SKELETAL COMPONENTS OF THE RIB CAGE AND THE UPPER GIRDLE
To begin our quest for chest physiotherapy we must first understand the meaning of the word “chest” and what it is made of. To understand chest physiotherapy, it is not only the knowledge of the structure and function of the lung that is relevant, but also how to use the musculo-skeletal mechanics of the thorax to ones advantage, to perform the act of breathing with minimum of energy expenditure.
We all know that the there is a bony vertebral column consists of thirty three vertebral bones. On the vertebral column is attached the bony rib cage and that houses the lungs and the heart.
The rib cage is made up of 12 pairs of C shaped ribs, which are attached at the back to the thoracic vertebra and majority of them also at the front to the sternum. The secondary components of the rib cage are the clavicle and the scapula. All of these bony components together make the thorax.
The Role of the Vertebral Column
The vertebral column is the axis of the thorax that has to meet the two contradictory requirements that of stability and flexibility at the same time, so that you can hold a heavy bag and turn around at the same time. The vertebral column can be viewed as the mast of a ship. This mast rests on the solid base of the pelvis, extending to the head. At the level of shoulder, it supports the main yard arm, set transversely. This is the scapular girdle. At all levels along the vertebral column, ligaments and muscles are arranged on either side to act as secondary fixators—linking the mast to its base, i.e. the pelvis. This secondary system of fixators is closely related to the scapular girdle and is diamond shaped with its long axis vertical and short axis horizontal. In the position of symmetry, the forces on either side are in equilibrium and the mast is held upright (Fig. 1.1).2
FIGURE 1.1: The vertebral column is like a flexible rod or ship's mast, fixed on the solid base of the pelvis. It is unique in its function that it can move in different axis at the same time, which provides the human body with its fluidity and grace of motion. The muscles in the front, back and sides of the thorax act as the stabilizers for the vertebral column, holding it upright against the force of gravity, allowing it to meet two contradictory requirements, i.e. stability, as well as, mobility. The bony rib cage further provides the thorax, as well as the vertebral column with the required structural rigidity.
Human beings are bi-pedal in nature, the vertical alignment of the vertebral column, in response to the gravitational force is most essential, to ensure unobstructed function of the lungs and other organs of the thoraco-abdominal cavity. The primary consideration of the chest therapist should, therefore, be to ensure upright vertebral posture and discourage stooping (Kyphosis) or tilting (Scoliosis) of the vertebral column.
The Rib Cage
The bony thorax protects the heart and lungs. It provides the site of attachment for the muscles of inspiration, and also gives attachment to the upper extremity muscles.
The posterior surface (back) is formed by the 12 thoracic vertebrae and the posterior part of the 12 ribs. The anterior part (front) is formed by the sternum and the costal cartilages and the lateral surface is formed by the ribs. At birth the thorax is almost circular, but during childhood and adolescence, it becomes more elliptical in shape, until in adulthood when it becomes wider from side to side then it is from front to back.
The ribs articulate posteriorly with the bodies and the transverse processes of the thoracic vertebrae and anteriorly join the sternum via the costal cartilages. The first seven ribs are known as the true ribs, as their cartilages attach directly to the sternum. The eighth to tenth ribs have common cartilaginous attachment to the ribs above. The eleventh and the twelfth ribs are floating ribs as they have no attachment with the sternum at all. Anteriorly, the sternum provides a bony protective plate over the heart, and is composed of the manubrium, the body and the xiphoid process.
Articulations of the chest wall include the manubriosternal, xiphisternal, costovertebral, costotransverse, costosternal and interchondral joints (Figs 1.2 and 1.3).
ARTHROKINEMATICS OF THE THORACIC CAGE: ANALYSIS OF MOVEMENT OF BREATHING
Each rib is connected to the vertebral column by two synovial joints: the costotransverse and the costovertebral. At the spinal end, each rib has two articular surfaces (Fig. 1.3).
The distal one articulates with the transverse process of the dorsal vertebra forming the costotransverse joint. It has strong ligaments that restrict gross ranges of motion. Proximally each rib articulates with the superior border of the lower vertebra and inferior border of the upper vertebra, forming the costovertebral joint. Anteriorly, each rib (except the eleventh and the twelfth) continues as the costal cartilage that articulates with the sternum. The first rib attaches to sternum directly forming a synchondrosis.1
Movement of the Ribs Occurring at these Joints
Ligaments restrain movement at the costovertebral and costotransverse joint. These two joints form a mechanical axis about which the movement of rib can take place. The direction of this axis with respect to the sagittal plane decides the direction of movement of the rib. For upper vertebrae, this axis is more mediolateral. The upper ribs rotate about this axis causing anterior elevation also known as the pump handle motion. For the lower vertebrae, the axis happens to be more anteroposterior, causing the ribs to elevate in a lateral direction causing what is also known as the bucket handle motion of inspiration.
Therefore, during inspiration, elevation of the ribs causes increase in the transverse diameter of the lower thorax and anteroposterior diameter of the upper thorax (Fig. 1.4).
Movement of Thoracic Vertebral Column
In the skeleton, the thoracic column by itself is more mobile where it is connected with the thoracic cage. The thoracic column is connected to the thoracic cage by multiple joints and all the components of the cage play a role in orienting and limiting the basic movements of the column.
Lateral Flexion
It occurs in frontal plane, range 20-40 degrees. The articular processes of two vertebra slide relative to each other. It is limited by impact of the articular process on the side of movement and also by the contralateral ligamentum flava and intertransverse ligaments.
5On the contralateral side: the thorax is elevated (1), the intercostal spaces widen (3), the thoracic cage is enlarged (5) and the chondrocostal angle of the tenth rib tends to open out (7). On the ipsilateral side; the thoracic cage is lowered (2) and shrinks (6), the intercostal spaces are narrowed (4) and the chondrocostal angle becomes smaller (8) (Fig. 1.5).
Axial Rotation
When one vertebra rotates, other articular processes slide relative to each other. This is followed by the rotation and twisting of the discs in the thoracic region. A similar movement is generated in the ribs leading to distortion of the thoracic cage:
- Accentuation of the concavity of the rib on the side of vertebral rotation
- Flattening of the concavity of the rib on the opposite side
- Accentuation of the costo-chondral concavity on the side opposite to vertebral rotation
- Flattening of the concavity of the costo-chondral angle on the side of rotation (Fig. 1.6).
6The range of movement decreases with age, as the flexibility of the thoracic column diminishes. As a result it is not uncommon to find the thorax almost rigid in the elderly.
Flexion
During flexion the space between two vertebrae opens out posteriorly. The range of movement (ROM) is 20-45 degrees. It occurs in the sagittal plane in forward bending. The ligamentum flavum, posterior longitudinal ligament, the interspinous and the supraspinous ligaments limit flexion. During flexion, all the angles between the various segments of the thorax and between the thorax and vertebral column open out. Conversely, during extension, all these angles become smaller (Fig. 1.7).
Extension
The ROM of extension of the thoracic spine is 20 to 45 degrees. It occurs in the sagittal plane. It is associated with the movement of backward bending, elevation of both arms, and during the inspiratory phase. It is limited by the articular and the spinous processes. The anterior longitudinal ligament becomes taut while the Ligamentum flavum, posterior longitudinal ligament, and the interspinous ligament are relaxed Thoracic movement during inspiration and expiration.2
Mechanics of Breathing
To take a breath in, the external intercostals muscles contract, moving the rib cage up and out. The diaphragm moves down at the same time, creating negative pressure within the thorax. The lungs are held to the thoracic wall by the pleural membranes, and so expand outwards as well. This creates negative pressure within the lungs, and so air rushes in through the upper and lower airways.7
Expiration is mainly due to the natural elasticity of the lungs, which tend to collapse if they are not held against the thoracic wall by the negative pressure (suction force) maintained within the pleural space. This is why lungs collapse if there is air in the pleural space, which is called the pneumothorax.
Contracting of the diaphragm and raising the ribs expand the thoracic cavity, producing a tidal flow of air in the lungs. Contraction of the diaphragm moves it downwards and expands the volume of the thoracic cavity, creating a negative pressure within the cavity, drawing atmospheric air, at a higher pressure into the lungs.
During quiet breathing, contraction of the diaphragm accounts for most of the force behind inspiration. Diaphragm is supplied by phrenic nerve which originates from cervical spinal cord (C 3-5). If spinal cord is damaged at or above this level, respiration is inhibited, sometimes leading to death. The external intercostals muscles, located between ribs, also aid inspiration, causing the ribs to move upward and outward, expanding the thoracic cavity further.
At rest expiration is mostly passive — lungs contract due to elasticity, expelling most of the air taken in during inspiration. During exertion, internal intercostals and the abdominal muscles aid expiration by pulling the ribs downward and inward, reducing thoracic cavity, to generate positive pressure within the thoracic cavity.
Inspiration | Expiration |
|---|---|
Diaphragm descends | Diaphragm ascends |
Rib cage elevates and/or expands | Rib cage descends and/or contracts |
Increased intrathoracic volume | Decreased intrathoracic volume |
Decreased intrathoracic pressure | Increased intrathoracic pressure |
‘High pressure’ atmospheric air flows into ‘low pressure’ lung. | ‘High pressure’ air in lung flows out toward ‘low pressure’ exterior. |
MUSCLES OF RESPIRATION AND THEIR FUNCTION IN DIFFERENT STAGES OF RESPIRATION
During quiet breathing, the predominant muscle of respiration is the diaphragm (Fig. 1.8). As it contracts, pleural pressure drops, which lowers the alveolar pressure, and draws air in down the pressure gradient from mouth to alveoli. Expiration during quiet breathing is predominantly a passive phenomenon, as the respiratory muscles are relaxed and the elastic lung and chest wall return passively to their resting volume, the functional residual capacity.
However, during exercise, many other muscles become important to respiration. During inspiration, the external intercostals raise the lower ribs up and out, increasing the lateral and anterior-posterior dimensions of the thorax. The scalene muscles and sternomastoids also become involved, serving to raise and push out the upper ribs and the sternum. During active expiration, 8the most important muscles are those of the abdominal wall (including the rectus abdominus, internal and external obliques, and transversus abdominus), which drive intra-abdominal pressure up when they contract, and thus push up the diaphragm, raising pleural pressure, which raises alveolar pressure, which in turn drives air out. The internal intercostals assist with active expiration by pulling the ribs down and in, thus decreasing thoracic volume.3
Shortening of diaphragmatic fibers pulls inferiorly on central tendon and superiorly on lower ribs. During inspiration, the diaphragm's central tendon descends until it is fixed or stabilized by forces that develop in: elongated mediastinal structures, which pull upward on the diaphragm and compress the abdominal contents, which push upward on the descending diaphragm.4 When the central tendon becomes stable, it is still superior to the diaphragm's mobile attachments on the lower ribs. Therefore, the diaphragm's muscular lines of application elevate the lower ribs (Fig. 1.9).
Type of Breathing | Muscles of Inspiration | Muscles of Expiration |
|---|---|---|
Quiet (primary muscles) | Diaphragm external intercostals | Expiration is passive Elastic recoil of lung tissue surface tension gravity on ribs internal intercostals |
Forced (secondary or accessory muscles) | Sternocleidomastoid Scalene Pectoralis major Pectoralis minor Serratus anterior Serratus posterior superior Upper iliocostalis | Abdominal muscles External oblique Internal oblique Rectus abdominus lower iliocostalis lower longissimus Serratus posterior inferior |
OUTLINE OF RESPIRATORY ANATOMY
This sub-section on Respiratory Anatomy represent a four part study of the respiratory system, following the path of air from the mouth and nose to the alveolar level, where oxygen trades places with carbon dioxide. The respiratory system is situated in the thorax, and is responsible for gaseous exchange between the circulatory system and the outside world. Air is taken in via the upper airways (the nasal cavity, pharynx and larynx) through the lower airways (trachea, primary bronchi and bronchial tree) and into the small bronchioles and alveoli within the lung tissue. The lungs are divided into lobes; the left lung is composed of the upper lobe, the lower lobe and the lingula (a small remnant next to the apex of the heart), the right lung is composed of the upper, the middle and the lower lobes (Fig. 1.10).
Part 1: Upper Respiratory Tract
The Upper Respiratory Tract or Airways extends from the mouth and the nasal passage to just above the larynx.
- The epiglottis is a leaf-shaped “flap” of cartilage that protects the rest of the respiratory system from foreign objects. The epiglottis acts as a valve or lid, automatically opening for breathing and closing when you swallow food or liquids. The epiglottis is also important in producing an effective cough. During a cough the epiglottis is closed and then when sufficient pressure is built up, suddenly opens for a quick release of air, producing cough.
- The external nares are the opening to the nasal cavity and are lined with fine hairs that serve as filters for large particles of dust suspended in the air that we breathe, and they form the first line of defense against inhaled dust partcles, bacteria, virus and other inhaled pathogens.
- The frontal sinuses are air pockets, located deep within the facial bones over and below the eyes, i.e. in the frontal and maxillary bones. Those pockets or cavities serve to strengthen and lighten these bones. They become painful and get inflamed when infected by airborne virus or bacterium. This condition is known as sinusitis.
- The hard palate forms the roof of the mouth and the floor of the nasal cavity.
- 10The soft palate extends from the hard palate and forms the back of the roof of the mouth. The soft palate supports the structure known as the uvula (that little thing that hangs down in the back of your throat). The soft palate and uvula play an important part in the development of certain kinds of obstructive sleep apnea.
- The nasal concha is mucus lined folds that cool, humidify, and filter the air after entering the nasal passage. The inferior nasal concha is the largest, located near the floor of the nasal cavity. It also covers the opening to the nasolacrimal ducts (tear ducts). The middle nasal concha is located midway up the nasal cavity and just behind the opening to the frontal sinus. This area is important for the sense of smell. The superior nasal concha is located near the roof of the nasal cavity and just before the opening to the sphenoid sinus. This area is also important for the sense of smell.
- The nasal cavity serves as a filter, air conditioner and humidifier for the inhaled air before it enters the lungs. It is also rich in nerve ending from the olfactory bulb that gives us the sense of smell. It is also where most attacks of cold begin.
- The nasal bone forms the base for the cartilage that forms the nose and nasal septum.The pharynx is the common opening of the digestive and respiratory systems. It receives air from the nasal cavity and air, food and water from the mouth. Inferiorly, the pharynx leads to separate openings of the respiratory system namely the larynx and of the digestive system, i.e. esophagus (Fig. 1.11). Pharynx can be divided into three (3) regions:
- Nasopharynx
- Oropharynx
- Laryngopharynx
- The naso-pharynx is the upper part of the pharynx and connects the nasal passages with the rest of the respiratory system. The pharynx is the area most commonly called the “back of the throat”.
- Oropharynx is the lower part of the pharynx and connects the upper airways to the larynx via the epiglottis, lined with stratified squamous epithelium that provides protection against abrasion.
- Laryngopharynx extends from the tip of the epiglottis to the openings of the larynx and esophagus. It is lined with squamous epithelium
- The eustachian tubes connects the middle ear with the upper airways. Mucus from colds or other infections can be forced up this tube with coughing, sneezing, or nose blowing and result in middle ear infections.
- 11Tonsils located along with the lingual and palatine surfaces are considered to be part of the lymphatic system, thus important in the immune system. At one time was common to have infected and inflamed tonsils removed surgically in the childhood, but with the advent of broad-spectrum antibiotics, that practice has been discarded.
- The tongue, located in the floor of the mouth is a muscle important for eating, speak, and the sense of taste.
Part 2: Lower Respiratory Tract
- The lower respiratory tract starts from the larynx (Figs 1.12A and B) and consists of trachea, and main bronchi, extending from the back of the throat to the first branching of the bronchial tree. The Larynx and its structures form the opening to the trachea and lower airways.
- The epiglottis is a leaf-shaped “flap” of cartilage that protects the rest of the respiratory system from foreign objects. The epiglottis acts as a valve or lid, automatically opening for breathing and closing when you swallow food or liquids. The epiglottis is also important in producing an effective cough. During a cough the epiglottis is closed and then when sufficient pressure is built up, suddenly opens for a quick release of air.
- The hyoid bone is the support structure for the tongue and various muscles that allows the tongue to function.
- The laryngeal prominence is also known as the “Adam's Apple”. It is the upper forward protruding part of the thyroid cartilage.
- The thyroid cartilage is the largest cartilage of the larynx and is attached by the thyroid membrane to the hyoid bone. The thyroid cartilage houses the structures of the epiglottis and vocal cords.
- The esophagus is the passageway to the stomach.
- The glottis is the opening between the Vocal Cords (Fig. 1.13). It differentiates the upper respiratory tract from the lower airways. Due to the narrowness of this opening, it is susceptible to inflammation and swelling of the vocal cords and surrounding tissues.
- The vocal cords form the opening called the Glottis. They also make speech possible by vibrating when air passes through them.
- The wall of laryngopharynx houses the larynx and opening to the Esophagus.The Trachea is the beginning of the Tracheo-Bronchial Tree (Fig. 1.14) and consists of the largest diameter of the lower airway tract. It is made up of a series of “C” shaped tracheal cartilages and connective tissue (Fig. 1.15). These cartilages form a rigid tube with a soft pliable area at the back of the trachea extending its full length and into the left and right main stem Bronchi.
- The tracheal cartilages or Ttacheal cartilaginous rings are the support structures of the trachea. These are not complete rings; they are “C” shaped. This shape allows the trachea to be ridged forward for structure 13and protection. It also allows the trachea to be soft and pliable in the back where it is in close proximity to the esophagus.
- The right and left main stem bronchi are similar in many ways to the Trachea. Their structure is supported with cartilaginous rings and lead into the right and left lungs.
- At a microscopic level the trachea and main stem bronchi are lined with structures referred to as cilia.
- Cilia propel mucus and foreign particles toward the larynx where they can enter the esophagus and be swallowed.Viewed at the microscopic level, the cilia appear like vast fields of waving wheat or grass (Fig. 1.16).
Cilia in the trachea and bronchi move mucus and any trapped particles up toward the larynx to be expelled from the lungs. There are also cilia in the naso and oropharynx that move secretions down toward the throat.
Interspersed among the cilia are specialized cells called Goblet cells that produce mucus. There are two types of mucus, one very thin and liquid. The other is thick and viscous. The thick layer of mucus sits on top of the thinner. Cilia are able to grab hold of this thicker layer and propel it in the intended direction (Fig. 1.17).The depths of the thin and thick layers of mucus are especially important for the cilia to be able to do their job. As asthmatics, we tend to develop an increase in the thick mucus during attacks, this overproduction of thick mucus interferers with the cilia's ability to move it.
Other factors that effect cilia are smoking and chronic infections (i.e. Chronic Bronchitis or Bronchiectasis). Cigarette smoke slows down the action of cilia; chronic infections decrease the number of ciliated cells and increase the number of goblet cells. Both of these factors decrease the ability of the lungs to clear foreign particles and bacteria, and the increased mucus production give bacteria a perfect place to grow, thus increasing the chances of infection.
Part 3: The Lungs and the Major Bronchi (Fig. 1.18):
- After the trachea splits into the main stem bronchi at the Carina, these main bronchi then continue to divide. Right bronchus is shorter and wider and is more vertical than the left bronchus.
- Main bronchi extend from the mediastinum to the lungs.
- The lining of the bronchi is the same as the trachea and the bronchi are supported by “C”-shaped cartilage rings
- The right main stem bronchus divides into three lobar branches; upper, middle, and lower lobe bronchi.
- The left main stem bronchus divides into two lobar branches — the upper and lower lobar bronchi.
- The lobar bronchi divide into the segmental bronchi; leading into
- Right upper lobe, anterior, apical, and posterior segments;
- Right middle lobe, medial and lateral segments;
- Right lower lobe, anterior, medial, lateral, posterior, and superior segments;
- Left upper lobe, apical-posterior, anterior, superior lingular, inferior lingular segments;
- Left lower lobe, anterior, medical, lateral, posterior, and superior segments.
- As they divide, the cartilaginous support, as in the trachea and main bronchi, slowly begins to disappear and is replaced by bronchial smooth muscle.
- When the diameter of the bronchi reach 1 mm, all cartilaginous support has gone, and we call these small bronchi Bronchioles.
- The bronchioles continue to divide until we reach the terminal bronchioles, which are made up of the respiratory bronchioles and alveolar ducts.
- These structures are at the very surface of the lungs, covered by the visceral pleura.
- This continuing branching of the airways creates the surface area of the lung.
- The total surface area of the alveoli is equivalent to the area of a tennis court.
- The significance of the change from cartilaginous support to smooth muscle is very important to patients with respiratory disorders, particularly in COPD.
- Lungs are the principal organs of respiration and on a volume basis; they are one of the largest organs of the body.
- Each lung is conical in shape with its base resting on the diaphragm and its apex extending superiorly to a point approximately 1” superior to each clavicle.
- Right lung is larger than the left lung.
- Right lung has three lobes and left lung two lobes (Fig. 1.19).
Part 4: The Microscopic Features of the Lungs and Bronchial Tree
Most of the working parts of the lungs that participate in the gas exchange are at the microscopic level. This passage concentrates on those microscopic features of the lungs.
Role of Alveoli in Respiration
The main function of the lungs is to facilitate gas exchange between carbon dioxide in the blood stream and oxygen in the air. At the very end of the bronchial tree are the alveoli. They appear like bunches of grapes at the ends of the bronchioles (Fig. 1.20). The alveoli first start to appear on the respiratory bronchioles, these bronchioles lack the smooth muscle of the terminal bronchioles. The smooth muscles surrounding the terminal bronchioles are those muscles that respond easily to emergency medications like bronchodilators, to relieve the muscle spasm. Anti-inflammatory agents like steroid work on the mucous membrane. During an attack these muscles contract, squeezing the bronchioles and the mucus layer swells up, making them still smaller. The inner lining of these airways are where steroids and other anti-inflammatory medications work. By reducing inflammation, the inner diameter of the airways is enlarged.
REFERENCES
- Clemente CD. Anatomy (2nd ed). Urban and Schwarzenberg 1981 Baltimore:
- Kapandji IA. Functional components of the vertebral column. In I.A. Kapandji (Ed): The physiology of the joints: Vol. 3. The trunk and the vertebral column. Churchill Livingstone New York: 1974.
- Rasch PJ, Burke RK. Kinesiology and Applied Anatomy (6th ed). Lea and Febiger Philadelphia: 1978.
- Poole DC, Sexton WL, Farkas GA, Powers SK, Reid MB. Diaphragm structure and function in health and disease. Medicine and Science in Sports and Exercise 1997; 29: 738-54.
- Diagrams and figures adapted from web site http://www.cayuga-cc.edu/people/facultypages/greer/biol204/resp3/resp1-3.html