Table 2.

Correlates of PPG ratios selected by stepwise regression

Parameters	PPG ratio
	Time intervals (s)
	0–30	30–60	60–90	90–120	120–150	150–180	180–210	210–240
Regression statistic
Model R2 (%)	9.7	21.4	22.5	19.8	19.2	16.3	13.2	12.2
Age (+10 years)*
β±SE	0.014±0.020 p=0.45	−0.0007±0.028 p=0.98	0.005±0.025 p=0.85	0.004±0.019 p=0.85	0.007±0.017 p=0.68	−0.0008±0.014 p=0.95	0.004±0.012 p=0.72	0.002±0.011 p=0.91
Partial r2 (%)	0.02	0	0.01	0.04	0.06	0	0.04	0.01
Female
β±SE	0.16±0.05 p=0.0004	0.49±0.68 p<0.0001	0.46±0.061 p<0.0001	0.35±0.050 p<0.0001	0.26±0.041 p<0.0001	0.20±0.035 p<0.0001	0.14±0.031 p<0.0001	0.12±0.03 p<0.0001
Partial r2 (%)	3.9	13.6	16.0	15.1	13.5	12	7.7	6.1
Current smoking (0,1)
β±SE	−0.30±0.07 p=0.0004	−0.39±0.09 p<0.0001	−0.29±0.085 p=0.0007	–	–	–	–	–
Partial r2 (%)	4.0	3.7	3.1	–	–	–	–	–
Body mass index (+1 kg/m²)
β±SE	−0.014±0.007 p=0.017	−0.027±0.009 p=0.003	−0.032±0.008 p<0.0001	−0.025±0.007 p<0.0001	−0.022±0.005 p<0.0001	−0.018±0.005 p<0.0001	−0.015±0.004 p=0.0002	−0.013±0.004 p=0.0008
Partial r2 (%)	1.7	3.0	3.4	3.4	4.5	4.5	4.1	3.5
Total cholesterol (+1 mmol/L)
β±SE	–	−0.068±0.034 p=0.045	–	–	–	–	–	–
Partial r2 (%)	–	1.1	–	–	–	–	–	–
Blood glucose (+1 mmol/L)
β±SE	0.10±0.04 p=0.013	–	–	0.07±0.04 p=0.026	0.06±0.03 p=0.034	–	0.05±0.02 p=0.027	0.06±0.02 p=0.006
Partial r2 (%)	1.9	–	–	1.3	1.2	–	1.4	2.2

Values are mutually adjusted partial regression coefficients ±SE. *Age was forced into all models. The covariables considered in stepwise models included sex, systolic and diastolic blood pressures, heart rate, body mass index, current smoking, total cholesterol, LDL cholesterol, haematocrit, blood glucose, antihypertensive and lipid-lowering drug treatment, and history of ischaemic heart disease.

LDL, low-density lipoprotein; PPG, photoplethysmography.