Objective To evaluate the blood supply to the penis during bicycling and thus determine whether the associated perineal compression might be responsible for some cases of impotence. Subjects and methods The transcutaneous penile oxygen partial pressure (pO2 ) at the glans of the penis was measured in 25 healthy athletic men; pO2 is readily measured by noninvasive techniques currently widely used in the management of premature infants, and which have been shown to give pO2 levels that correlate with arterial pO2 levels. The measurements in the healthy subjects were taken in various positions, before, during and after bicycling. Results The mean (sd) pO2 of the glans when standing before cycling was 61.4 (7.2) mmHg; it decreased after 3 min of cycling to 19.4 (4.7) mmHg. After 1 min of cycling in a standing position it increased significantly to 68 (7.6) mmHg; when cycling was continued in a seated position, after 3 min the pO2 fell to 18.4 (4.2) mmHg and there was a full return to normal pO2 values after a 10‐min recovery period. Conclusion The pO2 seems to correlate with the blood supply to the penis. The present results support the hypothesis that as the penile arteries are compressed against the pubic bone by the saddle during bicycling, the pO2 values decrease. Additionally, shifting from a seated to a standing position while cycling significantly improved the pO2 value of the penis and penile blood oxygenation was then even greater. Therefore, we suggest that cyclists change their body position frequently during cycling. Correcting the handlebars or the height of the saddle, tipping the nose of the saddle to produce a more horizontal, or even downward pointing position, and attention to the design of the saddle may be the only required precautions.

Objective  To study the rate of change in prostate specific antigen (PSA velocity) in patients with prostate cancer initially managed by ‘watchful waiting’. Patients and methods  Serial PSA levels were determined in 141 patients with prostate cancer confirmed by biopsy, who were initially managed expectantly and enrolled between May 1990 and December 1995. Sixty‐seven patients eventually underwent surgery (mean age 59 years) because they chose it (the decision for surgery was not based on PSA velocity). A cohort of 74 patients remained on ‘watchful waiting’ (mean age 69 years). Linear regression and logarithmic transformations were used to segregate those patients who showed a rapid rise, defined as a>50% rise in PSA per year (or a doubling time of <2 years) and designated ‘rapid risers’. Results  An initial analysis based on a minimum of two PSA values showed that 31% were rapid risers. Only 15% of patients with more than three serial PSA determinations over ≥6 months showed a rapid rise in PSA level. There was no advantage of log‐linear analysis over linear regression models. Conclusion  Three serial PSA determinations over ≥6 months in patients with clinically localized prostate cancer identifies a subset (15%) of patients with a rapidly rising PSA level. Shorter PSA surveillance with fewer PSA values may falsely identify patients with rapid rises in PSA level. However, further follow‐up is required to determine if a rapid rise in PSA level identifies a subset of patients with an aggressive biological phenotype who are either still curable or who have already progressed to incurability through metastatic disease.

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