BIOS4001 Human Structure and Function:  Practical class on the respiratory system

BIOS4001 Human Structure and Function:  Practical class on the respiratory system

Use the data provided on the results sheet to answer the following questions.  Using the same font size, please restrict your answer to the space allocated.

Exercise 1:  Spirometry and normal lung volumes

1. Use the spirometry trace in Figure 1 to measure approximately and calculate the following respiratory variables. Add your data to the table below.  Give the units in each case.

(5 marks)

2. Reference tables can be used to estimate lung volumes in human subjects, based on their sex, age, and height. What factors may cause your experimental measurements to be higher or lower than estimated?

(4 marks)

Experimental measurements may be higher or lower than estimated in that the vital capacity of individuals with lower height is higher than those with higher height due to increased surface area of lungs in relation to increasing height.

Total lung capacity varies with age in that after about the age of thirty-five years, lung function declines hence total lung volume leading to varying experimental measurements.

At birth, females have fewer respiratory volumes and smaller lungs than men. The percentage change between residual volume and total lung capacity and also between functional residual capacity and residual volume is higher in males than females. Males have larger nasal cavities, longer, narrower, higher nasal floors, and large airways than females of the same size all these leading to variation in experimental measurements.

Exercise 2:  Pulmonary function tests in normal subjects

3. Using the data in Table 1, present the mean, standard deviation, and coefficient of variation for each measurement. Give the units in each case.

(6 marks)

4. Comment on the range of values obtained from the class. What factors do you think may contribute to the differences observed in the pulmonary parameters between the subjects?

(5 marks)

Pulmonary parameters vary due to factors including age, sex, body build, height, and physical conditioning thus influencing lung volume capacity. Lung volume is usually at maximum in early adulthood and declines with age due to changes that affect lung tissue, muscles, and bones having an effect on breathing. Those with taller height have higher vital capacity than shorter ones due to increased surface area of lungs in relation to height.

Exercise 3:  Pulmonary function tests during simulated airway obstruction

5. Based on the experimental data, how have PEF, FVC, FEV1 and the FEV1/FVC ratio been affected by simulated airway obstruction and why?

(3 marks)

Decreased forced vital capacity is due to comorbid conditions that affect physical inactivity and include aging, cardiovascular diseases, metabolic syndrome, and obesity.

Decreased peak expiratory flow vary depending on age, gender, and height. This is due to pulmonary defects like asthma and chronic obstructive pulmonary disease thus reduction in the flow.

FEV1 decreases due to obstructive lung diseases thus obstruction of air escaping from the lungs.

FEV1/FVC decreases also due to decreased FEV1 and FVC due to either fibrosis or obstructive lung disease.

6. How is the FEV1/FVC ratio used in diagnostic tests of pulmonary function?

(3 marks)

FEV1/FVC ratio is the measurement of the amount of air one can forcefully exhale from the lungs. FEV1 is the volume of breath exhaled with effort in one second. FVC is the full amount of air that can be exhaled in a complete breath. This ratio is used in diagnosing and treating obstructive lung diseases like chronic obstructive pulmonary diseases by measuring the vital capacity of a person able to expire in the first second of the first expiration to full forced vital capacity.

Exercise 4:  Expiratory and inspiratory pressures

7. Which muscles are responsible for generating (a) maximal negative inspiratory pressures and (b) maximal positive expiratory pressures? Hint: how are lung volumes achieved below FRC?

(3 marks)

Maximal negative inspiration pressures use mouth muscles to generate maximal negative pressures from one inspiratory effort starting from functional residual capacity to achieve lung volumes below it.

Maximal positive expiratory pressures use both thoracic and abdominal muscles to generate maximum positive pressure from one expiratory effort starting from total lung capacity to reach their optimal force-length relationships at high pulmonary levels thus achieving the lung volume.

8. Consider a human subject breathing normally (not maximal inspiration or expiration). At what stage of the inspiratory cycle is the airway/intrapulmonary pressure most negative, and at what stage of the expiratory cycle is the airway/intrapulmonary pressure most positive?

(2 marks)

During inspiration, the diaphragm contracts making the abdominal cavity move inferiorly and the external intercostal muscles contract moving the ribs upward and outward which expands the ribcage and increases the volume of thoracic cavity decreasing the intrapulmonary pressure thus a pressure lower than atmospheric pressure.

During expiration, the diaphragm and intercostal muscles relax, thoracic, and lung volume decrease in volume making the interpulmonary pressure rise above atmospheric pressure thus being the most positive.

9. Define lung compliance. At what lung volumes is compliance of the respiratory system (lungs and chest wall) the highest?  What factors influence lung compliance?

(5 marks)

Lung compliance is the ability of the lung to stretch and expand due to the change in volume based on the change in pressure.

Compliance of the respiratory system is highest at moderate lung volumes since lungs have lower than normal levels of recoil indicating little pressure difference in pleural pressure which is needed to change the volume of the lungs.

Factors that influence lung compliance are the elasticity of lung tissue in which thickening of lung tissue decreases lung compliance and surface tension at air-water interfaces in which greater surface tension leads to lower lung compliance.

10. Imagine you are a fugitive hiding underwater in a swamp and breathing through a hollow reed that reaches above the surface of the water. From the data obtained in this class on maximal respiratory pressures, how deep underwater could you go before it would no longer be possible to inhale air?  Give an explanation for your answer.  Hint: for every meter below the surface, the hydrostatic pressure will increase by 100 cm of water.

(4 marks)

16 feet deep into the water since as one goes deeper pressure increases in the eardrums due to an increase in hydrostatic pressure. As the depths of water increase, the water pressure collapses the lungs to half the normal volume which is referred to as lung compression hence suffocation.

Total = 40 marks