Fig 3. Mean arterial pressure fluctuates during cough and the subsequent recovery back to breathing, and this fluctuation was more pronounced during cough induced hyperventilation than during isocapnia.

The upper panel shows traces of group means of end-tidal CO₂ values during cough induced hyperventilation (CHV, dashed) and isocapnic (ISO, solid) cough trials. Mean arterial carbon dioxide (PaCO₂) measures are also shown (as colored dots) at the approximate time they were obtained during each trial. In the isocapnic condition, the alveolar (ETCO₂) and arterial (PaCO₂) carbon dioxide measures are nearly identical, suggesting no ventilation/perfusion mismatch. However, in the CHV condition the ETCO₂ was 33% lower than the PaCO₂ value, suggesting a mismatch due to low perfusion. The bottom panel shows group means of mean arterial pressure (MAP) recorded via femoral arterial cannula. MAP drops during the beginning of both cough conditions; matching the CO₂ to control levels in the isocapnic condition attenuated this decrease. Both conditions resulted in a gradual increase in MAP after 30 seconds, but the CHV condition produced a more dramatic rise in MAP during the recovery period, throughout the transition back to eupneic breathing. A Paired t-test of aggregated BP data from this period is reported in Table 2. n = 12. Grey bands represent a 95% confidence interval.