Question

2a. A. Please calculate minute ventilation (VE), alveolar ventilation (VA), cardiac output (Q) and the ventilation perfusion ratio (VA/Q) for an exercising individual with the following variables. weight = 150 pounds; stroke volume = 140 ml/beat; tidal volume = 1050 ml/breath; heart rate = 140 beats/min; respiratory rate = 24 breaths /min.

Answer 1

1)Tidal volume is the amount of air inhaled or exhaled in one breath during relaxed quiet breathing .Normal is 500-750 ml/minute .
As the pateint is exercising the tidal volume is increased and it is 1050 ml

2)Anatomical dead space
It is the volume of gas within the conducting (from mouth, nose up to terminal bronchioles) system of respiration.

It is ~ 2 mL/kg in the upright position.
It also correspond to the weight in pounds .

In the question weight of individual is 150 pounds weight in pounds roughly is equal to Anatomical dead space so dead space is 150 ml

3)Minute ventilation determine the ventilation of alveoli occuring in one minute .

Minute Ventilation (MV)
=Tidal volume (TV)xrespiratory rate (RR)
= 1050 × 24 mL/min= 25,200 ml /min OR 25 .2 Litres / min.

4) Alveolar Ventilation:
(TV – dead space) × RR
= (1050 – 150) × 24 = 18,900mL/min
Or 18.9 Litres /min

5)Cardiac output is the amount of blood pumped out of ventricle during each heart beat .
Stroke volume is volume of blood pumped out by ventricles during each beat .
Cardiac output=Heart rate x Strokevolume
Cardiac output = 140 x 140 =19,600 ml Or
                           = 19.6 litres
                         

6) Ventilation / Perfusion ratio is the ration between the alveolar ventilation and cardiac output .
It determines the amount of air that is entering the alveoli during ventilation and much are well perfused with blood .
Normal V/Q ratio is 0.8
It is higher at Apex of lung and low at base of lung .
V/Q ratio =Alveolar ventilation / Cardiac output

V/Q ratio= 18.9 / 19.6 = 0.96