LV free wall and RV-LV apex pacing (CRTfw and CRTa, respectively) modeled CRT. Dyssynchrony was defined as the time difference in peak strain between earliest and latest segments. Torsion was calculated as the maximum difference between the apical and basal rotation. RA pacing had minimal dyssynchrony (52 ± 36 ms). RV pacing induced dyssynchrony (189 ± 61 ms, P < 0.05). CRTa decreased dyssynchrony (46 ± 36 ms, P < 0.05 vs. RV pacing), whereas CRTfw did not (110 ± 96 ms). Torsion during baseline RA was 6.6 ± 3.7°. RV pacing decreased torsion (5.1 ± 3.6°, P < 0.05 vs. control), and reduced SV, stroke work (SW), and dP/dt(max) compared with RA (21 ± 5 vs. 17 ± 5 ml, 252 ± 61 vs. 151 ± 64 mJ, and 2,063 ± 456 vs. 1,603 ± 424 mmHg/s, respectively, P < 0.05). CRTa improved torsion, SV, SW, and dP/dt(max) compared with RV pacing (7.7 ± 4.7°, 23 ± 3 ml, 240 ± 50 mJ, and 1,947 ± 647 mmHg/s, respectively, P < 0.05), whereas CRTfw did not (5.1 ± 3.6°, 18 ± 5 ml, 175 ± 48 mJ, and 1,699 ± 432 mmHg/s, respectively, P < 0.05). LV torsion changes covaried across conditions with SW (y = 0.94x+12.27, r = 0.81, P < 0.0001) and SV (y = 0.66x+0.91, r = 0.81, P < 0.0001). LV dyssynchrony changes did not correlate with SW or SV (r = -0.12, P = 0.61 and r = 0.08, P = 0.73, respectively). Thus, we conclude that LV torsion is primarily altered by dyssynchrony, and CRT that restores LV performance also restores torsion.     

Left ventricular catecholamines during acute myocardial infarction in the dog

To determine whether changes in left ventricular catecholamine content occur during the first 30 to 90 min of acute myocardial infarction, myocardial catecholamine (radioenzymatic assay) over the interval was studied in the dog. In nine pentobarbital-anesthetized opened-chest dogs without coronary ligation, myocardial catecholamine at 2.5 h after pentobarbital (i) consisted mainly of norepinephrine (87% total catecholamine), (ii) showed a base to apex gradient in norepinephrine (1.44 +/- 0.10 vs. 1.03 +/- 0.10 micrograms/g, p less than 0.05) and dopamine (0.20 +/- 0.03 vs. 0.12 +/- 0.02 micrograms/g, p less than 0.05) but not epinephrine (0.017 vs. 0.016 micrograms/g), and (iii) showed no difference in norepinephrine, dopamine, or epinephrine across basal, mid, and apical left ventricular transverse planes spanning the vascular territories of the two coronary arteries. In 18 pentobarbital-anesthetized dogs with coronary ligation, (i) norepinephrine, measured in 14 regions across the mid left ventricle after 90 min ischemia in four dogs, was less in the ischemic center of the occluded bed than normal myocardium (1.01 +/- 0.04 vs. 1.29 +/- 0.04 micrograms/g, p less than 0.05), and (ii) norepinephrine was unchanged in normal myocardium of 14 dogs at 30, 60, 90 min, and 48 h but decreased in ischemic myocardium by 31% at 60 min (0.89 +/- 0.10 vs. 1.29 +/- 0.08 micrograms/g, p less than 0.025) and 79% at 48 h (0.27 +/- 0.04 vs. 1.26 +/- 0.08 micrograms/g, p less than 0.001). Thus, norepinephrine depletion from ischemic but not normal myocardium is detectable by 60 min during acute myocardial infarction.     

Dynamics of blood pressure, pulse wave transit time and systolic timei intervals during acute gravity changes induced by parabolic flight

To investigate cardiovascular adaptation to transient microgravity (Microgravity), we measured RR intervals (RRI), arterial blood pressure (BP), pulse wave transit time (PTT) and systolic time intervals (STI) during parabolic flight. Our results demonstrate that during microgram RRI, BP and PTT are subject to a rapid adaptation likely mediated by the baroreflex whereas STI changes with microgravity but does not present further adaptation.     

Physiologic modulations of the systolic time intervals in the fetal lamb

To examine the modulation of fetal systolic time intervals of the ovine fetus in relation to fetal maturation, heart rate, respiratory activity, and circadian rhythm, studies were carried out on 13 fetal-maternal sheep preparations. The data obtained showed that there was a significant correlation between the ejection time (ET) and the RR intervals of the electrocardiogram. The pre-ejection period (PEP) and PEP/ET increased in relation to the fetal maturation (38 ms and 0.25 at 120 days to 52 ms and 0.33 at 145 days of gestation, respectively). When the circadian rhythmicity was analyzed, a relative tachycardia was in evidence during the 21- to 03-h period but systolic time intervals remained unchanged. Except for some tachycardia and cardiac rhythm variability, respiratory activity also had no influence on the systolic time intervals.     

Ferroxidases and xanthine oxidase in plasma of healthy newborn infants

In the neonatal period, there is a high iron load, while both the level and molar oxidase activity of ceruloplasmin are low. On the other hand, the neonatal xanthine oxidase (XO) activity is higher than later in life and XO has a significant iron-oxidizing capacity. We therefore studied the physiological contribution of XO to the ferroxidase activity of the plasma in 20 full-term newborn infants. Ferroxidase activity was measured spectrophotometrically, with Fe⁺⁺ as substrate. The uric acid formed by XO was assayed by means of HPLC, with electrochemical detection.

The total ferroxidase activity in the plasma was about one-fourth of the adult level and rapidly increased doubling within 3 days after birth. About 90% of the plasma ferroxidase activity was due to ceruloplasmin, the remainder being accounted for by ferroxidase II. The XO activity underwent a 30% (statistically non-significant) elevation at 24 h, though ferroxidase activity attributable to XO was not detected at any time.

Accordingly, XO does not seem to add substantially to the total iron-oxidizing capacity of the plasma in the neonatal period. The high molar ferroxidase activity is probably of importance at the endothelial cell surface.     

Leptin concentrations are elevated in newborn infants of diabetic mothers

BACKGROUND: Infants of diabetic mothers have been characterized by macrosomia due to hyperinsulinism. A relation has been observed between circulating levels of leptin and the intrauterine growth pattern. METHODS: We studied the leptin and insulin concentrations in the cord blood of 29 newborn infants of mothers with type 1 diabetes (iT1DM), 70 newborn infants of mothers with gestational diabetes and 105 newborn infants of nondiabetic mothers. RESULTS: There were significant differences (p < 0.001) between the 3 groups with the highest leptin levels 24.9 microg/l (range 1.7-94.1) in infants of mothers with iT1DM and the second-highest levels 14.0 microg/l (range 2.6-74.9) in infants of mothers with gestational diabetes (iGDM), whereas the control infants had the lowest leptin levels 10.0 microg/l (range 0.10-45.9). Girls had higher leptin concentrations than boys among the iT1DM and control infants. The insulin concentrations were 18.1 mU/l (range 1.9-123.3), 6.1 mU/l (range 1.1-51.4) and 3.6 mU/l (range 0.5-21.5) in the 3 groups (p < 0.001), respectively. A significant correlation was observed between leptin and insulin concentrations in iGDM and control infants (r = 0.51; p < 0.001 and r = 0.25; p < 0.05). Both absolute and relative birth weights correlated with leptin levels in all 3 groups (r = 0.60, p = 0.01 and r = 0.51, p = 0.05 in iT1DM; r = 0.51 and 0.56, p < 0.001 in iGDM and r = 0.42 and 0.59, p < 0.001 in control infants). CONCLUSION: Our results confirm the relation between leptin concentrations and birth weight. They also suggest that leptin may be involved in the increased accumulation of adipose tissue characteristic of infants of diabetic mothers.     

Ferroxidases and xanthine oxidase in plasma of healthy newborn infants

In the neonatal period, there is a high iron load, while both the level and molar oxidase activity of ceruloplasmin are low. On the other hand, the neonatal xanthine oxidase (XO) activity is higher than later in life and XO has a significant iron-oxidizing capacity. We therefore studied the physiological contribution of XO to the ferroxidase activity of the plasma in 20 full-term newborn infants. Ferroxidase activity was measured spectrophotometrically, with Fe⁺⁺ as substrate. The uric acid formed by XO was assayed by means of HPLC, with electrochemical detection.

The total ferroxidase activity in the plasma was about one-fourth of the adult level and rapidly increased doubling within 3 days after birth. About 90% of the plasma ferroxidase activity was due to ceruloplasmin, the remainder being accounted for by ferroxidase II. The XO activity underwent a 30% (statistically non-significant) elevation at 24 h, though ferroxidase activity attributable to XO was not detected at any time.

Accordingly, XO does not seem to add substantially to the total iron-oxidizing capacity of the plasma in the neonatal period. The high molar ferroxidase activity is probably of importance at the endothelial cell surface.     

Non-invasive evaluation of systolic and diastolic functions of the left ventricle in newborn infants

To assess possible changes in myocardial contractile function and relaxation occurring after mild perinatal asphyxia, maximal blood pressure and M-mode echocardiograms should be registered simultaneously in 32 normal term newborns (group 1) and in 22 term asphyxiated newborns (group II). The slope of end-systolic pressure-dimension relation (ESPDR) was used as a reliable index for evaluation of the myocardial contractility. The slope of ESPDR and some indices of ventricular relaxation decreased in newborns from group II. It is suggested that ESPDR and parameters of left ventricular relaxation and filling can serve as early and sensitive indices of hypoxic myocardial damage.     

Myocardial contractility in chickens (Gallus gallus): analysis of systolic time intervals

The avian cardiovascular system is of special interest because avian hearts are relatively larger than mammalian hearts, and activation of ventricular myocardium in birds has a "flash" pattern. Systolic time intervals and indices of myocardial contractility were examined in anaesthetized open-chest chickens by polycardiography, including synchronous recordings of electrocardiogram, phonocardiogram, and apex cardiogram. The asynchronous contraction time, isometric contraction time, pre-ejection period and ejection time were 26 +/- 3 (Mean +/- SD), 21 +/- 9, 47 +/- 12, and 83 +/- 23 ms, respectively, for heart rates of 260 +/- 57 bpm. The myocardial tension index, isometric contraction index and the pre-ejection period/ejection time ratio were 0.39 +/- 0.11, 0.42 +/- 0.10, and 0.54 +/- 0.14, respectively. A "flash" pattern of ventricular myocardial depolarization causes more rapid excitation and as a consequence shorter asynchronous contraction time of relatively larger chicken hearts compared with rabbit hearts. Inverse relation (P < 0.05) of the asynchronous contraction time to the heart rate in chickens is probably associated with the specific activation pattern of avian ventricles. Establishment of the values of systolic time intervals will facilitate a better understanding of cardiac function in birds. The obtained results are discussed in comparison with the rabbit. The indices calculated from the systolic time intervals show disadvantageous contractile function of chicken heart compared to rabbit heart.