Question

A 22-year-old man was in a motorcycle accident with resultant neck injuries that led to partial paralysis of the upper and lower limbs. Almost immediately his chest felt heavy and he became dyspneic. His pulmonary function values were as Vital capacity (supine) 650 mL Minute ventilation (supine) 6 L/min Respiratory rate (supine) 30 b/min PaO2 61 mm Hg PaCO2 47 mm Hg
1. What are the values for the tidal volume (TV) and the alveolar ventilation (AV) for this individual? (Assume a normal value for dead space.) Compare with normal.
2. What is contributing to the decreased alveolar ventilation?
3. Which nerves and muscles are involved in this problem?
4. How is the residual volume affected?
5. Define dyspnea
6. What is causing the dyspnea in this individual?
7. Describe the reflexes involved in causing tachypnea in this individual.

Answer 1

Answer:

We are given:

Minute Ventilation, MV = 6L/min

Respiratory Rate, RR = 30 b/min

PaO2 = 61mmHg

PaCO2 = 47mmHg

a) to find Tidal Volume, TV, we use:

TV = MV/RR

TV = 6/30

= 0.2litres => 200ml

For Alveolar ventilation, AV, we have:

AV = (Tidal Volume-dead space)×RR

AV = (200 - 150)×30

AV = 1500ml/min

The normal dead space value is 150ml.

Comparing both TV and AV with the normal values, it can be said that, since he has a TV of 200ml, he is defficient because a normal TV level is 500ml.

The man has an AV of 1500ml/min, which is low when compared to the normal AV value which is 4200ml/min.

2) The factor contributing to the deceased alveolar ventilation is the increase in PaCO2, in this case, the PaCO2 is 47mmHg, whereas the normal PaCO2 level is between 38-42mmHg

3) The muscle involved in this problem is the lower rib cage and thoracic cavity, while the nerve involved in this problem is the spinal cord.

4) The residual volume is decreased

5) Dyspenea simply means shortness of breath. It happens when a person experiences difficulty in breathing.

6) The cause of Dyspenea could be that the tidal Volume is lowered by the reduced diaphragmatic and intercoastal innervation or it could also be caused by chest trauma

7) The reflexes that causes tachypnea in this individual are the central and peripheral chemoreceptors. A individual has a PaO2 of 61mmHg and this low PaO2 causes the high breathing rate becauses peripheral chemoreceptors senses it and the medulla sends the signal out