Question

1. Given:

Tidal Volume = 400 ml

Inspiratory Reserve Volume = 2500 ml

Expiratory Reserve Volume = 800 ml

Breathing rate = 14 breaths/min

Ventilatory dead space = 120 ml

Ventilation/perfusion ratio = 0.8

Stroke volume = 70 ml/beat

Calculate:

Vital capacity = __________ml ( 1 pt)

Alveolar ventilation rate = ____________ml/min (2 pts)

Heart rate = ______ beats/min (2 pts)

Answer 1

1. Vital capacity is equal to:

Vital capacity= total inspiratory volume + total expiratory volume+ tidal volume.

Putting values in the above formula

2500+800+400 ml

Vital capacity = 3700 ml

2. Alveolar ventilation rate is given by:

Alveolar ventilation rate = Alveolar ventilation ( tidal volume - dead space volume) * Respiratory rate

Putting the given values in above equation we get,

Alveolar ventilation rate = (400-120) * 14 ml/min

= 3920 ml/min

3. Heart rate is given by:

heart rate = cardiac output/ stroke volume ---- (1)

We are given the stroke volume but we need to find cardiac output.

Given,

Alveolar Ventiation/ perfusion ratio= 0.8 ----- (2)

Alveolar ventilation rate = 3920 ml/min

Putting the value of alveolar ventilation rate in (2) we get

3920/ Perfusion = 0.8

Perfusion = 3920/ 0.8

Perfusion = 4900 ml/min

Caridac Output is same as perfusion for two lungs

So cardiac output = 4900 ml/min

Putting values of cardiac output and stroke volume in (1) we get,

Heart rate = 4900/ 70 beats/min

= 70 beats/min