A short period of apnoea causes a marked increase in coronary flow velocity: a transthoracic pulsed wave Doppler study

Coronary artery flow velocity during a short period of apnoea was investigated by transthoracic Doppler recording in 10 healthy men, aged 24-52. During breath holding for 29 +/- 6 s the oxygen saturation in the finger, measured by pulse oxymetry, decreased from 97.5 +/- 0.8 to 90.0 +/- 3.2% (P < 0.001). The maximal coronary blood flow velocity in the left anterior descending artery increased by 62% from 0.26 +/- 0.09 to 0.42 +/- 0.10 m s(-1) and the mean diastolic flow velocity by 47% from 0.19 +/- 0.04 to 0.28 +/- 0.08 m s(-1) (P < 0.001). In most subjects the increase of velocity started already after a few seconds of apnoea. Besides theoretical implications the results show that it is very important to be aware of the higher velocity during apnoea in order to avoid misinterpretation when using breath holding during magnetic resonance imaging or Doppler recording of coronary flow.