The cross sectional study was conducted on 50 young individuals (25 males and 25 females) and 50 old individuals (25 males and 25 females). Simple random sampling was employed

Signed informed consent forms were taken from every individual. Data collection forms were used. Laboratory equipments included sphygmomanometer, phonoarteriogram, pressure transducer and measuring tape. Data analysing software used was Lab Chart software and AD Instruments (these instruments analyse data from the blood pressure cuff and the phonoarteriogram and the software helps plot graphs from the appropriate readings taken) were used. The equipment along with the associated Lab chart software was made available at the Electrophysiology Lab at Osmania Medical College, Hyderabad.

A subject was made to sit comfortably. Age and gender of the subject was noted. The mid arm circumference of the subject was measured using tape. The left brachial artery was located by palpation and the phonoarteriogram was placed on the site and was secured by a Velcro. The sphygmomanometer cuff was tied 2cm above the cubital fossa of the left arm. The blood pressure was recorded using the Lab Chart software. The Korotkoff sounds picked up and transmitted by the phonoarteriogram were represented as distinct lines on the graphical recording.

Since it was not possible to determine using the software, which two lines exactly correspond to the beginning and end of the Korotkoff sounds, the procedure was repeated using a stethoscope instead of the phonoarteriogram. Using the values of the systolic and diastolic blood pressures obtained by auscultation, the corresponding points were then marked on the graph [Table/Fig-1].

[Table/Fig-1]:

Recording of blood pressure (red) and Korotkoff sounds (blue) obtained using the Lab Tutor software. The black points mark the beginning and end of the Korotkoff sounds as recorded by auscultation.

The length of each line in the recording was calculated in millimeters and the average of the length of all the lines was taken as the average amplitude of the Korotkoff sounds recorded for that subject. Although the scale on the y-axis showed the amplitude in millivolts (mV), the lengths were taken in millimeters (mm) for the ease of calculation and comparison.

The mean values of the average amplitudes of the subjects of the following categories were obtained - young males, young females, old males, and old females. The mean values are compared for any significant differences using independent samples t-test. The unpaired samples t-test was done and correlational coefficient was calculated to look for significance in the variations in mean amplitudes in relation to variations in pulse pressures in the different age groups. Null hypothesis was eliminated at p<0.05. Data was analysed using the SPSS software version 20.0 (SPSS Inc.).

There was a significant difference in the mean amplitudes of Korotkoff sounds among the different age groups and subject categories and by using the independent samples t-test, the significance of the difference in mean amplitudes for the different categories was analysed and the p-values obtained [Table/Fig-2,3]. A significant difference in pulse pressures was also seen among different age groups and subject categories. The decrease in the amplitudes of Korotkoff sounds in the older age group accompanies the increase in pulse pressures seen in this group [Table/Fig-4] and the same was seen among the different age groups within each sex [Table/Fig-5]. For correlating the variations in the pulse pressure with average amplitude in the different age groups among the sexes, the unpaired samples T-test was employed to calculate the correlation coefficient and the significance was determined by the p-value and a significant correlation was seen in both males [Table/Fig-6] and females [Table/Fig-7].

[Table/Fig-5]:

Comparison of mean pulse pressures and mean amplitudes of the different categories of subjects. The scatter plot shows four distinct groupings corresponding to the four categories of subjects. There is some degree of overlap between the two sexes within an age group.

Category	Mean Pulse Pressure (mm Hg)	Mean Amplitude (mm)
Young Male	45.84±3.41	14.49±3.55
Old Male	57.84±4.00	8.39±2.65
Young Female	43.60±3.11	6.28±2.46
Old Female	57.28±2.82	3.65±1.46

Korotkoff sounds have always been associated with the measurement of B.P. In a paper by Simon Rodbard, it was shown that the Korotkoff sounds varied in the case of reactive hyperaemia [1]. This shows that the Korotkoff sounds vary with the amount of blood flowing through the vessel. It was also shown that the sounds were produced due to the flutter of the arterial wall [1]. By using these findings, this study was taken up to see if the change in Korotkoff sounds holds good in conditions wherein the elasticity of the arterial wall differs.

The results of the study show that such a relationship can be drawn and that the amplitudes of the Korotkoff sounds do change with change in the vascular compliance. The study shows that in the older individuals, the mean amplitude is 6.02±3.20 mm, which is 4.37mm less than that of the younger individuals (p=0.001) who have an average amplitude of 10.39±5.13 mm. This occurs as a result of the phenomenon of arteriosclerosis which occurs in the ageing arterial wall [2]. Arteriosclerosis leads to a decrease in elasticity of the wall thus making it less compliant, and hence, being able to flutter less. Consequently, the amplitudes of the Korotkoff sounds should decrease which is shown by the results of the study.

As stated in studies by Dart AM et al., and Zieman SJ et al., the pulse pressure readings in the older individuals increase [4,5]. This is also due to the effect of arteriosclerosis of the vascular wall. As a result of the decreased vessel wall compliance the pulse wave velocity increases. This causes the pulse wave to rapidly rebound from the branching points in the artery and superpose earlier during systole resulting in systolic pressure augmentation. Hence, there is an increase in systolic blood pressure reading relative to the diastolic blood pressure reading resulting in an increase in pulse pressure. This is seen in the sample of subjects taken for the study wherein the values of mean systolic blood pressure, mean diastolic blood pressure and mean pulse pressure for old and young subjects are 130.52±9.35 mm Hg, 73.12±7.73 mm Hg, 57.56±3.44 mm Hg and 115.08±8.35 mm Hg, 70.32±7.50 mm Hg, 44.72±3.42 mm Hg respectively. When analysed for a correlation between the pulse pressure and average amplitude between the different age groups, in males, for the older individuals, the mean pulse pressure was higher by 12.00 mm Hg and the mean amplitude was lower by 6.10mm when compared to the younger individuals (r = -0.574, p = 0.001) and among females, for older individuals, the mean pulse pressure was higher by 13.68 mm Hg and the mean amplitude was lower by 2.63mm when compared to the younger individuals (r = -0.449, p = 0.002).

Both these observations - increase in pulse pressure and decrease in amplitude of Korotkoff sounds, seen in the older individuals are the result of decrease in vascular compliance with arterial ageing. Thus, the results obtained show that the amplitude of Korotkoff sounds does decrease as a result of decreased vascular compliance.

A noteworthy observation is the constant ratio between the amplitudes of young and old individuals (overall = 1.726, males = 1.727, females = 1.722). Since the amplitude is directly proportional to the vessel wall compliance, the factor of 1.72 may probably indicate how much more compliant the vessel wall is in a young individual compared to the older subjects. However, a study with a much larger sample size must be conducted to validate this hypothesis. It was also observed that there is a difference in the amplitude of the Korotkoff sounds between males and females of the same age group. This may be due to the differences in blood volume between the sexes [8]. The greater the blood volume, the more is the amount of blood flowing through the vessel, and hence, higher amplitude of Korotkoff sounds is observed [1]. The larger amplitude in males can also be attributed to more muscle mass which draws a greater amount of blood than compared to that of females [1].

The comparison between the amplitude of Korotkoff sounds and mid arm circumferences of the subjects could not be made effectively in this study. This is because the relative proportions of muscle and fat in the upper arm cannot be determined by the value of mid arm circumference alone. For such a study it will be necessary to take into account the derived parameters of the upper arm anthropometry like - mid upper arm area (MUAA), mid upper arm muscle area (MUAMA), mid upper arm fat area (MUAFA) and arm fat index (AFI) [9,10].

A study with a larger sample size can be taken up in order to standardize the values of the Korotkoff sounds amplitudes for healthy individuals in each category, namely - young males, young females, old males and old females.

In this study, since physiologically normal individuals were taken as subjects, a difference in amplitude of Korotkoff sounds was observed attributable to a naturally occurring change in vascular compliance. This could be extended to conditions wherein a change in vascular compliance is brought about by pathological alterations in the vascular wall as in atherosclerosis resulting from diabetes mellitus and hyperlipidaemia [11].

Further research can be done to see if this method can be used for following up the effect of drugs that affect either the amount of blood flowing through the artery as in anti-hypertensive vasodilator drugs [12] or drugs that affect the nature of the vessel wall as in anti-lipidaemic drugs [13,14].

If proven plausible, it can also be used to detect the severity of blood loss in conditions like cardiovascular shock and extensive burns [15] and it may also be used to follow up response to rehydration therapy [15,16] in such situations.

The amplitude of Korotkoff sounds gives us an idea of the nature of the arterial wall as shown by a decrease in amplitude in older individuals when compared to the younger individuals and of the volume of blood flowing through the artery as shown by the higher amplitudes observed in males when compared to females.

By standardizing the amplitude values for healthy individuals of different age groups in each gender by conducting larger studies, the values obtained in patients with cardiovascular diseases, metabolic dysfunctions and emergency situations can be compared with them to know the extent of decrease in circulating blood volume and vascular compliance.

Comparison can also be made between the standard reference values, the values obtained at admission to the hospital with a particular cardiovascular or metabolic complication and the values obtained after therapeutic intervention to effectively monitor the recovery of the patient.

Hence, measurement of amplitude of Korotkoff sounds can be used as a regular procedure for monitoring the cardiovascular status of patients admitted to the hospitals.