Question

1. 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 follows:

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 of 150 mls). Compare with normal.
2. What is contributing to decreased alveolar ventilation? Which nerves and muscles are involved in this problem?

Answer 1

A. We know .Minute volume= Tidal volume×respiratory rate

Hence Tidal volume = minute volume/resp rate

T.V=6000/30 ml/min

=200 ml/min

Alveolar ventilation=( TV-dead space )×resp rate

A.V =(200-150)×15

A.V=50×15

A.V=750.

Normally tidal volume is 500ml/min

and alveolar vent is (Tv-dead space)×resp rate

(500-150)×15 = 5250 ml /min

B...Decreased alveolar ventilation is contributed by insufficent ventilation and decreased tidal volume..

In neck injuries phrenic nerve neurons .c3,c4 nerves in cervical spinal cord gets damaged .which supplies diaphragm.