54
J. Kumar V. and K. A. Reddy
(100%) with oxygen. Each gram of fully saturated haemoglobin contains 1.3 mL of
oxygen. However, not all haemoglobin molecules participate in oxygen transport.
3.5 Functional and Dysfunctional Haemoglobin
Blood contains several forms of haemoglobin, of which some are useful in oxygen
transport and some are not. Functional haemoglobins are those that can carry oxygen
and include haemoglobin bounded with oxygen molecules, called oxyhaemoglobin
(oxygenated haemoglobin, HbO). Haemoglobin not bounded with any other
molecule is called reduced haemoglobin (deoxy-haemoglobin, Hb). Haemoglobin
which is incapable of carrying oxygen is called dysfunctional haemoglobin (dyshaemoglobin). These are haemoglobin bounded with molecule(s) other than oxygen.
They include carboxyhaemoglobin (COHb) and methaemoglobin (MetHb). COHb is
formed when carbon monoxide (CO) bond to haemoglobin. COHb exists in varying
degrees because of smoking and urban pollution. The level of COHb may become
as high as 45% as a result of smoke inhalation. MetHb is oxidized haemoglobin, and
in normal healthy persons will be less than 1% of the total haemoglobin. COHb and
MetHb are not capable of binding oxygen and hence cannot aid in oxygen transport.
Under normal conditions, HbO and Hb amount to 99% of the total haemoglobin
present in the blood.
3.6 Oxygen Saturation
Whether a person is sleeping, resting or active, every part of that person’s body
requires oxygen. The amount of oxygen required for a part of the body depends
on the degree of activity of that part but is never zero. While parts of the body
can tolerate deprivation of oxygen for limited periods of time, vital organs cannot
withstand reduction in oxygen, even for a very short period. These organs may
become irreversibly damaged with reduced oxygen supply. Of these vital organs, the
brain is by far the most sensitive to reduction in blood oxygen level and can become
dysfunctional if oxygen deficit occurs even for a short period. Hence it is necessary
that the amount of oxygen carried by the arterial blood is measured to estimate the
level of functioning of various parts of the cardio-pulmonary system. The direct
method of measurement of oxygen content in arterial blood is to perform complete
“gas analysis” and ascertain the various concentrations of gasses in arterial blood.
Such an analysis would require drawing of blood directly from an artery and hence
requires the services of a competent surgeon. Alternate methods for the determination
of the gas contents of arterial blood without the need for puncturing and drawing
blood from an artery have been proposed [8] wherein the amount of oxygen in arterial
blood is indirectly measured in terms of oxygen saturation in arterial blood [9, 10].
J. Kumar V. and K. A. Reddy
(100%) with oxygen. Each gram of fully saturated haemoglobin contains 1.3 mL of
oxygen. However, not all haemoglobin molecules participate in oxygen transport.
3.5 Functional and Dysfunctional Haemoglobin
Blood contains several forms of haemoglobin, of which some are useful in oxygen
transport and some are not. Functional haemoglobins are those that can carry oxygen
and include haemoglobin bounded with oxygen molecules, called oxyhaemoglobin
(oxygenated haemoglobin, HbO). Haemoglobin not bounded with any other
molecule is called reduced haemoglobin (deoxy-haemoglobin, Hb). Haemoglobin
which is incapable of carrying oxygen is called dysfunctional haemoglobin (dyshaemoglobin). These are haemoglobin bounded with molecule(s) other than oxygen.
They include carboxyhaemoglobin (COHb) and methaemoglobin (MetHb). COHb is
formed when carbon monoxide (CO) bond to haemoglobin. COHb exists in varying
degrees because of smoking and urban pollution. The level of COHb may become
as high as 45% as a result of smoke inhalation. MetHb is oxidized haemoglobin, and
in normal healthy persons will be less than 1% of the total haemoglobin. COHb and
MetHb are not capable of binding oxygen and hence cannot aid in oxygen transport.
Under normal conditions, HbO and Hb amount to 99% of the total haemoglobin
present in the blood.
3.6 Oxygen Saturation
Whether a person is sleeping, resting or active, every part of that person’s body
requires oxygen. The amount of oxygen required for a part of the body depends
on the degree of activity of that part but is never zero. While parts of the body
can tolerate deprivation of oxygen for limited periods of time, vital organs cannot
withstand reduction in oxygen, even for a very short period. These organs may
become irreversibly damaged with reduced oxygen supply. Of these vital organs, the
brain is by far the most sensitive to reduction in blood oxygen level and can become
dysfunctional if oxygen deficit occurs even for a short period. Hence it is necessary
that the amount of oxygen carried by the arterial blood is measured to estimate the
level of functioning of various parts of the cardio-pulmonary system. The direct
method of measurement of oxygen content in arterial blood is to perform complete
“gas analysis” and ascertain the various concentrations of gasses in arterial blood.
Such an analysis would require drawing of blood directly from an artery and hence
requires the services of a competent surgeon. Alternate methods for the determination
of the gas contents of arterial blood without the need for puncturing and drawing
blood from an artery have been proposed [8] wherein the amount of oxygen in arterial
blood is indirectly measured in terms of oxygen saturation in arterial blood [9, 10].