AMBIENT NOISE INTERFERES WITH AUSCULTATORY BLOOD-PRESSURE MEASUREMENTDURING EXERCISE

This study was designed to investigate whether the acoustical characte ristics of the Korotkoff sounds (K-sounds) were altered during exercis e and/or masked by the ambient noise. After signing informed consent, 11 subjects (8 females, 3 males; 27 +/- 2 yr; 166.2 +/- 3.2 cm; 62 +/- 5 kg; means +/- SD) underwent a cycle ergometer exercise test that in creased in workload by 30 W every 3 min until volitional fatigue. Hear t rate, auscultatory systolic (SEP) and diastolic blood pressure (DBP) , and oxygen consumption were monitored 1 and 2 min into each work sta ge. The auscultatory K-sounds were recorded with a microphone mounted in a stethoscope tube for later frequency (Hz) and sound pressure leve l (dB SPL) analysis. Frequency and SPL of ambient noise (99 +/- 13 Hz and 64 +/- 1 db at maximum, respectively) increased during the exercis e test to magnitudes similar to the SEP and DBP K-sounds (166 Hz, 66 d b; and 128 Hz, 69 db, respectively). Additionally, the ambient noise w as responsible for a significant damping of the frequency and SPL of t he measured blood pressure K sounds and a rise in the measured frequen cy of the SEP K-sounds. Furthermore, we observed ''inaudible'' K-sound s at lower frequencies than adjoining audible K-sounds (100 Hz vs 126 Hz), supporting the known under estimation of SEP by auscultation. The increase in ambient noise during exercise testing dampens and may mas k the auscultatory K-sounds, thus making detection of the proper K-sou nds during exercise difficult at best. Furthermore, the presence of in audible K-sounds may further explain the published discrepancies betwe en auscultatory and intraarterial blood pressure measurements during e xercise.