6.2 Applications and skills

6.2.4 Practical 6: Lung cancer, emphysema and the effect of exercise on ventilation

Lung cancer and emphysema are two fatal diseases caused by cigarette smoking and other factors.

Causes and consequences of lung cancer

  • Lung cancer develops in the cells that line the bronchi, as well as in the alveoli. There is a high mortality rate compared with other cancers.
  • By the time symptoms appear, the cancer is often well developed or metastasised. Symptoms include shortness of breath, fatigue, weight loss, chest pain, and coughing up blood.

Figure 6.2.4a – Lung cancer mortality rates are very highFigure 6.2.4a – Lung cancer mortality rates are very high

  • Major causes of lung cancer are long-term tobacco use, second-hand smoke, exposure to asbestos or particulate matter from the workplace, and atmospheric exposure to air-borne pollutants such as radon gas.
  • Lung cancer develops quickly through the stages set out in the following table.
Stage 0 The carcinoma is in situ and has not affected nearby tissue. Carcinoma may be removed by surgery.
Survival rate >75%
Stage I The tumour is small and has affected nearby tissues (early stage cancer). Treatment is removal by surgery followed by radiation or chemotherapy.
Survival rate 55–75%
Stages II and III The cancer has grown, infected other tissues, and has moved into the lymphatic system, but not yet metastasised. Treatment is radiation to shrink the tumour followed by surgery, or a combination of radiation and chemotherapy without surgery, as the tumour may be too large to remove safely.
Survival rate 10–50%
Stage IV The cancer has spread to other parts of the body (metastasis). Treatment is unlikely to cure these cancers.
Survival rate <5%

Causes and consequences of emphysema

Figure 6.2.4d – Measurable factors related to spirometryFigure 6.2.4b – Presentation of emphysema at the alveoli

  • Emphysema is a chronic obstructive pulmonary disease. ‘Chronic’ means that damage caused by the disease is irreversible. ‘Obstructive’ means it makes ventilation more difficult physically.
  • The disease develops as the inner surfaces of alveoli became less elastic, weaken and eventually rupture. Large spaces develop where alveoli have ruptured, resulting in a reduced overall surface area for gas exchange.
  • In its initial stages, the disease causes shortness of breath during strenuous exercise. As emphysema progresses, the ‘holes’ in the lungs become larger. Air may become trapped, preventing new air from entering the lungs. Breathing at rest becomes more difficult. At the latest stage, blood oxygen levels can fall to less than 50% of normal levels.
  • Cigarette smoke is the leading cause of emphysema. Long-term exposure to air-borne irritants, including air pollution and second-hand smoke, are other causes. Continued exposure to pollutants worsens the disease.
  • In rare cases, emphysema is caused by an auto-immune response that results from an inherited protein deficiency (alpha 1 anti-trypsin, AAT). AAT prevents certain white blood cells, called neutrophils, from attacking the alveolar lining.

Monitoring ventilation rate in humans (Practical 6)

Figure 6.2.4c – A spirometer measures lung capacityFigure 6.2.4c – A spirometer measures lung capacity

Figure 6.2.4d – Measurable factors related to spirometryFigure 6.2.4d – Measurable factors related to spirometry

  • Tidal volume – the volume of air displaced in a single breath.
  • Residual volume – the volume of air that remains in the lungs after expiration.

The aim of this experiment is to design a lab to investigate the effect of exercise on one aspect of ventilation.

Use this template to help you plan your experiment:

Independent variable At least five different values are necessary. This variable could be categorical (e.g. type of exercise) or continuous. For example, you could measure the ‘level of exertion’ by:
  • heart rate?
  • speed of walking on a treadmill?
  • number of push-ups or sit-ups?
Do you need to perform a pre-lab to determine an appropriate range of values for your independent variable?
Dependent variable This variable must be quantitative:
  • ventilation rate (number of breaths/minute)?
  • tidal volume?
Do you need to calibrate your equipment to an appropriate range of values? Do you need to practise the technique of using the equipment?
Control variables
  • Sex, age, height, weight and fitness level of participants
  • Trial duration, rest time, etc.
Ensure all your participants sign a consent form. Ensure you are not causing the participants harm.
Collecting data
  • How many repeated trials are sufficient? (Normally three or until results are consistent)
  • Do you need to re-calibrate your equipment?
Analysing data
  • Continuous data? Use a line graph.
  • Categorical data? Use a bar graph.
  • Which statistics are appropriate?
Concluding and discussing
  • What is the relationship between the two variables?
  • How reliable is your conclusion?
  • What are some limitations of your experimental design? How could you improve them?

Course link

Cancer is caused by mutations that result in uncontrolled mitosis. Review the cell cycle, control and how tumours form in Page 1.2.6.

Language help

  • In situ means ‘in place’. The tumour is growing at its origin. It hasn’t moved or invaded other tissues yet.
  • Carcinoma is a tumour that grows from epithelial cells.

6.2.4e - ChemotherapyFigure 6.2.4e – Chemotherapy
Chemotherapy kills cells that divide quickly. Cancer cells, but also hair follicles, cells of the intestinal lining, and white blood cells, are affected. That’s why patients often experience hair loss and a weakened immune system.

Nature of Science

Evidence: Epidemiology is the study of risk factors, and patterns of incidence and distribution of disease. It is also concerned with identifying possible control methods for disease and health-related issues. Epidemiological research uses non-experimental evidence-based methods. These methods are evidence-based because they rely on quantitative data, but do not involve controlled experiments (like a clinical trial). Therefore they are known as observational studies. For example:

  • Case studies – two groups (e.g. presence or absence of disease) are compared with respect to possible causes.
  • Cohort study – a group of people are repeatedly observed over a long period of time with respect to certain variables (e.g. lifestyle, progression of disease).
  • Cross-sectional study – data is collected from a subset of population at a specific moment in time (e.g. during an outbreak).

Epidemiological studies have contributed to our understanding of the causes of lung cancer.

Figure 6.2.4f – Lung cancer risk factorsFigure 6.2.4f – Lung cancer risk factors
Risk factors are identified and calculated using epidemiological research.

Further reading

To learn more about the history of cancer research, and especially how epidemiological research is performed and interpreted, see the Pulitzer Prize winning book:
Mukherjee, Siddartha (2010) The Emperor of all Maladies: A biography of cancer. New York: Scribner.

IA

Use this template to help you plan any lab in this course.

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