Amplitude variability of the action potential in hypoxic ventricular muscle

The effect of hypoxia on the amplitude variability of the action potential in guinea pig papillary muscle was investigated by high-resolution on-line computer analysis using a 6 kHz sampling rate and a 2 kHz low pass filter. Ensembles of 50 successive action potentials were carefully aligned in time, and the amplitude variability was determined by calculating the standard deviation (SD) for each sampling point within the action potential. In oxygenated muscle, the SD was about 0.5 mV at phases 1, 2 and 4 and about 2 mV at phase 3. During hypoxia (40 to 105 min) the SD peak at phase 3 declined from the control value of 2.21 +/- 0.23 mV (SE, n = 11) to 1.50 +/- 0.27 mV (SE, n = 6). It is concluded that previous reports suggesting an increase of the action potential variability during hypoxia may be due to improper recording and data processing procedures.