Echocardiographic assessment of right ventricular contractile reserve in healthy subjects.

BACKGROUND: Exercise-induced increase in pulmonary artery systolic pressure (PASP) as a possible measure of right ventricular (RV) contractile reserve has been shown to predict survival in severe pulmonary hypertension. However, RV contractile reserve can also be measured by changes in stroke volume (SV), tricuspid annular plane systolic excursion (TAPSE), or tricuspid annular systolic velocity (S'). The limits of normal values and the functional significance of these changes in healthy subjects are not well known. METHODS: In this prospective study, 90 healthy subjects (45 male, mean age 39 ± 13 years) underwent exercise stress echocardiography with measurement of TAPSE, S', TAPSE/PASP, SV, and PASP at rest and peak exercise. Maximum and minimum normal values were reported for all indices. RESULTS: Normal values of exercise-induced changes (Δ) were 4 to 10 mm for TAPSE, 6 to 14 cm/s for S', 12 to 57 mm Hg for PASP, 0 to 96 mL for SV, and -1.2 to 0 mm/mm Hg for TAPSE/PASP. At peak exercise, women showed lower ΔTAPSE/PASP, ΔPASP, ΔS', and ΔSV, but higher TAPSE/PASP than men. Aging was associated with decreased ΔTAPSE/PASP, ΔTAPSE, ΔS', ΔPASP, and ΔSV. In addition, ΔS', ΔTAPSE/PASP, ΔPASP, and ΔSV, but not ΔTAPSE, were directly correlated with maximum workload. CONCLUSIONS: Our results provide age- and sex-related limits of normal for RV contractile reserve as assessed by exercise stress echocardiography and demonstrate that RV systolic function indices (PASP, TAPSE, S', and TAPSE/PASP) correlate with maximum exercise capacity.

Effects of epoprostenol and sildenafil on right ventricular function in hypoxic volunteers: a tissue Doppler imaging study.

Sildenafil and epoprostenol are effective therapies in pulmonary arterial hypertension (PAH). Both drugs increase cardiac output, which has been in part attributed to improved right ventricular (RV) contractility. We therefore used tissue Doppler imaging (TDI) to test whether sildenafil and epoprostenol might differently affect RV function in normal subjects before and after induction of acute hypoxic pulmonary hypertension. Ten healthy volunteers underwent this randomized, double-blind, placebo-controlled cross-over study. Echocardiographic measurements were obtained 60 min after the intake of a placebo or 50 mg sildenafil or under 8 ng/kg/min iv epoprostenol, in normoxia or after 60 min of hypoxic breathing (FIO(2) of 0.12). Right ventricular systolic function was assessed by systolic strain (ε), strain rate (SR), isovolumic contraction acceleration (IVA) and tricuspid annulus plane systolic excursion (TAPSE), and diastolic function by tricuspid annulus E/A ratio and isovolumic relaxation time related to RR interval (IRT/RR). Pulmonary artery pressure was calculated from the acceleration time of pulmonary flow and cardiac output from the left ventricular outflow tract flow-velocity. Hypoxia increased pulmonary vascular resistance (PVR) by 78%, did not affect indices of RV systolic function, decreased E/A and increased IRT/RR. Epoprostenol more than sildenafil increased cardiac output, apical ε and TAPSE, the latter in proportion to decreased PVR. In addition, apical SR was increased only by epoprostenol. None of the drugs affected IVA, basal SR, E/A and IRT/RR. These results are not suggestive of intrinsic positive inotropic effects of either sildenafil or epoprostenol at maximal doses tolerated by normal subjects.

Effects of acetazolamide on aerobic exercise capacity and pulmonary hemodynamics at high altitudes.

Aerobic exercise capacity is decreased at altitude because of combined decreases in arterial oxygenation and in cardiac output. Hypoxic pulmonary vasoconstriction could limit cardiac output in hypoxia. We tested the hypothesis that acetazolamide could improve exercise capacity at altitude by an increased arterial oxygenation and an inhibition of hypoxic pulmonary vasoconstriction. Resting and exercise pulmonary artery pressure (Ppa) and flow (Q) (Doppler echocardiography) and exercise capacity (cardiopulmonary exercise test) were determined at sea level, 10 days after arrival on the Bolivian altiplano, at Huayna Potosi (4,700 m), and again after the intake of 250 mg acetazolamide vs. a placebo three times a day for 24 h. Acetazolamide and placebo were administered double-blind and in a random sequence. Altitude shifted Ppa/Q plots to higher pressures and decreased maximum O(2) consumption ((.)Vo(2max)). Acetazolamide had no effect on Ppa/Q plots but increased arterial O(2) saturation at rest from 84 +/- 5 to 90 +/- 3% (P < 0.05) and at exercise from 79 +/- 6 to 83 +/- 4% (P < 0.05), and O(2) consumption at the anaerobic threshold (V-slope method) from 21 +/- 5 to 25 +/- 5 ml.min(-1).kg(-1) (P < 0.01). However, acetazolamide did not affect (.)Vo(2max) (from 31 +/- 6 to 29 +/- 7 ml.kg(-1).min(-1)), and the maximum respiratory exchange ratio decreased from 1.2 +/- 0.06 to 1.05 +/- 0.03 (P < 0.001). We conclude that acetazolamide does not affect maximum exercise capacity or pulmonary hemodynamics at high altitudes. Associated changes in the respiratory exchange ratio may be due to altered CO(2) production kinetics.

Effects of sildenafil on exercise capacity in hypoxic normal subjects.

The phosphodiesterase-5 inhibitor sildenafil has been reported to improve hypoxic exercise capacity, but the mechanisms accounting for this observation remain incompletely understood. Sixteen healthy subjects were included in a randomized, double-blind, placebo-controlled, cross-over study on the effects of 50-mg sildenafil on echocardiographic indexes of the pulmonary circulation and on cardiopulmonary cycle exercise in normoxia, in acute normobaric hypoxia (fraction of inspired O2, 0.1), and then again after 2 weeks of acclimatization at 5000 m on Mount Chimborazo (Ecuador). In normoxia, sildenafil had no effect on maximum VO2 or O2 saturation. In acute hypoxia, sildenafil increased maximum VO2 from 27 +/- 5 to 32 +/- 6 mL/min/kg and O2 saturation from 62% +/- 6% to 68% +/- 9%. In chronic hypoxia, sildenafil did not affect maximum VO2 or O2 saturation. Resting mean pulmonary artery pressure increased from 16 +/- 3 mmHg in normoxia to 28 +/- 5 mmHg in normobaric hypoxia and 32 +/- 6 mmHg in hypobaric hypoxia. Sildenafil decreased pulmonary vascular resistance by 30% to 50% in these different conditions. We conclude that sildenafil increases exercise capacity in acute normobaric hypoxia and that this is explained by improved arterial oxygenation, rather than by a decrease in right ventricular afterload.

A simple echocardiographic score for the diagnosis of pulmonary vascular disease in heart failure.

AIMS: A simple echocardiographic score was designed for diagnosing precapillary vs postcapillary pulmonary hypertension and for discriminating between isolated postcapillary pulmonary hypertension (Ipc-PH) and combined precapillary and postcapillary pulmonary hypertension (Cpc-PH). METHODS: The score comprised 7 points (2 for E/e' ratio ≤10, 2 for a dilated non-collapsible inferior vena cava, 1 for a left ventricular eccentricity index ≥1.2, 1 for a right-to-left heart chamber dimension ratio >1 and 1 for the right ventricle forming the heart apex) and was applied to 230 consecutive patients referred for evaluation of pulmonary hypertension. RESULTS: Precapillary pulmonary hypertension and postcapillary pulmonary hypertension were diagnosed in 160 and 70 patients, respectively. In the latter, Ipc-PH was found in 51 and Cpc-PH in 19. The echo score was higher in precapillary vs postcapillary pulmonary hypertension patients (4.2 ±â€Š1.7 vs 1.6 ±â€Š1.7, P < 0.001) and in patients with Cpc-PH vs Ipc-PH (2.7 ±â€Š2.1 vs 1.2 ±â€Š1.3, P = 0.001). The sensitivity and specificity of the echo score at least 2 for precapillary pulmonary hypertension were 99 and 54%, respectively (area under the curve 0.85). In patients with postcapillary pulmonary hypertension, the sensitivity and specificity of the echo score at least 2 for Cpc-PH were 63 and 82% (area under the curve 0.73). CONCLUSION: A simple echocardiographic score helps in the differential diagnosis between precapillary and postcapillary pulmonary hypertension, and between Ipc-PH and Cpc-PH.

Echocardiographic prediction of pre- versus postcapillary pulmonary hypertension.

BACKGROUND: The differential diagnosis between pre- and postcapillary pulmonary hypertension (PH) is of major therapeutic relevance and thus requires optimal clinical probability assessment with echocardiography. METHODS: We prospectively analyzed 152 consecutive patients referred to a PH center over a 1-year period undergoing quasi-simultaneous (within 1 hour) echocardiography and right heart catheterization. Echocardiography was performed as usually recommended for the assessment of PH and left heart conditions. PH was defined as a mean pulmonary artery pressure ≥ 25 mm Hg. Postcapillary PH was diagnosed on the basis of a pulmonary capillary wedge pressure >15 mm Hg. RESULTS: Ten of 152 patients (7%) had no PH, 81 of 152 (53%) had precapillary PH, and 61 of 152 (40%) had postcapillary PH. The following five echocardiographic variables were found to predict precapillary PH: right heart chamber larger than the left (P = .0018), left ventricular eccentricity index > 1.2 (P = .0039), dilated inferior vena cava without inspiratory collapse (P = .0076), E/e' ratio ≤ 10 (P = .00001), and the right ventricle forming the heart apex (P = .0144). Beta coefficients from multiple logistic regression were significant for dilated inferior vena cava without inspiratory collapse (P = .0464) and E/e' ratio ≤ 10 (P = .0002). The score based on ß coefficients, ranging from 3 to 34 points, resulted in optimal discrimination at >5, with a positive predictive value of 67.9% and a negative predictive value of 77.5% for precapillary PH. CONCLUSION: Echocardiography enables a clinically satisfactory differential diagnosis between pre- and postcapillary PH.

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

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

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

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

Right and left ventricular adaptation to hypoxia: a tissue Doppler imaging study.

Hypoxia has been reported to alter left ventricular (LV) diastolic function, but associated changes in right ventricular (RV) systolic and diastolic function remain incompletely documented. We used echocardiography and tissue Doppler imaging to investigate the effects on RV and LV function of 90 min of hypoxic breathing (fraction of inspired O(2) of 0.12) compared with those of dobutamine to reproduce the same heart rate effects without change in pulmonary vascular tone in 25 healthy volunteers. Hypoxia and dobutamine increased cardiac output and tricuspid regurgitation velocity. Hypoxia and dobutamine increased LV ejection fraction, isovolumic contraction wave velocity (ICV), acceleration (ICA), and systolic ejection wave velocity (S) at the mitral annulus, indicating increased LV systolic function. Dobutamine had similar effects on RV indexes of systolic function. Hypoxia did not change RV area shortening fraction, tricuspid annular plane systolic excursion, ICV, ICA, and S at the tricuspid annulus. Regional longitudinal wall motion analysis revealed that S, systolic strain, and strain rate were not affected by hypoxia and increased by dobutamine on the RV free wall and interventricular septum but increased by both dobutamine and hypoxia on the LV lateral wall. Hypoxia increased the isovolumic relaxation time related to RR interval (IRT/RR) at both annuli, delayed the onset of the E wave at the tricuspid annulus, and decreased the mitral and tricuspid inflow and annuli E/A ratio. We conclude that hypoxia in normal subjects is associated with altered diastolic function of both ventricles, improved LV systolic function, and preserved RV systolic function.