Mean, also known as the average, is the most common measure of central tendency. It is the sum of all observed values divided by the number of observation. It is not useful for skewed data, which has an abnormal distribution. It is useful, instead, for numerical data that have symmetric distribution. It reflects the contributions of each data in the group, and are sensitive to outliers.

The median is the value that falls in the middle position when the observations are ranked in order from the smallest to the largest. If the number of observations is odd, the median is the middle number. If it is even, the median is the average of the two middle numbers. Unlike the mean, the median is useful on skewed data, and can be used for ordinal or numerical data if skewed.

The mode is the value that occurs with the greatest frequency in a set of observations, and is utilized for bimodal distribution.

The variance and the standard deviation are not measures of central tendency, but of dispersion.

In an adult, the trachea is approximately 15 cm long. It extends at the level of the 6th cervical vertebra, from the lower border of the cricoid cartilage.

The trachea terminates between T4 and T6 at the carina or bronchial bifurcation. This variation is because of changes during respiration.

The trachea has 16-20 C-shaped cartilaginous rings that maintain its patency.

The trachea is first of the 23 generations of air passages in the tracheobronchial tree (not 25), from the trachea to the alveoli..

The inferior thyroid arteries which are branches of the thyrocervical trunk, arise from the first part of the subclavian artery and supplies the trachea.

Muscle fibre myosin ATPase histochemistry is used to divide the biochemical classification into two groups: type 1 and type II.

Type I (slow twitch) muscle fibres rely on aerobic glycolytic and aerobic oxidative metabolism to function. They have a lot of mitochondria, a good blood supply, a lot of myoglobin, and they don’t get tired easily.

Because they contain more motor units, Type II (fast twitch) muscle fibres are thicker. They are more easily fatigued, but produce powerful bursts. The capillary networks and mitochondria are less dense in these white muscle fibres than in type I fibres. They have a low myoglobin content as well.

Muscle fibres of type II (fast twitch) are divided into three types:

Type IIa – aerobic/oxidative metabolism is used.
Type IIb – anaerobic/glycolytic metabolism is used by these fibres.

When compared to skeletal muscle, cardiac and smooth muscle twitch at a slower rate.

The ventilation/perfusion ratio varies in different areas of the lung. In an upright individual, although both ventilation and perfusion increase from the apex to the base of the lung, the increase in ventilation is less than the increase in blood flow. As a result, the normal V̇ /Q̇ ratio at the apex of the lung is much greater than 1 (ventilation exceeds perfusion), whereas the V̇ /Q̇ ratio at the base of the lung is much less than 1 (perfusion exceeds ventilation).

There is more volume in the alveoli found in the apices than in the bases of the lungs. This is due to the weight of the lung stretching the apical alveoli to the maximum size. Also, the weight of the lungs pull themselves away from the chest wall, creating a negative intrapleural pressure. These factors, however, do not directly affect the PAO2.

The principle by which a strain gauge works is that when a wire is stretched, it becomes longer and thinner, and as a result, its resistance increases.

A strain gauge, which is used in pressure transducers, acts as a resistor. When the pressure in a pressure transducer changes, the diaphragm moves, changing the tension in the resistance wire and thus changing the resistance.

Changes in current flow through the resistor are amplified and displayed as a pressure change measure.

A Wheatstone bridge, on the other hand, is frequently used to measure or monitor these changes in resistance.

T cells function as a part of the body’s adaptive immune system. There are different types of T cells, including:

Cytotoxic T cells: Function as killer cells by releasing cytotoxic granules into the membrane of targeted cells.

T-Helper cells: When activated, they function to activate other immune cell types, assist in antibody production with B cells and releasing cytokines including IL-2.

Memory T cells: Function as to provide immune memory against already encountered antigens.

T cells possess specific glycoproteins and receptors on their surface.

T-Helper cells work with HLA class II antigens on the cell surfaces in order to recognise foreign antigens

T cells survive ranges from a few weeks, to a lifetime depending on the subtype in question.

Immunoglobulins are expressed on the surface of, and secreted by B-lymphocytes.

Native antigens are recognised by B cells. T cells only recognise antigens that have been processed by the cells and presented on the surface of the cell.

The normal distribution is a symmetrical, bell-shaped distribution in which the mean, median and mode are all equal.

The first line of treatment in case of hypotension is fluid resuscitation.

Activated charcoal can be used within one hour of tricyclic antidepressant ingestion but an intact and secure airway must be checked before intervention. The risk of aspiration should be assessed.

Vasopressors are indicated for the treatment of hypotension following (Tricyclic Antidepressant) TCA overdose when patients fail to respond to fluids and bicarbonate.

The clinical potency of the anaesthetic agent is measured using minimal alveolar concentration(MAC).

MAC and oil: gas partition coefficient is inversely related. Anaesthetic agent Oil/gas partition coefficient and Minimal alveolar concentration (MAC) is given respectively as

Desflurane 18 6
Isoflurane 90 1.2
Nitrous oxide 1.4 104
Sevoflurane 53.4 2
Xenon 1.9 71

With these data, we can conclude Isoflurane is the most potent with the highest oil/gas partition coefficient of 90 and the lowest MAC of 1.2

Tonic-clonic (Grand mal) epilepsy is characterised by a general loss of consciousness with violent involuntary muscle contractions.

The NICE guidelines for treatment indicates the use of sodium valproate and lamotrigine, but sodium valproate unsuitable in this case and she is a woman of reproductive age and it is known to have teratogenic effects. Lamotrigine is a more suitable choice, prescribed as 800mg daily.

NICE guidelines also advice an additional prescription of 5mg of folic acid daily for women on anticonvulsant therapy looking to get pregnant. It also warns of the need for extra contraceptive precaution as there is a possibly that the anticonvulsant agent can reduce levels of contraceptive agents.

Stimulation of the vagal nerve stimulation is only necessary in patients who are refractory to medical treatment and not candidates for surgical resection.