Respiratory and cardiac effects of passive limb movements in man

The purpose of these experiments is to see if reflex nervous hyperventilation obtained by passive limb movements in man is a consequence of the activation of a direct ascending nervous pathway from mechanoreceptors of moving limbs to respiratory centres, or if it is the consequence of a primary enhanced cardiodynamic activity. Contemporaneous measurements of pulmonary ventilation and cardiac output (the latter with the trasthoracic bioimpedance method) were carried out in subjects whose ankles were passively moved at an angle of 10 degrees and a frequency of 1 Hz, each test lasting three breaths. Results showed a fast increase in pulmonary ventilation in all test breaths (+27% from control) mainly depending on respiratory frequency increases and accompanied by a tendency to reduce end tidal PCO2. Cardiac output did not change during tests because of a lack of changes in heart rate and stroke volume. The lack of cardiac output increases during this reflex hyperventilation supports the existence of a direct neural pathway from limb proprioreceptor afferents to respiratory structures.