The majority of right atrial filling occurs during which phase of respiration?

The majority of right atrial filling occurs during inspiration due to the physiological changes that occur in the thoracic cavity. When a person inhales, the diaphragm contracts and moves downward, increasing the volume of the thoracic cavity and creating a negative pressure environment. This negative pressure allows for increased venous return from the systemic circulation to the right atrium, enhancing right atrial filling.

During this phase, the pressure in the thoracic cavity falls, which assists venous blood flow from the inferior and superior venae cavae into the right atrium. This increased venous return is crucial for maintaining the efficiency of cardiac output, particularly in managing the fluctuating pressures during the respiratory cycle.

In contrast, during expiration, the pressure in the thoracic cavity increases, which can lead to a temporary decrease in venous return to the right atrium. This results in less filling during that phase. While there is some filling of the atrium during rest and forced exhalation, the dynamic changes in pressure during inspiration are the key factors that promote enhanced right atrial filling.