Noninvasive Assessment of Right Ventricle Function and Pulmonary Artery Pressure Using Transthoracic Echocardiography in Women With Pre-Eclampsia: An Exploratory Study

Background and objective

Pre-eclampsia (PEC) is associated with the release of anti-angiogenic factors that are incriminated in raising systemic and pulmonary vascular resistance (PVR). Compared to the left heart and systemic circulation, much less attention has been paid to the right heart and pulmonary circulation in patients with PEC. We used transthoracic echocardiography (TTE) to estimate pulmonary artery (PA) pressure and right ventricular (RV) function in women with PEC.

Materials and methods

We conducted a case-control study at a tertiary care academic center. Ten early PEC (<34-week gestation) and nine late PEC (≥34-week gestation) patients with 11 early and 10 late gestational age-matched controls were enrolled. Two-dimensional TTE was performed on all patients. The estimated mean PA pressure (eMPAP) was calculated based on PA acceleration time (PAAT). PVR was estimated from eMPAP and RV cardiac output (RV CO). RV myocardial performance index (RV MPI), tricuspid annular plane systolic excursion (TAPSE), tissue tricuspid annular displacement (TTAD), and lateral tricuspid annular tissue peak systolic velocity (S’) were measured.

Results

Compared to early controls, in early PEC, the eMPAP and estimated PVR (ePVR) were elevated, PAAT was reduced, RV MPI was increased, TTAD was reduced, and TAPSE and TV S’ were unchanged. Compared to late controls, in late PEC, the eMPAP and ePVR were elevated, PAAT was reduced, and RV MPI was increased, while TAPSE, TTAD, and TV S’ were unchanged.

Conclusions

In a sample of women with PEC, early PEC was found to be associated with increased eMPAP and ePVR and subclinical decrement of RV function as assessed by TTE. TTE may be a useful noninvasive screening tool for early detection of pulmonary hypertension and RV dysfunction in PEC. An adequately powered longitudinal study is needed to determine the implications of these findings on long-term outcomes.

Oxygen-dependent inhibition of respiration in isolated renal tubules by nitric oxide

BACKGROUND

The partial pressure (tension) of oxygen (PO2) in the kidney medulla has been established to be lower than that of the cortex. The kidney medulla has been shown to be particularly sensitive to hypoxia. However, the measured PO2 in the kidney medulla is sufficient to support maximal respiration. It has been recently shown that endogenously produced nitric oxide (NO) may inhibit oxygen consumption in the kidney. We studied whether NO plays a role in hypersensitivity of the kidney medulla to hypoxia.

METHODS

We studied the effect of added NO on isolated cortical and outer medullary renal tubules in simultaneous oxygen consumption and NO measurements at different oxygen concentrations.

RESULTS

We found that NO could potently and reversibly inhibit respiration at nanomolar concentrations. The inhibitory effect of NO was markedly increased at low physiological oxygen concentrations. The effect of NO was cGMP independent because the selective guanylyl cyclase inhibitor 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ) at a 10 microM concentration had no effect on basal or NO-inhibited respiration. The value for half-maximal NO-mediated inhibition of respiration was virtually identical to that found in isolated mitochondria, and therefore, NO was most likely directly acting on mitochondria. Interestingly, we found no differences in sensitivity to NO-mediated inhibition between outer medullary and cortical tubules.

CONCLUSIONS

We suggest that because of its low PO2, the renal outer medulla is more sensitive to hypoxia, not because of the low PO2 as such, but probably because of the competition between NO and oxygen to control respiration.