Question

Between breaths intra pleural pressure is approximately _________ $mm$ of Hg.
A. $1$
B. $-4$
C. $-8$
D. $10$

Answer 1

Hint: In physiology, intrapleural pressure (also known as intrathoracic pressure) refers to the pressure in the pleural cavity. Usually the pressure in the pleural cavity is slightly lower than atmospheric pressure, which is known as negative pressure. If the pleural cavity is damaged / torn and the intrapleural pressure equals or exceeds atmospheric pressure, a pneumothorax may occur. The intrapleural pressure depends on the ventilation phase, atmospheric pressure and the volume of the intrapleural cavity.

Complete answer:
> Breathing: The inflow (inspiration) and outflow (outflow) of air between the atmosphere and the alveoli is called breathing. It is affected by the expansion and contraction of the lungs.
> Inspiration: This is a process that brings fresh air to your lungs. The diaphragm, intercostal muscles and abdominal muscles play an important role.
> Expiration: This is a process in which impure air (carbon dioxide) is removed from the lungs.
The lungs are covered by the visceral pleura which affects the internal aspects of the chest wall and closes the potential cavity between its two layers known as the pleural cavity. The two layers, parietal and visceral, are kept moist and lubricated with several milliliters of fluid containing mucopolysaccharides in the intrapleural space, so that during breathing the lungs with the surrounding visceral pleura gently slide along the parietal pleura.
Normal intrapleural pressure, that is. The pressure in the pleural cavity was negative. This means the lungs have not completely collapsed and the alveoli remain partially inflated even after a full inhalation.
The intrapleural pressure between breaths is approximately $4mm$ Hg less than the atmospheric pressure.
The negative intrapleural pressure is mainly responsible for the flow of the inhaled air to the lungs. It is also responsible for maintaining patency of the airway. Exhaling is usually a passive process due to relaxation of the inspiratory muscle.

Thus the correct option is (A).

Note: The diaphragm and external intercostal spaces are the inspiratory muscles in normal respiration. However, during forced inspiration, contraction of the sternocleidomastoid, scalene, serratus anterior and platysma. These muscles are known as the inspiratory aid muscles.
Exhale muscles: Exhalation is a passive process. However, with forced exhalation, this phase also becomes an active process and requires active contraction of certain muscles. The muscles involved in forced exhalation are called auxiliary respiratory muscles and are the internal and anterior intercostal abdominal muscles.
Hiccups is a sharp jerky incomplete inspiratory sound which occurs due to sudden spasmodic contraction of diaphragm followed by sudden closure of the glottis.