Maintaining constant cardiac output in conscious dogs increased low-frequency MAP oscillations to 95.0% of total power compared to 75.5% during normal cardiac output variations (P < 0.05).
Does maintaining constant cardiac output alter spontaneous fluctuations in mean arterial pressure in conscious dogs?
Low-frequency oscillations in mean arterial pressure are primarily due to changes in peripheral resistance, while high-frequency changes stem from spontaneous changes in cardiac output.
Absolute Event Rate: 95% vs 75.5%
p-value: p=< 0.05
The objective of this study was to determine the role of cardiac output in mediating spontaneous fluctuations in mean arterial pressure (MAP) conscious dogs. Dogs were chronically instrumented to monitor MAP and cardiac output. Atrioventricular (AV) block was induced, and left ventricular and right atrial electrodes were implanted. After recovery, MAP was observed for 5 min under two conditions: 1) normal variation in heart rate and cardiac output via triggering the ventricular stimulator with each atrial depolarization (effectively reversing the AV block, AV-linked stimulation) and 2) computer control of ventricular rate to maintain cardiac output constant on a by-beat basis at the same level as observed during normal variations in heart rate and cardiac output. When cardiac output was held constant, large-amplitude, low-frequency oscillations in MAP were readily apparent. Spectral analysis by fast Fourier transform revealed that during constant cardiac output the power observed at low frequencies in the MAP spectrum represented 95.0 +/- 2.7% of the total power compared with 75.5 +/- 4.6% during normal variations in heart rate and cardiac output (P < 0.05). In addition, when cardiac output was held constant, the power observed at higher frequencies markedly decreased from 24.5 +/- 4.6% of total power during AV-linked stimulation to only 5.0 +/- 2.7% of total power during constant cardiac output (P < 0.05). We conclude that low-frequency oscillations in MAP are due to changes in peripheral resistance, whereas a significant amount of high-frequency changes in MAP stems from spontaneous changes in cardiac output.
O’Leary et al. (1996) studied Conscious dogs (animal model). Constant cardiac output via computer-controlled ventricular rate vs. Normal variation in heart rate and cardiac output (AV-linked stimulation) was evaluated on Power at low frequencies in the MAP spectrum (% of total power) (p=< 0.05). Maintaining constant cardiac output in conscious dogs increased low-frequency MAP oscillations to 95.0% of total power compared to 75.5% during normal cardiac output variations (P < 0.05).
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