Anatomy
Thorax
Which of the following occurs primarily to produce passive expiration:
Answer:
Passive expiration is produced primarily by relaxation of the inspiratory muscles (diaphragm and external intercostal muscles) and the elastic recoil of the lungs.Thoracic Wall Movements
Anatomy / Thorax / Thoracic Wall
Last Updated: 21st March 2023
Movement of the ribs at the costovertebral joints in respiration results in the 'pump handle' and 'bucket handle' movements:
- Because the anterior ends of the ribs are inferior to the posterior ends, when the ribs are elevated, the anterior end moves upwards and forwards, moving the sternum upwards and forwards in turn. This 'pump handle' upwards and forwards movement changes the anteroposterior (AP) dimension of the thorax.
- Because the middles of the shafts of the ribs are lower than either the anterior or posterior end, elevation of the ribs also moves the middles of the shafts laterally. This 'bucket handle' upwards and lateral movement increases the lateral dimensions of the thorax.
Reversal of these movements i.e. depression of the ribs, will reduce the anteroposterior and transverse dimensions of the thorax.
Thoracic Movements. (Image by OpenStax College [CC BY 3.0 , via Wikimedia Commons)
Inspiration
In inspiration, elevation of the sternal ends of the ribs ('pump handle' movement), elevation of the lateral shafts of the ribs ('bucket handle' movement) and depression of the diaphragm result in expansion of the thorax in an anteroposterior, transverse and vertical direction respectively. This results in an increased intrathoracic volume and decreased intrathoracic pressure and thus air is drawn into the lungs.
Passive inspiration is produced by contraction of the diaphragm (depressing the diaphragm) and the external intercostal muscles (elevating the ribs).
The accessory respiratory muscles (including the sternocleidomastoid, the scalene muscles and the serratus anterior amongst others) aid in forceful inspiration.
Expiration
In expiration, depression of the ribs and elevation of the diaphragm result in a reduction of the thorax in an anteroposterior, transverse and vertical direction. This results in a decreased intrathoracic volume and increased intrathoracic pressure and thus air is forced out of the lungs.
Passive expiration is produced primarily by relaxation of the inspiratory muscles (diaphragm and external intercostal muscles) and the elastic recoil of the lungs.
Forceful expiration is primarily produced by the deeper thoracic muscles (internal and innermost intercostal muscles, subcostals and transversus thoracis) aided by contraction of the abdominal wall muscles which increase intra-abdominal pressure thus further reducing the volume of the thorax.
Paradoxical Respiration
Normally as the diaphragm moves downwards in inspiration, the abdominal wall moves outwards (together with the chest wall), and the reverse occurs in expiration.
In complete airway obstruction, the diaphragm will move down and the abdominal wall out but as inspiratory effort continues against a closed airway, increasing intrathoracic pressure will draw the chest wall paradoxically inwards (against the opposing action of the intercostal muscles). To the observer, in inspiration there is abdominal expansion with chest collapse and during expiration the reverse is seen. As inspiratory effort increases and expiration becomes active, the see-sawing pattern becomes more pronounced.
Flail chest is a loss of stability of the thoracic cage that occurs when a segment of the anterior or lateral thoracic wall moves freely because of multiple rib fractures, allowing the loose segment to move paradoxically inward on inspiration and outward on expiration. If a large enough segment of the chest is affected, ventilation is impaired.
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- Biochemistry
- Blood Gases
- Haematology
| Biochemistry | Normal Value |
|---|---|
| Sodium | 135 – 145 mmol/l |
| Potassium | 3.0 – 4.5 mmol/l |
| Urea | 2.5 – 7.5 mmol/l |
| Glucose | 3.5 – 5.0 mmol/l |
| Creatinine | 35 – 135 μmol/l |
| Alanine Aminotransferase (ALT) | 5 – 35 U/l |
| Gamma-glutamyl Transferase (GGT) | < 65 U/l |
| Alkaline Phosphatase (ALP) | 30 – 135 U/l |
| Aspartate Aminotransferase (AST) | < 40 U/l |
| Total Protein | 60 – 80 g/l |
| Albumin | 35 – 50 g/l |
| Globulin | 2.4 – 3.5 g/dl |
| Amylase | < 70 U/l |
| Total Bilirubin | 3 – 17 μmol/l |
| Calcium | 2.1 – 2.5 mmol/l |
| Chloride | 95 – 105 mmol/l |
| Phosphate | 0.8 – 1.4 mmol/l |
| Haematology | Normal Value |
|---|---|
| Haemoglobin | 11.5 – 16.6 g/dl |
| White Blood Cells | 4.0 – 11.0 x 109/l |
| Platelets | 150 – 450 x 109/l |
| MCV | 80 – 96 fl |
| MCHC | 32 – 36 g/dl |
| Neutrophils | 2.0 – 7.5 x 109/l |
| Lymphocytes | 1.5 – 4.0 x 109/l |
| Monocytes | 0.3 – 1.0 x 109/l |
| Eosinophils | 0.1 – 0.5 x 109/l |
| Basophils | < 0.2 x 109/l |
| Reticulocytes | < 2% |
| Haematocrit | 0.35 – 0.49 |
| Red Cell Distribution Width | 11 – 15% |
| Blood Gases | Normal Value |
|---|---|
| pH | 7.35 – 7.45 |
| pO2 | 11 – 14 kPa |
| pCO2 | 4.5 – 6.0 kPa |
| Base Excess | -2 – +2 mmol/l |
| Bicarbonate | 24 – 30 mmol/l |
| Lactate | < 2 mmol/l |
