Question

Expiratory muscles contract at the time of
A. Deep inspiration
B. Normal inspiration and expiration
C. Forceful expiration
D. Normal expiration

Answer 1

The innate ability to induce a breathing movement is in all muscles attached to the human rib cage. The inspiratory muscles are called muscles that help expand the thoracic cavity because they assist in inhalation, whereas those that compress the thoracic cavity are called expiratory muscles and induce exhalation.

Complete Answer:
- Such muscles have almost the same basic structure as all other muscles of the skeleton, and work together to extend or compress the thoracic cavity.
- The speciality of these muscles is that they are made up of muscle fibres that are immune to exhaustion, regulated by both voluntary and involuntary mechanisms (if we want to take a breath we will, even if we don't think about breathing the body automatically takes it).
- The abdominal muscles are the accessory expiratory muscles: rectus abdominis, outer oblique, inner oblique, and transversus abdominis. And the lowest fibres of iliocostalis and longissimus, serratus posterior inferior and quadratus lumborum, are found in the thoracolumbar region.
- Natural tidal expiration is passive and no contraction of the muscle occurs. Expiratory contraction of the muscles is often incidental. Expiration muscles come into action when you force expiration. The expiratory muscles are the abdominal muscles and intercostals. It is rare if a patient is contracting abdominal muscles for quiet breathing and he is trying to force expiration.
- Forced Expiration: By forced expiration, only peak flows can be increased. By forcing expiration, flow rates can not be increased for much of the expiratory period. The rising positive pressure in the pleura compresses the airway and thus reduces the size of the airway, thus counteracting the increased expiratory force.
- Expiratory Power: The ability to blow a lit match at a length of 12 "from the mouth is crudely determined by the expiration power. This correlates to the peak expiratory flow. Failure to blow the matches at this length will mean reduced peak flows.

The correct Answer is option (C) Forced expiration.

Note: The time of expiration is determined by listening to Trachea with a stethoscope. Expiration, while physiologically longer than inspiration, would be shorter on auscultation over lung fields. During expiration, the air travels away from the alveoli into the central airway, so you can hear only the early third of expiration. However, the whole period of expiration can be heard over Trachea. The standard period of forced expiration is less than 5 seconds.