This study sought determine the HHR in our study population, compare it with previous studies, and to relate it with sex, stratified age groups, height and BMI. Our study had the highest values of central tendency for both the right and left hilar height ratio. The values of the right and left hilar height ratio for our study compared favourably with the original study done by Homer but with a lower level of variability (12).
The differences in hilar height ratio values in our study compared to previous studies done in Kenya (11), United states of America (USA) (12) and south Korea (13) (Table 4) could be explained by the difference in demographic characteristics, difference in sample sizes and the skewed male to female ratios.
Table 4
The comparison of the hilar height ratio with published specific reference ranges
|
Uganda, 2020
(Median IQR)
|
Kenya, 1995 (11)
(Mean ± SD)
|
Korea, 1979 (13)
(Mean ± SD)
|
USA, 1978 (12)
(Mean ± S.D.)
|
Right HHR
|
1.42 (1.31-1.57)
|
1.18 (0.97-1.43)
|
1.28 (1.14-1.42)
|
1.31 (1.1-1.52)
|
Left HHR
|
0.92 (0.86- 0.98)
|
0.86 (0.69-1.02)
|
0.88 (0.79-0.97)
|
0.84 (0.75-0.93)
|
The median right HHR and left HHR were 1.42 and 0.92 respectively. The mean right and left HHR in Kenyan population were 1.18 and 0.86, respectively (11) and in Korean population were 1.28 and 0.88 respectively (13). Our study showed the highest values of central tendency for both the right and left HHR. However, the Kenyan population had the greatest variability with the lowest values of its minimum right and left HHR of 0.97 and 0.69, respectively (11).
The median right and left HHR of this study was favorably compared with Homer's study in USA (12), where mean right and left HHR were 1.31 and 0.84, respectively. This could be explained by the difference in sample sizes (384 versus 90 in Homer’s study) and the skewed male to female ratio (85.7–14.3% versus 45.5–54.5% in Homer’s study).
Because mean was used as the measure of central tendency in the three previous studies, it is assumed that the data was normally distributed, and in normally distributed data, mean and median are equal (14); therefore, our data's median values can be compared to the means in the previous studies.
There was a significant difference (p=0.017) in the median values of the right HHR between males and females at 1.47 and 1.38 respectively whereas there was no significant difference (p=0.178) in the left HHR between males and females at 0.93 and 0.92 respectively. The mean right hilar height ratio between males and females in the study done by Homer (12) was 1.31 and 1.35, respectively whereas the left HHR between males and females was 0.89 and 0.82 respectively.
The mean right hilar height ratio between males and females in the Kenyan study done by Wanene (11) was 1.19 and 1.21 respectively whereas the left HHR between males and females was 0.86 and 0.84 respectively. In both the Kenyan and USA populations, females had a higher mean of the right HHR though not statistically significant. This is reversed in our study, in which females had a higher positioned right hilum compared to the males. The left hilum is, however, not affected by sex.
There was a significant mean difference (p = 0.001) in the right hilar height ratio among the age groups stratified into 15-year intervals. In contrast, there was no difference (p = 0.198) in the left hilar height ratio. There were no statistically significant differences in the different stratified age groups in the right and left hilar height ratios in the Kenyan study (11). However, the Kenyan study population was skewed to the left with only 3 (1.6%) of its population aged above 45 years, which could explain the differences. In our study population, the right hilar height ratios increased with age which implies the position of the right hilum lowered with increasing age while the left hilar position remained unchanged. This could be explained by the fact that the left hilum is anchored by its course above the left main and upper lobe bronchus. On the other hand, vessels that constitute the right hilum course anterior to the right main bronchus and its divisions and their positions are not fixed. To the best of our knowledge, our study is the first to document the lowering of the right hilum with increasing age.
The right and left hilar height ratios were generally not affected by changes in height and weight. It is, therefore, not necessary to measure height and weight when calculating hilar height ratios.