Abnormal Renal Resistive Index in Patients with Mild-to-moderate Chronic Obstructive Pulmonary Disease

Figures & data

Figure 1.  Disposition process for patient selection.

Table 1.  Clinical characteristics, arterial blood gas analysis, and pulmonary function of the study population*.

	Group 1†	Group 2†	Group 3†	Group 4†	p-Value
Clinical Characteristics
Age, yr	73.0 ± 10.4	75.8 ± 7.3	75.5 ± 4.7	72.5 ± 6.3	0.804
Systolic blood pressure, mmHg	130.7 ± 7.9	129.5 ± 6.7	132 ± 4.7	134 ± 6.3	0.696
Diastolic blood pressure, mmHg	80.5 ± 6.7	78.3 ± 8.2	81.8 ± 5.3	83.6 ± 3.8	0.573
Heart rate, beat/min	77.3 ± 6.2	78.3 ± 4.2	76.7 ± 5.3	74.4 ± 6.5	0.627
Smoking index, pack-year	36.2 ± 5.3	38.9 ± 6.3	39.1 ± 5.9	0	0.493
Body weight, kg	70.3 ± 4.0	67.8 ± 14.3	56.6 ± 11.5	56.6 ± 11.5	0.111
Height, cm	161.5 ± 1.9	167.5 ± 4.6	162.5 ± 8.6	162.5 ± 8.6	0.202
Body mass index, kg/m2	26.9 ± 1.3	24.1 ± 4.5	21.3 ± 3.5	21.3 ± 3.5	0.069
Arterial Blood Gas Analyses
pH	7.43 ± 0.02	7.44 ± 0.20	7.39 ± 0.49§	N/A	0.039
PaO2, mmHg	79.5 ± 4.1	83.1 ± 6.4	83.7 ± 6.0	N/A	0.492
PaCO2, mmHg	37.5 ± 7.0	36.3 ± 5.7	38.2 ± 7.5	N/A	0.856
HCO3, mEq/L	24.3 ± 3.9	24.1 ± 4.4	22.8 ± 4.7	N/A	0.798
Pulmonary Function Tests
FEV1 Actual value, L	2.29 ± 0.38	2.24 ± 0.30	1.24 ± 0.31‡§	3.47 ± 0.24	<0.001
% of predicted value	98.0 ± 9.7	92.3 ± 9.9	54.3 ± 7.8‡§	93.3 ± 3.8	<0.001
FVC Actual value, L	3.20 ± 0.39	3.34 ± 0.52	3.52 ± 0.56‡	4.21 ± 0.37	0.021
% of predicted value	97.3 ± 8.1	105.0 ± 9.3	110.3 ± 15.4‡	98.3 ± 12.2	0.019
FEV1/FVC	0.74 ± 0.02	0.64 ± 0.02‡	0.55 ± 0.04‡§	0.82 ± 0.07	0.001
Biochemistry Measurements
Blood urine nitrogen, mg/dl	16.8 ± 4.2	19.8 ± 5.2	19.8 ± 5.2	17.9 ± 0.51	0.137
Blood creatinine, mg/dl	0.98 ± 0.13	1.10 ± 0.16	1.10 ± 0.16	0.99 ± 0.25	0.498
Blood osmolality, mosm/kg	295.3 ± 4.5	294.4 ± 8.4	294.4 ± 8.4	N/A	0.858
Urine creatinine, mg/dl	123.3 ± 48.3	169.3 ± 66.5	169.3 ± 66.5	N/A	0.364
Urine osmolality, mosm/kg	572.3 ± 100.1	642.0 ± 34.7	642.0 ± 34.7	N/A	0.478
Glomerular filtration rate, ml/min/1.73 m2	54.3 ± 10.8	47.6 ± 12.2	47.6 ± 12.2	N/A	0.286


PaO2, PaCO2 = arterial oxygen and carbon dioxide tensions; FEV1 = forced expiratory volume in 1 second; FVC = forced vital capacity.

*Data were measured on the same day; they are shown as mean ± SD.

† Group 1: smokers with normal spirometry, 8 patients; Group 2: mild COPD, 8 patients; Group 3: moderate COPD, 8 patients; Group 4: nonsmoker control group, 8 subjects.

‡, § The values were significantly different from the other groups. ‡ compared with Group 1; § compared with Group 2, p < 0.05 by ANOVA tests and LSD post-hoc comparisons.

Figure 2.  Renal resistive index before and after protein loading in smoker patients with different severities of COPD and nonsmoker control subjects. The postprandial RRIs were significantly increased compared with the baseline values in the heavy smoking patients. Moderate COPD patients (FEV1 50–80% predicted, Group 3) had persistent RRI elevation for more than 90 minutes, and the RRI elevation lasted for only 45 minutes in the other two smoker groups. Group 1: smokers with normal spirometry, 8 patients; Group 2: mild COPD, 8 patients; Group 3: moderate COPD, 8 patients; Group 4: nonsmoker control group, 8 subjects. *p < 0.05,**p < 0.01 compared with baseline RRI by paired t-tests. § p < 0.05 compared with Group 1 at the same time points by the Student's t-test.

Figure 3.  Renal resistive index before and after protein loading in patients with high/low serum TNF-α levels. The RRIs were significantly increased from the baseline values in patients with high TNF-α (> 7 pg/ml) and low TNF-α (≤ 7 pg/ml) levels 45 min postprandial, while the RRI elevation lasted longer in patients with high TNF-α levels (*p < 0.05,**p < 0.01 compared with baseline RRI by paired t-tests). The RRI was also significantly more elevated in patients with high TNF-α levels compared with those with low TNF-α levels at 135 min (§ p < 0.05 by the Student's t-test).

Figure 4.  Renal resistive index 135 min after protein loading against airway obstruction and TNF-α serum levels. (A) The RRI was negatively correlated with the percentage of predicted values of FEV1 (Correlation Coefficient = –0.563, P = 0.010). (B) The RRI was positively correlated with serum TNF-α levels (Correlation Coefficient = 0.473, P = 0.035). The solid lines indicate the regression line and the dashed lines indicate the 95% confidence intervals.

Table 2.  Multiple linear regression of the final renal resistive indices.

	Regression Coefficient β	Standard Error	95% CI for β	p-Value
Variables in the Model
FEV1% of predicted value	–0.117	0.046	-0.205 –-0.019	0.023
TNF-α, pg/ml	0.030	0.009	0.012 –0.049	0.003
Age, yr	0.004	0.001	0.003 –0.006	0.001
Excluded Variables
Urine/serum ratio of osmolality	0.430	0.025	-0.010 –0.097	0.104
Body mass index, kg/m2	0.004	0.005	-0.006 –0.015	0.400
PaO2, mmHg	0.001	0.002	-0.004 –0.004	0.904
PaCO2, mmHg	0.001	0.002	-0.004 –0.006	0.691
Glomerular filtration rate, ml/min/1.73 m2	–0.001	0.001	-0.004 –0.002	0.571


CI = Confidence Interval; PaO2, PaCO2 = arterial oxygen and carbon dioxide tensions; FEV1 = forced expiratory volume in one second; TNF-α = tumor necrosis factor; PaO2, PaCO2 = arterial oxygen and carbon dioxide tensions. The final RRI = the fourth time point of RRI measured at 135 min after a protein loading.