Figure 4. The effect of upon P_a,CO2 and the effect of ΔP_aCO2 upon phrenic nerve activity; increased metabolism and CO₂ chemosensitivity during hypoglycaemia.

A, representative data taken from a single experiment. Steady-state P_a,CO2 is sampled at various levels of artificial measured as integrated tracheal airflow during euglycaemia (•) and hypoglycaemia (○). Data are shown fitted by hyperbolic functions: and during euglycaemia (r²= 0.98) and hypoglycaemia (r²= 0.95), respectively. During insulin-induced hypoglycaemia, there was an upward shift in the position of the curves. B, representative raw data from the same animal. Phrenic minute activity is measured at the same steady-state levels of P_a,CO2 shown in A. Data are shown fitted by linear regression: phrenic minute activity = 0.75P_a,CO2+ 6.6 and phrenic minute activity = 2.24P_a,CO2− 39.9 during euglycaemia (r²= 0.92) and hypoglycaemia (r²= 0.99), respectively. Linear regression showed an increase of phrenic CO₂ sensitivity during insulin-induced hypoglycaemia.