Effects of chronic hypoxia on cardiac function measured by pressure-volume catheter in fetal chickens

Hypoxia is a common component of many developmental insults and has been studied in earlystage chicken development. However, its impact on cardiac function and arterial-ventricular coupling in late-stage chickens is relatively unknown. To test the hypothesis that hypoxic incubation would reduce baseline cardiac function but protect the heart during acute hypoxia in late-stage chickens, white Leghorn eggs were incubated at 21% O₂ or 15% O₂. At 90% of incubation (19 days), hypoxic incubation caused growth restriction (-20%) and increased the LVto- body ratio (+41%). Left ventricular (LV) pressure-volume loops were measured in anesthetized chickens in normoxia and acute hypoxia (10% O₂). Hypoxic incubation lowered the maximal rate of pressure generation (∆P/∆t_Max; -22%) and output (-57%), whereas increasing end-systolic elastance (E_LV; +31%) and arterial elastance (E_A; +122%) at similar heart rates to normoxic incubation. Both hypoxic incubation and acute hypoxia lengthened the half-time of relaxation (τ; +24%). Acute hypoxia reduced heart rate (-8%) and increased end-diastolic pressure (+35%). Hearts were collected for mRNA analysis. Hypoxic incubation was marked by decreased mRNA expression of sarco(endo)plasmic reticulum Ca²⁺-ATPase 2, Na⁺/Ca²⁺ exchanger 1, phospholamban, and ryanodine receptor. In summary, hypoxic incubation reduces LV function in the late-stage chicken by slowing pressure generation and relaxation, which may be driven by altered intracellular excitation-contraction coupling. Cardiac efficiency is greatly reduced after hypoxic incubation. In both incubation groups acute hypoxia reduced diastolic function.