Patients scheduled to undergo right heart catheterization (RHC) as their standard of care will be included in the study.

The patient will be positioned supine at 0 degrees with normal restful breathing and patient looking straight up. After the right sternocleidomastoid muscle is identified, internal jugular vein (IJV) will be imaged at the apex of the triangle formed by the sternal and clavicular heads of the muscle. Similarly, the inferior vena cava (IVC) will be imaged at the caudal end of the sternum. The diameters of both the veins will be noted during normal respiration. The patients will then be asked to sniff and collapsibility of the veins will be noted. No pressure will be applied on the neck. The anticipated duration for image acquisition is between 5 to 10 minutes.

The patients will undergo the scheduled RHC within 1 hour as scheduled.

The respiratory variation percentage will assessed using M-mode of the ultrasound while the patient is breathing normally. The maximum and minimum anteroposterior diameter will be noted using M-mode (in mm).

Diameter variation index will be calculated as: (maximum diameter - minimum diameter)/ body surface area.

Complete collapse (0cm) of the anteroposterior diameter of IJV on sniff maneuver by the patient, as assessed by M-mode on the ultrasound.

Maximum diameter - noted using M-mode (in mm) of the ultrasound machine.

Respiratory variation - assessed using M-mode of the ultrasound while the patient is breathing normally. This will be calculated as (maximum diameter - minimum diameter)/maximum diameter and expressed as a percentage. The maximum and minimum diameters will be noted using M-mode (in mm).

Sniff collapsibility - Complete collapse (0cm) of the cross sectional diameter of IVC on sniff maneuver by the patient, as assessed by M-mode of the ultrasound.