A specialized near infrared spectrophotometry instrument for noninvasive, continuous monitoring of the hemodynamic events of erection in the human penis has been developed. Its potential application for the diagnostic evaluation of erectile dysfunction was investigated. Thirty-eight patients and 18 volunteer subjects underwent penile near infrared spectrophotometry using an optical sensor probe with wavelength selectivity for hemoglobin absorption spectra. Penile blood volume changes and their time courses were measured following intracavernous pharmaco-stimulation in patients and visual sexual stimulation in volunteers. Spectrophotometric results were compared with results obtained simultaneously using color duplex ultrasonography, strain gauge penile circumference monitoring, penile tonometry, and clinical assessments. Spectrophotometric recordings of penile erection showed measurable blood volume changes consistent with the hemodynamic events of this biological function. Blood volume per cent (BV%) increase correlated with clinical ratings of erection quality (P<0.001), penile rigidity measurements (P<0.005), and penile circumference increases (P<0.0001), and it correlated with mean peak systolic velocity measurements when BV% increase was restricted to values less than 50% (P<0.001). The time to reach half the maximum blood volume change (BV T1/2) correlated directly with the time to reach half the maximum penile circumference size increase (P<0.001), whereas BV T1/2 correlated inversely with mean resistive index measurements only when BV T1/2was restricted to values greater than 120 s (P<0.05). Spectrophotometric criteria consisting of BV % less than 35% and BV T1/2 greater than 120s affirmed the diagnosis of severe erectile impairment with a similar degree of accuracy as standard ultrasonographic criteria (P<0.002). Penile near infrared spectrophotometry is a safe, inexpensive and simply used biomedical optics technique that provides quantitative measurements of the vascular physiology of penile erection and appears to offer clinical utility in the diagnosis of vasculogenic erectile dysfunction. International Journal of Impotence Research (2000) 12, 247-254.
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