Table 7.

Association between oxygen saturation at rest, pNN50, peak heart rate, and chronotropic index.

	Univariable Analysis				Multivariable Analysis
	b	95% CI	p-Value	R2	b	95% CI	p-Value	R2
Sat. O2 rest	0.026	(0.004–0.047)	0.02	0.18	0.021	(0.006–0.035)	0.006
pNN50	0.016	(0.003–0.029)	0.018	0.19	0.011	(0.003–0.02)	0.013	0.7
Peak heart rate	0.005	(0.003–0.007)	<0.001	0.54	0.004	(0.002–0.006)	<0.001

Abbreviations: HRR, heart rate reserve; pNN50, percentage difference between adjacent NN intervals of >50 ms duration; Sat. O₂, oxygen saturation; 95% CI, 95% confidence interval; b—coefficient from linear regression; R²—coefficient of determination.