The 6th World Symposium on Pulmonary Hypertension, pre-capillary pulmonary hypertension (PH) has been defined as mean pulmonary arterial pressure (mPAP) >20 mm Hg with a pulmonary arterial wedge pressure (PAWP) ≤15 mm Hg and pulmonary vascular resistance (PVR) ≥3 Wood units (WU). The current classification of PH categorizes clinical conditions associated with PH based on similar pathophysiology, etiologies, clinical presentation, hemodynamic characteristics and therapeutic management. PH is classified into five groups. The group 1 pulmonary arterial hypertension (PAH), which comprises of diverse diseases that result in similar pathological changes within the pulmonary vasculature. This includes idiopathic, familial, drug and toxin induced PAH and associated forms of PAH like systemic sclerosis, portal hypertension, congenital heart disease and human immunodeficiency virus (HIV). The remaining 4 groups of PH are secondary to other conditions and are usually referred to as secondary PH

Right Heart Catheterization (RHC) is the diagnostic gold standard for pulmonary hypertension (PH), In fact, RHC is the definitive diagnostic technique for reliably confirming whether a patient has PAH .In addition to its use in diagnosis, RHC provides useful information on the degree of hemodynamic impairment, determines response to PAH therapy and establishes prognosis, thereby informing clinical decision-making in the management of PAH. Acute vaso-reactivity test (AVT) is defined as "a fall of at least 10 mmHg in mean pulmonary artery pressure (PAP); a fall to an absolute mean PAP less than 40 mmHg; and unchanged or increased cardiac output". AVT is typically performed with a short-acting agent such as inhaled nitric oxide, inhaled iloprost, intravenous epoprostenol, or adenosine. Baseline hemodynamic measurements are obtained prior to testing. AVT is performed for three reasons in pulmonary hypertension (PH): 1) identification of patients who may display a favorable long-term response to calcium channel blocker treatment, 2) gathering prognostic information,3) scientific research purposes.

The aim of this study is to evaluate the safety and efficacy of nebulized nitroglycerin as a vaso-reactive agent in pulmonary arterial hypertension.

Inclusion Criteria:

• All adult patients with clinical and echocardiographic features suggestive of pulmonary hypertension after exclusion of all secondary causes.

Exclusion Criteria:

• groups 2,3,4,5 Pulmonary hypertension
• Hemodynamic instability.
• Absolute contraindications to pulmonary artery catheter (PAC) placement include: Infection at the insertion site The presence of a right ventricular assist device Insertion during cardiopulmonary bypass Lack of consent
• Relative contraindications to the placement of a PAC include a coagulopathy (international normalized ratio >1.5), thrombocytopenia (platelet count <50,000/microL), electrolyte disturbances (hypo- or hyper-kalemia, -magnesemia, -natremia, -calcemia), and severe acid-base disturbances (eg, pH <7.2 or >7.5).