Introduction:

Hypoxia induces time-depending changes in several morpho-physiological aspects in both cardiac and respiratory systems. However, most of the studies have dedicated attention unconnectedly into one of the components of the cardio-respiratory system under short term exposure to hypoxia. Our goal was to study the cardio-respiratory changes as a unit, combining classical parameters from both systems over time during chronic exposure to hypoxia (CH).

Material & Methods:

Using a custom built whole body plethysmograph (WBP) chamber (150 mL) adult wild-type mice were exposed to normobaric hypoxia (FiO₂ 10%) during 21 days and every 7 days body weight and hematocrit parameters were measured and the animals were exposed to normoxia (FiO₂ 21%), challenges to hypoxia (FiO₂ 10%) and recovery (normoxia; FiO₂ 21%) to determine respiratory rate (f_R), V _T , and minute ventilation (V _E ) to characterize the HVR. The electrical activity of the heart was obtained using leads I and II. To calculate the VCG, the leads III, aVR, aVL and aVF ECG were obtained mathematically. The heart rate variability (HRV) was calculated from the RR interval and main parameters were obtained.

Result & Conclusion:

We observed a significant increase of the hematocrit and the heart weight and a decrease of the body weight. CH induced a potentiation of ventilation during hypoxic challenges with larger times for each inspiration/ expiration cycle. The ECG showed that the CH increased the heart rate and the JT interval and a reduction of QRS interval. The changes in the heart weight and on some ECG parameters were also reflected in the VCG analysis, where there was a reduction in the angle of the QRS peak. The HRV was modified by CH, where the high frequency activity was increased. The low frequency was also modified due to the known effect of CH on sympathetic system. These results showed that CH altered basic parameters of cardio-respiratory system and these changes are inter-connected.