B.Sc. (H) Biochemistry IInd Year, IVth Sem Human Physiology Lecture-3 & 4 Mechanism of , pulmonary ventilation and related volumes,

Dr. Prabha Arya Alveolar ventilation

The total ventilation per minute, termed the (VE), is equal to the multiplied by the : Minute ventilation = Tidal volume × Respiratory rate (ml/min) (ml/breath) (breaths/min)

VE = Vt · f

For example, at rest, a normal person moves approximately 500 ml of air in and out of the with each breath and takes 12 breaths each minute. The minute ventilation is therefore 500 ml/breath × 12 breaths/minute = 6000 ml of air per minute. These airways do not permit with the blood, the space within them is termed the anatomic dead space (VD).

Vander’s human physiology (2019) 15th ed Anatomic dead space

Tidal volume (Vt) = 500 ml

Anatomic dead space (VD) = 150 ml

Fresh air entering alveoli in one inspiration (VA) =

500 ml – 150 ml = 350 ml The total volume of fresh air entering the alveoli per minute is called the alveolar ventilation (V˙A): Alveolar ventilation = (Tidal volume –Dead Space)X Respiratory rate

VA = (Vt – VD) X f Alveolar dead space and Physiologic dead space Some fresh inspired air is not used for gas exchange with the blood even though it reaches the alveoli because some alveoli may, for various reasons, have little or no blood supply. This volume of air is known as alveolar dead space. It is quite small in normal persons but may be very large in persons with several kinds of disease. The sum of the anatomic and alveolar dead spaces is known as the physiologic dead space. This is also known as wasted ventilation because it is air that is inspired but does not participate in gas exchange with blood fl owing through the lungs. Exchange of gases in alveoli

Respiratory quotient (RQ) The amount of the cells consume and the amount of dioxide they produce are not necessarily identical. The balance depends primarily upon which nutrients are used for energy. The ratio of CO2 produced to O2 consumed is known as the respiratory quotient (RQ). On a mixed diet, the RQ is approximately 0.8; that is, 8 molecules of CO2 are produced for every 10 molecules of O2 consumed. The RQ is 1 for , 0.7 for fat, and 0.8 for . Vander’s human physiology (2019) 15th ed Summary of typical oxygen and exchanges between atmosphere, lungs, blood, and tissues during 1 min in a resting individual.

The volume of oxygen in 1 L of arterial blood is 200 ml O2/L of blood— that is, 1000 ml O2/5 L of blood. 4000 mL of air 21% is oxygen 840 mL O2

250 mL Crosses Rest is alveoli into the subsequently pulmonary capillaries exhaled

Blood The blood then flows from the lungs to contains the left side of the heart and is pumped by large amount the left ventricle through the aorta, of oxygen arteries, and arterioles into the tissue already capillaries, where 250 ml of oxygen leaves the blood per minute for cells to take up and utilize.

Quantities of oxygen added to the blood in the lungs and removed in the tissues are the same. The story reads in reverse for carbon dioxide.

Partial of gases, Dalton’s law In a mixture of gases, the pressure each gas exerts is independent of the pressure the others exert. This is because gas molecules are normally so far apart that they do not affect each other. Each gas in a mixture behaves as though no other gases are present. These individual , termed partial pressures. (for example: PO2) of gases in liquid, Henry’s law Alveolar gas pressure

The factors that determine the precise value of alveolar

PO2 are (1) the PO2 of atmospheric air, (2) the rate of alveolar ventilation, and (3) the rate of total-body oxygen consumption.

Vander’s human physiology (2019) 15th ed Partial Alveolar Gas Pressure in air pressure of Pressure (mmHg) (mmHg) gas

PO2 105 160

PCO2 40 .3

Redrawn from: Vander’s human physiology (2019) 15th ed Hypoventilation and hyperventilation

 Hypoventilation It exists when there is an increase in the ratio of carbon dioxide production to alveolar ventilation. In other words, a person is hypoventilating if the alveolar ventilation cannot keep pace with the carbon dioxide production. The result is that alveolar PCO2 rises above the normal value.

 Hyperventilation exists when there is a decrease in the ratio of carbon dioxide production to alveolar ventilation—that is, when alveolar ventilation is actually too great for the amount of carbon dioxide being produced. The result is that alveolar PCO2 decreases below the normal value. Ventilation- inequality The lungs are composed of approximately 300 million alveoli, each capable of receiving carbon dioxide from, and supplying oxygen to, the pulmonary capillary blood. To be most efficient, the correct proportion of alveolar air flow (ventilation) and capillary blood flow (perfusion) should be available to each alveolus. Any mismatching is termed ventilation-perfusion inequality. Ventilation-perfusion inequality

One effect of upright posture is to increase the filling of blood vessels at the bottom of the lung due to gravity, which contributes to a difference in blood flow distribution in the lung. Local - perfusion matching.

Vander’s human physiology (2019) 15th ed References

 1. Vander’s human physiology (2019) 15th ed., Widmaier, E.P., Raff, H. And strang, K.T., Mcgraw hill international publications (new york), ISBN: 978-1-259-90388-5. 2. Few Pictures from internet.