Comparison of the effect of inhaled nitric oxide and intravenous nitroglycerine on hypoxia-induced pulmonary hypertension in pigs:

Estimation of pulmonary arterial pressure by a neural network analysis using features based on time-frequency representations of the second heart sound

The objective of the study was to develop a non-invasive method for the estimation of pulmonary arterial pressure (PAP) using a neural network (NN) and features extracted from the second heart sound (S2). To obtain the information required to train and test the NN, an animal model of pulmonary hypertension (PHT) was developed, and nine pigs were investigated. During the experiments, the electrocardiogram, phonocardiogram and PAP were recorded. Subsequently, between 15 and 50 S2 heart sounds were isolated for each PAP stage and for each animal studied. A Coiflet wavelet decomposition and a pseudo smoothed Wigner-Ville distribution were used to extract features from the S2 sounds and train a one-hidden-layer NN using two-thirds of the data. The NN performance was tested on the remaining one-third of the data. NN estimates of the systolic and mean PAPs were obtained for each S2 and then ensemble averaged over the 15-50 S2 sounds selected for each PAP stage. The standard errors between the mean and systolic PAPs estimated by the NN and those measured with a catheter were 6.0 mmHg and 8.4 mmHg, respectively, and the correlation coefficients were 0.89 and 0.86, respectively. The classification accuracy, using 23 mmHg mean PAP and 30 mmHg systolic PAP thresholds between normal PAP and PHT, was 97% and 91%, respectively.

Inhalation of nebulized nitroglycerin in dogs with experimental pulmonary hypertension induced by U46619

BACKGROUND

Pulmonary hypertension (PH) causes mortality in some congenital and acquired heart and lung diseases. However, inhalation of NO gas requires complicated and expensive instruments and elaborate preparations to avoid toxic gas administration. We tested the effectiveness and safety of inhaled nebulized nitroglycerin (Neb-NTG) in dogs with experimental PH.

METHODS

Experimental PH was induced by continuous infusion of a thromboxane analog (U46619). The U46619 infusion rate was adjusted to maintain a systolic pulmonary artery pressure (PAP) at 40 mmHg in 10 anesthetized and mechanically ventilated dogs. Then, 20 micrograms/kg of NTG liquid nebulized by compressed air was inhaled.

RESULTS

After infusion of U46619, the systolic, diastolic and mean PAP increased by 119%, 228% and 169%, respectively, and the systolic, diastolic and mean systemic arterial pressures (SAP) increased by 19%, 29% and 23%, respectively. The systolic pulmonary to systemic pressure ratio (Pp/Ps) and mean Pp/Ps increased by 83% and 113%, respectively, and the pulmonary vascular resistance (PVR), systemic vascular resistance (SVR) and pulmonary to systemic resistance ratio (Rp/Rs) increased by 341%, 100% and 145%, respectively. After inhalation of Neb-NTG in dogs with experimental PH, systolic, diastolic and mean PAP and PVR decreased by 25 +/- 4, 26 +/- 11, 25 +/- 9 and 31 +/- 21%, respectively. There were no significant changes in systolic, diastolic and mean SAP, SVR, cardiac output and plasma methemoglobin concentrations. The systolic and mean Pp/Ps decreased by 18 +/- 7 and 20 +/- 7%, respectively. The Rp/Rs decreased by 25 +/- 13%.

CONCLUSIONS

The results of this study demonstrate that Neb-NTG is an effective and selective pulmonary vasodilator and may offer a new therapeutic option for PH.

Treatment of pulmonary hypertension during surgery with nitric oxide and vasodilators

PURPOSE

To describe the effects of the combination of several therapies on the pulmonary circulation and cardiac function in a patient with severe pulmonary hypertension.

CLINICAL FEATURES

We report the case of a female patient with chronic secondary pulmonary hypertension and cardiac failure who underwent right hemicolectomy under general anesthesia. Insertion of a pulmonary artery catheter before the operation revealed pulmonary artery pressure (PAP) of 55/24 mm Hg which was lowered moderately by 40 parts per million (ppm) inhNO. During surgery, the patient presented an episode of atrial fibrillation with a slow, irregular heart rate of 45-50 min(-1) and variable systemic pressure. A dipyridamole DPD (0.2 mg x kg(-1)) bolus stabilized systemic pressure and increased heart rate and cardiac output. However, PAP did not change. Nitroglycerine infusion was started at 10 mg x hr(-1) shortly after the initiation of DPD. The patient responded favourably to combined inhNO, intravenous DPD and NTG therapy with a marked and sustained reduction of PAP and a systemic hemodynamic stability.

CONCLUSION

We conclude that: 1) in combination with inhNO, DPD does not augment the inhNO-induced decrease in PAP; 2) DPD improves the hemodynamic profile and elevates cardiac output; 3) therapeutic combination (inhaled NO, NTG, DPD) has a potent effect on pulmonary pressure in cardiac failure patients.

Inhaled nitric oxide: clinical applications, indications, and toxicology

PURPOSE

Although the analogy of nitric oxide (NO) to Endothelium-derived Relaxing Factor remains controversial, medical use of exogenous NO gas by inhalation has grown exponentially. This review presents the mechanisms of action of inhaled NO in pulmonary hypertension, hypoxaemia, inflammation and oedema, as well as its therapeutic and diagnostic indications with emphasis on acute respiratory distress syndrome (ARDS) and toxicology.

SOURCE

Two medical databases (Current Contents, Medline) were searched for citations containing the above-mentioned key words to December 1996. Moreover, many presentations in congresses such as 4th International Meeting of Biology of Nitric Oxide, 52nd and 53rd Annual Meeting of Canadian Anaesthetists' Society or 10th Annual Meeting of European Association of Cardiothoracic Anaesthesiologists were used.

PRINCIPAL FINDINGS

Inhaled NO is now recognized as an invaluable tool in neonatal and paediatric critical care, and for heart/lung surgery. Other clinical applications in adults, such as chronic obstructive pulmonary disease and ARDS, require a cautious approach. The inhaled NO therapy is fairly inexpensive, but it would seem that it is not indicated for everybody with regards to the paradigm of its efficiency and potential toxicity. The recent discovery of its anti-inflammatory and extrapulmonary effects open new horizons for future applications.

CONCLUSION

Clinical use of inhaled NO was mostly reported in case series, properly designed clinical trials must now be performed to establish its real therapeutic role. These trials would permit adequate selection of the cardiopulmonary disorders, and subsequently the patients that would maximally benefit from inhaled NO therapy.