Lungs are the organs for purification of blood. Purification means oxygenation of blood & removal of Carbon dioxide. The deoxygenated blood (PO2- 40 mm of Hg)(PCO2-45 mm of Hg ) is pumped by right ventricle to reach the lungs. The oxygenated blood (PO2-104 mm of Hg) (PCO2-40 mm of Hg) is brought back to left atrium, to be pumped by left ventricle to reach each & every cell of the body.
(To be precise the effective PO2 is 95 mm of Hg).
Alveoli are the functional units of lungs. They are terminal ends of bronchial airways, where gaseous exchange takes place. They are surrounded by rich network of capillaries which bring blood for this exchange. There are two factors that determine the PO2 and PCO2 in the alveoli. These two factors are
- The rate of alveolar ventilation
- Amount of blood flowing through alveolar capillaries.
A highly quantitative concept is developed to understand the imbalance between alveolar ventilation & perfusion in alveolar capillaries. (Perfusion means the blood flow in a particular organ.) This is expressed as a ratio called VA/Q, where VA represents alveolar ventilation & Q represents alveolar capillary blood flow. When there is normal alveolar ventilation & normal alveolar capillary blood flow, the exchange through the respiratory membrane is nearly optimal. Thus under normal conditions, the alveolar air PO2 averages 104 mm of Hg & the PCO2 averages 40 mmHg.
However in a normal person in the upright position, the normal capillary blood flow in upper part of lungs is significantly less in relation with alveolar ventilation. Therefore at the top of lung VA/Q is greater, as much as 2.5 times of normal value. Hence this space is called Physiological Dead Space in lungs. At other extreme, in lower part of lungs, there is significant poor ventilation in relation with blood flow. So here, the VA/Q is 0.6 times of ideal, which is called Physiological Shunt.
However during exercise, the blood flow to the upper part of lungs increases & air entry to lower parts.
Role of Yogic Postures & Bucket Handle breathing in improving VA/Q in upper & lower lobes of lungs.
All back bending postures where cervical & thoracic spine is in extension, upper part of chest is directed towards gravity. Due to gravitational pull the amount of alveolar capillary perfusion increases significantly. This reduces the dead space in upper parts of lungs, improving the outcome, optimizing the VA/Q ratio. Examples of these postures are many but the simple one which can be done by everyone is Setubandha Asan.We need to increase the duration to be in this posture. Second example is Viparitdandasan on bench. This bench gives support to whole spine; hence one can remain in this posture for 10-15 minutes with comfort. Names of other back bending postures are, Ushtrasan, Matsyasan, Chakrasan. However it is not advisable to increase duration of these asanas as they lead to excessive compression in lumbar spine.
